First author: Pal, AK, Polymorphism Dependent 9-Phosphoanthracene Derivative Exhibiting Thermally Activated Delayed Fluorescence: A Computational Investigation,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 11025, (2020)
Abstract: Polymorphs of anthracene derivatives exhibit diverse photo-physical properties that can help to develop efficient organic-based photovoltaic devices. 10-Anthryl-9-phosphoanthracene (10-APA) shows different photo-physical behaviors for the solid state due to its variety in crystalline arrangement. Herein, we investigate the ground and excited-state properties of the monomer and two different polymorphs of 10-APA from first-principles. Calculations reveal that strong spin-orbit coupling (SOC) between first excited singlet state (S-1) and triplet manifolds at their S-1-optimized geometries enabling the reverse intersystem crossing (RISC). The electron-vibration coupling (Huang-Rhys factor) in the excited state is the most relevant factor here. For both ISC and RISC, a similarity in Huang-Rhys factors for the molecular vibration along the pi center dot center dot center dot pi stacking at low-frequency region makes the rates effective. On the other side, the nonvanishing vibronic relaxation modes provide a relatively slower RISC rate in the red crystal. However, for the red crystal, small reorganization energy (lambda) and large Huang-Rhys factor toward S-1 -> S-0 conversion reduce nonradiative decay, leading to a prompt fluorescence. As the feasibility of S-1 <-> T-1 conversion increases in the yellow dimer, it allows a delay in fluorescence emission, leading to thermally activated delayed fluorescence (TADF).
First author: Verevkin, SP, Weaving a Network of Reliable Thermochemistry around Lignin Building Blocks: Methoxy-Phenols and Methoxy-Benzaldehydes,
INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 59, 22626, (2020)
Abstract: The methoxy-, hydroxy-, and carbonyl-substituted benzenes are the simplest fragments from the lignin separation feedstocks. Extensive experimental thermochemical studies of these compounds were carried out, including combustion calorimetry, vapor pressure measurements, and differential scanning calorimetry. We have collected available primary experimental results on enthalpies of formation and vapor pressures as well as on phase transitions, liquid-gas, liquid-solid, and crystal-liquid. These data were evaluated using empirical, semiempirical, and quantum chemical methods. The consistent sets of evaluated thermodynamic data were used to design the method for predicting enthalpies of vaporization and enthalpies of formation of di- and trisubstituted benzenes. It is expected that parameters and pairwise interactions will be transferable to predict the thermochemical properties of poly methoxy-substituted and poly hydroxysubstituted benzenes that appear in reaction products of lignin transformations in the value-adding chemicals and materials.
First author: Xu, X, Investigating the Complexation and Release Behaviors of Iodine in Poly(vinylpyrrolidone)-Iodine Systems through Experimental and Computational Approaches,
INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 59, 22667, (2020)
Abstract: Poly( vinylpyrrolidone)-iodine (PVPI)-based materials have attracted significant attention, owing to their effective inhibition of COVID-19. However, the complexation and release manner of iodine in PVPI are not fully understood. This article reveals the role of halogen bonding in PVPI chemistry through a combination of experimental and computational approaches, including ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, electronic structure calculations, electronically excited-state analysis, electrostatic potential mapping on molecular van der Waals surfaces, halogen bond energy calculations, and thermodynamic equilibrium analysis. Our research shows that, in both the solid state and solution, PVPI contains iodine molecules bonded with carbonyl groups as well as polyiodides derived from the ionization and assembling of iodine molecules. The iodophors (i.e., PVP, iodide, and polyiodides) interact with iodine molecules through halogen bonds. The halogen bond energy is as low as 2-8 kcal/mol, enabling the easy release of iodine by the iodophors. In PVPI solutions, the complexation and release of iodine reach a chemical equilibrium that is susceptible to temperature and other iodophors. Raising the temperature favors the release of iodine. Some synthetic polymers, biological proteins, and phospholipids can extract iodine molecules from solutions of PVPI, demonstrating good iodophor abilities.
First author: Shaik, S, Stories of My Journeys Through Valence Bond Theory, DFT, MD and their Applications to Complex Objects,
ISRAEL JOURNAL OF CHEMISTRY, 62, 22667, (2022)
Abstract: This Rosarium Philosophorum essay tells the story of the author’s “conversion” to a theorist, and then the events which led him to stumble over valence bond (VB) theory, and his developments of “VB diagrams” as conceptual tools which enable one to describe all chemical reactions. The story continues to the adventure with the enzyme Cytochrome P450, and how this interest led eventually the author to treat the reactivity of this enzyme using VB diagrams. And finally, the essay describes the author’s struggle with complexity through molecular dynamics of these enzymes. This is also a story of interactions between individuals who seek insight and wisdom and how they influence one another through friendships and teacher-disciples relations. This is the key wisdom one garners through scientific life.
First author: van Hoeve, MD, Structure, reactions, and electronic spectra of the rare gas cyanohydrides and isocyanohydrides, HRgCN and HRgNC (Rg = Xe or Rn),
JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, 53, 22667, (2020)
Abstract: The low-energy electronic excitations of HRgCN and HRgNC (Rg = Xe, Rn) were computed at the TDDFT level of theory, both in the gas phase and in xenon cluster. It was found that the most prominent peak in the spectra was due to the highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) transition (similar to 6 eV for HRgCN and similar to 4.5 eV for HRgNC). Cluster confinement brought about bathochromic shifts in the spectra and better agreement with experiment for HXeCN. The effects of spin-orbit coupling (SOC) in the heavier Rn systems were investigated: for HRnCN, SOC red-shifted the HOMO-LUMO peak, while it blue-shifted the HOMO-LUMO peak for HRnNC. Geometry optimizations were carried out for the HRgCN and HRgNC systems to locate minima and transition states for dissociation and isomerization. Effects of isotopic substitution on reaction rates were predicted. A new model core potentials basis set was introduced and effectiveness of several pseudopotential basis sets was studied.
First author: Menzel, JP, Photoinduced Electron Injection in a Fully Solvated Dye-Sensitized Photoanode: A Dynamical Semiempirical Study,
JOURNAL OF PHYSICAL CHEMISTRY C, 124, 27965, (2020)
Abstract: Dye-sensitized solar cells and dye-sensitized photoelectrochemical cells have attracted much interest in recent years for solar energy conversion. More effort is still required to increase the efficiency of these devices, which is closely linked to the crucial process of photoinduced charge separation. Computational studies can provide insights into this fundamental process and suggest molecular components and interfaces that feature optimal energy-level alignment before time-consuming trial-and-error experimental realization. Here, we use a combination of density functional based tight binding and an extended Huckel approach to perform quantum classical simulations of photoinduced electron injection in a TiO2 dye-sensitized photoanode with explicit solvation at a reasonable computational cost. In particular, we evaluate injection capabilities of core-extended naphthalene diimide (NDI) dyes with three different anchoring groups. Our results stress the importance of nuclear motion as well as conformational and trajectory sampling for a realistic description of the injection process. Furthermore, explicit solvation highly influences the conformational space explored by the dye and anchoring molecules, especially concerning the adsorption mode. Taking these effects into account, the core-extended NDI with a catechol-based anchoring moiety is shown to be the most promising ultrafast electron injector. Our strategy allows for a more systematic computational search for appropriate molecular chromophores in dye-sensitized devices for solar energy conversion.
First author: Rodriguez, GM, Understanding the Deactivation Pathways of Iridium(III) Pyridine-Carboxiamide Catalysts for Formic Acid Dehydrogenation,
CHEMISTRY-A EUROPEAN JOURNAL, 27, 2050, (2021)
Abstract: The degradation pathways of highly active [Cp*Ir(kappa(2)-N,N-R-pica)Cl] catalysts (pica=picolinamidate; 1 R=H, 2 R=Me) for formic acid (FA) dehydrogenation were investigated by NMR spectroscopy and DFT calculations. Under acidic conditions (1 equiv. of HNO3), 2 undergoes partial protonation of the amide moiety, inducing rapid kappa(2)-N,N to kappa(2)-N,O ligand isomerization. Consistently, DFT modeling on the simpler complex 1 showed that the kappa(2)-N,N key intermediate of FA dehydrogenation (I-NH), bearing a N-protonated pica, can easily transform into the kappa(2)-N,O analogue (I-NH2; Delta G(not equal)approximate to 11 kcal mol(-1), Delta G approximate to-5 kcal mol(-1)). Intramolecular hydrogen liberation from I-NH2 is predicted to be rather prohibitive (Delta G(not equal)approximate to 26 kcal mol(-1), Delta G approximate to 23 kcal mol(-1)), indicating that FA dehydrogenation should involve mostly kappa(2)-N,N intermediates, at least at relatively high pH. Under FA dehydrogenation conditions, 2 was progressively consumed, and the vast majority of the Ir centers (58 %) were eventually found in the form of Cp*-complexes with a pyridine-amine ligand. This likely derived from hydrogenation of the pyridine-carboxiamide via a hemiaminal intermediate, which could also be detected. Clear evidence for ligand hydrogenation being the main degradation pathway also for 1 was obtained, as further confirmed by spectroscopic and catalytic tests on the independently synthesized degradation product 1 c. DFT calculations confirmed that this side reaction is kinetically and thermodynamically accessible.
First author: Brooks, JL, Plasmon-Mediated Intramolecular Methyl Migration with Nanoscale Spatial Control,
ACS NANO, 14, 17194, (2020)
Abstract: Plasmonic materials interact strongly with light to focus and enhance electromagnetic radiation down to nanoscale volumes. Due to this localized confinement, materials that support localized surface plasmon resonances are capable of driving energetically unfavorable chemical reactions. In certain cases, the plasmonic nanostructures are able to preferentially catalyze the formation of specific photoproducts, which offers an opportunity for the development of solar-driven chemical synthesis. Here, using plasmonic environments, we report inducing an intramolecular methyl migration reaction, forming 4-methylpyridine from N-methylpyridinium. Using both experimental and computational methods, we were able to confirm the identity of the N-methylpyridinium by making spectral comparisons against possible photoproducts. This reaction involves breaking a C-N bond and forming a new C-C bond, highlighting the ability of plasmonic materials to drive complex and selective reactions. Additionally, we observe that the product yield depends strongly on optical illumination conditions. This is likely due to steric hindrance in specific regions on the nanostructured plasmonic substrate, providing an optical handle for driving plasmonic catalysis with spatial specificity. This work adds yet another class of reactions accessible by surface plasmon excitation to the ever-growing library of plasmon-mediated chemical reactions.
First author: Lu, SI, The role of distributed atomic point charges and polarizabilities of solvent molecules on one- and two-photon absorption spectra of aqueous p-nitroaniline,
JOURNAL OF THE CHINESE CHEMICAL SOCIETY, 68, 429, (2021)
Abstract: In this work, we demonstrated the electrostatic and polarization effects created from distributed atomic point charges and polarizabilities of solvent molecules, respectively, when calculating optical response properties of solution-phase molecule within the context of the discrete solvent reaction field. Aqueous p-nitroaniline molecule was selected as the model system for our research purpose. One- and two-photon absorption spectra were constructed by carrying out the damped response theory calculations within time-dependent density functional theory. As compared to the full treatment, we investigated different effects of electrostatics and polarizations on spectral parameters of interest. Our calculations showed that the larger contributions to the calculated red shift in excitation energy was from electrostatic term, but polarization contribution was comparable in magnitude. On the other hand, electrostatic term was the principal feature for absorption strength and spectral width.
First author: Mooibroek, TJ, DFT and IsoStar Analyses to Assess the Utility of sigma- and pi-Hole Interactions for Crystal Engineering,
CHEMPHYSCHEM, 22, 141, (2021)
Abstract: The interpretation of 36 charge neutral ‘contact pairs’ from the IsoStar database was supported by DFT calculations of model molecules 1-12, and bimolecular adducts thereof. The ‘central groups’ are sigma-hole donors (H2O and aromatic C-I), pi-hole donors (R-C(O)Me, R-NO2 and R-C6F5) and for comparison R-C6H5 (R=any group or atom). The ‘contact groups’ are hydrogen bond donors X-H (X=N, O, S, or R2C, or R3C) and lone-pair containing fragments (R3C-F, R-C equivalent to N and R2C=O). Nearly all the IsoStar distributions follow expectations based on the electrostatic potential of the ‘central-‘ and ‘contact group’. Interaction energies (Delta E-BSSE) are dominated by electrostatics (particularly between two polarized molecules) or dispersion (especially in case of large contact area). Orbital interactions never dominate, but could be significant (similar to 30 %) and of the n/pi ->sigma*/pi* kind. The largest degree of directionality in the IsoStar plots was typically observed for adducts more stable than Delta E-BSSE approximate to-4 kcal.mol(-1), which can be seen as a benchmark-value for the utility of an interaction in crystal engineering. This benchmark could be met with all the sigma- and pi-hole donors studied.
First author: Pan, S, Intriguing structural, bonding and reactivity features in some beryllium containing complexes,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 141, (2020)
Abstract: Although the toxicity of beryllium compounds causes impediments in experiments involving them, beryllium chemistry has seen a recent upsurge of interest and considerable progress. Computations play a very important complementary role in analyzing the structure, stability and bonding of these compounds. In this perspective article, we highlighted our contribution to beryllium chemistry which is either completely through theoretical results or sometimes supported by experimental findings. It starts with the smallest 2 pi aromatic system, Be-3(2-), which also exhibits rare bond-stretch isomerism. Furthermore, its reactivity towards different transformations is mentioned. Because of the ability of beryllium to attain a high ionic potential, the beryllium center in an appropriate situation can act as an excellent Lewis acid which is utilized to bind noble gas (Ng) atoms, carbon monoxide and dinitrogen through donor-acceptor types of interactions. We made several efforts to have strong Ng-Be bonds which led us to NgBeNCN that is recorded to have the strongest Ng-Be bond among the neutral Ng-Be complexes reported so far. Significant dinitrogen activation was also achieved in (NN)(2)Be(eta(2)-N-2) and OCBeNN complexes. In the latter case, a complete cleavage of the N-N bond producing the most stable NBeNCO molecule has occurred. We also found viable M-2(NHBMe)(2) (M = Be, Mg) complexes having unusual bonding where the interacting fragments are best described as the neutral M-2 and (NHBMe)(2) but M-2 still possesses a single bond. We finally discussed the complex comprising an unusual Be(i) oxidation state, [Be-I(cAAC(Ar))(2)](+) and di-ortho-beryllated carbodiphosphorane exhibiting BeC double dative bonds.
First author: Zheng, XJ, Main-Group Metals Stabilized Polypyrrolic Uranyl(V) Complexes via Cation-Cation Interaction with the Uranyl exo-Oxo Atom: A Relativistic Density Functional Theory Study,
INORGANIC CHEMISTRY, 59, 18018, (2020)
Abstract: To explore the innovative uranyl(V) complexes by deeply understanding their coordination stability, relativistic density functional theory calculations have been performed to investigate the experimentally reported [(py)((R2AlOUO)-O-V)(py)(H2L)] [R = Me (1), Bu-i (2)] and [{(py)(3)(MOUO)-O-V}(py)(H2L)] [M = Li (3), Na (4), K (5)] and their uranyl(VI) counterparts. Structural and topological analyses along with transformation-reaction energies and redox potentials were systematically studied. Geometrical and quantum theory of atoms in molecules analyses implied a linear U-O-exo-M feature in 1-3 and a bent one in 4 and 5. The calculated free energies (Delta(r)G) of reactions transforming 1/2 into 3/ 4/5 confirmed a higher stability of the latter ones, which were further corroborated by their reduction potentials (E-0). The E-0 value of 5 versus uranyl(VI) is close to its experimental value, particularly in solvation with spin-orbit coupling. The highest occupied and lowest unoccupied molecular orbitals of uranyl(V) and uranyl(VI) have predominant U(5f delta) character. Compared to mononuclear uranyl(VI), the coordination of aluminum and alkali metals to uranyl exo-oxo significantly contributes to the stabilization of uranyl(V) by altering the E-0 value from -1.59 to -0.85, -0.91, -1.33, -1.50, and -1.46 V, respectively. The calculation results show a more positive E-0 than that of the precursor 6(VI)/6 without exo-oxo coordination. The calculated E-0 values of 3-5 are certainly more negative than those of 1 and 2. The alkali metals were found to activate U = O bonds more easily/readily than aluminum by coordination to the exo-oxo atom. In brief, the uranyl exo-oxo cation- cation-interaction enhanced the reduction ability from its uranyl(VI) analogue and raised the stability of the U-V, center.
First author: Klamm, BE, Exploring the Oxidation States of Neptunium with Schiff Base Coordination Complexes,
INORGANIC CHEMISTRY, 59, 18035, (2020)
Abstract: A pair of neptunium Schiff base coordination complexes, (NpO2L)-O-VI(MeOH) and (NpL2)-L-VI{H2L = N,N’-bis[(4,4′-diethylamino)salicylidene]-1,2-phenylenediaminel, have been synthesized and analyzed by several characterization methods including single-crystal X-ray diffraction, electronic absorption, H-1 NMR, cyclic voltammetry, and theoretical interpretation. Structural analysis reveals that (NpO2L)-O-VI(MeOH) and (NpL2)-L-IV are isomorphous with the previously reported (UO2)-O-IV L(MeOH) and (ML2)-L-IV (M = Pu, Ce, U, Th) complexes, respectively, allowing for a direct comparison across the series. The reduction of (NpO2)-O-VI L-(MeOH) in situ or direct synthesis from a ((NpO2)-O-V)(+) source shows evidence of a pentavalent neptunyl ((NpO2L)-O-V)(x)(n-) species as determined by UV/vis/NIR and H-1 NMR spectroscopy. The synthesis of ((NpO2L)-O-VI)(x)(n-) directly from a (NpVO2)(+) starting material gives a similar spectrum. Theoretical analysis offers insight into the electronic structure for a better understanding of the bonding patterns and relative stability of the different oxidation states. Computational results show that the Np-L covalent interactions in (NpL2)-L-V are similar to those in the (NpO2)-O-VI L(MeOH) complex, indicating that neither the presence of the axial oxo ligands nor the oxidation state significantly modify the nature of the Np-L bonds.
First author: Collins, TS, Origin of Bond Elongation in a Uranium(IV) cis-Bis(imido) Complex,
INORGANIC CHEMISTRY, 59, 18461, (2020)
Abstract: The activation of U-N multiple bonds in an imido analogue of the uranyl ion is accomplished by using a system that is very electron-rich with sterically encumbering ligands. Treating the uranium(VI) trans-bis(imido) UI2(NDIPP)(2)(THF)(3) (DIPP = 2,6-diisopropylphenyl and THF = tetrahydrofuran) with tert-butyl(dimethylsilyl)amide (NTSA) results in a reduction and rearrangement to form the uranium(IV) cis-bis(imido) [U(NDIPP)(2)(NTSA)(2)]K-2 (1). Compound 1 features long U-N bonds, pointing toward substantial activation of the N=U=N unit, as determined by X-ray crystallography and H-1 NMR, IR, and electronic absorption spectroscopies. Computational analyses show that uranium(IV)-imido bonds in 1 are significantly weakened multiple bonds due to polarization toward antibonding and nonbonding orbitals. Such geometric control has important effects on the electronic structures of these species, which could be useful in the recycling of spent nuclear fuels.
First author: Fonseca, J, Electro- and photoelectro-catalysts derived from bimetallic amorphous metal-organic frameworks,
CATALYSIS SCIENCE & TECHNOLOGY, 10, 8265, (2020)
Abstract: Fuel cells and electrochemical water splitting have attracted wide attention to address the demand of global energy and the depletion of fossil fuels. These promising and renewable energy alternatives implicate three pivotal reactions: oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The design and synthesis of materials for efficient catalysis toward HER, OER, and ORR are of paramount importance. To address these aims, electro- and photoelectro-catalysts based on the controlled pyrolysis of bimetallic amorphous metal-organic frameworks (MOFs) are developed. The present study provides a general method for the design and synthesis of bimetallic amorphous MOFs by merging our liquid-liquid interface synthesis method and the metalloligand approach. As a proof of concept, NEU-5 (= [Zn(FeTpyCOOH)(PF6)(2)](n)), NEU-6 (= [Zn(Ru(terpy*)(2))(PF6)(2)](n)), NEU-7 (= [Fe(Ru(terpy*)(2))(PF6)(2)](n)) and NEU-8 (= [Ti(Ru(terpy*)(2))(PF6)(2)](n)) are successfully synthesized, and subsequently pyrolyzed to prepare Fe2P@PNDCN, RuP@PNDCN, Fe3O4/RuO2@NEU-7 and Ru2O/TiN/TiO2@NEU-8, respectively. These electro- and photoelectro-catalysts exhibit excellent activity for ORR, OER and HER in both acidic and alkaline media.
First author: Theiss, S, Ligand-Programmed Consecutive Symmetry Break(s) in Nanoparticle Based Materials Showing Emergent Phenomena: Transitioning from Sixfold to Threefold Symmetry in Anisotropic ZnO Colloids,
ADVANCED FUNCTIONAL MATERIALS, 31, 8265, (2021)
Abstract: The central promise of nanoparticle-based materials is that cooperative properties may emerge, when individual quantum dots are positioned on a periodic lattice. Yet, there are only a few papers in the literature reporting such effects. Nevertheless, it is clear that the symmetry of the superlattice is decisive for the desired emergent phenomena. An interesting question is, how the symmetry of the initial monodisperse nanoparticles affects the structure of the colloidal crystal during self-assembly processes. For instance, particles with a hexagonal cross-section demonstrate self-organization, which is very similar to spherical colloids. Likewise, one would also expect that trigonal nanoparticles behave similarly. Unfortunately, it is very hard to obtain monodisperse semiconductor colloids with a trigonal shape, because this requires a symmetry break during morphogenesis of the nanocrystal. While such a symmetry break is known in the literature for structures attached to a solid substrate, herein, colloidal synthesis of trigonal ZnO nanorods is successfully demonstrated, and the mechanism is elucidated via experimental and theoretical methods. 2D-superlattices formed by such particles with trigonal cross-section are compared to hexagonal analogues. It is found that there are distinct differences, which result in important differences in properties such as the formation of voids and also in optical properties.
First author: Radicchi, E, Combined Computational and Experimental Investigation on the Nature of Hydrated Iodoplumbate Complexes: Insights into the Dual Role of Water in Perovskite Precursor Solutions,
JOURNAL OF PHYSICAL CHEMISTRY B, 124, 11481, (2020)
Abstract: Water is generally considered an enemy of metal halide perovskites, being responsible for their rapid degradation and, consequently, undermining the long-term stability of perovskite-based solar cells. However, beneficial effects of liquid water have been surprisingly observed, and synthetic routes including water treatments have shown to improve the quality of perovskite films. This suggests that the interactions of water with perovskites and their precursors are far from being completely understood, as water appears to play a puzzling dual role in perovskite precursor solutions. In this context, studying the basic interactions between perovskite precursors in the aqueous environment can provide a deeper comprehension of this conundrum. In this context, it is fundamental to understand how water impacts the chemistry of iodoplumbate perovskite precursor species, PbIx2-x. Here, we investigate the chemistry of these complexes using a combined experimental and theoretical strategy to unveil their peculiar structural and optical properties and eventually to assign the species present in the solution. Our study indicates that iodide-rich iodoplumbates, which are generally key to the formation of lead halide perovskites, are not easily formed in aqueous solutions because of the competition between iodide and solvent molecules in coordinating Pb2+ ions, explaining the difficulty of depositing lead iodide perovskites from aqueous solutions. We postulate that the beneficial effect of water when used as an additive is then motivated by its behavior being similar to high coordinative polar aprotic solvents usually employed as additives in one-step perovskite depositions.
First author: Zhang, Q, Comparison of computational chemistry methods for the discovery of quinone-based electroactive compounds for energy storage,
SCIENTIFIC REPORTS, 10, 11481, (2020)
Abstract: High-throughput computational screening (HTCS) is a powerful approach for the rational and time-efficient design of electroactive compounds. The effectiveness of HTCS is dependent on accuracy and speed at which the performance descriptors can be estimated for possibly millions of candidate compounds. Here, a systematic evaluation of computational methods, including force field (FF), semi-empirical quantum mechanics (SEQM), density functional based tight binding (DFTB), and density functional theory (DFT), is performed on the basis of their accuracy in predicting the redox potentials of redox-active organic compounds. Geometry optimizations at low-level theories followed by single point energy (SPE) DFT calculations that include an implicit solvation model are found to offer equipollent accuracy as the high-level DFT methods, albeit at significantly lower computational costs. Effects of implicit solvation on molecular geometries and SPEs, and their overall effects on the prediction accuracy of redox potentials are analyzed in view of computational cost versus prediction accuracy, which outlines the best choice of methods corresponding to a desired level of accuracy. The modular computational approach is applicable for accelerating the virtual studies on functional quinones and the respective discovery of candidate compounds for energy storage.
First author: Tang, JW, Effects of side-chain of non-fullerene small molecules on the property of electron transport materials in perovskite solar cells,
MOLECULAR PHYSICS, 119, 11481, (2021)
Abstract: Based on 4Cl-TAP, an organic small molecule transport material with high mobility, four derivatives containing thiophene or furan side chain were designed. The effect of pi conjugated group of side chain on the electron transport properties was investigated by the density functional theory. The results show that the introduction of thiophene and furan into the side chains reduces the electron reorganisation energies, shortens the centroid-to-centroid distances, enhances electron coupling, and forms effective face-to-face stacking, and thus results in larger mobility. Insertion of acetylene into the side chain of the derivatives significantly improves their solubility and electron transport performance. This work reveals the great potential of non-fullerene small molecules based on 4Cl-TAP as electron transport materials.
First author: Wang, B, Understanding the Hydrogen-Bonded Clusters of Ammonia (NH3)(n) (n=3-6): Insights from the Electronic Structure Theory,
ACS OMEGA, 5, 31724, (2020)
Abstract: Although it is well known that hydrogen bonds commonly exist in ammonia clusters and play an important role, there are still many challenges in understanding the electronic structure properties of hydrogen bonds. In this paper, the geometric and electronic structure properties of cyclic ammonia clusters are investigated by using first-principles density functional theory (DFT) and the Moller-Plesset perturbation theory (MP2). The calculation results show that the pentamer and hexamer have deviated from the perfect plane, while the trimer and tetramer present planarization that has been confirmed by infrared (IR) spectra. The electronic structure analysis further shows that the covalent properties play a non-negligible role in hydrogen bonding. The results also indicate that the electronic structure facilitates structure planarization. Our work not only provides insight into the role and nature of hydrogen bonds in ammonia clusters but also provides a theoretical basis for frontier science in fields such as atmospheric haze and biomolecular functions.
First author: Zhang, YN, How to produce isotope anomalies in mantle by using extremely small isotope fractionations: A process-driven amplification effect?,
GEOCHIMICA ET COSMOCHIMICA ACTA, 291, 19, (2020)
Abstract: One of the most important foundations of chemical geodynamics is that isotope anomalies of radiogenic isotopes observed in mantle-derived samples after correcting for natural and instrumental mass-dependent fractionations are mainly caused by radioactive decay of reservoirs with different parent-daughter ratios. It often denies the possibility of mass-independent fractionation processes at high temperatures. Therefore, isotope anomalies with very small magnitudes (ppm-level), such as W-182, has been used to identify different mantle reservoirs, the time scales of their formation and potential core-mantle interactions. W-182 anomalies are generally considered as the sole consequences of radioactivity and nucleosynthesis that could be explained via simple mixing models of multiple reservoirs. However, the nuclear field shift effect (NFSE), has proved to be capable of producing the “anomalous mass effect” especially for heavy metal isotope systems even under very high temperatures. Therefore, it is necessary to test whether such small NFSE-induced mass-independent isotope fractionations can be magnified during unique mantle evolutionary processes, such as multi-stage melting and crystallization, to produce the observed isotope anomalies in mantle-derived rocks. Here we design a multistage closed-system melting and crystallization evolution model (denoted as MC2-model), combined with ab-initio calculations and Monte Carlo simulations to test our hypothesis. Multi-stage melting and crystallization evolution can occur in magma chambers, during tectonic movements in the early earth, in complex partial melting processes or plume and its surrounding mantle. Our simulation results show that there is an amplification effect during such multi-stage evolution process. The final isotope fractionations are scaled as aN, where N is the total number of melting or crystallization processes and a is a factor that related to the evolution path and detailed melting or crystallization behaviors, such as partition coefficient (D) and degree of melting or crystallization (F). In other words, if a mantle source region experienced multi-stage melting, melt extraction and crystallization processes, the isotope effect will probably linearly magnified. Taking O and W isotopes as examples, we conduct a statistical analysis for the results of such multi-stage simulation experiments and concluded that some of the ppm-level W-182 anomalies, both positive and negative observed in Archean mantle-derived and modern plume-derived samples might be explained by this way, but our model seems to have difficulty in explaining O-17 anomalies observed in anorthosite and basalts. This study provides another perspective for the origin of isotope anomalies that are observed in mantle-derived samples.
First author: Marczenko, KM, High Lewis Acidity at Planar, Trivalent, and Neutral Bismuth Centers,
ORGANOMETALLICS, 39, 4287, (2020)
Abstract: Geometric perturbation away from classical structures can engender unusual frontier MO situations leading to high Lewis acidity. Recently we reported a T-shaped bismuth triamide, which exhibited planar Lewis acidity that was unprecedented for neutral group 15 compounds. We now report a comprehensive computational assessment of the origins of planar Lewis acidity in such compounds. We subsequently use several metrics such as MO energies, the Global Electrophilicity Index, ligand coordination strengths, and fluoride ion affinity to show that electronic variation can be combined with the unusual geometry at bismuth to achieve fine-tuning of Lewis acid strength. Our calculations reveal for the first time a surprisingly high electrophilicity, comparable to or exceeding that of polyfluorinated triarylboranes, as well as high rigidity at neutral planar bismuth triamides. These results foreshadow the potentially broad applications of a hitherto unexplored class of compounds, planar bismuthanes, in contexts that are currently dominated by Lewis acidic triarylboranes.
First author: Chen, R, Quantifying the enhancement mechanisms of surface-enhanced Raman scattering using a Raman bond model,
JOURNAL OF CHEMICAL PHYSICS, 153, 4287, (2020)
Abstract: In this work, a Raman bond model that partitions the Raman intensity to interatomic charge flow modulations or Raman bonds is extended from the static limit to frequency dependent cases. This model is based on damped response theory and, thus, enables a consistent treatment of off-resonance and resonance cases. Model systems consisting of pyridines and silver clusters are studied using time dependent density functional theory to understand the enhancement mechanisms of surface-enhanced Raman scattering (SERS). The Raman bonds in the molecule, the inter-fragment bond, and the cluster are mapped to the enhancement contributions of the molecular resonance mechanism, the charge transfer mechanism, and the electromagnetic mechanism. The mapping quantifies the interference among the coupled mechanisms and interprets the electromagnetic mechanism as charge flow modulations in the metal. The dependence of the enhancement on the incident frequency, the molecule-metal bonding, and the applied electric field is interpreted and quantified. The Raman bond framework offers an intuitive and quantitative interpretation of SERS mechanisms.
First author: Noodleman, L, Coupled transport of electrons and protons in a bacterial cytochrome c oxidase-DFT calculated properties compared to structures and spectroscopies,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 26652, (2020)
Abstract: After a general introduction to the features and mechanisms of cytochrome c oxidases (CcOs) in mitochondria and aerobic bacteria, we present DFT calculated physical and spectroscopic properties for the catalytic reaction cycle compared with experimental observations in bacterial ba(3) type CcO, also with comparisons/contrasts to aa(3) type CcOs. The Dinuclear Complex (DNC) is the active catalytic reaction center, containing a heme a(3) Fe center and a near lying Cu center (called Cu-B) where by successive reduction and protonation, molecular O-2 is transformed to two H2O molecules, and protons are pumped from an inner region across the membrane to an outer region by transit through the CcO integral membrane protein. Structures, energies and vibrational frequencies for Fe-O and O-O modes are calculated by DFT over the catalytic cycle. The calculated DFT frequencies in the DNC of CcO are compared with measured frequencies from Resonance Raman spectroscopy to clarify the composition, geometry, and electronic structures of different intermediates through the reaction cycle, and to trace reaction pathways. X-ray structures of the resting oxidized state are analyzed with reference to the known experimental reaction chemistry and using DFT calculated structures in fitting observed electron density maps. Our calculations lead to a new proposed reaction pathway for coupling the P-R -> F -> O-H (ferryl-oxo -> ferric-hydroxo) pathway to proton pumping by a water shift mechanism. Through this arc of the catalytic cycle, major shifts in pK(a)’s of the special tyrosine and a histidine near the upper water pool activate proton transfer. Additional mechanisms for proton pumping are explored, and the role of the Cu-B(+) (cuprous state) in controlling access to the dinuclear reaction site is proposed.
First author: Sorbelli, D, Ground and excited electronic states of AuH(2)via detachment energies on AuH2- using state-of-the-art relativistic calculations,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 26742, (2020)
Abstract: Photoelectron spectroscopy (PES) is a well-known technique which provides unique information about the electronic structure of anionic and neutral species of simple molecules containing heavy elements; however, the detailed interpretation of the resulting experimental spectra can be very complex and theoretical support is mandatory. In this work, based on the available vibrationally resolved PES experiments for gold dihydride (Liu, H.-T. et al., Chem. Sci., 2012, 3, 3286), we have employed several relativistic theoretical approaches with the aim of reproducing experimental photoelectron Detachment Energies (DEs) of AuH2- to give a neutral open-shell molecule, AuH2. The results are discussed in terms of relativistic effects, orbital relaxation and electron correlation. In order to reproduce accurate DEs it has been necessary to include all these effects in a consistent manner at a high degree of accuracy, by means of the equation-of-motion coupled-cluster theory (EOM-IP-CCSD) based on the relativistic exact two-component Hamiltonian (Shee A. et al. J. Chem. Phys., 2018, 174113). This method has also been applied for investigating the ground and low-lying electronic potential energy surfaces of the neutral open shell AuH2 species. The equilibrium geometry of the AuH2 ground state is found to be bent, which is fully consistent with the experimental findings, while all the excited states, including the first, which was previously suggested to have a slightly bent structure, are found to be linear. In the linear centrosymmetric nuclear configuration (which corresponds to the equilibrium geometry of the anion, AuH2-), we find that the first excited state and ground state are very close in energy and the ground state is characterized by an unexpected symmetry breaking in the direction of the asymmetric stretching, due to the pseudo-Jahn-Teller effect. This effect depends on the energy difference between these two electronic states and disappears when the spin-orbit coupling is neglected. The picture that emerges here is intriguing and demonstrates that the interpretation, for which the vibronic transitions that were previously assigned to a slightly bent structure of the first excited state needs to be revised and that a full rationalization of the PES spectra would require the explicit inclusion of the nuclear dynamical effects, beyond the Born-Oppenheimer (BO) approximation. From a methodological point of view, the relativistic EOM-IP-CCSD method results are highly accurate and capable of giving a well-balanced description of the anionic and neutral species, which is a key aspect for the interpretation of the PES spectra in open-shell heavy element compounds.
First author: Hough, MA, Nature of the copper-nitrosyl intermediates of copper nitrite reductases during catalysis,
CHEMICAL SCIENCE, 11, 12485, (2020)
Abstract: The design and synthesis of copper complexes that can reduce nitrite to NO has attracted considerable interest. They have been guided by the structural information on the catalytic Cu centre of the widespread enzymes Cu nitrite reductases but the chemically novel side-on binding of NO observed in all crystallographic studies of these enzymes has been questioned in terms of its functional relevance. We show conversion of NO2- to NO in the crystal maintained at 170 K and present ‘molecular movies’ defining events during enzyme turnover including the formation of side-on Cu-NO intermediate. DFT modelling suggests that both true {CuNO}(11) and formal {CuNO}(10) states may occur as side-on forms in an enzymatic active site with the stability of the {CuNO}(10) side-on form governed by the protonation state of the histidine ligands. Formation of a copper-nitrosyl intermediate thus needs to be accommodated in future design templates for functional synthetic Cu-NiR complexes.
First author: Ortolan, AO, The bonding situation in heteromultimetallic carbonyl complexes,
DALTON TRANSACTIONS, 49, 16762, (2020)
Abstract: The synthesis and characterization of heteromultimetallic complexes has been one of the biggest challenges faced by inorganic chemists in the last few years. Here, the physical nature behind the relative stability of tri-heteronuclear complexes, involving the [M(PR3)](+) (M = Au(I), Ag(I) and Cu(I); and R = Ph and H) cation bridged by the [Fe(CO)(4)](2-) anion, at the relativistic DFT-D3 level of theory is presented. Although the synthetic route to afford the [Fe(CO)(4)(AuPPh3)(2)] complex has been known for a long time, information about its copper and silver counterparts is scarce. The bonding situation is addressed via Kohn-Sham molecular orbitals coupled with a canonical energy decomposition analysis as the primary technique. The results show that complexes whose metal portion M-Fe-M is bent are more stable than linear ones. This stems from the dispersive interactions between the phenyl groups, but this also supports the presence of aurophilic d(10)-d(10) interactions. The bonding between the [Fe(CO)(4)](2-) and [Au-PPh3](+) fragments has a chiefly electrostatic character, but orbital interactions also represent a non-negligible role, as evidenced by the presence of : (i) sigma-donation from the iron-carbonyl groups to the metal-phosphorus fragment; (ii) small pi-donation from the metal to the iron center; and (iii) inner fragment polarization. The description of the metal-metal bonding situation in these complexes provides valuable information, useful to guide the synthesis of unprecedented multimetallic complexes containing coinage metals and other transition metals.
First author: Milovanovic, MR, Joint Isotherm Calorimetric Titration-DFT Investigation of the Demethoxy-Amination of Fischer Carbenes,
JOURNAL OF ORGANOMETALLIC CHEMISTRY, 929, 16762, (2020)
Abstract: The thermochemistry of the aminolysis of three methoxy Fischer carbenes, pentacar-bonyl(phenylmethoxyalkylidene)chromium(0), molybdenum(0) and tungsten(0), was studied experimentally and theoretically with three amines, namely benzylamine, aniline and 3-pyrroline. Enthalpies of reactions were all determined by Isotherm Calorimetric Titration (ITC) in chlorobenzene at 298.15 K, which provided in almost all cases values of Delta H-r larger than -15 kcal/mol suggesting energetically favourable transformations for all amines except aniline. No significant dependence of the enthalpy of reaction upon the nature of the metal atom of the carbene complex was found. Further ITC experiments confirmed the partial second-order reaction in amine. All COSMO-DFT computed enthalpies of reaction (spanning ca. -5.5 kcal/mol up to -20 kcal/mol) were found to be in excellent agreement with experimental values, while calculated Gibbs free energies suggested spontaneous processes for all reactions except the one with aniline.
First author: Zollner, MS, Influence of Electronic Structure Modeling and Junction Structure on First-Principles Chiral Induced Spin Selectivity,
JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 16, 7357, (2020)
Abstract: We have carried out a comprehensive study of the influence of electronic structure modeling and junction structure description on the first-principles calculation of the spin polarization in molecular junctions caused by the chiral induced spin selectivity (CISS) effect. We explore the limits and the sensitivity to modeling decisions of a Landauer/Green’s function/two-component density functional theory approach to CISS. We find that although the CISS effect is entirely attributed in the literature to molecular spin filtering, spin-orbit coupling being partially inherited from the metal electrodes plays an important role in our calculations on ideal carbon helices, even though this effect cannot explain the experimental conductance results. Its magnitude depends considerably on the shape, size, and material of the metal clusters modeling the electrodes. Also, a pronounced dependence on the specific description of exchange interaction and spin-orbit coupling is manifest in our approach. This is important because the interplay between exchange effects and spin-orbit coupling may play an important role in the description of the junction magnetic response. Our calculations are relevant for the whole field of spin-polarized electron transport and electron transfer, because there is still an open discussion in the literature about the detailed underlying mechanism and the magnitude of physical parameters that need to be included to achieve a consistent description of the CISS effect: seemingly good quantitative agreement between simulation and the experiment can be caused by error compensation, because spin polarization as contained in a Landauer/Green’s function/two-component density functional theory approach depends strongly on computational and structural parameters.
First author: Forster, A, Low-Order Scaling G(0)W(0) by Pair Atomic Density Fitting,
JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 16, 7381, (2020)
Abstract: We derive a low-scaling G(0)W(0) algorithm for molecules using pair atomic density fitting (PADF) and an imaginary time representation of the Green’s function and describe its implementation in the Slater type orbital (STO)-based Amsterdam density functional (ADF) electronic structure code. We demonstrate the scalability of our algorithm on a series of water dusters with up to 432 atoms and 7776 basis functions and observe asymptotic quadratic scaling with realistic threshold qualities controlling distance effects and basis sets of triple-zeta (TZ) plus double polarization quality. Also owing to a very small prefactor, a G(0)W(0) calculation for the largest of these clusters takes only 240 CPU hours with these settings. We assess the accuracy of our algorithm for HOMO and LUMO energies in the GW100 database. With errors of 0.24 eV for HOMO energies on the quadruple-zeta level, our implementation is less accurate than canonical all-electron implementations using the larger deft2-QZVP GTO-type basis set. Apart from basis set errors, this is related to the well-known shortcomings of the GW space-time method using analytical continuation techniques as well as to numerical issues of the PADF approach of accurately representing diffuse atomic orbital (AO) products. We speculate that these difficulties might be overcome by using optimized auxiliary fit sets with more diffuse functions of higher angular momenta. Despite these shortcomings, for subsets of medium and large molecules from the GW5000 database, the error of our approach using basis sets of TZ and augmented double-zeta (DZ) quality is decreasing with system size. On the augmented DZ level, we reproduce canonical, complete basis set limit extrapolated reference values with an accuracy of 80 meV on average for a set of 20 large organic molecules. We anticipate our algorithm, in its current form, to be very useful in the study of single-particle properties of large organic systems such as chromophores and acceptor molecules.
First author: He, C, Self-Catalyzed Sensitization of CuO Nanowires via a Solvent-free Click Reaction,
LANGMUIR, 36, 14539, (2020)
Abstract: Recent advances in organic surface sensitization of metal oxide nanomaterials focused on two-step approaches with the first step providing a convenient functionalized chemical “hook”, such as an alkyne functionality connected to a carboxylic group in prop-2-ynoic acid. The second step then took advantage of copper-catalyzed click chemistry to deliver the desired structure (such as benzyl or perylene) attached to an azide to react with the surface-bound alkyne. The use of this approach on CuO not only resulted in a successful morphology preserving chemical modification but also has demonstrated that surface Cu(I) can be obtained during the process and promote a surface-catalyzed click reaction without additional copper catalyst. Here, it is demonstrated that this surface-catalyzed chemistry can be performed on a surface of the CuO nanomaterial without a solvent, as a “dry click” reaction, as confirmed with spectroscopic and microscopic investigations with X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, solid-state nuclear magnetic resonance, and scanning electron microscopy. Computational studies provided instructive information on the interaction between the surface prop-2-yonate and azide functional group to better understand the mechanism of this surface-catalyzed click reaction.
First author: Puttock, EV, Solution-Processed Dendrimer-Based TADF Materials for Deep-Red OLEDs,
MACROMOLECULES, 53, 10375, (2020)
Abstract: We report the first example of a thermally activated delayed fluorescence (TADF) poly(dendrimer), composed of a norbornenyl-derived polymer backbone and dendritic side-chain chromophores comprising 2,3-dicyanopyrazino as the electron acceptor and a first-generation fluorenylcarbazole derivative as the electron donor. The TADF poly(dendrimer) homopolymer, with one dendritic side chain attached to each monomer unit, emitted deep-red light. The emission of the poly(dendrimer) was found to be red-shifted relative to the nonpolymeric doubly dendronized emitter composed of the same components. The simple dendrimer was found to have a solution photoluminescence quantum yield (PLQY) of around 70%. In contrast, the poly(dendrimer) had a PLQY of 9%, which was attributed to intramolecular interchromophore interactions. An interesting feature of the poly(dendrimer) was that oxygen did not quench the TADF emission. We found that the PLQY of the simple dendrimer decreased markedly in neat films, whereas that of the poly(dendrimer) did not, with both having a solid-state PLQY of around 10%. The results suggest that intrapolymer chromophore-chromophore interactions observed in solution for the poly(dendrimer) were similar to the intermolecular chromophore-chromophore interactions of the dendrimer in the solid state. Simple two-layer organic light-emitting diodes comprising nondoped films of the materials and an electron transport layer showed red emission with CIE coordinates of (x > 0.66, y < 0.34). The dendrimer-based device had a maximum external quantum efficiency of 2.4%, which is among the best for solution-processed deep-red emissive TADF-based OLEDs but in a simpler device architecture.
First author: Luy, JN, Complementary Base Lowers the Barrier in SuFEx Click Chemistry for Primary Amine Nucleophiles,
ACS OMEGA, 5, 31432, (2020)
Abstract: The sulfur(VI) fluoride exchange (SuFEx) reaction is an emerging scheme for connecting molecular building blocks. Due to its broad functional group tolerance and rather stable resulting linkage, it is seeing rapid adoption in various fields of chemistry. Still, to date the reaction mechanism is poorly understood, which hampers further development. Here, we show that the mechanism of the SuFEx reaction for the prototypical example of methanesulfonyl fluoride reacting with methylamine can be understood as an S(N)2-type reaction. By analyzing the reaction path with the help of density functional theory in vacuo and under consideration of solvent and co-reactant influence, we identify the often used complementary base as a crucial ingredient to lower the reaction barrier significantly by increasing the nucleophilicity of the primary amine. With the help of energy decomposition analysis at the transition state structures, we quantify the underlying stereoelectronic effects and propose new avenues for experimental exploration of the potential of SuFEx chemistry.
First author: Lu, CW, Large Non-planar Conjugated Molecule with Strong Intermolecular Interactions Achieved with Homoleptic Zn(II) Complex of Di(5-quinolylethynyl)-tetraphenylazadipyrromethene,
ACS OMEGA, 5, 31467, (2020)
Abstract: Zinc(II) complexes of tetraphenylazadipyrromethenes are potential non-planar n-type conjugated materials. To tune the properties, we installed 5-quinolylethynyl groups at the pyrrolic positions. Compared to the complex with 1-napthylethynyl, we found evidence for stronger intermolecular interactions in the new complex, including much higher overlap integrals in crystals. X-ray analysis revealed unconventional C-H center dot center dot center dot N hydrogen bonding between two quinolyls of neighboring molecules, pointing to a new strategy for the development of non-planar molecular semiconductors with stronger intermolecular interactions.
First author: Kim, M, Insights into the Metal-Exchange Synthesis of MAg24(SR)(18) (M = Ni, Pd, Pt) Nanoclusters,
CHEMISTRY OF MATERIALS, 32, 10216, (2020)
Abstract: The metal-exchange reaction is a powerful means to generate atomically precise alloy nanoclusters. Both galvanic and antigalvanic exchange strategies have been devised to produce various doped metal nanoclusters with atomic precision. Here we report new insights into the metal-exchange synthesis of MAg24(SPhMe2)(18) (M = Ni, Pd, Pt) nanoclusters. Based on the redox potential comparison of the Ag-25 template with metal ion dopants, we reveal that the metal-exchange reaction is a redox potential-driven process and propose a two-step metal-exchange model that includes dopant deposition and host dissolution steps. With the help of a co-reductant and a counterion, the high-yield metal-exchange syntheses of MAg24(SPhMe2)(18) nanoclusters are demonstrated, yielding center-doped [NiAg24(SPhMe2)(18)](0), [PdAg24(SPhMe2)(18)](2-), and [PtAg24(SPhMe2)(18)](2-) nanoclusters in >70% yield. Voltammetric and density functional investigations reveal that [NiAg24(SPhMe2)(18)](0) is a six-electron superatom having a distorted core due to the Jahn-Teller effect. The neutral [NiAg24(SPhMe2)(18)](0) becomes an eight-electron [NiAg24(SPhMe2)(18)](2-) superatom upon chemical reduction, which has an isotropic core as confirmed by single-crystal X-ray diffraction.
First author: Speelman, T, Electronic couplings for singlet fission: Orbital choice and extrapolation to the complete basis set limit,
JOURNAL OF COMPUTATIONAL CHEMISTRY, 42, 326, (2021)
Abstract: For the search for promising singlet fission candidates, the calculation of the effective electronic coupling, which is required to estimate the singlet fission rate between the initially excited state (S0S1) and the multiexcitonic state ((TT)-T-1, two triplets on neighboring molecules, coupled into a singlet), should be sufficiently reliable and fast enough to explore the configuration space. We propose here to modify the calculation of the effective electronic coupling using a nonorthogonal configuration interaction approach by: (a) using only one set of orbitals, optimized for the triplet state of the molecules, to describe all molecular electronic states, and (b) only taking the leading configurations into consideration. Furthermore, we also studied the basis set convergence of the electronic coupling, and we found, by comparison to the complete basis set limit obtained using the cc-pVnZ series of basis sets, that both the aug-cc-pVDZ and 6-311++G** basis sets are a good compromise between accuracy and computational feasibility. The proposed approach enables future work on larger clusters of molecules than dimers.
First author: Raynaud, C, P-31 Chemical Shifts in Ru(II) Phosphine Complexes. A Computational Study of the Influence of the Coordination Sphere,
INORGANIC CHEMISTRY, 59, 17038, (2020)
Abstract: The NMR chemical shift has been the most versatile marker of chemical structures, by reflecting global and local electronic structures, and is very sensitive to any change within the chemical species. In this work, Ru(II) complexes with the same five ligands and a variable sixth ligand L (none, H2O, H2S, CH3SH, H-2, N-2, N2O, NO+, C=CHPh, and CO) are studied by using as the NMR reporter the phosphorus P-A of a coordinated bidentate P-A-N ligand (P-A-N = o-diphenylphosphino-N,N’-dimethylaniline). The chemical shift of P-A in RuCl2(P-A-N)(PR3)(L) (R = phenyl, p-tolyl, or p-FC6H4) was shown to increase as the Ru-P-A bond distance decreases, an observation that was not rationalized. This work, using density functional theory (DFT) calculations, reproduces reasonably well the observed P-31 chemical shifts for these complexes and the correlation between the shifts and the Ru-P-A bond distance as L varies. An interpretation of this correlation is proposed by using a natural chemical shift (NCS) analysis based on the natural bonding orbital (NBO) method. This analysis of the principal components of the chemical shift tensors shows how the sigma-donating properties of L have a particularly high influence on the phosphine chemical shifts.
First author: Castro, AC, First-Principles Calculation of H-1 NMR Chemical Shifts of Complex Metal Polyhydrides: The Essential Inclusion of Relativity and Dynamics,
INORGANIC CHEMISTRY, 59, 17509, (2020)
Abstract: H-1 NMR spectroscopy has become an important technique for the characterization of transition-metal hydride complexes, whose metal-bound hydrides are often difficult to locate by X-ray diffraction. In this regard, the accurate prediction of H-1 NMR chemical shifts provides a useful, but challenging, strategy to help in the interpretation of the experimental spectra. In this work, we establish a density-functional-theory protocol that includes relativistic, solvent, and dynamic effects at a high level of theory, allowing us to report an accurate and reliable interpretation of H-1 NMR hydride chemical shifts of iridium polyhydride complexes. In particular, we have studied in detail the hydride chemical shifts of the [Ir-6(IMe)(8)(CO)(2)H-14](2+) complex in order to validate previous assignments. The computed H-1 NMR chemical shifts are strongly dependent on the relativistic treatment, the choice of the DFT exchange-correlation functional, and the conformational dynamics. By combining a fully relativistic four-component electronic-structure treatment with ab initio molecular dynamics, we were able to reliably model both the terminal and bridging hydride chemical shifts and to show that two NMR hydride signals were inversely assigned in the experiment.
First author: Huynh, W, Origin of the Si-29 NMR chemical shift in R3Si-X and relationship to the formation of silylium (R3Si+) ions,
DALTON TRANSACTIONS, 49, 16453, (2020)
Abstract: The origin in deshielding of Si-29 NMR chemical shifts in R3Si-X, where X = H, OMe, Cl, OTf, [CH6B11X6], toluene, and O-X (O-X = surface oxygen), as well as (Pr3Si+)-Pr-i and Mes(3)Si(+) were studied using DFT methods. At the M06-L/6-31G(d,p) level of theory the geometry optimized structures agree well with those obtained experimentally. The trends in Si-29 NMR chemical shift also reproduce experimental trends; (Pr3Si)-Pr-i-H has the most shielded Si-29 NMR chemical shift and free (Pr3Si+)-Pr-i or isolable Mes(3)Si(+) have the most deshielded Si-29 NMR chemical shift. Natural localized molecular orbital (NLMO) analysis of the contributions to paramagnetic shielding (sigma(p)) in these compounds shows that Si-R (R = alkyl, H) bonding orbitals are the major contributors to deshielding in this series. The Si-R bonding orbitals are coupled to the empty p-orbital in (Pr3Si+)-Pr-i or Mes(3)Si(+), or to the orbital in R3Si-X. This trend also applies to surface bound R3Si-O-X. This model also explains chemical shift trends in recently isolated (Bu2SiH2+)-Bu-t, (BuSiH2+)-Bu-t, and SiH3+ that show more shielded Si-29 NMR signals than R3Si+ species. There is no correlation between isotropic Si-29 NMR chemical shift and charge at silicon.
First author: Zhao, YN, A computational study of the reactivity of rare-earth/phosphorus Lewis pairs toward polymerization of conjugated polar alkenes,
INORGANIC CHEMISTRY FRONTIERS, 7, 4600, (2020)
Abstract: The polymerization mechanism of methyl methacrylate (MMA) catalyzed by rare-earth/phosphorus (RE/P) Lewis pairs has been systematically studied through density functional theory (DFT) calculations. Having achieved an agreement between theory and experiment, it is found that the polymerization of MMA mediated by intermolecular RE/P Lewis pairs mainly follows the bimetallic mechanism, while the monometallic pathway could not be excluded in the case of a La analogue. In comparison with phenyl phosphorus as a Lewis base, the higher activity of cyclohexyl phosphorus toward MMA polymerization could be ascribed to the electron-donation ability, rendering more electron flow in the addition reaction. Besides, a computational modelling of analogous intramolecular RE/P systems indicates that the size of the central metal and the length of the chain connecting Lewis pairs play an important role in the catalytic activity.
First author: Chen, DD, Aromaticity Survival in Hydrofullerenes: The Case of C66H4 with Its pi-Aromatic Circuits,
CHEMISTRY-A EUROPEAN JOURNAL, 27, 802, (2021)
Abstract: The isolated-pentagon rule (IPR) is a determining structural feature that accounts for hollow fullerene stabilization and properties related to C-n (n >= 60) cages. The recent characterization of an unprecedented non-IPR hydrofullerene, C-2v C66H4, bearing two heptagons with adjacent fused-pentagon motifs, largely dismisses this feature. Herein, employing DFT calculations, the C-13 NMR spectroscopy and aromatic behavior of C-2v C66H4 are explored. The results show the presence of three pi-aromatic circuits at the bottom boat section of C66H4, indicating the unique features of this hydrofullerene in comparison to those of pristine C-60. In addition, under specific orientations of the external field, certain pi-aromatic circuits are enabled, resulting in a more aromatic fullerene than that of C-60, but lower than that of the spherical aromatic C-60(6-) fulleride. Notably, under a field aligned with the saturated carbon atoms, nonaromatic characteristics are exposed. This reveals that spherical-like cages can involve a complex magnetic response that heavily depends on the orientation of the applied field.
First author: Deng, GH, Generation and Identification of the Linear OCBNO and OBNCO Molecules with 24 Valence Electrons,
CHEMISTRY-A EUROPEAN JOURNAL, 27, 412, (2021)
Abstract: Two structural isomers containing five second-row element atoms with 24 valence electrons were generated and identified by matrix-isolation IR spectroscopy and quantum chemical calculations. The OCBNO complex, which is produced by the reaction of boron atoms with mixtures of carbon monoxide and nitric oxide in solid neon, rearranges to the more stable OBNCO isomer on UV excitation. Bonding analysis indicates that the OCBNO complex is best described by the bonding interactions between a triplet-state boron cation with an electron configuration of (2s)(0)(2p(sigma))(0)(2p(pi))(2) and the CO/NO- ligands in the triplet state forming two degenerate electron-sharing pi bonds and two ligand-to-boron dative sigma bonds.
First author: Surmenev, RA, Ab initio calculations and a scratch test study of RF-magnetron sputter deposited hydroxyapatite and silicon-containing hydroxyapatite coatings,
SURFACES AND INTERFACES, 21, 412, (2020)
Abstract: A crucial property for implants is their biocompatibility. To ensure biocompatibility, thin coatings of hydroxyapatite (HA) are deposited on the actual implant. In this study, we investigate the effects of the addition of silicate anions to the structure of hydroxyapatite coatings on their adhesion strength via a scratch test and ab initio calculations. We find that both the grain size and adhesion strength decrease with the increase in the silicon content in the HA coating (SiHA). The increase in the silicon content to 1.2 % in the HA coating leads to a decrease in the average crystallite size from 28 to 21 nm, and in the case of 4.6 %, it leads to the formation of an amorphous or nanocrystalline film. The decreases in the grain and crystallite sizes lead to peeling and destruction of the coating from the titanium substrate at lower loads. Further, our ab initio simulations demonstrate an increased number of molecular bonds at the amorphous SiHA-TiO2 interface. However, the experimental results revealed that the structure and grain size have more pronounced effects on the adhesion strength of the coatings. In conclusion, based on the results of the ab initio simulations and the experimental results, we suggest that the presence of Si in the form of silicate ions in the HA coating has a significant impact on the structure, grain size, and number of molecular bonds at the interface and on the adhesion strength of the SiHA coating to the titanium substrate.
First author: Pronin, AS, Cyanide Complexes Based on {Mo6I8}(4+) and {W6I8}(4+) Cluster Cores,
MOLECULES, 25, 412, (2020)
Abstract: Compounds based on new cyanide cluster anions [{Mo6I8}(CN)(6)](2-), trans-[{Mo6I8}(CN)(4)(MeO)(2)](2-) and trans-[{W6I8}(CN)(2)(MeO)(4)](2-) were synthesized using mechanochemical or solvothermal synthesis. The crystal and electronic structures as well as spectroscopic properties of the anions were investigated. It was found that the new compounds exhibit red luminescence upon excitation by UV light in the solid state and solutions, as other cluster complexes based on {Mo6I8}(4+) and {W6I8}(4+) cores do. The compounds can be recrystallized from aqueous methanol solutions; besides this, it was shown using NMR and UV-Vis spectroscopy that anions did not undergo hydrolysis in the solutions for a long time. These facts indicate that hydrolytic stabilization of {Mo6I8} and {W6I8} cluster cores can be achieved by coordination of cyanide ligands.
First author: Koyama, S, Synthesis, Structure and Physical Properties of (trans-TTF-py(2))(1.5)(PF6)center dot EtOH: A Molecular Conductor with Weak CH center dot center dot center dot N Hydrogen Bondings,
CRYSTALS, 10, 412, (2020)
Abstract: The studies of crystal structures with hydrogen bonds have been actively pursued because of their moderate stabilization energy for constructing unique structures. In this study, we synthesized a molecular conductor based on 2,6-bis(4-pyridyl)-1,4,5,8-tetrathiafulvalene (trans-TTF-py(2)). Two pyridyl groups were introduced into the TTF skeleton toward the structural exploration in TTF-based molecular conductors involved by hydrogen bonds. In the obtained molecular conductor, (trans-TTF-py(2))(1.5)(PF6)center dot EtOH, short contacts between the pyridyl group and the hydrogen atom of the TTF skeleton were observed, indicating that hydrogen bonding interactions were introduced in the crystal structure. Spectroscopic measurements and conductivity measurement revealed semiconducting behavior derived from pi-stacked trans-TTF-py(2) radical in the crystal structure. Finally, these results are discussed with the quantified hydrogen bonding stabilization energy, and the band calculation of the crystal obtained from density functional theory calculation.
First author: Carlotto, S, Spin state, electronic structure and bonding on C-scorpionate [Fe (II)Cl-2(tpm)] catalyst: An experimental and computational study,
CATALYSIS TODAY, 358, 403, (2020)
Abstract: The Fe(II) spin state in the condensed phase of [Fe(II)Cl2(tpm)] (tpm = [tris(pyrazol-1-yl)methane]; 1) catalyst has been determined through a combined experimental and theoretical investigation of X-Ray Absorption Spectroscopy (XAS) at the L-Fe(2,3)-edges and K-N-edge. Results indicated that in this phase a mixed singlet/triplet state is plausible. These results have been compared with the already know Fe singlet spin state of the same complex in water solution. A detailed analysis of the electronic structure and bonding mechanism of the catalyst showed that the preference for the low-spin diamagnetic ground state, strongly depends upon the ligands, the bulk solvent and the interaction of the complex’s vacant site (the sixth) with a further ligand. Moreover, comparison of the electronic properties of the complex in condensed phase and water solution showed an increased Lewis acidity of the catalyst in solution phase, due to a decreasing of the LUMO energy of about 8 kcal/mol. These results gave an overall picture of the electronic behavior of the complex investigated, on going from condensed to water solution phase, explaining the preferred use of 1 as catalyst in homogeneous catalysis. The NeFe(II) interaction has been thoroughly investigated by means of DFT Kohn-Sham and EDA bond analysis applied to i) the isolated [Fe(II)Cl-2(tpm)] and ii) the [Fe(II)Cl-2(tpm)] interacting with water as a solvent within the Conductor-like Screening Mode (COSMO) framework. Results showed that both tpm -> Fe(II) sigma and tpm?Fe (II) pi Charge Transfer (CT) interactions characterize the Fe(II)-tpm interaction. Moreover, the three tpm N atoms do not equally interact with the Fe(II) and one of them shares a suitable available iron-based d virtual orbital, to bind a further ligand in trans position.
First author: Evtushenko, DN, A cocrystal of L-ascorbic acid with picolinic acid: the role of O-H center dot center dot center dot O, N-H center dot center dot center dot O and C-H center dot center dot center dot O hydrogen bonds and L-ascorbic acid conformation in structure stabilization,
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING, 76, 967, (2020)
Abstract: A new 1:1 cocrystal (L-Asc-Pic) of L-ascorbic acid (vitamin C) with picolinic acid was prepared as a powder and as single crystals. The crystal structure was solved and refined from single-crystal X-ray diffraction (SCXRD) data collected at 293 (2) and 100 (2) K. The samples of the L-Asc-Pic cocrystal were characterized by elemental (HCNS) analysis and titrimetric methods, TG/DTG/DSC, and IR and Raman spectroscopy. The asymmetric unit comprises a picolinic acid zwitterion and an L-ascorbic acid molecule. The stabilization energy of intermolecular interactions involving hydrogen bonds, the vibrational spectrum and the energies of the frontier molecular orbitals were calculated using the GAUSSIAN09 and the CrystalExplorer17 programs. The charge distribution on the atoms of the L-Asc-Pic cocrystal, L-ascorbic acid itself and its 12 known cocrystals (structures from Version 5.40 of the Cambridge Structural Database) were calculated by the methods of Mulliken, Voronoi and Hirshfeld charge analyses (ADF) at the bp86/TZ2P+ level of theory. The total effective charges and conformations of the L-ascorbic acid molecules in the new and previously reported cocrystals were compared with those of the two symmetry-independent molecules in the crystals of L-ascorbic acid. A correlation between molecular conformation and its effective charge is discussed.
First author: Chong, DP, Calculation of reliable non-resonant K alpha X-ray emission spectra of organic molecules and other small molecules,
CANADIAN JOURNAL OF CHEMISTRY, 98, 741, (2020)
Abstract: For reliable calculation of vertical ionization energies (VIEs) of both core and valence electrons of gas-phase organic molecules and other small molecules, we developed DFT procedures in 1999 and 2009. The difference between core and valence VIEs give the energies for X-ray emission spectra (XES). The dipole matrix elements between core and valence electrons required for calculation of the XES intensities are now easily available. The simple procedure for calculation of reliable XES is demonstrated by comparison with known XES for H2O(g), NH3(g), CO(g), CO2(g), N-2(g), and NNO(g). Consequently, the XES of H2CO(g), formamide(g), 1-nitrosamine(g), N-methylfonnamide(g), 1-nitrosoaziridine(g), and oxirane(g) are predicted with confidence.
First author: Conradie, MM, Rhodium(triphenylphosphine)carbonyl-2,4-dioxo-3-pentyl-4-decanyloxybenzo ate: A DFT study of oxidative addition and methyl migration,
INORGANICA CHIMICA ACTA, 513, 741, (2020)
Abstract: A density functional theory (DFT) study of the oxidative addition of iodomethane to a [Rh(beta-diketonato)(CO) (PPh3)] complex containing a beta-diketonato ligand, beta-L1 = (CH3COC(C10H21OC6H4COO)COCH3)(-), with a long chain (R-3 = C10H21OC6H4COO) substituted at the C3 position of the beta-diketonato ligand, is presented and compared to the oxidative addition of iodomethane to the mother compound [Rh(acac)(CO)(PPh3)], acac = (CH3COCHCOCH3)(-), with a H at the C3 position The oxidative addition of iodomethane to both compounds follows a similar mechanism to form the first Rh(III)-alkyl1 product with methyl and iodide in the positions below and above the square plane formed by the C-CO, P-PPh3 and the two beta-diketonato oxygens (O-beta). The followup carbonyl insertion and deinsertion steps, however, follow a different mechanism to from the second experimentally observed Rh(III)-alkyl2 product.
First author: Ang, TN, Enrichment of surface oxygen functionalities on activated carbon for adsorptive removal of sevoflurane,
CHEMOSPHERE, 260, 741, (2020)
Abstract: Activated carbons have been reported to be useful for adsorptive removal of the volatile anaesthetic sevoflurane from a vapour stream. The surface functionalities on activated carbons could be modified through aqueous oxidation using oxidising solutions to enhance the sevoflurane adsorption. In this study, an attempt to oxidise the surface of a commercial activated carbon to improve its adsorption capacity for sevoflurane was conducted using 6 mol/L nitric acid, 2 mol/L ammonium persulfate, and 30 wt per cent (wt%) of hydrogen peroxide (H2O2). The adsorption tests at fixed conditions (bed depth: 10 cm, inlet concentration: 528 mg/L, and flow rate: 3 L/min) revealed that H2O2 oxidation gave desirable sevoflurane adsorption (0.510 +/- 0.005 mg/m(2)). A parametric study was conducted with H2O2 to investigate the effect of oxidation conditions to the changes in surface oxygen functionalities by varying the concentration, oxidation duration, and temperature, and the Conductor-like Screening Model for Real Solvents (COSMORS) was applied to predict the interactions between oxygen functionalities and sevoflurane. The H2O2 oxidation incorporated varying degrees of both surface oxygen functionalities with hydrogen bond (HB) acceptor and HB donor characters under the studied conditions. Oxidised samples with enriched oxygen functionalities with HB acceptor character and fewer HB donor character exhibited better adsorption capacity for sevoflurane. The presence of a high amount of oxygen functional groups with HB donor character adversely affected the sevoflurane adsorption despite the enrichment of oxygen functional groups with HB acceptor character that have a higher tendency to adsorb sevoflurane.
First author: de Bruijn, HM, The Hydrogenation Problem in Cobalt-based Catalytic Hydroaminomethylation,
CHEMISTRYSELECT, 5, 13981, (2020)
Abstract: The hydroaminomethylation (HAM) reaction converts alkenes into N-alkylated amines and has been well studied for rhodium- and ruthenium-based catalytic systems. Cobalt-based catalytic systems are able to perform the essential hydroformylation reaction, but are also known to form very active hydrogenation catalysts, therefore we examined such a system for its potential use in the HAM reaction. Thus, we have quantum-chemically explored the hydrogenation activity of [HCo(CO)(3)] in model reactions with ethene, methyleneamine, formaldehyde, and vinylamine using dispersion-corrected relativistic density functional theory at ZORA-BLYP-D3(BJ)/TZ2P. Our computations reveal essentially identical overall barriers for the catalytic hydrogenation of ethene, formaldehyde, and vinylamine. This strongly suggests that a cobalt-based catalytic system will lack hydrogenation selectivity in experimental HAM reactions. Our HAM experiments with a cobalt-based catalytic system (consisting of Co-2(CO)(8) as cobalt source and P(n-Bu)(3) as ligand) resulted in the formation of the desired N-alkylated amine. However, significant amounts of hydrogenated starting material as well as alcohol (hydrogenated aldehyde) were always formed. The use of cobalt-based catalysts in the HAM reaction to selectively form N-alkylated amines seems therefore not feasible. This confirms our computational prediction and highlights the usefulness of state-of-the-art DFT computations for guiding future experiments.
First author: Wu, QY, Electronic structures and bonding of the actinide halides An(TRENTIPS)X (An = Th-Pu; X = F-I): a theoretical perspective,
DALTON TRANSACTIONS, 49, 15895, (2020)
Abstract: To evaluate how halogen and actinide atoms affect the electronic structures and bonding nature, we have theoretically investigated a series of the actinide halides An(TRENTIPS)X (An = Th-Pu; X = F-I); several of them have been synthesized by Liddle’s group. The An-X bond distances decrease from An = Th to Pu for the same halides, and the harmonic vibrational frequencies for the An-X bonds are more susceptible to being affected by the halogen atoms. The analyses of bonding nature reveal that the An-X bonds have a certain covalency with a polarized character, and the sigma-bonding component in the total orbital contribution is greatly larger than the corresponding pi-bonding ones based on the analysis of the NOCVs (the natural orbitals for chemical valence). Furthermore, the electronic structures of the thorium complexes are obviously different from those of the uranium and transuranic analogues due to more valence electrons in Th 6d orbitals. In addition, thermodynamic results suggest that the U(TRENTIPS)Br complex is the most stable and U(TRENTIPS)Cl has the highest reactivity based on the halide exchange reaction of U(TRENTIPS)X complexes using Me3SiX. The reduction ability of the tetravalent An(TRENTIPS)X is sensitive to halogen atoms according to the calculated electron affinity of the An(TRENTIPS)X and the reactions An(TRENTIPS)X + K -> An(TRENTIPS) + KX. This work presents the effect of the halogen and the actinide atoms on the structures, bonding nature and redox ability of a series of the tetravalent actinide halides with TREN ligand and facilitates our in-depth understanding of f-block elements, which could provide theoretical guidance for experimental work on actinide halides, especially for the synthetic chemistry of transuranic halides.
First author: Das, P, Electride Characteristics of Some Binuclear Sandwich Complexes of Alkaline Earth Metals, M-2(eta(5)-L)(2) (M = Be, Mg; L = C5H5-, N-5(-), P-5(-), As-5(-)),
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 9801, (2020)
Abstract: Ab initio calculations have been performed for a series of binuclear sandwich complexes, M-2(eta(5)-L)(2). It has been observed that the eclipsed and staggered conformations have almost equal amount of energies. The M-M bond lengths are comparable with those in the free M-2 molecules (M = Be, Mg). The nuclear-independent chemical shift (NICS) values indicate the aromaticity of these complexes. The stability of Be-2(eta(5)-L)(2) complexes is higher than that of the Mg-2(eta(5)-L)(2 )complexes. The natural bond orbital (NBO) analysis and electron density descriptors proved the existence of a single covalent M-M bond in an M-2(2+) fragment. It has been observed that each M-M bond contains a non-nuclear attractor (NNA) at the center of the respective bond. The Laplacian of electron density [V-2 rho(r)] is negative at the NNAs. The energy decomposition analysis (EDA) showed that M-2(2+) and 2L(-) represent the bonding interaction in the complexes. All of the designed binuclear sandwich complexes behave as electrides.
First author: Mughal, EU, Terpyridine-metal complexes: effects of different substituents on their physico-chemical properties and density functional theory studies,
ROYAL SOCIETY OPEN SCIENCE, 7, 9801, (2020)
Abstract: A series of different substituted terpyridine (tpy)-based ligands have been synthesized by Krohnke method. Their binding behaviour was evaluated by complexing them with Co(II), Fe(II) and Zn(II) ions, which resulted in interesting coordination compounds with formulae, [Zn(tpy)(2)]PF6, [Co(tpy)(2)](PF6)(2), [Fe(tpy)(2)](PF6)(2) and interesting spectroscopic properties. Their absorption and emission behaviours in dilute solutions were investigated in order to explain structure-property associations and demonstrate the impact of different aryl substituents on the terpyridine scaffold as well as the role of the metal on the complexes. Photo-luminescence analysis of the complexes in acetonitrile solution revealed a transition from hypsochromic to bathochromic shift. All the compounds displayed remarkable photo-luminescent properties and various maximum emission peaks owing to the different nature of the functional groups. Furthermore, the anti-microbial potential of ligands and complexes was evaluated with docking analyses carried out to investigate the binding affinity of terpyridine-based ligands along with corresponding proteins (shikimate dehydrogenase and penicillin-binding protein) binding sites. To obtain further insight into molecular orbital distributions and spectroscopic properties, density functional theory calculations were performed for representative complexes. The photophysical activity and interactions between chromophore structure and properties were both investigated experimentally as well as theoretically.
First author: Oh-e, M, Advancing the a Posteriori Quest for Deep-Blue Phosphorescence: Quantifying Excitation-Induced Metal-to-Ligand Charge Transfer as a Guiding Indicator,
ORGANOMETALLICS, 39, 3951, (2020)
Abstract: To advance the a posteriori quest for deep-blue phosphorescence, we quantify the degree of metal-to-ligand charge transfer (MLCT) upon excitation using density functional theory calculations. We also comprehensively determine how the MLCT nature of a state is correlated with the wavelength of potential phosphorescence through comparing the results of two typical ligand structures, i.e., 2-phenylpyridine and 1-phenyl-3-methyl-imidazolin-2-ylidene, with those of their derivatives. The MLCT nature can be defined as the difference in the electron density over the central metal ion that contributes to the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO, respectively). This study focuses on how the MLCT nature can be characterized upon excitation depending on the admixtures of molecular orbitals and how a stronger MLCT nature is preferable for efficient phosphorescence, while the MLCT nature exhibits a trade-off relationship with the wavelengths of phosphorescence in the blue region. Moreover, we elucidate how iridium(III) complexes are suitable for efficient phosphorescence and discuss a conceptual grand design for transition-metal complexes with deep-blue phosphorescence using the ligand field theory. We examine why strong MLCT nature upon excitation does not necessarily ensure highly efficient phosphorescence, taking into account possible relative energy gaps between the singlet MLCT, triplet locally excited, and d-d transition states in a transition-metal complex formed after excitation. Nevertheless, the initial MLCT serves as a necessary condition that induces corollary energy-state configurations as well as decay from the excited states. Therefore, quantifying the nature of that MLCT, which is the first process upon excitation, with the possible wavelength of phosphorescence is a useful parameter for a conceptual grand design for candidate complexes that can efficiently emit deep-blue phosphorescence. This reverse method of analyzing candidate complexes before experimentally formulating and studying them can accelerate the a posteriori quest for deep-blue-emitting materials.
First author: Behnia, A, Cycloneophylpalladium(IV) Complexes: Formation by Oxidative Addition and Selectivity of Their Reductive Elimination Reactions,
ORGANOMETALLICS, 39, 4037, (2020)
Abstract: The cycloneophylpalladium(II) complexes [Pd-(CH2CMe2C6H4)(kappa(2)-N,N’-L)] (L = RO(CH2)(3)N(CH2-2-C5H4N)(2), R = H, Me) undergo oxidation to Pd(IV) with bromine or iodine to give [PdX(CH2CMe2C6H4)(kappa(3)-N,N’,N ”-L)PC (X = Br, I) or with methyl iodide to give the transient complexes [PdMe(CH2CMe2C6H4)(kappa(3)-N,N’,N ”-L)]I. The products of Br2 and Br, I), are sufficiently stable to be isolated, but they decompose slowly in solution by reductive elimination to give the palladium- (II) products [PdX(kappa(3)-N,N’,N ”-L)]X (X = Br, I). The organic products are formed via either CH2-Ar or CH2-X bond formation. In the latter case, neophyl rearrangement and protonolysis steps follow reductive elimination to give a mixture of organic products. The methylpalladium(IV) complexes [PdMe(CH2CMe2C6H4)(kappa(3)-N,N’,N ”-L)]I decompose at 0 degrees C by selective reductive elimination with Me-Ar bond coupling to give the alkylpalladium(II) complex [Pd(CH2CMe2-2-C6H4Me)(kappa(3)-N,N’,N ”-L)]I. The mechanisms of the reactions have been explored by kinetic studies.
First author: Dalla Tiezza, M, Proton Transfer and S(N)2 Reactions as Steps of Fast Selenol and Thiol Oxidation in Proteins: A Model Molecular Study Based on GPx,
CHEMPLUSCHEM, 86, 525, (2021)
Abstract: The so-called peroxidatic cysteines and selenocysteines in proteins reduce hydroperoxides through a dual attack to the peroxide bond in a two-step mechanism. First, a proton dislocation from the thiol/selenol to a close residue of the enzymatic pocket occurs. Then, a nucleophilic attack of the anionic cysteine/selenocysteine to one O atom takes place, while the proton is shuttled back to the second O atom, promoting the formation of a water molecule. In this computational study, we use a molecular model of GPx to demonstrate that the enzymatic environment significantly lowers the barrier of the latter S(N)2 step. Particularly, in our Se-based model the energy barriers for the two steps are 29.82 and 2.83 kcal mol(-1), both higher than the corresponding barriers computed in the enzymatic cluster, i. e., 21.60 and null, respectively. Our results, obtained at SMD-B3LYP-D3(BJ)/6-311+G(d,p), cc-pVTZ//B3LYP-D3(BJ)/6-311G(d,p), cc-pVTZ level of theory, show that the mechanistic details can be well reproduced using an oversimplified model, but the energetics is definitively more favorable in the GPx active site. In addition, we pinpoint the role of the chalcogen in the peroxide reduction process, rooting the advantages of the presence of selenium in its acidic and nucleophilic properties.
First author: Saes, BWH, Tuning the Optical Characteristics of Diketopyrrolopyrrole Molecules in the Solid State by Alkyl Side Chains,
JOURNAL OF PHYSICAL CHEMISTRY C, 124, 25229, (2020)
Abstract: The optical properties of two sets of donor-acceptor-donor molecules with terminal bithiophene donor units and a central diketopyrrolopyrrole (DPP) acceptor unit are studied. The two sets differ in the alkyl chains on the DPP, which are either branched at the a-carbon (3-pentyl) (1-4) or linear (n-hexyl) (5-8). Within each set, the molecules differ by the absence or presence of n-hexyl chains on the terminal thiophene rings in the 3′, 4′, or 5′ positions. While in solution, the optical spectra differ only subtly; they differ dramatically in the solid state. In contrast to 5-8, 1-4 are nonplanar as a consequence of the sterically demanding 3-pentyl groups, which inhibit pi-stacking of the DPP units. Using the crystal structures of 2 (brick layer stacking) and 6 (slipped stacking), we quantitatively explain the solid state absorption spectra. By computing the molecular transition charge density and solving the dispersion relation, the optical absorption of the molecules in the crystal is predicted and in agreement with experiments. For 2, a single resonance frequency is obtained, while for 6 two transitions are seen, with the lower-energy transition being less intense. The results demonstrate how subtle changes in substitution exert large effects in optical properties.
First author: Kim, JW, Holistic Approach to the Mechanism Study of Thermal Degradation of Organic Light-Emitting Diode Materials,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 9589, (2020)
Abstract: The design of stable organic light-emitting diode materials is the key to long lifetime displays under various stressful conditions. Elucidating the degradation mechanism of the materials at the molecular level provides useful information for securing high stability. Previous works based on experiments or computations disclosed only a part of the whole degradation process. Here, we propose a holistic approach to the systematic analysis of the degradation mechanism by combining experimental mass analysis Sample from and computation in a semi-automated fashion. The mass analysis device identifies molecular weights of feasible products from degradation reactions. Then, the computational analysis goes through initiation, propagation, and termination phases. The initiation phase determines radical fragments and reactive sites, triggering the propagation process. hi the propagation phase, we subsequently perform intermediate sampling, reaction network construction, and kinetic analysis. As a proof of concept, this approach was applied to the thermal degradation problem during the sublimation purification process. Two major pathways were successfully elucidated with full atomistic details.
First author: Dai, YZ, Solid-State O-17 NMR Studies of Sulfonate Jump Dynamics in Crystalline Sulfonic Acids: Insights into the Hydrogen Bonding Effect,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 9597, (2020)
Abstract: We report variable-temperature (VT) O-17 solid-state nuclear magnetic resonance (NMR) spectra for three crystalline sulfonic acids: L-cysteic acid monohydrate (CA), 3-pyridinesulfonic acid (PSA), and p-toluenesulfonic acid monohydrate (TSA). We were able to analyze the experimental VT O-17 NMR spectra to obtain the activation barriers for SO3- jumps in these systems. Using the density functional-based tight-binding (DFTB) method, we performed potential energy surface scans for SO3- jumps in the crystal lattice of CA, PSA, and TSA, as well as for three related crystalline sulfonic acids (taurine, homotaurine, and 4-aminobutane-1-sulfonic acid) for which relevant O-17 solid-state NMR data are available in the literature. The calculated activation barriers are in reasonable agreement with the experimental values. On the basis of the DFTB results, we hypothesized that activation barriers for SO3- jumps in the crystal lattice depend largely on the hydrogen bonding energy difference between the ground state and the transition state.
First author: Konnova, ME, Thermochemical Properties and Dehydrogenation Thermodynamics of Indole Derivates,
INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 59, 20539, (2020)
Abstract: Indole and methylindole are heterocyclic aromatics, which can be hydrogenated and used for hydrogen storage. A huge advantage of heterocyclic components compared to homocyclic aromatics is the lower enthalpy of reaction for hydrogen release by dehydrogenation. In this study, thermochemical properties of indole and 2-methylindole and its partially and fully hydrogenated derivatives have been determined. Hydrogenation of indoles is a two-step reaction, which is highly influenced by reaction thermodynamics. High precision combustion calorimetry was used to measure enthalpies of formation of indole derivatives. The gas-phase enthalpies of formation were derived with the help of vapor pressure measurements. The high-level quantum-chemical methods were used to establish consistency of the experimental data. The standard molar thermodynamic functions of formation (enthalpy, entropy, and Gibbs energy) of indole derivatives were derived. The results showed that the partially hydrogenated species, 2-methylindoline, tends to dehydrogenate easily under hydrogen release conditions. Thus, indoline is only expected in trace amounts in the respective reaction mixture.
First author: Nomizu, D, Solvation structure and thermodynamics for lanthanide complexes in phosphonium-based ionic liquid evaluated by Raman spectroscopy and density functional theory,
JOURNAL OF MOLECULAR LIQUIDS, 318, 20539, (2020)
Abstract: Coordination states of the divalent and trivalent lanthanide complexes in an ionic liquid (IL), triethyl-n-pentylphosphonium bis(trifluoromethyl-sulfonyl) amide [P-2225][NTf2], were investigated by Raman spectroscopy and density functional theory (DFT) with the Amsterdam density functional package (ADF). Thermodynamic properties (Delta(iso)G, Delta H-iso, and Delta S-iso) for the trans-to-cis isomerism of [NTf2] in bulk and the first solvation sphere of the [Ln(3+)] cation in the IL were evaluated from their temperature dependence in the range 298-398 K. The Delta(iso)G(bulk), Delta H-iso/(bulk), and T Delta S-iso(bulk) values at 298 K were -0.71, 7.63, and 8.34 kJ mol(-1), respectively. The trans-[NTf2] isomer had the highest enthalpy due to the positive value of Delta H-iso(bulk); T Delta S-iso(bulk) was slightly higher than Delta H-iso(bulk), and hence, cis-[NTf2] was entropy-controlled in the IL In the first solvation sphere of the [Nd3+] cation, the negative value of Delta H-iso(Nd) (-47.79 kJ mol(-1)) remarkably increased, which implied that the cis-[NTf2] isomers were stabilized for enthalpy. This result revealed that cis-[NTf2] bound to the [Ln(3+)] (Ln=Nd or Dy) cation was preferred and the coordination state of [Ln((III))(cis-NTf2)(5)](2- )was stable in the IL The optimized geometries and the bonding energies of the [Ln((II) )(cis-NTf2)(4)](2-) and [Ln((III))(cis-NTf2)(5)](2-) clusters were also investigated using the ADF. The bonding energy, Delta E-b, was calculated from Delta E-b = E-tot (cluster) – E-tot(Ln(2,3+)) nE(tot)([NTf2](-)). The Delta E-b([Nd-(II)(cis-NTf2)(4)](2-)), Delta E-b([Nd-(III)(cis-NTF2)(5)](2-)). Delta E-b([Dy-(II)(cis-NTf2)(4)](2-)), and Delta E-b([Dy-(III)(cis-NTf2)(5)](2-)), values were -2219.2, -4340.5, -2118.3, and -4258.5 kJ mol(-1), respectively. This result showed that the [Ln((III))(cis-NTf2)(5)](2-) cluster formed stronger coordination bonds than the [Ln((II))(cis-NTf2)(4)](2-) cluster.
First author: Keskic, T, Synthesis, X-ray structures and magnetic properties of Ni(II) complexes of heteroaromatic hydrazone,
POLYHEDRON, 191, 20539, (2020)
Abstract: Two binuclear double end-on azido bridged Ni(II) complexes, [Ni2L2(mu-(1,1)-N-3)(2)(N-3)(2)]center dot 2H(2)O (1a), and [Ni2L2(mu-(1,1)-N-3)(2)(N-3)(2)]center dot 4H(2)O (1b) having the same inner sphere, where L=((E)-N,N,N-trimethyl-2-oxo-2-(2-(1-(thiazol-2-yl)ethylidene)hydrazinyl)ethan-1-aminium, were synthesized from the same solution and characterized by single-crystal X-ray diffraction methods. Variable-temperature magnetic susceptibility measurements showed intra-dimer ferromagnetic coupling between Ni(II) ions. The ferromagnetic coupling is supported by the broken-symmetry DFT calculations, with the level of theory chosen based on a benchmark study on 19 additional structurally related binuclear Ni(II) complexes. The role of water molecules in crystals of 1a and 1b is explained by DFT based energy decomposition analysis.
First author: Ang, TN, Tailoring of activated carbon with ammonia for enhanced anaesthetic sevoflurane adsorption,
SEPARATION AND PURIFICATION TECHNOLOGY, 251, 20539, (2020)
Abstract: Activated carbon (AC) has been reported to be useful for removing waste volatile anaesthetics that are highly potent greenhouse gases. Surface functionalities play essential roles in sevoflurane adsorption. However, the relationship between surface nitrogen functionalities and sevoflurane adsorption has not been investigated. In this study, both single-and two-step nitrogenation of a granular AC were conducted to examine the effect of surface nitrogen functionality on sevoflurane adsorptivity under otherwise fixed experimental conditions (bed depth: 10 cm, inlet concentration: 528 mg/L, and flow rate: 3 L/min). The potential interaction between sevoflurane molecules and surface nitrogen functionality were examined using the conductor-like screening model for real solvents (COMOS-RS). COSMO-RS prediction suggested that the nitrogen groups containing C-N-C structures had a higher tendency for sevoflurane to adsorb to activated carbon. The findings agreed with the experimental adsorption results, where the pyrrolic or pyridonic groups showed an enhancing effect on sevoflurane adsorption. These findings are a useful foundation for future tailoring of activated carbon adsorbents for selective enrichment of beneficial surface functionality to remove sevoflurane before emission of anaesthetic gases.
First author: Pan, S, Quadruple bonding of bare group-13 atoms in transition metal complexes,
DALTON TRANSACTIONS, 49, 14815, (2020)
Abstract: Density functional theory calculations at the M06-D3/def2-TZVPPD level of the group-13 anion complexes EFe(CO)(3)(-) (E = B-Tl) and the isoelectronic neutral and charged boron adducts BTM(CO)(3)(q) (TMq = Fe-, Ru-, Os-, Co, Rh, Ir, Ni+, Pd+, Pt+) give tetrahedral (C-3v) geometries in the (1)A(1) electronic ground state as equilibrium structures. The analysis of the bonding situation with the energy decomposition analysis in combination with natural orbital for chemical valence method suggests that the E-TM(CO)(3)(q) bonds possess four bonding components: (a) one strong electron-sharing sigma bond E-TM(CO)(3)(q); (b) two pi backdonations E paired left arrows TM(CO)(3)(q) and (c) one weak sigma donation E -> TM(CO)(3)(q). The relative strength of the four bonding components depends on the charge of the system, the transition metal TM and the group-13 atom E. The sigma donation E -> TM(CO)(3)(q) is in all systems rather weak while the associated charge migration is not negligible. A similar situation of the bonding of terminal group-13 atoms Ga and In is found in Ga-TM(GaCp)(4)(+) and E-Pt(PMe3)(3)(+) (TM = Ni, Pd, Pt; E = Ga, In), which are model compounds for the stable complexes GaTM(GaCp*)(4)(+) (TM = Ni, Pt) and InPt(PPh3)(3)(+). The quadruple bonds E -> TML2 are hybrids of electron-sharing and dative bonds.
First author: Racioppi, S, On generalized partition methods for interaction energies,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 24291, (2020)
Abstract: The breakdown of interaction energy has always been a very important means to understand chemical bonding and it has become a seamlessly useful tool for modern supramolecular chemistry. Many interaction schemes and partitioning methods are known and widely adopted. Their common mechanism is the fragmentation of a chemical system into smaller moieties and the identification of interaction energy contributions somewhat related to a physical phenomenon. However, the definitions of energy terms and of the molecular fragments are not universal, leading to complicated comparisons among different approaches and controversial interpretations. The most adopted methodologies use a partition of the Hilbert space or of the position space. In this paper, we propose a protocol to compare energy decomposition methods based on two schemes representative of each category, namely the energy decomposition analysis (EDA, Hilbert space) and the interacting quantum atom (IQA, position space).
First author: van der Lubbe, SCC, Tuning the Binding Strength of Even and Uneven Hydrogen-Bonded Arrays with Remote Substituents,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 9451, (2020)
Abstract: We investigated the tunability of hydrogen bond strength by altering the charge accumulation around the frontier atoms with remote substituents. For pyridine-H2O with NH2 and CN substituted at different positions on pyridine, we find that the electron-withdrawing CN group decreases the negative charge accumulation around the frontier atom N, resulting in weakening of the hydrogen bond, whereas the electron-donating NH2 group increases the charge accumulation around N, resulting in strengthening of the hydrogen bond. By applying these design principles on DDAA-AADD, DADA-ADAD, DAA-ADD, and ADA-DAD hydrogen-bonded dimers, we find that the effect of the substituent is delocalized over the whole molecular system. As a consequence, systems with an equal number of hydrogen bond donor (D) and acceptor (A) atoms are not tunable in a predictable way because of cancellation of counteracting strengthening and weakening effects. Furthermore, we show that the position of the substituent and long-range electrostatics can play an important role as well. Overall, the design principles presented in this work are suitable for monomers with an unequal number of donor and acceptor atoms and can be exploited to tune the binding strength of supramolecular building blocks.
First author: Liu, QL, Machine learning-based atom contribution method for the prediction of surface charge density profiles and solvent design,
AICHE JOURNAL, 67, 9451, (2021)
Abstract: Solvents are widely used in chemical processes. The use of efficient model-based solvent selection techniques is an option worth considering for rapid identification of candidates with better economic, environment and human health properties. In this paper, an optimization-based MLAC-CAMD framework is established for solvent design, where a novel machine learning-based atom contribution method is developed to predict molecular surface charge density profiles (sigma-profiles). In this method, weighted atom-centered symmetry functions are associated with atomic sigma-profiles using a high-dimensional neural network model, successfully leading to a higher prediction accuracy in molecular sigma-profiles and better isomer identifications compared with group contribution methods. The new method is integrated with the computer-aided molecular design technique by formulating and solving a mixed-integer nonlinear programming model, where model complexities are managed with a decomposition-based strategy. Finally, two case studies involving crystallization and reaction are presented to highlight the wide applicability and effectiveness of the MLAC-CAMD framework.
First author: Rusakova, IL, Quantum chemical calculations of Se-77 and Te-125 nuclear magnetic resonance spectral parameters and their structural applications,
MAGNETIC RESONANCE IN CHEMISTRY, 59, 359, (2021)
Abstract: An accurate quantum chemical (QC) modeling of Se-77 and Te-125 nuclear magnetic resonance (NMR) spectra is deeply involved in the NMR structural assignment for selenium and tellurium compounds that are of utmost importance both in organic and inorganic chemistry nowadays due to their huge application potential in many fields, like biology, medicine, and metallurgy. The main interest of this review is focused on the progress in QC computations of Se-77 and Te-125 NMR chemical shifts and indirect spin-spin coupling constants involving these nuclei. Different computational methodologies that have been used to simulate the NMR spectra of selenium and tellurium compounds since the middle of the 1990s are discussed with a strong emphasis on their accuracy. A special accent is placed on the calculations resorting to the relativistic methodologies, because taking into account the relativistic effects appreciably influences the precision of NMR calculations of selenium and, especially, tellurium compounds. Stereochemical applications of quantum chemical calculations of Se-77 and Te-125 NMR parameters are discussed so as to exemplify the importance of integrated approach of experimental and computational NMR techniques.
First author: Fujisawa, K, Multinuclear magnetic resonance studies of five silver(I) trinuclear pyrazolate complexes,
STRUCTURAL CHEMISTRY, 32, 215, (2021)
Abstract: Experimental multinuclear determination of the chemical shifts, especially N-15 and Ag-109, of five silver(I) trinuclear pyrazolate complexes, (PzAg)(3), coupled with ZORA (zeroth-order regular approximation) and GIAO (gauge-independent atomic orbital) calculations, has shed new light on these compounds. An almost complete collection of spin-spin coupling constants has been measured for the first time for several of these compounds. The aromaticity of (PzAg)(3) was examined using NICS (nucleus-independent chemical shift) and ACID (anisotropy of the induced current density) approaches reaching the conclusion of its absence.
First author: Wolanski, L, Pt-X as the limit of high oxidation states in oxide-nitride species,
CHEMICAL COMMUNICATIONS, 56, 13137, (2020)
Abstract: A series of pentaatomic species has been investigated theoretically with relativistic DFT using the M06-L functional with both ZORA scalar relativistic correction, and including spin-orbit coupling effects. The distorted quasi-octahedral local minima for PtNO3+, PtN2O2 and PtN3O- corresponding to decavalent Pt were found to be unstable with respect to the elimination of O-2, NO or N-2. However, barriers surrounding these minima suggest that these species could be achieved under low-temperature conditions, similar to what was predicted for PtO42+ dications. Decavalent platinum sets the upper limit for high oxidation states of the chemical elements.
First author: Oh, C, The electronic structure of a beta-diketiminate manganese hydride dimer,
DALTON TRANSACTIONS, 49, 14463, (2020)
Abstract: The electronic structure of a dimeric manganese hydride catalyst supported by beta-diketiminate ligands, [(2,6-iPr2PhBDI)Mn(mu-H)](2), was investigated with density functional theory. A triple bond between the manganese centres was anticipated from simple electron-counting rules; however, calculations revealed Mn-Mn Mayer bond orders of 0.21 and 0.27 for the ferromagnetically-coupled and antiferromagnetically-coupled extremes, respectively. In accordance with experimentally determined Heisenberg exchange coupling constants of -15 +/- 0.1 cm(-1) (SQUID) and -10.2 +/- 0.7 cm(-1) (EPR), the calculated J(0) value of -10.9 cm(-1) confirmed that the ground state involves antiferromagnetic coupling between high spin Mn(II)-d(5) centres. The effect of steric bulk on the bond order was examined via a model study with the least sterically-demanding version of the beta-diketiminate ligand and was found to be negligible. Mixing between metal- and beta-diketiminate-based orbitals was found to be responsible for the absence of a metal-metal multiple bond. The bridging hydrides give rise to a relatively close positioning of the metal centres, while bridging atoms possessing 2p orbitals result in longer Mn-Mn distances and more stable dimers. The synthesis and characterization of the bridging hydroxide variant, [(2,6-iPr2PhBDI)Mn(mu-OH)](2), provides experimental support for these assessments.
First author: Babetto, L, Antenna triplet DFT calculations to drive the design of luminescent Ln(3+) complexes,
DALTON TRANSACTIONS, 49, 14556, (2020)
Abstract: Density functional theory-based methods have been exploited to look into the structural, vibrational and electronic properties of antenna ligands, all of them being crucial factors for the reliable design of customized luminescent lanthanide (Ln(3+)) complexes. The X-ray structures, UV-Vis absorption spectra and triplet (T-1) energies of three novel beta-diketone ligands with a thienyl group and naphthyl (L1), phenanthryl (L2), and pyrenyl (L3) polycyclic aromatic hydrocarbons as substituents have been modelled. Vibronic progressions provide a strong contribution to the L1 and L2 absorption spectra, while the L3 absorption spectrum needs the assumption of different conformational isomers in solution. T-1 energies have been estimated either through the vertical- or the adiabatic-transition approach. The comparison with the phosphorescence spectra of Gd3+ complexes allowed us to infer that the latter approach is the most suitable one, in particular when sizable ligands are involved. Results obtained for the isolated antennas can be directly compared with those of the corresponding Ln(3+) complexes, due to the unanimously accepted assumption that the excitation is ligand-centred.
First author: Sruthi, PK, Unusual blue to red shifting of C-H stretching frequency of CHCl3 in co-operatively PCl phosphorus bonded POCl3-CHCl3 heterodimers at low temperature inert matrixes,
JOURNAL OF CHEMICAL PHYSICS, 153, 14556, (2020)
Abstract: Heterodimers of POCl3-CHCl3 were generated in Ne, Ar, and Kr matrixes at low temperatures and were studied using infrared spectroscopy. The remarkable role of co-operative pentavalent phosphorus bonding in the stabilization of the structure dictated by hydrogen bonding is deciphered. The complete potential energy surface of the heterodimer was scanned by ab initio and density functional theory computational methodologies. The hydrogen bond between the phosphoryl oxygen of POCl3 and C-H group of CHCl3 in heterodimers induces a blue-shift in the C-H stretching frequency within the Ne matrix. However, in Ar and Kr matrixes, the C-H stretching frequency is exceptionally red-shifted in stark contrast with Ne. The plausibility of the Fermi resonance by the C-H stretching vibrational mode with higher order modes in the heterodimers has been eliminated as a possible cause within Ar and Kr matrixes by isotopic substitution (CDCl3) experiments. To evaluate the influence of matrixes as a possible cause of red-shift, self-consistent Iso-density polarized continuum reaction field model was applied. This conveyed the important role of the dielectric matrixes in inducing the fascinating vibrational shift from blue (Ne) to red (Ar and Kr) due to the matrix specific transmutation of the POCl3-CHCl3 structure. The heterodimer produced in the Ne matrix possesses a cyclic structure stabilized by hydrogen bonding with co-operative phosphorus bonding, while in Ar and Kr the generation of an acyclic open structure stabilized solely by hydrogen bonding is promoted. Compelling justification regarding the dispersion force based influence of matrix environments in addition to the well-known dielectric influence is presented.
First author: Orenha, RP, The simultaneous recognition mechanism of cations and anions using macrocyclic-iodine structures: insights from dispersion-corrected DFT calculations,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 23795, (2020)
Abstract: The recent development of compounds for recognizing ions highlights the applicability of this area. In this work, the simultaneous recognition of cations (Li+, Na+ and K+) and anions (F-, Cl- and I-) using a macrocycle comprising a simple crown ether and an iodine-triazole unit is investigated. The roles of the (i) cation radius, (ii) anion radius, and (iii) electron withdrawing (-CN) and donor (-OH) groups of the receptor in ionic recognition were evaluated. Energy decomposition analysis (EDA) shows that the ion-receptor interactions are attractive and predominantly electrostatic. Molecular electrostatic potential plots and EDA analysis reveal that a decreasing cation radius favors interactions with the oxygen atoms present in the crown ether. A decreasing anion radius increases the sigma-hole interactions with the iodine atoms present in the receptors. In compounds containing -CN and -OH groups, the oxygen atoms in the crown ether show lower ability to interact with the Na+ cation. Nevertheless, in the receptor-OH structure, the Na+MIDLINE HORIZONTAL ELLIPSISOH interactions counterbalance the lower ability of the crown ether oxygens to interact with the Na+ cation. I- recognition is enhanced by the presence of -OH and, more strongly, -CN groups, occurring due to the increased sigma-hole area in the receptor-CN structure, as supported by a C-HMIDLINE HORIZONTAL ELLIPSISI- interaction in the receptor-OH compound. The reported results are useful for the design of compounds with improved capabilities for both cation and anion recognition prior to engaging in exploratory synthesis efforts.
First author: Cui, ZH, Inverse sandwich complexes of B7M2-, B8M2, and B9M2+ (M = Zr, Hf): the nonclassical M-M bonds embedded in monocyclic boron rings,
NEW JOURNAL OF CHEMISTRY, 44, 17705, (2020)
Abstract: A number of doped boron clusters with metals have been achieved with intriguing electronic and structural properties. In this work, we found the inverse sandwich complexes of B7M2-, B8M2, and B9M2+ (M = Zr, Hf) to be a global minimum, where the M-2 motif perpendicularly embeds in the B-7, B-8, and twist B-9 monocyclic boron rings. The interactions between M-2 and boron rings, including the d(p)-pi interactions and the electrostatic interactions originating from the charge transfer from the M to the boron rings, provide driving forces that stabilize such title complexes. The effective charge transfer gives rise to perfectly delocalized (3 pi + 3 sigma) orbitals, leading to double aromaticity of the whole species, especially when the three delocalized sigma orbitals of the boron rings are perpendicularly mixed with one negligible sigma and two pi bonds of the M-2 motifs, giving rise to less pronounced and nonclassical bonding interactions between two short-contact M atoms.
First author: Orenha, RP, On the recognition of chloride, bromide and nitrate anions by anthracene-squaramide conjugated compounds: a computational perspective,
NEW JOURNAL OF CHEMISTRY, 44, 17831, (2020)
Abstract: Anion recognition is widely used in several biological fields. Squaramide derived compounds appear as potential structures to recognize anions. Here, the bond mechanisms between the chloride (Cl-), bromide (Br-) and nitrate (NO3-) anions and anthracene-squaramide conjugated compounds are elucidated considering the influence of the: (i) number, (ii) nature, and (iii) position of the substituents: trifluoromethyl (-CF3) and nitro (-NO2). Energy decomposition analysis (EDA) shows that the interactions between Cl-, Br- and NO3- and anthracene-squaramide have an attractive interaction energy supported predominantly by electrostatic energy followed by orbital contribution. Molecular electrostatic potential (MEP) surfaces imply electrostatic interactions between Cl-, Br- and the oxygen atom from NO3- and the hydrogen atoms from N-H and C-H bonds present in the squaramide structure, and an aryl group, respectively. Cl- interacts with the receptors more strongly than Br-. The NO3- recognition is less attractive than those presented by Cl- and Br-, in agreement with the hardness-softness features of these anions. Importantly, one and, mostly, two group substitutions, -H -> -CF3 or -NO2, favor the recognition of Cl-, Br- and NO3- due to the increase of the polarization in the receptor-NHMIDLINE HORIZONTAL ELLIPSISanion interaction. The -NO2 group promotes a larger effect relative to the -CF3 ligand. The -NO2 ligand positioned at the largest distance conceivable to the benzene-NH group promotes the lowest interference in the N-HMIDLINE HORIZONTAL ELLIPSISCl- interaction. These results provide information to design receptors with a larger capability to recognize anions.
First author: Vermeeren, P, S(N)2 versus E2 Competition of F- and PH2- Revisited,
JOURNAL OF ORGANIC CHEMISTRY, 85, 14087, (2020)
Abstract: We have quantum chemically analyzed the competition between the bimolecular nucleophilic substitution (S(N)2) and base-induced elimination (E2) pathways for F- + CH3CH2Cl and PH2- + CH3CH2Cl orbital control using the activation strain model and Kohn-Sham molecular orbital theory at ZORA-OLYP/QZ4P. Herein, we correct an earlier study that intuitively e H attributed the mechanistic preferences of F(- )and PH2- , i.e., E(2 )and S(N)2, respectively, to a supposedly unfavorable shift in the polarity of the abstracted beta-proton along the PH2–induced E2 pathway while claiming that “…no correlation between the thermodynamic basicity and E2 rate should be expected.” Our analyses, however, unequivocally show that it is simply the 6 kcal mol(-1) higher proton affinity of F- that enables this base to engage in a more stabilizing orbital interaction with CH3CH2Cl and hence to preferentially react via the E2 pathway, despite the higher characteristic distortivity (more destabilizing activation strain) associated with this pathway. On the other hand, the less basic PH(2)(- )has a weaker stabilizing interaction with CH3CH2Cl and is, therefore, unable to overcome the characteristic distortivity of the E2 pathway. Therefore, the mechanistic preference of PH2- is steered to the S(N)2 reaction channel (less-destabilizing activation strain).
First author: Wang, ZP, From “S” to “O”: experimental and theoretical insights into the atmospheric degradation mechanism of dithiophosphinic acids,
RSC ADVANCES, 10, 40035, (2020)
Abstract: Dithiophosphinic acids (DPAHs, expressed as R1R2PSSH) are a type of sulfur-donor ligand that have been vastly applied in hydrometallurgy. In particular, DPAHs have shown great potential in highly efficient trivalent actinide/lanthanide separation, which is one of the most challenging tasks in separation science and is of great importance for the development of an advanced fuel cycle in nuclear industry. However, DPAHs have been found liable to undergo oxidative degradation in the air, leading to significant reduction in the selectivity of actinide/lanthanide separation. In this work, the atmospheric degradation of five representative DPAH ligands was investigated for the first time over a sufficiently long period (180 days). The oxidative degradation process of DPAHs elucidated by ESI-MS, P-31 NMR, and FT-IR analyses is R1R2PSSH -> R1R2PSOH -> R1R2POOH -> R1R2POO-OOPR1R2, R1R2PSSH -> R1R2PSS-SSPR1R2, and R1R2PSSH -> R1R2PSOH -> R1R2POS-SOPR1R2. Meanwhile, the determination of pK(a) values through pH titration and oxidation product by PXRD further confirms the S -> O transformation in the process of DPAH deterioration. DFT calculations suggest that the hydroxyl radical plays the dominant role in the oxidation process of DPAHs and the order in which the oxidation products formed is closely related to the reaction energy barrier. Moreover, nickel salts of DPAHs have shown much higher chemical stability than DPAHs, which was also elaborated through molecular orbital (MO) and adaptive natural density portioning (AdNDP) analyses. This work unambiguously reveals the atmospheric degradation mechanism of DPAHs through both experimental and theoretical approaches. At the application level, the results not only provide an effective way to preserve DPAHs but could also guide the design of more stable sulfur-donor ligands in the future.
First author: Arbouch, I, Influence of the nature of the anchoring group on the interfacial energy level alignment in dye-sensitized solar cells: A theoretical perspective,
PHYSICAL REVIEW MATERIALS, 4, 40035, (2020)
Abstract: We investigate at the theoretical (time-dependent) density functional theory level the influence of the nature of the anchoring group on the electronic and optical properties of oligothiophene dyes when adsorbed on TiO2 surface. The computed electronic structures point to a strong orbital hybridization between the dye and the substrate in the presence of the carboxylic acid and thiocarboxylic acid group, leading to a pronounced pinning effect of the lowest unoccupied molecular orbital (LUMO) level and faster electron injection. In contrast, phosphonic acid and catechol promote a weak electronic coupling between the two components and hence slower injection times. The simulated absorption spectra demonstrate that carboxylic and thiocarboxylic anchoring groups can induce a large redshift of the lowest optical transition of the dye upon adsorption due to a strong stabilization of the LUMO level triggered by the pinning effect while a small redshift prevails for phosphonic and catechol dyes. When pinning is active, the chain-size evolution of the lowest optical transition is also less sensitive to the conjugation length compared to the free dyes.
First author: Gopi, R, The structure of benzonitrile-water complex as unveiled by matrix isolation infrared spectroscopy: Is it linear or cyclic at low temperatures?,
JOURNAL OF MOLECULAR STRUCTURE, 1219, 40035, (2020)
Abstract: The hydrogen bonded interaction of benzonitrile (C6H5CN)-water (H2O) complexes have been studied experimentally using matrix isolation infrared spectroscopy to elucidate the structure(s) of the binary complexes produced at low temperatures. Computations performed at MP2 and B3LYP-D3 level of theory with aug-cc-pVDZ basis set predicted two complexes, of which global minimum complex A has a cyclic structure with the interactions occurring between ortho-hydrogen of C6H5CN and oxygen of H2O and the hydrogen of H2O with pi-cloud of C N in C6H5CN. The linear acylic complex B, a local minimum is stabilized through a straight C-H center dot center dot center dot N interaction between nitrogen of C6H5CN and hydrogen of H2O and is present at a relative energy of similar to 0.7 kcal/mol with respect to global minimum. While previous gas phase studies using a number of spectroscopic probes identify exclusively the cyclic global complex, our experiments performed under isolated conditions at low temperatures uniquely produced the acyclic linear C6H5CN-H2O complex, a local minimum in the potential energy surface. The C N stretching vibrational mode of C6H5CN was exploited as a unique marker to confirm the generation of local minimum. The effect of matrixes was simulated using Onsager self-consistent reaction field model and as a result, the linear complex (complex B) turned out to be energetically favored isomer under the influence of matrixes. The hydrogen bonding interaction in both the complexes was characterized using Atoms in Molecules, Natural Bond Orbital, Energy Decomposition and Non-Covalent Interaction analyses.
First author: Krisyuk, VV, Structural Diversity and Spectral Properties of the Crystals of Heterometallic Complexes Derived from TM(acacen) and Pb(diketonate)(2), TM = Cu, Ni, Pd,
CRYSTAL GROWTH & DESIGN, 20, 7260, (2020)
Abstract: Six stable heterometallic complexes with metal ratios 1:1 and 2:1 were prepared by crystallization of TM(acacen) and Pb(hfa)(2) from organic solvents (TM = Cu(II), Ni(II), Pd(II); acacen = N,N’-ethylenebis(acetylacetoniminate); hfa = hexafluoroacetylacetonate). The prepared complexes show unique molecular structures. Tetranuclear heterocomplexes [TM(acacen)Pb(hfa)(2)](2) with a special arrangement of metal atoms are basic units of crystals of 1:1 heterometallic complexes. At the components ratio of 2:1, trinuclear complexes [(TM(acacen))(2)Pb(hfa)(2)] are formed whose shape and crystal packing are TM-specific. The chemical interactions between monometallic subunits are shown to differ depending on the TM used and to alter crystal structure features and optical properties of the prepared heterometallic complexes. Among the compounds obtained, only crystals of [Ni(acacen)Pb(hfa)(2)](2) exhibit high-contrast dichroism which is observed as the Alexandrite effect for visible light and by optical microscopy under irradiation with polarized light. TD-DFT study of the electronic excited states in the range 350-750 nm confirmed the charge transfer between the monometallic subunits in the complex alters the position of absorption bands to favor the observed optical properties. All prepared compounds are volatile and can sublimate under heating in vacuum with partial decomposition.
First author: Venkatesh, A, The Structure of Molecular and Surface Platinum Sites Determined by DNP-SENS and Fast MAS Pt- 195 Solid-State NMR Spectroscopy,
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 142, 18936, (2020)
Abstract: The molecular level characterization of heterogeneous catalysts is challenging due to the low concentration of surface sites and the lack of techniques that can selectively probe the surface of a heterogeneous material. Here, we report the joint application of room temperature proton-detected NMR spectroscopy under fast magic angle spinning (MAS) and dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP-SENS), to obtain the Pt-195 solid-state NMR spectra of a prototypical example of highly dispersed Pt sites (single site or single atom), here prepared via surface organometallic chemistry, by grafting [(COD)Pt(OSi(OtBu)(3))(2)] (1, COD = 1,5-cyclooctadiene) on partially dehydroxylated silica (1psi02). Compound 1@SiO2 has a Pt loading of 3.7 wt %, a surface area of 200 m(2)/g, and a surface Pt density of around 0.6 Pt site/nm(2). Fast MAS H-1{Pt-195} dipolar-HMQC and S-REDOR experiments were implemented on both the molecular precursor 1 and on the surface complex 1@SiO2, providing access to Pt-195 isotropic shifts and Pt-H distances, respectively. For 1@SiO2, the measured isotropic shift and width of the shift distribution constrain fits of the static wide-line DNP-enhanced Pt-195 spectrum, allowing the Pt-195 chemical shift tensor parameters to be determined. Overall the NMR data provide evidence for a well-defined, single-site structure of the isolated Pt sites.
First author: van der Lubbe, SCC, The Nature of Nonclassical Carbonyl Ligands Explained by Kohn-Sham Molecular Orbital Theory,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 15690, (2020)
Abstract: When carbonyl ligands coordinate to transition metals, their bond distance either increases (classical) or decreases (nonclassical) with respect to the bond length in the isolated CO molecule. C-O expansion can easily be understood by pi-back-donation, which results in a population of the CO’s pi*-antibonding orbital and hence a weakening of its bond. Nonclassical carbonyl ligands are less straightforward to explain, and their nature is still subject of an ongoing debate. In this work, we studied five isoelectronic octahedral complexes, namely Fe(CO)(6)(2+), Mn(CO)(6)(+), Cr(CO)(6), V(CO)(6)(-) and Ti(CO)(6)(2-), at the ZORA-BLYP/TZ2P level of theory to explain this nonclassical behavior in the framework of Kohn-Sham molecular orbital theory. We show that there are two competing forces that affect the C-O bond length, namely electrostatic interactions (favoring C-O contraction) and pi-back-donation (favoring C-O expansion). It is a balance between those two terms that determines whether the carbonyl is classical or nonclassical. By further decomposing the electrostatic interaction Delta V-elstat into four fundamental terms, we are able to rationalize why Delta V-elstat gives rise to the nonclassical behavior, leading to new insights into the driving forces behind C-O contraction.
First author: Sun, YZ, Surface-enhanced resonance Raman detection of 1,1-diamino-2,2-dinitroethylene (FOX-7) on metal-doped Au-12 and Ag-12 clusters,
JOURNAL OF RAMAN SPECTROSCOPY, 51, 2425, (2020)
Abstract: Detection of explosive molecules is an important challenge due to the aggravating of global terrorism. It is known that surface-enhanced resonance Raman scattering (SERRS) is a promising analysis technique for detecting various analytes in complex samples due to its high signal enhancement. Using density functional theory, the enhancement effect of SERRS for FOX-7 adsorbed on M@Au-12 and M@Ag-12 (M (sic) V-, Nb-, Cr, Mo, W, and Mn+) clusters is explored. It is found that the electronic excitations can strongly enhance the SERRS of FOX-7 in the visible and infrared regions. The intensity of SERRS spectra of FOX-7-M@Au-12/Ag-12 is strongly enhanced by up to 6 x 10(4) compared with the static Raman intensity of FOX-7, and the enhancement factor of FOX-7 on Ag clusters is better than that of FOX-7 on Au clusters. In addition, the enhanced vibration modes of FOX-7 molecule are governed, to a large extent, by the charge state of the metal clusters and the energy of the incident light. The anionic Ag and Au complexes excited near 900 nm provide the strongest enhancement by about 10(4). Our results provide valuable guidance for the improvement of the explosives detection with high accuracy and also serve as a useful guidance to explore the experimental synthesis of multicomponent SERRS substrates.
First author: Miloserdov, FM, Impact of the Novel Z-Acceptor Ligand Bis{(ortho-diphenylphosphino)phenyl}zinc (ZnPhos) on the Formation and Reactivity of Low-Coordinate Ru(0) Centers,
INORGANIC CHEMISTRY, 59, 15606, (2020)
Abstract: The preparation and reactivity with H-2 of two Ru complexes of the novel ZnPhos ligand (ZnPhos = Zn(o-C6H4PPh2)(2)) are described. Ru(ZnPhos)(CO)(3) (2) and Ru(ZnPhos)(IMe4) 2 (4; IMe4 = 1,3,4,5-tetramethylimidazol-2-ylidene) are formed directly from the reaction of Ru(PPh3)(C6H4PPh2)(2)(ZnMe)(2) (1) or Ru(PPh3)(3)HCl/LiCH2TMS/ZnMe2 with CO and IMe4, respectively. Structural and electronic structure analyses characterize both 2 and 4 as Ru(0) species in which Ru donates to the Z-type Zn center of the ZnPhos ligand; in 2, Ru adopts an octahedral coordination, while 4 displays square-pyramidal coordination with Zn in the axial position. Under photolytic conditions, 2 loses CO to give Ru(ZnPhos)(CO)(2) that then adds H-2 over the Ru-Zn bond to form Ru(ZnPhos)(CO)(2)(mu-H) 2 (3). In contrast, 4 reacts directly with H-2 to set up an equilibrium with Ru(ZnPhos)(IMe4)(2)H-2 (5), the product of oxidative addition at the Ru center. DFT calculations rationalize these different outcomes in terms of the energies of the square-pyramidal Ru(ZnPhos)L-2 intermediates in which Zn sits in a basal site: for L = CO, this is readily accessed and allows H-2 to add across the Ru-Zn bond, but for L = IMe4, this species is kinetically inaccessible and reaction can only occur at the Ru center. This difference is related to the strong pi-acceptor ability of CO compared to IMe4. Steric effects associated with the larger IMe4 ligands are not significant. Species 4 can be considered as a Ru(0)L-4 species that is stabilized by the Ru. Zn interaction. As such, it is a rare example of a stable Ru(0)L4 species devoid of strong pi-acceptor ligands.
First author: Pei, GR, Stabilities, Electronic Structures, and Bonding Properties of Iron Complexes (E1E2)Fe(CO)(2)(CNArTripp2)(2) (E1E2=BF, CO, N-2, CN-, or NO+)**,
CHEMISTRYOPEN, 9, 1195, (2020)
Abstract: The coordination of 10-electron diatomic ligands (BF, CO N-2) to iron complexes Fe(CO)(2)(CNArTripp2)(2) [Ar-Tripp2=2,6-(2,4,6-(iso-propyl)(3)C6H2)(2)C6H3] have been realized in experiments very recently (Science, 2019, 363, 1203-1205). Herein, the stability, electronic structures, and bonding properties of (E1E2)Fe-(CO)(2)(CNArTripp2)(2) (E1E2=BF, CO, N-2, CN-, NO+) were studied using density functional (DFT) calculations. The ground state of all those molecules is singlet and the calculated geometries are in excellent agreement with the experimental values. The natural bond orbital analysis revealed that Fe is negatively charged while E-1 possesses positive charges. By employing the energy decomposition analysis, the bonding nature of the E2E1-Fe(CO)(2)(CNArTripp2)(2) bond was disclosed to be the classic dative bond E2E1 -> Fe(CO)(2)(CNArTripp2)(2) rather than the electron-sharing double bond. More interestingly, the bonding strength between BF and Fe(CO)(2)(CNArTripp2)(2) is much stronger than that between CO (or N-2) and Fe(CO)(2)(CNArTripp2)(2), which is ascribed to the better sigma-donation and pi back-donations. However, the orbital interactions in CN–> Fe(CO)(2)(CNArTripp2)(2) and NO+-> Fe(CO)(2)(CNArTripp2)(2) mainly come from sigma-donation and pi back-donation, respectively. The different contributions from sigma donation and pi donation for different ligands can be well explained by using the energy levels of E1E2 and Fe(CO)(2)(CNArTripp2)(2) fragments.
First author: Simonne, DH, THORONDOR: a software for fast treatment and analysis of low-energy XAS data,
JOURNAL OF SYNCHROTRON RADIATION, 27, 1741, (2020)
Abstract: THORONDOR is a data treatment software with a graphical user interface (GUI) accessible via the browser-based Jupyter notebook framework. It aims to provide an interactive and user-friendly tool for the analysis of NEXAFS spectra collected during in situ experiments. The program allows on-the-fly representation and quick correction of large datasets from single or multiple experiments. In particular, it provides the possibility to align in energy several spectral profiles on the basis of user-defined references. Various techniques to calculate background subtraction and signal normalization have been made available. In this context, an innovation of this GUI involves the usage of a slider-based approach that provides the ability to instantly manipulate and visualize processed data for the user. Finally, the program is characterized by an advanced fitting toolbox based on the lmfit package. It offers a large selection of fitting routines as well as different peak distributions and empirical ionization potential step edges, which can be used for the fit of the NEXAFS rising-edge peaks. Statistical parameters describing the goodness of a fit such as chi(2) or the R-factor together with the parameter uncertainty distributions and the related correlations can be extracted for each chosen model.
First author: Yang, YG, Structure-lock induced phosphorescence lifetime enhancing of (9H-carbazol-9-yl)(phenyl)methanone: An organic phosphorescent materials,
JOURNAL OF LUMINESCENCE, 227, 1741, (2020)
Abstract: Different molecular design strategies have been performed to study purely organic materials with room-temperature phosphorescence (RTP) by suppressing nonradiative deactivation and facilitating intersystem crossing. In this work, a synthetic strategy based on CPM ((9H-carbazol-9-yl)(phenyl)methanone) has been performed to achieve long lived RTP by immobilizing the torsion of benzophenone moiety and forming a six-membered heterocyclic ring containing nitrogen element. This synthesized locked-CPM (8H-indolo [3,2,1-de] phenanthridin-8-one) with higher rigidity has planar configuration both in the singlet state and the triplet state, whose locking configuration effectively inhibits the twist intramolecular charge transfer (TICT) of CPM and significantly reduces the energy gap between the singlet and triplet states to 0.89 ev. This change facilitates intersystem crossing and the generalization of triplet excitons. By fitting the phosphorescence decay curves, we demonstrate that the phosphorescence lifetime of the locked-CPM has increased by nearly forty times compared with that of the CPM, indicating that the presented strategy will bring insight into the developing long lived RTP materials. It is noted that suppress the vibration and torsion of molecular and reduce the energy gap between single-triplet states will favors of long phosphorescence lifetime.
First author: Artemkina, S, Amorphous pentasulfides MS5 (M = Mo, W) in reactions with thiuram disulfide and halogens,
INORGANICA CHIMICA ACTA, 512, 1741, (2020)
Abstract: Amorphous pentasulfides MoS5 and WS5 were studied in a series of chemical reactions for the first time. Interaction of MoS5 and WS5 with melt of tetramethylthiuramdisulfide resulted in two new molecular complexes, [{Mo3S7}(dtC)(3)](S3H) and [{W3S4}(dtc)(4)(Me2NCHS)]. Halogenation of MoS5 and WS5 resulted in cluster coordination polymers M(3)S(7)Hal(4) (M = Mo, W; Hal = Cl, Br).
First author: Confer, MP, Potential main group amine borane-based chemical hydrogen storage molecular systems,
COMPUTATIONAL AND THEORETICAL CHEMISTRY, 1189, 1741, (2020)
Abstract: The thermodynamics as a function of the temperature for the decomposition of the substituted amine boranes X (NH2BH3)(3) and X(BH2NH3)(3) for X = N and P and E(NH2BH3)(4) and E(BH2NH3)(4) for E = C and Si were predicted using composite correlated molecular orbital G3(MP2) theory. The relative stabilities of isomers were explained using bond dissociation energies. Equilibrium concentrations of products with respect to temperature were determined using Gibbs free energy minimization. The activation energy for loss of the first H-2 was calculated at the G3(MP2)B3 level and is larger than the respective bond dissociation energy to lose terminal BH3 or NH3 via dative bond cleavage. Dipole moments and polarizabilities were calculated at the DFT/B3LYP level and boiling points were calculated at the DFT/BP/COSMO-RS level. Planar fits were developed for the boiling points of N (BH2NH3)(3), P(BH2NH3)(3), C(BH2NH3)(4), and Si(BH2NH3)(4) dehydrogenation products using dipole moment, polarizability, and solvent cavity surface area.
First author: Sherman, DM, Isotopic disequilibrium of Cu in marine ferromanganese crusts: Evidence from ab initio predictions of Cu isotope fractionation on sorption to birnessite,
EARTH AND PLANETARY SCIENCE LETTERS, 549, 1741, (2020)
Abstract: In the oceans, Cu is strongly scavenged by ferromanganese (Fe-Mn) crusts. The isotopic fractionation of Cu between seawater and crusts provides insight into the mechanisms of trace metal cycling in the oceans. Dissolved Cu in seawater is isotopically heavy (+0.66 +/- 0.19 parts per thousand) relative to Cu in crusts (+0.31 +/- 0.24 parts per thousand). The primary mineral phase sorbing divalent trace metals in Fe-Mn crusts is birnessite. Recent laboratory measurements show that isotopically light Cu is preferentially sorbed on birnessite, with a fractionation factor of 0.45 +/- 0.18 parts per thousand. Here, we use first-principles (quantum mechanical) calculations to predict the isotopic fractionation between aqueous Cu2+ complexes and Cu as a surface complex on birnessite. We find that isotopic fractionation between the Cu(H2O)(5)(+) complex and sorbed Cu should be 0.49 parts per thousand (at 25 degrees C), in close agreement with experiments, confirming that these experimental results reflects equilibrium fractionation. We then predict the isotopic fractionation between dissolved inorganic Cu in seawater and birnessite given the thermodynamic speciation of dissolved Cu at pH 8. We find dissolved inorganic Cu should be 0.94 parts per thousand (at 5 degrees C) heavier than Cu sorbed to birnessite. This value is substantially greater than the observed fractionation between seawater and Fe-Mn crusts (Delta(sw-fmc) approximate to , +0.35 parts per thousand). Moreover, it is well established that dissolved Cu in seawater is strongly complexed by organic ligands. Based on model Cu complexes and published experimental data, we estimate that fractionation of Cu by organic ligands should increase the equilibrium fractionation between seawater and Fe-Mn crusts by 0.2 to 1.5 parts per thousand to yield Delta(sw-fmc) = +1.1 to 2.4 parts per thousand. We conclude that Cu in marine Fe-Mn crusts in not in isotopic equilibrium with dissolved Cu in seawater, and consider the possible explanations of this surprising finding.
First author: Colombo, G, Boron difluoride functionalized (tetrahydroimidazo[1,5-a]pyridin-3-yl) phenols: Highly fluorescent blue emissive materials,
DYES AND PIGMENTS, 182, 1741, (2020)
Abstract: Some (tetrahydroimidazo[1,5-a]pyridin-3-yl)phenols were reacted with boron trifluoride diethyl etherate and the resulting BF2-functionalized compounds were fully characterized both in solution using H-1, C-13, B-11, F-19 NMR spectroscopy and in the solid state (infrared, fluorescence, X-ray). When excited with UV light these boron difluoride derivatives show in dichloromethane solution an intense fluorescence emission in the UV region, with lambda(max) of emission varying from 357 to 390 nm. Good absolute quantum yields are recorded for most of the compounds. In the solid state, they are characterized by a strong blue emission (388-435 nm), with high absolute quantum yields (up to 0.68) and x,y color coordinates (CIE 1931) close to those expected for standard blue. Time Dependent Density Functional Theory (TD-DFT) calculations were used to define the nature of the electronic transitions and excited states involved in the fluorescence process.
First author: Kwon, H, ReaxFF-based molecular dynamics study of bio-derived polycyclic alkanes as potential alternative jet fuels,
FUEL, 279, 1741, (2020)
Abstract: This work investigates the initial stages of the pyrolysis of HtH-1 (C18H32; 2,2,7,7,8a,8b-hexamethyl-dodecahydrobiphenylene) and HtH-2 (C18H34; 1,1 ‘,3,3,3 ‘,3 ‘-hexamethyl-1,1 ‘-bi(cyclohexane)), which are bio-derived polycyclic alkanes and potential jet fuels, using ReaxFF force field based molecular dynamics (MD) simulations. Global Arrhenius parameters, such as activation energies and pre-exponential factors, are calculated and used to analyze the overall decomposition kinetics of the fuels. HtH-1 decomposes faster than HtH-2 at the same temperature and density conditions, and they have a faster decomposition rate compared to some existing jet-fuels, such as JP-10. A systematic reaction analysis framework developed in this work is applied to determine a temperature-dependent decomposition mechanism. At lower temperature, the central C-C bond connecting the two cyclohexane rings is dominantly broken in both HtH-1 and HtH-2. However, C-CH3 bond breaking becomes dominant with increasing temperature due to the large increase in entropy during this reaction. Major products from HtH-1 are C5H8 and C4H8, and those from HtH-2 are C4H8 and C2H4. The major products predict that HtH-1 has a higher sooting tendency than HtH-2, which is consistent with measurements. The impact of HtH-2 on the pyrolysis of HtH-1 is also investigated in their binary mixtures. HtH-1 and HtH-2 decompose by unimolecular reactions, and they rarely interact with each other during the pyrolysis of the mixtures. This work demonstrates that ReaxFF can be used to investigate pyrolysis and combustion chemistry of existing or future fuels and to contribute to the development of their chemical kinetic models without any a priori input and chemical intuition.
First author: Gordon, CP, Efficient epoxidation over dinuclear sites in titanium silicalite-1,
NATURE, 586, 708, (2020)
Abstract: Titanium silicalite-1 (TS-1) is a zeolitic material with MFI framework structure, in which 1 to 2 per cent of the silicon atoms are substituted for titanium atoms. It is widely used in industry owing to its ability to catalytically epoxidize olefins with hydrogen peroxide (H2O2), leaving only water as a byproduct(1,2); around one million tonnes of propylene oxide are produced each year using this process(3). The catalytic properties of TS-1 are generally attributed to the presence of isolated Ti(iv) sites within the zeolite framework1. However, despite almost 40 years of experimental and computational investigation(4-10), the structure of these active Ti(iv) sites is unconfirmed, owing to the challenges of fully characterizing TS-1. Here, using a combination of spectroscopy and microscopy, we characterize in detail a series of highly active and selective TS-1 propylene epoxidation catalysts with well dispersed titanium atoms. We find that, on contact with (H2O2)-O-17, all samples exhibit a characteristic solid-state O-17 nuclear magnetic resonance signature that is indicative of the formation of bridging peroxo species on dinuclear titanium sites. Further, density functional theory calculations indicate that cooperativity between two titanium atoms enables propylene epoxidation via a low-energy reaction pathway with a key oxygen-transfer transition state similar to that of olefin epoxidation by peracids. We therefore propose that dinuclear titanium sites, rather than isolated titanium atoms in the framework, explain the high efficiency of TS-1 in propylene epoxidation with H2O2. This revised view of the active-site structure may enable further optimization of TS-1 and the industrial epoxidation process.
First author: Jamshidi, Z, Not Completely Innocent: How Argon Binding Perturbs Cationic Copper Clusters,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 9004, (2020)
Abstract: Argon is often considered as an innocent probe that can be attached and detached to study the structure of a particular species without perturbing the species too much. We have investigated whether this assumption also holds for small copper cationic clusters and demonstrated that small but significant charge transfer from argon to metal changes the remaining binding positions, leading in general, to weaker binding of other argon atoms. The exception is binding to just one copper ion, where the binding of the first argon facilitates the binding of the second.
First author: Ren, XY, Electron-withdrawing functional ligand promotes CO2 reduction catalysis in single atom catalyst,
SCIENCE CHINA-CHEMISTRY, 63, 1727, (2020)
Abstract: Electrochemical carbon dioxide reduction reaction (CO2RR) powered by renewable electricity offers an attractive approach to reduce carbon emission and at the same time produce valuable chemicals/fuels. To design efficient CO2 reduction electrocatalyst, it is important to understand the structure-activity relationship. Herein, we design a series of single Co atoms electrocatalysts with well-defined active sites electronic structures, which exhibit outstanding CO2RR activity with controllable selectivity to CO. Experimental and density functional theory (DFT) calculation studies show that introducing nitro (amino) ligand next to single Co atom catalytic center with electron-withdrawing (electron-donating) capability favors (hinders) CO2 reduction catalysis. This work provides an in-depth understanding of how functional ligand affects the splitting of transition metal 3d electron orbital, thereby changing the electron transfer from transition metal active site to CO2, which is closely related to the Gibbs free energy of the rate-determining step (CO2+e(-)+*->*CO2-).
First author: Li, G, Infrared spectroscopic study of hydrogen bonding topologies in the smallest ice cube,
NATURE COMMUNICATIONS, 11, 1727, (2020)
Abstract: The water octamer with its cubic structure consisting of six four-membered rings presents an excellent cluster system for unraveling the cooperative interactions driven by subtle changes in the hydrogen-bonding topology. Despite prediction of many distinct structures, it has not been possible to extract the structural information encoded in their vibrational spectra because this requires size-selectivity of the neutral clusters with sufficient resolution to identify the contributions of the different isomeric forms. Here we report the size-specific infrared spectra of the isolated cold, neutral water octamer using a scheme based on threshold photoionization using a tunable vacuum ultraviolet free electron laser. A plethora of sharp vibrational bands features are observed. Theoretical analysis of these patterns reveals the coexistence of five cubic isomers, including two with chirality. The relative energies of these structures are found to reflect topology-dependent, delocalized multi-center hydrogen-bonding interactions. These results demonstrate that even with a common structural motif, the degree of cooperativity among the hydrogen-bonding network creates a hierarchy of distinct species. The implications of these results on possible metastable forms of ice are speculated. Spectroscopic studies of water clusters provide insight into the hydrogen bond structure of water and ice. The authors measure infrared spectra of neutral water octamers using a threshold photoionization technique based on a tunable vacuum-UV free electron laser, identifying two cubic isomers in addition to those previously observed.
First author: Zheng, X, Understanding the interactions between the bis(trifluoromethylsulfonyl)imide anion and absorbed CO2 using X-ray diffraction analysis of a soft crystal surrogate,
COMMUNICATIONS CHEMISTRY, 3, 1727, (2020)
Abstract: The selective carbon dioxide (CO2) absorption properties of ionic liquids (ILs) are highly pertinent to the development of methods to capture CO2. Although it has been reported that fluorinated components give ILs enhanced CO2 solubilities, it has been challenging to gain a deep understanding of the interactions occurring between ILs and CO2. In this investigation, we have utilized the soft crystalline material [Cu(NTf2)(2)(bpp)(2)] (NTf2- = bis(trifluoromethylsulfonyl)imide, bpp = 1,3-bis-(4-pyridyl)propane) as a surrogate for single-crystal X-ray diffraction analysis to visualize interactions occurring between CO2 and NTf2-, the fluorinated IL component that is responsible for high CO2 solubility. Analysis of the structure of a CO2-loaded crystal reveals that CO2 interacts with both fluorine and oxygen atoms of NTf2- anions in a trans rather than cis conformation about the S-N bond. Theoretical analysis of the structure of the CO2-loaded crystal indicates that dispersion and electrostatic interactions exist between CO2 and the framework. The overall results provide important insight into understanding and improving the CO2 absorption properties of ILs.
First author: Dossmann, H, Exploring Phosphine Electronic Effects on Molybdenum Complexes: A Combined Photoelectron Spectroscopy and Energy Decomposition Analysis Study,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 8753, (2020)
Abstract: In organometallic chemistry, especially in the catalysis area, accessing the finest tuning of a catalytic reaction pathway requires a detailed knowledge of the steric and electronic influences of the ligands bound to the metal center. Usually, the M-L bond between a ligand and metal is depicted by the Dewar-Chatt-Duncanson model involving two opposite interactions, sigma- donor and pi-acceptor effects of the ligand. The experimental evaluation of these effects is essential and complementary to in-depth theoretical approaches that are able to provide a detailed description of the M-L bond. In this work, we present a study of LMo(CO)(5) complexes with L being various tertiary phosphine ligands by means of mass-selected high-resolution photoelectron spectroscopy (PES) performed with synchrotron radiation, DFT, and energy decomposition analyses (EDA) combined with the natural orbitals for chemical valence (NOCV) analysis. These methods enable a separated access of the alpha-donor and pi-acceptor effects of ligands by probing either the electronic configuration of the complex (PES) or the interaction of the ligand with the metal (EDA). Three series of PR3 ligands with various electronic influences are investigated: the strong donating alkyl substituents (PMe3, PEt3, and PiPr(3)), the intermediate PPhxMe(3-x) (x = 0-3) set, and the PPh(x)Pyrl((3-x)) set (x = 0-3 with Pyrl being the strong electron withdrawing pyrrolyl group C4H4N). For each complex, their adiabatic and vertical ionization energies (IEs) could be determined with a 0.03 eV precision. Experiment and theory show an excellent agreement, either for the IE determination or electronic effect analysis. The ability to interpret the spectra is shown to depend on the character of the ligand. “Innocent” ligands provide the spectra that are the most straightforward to analyze, whereas the “non-innocent” ligands (which are ionized prior to the metal center) render the analysis more difficult due to an increased number of molecular orbitals in the energy range considered. A very good linear correlation is finally found between the measured adiabatic ionization energies and the interaction energy term obtained by EDA for each of these two types of ligands, which opens interesting perspective for the prediction of ligand characters.
First author: Sadik, MNK, S2N2- A 6 pi-Electron Ligand with Tunable sigma- and pi- Donor-Acceptor Property,
CHEMISTRYSELECT, 5, 12176, (2020)
Abstract: The usage of inorganic cyclic N-donor based ligands, whose electronic properties can be easily and extensively tuned, are still underdeveloped. One such system is sulfur-nitrogen compounds known to form eta(1)and eta(2)-complexes with mono- and bi-metallic transition metal fragments. We have undertaken an extensive theoretical investigation of the bonding nature betweenS(2)N(2)and 14 valence electron (VE) metal fragments in the mono and bi-metallic S2N2[Mo(NO)Cl-4](-)and S2N2[Mo-2(NO)(2)(Cl)(8)](2-). Our results indicate thatS(2)N(2)is a sigma-donor and pi-acceptor ligand. The EDA-NOCV analysis demonstrates that the interaction betweenS(2)N(2)and metal fragments has a higher electrostatic character than a covalent character. On the contrary, the sigma-lone pair on N-atom inS(2)N(2)is donated to the electron-deficient 12 valence electron [Mo(NO)Cl-4](+)fragment in S2N2[Mo(NO)Cl-4](+)and S2N2[Mo-2(NO)(2)(Cl)(8)](2+), while the electrons from theS(2)N(2)pi-MO are donated to the vacant d-orbitals of the metal fragment. Besides, all these complexes show donation of lone pair on Cl attached to transition metal fragment to the S-N sigma*-MO, which can be considered as a sigma-hole that is involved in the chalcogen bond formation. Hence, our theoretical calculations suggest that theS(2)N(2)is a versatile ligand which can be tuned as sigma-donor, sigma-acceptor, pi-donor and pi-acceptor.
First author: Andrada, DM, Energy components in energy decomposition analysis (EDA) are path functions; why does it matter?,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 22459, (2020)
Abstract: Here, we discuss that unlike bond dissociation energy (BDE) that is a state function quantity, the energy components of the energy decomposition analysis (EDA), i.e. electrostatic interaction, Pauli repulsion, and orbital interaction, are path (process) function quantities. Being a path function means that EDA energy components are not uniquely defined, i.e. the relative magnitudes of the orbital interaction, Pauli repulsion, and electrostatic components may vary depending on the selected pathway for EDA. Therefore, at best, EDA can define whether closely related chemical bonds are more or less ionic/covalent compared with each other. However, a precise assessment of the nature of a certain type of chemical bond using EDA is a questionable task. Besides, we briefly discuss that the widely used EDA pathway, which is merely an arbitrary choice among infinite possible paths, comes to conclusions not consistent with our widely accepted knowledge of bond formation even for the simplest molecules.
First author: Silva, DR, Nature and Strength of Lewis Acid/Base Interaction in Boron and Nitrogen Trihalides,
CHEMISTRY-AN ASIAN JOURNAL, 15, 4043, (2020)
Abstract: We have quantum chemically investigated the bonding between archetypical Lewis acids and bases. Our state-of-the-art computations on the X3B-NY(3)Lewis pairs have revealed the origin behind the systematic increase in B-N bond strength as X and Y are varied from F to Cl, Br, I, H. For H3B-NY3, the bonding trend is driven by the commonly accepted mechanism of donor-acceptor [HOMO(base)-LUMO(acid)] interaction. Interestingly, for X3B-NH3, the bonding mechanism is determined by the energy required to deform the BX(3)to the pyramidal geometry it adopts in the adduct. Thus, Lewis acids that can more easily pyramidalize form stronger bonds with Lewis bases. The decrease in the strain energy of pyramidalization on going from BF(3)to BI(3)is directly caused by the weakening of the B-X bond strength, which stems primarily from the bonding in the plane of the molecule (sigma-like) and not in the pi system, at variance with the currently accepted mechanism.
First author: Elinburg, JK, Formation of monomeric Sn(II) and Sn(IV) perfluoropinacolate complexes and their characterization by Sn-119 Mossbauer and Sn-119 NMR spectroscopies,
DALTON TRANSACTIONS, 49, 13773, (2020)
Abstract: The synthesis and characterization of a series of Sn(II) and Sn(IV) complexes supported by the highly electron-withdrawing dianionic perfluoropinacolate (pin(F)) ligand are reported herein. Three analogs of ISnIV(pin(F))(3)](2-) with NEt3H+ (1), K+ (2), and {K(18C6)}* (3) counter cations and two analogs of [Sn-II(pin(F))(2)](2-) with K+ (4) and {K(15C5)(2)}* (5) counter cations were prepared and characterized by standard analytical methods, single-crystal X-ray diffraction, and Sn-119 Mossbauer and NMR spectroscopies. The six-coordinate Sn-IV(pin(F)) complexes display Sn-119 NMR resonances and Sn-119 Mossbauer spectra similar to SnO2 (cassiterite). In contrast, the four-coordinate Sn-II(pin(F)) complexes, featuring a stereochemically-active lone pair, possess low Sn-119 NMR chemical shifts and relatively high quadrupolar splitting. Furthermore, the Sn(II) complexes are unreactive towards both Lewis bases (pyridine, NEt3) and acids (BX3, Et3NH+). Calculations confirm that the Sn(II) lone pair is localized within the 5s orbital and reveal that the Sn 5p(x) LUMO is energetically inaccessible, which effectively abates reactivity.
First author: Mewes, L, Ultrafast Intersystem Crossing and Structural Dynamics of [Pt(ppy)(mu-(t)Bu(2)pz)](2),
INORGANIC CHEMISTRY, 59, 14643, (2020)
Abstract: Intersystem crossing (ISC) rates of transition-metal complexes are determined by the complex interplay of a molecule’s electronic and structural dynamics. To broaden our understanding of these key factors, we investigate the case of the prototypical d(8)-d(8) dimetal complex [Pt(ppy)(mu-(t)Bu(2)pz)](2) using broad-band transient absorption anisotropy in combination with ultrafast fluorescence up-conversion and ab initio calculations. We find that, upon excitation of the molecule’s metal-metal-to-ligand chargetransfer transition, ISC occurs in hundreds of femtoseconds from the lowest excited singlet state S-1 to the triplet state T-2, from where the energy relaxes to the lowest energy triplet state T-1. ISC to the T-2 state, rather than T-1, is further rationalized through supporting arguments. Observed vibrational coherences along the Pt-Pt mode are attributed to the formation of nuclear wavepackets on the ground and excited electronic states that dephase prior to ISC because of the structural flexibility of the complex. Beyond demonstrating the relationship between the energy relaxation and structural dynamics of [Pt(ppy) (mu-(t)Bu(2)pz)](2), our results provide new insights into the photoinduced dynamics of d(8)-d(8) dimetal complexes more generally.
First author: Wei, JY, Toward the Formation of N-Heterocyclic-Carbene-Protected Gold Clusters of Various Nuclearities. A Comparison with Their Phosphine-Protected Analogues from Density Functional Theory Calculations,
INORGANIC CHEMISTRY, 59, 15240, (2020)
Abstract: The structure and bonding of a series of selected phosphine-protected gold clusters (Au-n-P) of nuclearity varying from n = 6 to 13 were investigated by density functional theory (DFT) calculations and compared to those of the hypothetical homologues in which phosphines were replaced by N-heterocyclic carbene (NHC) analogues (Au-n-C). Both the Au-n-P and Au-n-C series exhibit similar stabilities and structural features, except for n = 6, where some differences are noted. The NHC ligands are found to be even slightly more strongly bonded to the gold core (by a few kilocalories per mole per ligand) than phosphines. Investigation of the optical properties of both series using time-dependent DFT calculations indicates similarities in the nature and energies of the UV-vis optical transitions and, consequently, relatively similar shapes of the simulated spectra, with a general blue-shift tendency when going from Au-n-P to Au-n-C. The fluorescence behavior observed experimentally for some of the Au-n-P species is expected to occur also for their Au-n-C analogues, which can be extended to other carbene-ligand-protected nanoclusters. Our results show that it should be possible to stabilize gold clusters with NHC ligands, in relation to the seminal Au-n-ligand-protected core, offering novel building blocks for the design of nanostructured materials with various properties.
First author: Jian, J, Probing Halogen-pi versus CH-pi Interactions in Molecular Balance,
ORGANIC LETTERS, 22, 7870, (2020)
Abstract: Molecular balances based on the dibenzobicyclo[3.2.2]-nonane template enable probing of the competition between halogen-pi and CH-pi interactions. Structural, NMR spectroscopic, and computational analyses revealed that the pi system can favorably interact both with C-X or C-H functionalities, depending on the size of the functional group.
First author: Chang, R, Unveiling the Mechanism, Origin of Stereoselectivity, and Ligand-Dependent Reactivity in the Pd(II)-Catalyzed Unbiased Methylene C(sp(3))-H Alkenylation-Aza-Wacker Cyclization Reaction,
JOURNAL OF ORGANIC CHEMISTRY, 85, 13191, (2020)
Abstract: The mechanism, origin of stereoselectivity, and ligand-dependent reactivity of Pd(II)-catalyzed methylene C(sp(3))-H alkenylation-aza-Wacker cyclization to form (E)-beta-stereogenic gamma-lactam have been comprehensively studied by density functional theory (DFT) calculations. The calculated results reveal that the methylene C-H activation assisted by K2CO3 via the concerted metalation- deprotonation mechanism is found to be the most preferred pathway, where the enantioselectivity is distinguished by the orientation of the methyl group of a substrate relative to a chiral ligand. However, the stereochemistry of the olefin moiety in the generated product is mainly determined by the oxidative addition step, where the coulombic interaction and dispersion effect differentiate the energy difference of diastereomeric transition states. In terms of the agostic interaction nature of “three-center two-electron” transition states, the discrepancy of reactivities caused by different Pd catalysts is attributed to the electron induction effect of substituents on the chiral ligands. In other words, the use of an electron-withdrawing group (e.g., -CN) in place of an electron-donating group (e.g., -OMe) enhances the oxidation state of the Pd atom and lowers vacant d orbitals of the palladium atom of the catalyst and in turn facilitates a larger amount of sigma-electronic-charge injection into an empty 3d shell of the palladium center. Thus, the higher catalytic activity of the Pd catalyst with ligands substituted by an electron-withdrawing group is anticipated.
First author: Galvao, BRL, Reliability of semiempirical and DFTB methods for the global optimization of the structures of nanoclusters,
JOURNAL OF MOLECULAR MODELING, 26, 13191, (2020)
Abstract: In this work, we explore the possibility of using computationally inexpensive electronic structure methods, such as semiempirical and DFTB calculations, for the search of the global minimum (GM) structure of chemical systems. The basic prerequisite that these inexpensive methods will need to fulfill is that their lowest energy structures can be used as starting point for a subsequent local optimization at a benchmark level that will yield its GM. If this is possible, one could bypass the global optimization at the expensive method, which is currently impossible except for very small molecules. Specifically, we test our methods with clusters of second row elements including systems of several bonding types, such as alkali, metal, and covalent clusters. The results reveal that the DFTB3 method yields reasonable results and is a potential candidate for this type of applications. Even though the DFTB2 approach using standard parameters is proven to yield poor results, we show that a re-parametrization of only its repulsive part is enough to achieve excellent results, even when applied to larger systems outside the training set.
First author: Neto, ANC, Overlap integrals and excitation energies calculations in trivalent lanthanides 4f orbitals in pairs Ln-L (L = Ln, N, O, F, P, S, Cl, Se, Br, and I),
CHEMICAL PHYSICS LETTERS, 757, 13191, (2020)
Abstract: In this work, DFT-based calculations of overlap integrals (rho) and excitations energies (Delta epsilon) associated with the diatomic-like pairs Ln(3+)-Ligand and Ln-Ln’ are presented. The rho and Delta epsilon quantities are useful for the calculations of overlap polarizability, charge factors, intensity parameters (using the Simple Overlap and Bond Overlap models), 4f shielding factors, and energy transfer process (ligand-to-Ln and Ln-Ln). A comprehensive set of parametric curves of the type exp(a + bR + cR(2)) are presented to easily determine these properties at a given distance R. Some literature is presented to indicate the importance of rho and Delta epsilon quantities in photophysical properties of lanthanide-based compounds.
First author: Bae, YJ, Balancing Charge Transfer and Frenkel Exciton Coupling Leads to Excimer Formation in Molecular Dimers: Implications for Singlet Fission,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 8478, (2020)
Abstract: Photoexcitation of molecular chromophore aggre-gates can form excimer states that play a significant role in photophysical processes such as charge and energy transfer as well as singlet fission. An excimer state is commonly defined as a superposition of Frenkel exciton and charge transfer states. In this work, we investigate the dynamics of excimer formation and decay in pi-stacked 9,10-bis(phenylethynyl)anthracene (BPEA) covalent dimers appended to a xanthene spacer, where the electronic coupling between the two BPEA molecules is adjusted by changing their longitudinal molecular slip distances. Using exciton coupling calculations, we quantify the relative contributions of Frenkel excitons and charge transfer states and find that there is an upper and lower threshold of the charge transfer contribution for efficient excimer formation to occur. Knowing these thresholds can aid the design of molecular aggregates that optimize singlet fission.
First author: Gorski, A, Matrix isolation studies of vibrational structure of hemiporphycene,
JOURNAL OF MOLECULAR STRUCTURE, 1218, 8478, (2020)
Abstract: Photoexcitation of molecular chromophore aggre-gates can form excimer states that play a significant role in photophysical processes such as charge and energy transfer as well as singlet fission. An excimer state is commonly defined as a superposition of Frenkel exciton and charge transfer states. In this work, we investigate the dynamics of excimer formation and decay in pi-stacked 9,10-bis(phenylethynyl)anthracene (BPEA) covalent dimers appended to a xanthene spacer, where the electronic coupling between the two BPEA molecules is adjusted by changing their longitudinal molecular slip distances. Using exciton coupling calculations, we quantify the relative contributions of Frenkel excitons and charge transfer states and find that there is an upper and lower threshold of the charge transfer contribution for efficient excimer formation to occur. Knowing these thresholds can aid the design of molecular aggregates that optimize singlet fission.
First author: Liu, Z, TD-DFTB study of optical properties of silver nanoparticle homodimers and heterodimers,
JOURNAL OF CHEMICAL PHYSICS, 153, 8478, (2020)
Abstract: The absorption spectra for face-centered cubic nanoparticle dimers at various interparticle distances are investigated using time-dependent density functional tight binding. Both homodimers and heterodimers are investigated in this work. By studying nanoparticles at various interparticle distances and analyzing their vertical excitations, we found that as the interparticle distance decreases, a red shift arises from contributions of the transition dipole moment that are aligned along the z-axis with nondegenerate features; blue shifts occur for peaks that originate from transition dipole moment components in the x and y directions with double degeneracy. When the nanoparticles are similar in size, the features in the absorption spectra become more sensitive to the interparticle distances. The best-fit curves from vertical excitation energy in the form of AR(-b) for Delta E-redshift/Delta E-blueshift vs R are determined. In this way, we determined trends for absorption peak shifts and how these depend on the interparticle distance.
First author: Philip, AM, Directing charge transfer in perylene based light-harvesting antenna molecules,
JOURNAL OF CHEMICAL PHYSICS, 153, 8478, (2020)
Abstract: Directing energy and charge transfer processes in light-harvesting antenna systems is quintessential for optimizing the efficiency of molecular devices for artificial photosynthesis. In this work, we report a novel synthetic method to construct two regioisomeric antenna molecules (1-D2A2 and 7-D2A2), in which the 4-(n-butylamino)naphthalene monoimide energy and electron donor is attached to the perylene monoimide diester (PMIDE) acceptor at the 1- and 7-bay positions, respectively. The non-symmetric structure of PMIDE renders a polarized distribution of the frontier molecular orbitals along the long axis of this acceptor moiety, which differentiates the electron coupling between the donor, attached at either the 1- or the 7-position, and the acceptor. We demonstrate that directional control of the photo-driven charge transfer process has been obtained by engineering the molecular structure of the light-harvesting antenna molecules.
First author: Dominikowska, J, Halogen-bonded haloamine trimers – modelling the X(3)synthon,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 21938, (2020)
Abstract: Halogen-halogen bonded haloamine trimers serve as model systems for the X(3)synthon present in numerous crystal structures and in two-dimensional self-assembled nanoarchitectures. Halogen bonds forming the synthon are often considered to display cooperativity. Synergy effects were previously found for halogen-halogen bonded bromoamine and iodoamine tetramers. In the present study comparison between haloamine cyclic trimers and tetramers is made. The cooperativity occurring in bromoamine and iodoamine clusters is significantly weaker in the case of the trimers. The present study demonstrates that the bromoamine and iodoamine trimers display weaker cooperativity due to a smaller number of synergy components in comparison to the corresponding tetramers of stronger cooperativity. Moreover, the halogen-halogen interactions in bromoamine and iodoamine dimers with the geometries of the corresponding trimers and tetramers are examined using energy decomposition analysis methods (supermolecular, canonical EDA and SAPT) and the Kohn-Sham molecular orbital model. The results of the analysis indicate that although the interaction energy values for the dimers of the different spatial arrangement are very close to each other, their origin is substantially different. For pairs with the geometry of the trimers orbital interactions and electrostatic attraction are both weaker than for the corresponding dimers with the geometry of the tetramers. This is especially important because both donor-acceptor interactions and electrostatic attraction were previously proven to be responsible for cooperative effects occurring in the bromoamine and iodoamine tetramers.
First author: Zhang, WW, Atomistic-Scale Simulations of the Graphene Growth on a Silicon Carbide Substrate Using Thermal Decomposition and Chemical Vapor Deposition,
CHEMISTRY OF MATERIALS, 32, 8306, (2020)
Abstract: Molecular dynamics (MD) studies of graphene growth at the atomistic level can provide valuable insight for understanding its growth mechanism, which is helpful to optimize the growth conditions for synthesizing high-quality, large-scale graphene. In this work, we performed nanosecond timescale MD simulations to explore the graphene growth on a silicon carbide (SIC) substrate with the use of a newly developed ReaxFF reactive force field. On the basis of simulation results at various temperatures from 1000 to 3000 K, we identify the optimal temperature at which the high-quality graphene might be produced. Based on this, we further studied the graphene growth with the silicon thermal decomposition method, and we propose different growth mechanisms on the C-terminated (00 (1) over bar) and Si-terminated (001) SiC surfaces. We also simulated graphene growth on the Si-facet of SiC substrate using the chemical vapor deposition (CVD) method through sequential C2H2 addition, in which the surface catalytic dehydrogenation reactions are included. Furthermore, the temperature effect on catalytic efficiency is discussed. The defect and grain boundary structures of the grown graphene with these two growing strategies are investigated as well. We also provide detailed guidelines on how our atomistic-scale results can assist experimental efforts to synthesize layer-tunable graphene with different growth methods.
First author: Gorantla, SMNVT, Stabilization of Linear C(3)by Two Donor Ligands: A Theoretical Study of L-C-3-L (L=PPh3, NHCMe, cAAC(Me)),
CHEMISTRY-A EUROPEAN JOURNAL, 26, 14211, (2020)
Abstract: Quantum chemical studies using density functional theory and ab initio methods have been carried out for the molecules L-C-3-L with L=PPh3(1), NHCMe (2, NHC=N-heterocyclic carbene), and cAAC(Me)(3, cAAC=cyclic (alkyl)(amino) carbene). The calculations predict that 1 and 2 have equilibrium geometries where the ligands are bonded with rather acute bonding angles at the linear C-3 moiety. The phosphine adduct 1 has a synclinal (gauche) conformation where as 2 exhibits a trans conformation of the ligands. In contrast, the compound 3 possesses a nearly linear arrangement of the carbene ligands at the C-3 fragment. The bond dissociation energies of the ligands have the order1<2<3. The bonding analysis using charge and energy decomposition methods suggests that 3 is best described as a cumulene with electron-sharing double bonds between neutral fragments (cAAC(Me))(2) and C-3 in the respective electronic quintet state yielding (cAAC(Me)) = C-3 = (cAAC(Me)). In contrast, 1 and 2 possess electron-sharing and dative bonds between positively charged ligands [(PPh3)(2)](+)or [(NHCMe)(2)](+) and negatively charged [C-3](-) fragments in the respective doublet state.
First author: Pathak, S, Experimental and theoretical insight into the extraction mechanism, kinetics, thermodynamics, complexation and radiolytic stability of novel calix crown ether in ionic liquid with Sr2+,
JOURNAL OF MOLECULAR LIQUIDS, 316, 14211, (2020)
Abstract: A comparative evaluation was carried out for the extraction of Sr2+ using novel calix crown ether in molecular diluent and in ionic liquid. Though the trend in extraction profiles was found to be similar for both the systems, still, almost 5 times higher distribution ratio (D) values were observed in ionic liquid. The speciation studies revealed that; neutral Sr (NO3)(2). DHCC species was formed in dodecane and the extraction followed through ‘solvation’ mechanism. However, ionic liquid medium (IL), anionic species, [Sr(NO3)(3). DHCC](-) was found to be predominating indicating ‘anion exchange’ mechanism. The slower kinetics of extraction in IL was attributed to the high viscosity of IL. The extraction process was found to be spontaneous, endothermic and entropy driven.IL based system was found to be radiolytically more stable compared to the molecular diluent (Mol dil) based system. The electron paramagnetic resonance (EPR) spectroscopic investigation revealed the formation of oxygen centered radical with orthorhombic symmetry (g(x) = 2.00105, g(y) = 2.00475, g(z) = 2.00835) in irradiated ligand. The density functional theoretical (DFT) calculation was utilized to investigate the complexation and speciation in detail in microscopic level.
First author: Ma, FF, Binding properties of cucurbit[7]uril to neutral and protonated amino acids: A theoretical study,
INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 121, 14211, (2021)
Abstract: We systematically investigate the binding nature of cucurbit[7] (CB[7]) toward 20 amino acids in both neutral (AAs) and protonated (AAs(+)) states using quantum chemistry methods. The result indicates that, among AAs, Arg and Asn show the largest binding strength to CB[7], and for AAs(+), Gln(+)and Asn(+)bind to CB[7] the strongest. The binding strength of protonated CB[7]/AA(+)is much stronger than that of neutral CB[7]/AA counterpart due to the introduction of ion-dipole interaction and the increase in number and strength of hydrogen bonds. Energy decomposition analysis indicates that electrostatic interactions play major roles in both CB[7]/AAs and CB[7]/AAs(+)complexes. Moreover, we analyzed the dependence of binding strength on single AA volume and dipole moment. This study is beneficial for providing valuable information in predicting the recognition sites for a sequence-based peptide or protein by CB[7] and rationally designing a synthetic host molecule for specific peptide or protein recognition.
First author: Carey, DM, VisualizingNMR-shielding effect infullerene-ZnPcaggregates: Characteristic patterns ofZnP-basedhosts and encapsulation nature fromDFTcalculations,
INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 121, 14211, (2021)
Abstract: The formation of supramolecular aggregates incorporating C(60)fullerenes can be followed and characterized by nuclear magnetic resonance (NMR) measurements. Here, we unravel the particular patterns provided by zinc-porphyrin (ZnP)-bridged dimers, where the aromatic character of each ZnP unit leads to an enhanced shielding region for the closest fullerene atoms, denoting a slight shielding effect for the equatorial atoms. The nature of the stabilization is discussed and compared to a single ZnP-C(60)aggregate and a ZnP-dimer (ZnP2-C-60) model, with a significant contribution from noncovalent pi-pi interactions, allowing us to address the role of bridging chains. The experimental(13)C-NMR spectrum of C(60)in a bridged ZnP dimer shows a single peak owing to the constant tumbling inside the host, which averages the different groups of carbon atoms. The calculations in a static scenario reveal information concerning the local chemical environment underlying the observed shift in relation to isolated C-60. We expect that the current approach can be useful to rationalize and predict the origin of the NMR shift upon the formation of host-guest aggregates involving small and large host species.
First author: Junejo, R, Effective Removal of the Direct Black-38 Dye from Wastewater Using a New Silica-Modified Resin: Equilibrium and Thermodynamics Modeling Studies,
JOURNAL OF CHEMICAL AND ENGINEERING DATA, 65, 4805, (2020)
Abstract: In this study, the synthesis of p-diethanolaminomethylcalix[4]arene and its immobilization on a silica surface have been performed for the removal of the direct black (DB-38) dye from wastewater samples. The newly synthesized p-diethanolaminomethylcalix[4]arene-immobilized silica (DIS) resin has been analyzed and characterized by FTIR spectroscopy and SEM techniques. To check the efficiency of the DIS resin, batch and column adsorption procedures have been applied under the optimized parameters, i.e., resin dosage, pH, and temperature. To validate the experimental data, Langmuir, Freundlich, and D-R models have been applied. The results show that adsorption follows the Freundlich model well with a good correlation coefficient (R-2 = 0.999). Moreover, the energy E (kJ/mol) was calculated with the help of the D-R model, which suggested that the adsorption has an ion exchange nature. The DIS resin was also applied to real industrial samples of DB-38 dye wastewater. The results show that the DIS resin removes 99% of the dye successfully. Thermodynamics studies were conducted to know the feasibility and the mechanism of the adsorption reaction. The thermodynamic parameters show that the adsorption is spontaneous and exothermic. The theoretical calculation was performed at the B3LYP/DZP calculation level of the ADF program, and the power of the interaction between adsorbent and dye molecules can be determined in the light of chemical reactivity analysis.
First author: Gorski, A, Magnetic Circular Dichroism of meso-Phenyl-Substituted Pd-Octaethylporphyrins,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 8144, (2020)
Abstract: Absorption and magnetic circular dichroism (MCD) spectra have been measured and theoretically simulated for a series of palladium octaethylporphyrins substituted at the meso positions with phenyl groups (n = 0-4). Analysis of the spectra included the perimeter model and time-dependent density functional theory (TDDFT) calculations. With the increasing number of phenyl substituents, the molecule is transformed from a positive hard (Delta HOMO > Delta LUMO) to a soft (Delta HOMO approximate to Delta LUMO) chromophore. This is manifested by a drastic decrease of the absorption intensity in the 0-0 region of the Q-band and by the strongly altered ratio of MCD intensities in the Q and Soret regions. Such behavior can be readily predicted using perimeter model, by analyzing frontier orbital shifts caused by various perturbations: alkyl and aryl substitution, insertion of a metal, and deviations from planarity. TDDFT calculations confirm the trends predicted by the perimeter model, but they fail in cases of less symmetrical derivatives to properly reproduce the MCD spectra in the Soret region. Our results confirm the power of the perimeter model in predicting absorption and MCD spectra of large organic molecules, porphyrins in particular. We also postulate, contrary to previous works, that the isolated porphyrin dianion is not a soft chromophore, but rather a strongly positive-hard one.
First author: Ye, HY, F2BMF (M = V, Nb, and Ta) and FBMF2 (M = Nb and Ta): A Combined Matrix Isolation Infrared Spectroscopic and Quantum Chemical Investigation,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 8192, (2020)
Abstract: Through matrix isolation infrared spectrometry and quantum chemical calculations, the reactions of laser ablated V, Nb, and Ta with boron trifluoride were investigated in excess solid neon at 4 K. The possible reaction products FBMF2 , F-2 BMF, and BMF3 (M = V, Nb, and Ta) were calculated at the B3LYP, BPW91, and CCSD(T) levels of theory. The B-M bond strength in FBMF2 molecules is confirmed by energy decomposition analysis-natural orbitals for chemical valence calculations, CASSCF calculation, and natural bond orbital analysis, which favors one sigma bond and two half pi bonds.
First author: Sandoval, TE, Effect of Heteroaromaticity on Adsorption of Pyrazine on the Ge(100)-2×1 Surface,
JOURNAL OF PHYSICAL CHEMISTRY C, 124, 22055, (2020)
Abstract: The reaction of pyrazine with the Ge(100)-2×1 surface has been investigated by X-ray photoelectron spectroscopy (XPS) and density functional theory calculations. Results show that pyrazine reacts with the surface through both the nitrogen and carbon atoms of the ring to form N-dative bonds and cycloaddition products, respectively. These products are assigned based on calculated electron core level binding and adsorption energies, as well as experimental XPS results. We find that the product distribution changes as a function of coverage and temperature, and in all cases, both dative bonded and cycloaddition products are present. A temperature dependence analysis shows evidence of molecular desorption as well as changes in the product distribution. We found that the number of nitrogen dative bonds is maximized at low temperature through kinetic trapping, while carbon cycloaddition products are promoted with increasing thermal energy. Coverage dependence analysis shows that as the surface becomes crowded, most of the reactions occur through the nitrogen moiety. The nature of surface-adsorbate bonding is revealed by natural population analysis and energy decomposition analysis. We find strong evidence for the dative bond character from molecule to surface donation of the nitrogen lone pairs and surface to molecule back-donation from Ge-Ge-subsurface bonds. A loss of aromaticity is found for the structure with two dative bonds. The reaction to the cycloaddition product shows signatures of an inverse electron-demand Diels-Alder reaction.
First author: Petrov, PA, A Sterically Hindered Derivative of 2,1,3-Benzotelluradiazole: A Way to the First Structurally Characterised Monomeric Tellurium-Nitrogen Radical Anion,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 14688, (2020)
Abstract: Interaction of the tetradentate redox-active 6,6 ‘-[1,2-phenylenebis(azanediyl)]bis(2,4-di-tert-butylphenol) (H4L) with TeCl(4)leads to neutral diamagnetic compound TeL (1) in high yield. The molecule of1has a nearly planar TeN(2)O(2)fragment, which suggests the formulation of1as (TeL2-)-L-II, in agreement with the results of DFT calculations and QTAIM and NBO analyses. Reduction of1with one equivalent of [CoCp2] leads to quantitative formation of the paramagnetic salt [CoCp2](+)[1](.-), which was characterised by single-crystal XRD. The solution EPR spectrum of [CoCp2](+)[1](.-)at room temperature features a quintet due to splitting on two equivalent(14)N nuclei. Below 150 K it turns into a broad singlet line with two weak satellites due to the splitting on the(125)Te nucleus. Two-component relativistic DFT calculations perfectly reproduce thea(N-14) HFI constants andA(parallel to)(Te-125) value responsible for the low-temperature satellite splitting. Calculations predict that the additional electron in1(.-)is localised mainly on L, while the spin density is delocalised over the whole molecule with significant localisation on the Te atom (>= 30 %). All these data suggest that1(.-)can be regarded as the first example of a structurally characterised monomeric tellurium-nitrogen radical anion.
First author: Nieuwland, C, Understanding alkali metal cation affinities of multi-layer guanine quadruplex DNA,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 21108, (2020)
Abstract: To gain better understanding of the stabilizing interactions between metal ions and DNA quadruplexes, dispersion-corrected density functional theory (DFT-D) based calculations were performed on double-, triple- and four-layer guanine tetrads interacting with alkali metal cations. All computations were performed in aqueous solution that mimics artificial supramolecular conditions where guanine bases assemble into stacked quartets as well as biological environments in which telomeric quadruplexes are formed. To facilitate the computations on these significant larger systems, optimization of the DFT description was performed first by evaluating the performance of partial reduced basis sets. Analysis of the stabilizing interactions between alkali cations and the DNA bases in double and triple-layer guanine quadruplex DNA reproduced the experimental affinity trend of the order Li+< Rb+< Na+< K+. The desolvation and the size of alkali metal cations are thought to be responsible for the order of affinity. Nevertheless, for the alkali metal cation species individually, the magnitude of the bond energy stays equal for binding as first, second or third cation in double, triple and four-layer guanine quadruplexes, respectively. This is the result of an interplay between a decreasingly stabilizing interaction energy and increasingly stabilizing solvation effects, along the consecutive binding events. This diminished interaction energy is the result of destabilizing electrostatic repulsion between the hosted alkali metal cations. This work emphasizes the stabilizing effect of aqueous solvent on large highly charged biomolecules.
First author: Conradie, MM, Data of the rhodium(triphenylphosphine)carbony1-2,4-dioxo-3-penty1-4-hydroxybenzoate plus iodomethane oxidative addition and follow-up reactions,
DATA IN BRIEF, 32, 21108, (2020)
Abstract: Density functional theory (DFT) free energy data and the reaction mechanism of the rhodium(triphenylphosphine)carbonyl-2,4-dioxo-3-pentyl-4-hydroxybenzoate plus iodomethane reaction are presented. The rhodium(I) reactant is a simplified model of the rhodium(I) of the rhodium(triphenylphosphine)carbonyl-2,4-dioxo-3-pentyl-4-decanyloxybenzoate plus iodomethane reaction (full model), presented in the related research article “Rhodium(triphenylphosphine)carbonyl-2,4-dioxo-3-pentyl-4-decanyloxybenzoate: A DFT study of Oxidative Addition and Methyl Migration” [1]. The goal is to illustrate that DFT calculations of a simplified model give the same information regarding the reaction scheme and free energy data as for the full model, while it requires much less computational resources to obtain the data. Furthermore the reaction scheme of the simplified model are in agreement with experimental observation of the full model [2].
First author: Smirnova, KS, Zinc complexes with 1-(1H-benzimidazol-1-ylmethyl)-1H-benzotriazole: the structure, quantum chemical calculations, and luminescence properties,
RUSSIAN CHEMICAL BULLETIN, 69, 1873, (2020)
Abstract: An organic ligand 1-(1H-benzimidazol-1-ylmethyl)-1H-benzotriazole (bta) and two zinc complexes of the composition [Zn(bta)(2)Hal(2)] (Hal = Cl, Br) were synthesized. The crystal structure of the complex [Zn(bta)(2)Cl-2] was determined and its features were discussed. According to X-ray diffraction data, the central atom has a tetrahedral environment composed of two nitrogen atoms from two ligand molecules coordinated in monodentate mode and two terminal chloride ions. Density functional theory (DFT) calculations of the ligand and complex [Zn(bta)(2)Cl-2] were carried out. A study of the luminescence properties of the compounds synthesized suggests that excitation of the zinc complexes gives rise to a dual-band luminescence similar to that of the free ligand. Most probably, the emission originates from pi-pi* and pi-pi* intra-ligand transitions.
First author: Bella, G, Theoretical prediction of C-13 NMR spectrum of mixed triglycerides by mean of GIAO calculations to improve vegetable oils analysis,
CHEMISTRY AND PHYSICS OF LIPIDS, 232, 1873, (2020)
Abstract: This pioneering study based on GIAO-DFT methods is aimed to the best prediction of C-13 Nuclear Magnetic Resonances (NMR) arising from triglycerides (and also glycerols), known to be the main component of vegetable oils. Provided that fatty esters bound to the glycerol moiety are not affected by the other esterification chains, and slightly affected by their own esterification position (2- internal, or 1/3- external), eight natural molecules are first optimized despite the challenging presence of many non-hydrogen atoms and the large conformational freedom. This preliminary study sheds light on the total chemical shift prediction concerning five fatty esters (Oleic, Palmitic, Linoleic, Stearic and Linolenic) either present in internal or external positions (ten fragments in total); these results display a very good matching to the experimental profile recorded for several vegetable oils chosen as natural mixtures of glycerides. In order to further improve the theoretical to experimental matching, ten simplified triglycerides with the mentioned fatty esters in the two different esterification positions, and flanked by acetyl esters, were studied and optimized. Beyond the best matching reached so far, we notice that the theoretical rationalisation of the overcrowding in the 28.7-29 ppm spectral region in unable to decode the necessary resolution, nonetheless the same theoretical prediction can still drive the appropriate assignments (as for the fifth and sixth carbon attribution of every chain) even against actual misleading reports.
First author: Loginov, DA, Two different faces of the triangular cluster Rh3Cp3(mu(2)-CO)(3) towards metalloelectrophiles: Structural and theoretical study,
JOURNAL OF ORGANOMETALLIC CHEMISTRY, 924, 1873, (2020)
Abstract: The tetrahedral clusters [(C4Me4)CoRh3Cp3′(mu(3)-CO)(3)](+) (2; Cp’ = C5H4Me) and [(Ph3P)AuRh3CP3′(mu(2)-CO)(3)](+) (3) were synthesized by reactions of Rh3Cp3′(mu(2)-CO)(3) (1b) with metalloelectrophiles [(C4Me4)Co](+) (generated from [(C4Me4)Co(C6H6)](+) under visible-light irradiation) and [(Ph3P)Au](+) (generated from (Ph3P)AuCl/Tl+). They were isolated as salts with PF6 anion, and the structures of 2PF(6) and 3PF(6) were determined by X-ray diffraction. The structural data gave evidence that the coordination of [(C4Me4)Co](+) occurs to the face of 1b with the CO ligands, while the [(Ph3P)Au](+) species reacts with the opposite face of 1b. The latter interaction is accompanied by elongation of the Rh-Rh bonds within the rhodium triangle by 0.1 angstrom. DFT calculations (at the BP86/TZP level) revealed that the selectivity of the metalloelectrophile coordination is determined by orbital control.
First author: Li, Y, Interesting spin state properties of iron(II) polypyridine complex substituted by fluorine: A theoretical study,
ORGANIC ELECTRONICS, 85, 1873, (2020)
Abstract: The special iron(II) polypyridyl complex substituted by fluorine ([Fe(dftpy)(2)](2+), dftpy = 6,6 ”-difluoro-2,2′; 6’2 ”-terpyridine) with uncommon mixed ground states has been detected recently, but the related explanation and characterization are not enough, especially for the influence of substituents. On the basis of previous studies, the key problem of mixed spin states is expected to be described very well by means of theoretical calculations. In this work, density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations have been carried out to study the characteristics of the excited states in detail. Comparing with the parent complex [Fe(tpy)(2)](2+) (tpy = 2,2′ :6′,2 ”-terpyridine) and corresponding bromine or chlorine substituted derivates, the ground states of [Fe(dftpy)(2)](2+) stay around the mixture of singlet state and quintet state, but also there is rare high spin excited state lifetime. Among the halogen substituted complexes, [Fe(dftpy)(2)](2+) has the shortest MLCT state lifetime of 14.0 ps which has been much longer than subpicosecond lifetime of [Fe(tpy)(2)](2+). The reason is explored by the combination of electronic structures, absorption properties, extended transition state coupled with natural orbitals for chemical valence (ETS-NOCV) and potential energy curves (PECs). We can find that the bond lengths of Fe-Nt play a significant role on the change of metal centered (MC) ground states. With Fe-N-t extended by fluorine atoms, the quintet state becomes lower than the singlet state. Due to the deformation of structures, the interactions between metal and ligands diminish and give rise to weaker d orbital splitting than that of [Fe(tpy)(2)](2+), but slightly impact the pairwise orbital deformation density characteristics. And the PEC of (MC)-M-5 intersects with (MC)-M-1,3 which renders faster non-radiative deactivation through low-lying energy crossing points.
First author: Zhong, YL, Major Factors for the Persistent Folding of Hybrid alpha, beta, gamma-Hybrid Peptides Into Hairpins,
FRONTIERS IN CHEMISTRY, 8, 1873, (2020)
Abstract: Factors responsible for the persistent adoption of hairpin conformations by hybrid oligopeptides, each having a central beta/alpha dipeptide segment flanked by aromatic gamma-amino acid (gamma Ar) residues, are probed. Our recent studies revealed that tetrapeptide1and2, having central dipeptide segments consisting of beta-alanine (beta-Ala) and glycine (Gly), and L-beta-homophenylalanine (L-beta-homoPhe) and Gly residues, respectively, that are flanked by gamma Ar residues, fold into well-defined, expanded beta-turns with doubly H-bonded gamma Ar residues. Replacing the gamma Ar residues of1and2with L-Val and L-Leu residues results in tetrapetides1 ‘ and2 ‘ that fail to fold into defined conformations, which confirms the decisive role played by the H-bonded gamma Ar residues in the promoting folding of1and2. Attaching L-Val and L-Leu residues to the termini of1affords hexapeptide1a. With an additional H-bond between its L-Val and L-Leu residues, peptide1afolds into a hairpin with higher stability than that of1, indicating that the expanded beta-turn can nucleate and stabilize beta-hairpin with longer beta-strands. Attaching L-Val and L-Leu residues to the termini of2affords hexapeptide2a. Substituting the L-beta-homoPhe residue of2awith a D-beta-homoPhe residue gives hexapeptide2b. Surprisingly, hexapeptide2afold into a hairpin showing the similar stability as those of tetrapeptides1and2. Hexapeptide2b, with its combination of a D-beta-homoPhe residue and the L-Val/L-Leu pair, fold into a hairpin that is significantly more stable than the other hybrid peptides, demonstrating that a combination of hetero-chirality between the beta-amino acid residue of the dipeptide loop and the alpha-amino acid residues of the beta-strands enhances the stability of the resultant beta-hairpin.
First author: Fernandez, I, The Valence Orbitals of the Alkaline-Earth Atoms,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 14194, (2020)
Abstract: Quantum chemical calculations of the alkaline-earth oxides, imides and dihydrides of the alkaline-earth atoms (Ae=Be, Mg, Ca, Sr, Ba) and the calcium cluster Ca6H9[N(SiMe3)(2)](3)(pmdta)(3)(pmdta=N,N,N ‘,N ”,N ”-pentamethyldiethylenetriamine) have been carried out by using density functional theory. Analysis of the electronic structures by charge and energy partitioning methods suggests that the valence orbitals of the lighter atoms Be and Mg are the (n)s and (n)p orbitals. In contrast, the valence orbitals of the heavier atoms Ca, Sr and Ba comprise the (n)s and (n-1)d orbitals. The alkaline-earth metals Be and Mg build covalent bonds like typical main-group elements, whereas Ca, Sr and Ba covalently bind like transition metals. The results not only shed new light on the covalent bonds of the heavier alkaline-earth metals, but are also very important for understanding and designing experimental studies.
First author: Isukapalli, SVK, Formation of excited triplet states in naphthalene diimide and perylene diimide derivatives: A detailed theoretical study,
JOURNAL OF CHEMICAL PHYSICS, 153, 14194, (2020)
Abstract: Mechanistic details of the excited triplet state formation upon photoexcitation to the low-lying singlet manifold in naphthalene diimide and perylene diimide derivatives are explored theoretically. Static and dynamic aspects of two singlets (S-1 and S-2) and six triplets (T-1-T-6) of these molecules are investigated. Suitable vibronic Hamiltonians are constructed to investigate the internal conversion dynamics in both the singlet and triplet manifolds. Computed singlet-triplet energetics, spin-orbit coupling matrix elements, and intersystem crossing rates strongly suggest an efficient intersystem crossing process involving higher triplet states (T-6, T-5, and T-4). Separate full dimensional quantum wavepacket simulations of singlet and triplet manifolds in the approximate linear vibronic model by assuming initial Franck-Condon conditions are carried out to unravel the internal conversion decay dynamics in the respective manifolds. The obtained diabatic electronic populations and nuclear densities are analyzed to illustrate the triplet generation pathways involving higher triplet states in these molecules. Published under license by AlP Publishing.
First author: Trivedi, DJ, Understanding the chemical contribution to the enhancement mechanism in SERS: Connection with Hammett parameters,
JOURNAL OF CHEMICAL PHYSICS, 153, 14194, (2020)
Abstract: The enhancement mechanism due to the molecule-surface chemical interaction in surface-enhanced Raman scattering (SERS) has been characterized using a theoretical approach based on time dependent density functional theory. This includes a systematic study of the chemical mechanism (CM) to the SERS enhancement for halogen substituted benzenethiols interacting with a silver cluster. Changing the halogen on benzenethiol enables us to systematically modulate interactions between the benzenethiol ring and the metal cluster. We observe a decrease in the CM enhancement factor with an increase in the atomic number of the halogen for para-substitutions. For meta-substitutions, there is no such trend. However, the results scale linearly with the Hammett parameters for both meta and para halogens, which provides an important predictive tool for interpreting chemical enhancements. We also study the effect of solvation on the CM, showing that there is a systematic increase in enhancement with the increasing solvent dielectric constant. The correlation of CM with other properties, such as the amount of charge transfer between adsorbate and metal and the excitation energies of charge transfer states, is much less predictive than the Hammett parameter correlation.
First author: Wang, Q, Electron count and electronic structure of bare icosahedral Au-32 and Au-33 ionic nanoclusters and ligated derivatives. Stable models with intermediate superatomic shell fillings,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 20751, (2020)
Abstract: DFT calculations were carried out on bare Au(32)and Au(33)nanoclusters with various charges, in order to analyze their stability with respect to different cluster electron numbers. Results indicate that in addition to the neutral Au(32)hollow species, significant HOMO-LUMO gaps are computed for [Au-32](8+)(hollow) and [Au-32](4+)(two-shell structure). Species with smaller HOMO-LUMO gaps can reach stability upon “passivation” by a ligand shell, as experimentally exemplified. Icosahedral frameworks ofI(h)or lower symmetry are favored for the cationic nanoclusters whereas different structures are computed for the anionic ones.
First author: Yang, MC, A theoretical study of the reactivity of ethene and benzophenone with a hyper-coordinated alkene containing a so-called E=E (E = C, Si, Ge, Sn, and Pb) unit,
DALTON TRANSACTIONS, 49, 12842, (2020)
Abstract: The reactivity of a reported hyper-coordinated alkene (Rea-E; Rea = reactant; E = group 14 element) featuring a central E=E moiety was theoretically analyzed using DFT (density functional theory) and the EDA-NOCV (energy decomposition analysis-natural orbitals for chemical valence) method. M06-2X/def2-SVP and B3LYP-D3/def2-SVP results demonstrate that five Rea-E molecules have an energy minimum as their structures have no imaginary frequency. Theoretical examinations based on three types of bond order calculations (Wiberg, Mayer, and Fuzzy), the LOL (localized orbital locator) analyses, Lewis structures and the NBO (natural bond orbital) analyses suggest that a very weak central Si-Si single bond and an extremely weak central Ge-Ge single bond, rather than a double bond, are present in the Rea-Si and Rea-Ge molecules, respectively. On the other hand, no bond is found between the two central group 14 atoms in Rea-C, Rea-Sn, and Rea-Pb. The theoretical investigation demonstrates that the reactivity of the Rea-E compound decreases in the order Rea-Si > Rea-Ge > Rea-C, a trend that results from the differences in the atomic radii of the group 14 elements. Carbon has the smallest atomic radius in the group 14 family, causing steric crowding between Rea-C and other attacking species. This circumstance, in turn, increases the activation energies of its addition reactions and renders these reactions energetically infeasible. For the cyclic product of Rea-Ge, the theoretical evidence reveals that the comparatively large atomic radius of Ge induces the weakest Pauli repulsions and the smallest overlap integrals between Rea-Ge and the other doubly bonded molecules. This situation, in turn, makes the overall cyclization reaction of Rea-Ge endothermic. As a result, only the silicon-centered molecule, Rea-Si, can undergo the [2 + 2] cycloaddition reactions with doubly bonded molecules without kinetic or thermodynamic difficulty, which agrees well with the available experimental findings.
First author: Almerindo, GI, Kinetics and adsorption calculations: insights into the MgO-catalyzed detoxification of simulants of organophosphorus biocides,
JOURNAL OF MATERIALS CHEMISTRY A, 8, 19011, (2020)
Abstract: We report the targeted decomposition of the organophosphate methyl paraoxon by means of its transesterification with 1-propanol catalyzed by magnesium oxide. Catalyst characterization by energy dispersive X-ray fluorescence (EDXRF), nitrogen adsorption/desorption measurements (BET and BJH methods), and temperature programmed desorption of CO2(CO2-TPD) showed that the employed MgO presents properties favorable for the methyl paraoxon adsorption and transesterification to occur. A thorough kinetic investigation showed that rate enhancements up to 3 x 10(6)-fold can be achieved in comparison with the spontaneous propanolysis of the substrate, and that the material can be used in additional cycles without loss of catalytic activity, with the catalyst recovery achieved through a simple washing procedure. Energies for adsorption of 1-propanol and methyl paraoxon onto a MgO model surface were obtained by density functional theory calculations, which showed that the latter displays a stronger affinity for the catalyst surface, and that the reaction should proceed with methyl paraoxon and 1-propanol molecules juxtapositioned at adjacent Mg(2+)sites, with nucleophilic and electrophilic centersca.2.4 angstrom away from each other. Additionally, MgO also promoted rate enhancements up to 5 x 10(4)-fold in the propanolysis of a further range of representative phosphate triesters, and in most of the cases the final transesterified products are trialkyl phosphates structurally related to a family of flame-retardants. The results thus provide insights into the development of novel systems for the targeted conversion of organophosphorus compounds into value-added products by employing simple, highly efficient, and low-cost metal oxide catalysts.
First author: Boucenina, S, Electronic structure and magnetic properties of naphthalene- and stilbene-diimide-bridged diuranium(V) complexes: a theoretical study,
JOURNAL OF MOLECULAR MODELING, 26, 19011, (2020)
Abstract: The magnetic exchange coupling between two diuranium(V) ions exhibiting the 5f(1)-5f(1) configuration in diimide-bridged complexes [Cp3UV](2)(mu -L) (L = stilbene-, naphthalene-diimide) has been investigated theoretically using relativistic ZORA/DFT calculations. Using two different hybrid PBE0 and B3LYP functionals, combined with the broken symmetry (BS) approach, we found that the BS states of both naphthalene and stilbene complexes have lower energy than the corresponding high-spin (HS) triplet ones. The B3LYP/BS estimated exchange coupling J constants (-16.1 vs. -9.0 cm(-1) respectively for the naphthalene and stilbene complexes) corroborate well with those obtained previously for other pentavalent diuranium(V) diimide-bridged systems. The computed J value is found to be sensitive to -network linking the two magnetic U(V) centers. The natural spin density distributions and molecular orbital analyses explain well the antiferromagnetic character of these compounds and clarify the crucial role of the aromatic spacer in promoting spin polarization and delocalization favoring the magnetic coupling. Furthermore, the effective involvement of the 6d/5f metal orbitals in metal-ligand bonding plays an important role for the magnetic communication between the two active U(V) 5f electrons.
First author: Raychaudhuri, D, On the Nature of the Carbonyl versus Phosphoryl Binding in Uranyl Nitrate Complexes,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 7805, (2020)
Abstract: The electronic structure of ligands with phosphoryl and carbonyl binding sites and their complexation behavior with uranyl nitrate were investigated using density functional theory (DFT). The quantum chemical calculations indicate that the electronic charges on both phosphoryl and carbonyl groups are more polarized toward oxygen atoms in isolated ligands. This effect is predominant in the case of complexes of the former. Both P = O and C = O groups are positively charged with the exception in methylisobutylketone (MIBK), where the C=O group is virtually neutral. The fragment molecular orbital analysis suggests that during complexation, a certain amount of charge transfer occurs from the filled pp-orbitals [px (CO/PO) and py (CO/PO)] of the ligand to 5f, 6d, and 7s orbitals of the uranium atom (fs* and dss*). The NBO analysis reaffirms the charge transfer mechanism. The observed red shift in nu(C = O) and nu(P = O) identified in the simulated infrared spectrum of the corresponding complexes implies a moderate weakening of both carbonyl and phosphoryl bonds upon complexation. The atoms in molecules (AIM) analysis suggests a stronger phosphoryl binding compared to carbonyl interactions and an ionic U-O bond. The estimated complexation energies are considerable for phosphoryl ligands compared to those of the carbonyl analogue, with a reasonably large value derived for tri-n-butyl phosphate (TBP). The energy decomposition analysis marked significant stabilizing orbital interactions for phosphoryl ligands. The contributions of estimated dispersion energies are considerable in all complexes and extensively depend on the alkyl unit.
First author: Bondi, L, Quantitative and Chemically Intuitive Evaluation of the Nature of M-L Bonds in Paramagnetic Compounds: Application of EDA-NOCV Theory to Spin Crossover Complexes,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 13677, (2020)
Abstract: To improve understanding ofM-Lbonds in 3d transition metal complexes, analysis by energy decomposition analysis and natural orbital for chemical valence model (EDA-NOCV) is desirable as it provides a full, quantitative and chemically intuitive ab initio description of theM-Linteractions. In this study, a generally applicable fragmentation and computational protocol was established and validated by using octahedral spin crossover (SCO) complexes, as the transition temperature (T-1/2) is sensitive to subtle changes inM-Lbonding. Specifically, EDA-NOCV analysis of Fe-N bonds in five [Fe-II(L-azine)(2)(NCBH3)(2)], in both low-spin (LS) and paramagnetic high-spin (HS) states led to: 1) development of a general, widely applicable, corrected M+L(6)fragmentation, tested against a family of five LS [Fe-II(L-azine)(3)](BF4)(2)complexes; this confirmed that threeL(azine)are stronger ligands (Delta E-orb,E-sigma+pi=-370 kcal mol(-1)) than2 L-azine+2 NCBH3(=-335 kcal mol(-1)), as observed. 2) Analysis of Fe-Lbonding on LS -> HS, reveals more ionic (Delta E-elstat) and less covalent (Delta E-orb) character (Delta E-elstat:Delta E(orb)55:45 LS -> 64:36 HS), mostly due to a big drop in sigma (Delta E-orb,E-sigma down arrow 50 %; -310 ->-145 kcal mol(-1)), and a drop in pi contributions (Delta E-orb,E-pi down arrow 90 %; -30 ->-3 kcal mol(-1)). 3) Strong correlation of observedT(1/2)and Delta E-orb,E-sigma+pi, for both LS and HS families (R-2=0.99 LS,R-2=0.95 HS), but no correlation ofT(1/2)and Delta Delta E-orb,E-sigma+pi(LS-HS) (R-2=0.11). Overall, this study has established and validated an EDA-NOCV protocol forM-Lbonding analysis of any diamagnetic or paramagnetic, homoleptic or heteroleptic, octahedral transition metal complex. This new and widely applicable EDA-NOCV protocol holds great promise as a predictive tool.
First author: Baghdasaryan, A, Ligand exchange reactions on the chiral Au-38 cluster: CD modulation caused by the modification of the ligand shell composition,
NANOSCALE, 12, 18160, (2020)
Abstract: Ligand exchange reactions have become a highly versatile post-synthetic strategy to accurately engineer the ligand shell of atomically precise noble metal nanoclusters. Modifying the chemical structure of the exchanging ligand with chromophore substituents or adding chiral centers allow direct functionalization of the cluster with desired properties. As such, post-functionalized gold nanoclusters with unique physicochemical properties find applications in optoelectronics, catalysis and biomedicine. Herein, we successfully carried out ligand exchange reactions between the chiral Au-38(2-PET)(24)cluster (both racemic and enantiopure forms) and the helically chiral but configurationally labile 2-thio[4]helicene ligand (TH4). The reaction products with a composition of Au-38(2-PET)(24-x)(TH4)(x)were analyzed using UV-vis spectroscopy and MALDI mass spectrometry. It was found that up to ten 2-PET ligands can be replaced with the helicene ligand on the cluster surface according to MALDI analysis. Consequently, the UV-vis and CD spectra of the cluster have been strongly affected by the ligand exchange reaction. The intensities of the CD signals of Au-38(2-PET)(24-x)(TH4)(x)were drastically reduced and red shifted with respect to the reference Au-38(2-PET)(24)cluster. Moreover, the appearance of the other enantiomer in the HPLC chromatogram revealed the partial racemization of the cluster. DFT calculations were performed and they support the experimental observations and show that the observed chiroptical changes in UV-vis and CD spectra are exchange-site dependent. The calculations also demonstrate that charge transfer (CT) transitions occur between the Au(38)cluster and the helicene ligand. Thus the ligand is directly involved in these transitions and contributes to the electronic states comprising those transitions.
First author: Bacha, RUS, Atomic uranium modified graphdiyne as catalytic material for hydrogen evolution reaction: An interfacial descriptor led mechanistic study,
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 45, 24604, (2020)
Abstract: Catalysis operated on supported single metal atom is considered as one of the vital efforts for chemical and energy conversion. Despite the enormous amount of research on single transition metal (TM) enhanced graphdiyne (GDY) material, its modification with slightly depleted uranium remains unexplored. Herein, we conducted relativistic density functional theory (DFT) calculations for the accumulation of atomic uranium inside size suitable GDY pore. The stability of graphdiyne-uranium (GDY-U) is corroborated in terms of short U-C bond distances (2.34-2.44 angstrom), with local depletion of charge and greater U(5f)C(p) molecular orbital overlap. The magnificent structural and electronic properties of GDY-U system qualify it for the investigation of hydrogen evolution reaction (HER). The HER performance of all exposed sites, including central metal atom and four dissimilarly coordinated acetylenic carbons has been examined and compared with that of pure GDY. As the overall HER interfacial descriptor, free energy change of the intermediate state (DGH*) at the central metal surface of GDY-U was found to be most favorable (0.153 eV) amongst all sites and far superior to those of pure GDY. In addition to the uranium surface, the coordinated carbons also show improved HER activity, indicating the enhancement of the system upon metal insertion. The calculated DGH* of the GDY-U system here is comparable to some of the recently reported GDY-TM materials, suggesting that atomic uranium could be an exceptional alternative for applied common catalysts.
First author: Chetioui, S, Synthesis, spectroscopic characterization, crystal structure and theoretical investigation of two azo-palladium (II) complexes derived from substituted (1-phenylazo)-2-naphtol,
TRANSITION METAL CHEMISTRY, 46, 91, (2021)
Abstract: Theortho-substituted (E)-1-((2-methoxyphenyl)diazenyl)naphthalen-2-ol and themeta-substituted (E)-1-((3-methoxyphenyl)diazenyl)naphthalen-2-ol were, respectively, used in the synthesis of two new complexes, bis[1-(2-methoxyphenylazo)-2-naphthoxy]palladium(II) and bis[1-(3-methoxyphenylazo)-2-naphthoxy]palladium(II), noted (I) and (II), respectively. (I) and (II) were characterized by physicochemical and spectroscopic methods, and their molecular structures were determined by X-ray crystallography. Both complexes display a square-planar geometry, which is reproduced by full geometry optimizations at the DFT/B3LYP level. Calculations were also performed on the free ligands (in their precursor form), as well as theirpara-substituted isomer (E)-1-((4-methoxyphenyl)diazenyl)naphthalen-2-ol and its hypothetical complex bis[1-(4-methoxyphenylazo)-2-naphthoxy]palladium(II) (compound (III). Calculations were also performed on the free p-phenylazo-2-naphthol ligand (p-MoxyPhNap), in order to understand their bonding and to analyze their electronic structure. TD-DFT calculations were also performed on the three complexes to simulate their absorption spectra from and compare to the experimental UV-Vis data of (I) and (II). The main peaks in the spectrum of (I) are assigned to mixed LMCT/LLCT and pi-pi* (ILCT) transition, while the unique major peak afforded by (II) is assigned to MLCT and LLCT transitions.
First author: Swart, M, Bond orders in metalloporphyrins,
THEORETICAL CHEMISTRY ACCOUNTS, 139, 91, (2020)
Abstract: A new concept of bond order density of shared electron pairs is introduced to study the electronic structure in molecules. This BODSEP analysis is applied to the distortion of benzene toward its building blocks (acetylenes), metalloporphyrins and two recent examples from the literature. The S12g/TZ2P results show the gradual disappearance of the bonds while distorting benzene and strengthening the bonds in acetylene to reach a final triple bond value. A large range of bond orders are observed for the metalloporphyrins, which are consistent with aromaticity indices from the literature [Can. J. Chem. 2009, 87, 1063]; with an ideal value of 1.5 for aromatic molecules (because of resonance), it suggests that (BODSEP) bond orders might be used for aromaticity measures. Finally, the delocalized bonds in porphyrins are localizing in the corrphycenes, and bond order strengths for different spin states of dipyrrolonaphthyridinedione have been assigned, which differ from the original description.
First author: Goricke, F, Phosphoric Acid Catalyzed Formation of Hydrogen-Bonded o-Quinone Methides. Enantioselective Cycloaddition with beta-Dicarbonyl Compounds toward Benzannulated Oxygen Heterocycles,
JOURNAL OF ORGANIC CHEMISTRY, 85, 11699, (2020)
Abstract: A full account of the Bronsted acid catalyzed, enantioselective synthesis of 4H-chromenes and 1H-xanthen-1-ones from o-hydroxybenzyl alcohols and beta-dicarbonyl compounds is provided. The central step of our strategy is the BINOL-phosphoric acid catalyzed, enantioselective cycloaddition of beta-diketones, beta-keto nitriles, and beta-keto esters to in situ generated, hydrogen-bonded o-quinone methides. Upon acid-promoted dehydration, the desired products were obtained with generally excellent yields and enantioselectivity. Detailed mechanistic studies including online-NMR and ESI-MS measurements were conducted to identify relevant synthetic intermediates. A reversible formation of a dimer from the starting alcohol and the reactive o-quinone methide in an off-cycle equilibrium was observed, providing a reservoir from which the o-quinone methide can be regenerated and introduced into the catalytic cycle again. Reaction progress kinetic analysis was utilized to determine kinetic profiles and rate constants of the reaction uncovering o-quinone methide formation as the rate-limiting step. In combination with Hammett plots, these studies document the relationship between o-quinone methide stabilization by electronic effects provided by the substituents and the reaction rate of the described process. In addition, DFT calculations reveal a concerted yet highly asynchronous [4 + 2]-cycloaddition pathway and an attractive CH-p interaction between the catalyst’s tBu group and the o-quinone methide as an important stereochemical control element.
First author: Damirchi, B, ReaxFF Reactive Force Field Study of Polymerization of a Polymer Matrix in a Carbon Nanotube-Composite System,
JOURNAL OF PHYSICAL CHEMISTRY C, 124, 20488, (2020)
Abstract: Human transport to Mars and deep-space explorations demand the development of new materials with extraordinarily high performance-to-mass ratios. Promising candidates to fulfill these requirements are ultrahigh-strength lightweight materials, which consist of polymer matrices fortified by pristine carbon nanotubes (CNTs). Previous investigations have showed that with an increase in the CNT diameter, its preferred configuration changes from a circular form to a flattened shape that can be obtained under high pressure or tension conditions. The ReaxFF reactive force field can reveal detailed chemical interactions at the atomistic scale. To enable ReaxFF simulations on CNT/polymer interfaces, we trained force-field parameters to capture the proper structure of flattened CNTs (flCNTs), i.e., dumbbell-like shape CNTs, against available polymer consistent force field-interface force field data, which have good proximity to density functional theory data. In this study, we used accelerated ReaxFF molecular dynamics simulation using the optimized force field to study the polymerization of diglycidyl ether of bisphenol F and diethyltoluenediamine molecules in the vicinity of circular and flCNTs. Our results indicate that the flat regions of flCNTs are more favorable spots for the polymers to settle compared to the curved regions due to the higher binding energies. Moreover, higher dimer generation around flCNTs results in more effective coating of the nanotube, which leads to higher load transfer when compared to circular CNTs. According to our results, there is high alignment between polymers and the nanotube surface, which is due to the strong p-p interactions of aromatic carbon rings in the polymers and nanotubes. These atomistic ReaxFF simulations indicate the capability of this method to simultaneously observe the polymerization of monomers along with their interactions with CNTs.
First author: Liu, XY, Nonadiabatic Exciton and Charge Separation Dynamics at Interfaces of Zinc Phthalocyanine and Fullerene: Orientation Does Matter,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 7388, (2020)
Abstract: Interface orientation between zinc phthalocyanine (ZnPc) and fullerene (C-60) affects their interfacial charge separation dynamics; however, the underlying physical origin is still elusive. In this work, we have employed the time-dependent density functional theory (TDDFT) method to explore excited-state properties of ZnPc and C-60 heterojunctions with both face-on and edge-on configurations. Spectroscopically bright absorption is from locally excited (LE) singlet excitons within ZnPc. In the face-on configuration, LE excitons are much higher in energy than charge-transfer (CT) excitons, thereby making charge separation process favorable. However, in the edge-on configuration, LE excitons are the lowest ones and CT ones are higher in energy; thus, charge separation is not efficient. Subsequently, we have carried out TDDFT-based nonadiabatic dynamics method to simulate photoinduced exciton and charge separation dynamics of ZnPc and C-60 heterojunctions with both edge-on and face-on configurations. In the former, there are no exciton transfer and charge separation processes observed within 300 fs simulation time; while, in the latter, fragment-based electronic transition density matrix analysis reveals that only LE excitons vertical bar C60ZnPC*> and CT excitons vertical bar C60-ZnPC+> are involved. The exciton transfer from vertical bar C60ZnPC*> to vertical bar C60-ZnPC+> is completed within about 100 fs in which charge separation takes place with electron-hole distances increasing from 1.0 to 4.5 angstrom. This exciton transfer process is essentially in company with electron transfer from ZnPc to C-60 but almost not involving hole transfer. These gained insights not only rationalize experiments but also enrich our knowledge to design donor-acceptor orientations to optimize organic photovoltaic performance.
First author: Reimann, M, Evaluation of an Efficient 3D-RISM-SCF Implementation as a Tool for Computational Spectroscopy in Solution,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 7439, (2020)
Abstract: The 3D-RISM-SCF solvent-model implementation of Gusarov et al. [J. Phys. Chem. A 2006, 110, 6083-6090] in the Amsterdam density functional program has been improved and extended. In particular, an accurate yet efficient representation of the solute electrostatic potential is provided. The Coulomb-potential fitting of many DFT codes can be used advantageously in this context. The extra effort compared to a point-charge representation is small for a given SCF cycle and compensated by faster SCF convergence. This allows applications to large solutes, as demonstrated by evaluation of the solvatochromism of Reichardt’s dye. In general, TDDFT applications to excitation energies in solution stand out and are highlighted. Applications to the O-17 NMR chemical shifts of N-methylformamide in different solvents also demonstrate the distinct advantages of 3D-RISM over continuum solvents. Limitations are observed in this case for water solvent, where the solvent shielding is overestimated. This shortcoming applies also to the O-17 gas-to-liquid shift of water, where we used localized molecular orbital analyses for a deeper understanding. For such cases of extremely strong solute-solvent interactions, couplings between solute and solvent orbitals induced by the magnetic perturbation are relevant. These clearly require a quantum-mechanical treatment of the most closely bound solvent molecules. Except for such extreme cases, 3D-RISM-SCF is very well suited to treat solvent effects on NMR parameters. More serious limitations pertain to the treatment of vibrational spectra, where the absence of the coupling between solute and solvent vibrational modes limits the accuracy of applications of 3D-RISM-SCF. The reported extended, efficient, and numerically accurate 3D-RISM-SCF implementation should provide a useful tool to study chemical and spectroscopic properties of molecules of appreciable size in a realistic solvent environment.
First author: Munch, A, Insight into the Bonding and Aggregation of Alkyllithiums by Experimental Charge Density Studies and Energy Decomposition Analyses,
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 142, 15897, (2020)
Abstract: In this Article, the organolithiums [((-)-sparteine)-(LiBu)-Bu-t] (1), [(ABCO)(LiBu)-Bu-t](2) (2), and [(ABCO)(2)((LiPr)-Pr-i)(4)] (3) are investigated by means of experimental and theoretical charge density determination to elucidate the nature of the Li-C and Li-N bonds. Furthermore, the valence shell charge concentrations (VSCCs) in the nonbonding region of the deprotonated C-alpha-atom will provide some insight on the localization of the carbanionic lone pair. Analysis of the electron density (rho(r(BCP))), Laplacian (del(2)rho(r(BCP))), and the energy decomposition (EDA) confirmed that the Li-C/N bond exhibits astonishingly similar characteristics, to reveal an increasingly polar contact with decreasing aggregate size. This explains former observations on the incorporation of halide salts in organolithium reagents. Furthermore, it could be shown that the bonding properties of the Pr-i group are similar to those of the Bu-t substituent. The accuracy of fit to all previously determined properties in organolithiums is remarkable.
First author: Zhao, XY, Donor-acceptor duality of the transition-metal-like B-2 core in core-shell-like metallo-borospherenes La-3&[B-2@B-17](-) and La-3&[B-2@B-18](-),
RSC ADVANCES, 10, 34225, (2020)
Abstract: Transition-metal doping induces dramatic structural changes and leads to earlier planar -> tubular -> spherical -> core-shell-like structural transitions in boron clusters. Inspired by the newly discovered spherical trihedral metallo-borosphereneD(3h)La(3)&B-18(-)(1) (Chen,et al., Nat. Commun., 2020,11, 2766) and based on extensive first-principles theory calculations, we predict herein the first and smallest core-shell-like metallo-borospherenesC(2v)La(3)&[B-2@B-17](-)(2) andD(3h)La(3)&[B-2@B-18](-)(3) which contain a transition-metal-like B(2)core at the cage center with unique donor-acceptor duality in La-3&B(n)(-)spherical trihedral shells (n= 17, 18). Detailed energy decomposition and bonding analyses indicate that the B(2)core in these novel complexes serves as a pi-donor in the equatorial direction mainly to coordinate three La atoms on the waist and a pi/sigma-acceptor in the axial direction mainly coordinated by two B(6)triangles on the top and bottom. These highly stable core-shell complexes appear to be spherically aromatic in nature in bonding patterns. The IR, Raman, and photoelectron spectra of2and3are computationally simulated to facilitate their spectroscopic characterizations.
First author: Wang, Y, Two-photon excited deep-red and near-infrared emissive organic co-crystals,
NATURE COMMUNICATIONS, 11, 34225, (2020)
Abstract: Two-photon excited near-infrared fluorescence materials have garnered considerable attention because of their superior optical penetration, higher spatial resolution, and lower optical scattering compared with other optical materials. Herein, a convenient and efficient supramolecular approach is used to synthesize a two-photon excited near-infrared emissive co-crystalline material. A naphthalenediimide-based triangular macrocycle and coronene form selectively two co-crystals. The triangle-shaped co-crystal emits deep-red fluorescence, while the quadrangle-shaped co-crystal displays deep-red and near-infrared emission centered on 668 nm, which represents a 162 nm red-shift compared with its precursors. Benefiting from intermolecular charge transfer interactions, the two co-crystals possess higher calculated two-photon absorption cross-sections than those of their individual constituents. Their two-photon absorption bands reach into the NIR-II region of the electromagnetic spectrum. The quadrangle-shaped co-crystal constitutes a unique material that exhibits two-photon absorption and near-infrared emission simultaneously. This co-crystallization strategy holds considerable promise for the future design and synthesis of more advanced optical materials.
First author: Zuo, YN, Mechanism study on asymmetric Michael addition reaction between alkynone and alpha-angelica lactone catalyzed by chiral N, N ‘-dioxide-Sc(III) complex,
CATALYSIS TODAY, 355, 635, (2020)
Abstract: The reaction mechanism and enantioselectivity of asymmetric Michael addition reaction between alkynone (R1) with a-angelica lactone (R2) catalyzed by chiral N, N’-dioxide-Sc(III) complex were investigated at the M06/6-31G(d,p) (acetonitrile, SMD) level. The alpha-angelica lactone substrate could isomerize to the active enolized form in the presence of Sc(OTf)(3) reagent, assisted by the counter trifluoromethanesulfonate anion OTf-. The alkynone substrate and enolized angelica lactone (or its anion) coordinated to Sc(III) center of N,N’-dioxide-Sc(III) complex catalyst simultaneously, forming a high active hexacoordinate-Sc(III) complex. The catalytic reaction occurred via a two-step mechanism, in which C-2-C-gamma bond formation was predicted to be the chirality-controlling step as well as the rate-determining step (RDS), affording predominant S-enantiomer. The counterion OTf- facilitated C-H construction as a proton-shuttle, producing mainly E-configuration product observed in experiment. The steric repulsion from the ortho-substituent of amide moiety as well as the chiral backbone of N, N’-dioxide-Sc(III) catalyst played the key role for chiral induction in the asymmetric reaction. The less destabilizing Pauli repulsion and more stabilizing attractive interaction, especially the orbital interaction, along the si-face attack pathway enhanced the enantiodifference of the two competing pathways for high enantioselectivity. The energy barriers for E/Z isomerization of S or R-enantiomer assisted by HOTf was as high as 34.6-35.0 kcal mol(-1), indicating that the product with Z-conformation was difficult to be obtained. These results were in good agreement with experimental observations.
First author: Shao, Y, Tuning the Proton-Coupled Electron-Transfer Rate by Ligand Modification in Catalyst-Dye Supramolecular Complexes for Photocatalytic Water Splitting,
CHEMSUSCHEM, 14, 479, (2021)
Abstract: In view of the considerably high activation energy barrier of the O-O bond formation photocatalytic step in water oxidation, it is essential to understand if and how nonadiabatic factors can accelerate the proton-coupled electron transfer (PCET) rate in this process to find rational design strategies facilitating this step. Herein, constrainedab initiomolecular dynamics simulations are performed to investigate this rate-limiting step in a series of catalyst-dye supramolecular complexes functionalized with different alkyl groups on the catalyst component. These structural modifications lead to tunable thermodynamic driving forces, PCET rates, and vibronic coupling with specific resonant torsional modes. These results reveal that such resonant coupling between electronic and nuclear motions contributes to crossing catalytic barriers in PCET reactions by enabling semiclassical coherent conversion of a reactant into a product. Our results provide insight on how to engineer efficient catalyst-dye supramolecular complexes by functionalization with steric substituents for high-performance dye-sensitized photoelectrochemical cells.
First author: Babaei, S, Chemical reactivity descriptors as a tool of prediction in the synthesis of sandwich type polyoxometalate organic-inorganic hybrid compounds,
POLYHEDRON, 188, 479, (2020)
Abstract: In the present study a predictive model aimed at the selection of organic ligands for the successful synthesis of Cobalt sandwich-type polyoxometalate (Co-STPs) organic-inorganic hybrid compounds in aqueous solution, has been introduced. The computations were performed using Gaussian09 and the results have been evaluated by the graphic interface program, GaussView05. Geometry optimization and frequency calculations have been performed at B3LYP level with 6-311G basis set. Dipole moment was recalled from optimization results and reactivity descriptors were calculated via Fukui function using atomic charges and frontier orbitals energies. Firstly the organic molecules with dipole moments more than water are filtered.
First author: Buchner, MR, Di-ortho-beryllated Carbodiphosphorane: A Compound with a Metal Carbon Double Bond to an Element of the s-Block,
ORGANOMETALLICS, 39, 3224, (2020)
Abstract: Double bonds have been realized fora wide variety of lements in the p -, d-, and f-blocks. However, no s-block metal complexes with a don hie bond have been identified. Here we report the synthesis and characterization of a di-ortho-beryllated carbodiphosphorane, which exhibits a double dative Be = C bond. This species shows an unprecedented bonding situation at the metal center, which was extensively analyzed by experimental and comPutational means
First author: Nagurniak, GR, What is the driving force behind molecular triangles and their guests? A quantum chemical perspective about host-guest interactions,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 19213, (2020)
Abstract: The physical nature of host-guest (HG) interactions occurring between molecular triangles and linear anions was explored using density functional theory (DFT) calculations combined with energy decomposition analyses (EDA), nuclear independent chemical shift (NICS), and non-covalent interaction index (NCI). We demonstrate that: (i) in addition to the host being significantly rigid, the strain energies are not negligible, especially for host2; (ii) halogen anions interact mainly by electrostatic forces (Delta E-elst> Delta Eorbtot > Delta E-disp), meanwhile; (iii) trihalogen anions interact mostly by dispersion forces (Delta E-disp> Delta E-elst approximate to Delta Eorbtot). The NICS and NCI calculations corroborate the idea that HG interactions are considerably mediated through dispersion terms, and also indicate an antiaromatic character inside the host walls.
First author: Grabias, E, New uranium(VI) and isothiouronium complexes: synthesis, crystal structure, spectroscopic characterization and a DFT study,
CRYSTENGCOMM, 22, 5678, (2020)
Abstract: The crystal structures of S,S’-2,5-dimethylbenzene-1,4-diylbis(methylisothiouronium) diacetate (1_ac),S,S’-2,5-dimethylbenzene-1,4-diylbis(methylisothiouronium) dichloride (1_Cl),1_Ucomplex,S,S’-naphthalene-1,4-diylbis(methylisothiouronium) dichloride (2_Cl), and2_Ucomplex were determined for the first time. The supramolecular structures of the compounds obtained are mainly based on hydrogen bonding and ionic interactions between the isothiouronium cations and the counter anions Cl-, CH3COO-, and [UO2(CH3COO)(3)](-). Their structural and spectroscopic properties were studied, and the results of DFT calculations were compared with the experimental findings to provide insights into the properties of these new compounds. The DFT calculations indicate a strong preference for the formation of the outer-sphere complex (ion-pair) between the uranyl species and an isothiouronium cation, and very large stabilization energies of the interactions, which can be utilized for the selective binding of U(vi). The compounds obtained are the first f-element and isothiouronium salt complexes described so far.
First author: Urzua-Leiva, R, Effects of the methylammonium ion substitution by 5-ammoniumvaleric acid in lead trihalide perovskite solar cells: a combined experimental and theoretical investigation,
NEW JOURNAL OF CHEMISTRY, 44, 14642, (2020)
Abstract: In the last decade, lead triiodide perovskite (APbI(3)) (A: organic cation) solar cells (PSCs) have been broadly studied due to their promising features related to the low cost, easy manufacturing process, and stability. Strategies to improve the device stability include the application of techniques such as compositional engineering of the cation of these halide perovskites, but it is still a complex task to find the right balance between the stability and power conversion efficiency of materials and complete devices. In this work, we performed a combined study of five samples of [5-AVA((1-x))MA(x)]PbI3(5-AVA: ammonium valeric acid and MA: methylammonium) withx= 1.0, 0.75, 0.5, 0.25 and 0.0, using X-ray diffraction (XRD) and UV-VIS spectroscopy measurements in combination with periodic density functional theory (DFT) based calculations. Our samples showed an optical bandgap of 1.58 eV and the coexistence of the two phases as observed by XRD analyses. The theoretical results of the bandgaps for the no mixed phases (x= 1.0 andx= 0.0) show good agreement with the experiment, obtaining bandgap values overestimated by 0.18 eV and 0.33 eV, respectively. A direct relation between the number of 5-AVA ions in the samples and the stability of the phases was theoretically found and proved through the increment observed in the bandgap and the cohesive energy. We proposed a compositional strategy for perovskites [5-AVA((1-x))MA(x)]PbI(3)withxvalues of at most 0.5, based on the small blue-shift and the low absorbance reduction of the spectrum curve, added to the small phase stabilization found.
First author: Wolzak, LA, Titanium-catalyzed esterification reactions: beyond Lewis acidity,
CHEMCATCHEM, 12, 5229, (2020)
Abstract: Esterification is a key reaction and is used in many synthetic and industrial processes, yet the detailed mechanism of operation of often-used (Lewis acid) catalysts is unknown and subject of little research. Here, we report on mechanistic studies of a titanium aminotriphenolate catalyst, using stoichiometric and catalytic reactions combined with kinetic data and density functional theory (DFT) calculations. While often only the Lewis acidity of the Ti-center is taken into account, we found that the amphoteric nature of this catalyst, combining this Lewis acidity with Bronsted basicity of a Ti-bound andin situformed carboxylate group, is crucial for catalytic activity. Furthermore, hydrogen bonding interactions are essential to pre-organize substrates and to stabilize various intermediates and transition states and thus enhancing the overall catalytic reaction. These findings are not only applicable to this class of catalysts, but could be important for many other esterification catalysts.
First author: Bobo, MV, A Series of Green Light Absorbing Organic Photosensitizers Capable of Oxidative Quenching Photocatalysis,
CHEMPHOTOCHEM, 5, 51, (2021)
Abstract: In order to design a series of photoredox compounds with a broad range of reactivity, eosin Y, a xanthene derivative, was chosen as a precursor to synthesize a new series of organic photocatalysts. The synthesis and characterization of these four new organic photocatalysts was undertaken. Redox potentials of this series of photocatalysts varied by 110 mV, which shows that these catalysts can be tuned for specific reactions. The measured fluorescence quantum yields ranged from 0.33 to 0.65 which outperform most transition metal photocatalysts. The excited state lifetimes (ns) of the new photocatalysts are comparable to those of the parent complex, but the lambda(max) value for absorption was red-shifted into the green light region of the solar spectrum. Despite the absorbance shift to lower energy wavelengths, the new photocatalysts were more potent reductants compared to the parent complex and were able to undergo oxidative quenching and promote the photocatalytic enol arylation reaction.
First author: Patel, N, DivalentN(I)Compounds: Identifying new Carbocyclic Carbenes to Design Nitreones using Quantum Chemical Methods,
JOURNAL OF COMPUTATIONAL CHEMISTRY, 41, 2624, (2020)
Abstract: Nitreones are compounds with oxidation state 1 at the nitrogen, these compounds carry formal positive charge as well as two lone pairs of electrons at nitrogen center. These compounds are also known as divalent N(I)compounds and can be represented with the general formula L -> N+ <- L, where L is an electron donating ligand. In the recent past, several divalent N(I)compounds have been reported with L =N-heterocyclic carbene (NHC), remoteN-heterocyclic carbene (rNHC), carbocyclic carbene (CCC) and diaminocarbene. Recently, our group reported that a novel six-membered CCC (cyclohexa-2,5-diene-4-[diaminomethynyl]-1-ylidene) can stabilize N(+)center in nitreones. As an independent carbene, this species is very unstable. In this work, modulation of this CCC using (a) annulation, (b) heterocyclic ring modification, (c) substitutions adjacent to the carbenic carbon, (d) exocyclic double bond insertion and (e) ring contraction, has been reported. These modulations and quantum chemical analyses helped in the identification of five new six-membered CCCs which carry improved donation and stability properties. Further, these CCCs were employed in the design of new divalent N(I)compounds (nitreones) which carry coordination bonds between ligands and N(+)center. The molecular and electronic structure properties, and the donor -> acceptor coordination interactions present in the resultant low oxidation state divalent N(I)compounds have been explored.
First author: Zhao, JJ, Endohedrally Doped Cage Clusters,
CHEMICAL REVIEWS, 120, 9021, (2020)
Abstract: The discovery of carbon fullerene cages and their solids opened a new avenue to build materials from stable cage clusters as “artificial atoms” or “superatoms” instead of atoms. However, cage clusters of other elements are generally not stable. In 2001, ab initio calculations showed that endohedral doping of Zr and Ti atoms leads to highly stable Zr@Si-16 fullerene and Ti@ Si-16 Frank-Kasper polyhedral clusters with large HOMO-LUMO gaps. In 2002, Zr@Ge-16 was shown to form a Frank-Kasper polyhedron, suggesting the possibility of designing novel clusters by tuning endohedral and cage atoms. These results were subsequently confirmed from experiments. In the past nearly two decades, many experimental and theoretical studies have been carried out on different clusters, and many very stable cage clusters with possibly high abundance have been found by endohedral doping. Indeed in 2017, Ta@Si-16 and Ti@Si-16 cage clusters have been synthesized in bulk quantity of about 100 mg using a dry-chemistry method, giving rise to a new hope of developing cluster-based materials in macroscopic quantity besides the well-known C-60 fullerene solid. Also, wet-chemistry methods have been used to synthesize endohedrally doped clusters as well as ligated clusters and their solids, which auger well for the development of novel nanostructured materials using atomically precise clusters with unique properties. In this comprehensive review, we present results of many such developments in this fast-growing field including (i) endohedrally doped Al, Ga, and In clusters, (ii) small endohedral carbon fullerene cages with <= 28 carbon atoms, (iii) metal doped boron cages, (iv) endohedrally doped cages of group 14 elements (Si, Ge, Sn, and Pb), (v) coinage metal (Cu, Ag, Au) cages doped with a transition metal atom as well as their ligated clusters and crystals, (vi) endohedrally doped cages of compound semiconductors, and (vii) multilayer Matryoshka cages and core-shell structures. In a large number of cases, we have performed ab initio calculations to present updated results of the most stable atomic structures and fundamental electronic properties of the endohedrally doped cage clusters. We discuss electronic, magnetic, optical, and catalytic properties in order to shed light on their potential applications. The stability of the doped cage clusters has been correlated to the concept of filling the electronic shells for superatoms such as within a spherical potential model and also using various electron counting rules including Wade-Mingos rules, systems with 18 and 32 electrons, and the spherical aromaticity rule. We also discuss cluster-cluster interaction in cluster dimers and assemblies of some of the promising doped cage clusters in different dimensions. Finally, we give a perspective of this field with a bright future.
First author: He, TF, Molecular-Level Insight of Cu(I) Complexes with the 7,8-Bis(diphenylphosphino)-7,8-dicarba-nido-undecaborate Ligand as a Thermally Activated Delayed Fluorescence Emitter: Luminescent Mechanism and Design Strategy,
INORGANIC CHEMISTRY, 59, 12039, (2020)
Abstract: Investigation of the clear structure-property relationship and microscopic mechanism of thermally activated delayed fluorescence (TADF) emitters with high emission quantum yield is a direction worthy of continuous efforts. The instructive theoretical principle of TADF material design is critical and challenging. Here, we carried out theoretical calculation on two experimental Cu(I) complexes with the same 7,8-bis(diphenylphosphino)-7,8-dicarba-nido-undecaborate (dppnc) but different N<^>N ligands [dmbpy = 6,6′-dimethyl-2,2′-bipyridine (1) or dmp = 2,9-dimethyl-1,10-phenanthroline (2)] to briefly elaborate the structure-TADF performance relationship and luminescence mechanism. It was found that enhanced rigidity by the fused benzene ring between two pyridyl units in complex 2 leads to (i) higher allowedness of S-1 -> S-0, (ii) more effective reverse intersystem crossing (RISC), and (iii) better relative stability of the T-1 state, which could be responsible for its excellent TADF behavior. Thus, a strategy of extending pi conjugation in the N<^>N ligand could be deduced to further enhance the quantum yield. We validated it and have succeeded in designing analogue complex 4 by extending pi conjugation with an electron-withdrawing pyrazinyl. Benefiting from the smaller energy gap (Delta E-ST) and plunged reorganization energy between the S-1 and T-1 states, the rate of RISC in complex 4 (1.05 x 10(8) s(-1)) increased 2 orders of magnitude relative to that of 2 (5.80 x 10(6) s(-1)), showing more superiority of the TADF behavior through a better balance of RISC, fluorescence, and phosphorescence decay. Meanwhile, the thermally activated temperature of 4 is only 165 K, implying that there is a low-energy barrier. All of these indicate that the designed complex 4 may be a potential TADF candidate.
First author: Bottger, S, Solvent-Induced Bond-Bending Isomerism in Hexaphenyl Carbodiphosphorane: Decisive Dispersion Interactions in the Solid State,
INORGANIC CHEMISTRY, 59, 12054, (2020)
Abstract: Previous reports in the literature describe that the crystallization of hexaphenyl carbodiphosphorane (CDPPh) from a variety of solvents gives a “bent” geometry for the P-C-P moiety as the solid-state molecular structure. However, a linear structure is observed when CDPPh is crystallized from benzene. Here, we report detailed spectroscopic and theoretical studies on the linear and bent structures. X-ray powder diffraction examinations show a phase transition of linear CDPPh upon the loss of co-crystallized benzene molecules, which is accompanied by the bending of the P-C-P unit. Studies on the linear and bent structures (i.e., X-ray powder diffraction, solid-state NMR, UV-vis spectroscopy, and IR spectroscopy) show significant differences in their properties. Investigations of the solid-state structures with density functional theory-based methods (PBE-D3) point toward subtle dispersion effects being responsible for this solvent-induced bond-bending isomerism in CDPPh.
First author: Elleuchi, S, Computational Studies on the Binding Preferences of Molybdenum(II) Phenanthroline Complexes with Duplex DNA. The Important Role of the Ancillary Ligands,
INORGANIC CHEMISTRY, 59, 12711, (2020)
Abstract: The interaction of two isomers, equatorial (Eq) and axial (Ax), of the [Mo(eta(3)-C3H5)Br(CO)(2)(phen)] metal complex with DNA was studied by using large scaling density functional theory methods including dispersion for the whole system, represented as a d(AGACGTCT)(2) DNA octamer, to gain insight into its experimentally found cytotoxicity. Three different modes of interaction were considered: (1) minor groove (mg) binding, (2) intercalation through the major groove (MG), and (3) the apparently unexpected intercalation via the mg. Computed formation energies, energy decomposition analysis, solvation energies, and noncovalent interaction analysis explain the preference for Eq and Ax isomers of the complex for intercalation via the mg pi-pi interactions of the phenanthroline (phen) flat ligand that appear in the intercalation mode and do not exist for the mg binding mode suggest the preference of [Mo(eta(3)-C3H5)Br(CO())2(phen)] for intercalation. On the other hand, the role of the ancillary ligands is crucial for better interaction of the metal complex including phen than when the phen ligand alone is considered because of their additional interactions with base pairs (bps). The role of the ancillary ligands is enhanced when intercalation takes place through the mg because such ligands are able to interact not only with bps but also with the sugar and phosphate backbone, whereas for intercalation through the MG, the interaction of these ligands is only with bps. This feature explains the preference of [Mo(eta(3)-C3H5)Br(CO)(2)(phen)] for intercalation via the mg in crystal structures. Finally, the solvation penalty is more important for intercalation through the mg than via the MG, which suggests a subtle mechanism involving weak interactions with solvent molecules to explain the selectivity for intercalation in solution to answer the MG versus mg question.
First author: De Santis, M, Environmental Effects with Frozen-Density Embedding in Real-Time Time-Dependent Density Functional Theory Using Localized Basis Functions,
JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 16, 5695, (2020)
Abstract: Frozen-density embedding (FDE) represents a versatile embedding scheme to describe the environmental effect on electron dynamics in molecular systems. The extension of the general theory of FDE to the real-time time-dependent Kohn-Sham method has previously been presented and implemented in plane waves and periodic boundary conditions [Pavanello, M.; et al. J. Chem. Phys. 2015, 142, 154116]. In the current paper, we extend our recent formulation of the real-time time-dependent Kohn-Sham method based on localized basis set functions and developed within the Psi4NumPy framework to the FDE scheme. The latter has been implemented in its “uncoupled” flavor (in which the time evolution is only carried out for the active subsystem, while the environment subsystems remain at their ground state), using and adapting the FDE implementation already available in the PyEmbed module of the scripting framework PyADF. The implementation was facilitated by the fact that both Psi4NumPy and PyADF, being native Python API, provided an ideal framework of development using the Python advantages in terms of code readability and reusability. We employed this new implementation to investigate the stability of the time-propagation procedure, which is based on an efficient predictor/corrector second-order midpoint Magnus propagator employing an exact diagonalization, in combination with the FDE scheme. We demonstrate that the inclusion of the FDE potential does not introduce any numerical instability in time propagation of the density matrix of the active subsystem, and in the limit of the weak external field, the numerical results for low-lying transition energies are consistent with those obtained using the reference FDE calculations based on the linear-response TDDFT. The method is found to give stable numerical results also in the presence of a strong external field inducing nonlinear effects. Preliminary results are reported for high harmonic generation (HHG) of a water molecule embedded in a small water cluster. The effect of the embedding potential is evident in the HHG spectrum reducing the number of the well-resolved high harmonics at high energy with respect to the free water. This is consistent with a shift toward lower ionization energy passing from an isolated water molecule to a small water cluster. The computational burden for the propagation step increases approximately linearly with the size of the surrounding frozen environment. Furthermore, we have also shown that the updating frequency of the embedding potential may be significantly reduced, much less than one per time step, without jeopardizing the accuracy of the transition energies.
First author: Adcock, AK, Synthesis and photoluminescence of three bismuth(iii)-organic compounds bearing heterocyclic N-donor ligands,
DALTON TRANSACTIONS, 49, 11756, (2020)
Abstract: Three bismuth(iii)-organic compounds, [Bi4Cl8(PDC)(2)(phen)(4)]center dot 2MeCN (1), [BiCl3(phen)(2)] (2), and [Bi2Cl6(terpy)(2)] (3), were prepared from solvothermal reactions of bismuth chloride, 2,6-pyridinedicarboxylic acid (H2PDC), and 1,10-phenanthroline (phen) or 2,2 ‘;6 ‘,2 ”-terpyridine (terpy). The structures were determined through single crystal X-ray diffraction and the compounds were further characterizedviapowder X-ray diffraction, Raman and infrared spectroscopy, and thermogravimetric analysis. The photoluminescence properties of the solid-state materials were assessed using steady state and time-dependent techniques to obtain excitation and emission profiles as well as lifetimes. The compounds exhibit visible emission ranging from the yellow-green to orange region upon UV excitation. Theoretical quantum mechanical calculations aimed at elucidating the observed emissive behavior show that the transitions can be assigned as predominantly ligand-to-ligand and ligand-to-metal charge transfer transitions. The solid-state structural chemistry, spectroscopic properties, and luminescence behavior of the bismuth compounds are presented herein.
First author: Ilias, M, Carbonyl compounds of Rh, Ir, and Mt: electronic structure, bonding and volatility,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 18681, (2020)
Abstract: With the aim to render assistance to future experiments on the production and investigation of chemical properties of carbonyl compounds of element 109, Mt, calculations of the molecular properties of M(CO)(4)and MH(CO)(4), where M = Rh, Ir, and Mt, and of the products of their decomposition, M(CO)(3)and MH(CO)(3), were performed using relativistic Density Functional Theory and Coupled-Cluster methods implemented in the ADF, ReSpect and DIRAC software suites. According to the results, MH(CO)(4)should be formed at experimental conditions from the M atom with a mixture of CO and He gases. The calculated first M-CO bond dissociation energies (FBDE) of Mt(CO)(4)and MtH(CO)(4)turned out to be significantly weaker than those of the corresponding Ir homologs. The reason for that is the relativistic destabilization and expansion of the 6d AOs, responsible for both the weaker sigma(CO) -> d(M) forth and d(M) -> pi(CO) back electron density donation in the Mt compounds. The relativistic FBDEs of MH(CO)(4)have, therefore, a ?-shape behavior in the row Rh-Ir-Mt, while the non-relativistic values increase towards Mt. Using the results of the calculations and a molecule-slab interaction model, the adsorption enthalpies, Delta H-ads, serving as a measure of volatilty, of the group-9 carbonyl hydrides on surfaces of quartz and Teflon were estimated. Accordingly, MtH(CO)(4)should be almost as volatile as RhH(CO)(4)and IrH(CO)(4); however, its interaction with the surfaces should be somewhat weaker than that of IrH(CO)(4). It will, therefore, be difficult to distinguish between group-9 MH(CO)(4)species by measuring their Delta H(ads)on surfaces of Teflon and quartz with an experimental uncetainty of +/- 3 kJ mol(-1). The trends in the properties of group-9 carbonyl hydrides should be similar to those of group-6, 7 and 8 carbonyl compounds including those of Sg, Bh and Hs, respectively.
First author: Alessandri, R, Resolving Donor-Acceptor Interfaces and Charge Carrier Energy Levels of Organic Semiconductors with Polar Side Chains,
ADVANCED FUNCTIONAL MATERIALS, 30, 18681, (2020)
Abstract: Organic semiconductors consisting of molecules bearing polar side chains have been proposed as potential candidates to overcome the limitations of organic photovoltaics owing to their enhanced dielectric constant. However, introducing such polar molecules in photovoltaic devices has not yet resulted in higher efficiencies. A microscopic understanding of the impact of polar side chains on electronic and structural properties of organic semiconductors is paramount to rationalize their effect. Here, the impact of such side chains on bulk heterojunction overall morphology, molecular configurations at donor-acceptor (DA) interfaces, and charge carrier energy levels is investigated. The multiscale modeling approach used allows to resolve DA interfaces with atomistic resolution while taking into account the large-scale self-organization process which takes place during the processing of an organic thin film. The polar fullerene-based blends are compared to the well-studied reference system, poly(3-hexyl-thiophene) (P3HT):phenyl-C-61-butyric acid methyl ester (PCBM). Introduction of polar side chains on a similar molecular scaffold does not affect molecular orientations at the DA interfaces; such orientations are, however, found to be affected by processing conditions and polymer molecular weight. Polar side chains, instead, are found to impact considerably the charge carrier energy levels of the organic blend, causing electrostatic-induced broadening of these levels.
First author: Madabeni, A, Chalcogen-mercury bond formation and disruption in model Rabenstein’s reactions: A computational analysis,
JOURNAL OF COMPUTATIONAL CHEMISTRY, 41, 2045, (2020)
Abstract: Methylmercury is a highly toxic compound and human exposure is mainly related to consumption of polluted fish and seafood. The inactivation of thiol-based enzymes, promoted by the strong affinity binding of electrophilic mercuric ions to thiol and selenol groups of proteins, is likely an important factor explaining its toxicity. A key role is played by the chemistry and reactivity of the mercury-chalcogens bond, particularly Hg-S and Hg-Se, which is the focus of this computational work (level of theory: (COSMO)-ZORA-BLYP-D3(BJ)/TZ2P). We analyze nine ligand-exchange model reactions (the so-called Rabenstein’s reactions) involving an entering ligand (methylchalcogenolate) and a substrate (methylchalcogenolatemethylmercury). Trends in reaction and activation energies are discussed and a change in mechanism is reported for all cases when going from gas phase to water, that is, from a single-well potential energy surface (PES) to a canonical S(N)2-like mechanism. The reasons accounting for the biochemically challenging and desired displacement of methylmercury from a seleno/thiol protein can be found already in these model reactions, as can be seen from the similarities of the ligand exchange reactions in solution in thermodynamics and kinetics.
First author: Jezuita, A, Substituent effects of nitro group in cyclic compounds,
STRUCTURAL CHEMISTRY, 32, 179, (2021)
Abstract: Numerous studies on nitro group properties are associated with its high electron-withdrawing ability, by means of both resonance and inductive effect. The substituent effect of the nitro group may be well described using either traditional substituent constants or characteristics based on quantum chemistry, i.e., cSAR, SESE, and pEDA/sEDA models. Interestingly, the cSAR descriptor allows to describe the electron-attracting properties of the nitro group regardless of the position and the type of system. Analysis of classical and reverse substituent effects of the nitro group in various systems indicates strongpi-electron interactions with electron-donating substituents due to the resonance effect. This significantly affects thepi-electron delocalization of the aromatic ring decreasing the aromatic character, evidenced clearly by HOMA values. Use of the pEDA/sEDA model allows to measure the population of electrons transferred from the ring to the nitro group.
First author: Miguel, A, Understanding the Molecular Structure of the Elastic and Thermoreversible AlCl3 : Urea/Polyethylene Oxide Gel Electrolyte,
CHEMSUSCHEM, 13, 5523, (2020)
Abstract: It is possible to prepare elastic and thermoreversible gel electrolytes with significant electroactivity by dissolving minimal weight fractions of ultra-high molecular weight polyethylene oxide (UHMW PEO) in an aluminum deep eutectic solvent (DES) electrolyte composed of AlCl(3)and urea at a molar ratio of 1.5 : 1 (AlCl3/urea). The experimental vibrational spectra (FTIR and Raman) provide valuable information on the structure and composition of the gel electrolyte. However, the complexity of this system requires computational simulations to help interpretation of the experimental results. This combined approach allows us to elucidate the speciation of the DES liquid electrolyte in the gel and how it interacts with the polymer chains to give rise to an elastic network that retains the electroactivity of the liquid electrolyte to a very great extent. The observed reactions occur between the ether in the polymer and both the amine groups in urea and the aluminum species. Thus, similar elastomeric gels may likely be prepared with other aluminum liquid electrolytes, making this procedure an effective way to produce families of gel aluminum electrolytes with tunable rheology and electroactivity.
First author: Lv, Y, Core Charge Density Dominated Size-Conversion from Au6P8 to Au8P8Cl2,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 12382, (2020)
Abstract: The stimulus-response of metal nanoclusters is crucial to their applications in catalysis and bio-clinics, etc. However, its mechanistic origin has not been well studied. Herein, the mechanism of the (AuPPh3Cl)-P-I-induced size-conversion from [Au-6(DPPP)(4)](2+)to [Au-8(DPPP)(4)Cl-2](2+)(DPPP is short for 1,3-bis(diphenylphosphino)propane) is theoretically investigated with density functional theory (DFT) calculations. The optimal size-growth pathway, and the key structural parameters were elucidated. The Au-P bond dissociation steps are key to the size-growth, the easiness of which was determined by the charge density of the metallic core of the cluster precursors (i.e., “core charge density”). This study sheds light on the inherent structure-reactivity relationships during the size-conversion, and will benefit the deep understanding on the kinetics of more complex systems.
First author: Sarwono, YP, Numerical variational solution of hydrogen molecule and ions using one-dimensional hydrogen as basis functions,
NEW JOURNAL OF PHYSICS, 22, 12382, (2020)
Abstract: The ground state solution of hydrogen molecule and ions are numerically obtained as an application of our scheme to solve many-electron multi-center potential Schrodinger equation by using one-dimensional hydrogen wavefunctions as basis functions. The all-electron sparse Hamiltonian matrix for the given system is generated with the standard order finite-difference method, then the electronic trial wavefunction to describe the ground state is constructed based on the molecular orbital treatment, and finally an effective and accurate iteration process is implemented to systematically improve the result. Many problems associated with the evaluation of the matrix elements of the Hamiltonian in more general basis and potential are circumvented. Compared with the standard results, the variationally obtained energy of H(2)(+)is within 0.1 mhartree accuracy, while that of H(2)and H(3)(+)include the electron correlation effect. The equilibrium bond length is highly consistent with the accurate results and the virial theorem is satisfied to an accuracy of -V/T= 2.0.
First author: Sarmah, A, Directly linked metalloporphyrins: a quest for bio-inspired materials,
MATERIALS ADVANCES, 1, 1895, (2020)
Abstract: The directly-linked iron-diporphyrin complexes are appealing candidates and fundamental precursors for an extended metalloporphyrin array that can potentially mimic the biological design of energy-harvesting materials. This encouraged us to appraise the layout for the modular fusion of two iron-porphyrin units. Herein, DFT-based calculations suggest that the electronic environment of diporphyrin systems can be tuned according to the topological attachment between the porphyrin units. Subsequently, a gradual increase in the electronic interaction between the constituent porphyrin units triggers a decrease in the HOMO-LUMO gap. This is essential to achieve higher electric conductivity. The spin-polarized electronic transmission is another interesting aspect of these iron-diporphyrin systems and is promising for spintronic applications. The successive theoretical interpretation of the existence of two-dimensional (2D) metalloporphyrin arrays could be the route to design a graphene analog of the covalent metal-organic framework.
First author: Yao, CH, Atomically-precise dopant-controlled single cluster catalysis for electrochemical nitrogen reduction,
NATURE COMMUNICATIONS, 11, 1895, (2020)
Abstract: The ability to precisely engineer the doping of sub-nanometer bimetallic clusters offers exciting opportunities for tailoring their catalytic performance with atomic accuracy. However, the fabrication of singly dispersed bimetallic cluster catalysts with atomic-level control of dopants has been a long-standing challenge. Herein, we report a strategy for the controllable synthesis of a precisely doped single cluster catalyst consisting of partially ligand-enveloped Au4Pt2 clusters supported on defective graphene. This creates a bimetal single cluster catalyst (Au4Pt2/G) with exceptional activity for electrochemical nitrogen (N-2) reduction. Our mechanistic study reveals that each N-2 molecule is activated in the confined region between cluster and graphene. The heteroatom dopant plays an indispensable role in the activation of N-2 via an enhanced back donation of electrons to the N-2 LUMO. Moreover, besides the heteroatom Pt, the catalytic performance of single cluster catalyst can be further tuned by using Pd in place of Pt as the dopant. The fabrication of singly dispersed metal cluster catalysts with atomic-level control of dopants is a long-standing challenge. Here, the authors report a strategy for the synthesis of a precisely doped single cluster catalyst which shows exceptional activity for electrochemical dinitrogen reduction.
First author: Zadok, I, Unexpected hydroxide ion structure and properties at low hydration,
JOURNAL OF MOLECULAR LIQUIDS, 313, 1895, (2020)
Abstract: Understanding the behavior of hydroxide ions in aqueous and non-aqueous media is fundamental to many chemical, biological, and electrochemical processes. Research has primarily focused on a single fully solvated hydroxide ion, either as an isolated cluster or in bulk. This work presents the first computational study to consider hydroxide under low hydration levels in detail, where the anion may not be fully solvated. Under such conditions, we find that the anions are predominantly present as unique water-bridged hydroxide pair complexes, distinct from previously reported structures under fully hydrated conditions. Although similar hydroxide pair structures were previously reported, we analyze these structures for the first time in the disordered liquid state where they are found to be unusually stable in the presence of bulky quatemary ammonium cations. Our findings help explain the unusual diffusion behavior as well as the higher reactivity of hydroxide anions observed under low hydration conditions.
First author: Zeng, L, Molecular dynamics simulation and DFT calculations on the oil -water mixture separation by single -walled carbon nanotubes,
APPLIED SURFACE SCIENCE, 523, 1895, (2020)
Abstract: Understanding the behavior of hydroxide ions in aqueous and non-aqueous media is fundamental to many chemical, biological, and electrochemical processes. Research has primarily focused on a single fully solvated hydroxide ion, either as an isolated cluster or in bulk. This work presents the first computational study to consider hydroxide under low hydration levels in detail, where the anion may not be fully solvated. Under such conditions, we find that the anions are predominantly present as unique water-bridged hydroxide pair complexes, distinct from previously reported structures under fully hydrated conditions. Although similar hydroxide pair structures were previously reported, we analyze these structures for the first time in the disordered liquid state where they are found to be unusually stable in the presence of bulky quatemary ammonium cations. Our findings help explain the unusual diffusion behavior as well as the higher reactivity of hydroxide anions observed under low hydration conditions.
First author: Huhn, WP, GPU acceleration of all-electron electronic structure theory using localized numeric atom-centered basis functions,
COMPUTER PHYSICS COMMUNICATIONS, 254, 1895, (2020)
Abstract: We present an implementation of all-electron density-functional theory for massively parallel GPU-based platforms, using localized atom-centered basis functions and real-space integration grids. Special attention is paid to domain decomposition of the problem on non-uniform grids, which enables compute- and memory-parallel execution across thousands of nodes for real-space operations, e.g. the update of the electron density, the integration of the real-space Hamiltonian matrix, and calculation of Pulay forces. To assess the performance of our GPU implementation, we performed benchmarks on three different architectures using a 103-material test set. We find that operations which rely on dense serial linear algebra show dramatic speedups from GPU acceleration: in particular, SCF iterations including force and stress calculations exhibit speedups ranging from 4.5 to 6.6. For the architectures and problem types investigated here, this translates to an expected overall speedup between 3-4 for the entire calculation (including non-GPU accelerated parts), for problems featuring several tens to hundreds of atoms. Additional calculations for a 375-atom Bi2Se3 bilayer show that the present GPU strategy scales for large-scale distributed-parallel simulations.
First author: Tian, YX, Probing the effect of substituent groups in Ir(III) bis-tridentate complexes during deep -blue phosphorescent illuminating,
ORGANIC ELECTRONICS, 84, 1895, (2020)
Abstract: We present an implementation of all-electron density-functional theory for massively parallel GPU-based platforms, using localized atom-centered basis functions and real-space integration grids. Special attention is paid to domain decomposition of the problem on non-uniform grids, which enables compute- and memory-parallel execution across thousands of nodes for real-space operations, e.g. the update of the electron density, the integration of the real-space Hamiltonian matrix, and calculation of Pulay forces. To assess the performance of our GPU implementation, we performed benchmarks on three different architectures using a 103-material test set. We find that operations which rely on dense serial linear algebra show dramatic speedups from GPU acceleration: in particular, SCF iterations including force and stress calculations exhibit speedups ranging from 4.5 to 6.6. For the architectures and problem types investigated here, this translates to an expected overall speedup between 3-4 for the entire calculation (including non-GPU accelerated parts), for problems featuring several tens to hundreds of atoms. Additional calculations for a 375-atom Bi2Se3 bilayer show that the present GPU strategy scales for large-scale distributed-parallel simulations.
First author: Xiao, M, Effect of micro-H2O and micro-O(2)on the decomposition characteristics of insulating medium C3F7CN gas using molecular dynamics and transition state method,
JOURNAL OF MOLECULAR MODELING, 26, 1895, (2020)
Abstract: In recent years, heptafluoroisobutyronitrile (C3F7CN) has been proved to be a potential eco-friendly insulating medium to replace sulfur hexafluoride (SF6, the strong greenhouse gas). In this paper, the effect of micro-H2O and micro-O(2)on the decomposition of C3F7CN was investigated based on the reactive force field molecular dynamics (ReaxFF-MD) and transition state theory (TST). It was found that H2O obviously promoted the decomposition of C3F7CN, and new products HF, COF2, CO, and NO were generated. The influence of O(2)on the C3F7CN dissociation was weaker than that of H2O, and O(2)slightly promoted the C3F7CN decomposition only when 50 O(2)molecules were added. The simultaneous presence of H2O and O(2)promoted the decomposition of C3F7CN, the promotion of which was closed to H2O existing alone. The calculation results showed that the energy barriers of the two reactions forming COF(2)were 31.38 kcal/mol and 23.85 kcal/mol, respectively, which indicated that the reactions were difficult to proceed spontaneously. The energy barrier of F + H2O -> HF + OH was relatively lower than that of COF2. These values corresponded well to the ReaxFF simulation results. This study provides theoretical support for the effect of H2O and O(2)on the decomposition of C3F7CN.
First author: Mahmoudi, G, Lead(II) coordination polymers driven by pyridine-hydrazine donors: from anion-guided self-assembly to structural features,
DALTON TRANSACTIONS, 49, 11238, (2020)
Abstract: In this work, we report extensive experimental and theoretical investigations on a new series of Pb(II)coordination polymers exhibiting extended supramolecular architectures, namely [Pb-2(L-I)(NCS)(4)](n)(1), [Pb(HLII)I-2](n)(2), [Pb(L-III)I](n)(3) and [Pb(HLIV)(NO3)(2)](n)center dot nMeOH (4), which were self-assembled from different Pb(II)salts and various pyridine-hydrazine based linkers, namely 1,2-bis(pyridin-3-ylmethylene)hydrazine (L-I), (pyridin-4-ylmethylene)isonicotinohydrazide (HLII), 1-(pyridin-2-yl)ethylidenenicotinohydrazide (HLIII) and phenyl(pyridin-2-yl)methylenenicotinohydrazide (HLIV), respectively. It is recognized that the origin of self-assembling is fundamentally rooted in a dual donor (6s(2)/6p(0) hybridized lone electron pair) and electrophilic behaviour of Pb-II. This allows production of extended topologies from a 1D polymeric chain in 4 through a 2D layer in 2 to the 3D frameworks in 1 and 3, predominantly due to the cooperative action of both covalent and non-covalent tetrel interactions of the overall type Pb-X (X = O, N, S, I). Counterintuitively, the latter, seemingly weak interactions, have appeared to be even stronger than the typical covalent bonds due to the presence of a bunch of supportive London dispersion dominated contacts: pi center dot center dot center dot pi, Lp center dot center dot center dot pi, C-H center dot center dot center dot O, C-H center dot center dot center dot I, C-H center dot center dot center dot H-C as well as more typical mainly electrostatically driven N-H center dot center dot center dot O or N/O-H center dot center dot center dot O hydrogen bonds. It is revealed that the constituting generally strong tetrel type Pb-X (X = O, N, S, I) bonds, though dominated by a classic Coulomb term, are therefore characterized by a very important London dispersion constituent, extremely strong relativistic effects and the two way dative-covalent Pb <-> X electron charge delocalization contribution as revealed by the Extended Transition State Natural Orbital for Chemical Valence (ETS-NOCV) charge and energy decomposition scheme. It unravels that the pyridine-hydrazine linkers are also excellent London dispersion donors, and that together with the donor-acceptor properties of the heavy (relativistic) Pb-II atoms and nucleophilic counterions lead to extended self-assembling of 1-4.
First author: Zhang, BH, GridMol2.0: Implementation and application of linear-scale quantum mechanics methods and molecular visualization,
INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 120, 11238, (2020)
Abstract: GridMol is a “one-stop” platform for molecular structure building, scientific computing, and molecular visualization aided by a high-performance computing environment. GridMol version 2.0 introduces two unique features: the first is fragment-based linear-scaling quantum chemistry methods, such as molecular fractionation with conjugate caps and fragment molecular orbital methods; the second is that GridMol enables users to visualize molecular geometries along a geometry optimization and an intrinsic reaction coordinate calculation. Compared with version 1.0, fragment-based linear-scaling quantum chemistry methods implemented in GridMol version 2.0 can be used as a useful tool for performing quantum calculations for large molecular systems to explore the mechanisms involved in protein-ligand or targeted drug interactions.
First author: Loan, HTP, In-Depth Investigation of a Donor-Acceptor Interaction on the Heavy-Group-14@Group-13-Diyls in Transition-Metal Tetrylone Complexes: Structure, Bonding, and Property,
ACS OMEGA, 5, 21271, (2020)
Abstract: Stabilization for tetrylone complexes, which carry ylidone(0) ligands [(CO)(5)W-X (YCp*)(2)] (X = Ge, Sn, Pb; Y = B-Tl), has become an active theoretical research because of their promising application. Structure, bonding, and quantum properties of the transition-metal donor-acceptor complexes were theoretically investigated at the level of theory BP86 with several types of basis sets including SVP, TZVPP, and TZ2P+. The optimized structures reveal that all ligands X (YCp*)(2) are strongly bonded in tilted modes to the metal fragment W(CO)(5), and Cp* rings are mainly eta(5)-bonded to atom X. DFT-based bonding analysis results in an implication that the stability of W-X bond strength primarily stems from the donation (CO)(5)W <- X(YCp*)(2) formed by both sigma- and pi-bondings and the electrostatic interaction Delta E-elstat. The W-X bond possesses a considerable polarizability toward atom X, and analysis on its hybridization is either sp(2)-characteristic or mainly p-characteristic. EDA-NOCV-based results further imply that the ligands XY perform as significant pi-donors but minor pi-donors. The visual simulations of NOCV pairs and the deformation densities assemble a comprehensive summary on different components of the chemical bond via sigma- and pi-types in the complexes. This work contributes to the literature as an in-depth overview on predicted molecular structures and quantum parameters of the complexes [(CO)(5)W-X(YCp*)(2)] (X = Ge, Sn, Pb; Y = B-Tl), conducive to either further theoretical reference or extending experimental research.
First author: Gimeno, L, Non-Symmetrical Sterically Challenged Phenanthroline Ligands and Their Homoleptic Copper(I) Complexes with Improved Excited-State Properties,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 11887, (2020)
Abstract: A strategy is presented to improve the excited state reactivity of homoleptic copper-bis(diimine) complexes CuL(2)(+)by increasing the steric bulk around Cu(I)whereas preserving their stability. Substituting the phenanthroline at the 2-position by a phenyl group allows the implementation of stabilizing intramolecular pi stacking within the copper complex, whereas tethering a branched alkyl chain at the 9-position provides enough steric bulk to rise the excited state energyE(00). Two novel complexes are studied and compared to symmetrical models. The impact of breaking the symmetry of phenanthroline ligands on the photophysical properties of the complexes is analyzed and rationalized thanks to a combined theoretical and experimental study. The importance of fine-tuning the steric bulk of the N-N chelate in order to stabilize the coordination sphere is demonstrated. Importantly, the excited state reactivity of the newly developed complexes is improved as demonstrated in the frame of a reductive quenching step, evidencing the relevance of our strategy.
First author: Boda, A, Density functional theoretical tailoring of electronic effect through various substituents on calix[4]arene-crown-6 for efficient Cs(+)ion encapsulation and extraction,
INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 121, 11887, (2021)
Abstract: The structure, energetic, and quantum chemical descriptors of Cs(+)complexes of calix[4]arene-crown-6 (C4C6) and substituted C4C6, that is, 1,3 alternate-diethoxy C4C6, are reported here based on the analysis of results obtained using density functional theory (DFT). Substitution of benzo group in both C4C6 and 1,3 alternate-diethoxy C4C6 resulted in a reduction of binding energy (BE). Further substitution of the benzo group with methyl, methoxy, and amino groups leads to an increase in BE, and nitro substitution leads to decrease in BE for C4C6, whereas in the case of 1,3 alternate-diethoxy calix[4]arenebenzocrown-6, methoxy substitution leads to the highest BE compared to other complexes. The calculated Gibbs free energy, Delta G(gas)also followed the same order as BE in the case of 1,3 alternate-diethoxy C4C6 and their substituted ligands. Furthermore, the Delta Gof complexation was computed using a thermodynamic cycle with conductor-like screening model in different solvents: toluene, chloroform, octanol, and nitrobenzene. The values of Delta G(ext)are found to be increased with an increase in the dielectric constant of the solvent and were found to be highest in the nitrobenzene. The atoms in molecule analysis reveals partial ionic character in the Cs-O bond. Among all the studied complexes, 1,3 alternate-diethoxy calix[4]arene 3 ‘-methoxy benzo crown-6 displays highest Delta G(ext)in nitrobenzene. The calculated value of increment increment G(ext)( increment increment G= increment G(Cs+)- increment G(Na+)) is found to be -41.82 kcal/mol with 1,3 alternate-diethoxy calix[4]arene 3 ‘-methoxy benzocrown-6, which is higher than that obtained with calix [4] bis-crown-6 (-5.24 kcal/mol). The newly designed ligand might be suitable for the selective extraction of Cs(+)over Na(+)in the reprocessing of nuclear waste and thus invites experimentalists to test this DFT finding in the laboratory.
First author: Li, Y, Enhancement of charge transfer in thermally-expanded and strain-stabilized TIPS-pentacene thin films,
PHYSICAL REVIEW RESEARCH, 2, 11887, (2020)
Abstract: We present an extensive study of the optical and electronic properties of TIPS-pentacene thin films utilizing in situ x-ray diffraction, polarized optical spectroscopy, and ab initio density functional theory. The influence of molecular packing on the properties are reported for thin films deposited in the temperature range from 25 degrees C to 140 degrees C and for films that are strain stabilized at their as-deposited lattice spacings after cooling to room temperature. Anisotropic thermal expansion causes relative displacement of neighboring molecules while maintaining a nearly constant stacking distance. This leads to a large blueshift in the absorption spectrum as the temperature increases. The blueshift largely reverses a redshift at room temperature compared to the solution absorption spectrum. A reduction in the ratio of the first two vibronic peaks relative to the solution spectrum is also observed. This combination of electronic and vibronic effects is a signature of charge transfer excitonic coupling with a positive coupling constant J(CT), which depends sensitively on the alignment of the nodes of the frontier molecular orbitals with those on neighboring molecules. These effects are also correlated with the sign and magnitude of electron and hole charge transfer integrals t(e) and t(h) calculated from density functional theory that provide additional evidence for charge transfer mediated coupling, as well as insight into the origin of an experimentally observed enhancement of the field-effect transistor mobility in strain-stabilized thin films. The results suggest approaches to improve carrier mobility in strained thin films and for optical monitoring of electronic changes.
First author: Sim, HS, Enhanced Fuel Decomposition in the Presence of Colloidal Functionalized Graphene Sheet-Supported Platinum Nanoparticles,
ACS APPLIED ENERGY MATERIALS, 3, 7637, (2020)
Abstract: Experiments and simulations were used to demonstrate that decorating functionalized graphene sheets (FGSs) with platinum nanoparticles (Pt@FGS) stabilized these particles. Addition of these particles to liquid hydrocarbon fuels was observed to significantly affect decomposition under supercritical conditions at a pressure of 4.75 MPa and temperatures from 753 to 803 K. The suspension of only 50 ppmw Pt@FGS in the fuel (equivalent to adding 10 ppmw Pt) enhanced fuel conversion rates (by up to 24%) with a major effect on specific product yields. The production of low-molecular-weight species increased in the pyrolysis products (with the hydrogen yield increasing by a factor of 12.5). ReaxFF molecular dynamics (MD) simulations supported a mechanism in which synergy between Pt and FGS catalyzed dehydrogenation during n-C12H26 pyrolysis. The highest conversion rates and greatest yields of hydrogen and low-molecular-weight species were observed for fuels containing Pt@FGS particles rather than those containing either FGSs or Pt-clusters alone. Analysis of the platinum decorated FGSs post reaction indicated no deterioration of the composite particles.
First author: Koenis, MAJ, Vibrational circular dichroism spectroscopy for probing the expression of chirality in mechanically planar chiral rotaxanes,
CHEMICAL SCIENCE, 11, 8469, (2020)
Abstract: Mechanically interlocked molecules can exhibit molecular chirality that arises due to the mechanical bond rather than covalent stereogenic units. Developing applications of such systems is made challenging by the absence of techniques for assigning the absolute configuration of products and methods to probe how the mechanical stereogenic unit influences the spatial arrangements of the functional groups in solution. Here we demonstrate for the first time that Vibrational Circular Dichroism (VCD) can be used to not only discriminate between mechanical stereoisomers but also provide detailed information on their (co)conformations. The latter is particularly important as these molecules are now under investigation in catalysis and sensing, both of which rely on the solution phase shape of the interlocked structure. Detailed analysis of the VCD spectra shows that, although many of the signals arise from coupled oscillators isolated in the covalent sub-components, intercomponent coupling between the macrocycle and axle gives rise to several VCD bands.
First author: Jana, G, Effect of substitution on the bonding in He dimer confined within dodecahedrane: A computational study,
JOURNAL OF COMPUTATIONAL CHEMISTRY, 41, 2398, (2020)
Abstract: The effect of substitution in the dodecahedrane (C20H20) cage on bonding in the confined He dimer is analyzed. The He-He distances inside the halogenated dodecahedrane C20X20(X = F-Br) cages are found to be less than half of that in the free He dimer. Comparing the equilibrium structure of He-2@C(20)H(20)with He-2@C(20)X(20)at omega B97XD/def2-TZVPP level, it is found that the He-He distances are relatively larger in the latter cases indicating the influence of halogen groups on the interaction between the cage and the trapped He pair. The viability of the He-2@C(20)X(20)complexes is reflected in the presence of a very high activation energy barrier against the thermochemically feasible dissociation process producing free He(2)and C20X20. Quantum theory of atoms in molecules (QTAIM) approach reveals a partial covalent interaction between He pair.
First author: Jimenez-Cruz, JC, Preparation of aromatic gamma-hydroxyketones by means of Heck coupling of aryl halides and 2,3-dihydrofuran, catalyzed by a palladium(ii) glycine complex under microwave irradiation,
NEW JOURNAL OF CHEMISTRY, 44, 13382, (2020)
Abstract: A series of aromatic gamma-hydroxyketones were prepared by means of Heck coupling reaction of aryl halides and 2,3-dihydrofuran, catalyzed by PdCl2 center dot Gly(2)and under microwave irradiation. This synthetic transformation involves the formation of an aryl-dihydrofuranoic intermediate, followed by an unusual opening of the heterocycle promoted by a water molecule and the formation of the ketone carbonyl function through keto-enol tautomerism.
First author: Altaf, Y, Main-group metal cyclophane complexes with high coordination numbers,
RSC ADVANCES, 10, 30796, (2020)
Abstract: Density functional theory calculations using the PBE0-D3BJ hybrid functional have been employed to investigate the complexation of main-group metal-cations with [2.2.2]paracyclophane and deltaphane. Geometry optimization under symmetry constraints was performed to observe the mode of coordination that a metal-cation adopts when it resides inside the cyclophane cavity. Thermodynamic properties were investigated to note the trends of stability along a group of metals. To further investigate the bonding properties, Morokuma-Ziegler energy decomposition analysis, natural bond orbital analysis and Bader’s analysis were employed. It was observed that most of the main-group metal complexes with cyclophanes prefer an eta(6)eta(6)eta(6)coordination mode where the metal-cation sits in the centre of the cyclophane cavity. There is an increased thermodynamic stability in [2.2.2]paracyclophane complexes compared to their deltaphane analogues while the reverse is true regarding the strength of coordination based on interaction energy.
First author: Liu, Y, Theoretical Prediction of the Potential Applications of Phenanthroline Derivatives in Separation of Transplutonium Elements,
INORGANIC CHEMISTRY, 59, 11469, (2020)
Abstract: Recovery of transplutonium elements from adjacent actinides is extremely complicated in spent fuel reprocessing. Uncovering the electronic structures of transplutonium compounds is essential for designing robust ligands for in-group separation of transplutonium actinides. Here, we demonstrate the in-group transplutonium actinides separation ability of the recent developed phenanthroline ligand Et-Tol-DAPhen (N-2,N-9-diethyl-N-2,N-9-di-p-tolyl-1,10-phenanthroline-2,9-dicarboxamide, L-a) and its derivatives (5-bromo-(N-2,N-9-diethyl-N-2,N-9-di-p-tolyl-1,10-phenanthroline-2,9-dicarboxamide, L-b), and 5-(4-(lambda(1)-oxidaneyl)phenyl)-(N-2,N-9-diethyl-N-2,N-9-di-p-tolyl-1,10-phenanthroline-2,9- dicarboxamide, L-c) through quasi-relativistic density functional theory (DFT). Both electrostatic potential and molecular orbital analyses of the ligands indicate that the electron-donating group substituted ligand L-c is a better electron donor to actinides than L-a and L-b. The possible extracted complexes AnL(NO3)(3) and [AnL(2)(NO3)](2+) (L = L-a, L-b, L-c; An = Am, Cm, Bk, Cf) possess similar structures. Bonding nature analysis validates that the covalent interactions of the metal-ligand bonds are enhanced across actinide series from Am to Cf, which stem from the energy degeneracy of the 5f orbitals of actinides and the 2p orbitals of the ligand coordinating atoms. The L-c ligand displays slightly stronger covalent bonding compared to the other two ligands. Simultaneously, thermodynamic analysis confirms the stronger metal-ligand bonding of the Cf3+ complexes and the higher stability of the extraction species with L-c. Consequently, the covalency between the DAPhen derivatives and transplutonium actinides seems to be positively correlated with the extraction ability of these ligands. Nevertheless, these ligands exhibit diverse separation abilities to in-group actinide recovery. Therefore, the enhancement of covalency does not necessarily lead to the improvement of separation ability due to different extraction capabilities. We hope that these results will provide some inspiration for designing novel ligands for in-group transplutonium separation.
First author: Amati, M, Origin of the Enhanced Binding Capability toward Axial Nitrogen Bases of Ni(II) Porphyrins Bearing Electron-Withdrawing Substituents: An Electronic Structure and Bond Energy Analysis,
INORGANIC CHEMISTRY, 59, 11528, (2020)
Abstract: Axial coordination to metalloporphyrins is important in many biological and catalytic processes. Experiments found the axial coordination of nitrogenous bases to nickel(II) porphyrins to be strongly favored by electron-withdrawing substituents such as perfluorophenyls at the meso carbon positions. Careful analysis of the electronic structure reveals that the natural explanation in terms of density change of the nickel(II) porphyrin system (in particular the metal), does not apply. Electron density changes, by the assumed inductive or polarizing effects on the metal or on the porphyrin ring system, are slight. The effect is caused by a remarkable through-space electric field effect on the metalloporphyrin system, originating from the charge distribution inside the perfluorphenyl groups (mostly the C-F dipoles).
First author: Stasyuk, OA, Effect of Alkali Metal Cations on Length and Strength of Hydrogen Bonds in DNA Base Pairs,
CHEMPHYSCHEM, 21, 2112, (2020)
Abstract: For many years, non-covalently bonded complexes of nucleobases have attracted considerable interest. However, there is a lack of information about the nature of hydrogen bonding between nucleobases when the bonding is affected by metal coordination to one of the nucleobases, and how the individual hydrogen bonds and aromaticity of nucleobases respond to the presence of the metal cation. Here we report a DFT computational study of nucleobase pairs interacting with alkali metal cations. The metal cations contribute to the stabilization of the base pairs to varying degrees depending on their position. The energy decomposition analysis revealed that the nature of bonding between nucleobases does not change much upon metal coordination. The effect of the cations on individual hydrogen bonds were described by changes in VDD charges on frontier atoms, H-bond length, bond energy from NBO analysis, and the delocalization index from QTAIM calculations. The aromaticity changes were determined by a HOMA index.
First author: Milovanovic, MR, The Affinity of Some Lewis Bases for Hexafluoroisopropanol as a Reference Lewis Acid: An ITC/DFT Study,
CHEMPHYSCHEM, 21, 2136, (2020)
Abstract: To figure out the possible role of 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP) as well as to provide reference thermochemical data in solution, the formation of Lewis acid-base complexes between HFIP (Lewis acid) and a series of 8 different Lewis bases (3 sulfoxides, 3 Nsp(2)pyridine derivatives, 1 aromatic amine, 1 cyclic aliphatic ether) was examined by isothermal titration calorimetry (ITC) experiments and static density functional theory augmented with Dispersion (DFT-D) calculations. Measured ITC association enthalpy values (Delta H-a) lie between -9.3 and -14 kcal mol(-1). Computations including a PCM implicit solvation model produced similar exothermicity of association of all studied systems compared to the ITC data with Delta H-a values ranging from -8.5 to -12.7 kcal mol(-1). An additional set of calculations combining implicit and explicit solvation by chlorobenzene of the reactants, pointed out the relatively low interference of the solvent with the HFIP-base complexation: its main effect is to slightly enhance the Gibbs energy of the HFIP-Lewis base association. It is speculated that the interactions of bulk HFIP with Lewis bases therefore may significantly intervene in catalytic processes not only via the dynamic microstructuring of the medium but also more explicitly by affecting bonds’ polarization at the Lewis bases.
First author: Chung, P, Synthesis, characterization, X-ray structure, electrochemistry, photocatalytic activity and DFT studies of heterotrinuclear Ni(II), Pd(II) and Zn(II) complexes containing a formylferrocene thiosemicarbazone ligand,
APPLIED ORGANOMETALLIC CHEMISTRY, 34, 2136, (2020)
Abstract: Three complexes of the general formula M{CpFe(eta(5)-C5H4CH=N-N=C(S)NH2}(2)[where M = Ni-II(2a), Pd-II(2b) and Zn-II(2c)] were synthesized with formylferrocene thiosemicarbazone (1) as a bidentate ligand. All compounds were characterized using conventional spectroscopic and analytical techniques (infrared,H-1 and(13)C NMR, mass spectrometry and elemental analysis). The molecular structure of2bwas confirmed by single-crystal X-ray analysis. To study the photocatalytic activity of the new complexes (2a-c), methylene blue (MB) was selected as a model pollutant. After 180 min, the degradation efficiency of MB reached 87% for2a, 76% for2band 85% for2c, and all complexes showed a higher photocatalytic activity than the formylferrocene thiosemicarbazone free ligand1. Theoretical studies were used to characterize the geometry and electronic structure of the compounds and to provide a rational explanation for the measured photocatalytic activity.
First author: Shakourian-Fard, M, Unraveling the effect of nitrogen doping on graphene nanoflakes and the adsorption properties of ionic liquids: A DFT study,
JOURNAL OF MOLECULAR LIQUIDS, 312, 2136, (2020)
Abstract: Nitrogen doping manipulates the local electronic structure and enhances the binding of the surface with ions present in the electrolyte. This feature improves the device performance in various applications such as fuel cells, biosensors, electronic devices and high-capacity energy storage devices. In this study, we employ Density Functional Theory (DFT) method to study the adsorption behavior of ionic liquids (ILs) on the nitrogen-doped graphene nanofiake surfaces (GNF@1N, GNF@2N, GNF@3N and GNF@4N). We find that the adsorption of ILs on the N-doped GNFs is controlled through several noncovalent interactions (mainly dispersion forces) and the binding process proceeds spontaneously. The Theory of Atoms in Molecules (AIM) and noncovalent interaction (NCI) analyses show that the interactions between ILs and N-doped GNFs are noncovalent in nature. The interaction strength of ILs with the surfaces increases with increasing the number of nitrogen atoms in the nanofiake surfaces and follows the order of GNF@4N…IL > GNF@3N…IL > GNF@2N…IL > GNF@1N…IL. The HOMO-LUMO energy gap of the N-doped GNF surfaces decreases slightly upon IL adsorption. The nitrogen atoms on the nanoflakes significantly affect the binding energy of ILs and the optical properties verified by changes in the calculated UV-Vis absorption spectra. The UV-Vis absorption spectra of the N-doped GNFs are mainly related to the pi((C=C)) -> pi*((C=C)), pi((C=N)) -> pi*((C=N)), and n((N)) -> pi*((C=N)) transitions. These peaks generally become red-shifted upon IL adsorption. The most significant changes in the absorption spectra of the surfaces are seen with adsorption of ILs on the GNF@4N surface due to stronger interaction of ILs with the GNF@4N surface. The transition density matrix (TDM) heal maps based on fragments show that the electron excitation does not cause a significant electron transfer between N-doped GNF surfaces, cations and anions. Therefore, the electron transitions in the N-doped GNF…IL complexes are regarded as local excitation and mainly occur in the N-doped GNF surfaces. Further, this work attempts to lay a fundamental foundation on our understanding of the interfacial interactions at the electrolyte-electrode interface in the solar cells, supercapacitors and ion-batteries.
First author: Brela, MZ, A comparison of the hydrogen bond interaction dynamics in the adenine and thymine crystals: BOMD and spectroscopic study,
SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY, 237, 2136, (2020)
Abstract: In this workwe present the comparison study of Adenine and Thymine crystals based on the hydrogen bond dynamics. The ab initiomolecular dynamics have been used as the base for the further studied interactions observed inside crystals. The generated power spectra, as well as the fluctuation of the interaction energies, showed large differences between hydrogen bond networks in the considered crystals. The analysis of intermolecular interactions have been done base on the reactivity descriptors as well frontiers orbitals along trajectories. The main results showed that in adenine crystals the intermolecular interactions have three directions and fluctuate, while in the thymine crystal have only two directions and are weak but stable. These results explain also on the difference between adenine and thymine melting temperature.
First author: Hernandez-Juarez, G, Structural effects of alkali-metals on the B(12)skeleton,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 17344, (2020)
Abstract: After an exhaustive exploration of the potential energy surface of B(12)E(-)and B12E2(E = Li-Cs) systems, it was found that for the anionic series, a cage-type and a quasi-planar structure (very similar to the naked B(12)cluster) compete to be the putative global minimum. For neutral systems, competition arises between the quasi-planar cluster and a double-ring with the alkali-metals on the highest-symmetry axis. The chemical bonding analyses show that for the entire series, the interaction, predominantly electrostatic, is essentially indistinguishable regardless of the alkali-metal and insufficient for determining the isomeric preference. The isomerization energy decomposition analysis (IEDA) reveals that in the anions, the structural change in the lighter complexes is possible because of the relatively low energy required for the boron skeleton deformation, as opposed to the case of heavy metals. In the case of the neutral systems, the factor determining one isomer over the other corresponds to that of the energy deformation of the alkali-metal dimer.
First author: Heitkemper, T, A Cationic NHC-Supported Borole,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 11684, (2020)
Abstract: This work describes the synthesis and characterization of a highly reactive cationic borole. Halide abstraction with Li{Al[OC(CF3)(3)](4)} from the NHC-chloroborole adduct yields the first stable NHC-supported 1-((NHC)-N-Me)-2,5-(SiMe3)(2)-3,4-(Ph*)(2)-borole cation. Electronically, it features both a five-membered cyclic conjugated 4 pi-electron system and a cationic charge and thus resembles the yet elusive cyclopentadienyl cation. The borole cation was characterized crystallographically, spectroscopically (NMR, UV/Vis), by cyclovoltammetry, microanalysis and mass-spectrometry and its electronic structure was probed computationally. The cation reacts with tolane and reversibly binds carbon monoxide. Direct comparison with the structurally related, yet neutral, 1-mesityl borole reveals strong Lewis acidity, reduced HOMO-LUMO gaps, and increasedanti-aromatic character.
First author: Jayasundara, WJMJSR, Theoretical Study of p- and n-Doping of Polythiophene- and Polypyrrole-Based Conjugated Polymers,
JOURNAL OF PHYSICAL CHEMISTRY C, 124, 17528, (2020)
Abstract: Density functional theory (DFT) calculations were carried out to investigate the tunable nature of band gaps of polythiophene (PTh)- and polypyrrole (PPy)-based conjugated polymers. Two series of conjugated polymers were studied as S is replaced in PTh with O, Se, and Te, and N is replaced in PPy with P, As, and Sb in the presence of Li and Cl atomic dopants. Li and Cl atoms facilitate n-type and p-type doping, respectively. Molecular and periodic calculations were carried out with a GGA functional (PBE) incorporating dispersion corrections. Narrowing band gaps or HOMO-LUMO gaps were obtained when going from O to Te in PTh analogs and P to Sb in PPy analogs. Further reduction in band gaps was observed upon doping especially in the series of PTh and analogs. A slight increase in band gaps was observed with doping in PPy analogs but the band gap is very narrow. Overall, the electronic structure of conjugated polymers can be tuned with Li and Cl atomic dopants, and this is useful in electronic device applications of conjugated polymers. Similar trends are observed for the band gaps in molecular calculations when other functionals (PBE0, B3LYP, M06) are used.
First author: Heshmat, M, Optimizing the Energetics of FLP-Type H-2 Activation by Modulating the Electronic and Structural Properties of the Lewis Acids: A DFT Study,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 6399, (2020)
Abstract: The great potential of frustrated Lewis pairs (FLPs) as metal-free catalysts for activation of molecular hydrogen has attracted increasing interest as an alternative to transition-metal catalysts. However, the complexity of FLP systems, involving the simultaneous interaction of three molecules, impedes a detailed understanding of the activation mechanism and the individual roles of the Lewis acid (LA) and Lewis base (LB). In the present work, using density functional theory (DFT) calculations, we examine the reactivity of 75 FLPs for the H-2 splitting reaction, including a series of experimentally investigated LAs combined with conventional phosphine-based (tBu(3)P) and oxygen-based (i.e., ethereal solvent) Lewis bases. We find that the catalytic activity of the FLP is the result of a delicate balance of the LA and LB strengths and their bulkiness. The H-2 splitting reaction can be changed from endergonic to exergonic by tuning the electrophilicity of the LA. Also, a more nucleophilic LB results in a more stable ion pair product and a lower barrier for the hydrogen splitting. The bulkiness of the LB leads to an early transition state to reduce steric hindrance and lower the barrier height. The bulkiness of the fragments determines the cavity size in the FLP complex, and a large cavity allows for a larger charge separation in the ion pair configuration. A shorter proton-hydride distance in this product complex correlates with a stronger attraction between the fragments, which forms more reactive ion pairs and facilitates the proton and hydride donations in the subsequent hydrogenation process. These insights may help with rationalizing the experimentally observed reactivities of FLPs and with designing better FLP systems for hydrogenation catalysis and hydrogen storage.
First author: Cabrera-Trujillo, JJ, Rationalizing the Al-I-Promoted Oxidative Addition of C-C Versus C-H Bonds in Arenes,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 11806, (2020)
Abstract: The factors controlling the oxidative addition of C-C and C-H bonds in arenes mediated by Al(I)have been computationally explored by means of Density Functional Theory calculations. To this end, we compared the processes involving benzene, naphthalene and anthracene which are promoted by a recently prepared anionic Al-I-carbenoid. It is found that this species exhibits a strong tendency to oxidatively activate C-H bonds over C-C bonds, with the notable exception of benzene, where the C-C bond activation is feasible but only under kinetic control reaction conditions. State-of-the-art computational methods based on the combination of the Activation Strain Model of reactivity and the Energy Decomposition Analysis have been used to rationalize the competition between both bond activation reactions as well as to quantitatively analyze in detail the ultimate factors controlling these transformations.
First author: Spence, P, Beyond Solvent Exclusion: i-Motif Detecting Capability and an Alternative DNA Light-Switching Mechanism in a Ruthenium(II) Polypyridyl Complex,
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 142, 13856, (2020)
Abstract: (C)ytosine-rich DNA can fold into secondary structures known as i-motifs. Mounting experimental evidence suggests that these non-canonical nucleic acid structures form in vivo and play biological roles. However, to date, there are no optical probes able to identify i-motif in the presence of other types of DNA. Herein, we report for the first time the interactions between the three isomers of [Ru(bqp)(2)](2+) with i-motif, G-quadruplex, and double-stranded DNA. Each isomer has vastly different light-switching properties: mer is “on”, trans is “off’, and cis switches from “off” to “on” in the presence of all types of DNA. Using emission lifetime measurements, we show the potential of cis to light up and identify i-motif, even when other DNA structures are present using a sequence from the promoter region of the death-associated protein (DAP). Moreover, separated cis enantiomers revealed Lambda-cis to have a preference for the i-motif, whereas Lambda-cis has a preference for double-helical DNA. Finally, we propose a previously unreported light-switching mechanism that originates from steric compression and electronic effects in a tight binding site, as opposed to solvent exclusion. Our work suggests that many published non-emissive Ru complexes could potentially switch on in the presence biological targets with suitable binding sites, opening up a plethora of opportunity in the detection of biological molecules.
First author: Vicha, J, Relativistic Heavy-Neighbor-Atom Effects on NMR Shifts: Concepts and Trends Across the Periodic Table,
CHEMICAL REVIEWS, 120, 7065, (2020)
Abstract: Chemical shifts present crucial information about an NMR spectrum. They show the influence of the chemical environment on the nuclei being probed. Relativistic effects caused by the presence of an atom of a heavy element in a compound can appreciably, even drastically, alter the NMR shifts of the nearby nuclei. A fundamental understanding of such relativistic effects on NMR shifts is important in many branches of chemical and physical science. This review provides a comprehensive overview, of the tools, concepts, and periodic trends pertaining to the shielding effects by a neighboring heavy atom in diamagnetic systems, with particular emphasis on the “spin-orbit heavy-atom effect on the light-atom” NMR shift (SO-HALA effect). The analyses and tools described in this review provide guidelines to help NMR spectroscopists and computational chemists estimate the ranges of the NMR shifts for an unknown compound, identify intermediates in catalytic and other processes, analyze conformational aspects and intermolecular interactions, and predict trends in series of compounds throughout the Periodic Table. The present review provides a current snapshot of this important subfield of NMR spectroscopy and a basis and framework for including future findings in the field.
First author: Grabarz, A, Noncovalent Bonds between Tetrel Atoms,
CHEMPHYSCHEM, 21, 1934, (2020)
Abstract: The pairing of TFH(3)with a TH(2)CH(3)(-)anion, where T represents tetrel atoms C, Si, Ge, Sn, Pb, results in a strong direct interaction between the two T atoms. The interaction energy is sensitive to the nature of the two T atoms but can be as large as 90 kcal/mol. The noncovalent bond strength rises quickly as the basic T atom of the anion becomes smaller, or as the Lewis acid T grows larger, although there is less sensitivity to the latter atom. The electrostatic component makes up some 55-70 % of the total attraction energy. This term is well accounted for by simple combination of the maximum and minimum values of the molecular electrostatic potential of the Lewis acid and base units, respectively. The complexation induces a rearrangement in the TFH(3)molecule from tetrahedral to trigonal pyramidal. The associated deformation energy reduces the exothermicity of the complexation reaction. Electron density shift patterns reveal a density loss on the basic T atom, along with accompanying increases on the acidic T and its attached F atom.
First author: Bannwarth, C, Extendedtight-bindingquantum chemistry methods,
WILEY INTERDISCIPLINARY REVIEWS-COMPUTATIONAL MOLECULAR SCIENCE, 11, 1934, (2021)
Abstract: This review covers a family of atomistic, mostly quantum chemistry (QC) based semiempirical methods for the fast and reasonably accurate description of large molecules in gas and condensed phase. The theory is derived from a density functional (DFT) perturbation expansion of the electron density in fluctuation terms to various orders similar to the original density functional tight binding model. The term “eXtended” in their name (xTB) emphasizes the parameter availability for almost the entire periodic table of elements (Z <= 86) and improvements of the underlying theory regarding, for example, the atomic orbital basis set, the level of multipole approximation and the treatment of the important electrostatic and dispersion interactions. A common feature of most members is their consistent parameterization on accurate gas phase theoretical reference data for geometries, vibrational frequencies and noncovalent interactions, which are the primary properties of interest in typical applications to systems composed of up to a few thousand atoms. Further specialized versions were developed for the description of electronic spectra and corresponding response properties. Besides a provided common theoretical background with some important implementation details in the efficient and freextbprogram, various benchmarks for structural and thermochemical properties including (transition-)metal systems are discussed. The review is completed by recent extensions of the model to the force-field (FF) level as well as its application to solids under periodic boundary conditions. The general applicability together with the excellent cost-accuracy ratio and the high robustness make the xTB family of methods very attractive for various fields of computer-aided chemical research. This article is categorized under: Electronic Structure Theory > Ab Initio Electronic Structure Methods Electronic Structure Theory > Semiempirical Electronic Structure Methods Software > Quantum Chemistry
First author: Faltracco, M, Diastereoselective Synthesis of beta-Lactams by Ligand-Controlled Stereodivergent Intramolecular Tsuji-Trost Allylation,
JOURNAL OF ORGANIC CHEMISTRY, 85, 9566, (2020)
Abstract: The diastereoselective synthesis of highly substituted beta-lactams by intramolecular Tsuji-Trost allylation is reported. Judicious selection of the ligand on palladium allows selective access to either the trans isomer (in generally good to excellent yield with very high diastereomeric excess) or cis isomer (with yields and diastereoselectivity ranging from modest to excellent depending on the substrate). The reaction proceeds under exceedingly mild conditions (rt, no additives) with a broad range of substrates, which are readily accessible by the Ugi reaction.
First author: Zhang, ZF, Understanding the reactivity of carbene-analogous phosphane complexes with group 13 elements as a central atom: a theoretical investigation,
NEW JOURNAL OF CHEMISTRY, 44, 12815, (2020)
Abstract: The reactions of carbenic cations (PtBu3)(2)M+ (M = B, Al, Ga, In, and Tl) with methane and ethene are studied using density functional theory. The activation energies and reaction enthalpies are analyzed by the energy decomposition analysis (EDA) to understand the reactivity of the reactions. For the reactions with methane, the activation energies and reaction enthalpies increase with the atomic numbers of the group 13 elements (M). For the reactions with ethene, the activation energies and reaction enthalpies also increase with the atomic numbers of M but with a notable exception. The activation energy of the reaction of (PtBu3)(2)B+ with ethene is abnormally higher than those of (PtBu3)(2)Al+ and (PtBu3)(2)Ga+. The activation energy abnormality is due to the excessive strain energy associated with the tremendous structural deformation, in which (PtBu3)(2)B+ has to reform in order to reach the prepared conformation of the transition state. The present theoretical evidence reveals that the atomic radius of the central group 13 element M of the carbenic (PtBu3)(2)M+ species plays a key role in both insertion and [1+2] cycloaddition reactions. In other words, this can be traced back to the fundamental reason that the 2s and 2p orbitals are more amenable to hybridize than the other ns and np orbitals for n >= 3.
First author: Yu, S, Understanding the 1,3-Dipolar Cycloadditions of Allenes,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 11529, (2020)
Abstract: We have quantum chemically studied the reactivity, site-, and regioselectivity of the 1,3-dipolar cycloaddition between methyl azide and various allenes, including the archetypal allene propadiene, heteroallenes, and cyclic allenes, by using density functional theory (DFT). The 1,3-dipolar cycloaddition reactivity of linear (hetero)allenes decreases as the number of heteroatoms in the allene increases, and formation of the 1,5-adduct is, in all cases, favored over the 1,4-adduct. Both effects find their origin in the strength of the primary orbital interactions. The cycloaddition reactivity of cyclic allenes was also investigated, and the increased predistortion of allenes, that results upon cyclization, leads to systematically lower activation barriers not due to the expected variations in the strain energy, but instead from the differences in the interaction energy. The geometric predistortion of cyclic allenes enhances the reactivity compared to linear allenes through a unique mechanism that involves a smaller HOMO-LUMO gap, which manifests as more stabilizing orbital interactions.
First author: Rodrigues, AI, Luminescent halogen-substituted 2-(N-arylimino)pyrrolyl boron complexes: the internal heavy-atom effect,
DALTON TRANSACTIONS, 49, 10185, (2020)
Abstract: A group of new boron complexes [BPh2{kappa N-2,N ‘-NC4H3-2-C(H)= N-C6H4X}] (X = 4-Cl 4c, 4-Br4d, 4-I4e, 3-Br4f, 2-Br4g, 2-I4h) containing different halogens as substituents in theN-aryl ring have been synthesized and characterized in terms of their molecular properties. Their photophysical characteristics have been thoroughly studied in order to understand whether these complexes exhibit an internal heavy-atom effect. Phosphorescence emission was found for some of the synthesized halogen-substituted boron molecules, particularly for4gand4h. DFT and TDDFT calculations showed that the lower energy absorption band resulted from the HOMO to LUMO (pi-pi*) transition, except for 2-I4h, where the HOMO-1 to LUMO transition was also involved. The strong participation of iodine orbitals in HOMO-1 is reflected in the calculated absorption spectra of the iodine derivatives, especially 2-I4h, when spin-orbit coupling (SOC) was included. Organic light-emitting diodes (OLEDs) based on these complexes, in the neat form or dispersed in a matrix, were also fabricated and tested. The devices based on films prepared by thermal vacuum deposition showed the best performance. When neat complexes were used, a maximum luminance (L-max) of 1812 cd m(-2)was obtained, with a maximum external quantum efficiency (EQE(max)) of 0.15%. An EQE(max)ofca.1% along with a maximum luminance of 494 cd m(-2)were obtained for a device fabricated by co-deposition of the boron complex and a host compound (1,3-bis(N-carbazolyl)benzene, mCP).
First author: Shi, HT, Monitoring Local Electric Fields using Stark Shifts on Napthyl Nitrile-Functionalized Silicon Photoelectrodes,
JOURNAL OF PHYSICAL CHEMISTRY C, 124, 17000, (2020)
Abstract: We report spectroscopic measurements of the local electric field using vibrational Stark shifts of napthyl nitrile-functionalized silicon under electrochemical working conditions. The C N bond is particularly sensitive to applied electric fields and serves as a good probe for the local electric fields at the silicon-aqueous interface. Here, surface-enhanced Raman spectra (SERS) are collected at a silicon surface using a water immersion lens as a function of the reference potential in a three-terminal potentiostat. In deionized (DI) water and KCl solutions, the nitrile (i.e., C N) stretch downshifts by 4.7 and 8.6 cm(-1), respectively, under an applied potential of -1 V vs Ag/AgCl. Density functional theory (DFT) calculations of the napthyl nitrile complex carried out under various electric fields establish the Stark tuning rate to be 0.5622 cm(-1)/(MV cm(-1)). Based on this relation, electric fields of -8.4 and -15.2 MV/cm were obtained under negative applied potentials. These measurements report the electric field strength within the double (i.e., Helmholtz) layer, which is responsible for pulling positively charged ions (e.g., H+) toward the surface in reduction reaction processes.
First author: Radicchi, E, Structural and Optical Properties of Solvated PbI2 in gamma-Butyrolactone: Insight into the Solution Chemistry of Lead Halide Perovskite Precursors,
JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 11, 6139, (2020)
Abstract: We employ a fine-tuned theoretical framework, combining ab initio molecular dynamics (AIMD), density functional theory (DFT), and time-dependent (TD) DFT methods, to investigate the interactions and optical properties of the iodoplumbates within the low coordinative gamma-butyrolactone (GBL) solvent environment, widely employed in the perovskite synthesis. We uncover the extent of GBL coordination to PbI2 investigating its relation to the solvated PbI2 optical properties. The employed approach has been further validated by comparison with the experimental UV-vis absorption spectrum of PbI2 in GBL solvent. A comparison with other solvents, commonly employed in the perovskite synthesis, such as N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) is also reported. The methodology developed in this work can be reasonably extended to the investigation of similar systems.
First author: Ostrom, I, In Silico Design of Cylindrophanes: The Role of Functional Groups in a Fluoride Selective Host,
CHEMPHYSCHEM, 21, 1989, (2020)
Abstract: Molecular recognition is the key driver in the formation of supramolecular complexes, enabling the selective encapsulation of specific guests. Here, we explore the delicate balance between different energetic terms in the formation of an efficient host for fluoride anions based on a cylindrophane structure, which can be achieved by the incorporation of ligand sites into a cyanuric acid based cyclophane framework, resulting a close proximity between the ammonium hydrogens and the anion. This study describes the character and contribution of different energetic and repulsive terms that favor the efficient inclusion of fluoride. Our findings are useful for further rational design and synthesis of efficient and highly selective fluoride hosts, which have been generally less well described than complexing agents for other halides.
First author: Qiao, L, [Cu-4@E-18](4-) (E = Sn, Pb): Fused Derivatives of Endohedral Stannaspherene and Plumbaspherene,
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 142, 13288, (2020)
Abstract: We report the synthesis of two new cluster anions, [Cu-4@E-18](4-) (E = Sn, Pb), in which a Cu-4 subunit is incorporated into a continuous E-18 tetrel cage. Both anions are characterized by X-ray crystallography and mass spectrometry, complemented by quantum-chemical calculations that highlight the relationships to known Zintl clusters, including the stannaspherenes and plumbaspherenes [M@Sn-12](q-) and [M@Pb-12](q-), the Matryoshka bronze [Sn@Cu-12@Sn-20](12-), and also [Pd-2@E'(18)](4-) (E’ = Ge, Sn).
First author: Saouli, S, Synthesis, spectroscopic characterization, crystal structure, DFT studies and biological activities of new hydrazone derivative: 1-(2,5-bis((E)-4-isopropylbenzylidene)cyclopentylidene)-2-(2,4-dinitroph enyl) hydrazine,
JOURNAL OF MOLECULAR STRUCTURE, 1213, 13288, (2020)
Abstract: An aromatic a, b-unsaturated Ketone (2E,5E)-2,5 bis(4-isopropyl benzylidene) cyclopentanone (A) have been achieved by a Claisen-Schmidt reaction. A new hydrazone derivative 1-(2,5-bis((E)-4-isopropyl benzylidene) cyclopentylidene)-2-(2,4-dinitrophenyl) hydrazine (B) was synthesized by reacting under reflux chalcone (A) with 2,4-dinitrophenylhydrazine and evaluated for its biological activities. The structure of the title compound (B) was studied using different spectroscopic techniques such as 1H and 13C NMR, FT-IR, UVevisible and confirmed by low-temperature single-crystal X-ray diffraction analysis. Complementary computation studies using DFT and TD-DFT at B3LYP reproduced well the experimental geometrical parameters and the spectroscopic properties. The obtained biological results revealed that the synthesized compound displayed higher antioxidant activity (IC50 1/4 6.95 +/- 0.03 mM) in comparison to BHA and BHT standards by superoxide anion radical assay, and an interesting anti-tyrosinase activity (IC50 1/4 15.84 +/- 1.10 mM), approximately 2-fold more than that of Kojic acid which was used as a reference.
First author: Talotta, F, Early Relaxation Dynamics in the Photoswitchable Complextrans-[RuCl(NO)(py)(4)](2+),
CHEMISTRY-A EUROPEAN JOURNAL, 26, 11522, (2020)
Abstract: The design of photoswitchable transition metal complexes with tailored properties is one of the most important challenges in chemistry. Studies explaining the underlying mechanisms are, however, scarce. Herein, the early relaxation dynamics towards NO photoisomerization intrans-[RuCl(NO)(py)(4)](2+)is elucidated by means of non-adiabatic dynamics, which provided time-resolved information and branching ratios. Three deactivation mechanisms (I, II, III) in the ratio 3:2:4 were identified. Pathways I and III involve ultrafast intersystem crossing and internal conversion, whereas pathway II involves only internal conversion.
First author: Tosato, M, Highly Stable Silver(I) Complexes with Cyclen-Based Ligands Bearing Sulfide Arms: A Step Toward Silver-111 Labeled Radiopharmaceuticals,
INORGANIC CHEMISTRY, 59, 10907, (2020)
Abstract: With a half-life of 7.45 days, silver-111 (beta(max) 1.04 MeV, E-gamma 245.4 keV [I-gamma 1.24%], E-gamma 342.1 keV [I-gamma 6.7%]) is a promising candidate for targeted cancer therapy with beta(-) emitters as well as for associated SPECT imaging. For its clinical use, the development of suitable ligands that form sufficiently stable Ag+-complexes in vivo is required. In this work, the following sulfur-containing derivatives of tetraazacyclododecane (cyclen) have been considered as potential chelators for silver-111: 1,4,7,10-tetrakis(2-(methylsulfanyl)ethyl)-1,4,7,10-tetraazacyclododecane (DO4S), (2S,5S,8S, 11S)-2,5,8,11-tetramethyl-1,4,7,10-tetrakis(2-(methylsulfanyl)ethyl)-1,4,7,10-tetraazacyclododecane (DO4S4Me), 1,4,7-tris(2-(methylsulfanyl)ethyl)-1,4,7,10-tetraazacyclododecane (DO3S), 1,4,7-tris(2-(methylsulfanyl) ethyl)-10-acetamido-1,4,7,10-tetraazacyclododecane (DO3SAm), and 1,7-bis(2-(methylsulfanyl)ethyl)-4,10, diacetic acid-1,4,7,10-tetraazacyclododecane (DO2A2S). Natural Ag+ was used in pH/Ag-potentiometric and UV-vis spectrophotometric studies to determine the metal speciation existing in aqueous NaNO3 0.15 M at 25 degrees C and the equilibrium constants of the complexes, whereas NMR and DFT calculations gave structural insights. Overall results indicated that sulfide pendant arms coordinate Ag+ allowing the formation of very stable complexes, both at acidic and physiological pH. Furthermore, radiolabeling, stability in saline phosphate buffer, and metal-competition experiments using the two ligands forming the strongest complexes, DO4S and DO4S4Me, were carried out with [Ag-111]Ag+ and promising results were obtained.
First author: Wada, Y, Organic light emitters exhibiting very fast reverse intersystem crossing,
NATURE PHOTONICS, 14, 643, (2020)
Abstract: An organic molecule, TpAT-tFFO, which is designed to support rapid reverse intersystem crossing allows the fabrication of efficient organic light-emitting diodes.
First author: Marin-Luna, M, A GIPAW versus GIAO-ZORA-SO study of C-13 and N-15 CPMAS NMR chemical,
SOLID STATE NUCLEAR MAGNETIC RESONANCE, 108, 643, (2020)
Abstract: Theoretical simulation of NMR parameters in compounds bearing heavy atoms generally requires the application of relativistic corrections. We report herein the theoretical characterization of C-13 and N-15 CPMAS NMR of known bromo-derivative crystals by using both the GIPAW and the combined GIAO-ZORA-SO approximation methods. Several statistical analyses were performed to compare both approaches, with non-relativistic GIPAW method being more useful to predict the C-13 and N-15 chemical shifts. The problem of applying GIPAW to crystal structures showing static or dynamic crystalline disorder of the special class resulting in half-protons will be discussed in detail.
First author: Janicki, R, Analysis of charge density in nonaaqua-gadolinium(III) trifluoromethanesulfonate – insight into Gd-III-OH2 bonding,
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING, 76, 572, (2020)
Abstract: The experimental charge-density distribution in [Gd(H2O)(9)](CF3SO3)(3) has been analysed and compared with the theoretical density functional theory calculations. Although the Gd- OH2 bonds are mainly ionic, a covalent contribution is detectable when inspecting both the topological parameters of these bonds and the natural bond orbital results. This contribution originates from small electron transfer from the lone pairs of oxygen atoms to empty 5d and 6s spin orbitals of Gd3+.
First author: Chen, AH, Intramolecular bonding properties in actinide embedded nearly planar superatoms,
CHEMICAL PHYSICS LETTERS, 752, 572, (2020)
Abstract: The electronic structure of isoelectronic superatoms formed by actinides embedded gold ring, An@Au-6 ([Ac@Au-6](-) and Th@Au-6, [Pa@Au-6](+)), have been analyzed to investigate the intramolecular interaction using density functional theory. The bonding properties are similar but not identical. The probability densities of 1P and 1D superatomic molecular orbitals are similar, and compared with 6d orbitals, 5f orbitals show localization behaviors, and the change in their contribution of the covalent bonding relate to the decrease in 5f energy levels. Moreover, additional evidence for the bonding being affected by the uncertainty of electronic configuration could be gathered.
First author: Han, P, Excited -state hydrogen bonding: Detecting ammonia using an HHTP-DPB covalent organic framework,
CHEMICAL PHYSICS, 536, 572, (2020)
Abstract: The electronic structure of isoelectronic superatoms formed by actinides embedded gold ring, An@Au-6 ([Ac@Au-6](-) and Th@Au-6, [Pa@Au-6](+)), have been analyzed to investigate the intramolecular interaction using density functional theory. The bonding properties are similar but not identical. The probability densities of 1P and 1D superatomic molecular orbitals are similar, and compared with 6d orbitals, 5f orbitals show localization behaviors, and the change in their contribution of the covalent bonding relate to the decrease in 5f energy levels. Moreover, additional evidence for the bonding being affected by the uncertainty of electronic configuration could be gathered.
First author: Ovando-Vazquez, C, Nanoscale Properties of the Methylation in GpC Dinucleotide Systems,
CHEMISTRYSELECT, 5, 8616, (2020)
Abstract: The incorporation of a methyl group to DNA nucleotides (methylation) is a well known phenomenon in epigenetic regulation. Methylation can result in gene silencing. Here we investigate the electronic properties of cytosine methylation in different DNA systems using first-principles density functional theory calculations. Specifically, four systems are investigated consisting of two stacked base pairs, including the deoxyribose-phosphate backbone. These four systems are the unmethylated GpC-CpG, the single methylated GpC-mCpG, the double symmetrical methylated GpCm-mCpG, and the quadruple symmetrical GpCmm-mmCpG. Single base-pair cases are also considered with and without the deoxyribose-phosphate backbone (with: pG-pC, pG-pCm, and pG-pCmm; without: G-C, G-Cm, and G-Cmm). These structures are relaxed using the conjugate gradient method. Nanoscale properties, such as the electronic density of states, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) wave functions, charge Mulliken population, hydrogen bond energy, binding energy, and dipole moments between unmethylated and methylated relaxed structures are obtained and compared. These results demonstrate that the deoxyribose-phosphate backbone plays a crucial role in the spatial distribution of HOMO and LUMO wave functions in the stacked systems modulating reactivity and stability. Cytosine methylation on the GpC-CpG system results in a stabilization effect. Dipole moment modification in the studied systems could favor specific protein-DNA interactions due to the methyl group non-polarity, producing hydrophobic DNA regions. These findings suggest specific rules of interaction between methylated regions and gene silencing elements at the nanoscale level.
First author: Ramle, AQ, Spectroscopic and theoretical optical properties of indoleninyl-substituted dibenzotetraaza[14]annulenes,
JOURNAL OF HETEROCYCLIC CHEMISTRY, 57, 3566, (2020)
Abstract: Two new macrocyclic dibenzotetraaza[14]annulene (DBTAA) compounds with indolenine (5) and pyridoindolenine (6) moieties were synthesized and characterized by spectroscopy. Both DBTAAs exhibit strong UV-Vis absorption properties in the Soret band region. The theoretical second-order nonlinear optical property, electric dipole moment (mu), dispersion-free dipole polarizability (alpha) and first hyper-polarizability values were calculated by density functional theory and time dependent density functional theory. The ab-initio quantum mechanical calculation by time-dependent Hartree-Fock method was utilized to investigate the dynamic dipole polarizabilities, dynamic second-order, static, and dynamic third-order (gamma) hyper-polarizabilities of the DBTAAs. The configuration interaction technique of all doubly occupied molecular orbitals possesses theoretically defined single-photon absorption (OPA) specifications for the examined structures. The computed maximum OPA wavelengths on both macrocyclic compounds coincide with the preceding measurement outcomes.
First author: Apostolidis, C, Tris-{hydridotris(1-pyrazolyl)borato}actinide Complexes: Synthesis, Spectroscopy, Crystal Structure, Bonding Properties and Magnetic Behaviour,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 11293, (2020)
Abstract: The isostructural compounds of the trivalent actinides uranium, neptunium, plutonium, americium, and curium with the hydridotris(1-pyrazolyl)borato (Tp) ligand An[eta(3)-HB(N2C3H3)(3)](3)(AnTp(3)) have been obtained through several synthetic routes. Structural, spectroscopic (absorption, infrared, laser fluorescence) and magnetic characterisation of the compounds were performed in combination with crystal field, density functional theory (DFT) and relativistic multiconfigurational calculations. The covalent bonding interactions were analysed in terms of the natural bond orbital (NBO) and quantum theory of atoms in molecules (QTAIM) models.
First author: Semivrazhskaya, O, Regioselective Synthesis and Characterization of Tris- and Tetra-Prato Adducts of M3N@C-80 (M = Y, Gd),
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 142, 12954, (2020)
Abstract: The tris- and tetra-adducts of M3N@I-h-C-80 metallofullerenes were synthesized and characterized for the first time. The 1,3-dipolar cycloaddition (Prato reaction) of Y3N@I-h-C-80 and Gd3N@I-h-C-80 with an excess of N-ethylglycine and formaldehyde provided tris- and tetra-fulleropyrrolidine adducts in a regioselective manner. Purification by HPLC and analyses of the isolated peaks by NMR, MS, and vis-NIR spectra revealed that the major products were four tris- and one tetra-isomers for both Y3N@I-h-C-80 and Gd3N@I-h-C-80. Considering the large number of possible isomers (e.g., at least 1140 isomers for the tris-adduct), the limited number of isomers obtained indicated that the reactions proceeded with high regioselectivity. NMR analyses of the Y3N@I-h-C-80 adducts found that the tris-adducts were all-[6,6]- or [6,6][6,6][5,6]-isomers and that some showed mutual isomerization or remained intact at room temperature. The tetra-adduct obtained as a major product was all-[6,6] and stable. For the structural elucidation of Gd3N@I-h-C-80 tris- and tetra-adducts, density functional theory (DFT) calculations were performed to estimate the relative stabilities of tris- and tetra-adducts formed upon Prato functionalization of the most pyramidalized regions of the fullerene structure. The most stable structures corresponded to additions on the most pyramidalized (i.e., strained) bonds. Taking together the experimental vis-NIR spectra, NMR assignments, and the computed relative DFT stabilities of the potential tris- and tetra-adducts, the structures of the isolated adducts were elucidated. Electron resonance (ESR) measurements measurements of pristine, bis-, and tris-adducts of Gd3N@C-80 suggested that the rotation of the endohedral metal cluster slowed upon increase of the addition numbers to C-80 cage, which is favored for accommodating the Gd atoms of the relatively large Gd3N cluster inner space at the sp(3) addition sites. This is presumably related to the high regioselectivity in the Prato addition reaction driven by the strain release of the Gd3N@C-80 fullerene structure.
First author: Pratik, SM, Engineering Electrical Conductivity in Stable Zirconium-Based PCN-222 MOFs with Permanent Mesoporosity,
CHEMISTRY OF MATERIALS, 32, 6137, (2020)
Abstract: Electrically conductive metal-organic frameworks (MOFs) featuring zirconium-based nodes are of great interest for electrochemical and optoelectronic applications due to their exceptional thermal and chemical stability, although the number of such MOFs remains limited. Herein, we demonstrate that electron deficient molecules such as transition metal(IV) bis(dicarbollide) (TMIV(C2B9H11)(2); (TiCB)-C-IV for short, where TM = Ni, Pd, and Pt) or C-60, spatially infiltrated in the microporous channels of the zirconium-based porphyrinic MOFs PCN-222 and PCN-222-Zn, generate highly stable and electrically conductive frameworks in which the mesopores remain accessible to other guests. Solid-state density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations indicate incorporation of (NiCB)-C-IV and C-60 in the MOF micropores is energetically and structurally feasible. Interestingly, in contrast to the free species, strong donor-acceptor interactions between the MOF and (NiCB)-C-IV restrain it to a single conformation. Calculated electronic structures and charge-hopping conduction probabilities illustrate that efficient charge-transfer (CT) from photoexcited linkers to the guest molecules facilitates charge hopping in the framework, making the MOFs electrically conductive. The donor- acceptor conjugates also enhance exciton dissociation at their heterojunctions, fostering the formation of long-lived electron-trapped states with potential utility for photo- and electrochemical devices.
First author: Sondermann, C, Analysis of a Diimine-Organonickel Redox Series,
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 2020, 3010, (2020)
Abstract: Complex cations [Ni(C5R5)(L)](+), L = 1,4-diphenyl-2,3-dimethyl-1,4-diaza-1,3-butadiene, were compared as structurally characterized BF4-(R = H) and SbF(6)(-)salts (R = Me). These Ni-II(L-0) compounds are reversibly reduced (R = H,Me) or oxidized (R = Me) and their one-electron oxidized and reduced forms studied by EPR and UV/Vis spectroelectrochemistry, supported by DFT calculations. Surprisingly similar EPR features were observed for [Ni(C5Me5)(L)](0)and [Ni(C5Me5)(L)](2+). Whereas the oxidation is largely metal centered to yield a Ni(III)species (R = Me), the reduction reveals energetically close-lying alternatives (redox isomers) Ni-I(L-0) and Ni-II(L center dot-).
First author: Hu, SX, New theoretical insights into high-coordination-number complexes in actinides-centered borane,
NANOSCALE, 12, 15054, (2020)
Abstract: The coordination number of a given element affects its behavior, and consequently, there is great interest in understanding the related chemistry, which could greatly promote the extension and development of new materials, but remains challenging. Herein, we report a new record high coordination number (CN) for actinides established in the cage-like An(BH)(24) (An = Th to Cm) via using relativistic quantum chemistry methods. Analysis of U(BH)(n) (n = 1 to 24) confirmed these series of systems as being geometric minima, with the BH acting as a ligand located in the first shell around the uranium. In contrast, global searches revealed a low CN half-cage structure for UB24, which could be extended to the series of AnB(24) materials and which prevails over the competing structural isomers, such as cages. The intrinsic geometric difference for AnB(24) and An(BH)(24) mainly arise from the B sp(3) hybridization in borane inducing strong interactions between An 5f6d7s hybrid orbitals and B 2p(z) orbitals in An(BH)(24) compared to that of AnB(24). This fundamental trend presents a valuable insight for future experimental endeavors searching for isolable complexes with high-coordination actinide and provides details of a new structural motif of boron clusters and nanostructures.
First author: Zhang, L, Dual catalytic enantioselective desymmetrization of allene-tethered cyclohexanones,
CHEMICAL SCIENCE, 11, 7444, (2020)
Abstract: The construction of enantioenriched azabicyclo[3.3.1]nonan-6-one heterocyclesviaan enantioselective desymmetrization of allene-linked cyclohexanones, enabled through a dual catalytic system, that provides synchronous activation of the cyclohexanone with a chiral prolinamide and the allene with a copper(i) co-catalyst to deliver the stereodefined bicyclic core, is described. Successful application to oxygen analogues was also achieved, thereby providing a new enantioselective synthetic entry to architecturally complex bicyclic ethereal frameworks. The mechanistic pathway and the origin of enantio- and diastereoselectivities has been uncovered using density functional theory (DFT) calculations.
First author: Mews, NM, A four-parameter system for rationalising the electronic properties of transition metal-radical ligand complexes,
DALTON TRANSACTIONS, 49, 9735, (2020)
Abstract: A system of four principal parameters is reported that provides a unified description of the electronic and chemical properties of radical-ligand coordination compounds. This type of parametrisation applies to compositionally different types of radical-ligands, and the principal parameters rank in the following order: (a) coordination mode (metal-ligand orbital alignment) > (b) metal linkage > (c) ligand charge > (d) geometric strain (on orbital overlap). A series of group-10 metal complexes of an open-shell thiolate-arene-thiolate ligand suits to differentiate between three of the four effects in a clear-cut fashion, which allowed sorting these into a semi-quantitative order for the first time. Combined experimental and TD-DFT data aided in distinguishing structural effects from metal specific contributions such as relativistic effects. The applicability of spectroscopic and structure properties to serve as characteristic markers for comparison is discussed with regard to the large body of planar radical-ligand structures.
First author: Wu, FL, Making Base-Assisted C-H Bond Activation by Cp*Co(III) Effective: A Noncovalent Interaction-Inclusive Theoretical Insight and Experimental Validation,
ORGANOMETALLICS, 39, 2609, (2020)
Abstract: The base-assisted cyclometalation of 2-phenylpyridine (2-phpyH) by Cp*Co(III) was holistically addressed both theoretically and experimentally. Combined DFT and DLPNO-CCSD(T) methods assisted by QTAIM-based noncovalent interactions plots (NCI plots), interacting quantum atoms (IQA), and local energy decomposition (LED) analyses have been used for a comparative study of the CMD-promoted cyclocobaltation and the parent cycloiridation of the 2-phpyH. Results suggest a remarkable contribution of noncovalent interactions, especially local electrostatic interactions, in the evolution of the reactive site giving a rationale for the optimization of cyclocobaltation. The theoretically predicted benefits of using the acetamidate anion as a base is rationalized and verified experimentally. Cobaltacycle [Cp*Co(2-phpy-kappa C,kappa N)I] was efficiently synthesized from the air-stable [Cp*CoI2](2) and 2-phpyH, in the presence of LiNHAc as base in 83% yield, whereas with anhydrous NaOAc as base only a 12% yield was achieved under similar conditions. By applying the [NHAc](-) promoted cyclometalation various cobaltacycles were synthesized and analytically characterized, and their structures were resolved by X-ray crystallization analysis, confirming the importance of the acetamidate in the base-assisted cyclometalation. Experimental kinetic isotope effect (KIE) studies validated by Bigeleisen equation based KIE computations confirm that the formation of the agostic transient is indeed the kinetic determining step of the CMD mechanism in dichloromethane. Application of the [Cp*CoI2](2)/LiNHAc mixture to the catalysis of the condensation of 1,2-diphenyacetylene to various aromatics reveals the coexistence of two mechanisms, i.e. CMD and electrophilic C-H activation.
First author: Krahfuss, MJ, N-Heterocyclic Silylenes as Ligands in Transition Metal Carbonyl Chemistry: Nature of Their Bonding and Supposed Innocence,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 11276, (2020)
Abstract: A study on the reactivity of theN-heterocyclic silylene Dipp(2)NHSi (1,3-bis(diisopropylphenyl)-1,3-diaza-2-silacyclopent-4-en-2-yliden) with the transition metal complexes [Ni(CO)(4)], [M(CO)(6)] (M=Cr, Mo, W), [Mn(CO)(5)(Br)] and [(eta(5)-C5H5)Fe(CO)(2)(I)] is reported. We demonstrate thatN-heterocyclic silylenes, the higher homologues of the now ubiquitous NHC ligands, show a remarkably different behavior in coordination chemistry compared to NHC ligands. Calculations on the electronic features of these ligands revealed significant differences in the frontier orbital region which lead to some peculiarities of the coordination chemistry of silylenes, as demonstrated by the synthesis of the dinuclear, NHSi-bridged complex [{Ni(CO)(2)(mu-Dipp(2)NHSi)}(2)] (2), complexes [M(CO)(5)(Dipp(2)NHSi)] (M=Cr3, Mo4, W5), [Mn(CO)(3)(Dipp(2)NHSi)(2)(Br)] (9) and [(eta(5)-C5H5)Fe(CO)(2)(Dipp(2)NHSi-I)] (10). DFT calculations on several model systems [Ni(L)], [Ni(CO)(3)(L)], and [W(CO)(5)(L)] (L=NHC, NHSi) reveal that carbenes are typically the much better donor ligands with a larger intrinsic strength of the metal-ligand bond. The decrease going from the carbene to the silylene ligand is mainly caused by favorable electrostatic contributions for the NHC ligand to the total bond strength, whereas the orbital interactions were often found to be higher for the silylene complexes. Furthermore, we have demonstrated that the contribution of sigma- and pi-interaction depends significantly on the system under investigation. The sigma-interaction is often much weaker for the NHSi ligand compared to NHC but, interestingly, the pi-interaction prevails for many NHSi complexes. For the carbonyl complexes, the NHSi ligand is the better sigma-donor ligand, and contributions of pi-symmetry play only a minor role for the NHC and NHSi co-ligands.
First author: Ponzi, A, Photoionization of pyrrole from the B-2 state: a computational study on the effects of Rydberg-valence mixing,
THEORETICAL CHEMISTRY ACCOUNTS, 139, 11276, (2020)
Abstract: Does the optically bright B-2 (pi -> pi*) transition in pyrrole correspond to an inter-valence or to a mixed valence-Rydberg transition? State-of-the-art electronic structure methods provide inconclusive results and relegate the answer to future time-resolved photoelectron spectroscopy experiments. Here, benchmark calculations of photoionization cross sections, asymmetry parameters and molecular frame photoelectron angular distributions (MFPADs) have been performed with the aim of discerning between the two types of transitions. In particular, we show that MFPADs are very sensitive probes of the electronic wave function and that accurate experimental MFPADs could be used to identify the electronic character of the B-2 state.
First author: Ohki, S, A dinuclear Mo(2)H(8)complex supported by bulky C(5)H(2)(t)Bu(3)ligands,
CHEMICAL COMMUNICATIONS, 56, 8035, (2020)
Abstract: Hydride-bridged transition metal complexes have been found to serve as suitable precursors for the activation of small molecules without the use of reducing agents. In this study, we synthesized a dinuclear Mo(2)H(8)complex supported by bulky (C5H2Bu3)-Bu-t(Cp-double dagger) ligands, (Cp2Mo2H8)-Mo-double dagger(1), from the reaction of Cp(double dagger)MoCl(4)with KC(8)under H-2. The hydrides of complex1can be replaced with benzene at 60 degrees C to afford a mu-benzene complex (Cp2Mo2H2)-Mo-double dagger(mu-C6H6) (2).
First author: Blundell, TJ, A transition metal-gallium cluster formed via insertion of ” GaI ”,
CHEMICAL COMMUNICATIONS, 56, 8139, (2020)
Abstract: The reaction between a two-coordinate Co(ii) diaryl complex and “GaI” affords 2,6-Pmp(2)C(6)H(3)CoGa(3)I(5), in a new geometry for a heavier group 13-transition metal cluster. Experimental and computational investigations show that this compound is best described as anidometalla-group 13 cluster.
First author: Braunwarth, L, Exploring the Structure-Activity Relationship on Platinum Nanoparticles,
TOPICS IN CATALYSIS, 63, 1647, (2020)
Abstract: The design of active and stable Pt-based nanoscale electrocatalysts for the oxygen reduction reaction (ORR) plays the central role in ameliorating the efficiency of proton exchange membrane fuel-cells towards future energy applications. On that front, theoretical studies have contributed significantly to this research area by gaining deeper insights and understanding of the ongoing processes. In this work, we present an approach capable of characterizing differently-shaped platinum nanoparticles undergoing thermally- and adsorbate-induced restructuring of the surface. Further, by performing ReaxFF-Grand Canonical Molecular Dynamics simulations we explored the water formation on these roughened (“realistic”) nanoparticles in a H-2/O(2)environment. Taking into consideration the coverage of oxygen-containing intermediates and occurring surface roughening the nanoparticles’ activities were explored. Hereby, we succeeded in locally resolving the water formation on the nanoparticles’ surfaces, allowing an allocation of the active sites for H2O production. We observed that exposed, low-coordinated sites as well as pit-shaped sites originating from roughening of vertices and edges are most active towards H2O formation.
First author: Kozlova, SG, Effect of spin-phonon interactions on Urbach tails in flexible [M-2(bdc)(2)(dabco)],
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 15242, (2020)
Abstract: The optical properties of metal-organic frameworks [M-2(bdc)(2)(dabco)] (M = Co, Ni, Cu, Zn) in the wavelength region of 300-1000 nm were studied, and the electronic band-to-band transitions were determined and characterized by the Kubelka-Munk approach and DFT calculations. Urbach edges for band-to-band transitions were determined. The effect of spin-phonon interactions on the width of Urbach edges in paramagnetic [M-2(bdc)(2)(dabco)] is discussed. The obtained data may be useful to interpret polymerization, hybridization, and catalytic reactions in [M-2(bdc)(2)(dabco)] pores and to design electronic and optical devices.
First author: Sinharoy, P, Ligand architectural effect on coordination, bonding, interaction, and selectivity of Am(iii) and Ln(iii) ions with bitopic ligands: synthesis, solvent extraction, and DFT studies,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 15448, (2020)
Abstract: The isolation of Am(iii) ion from Ln(iii) ions is very crucial for the safe disposal of nuclear wastes and thus, studies are being continuously pursued to accomplish this goal. In view of this, herein, a new conformationally rigid bitopic ligand,N,N,N ‘,N ‘-tetra(2-ethylhexyl)piperazine-di-methylenecarboxamide (PIPDA) has been synthesized and studied for the separation of Am(iii) from Ln(iii) ions. The effect of structural rigidification on the selectivity of Am(iii) over Ln(iii) was compared with an open chain flexible compound, namely,N,N,N ‘,N ‘-tetra(2-ethylhexyl)-3,6-(N ”,N ”’-dibutyl)diaza-octane-1,8-diamide (DADA). Two oxygen atoms of the diamide moiety seem to be responsible for controlling the metal ion extraction ability of PIPDA, whereas two nitrogen atoms of the piperazine moiety most probably dictate the separation factor between the Am(iii) and Eu(iii) ions in PIPDA. In addition, scalar relativistic density functional theory (DFT) in conjunction with Born-Haber thermodynamics was used herein to compliment the experimental selectivity. The experimentally observed preferential selectivity of PIPDA for Am(iii) ion over the Ln(iii) ion was corroborated by the computed extraction free energy, Delta G(ext). The covalent nature of bonding between the metal ions and the ligand was confirmed by analyzing the Mayer bond order and bond character analysis using the atom in molecule concept. Though the conformational rigidity of PIPDA gives stronger interaction than DADA, it does not offer a significant advantage over DADA in terms of the separation factor. The marginal increase in the separation factor for PIPDA over DADA might be attributed to the piperazine nitrogen and to the ligand architecture during complex formation.
First author: Anumula, R, Ligand accommodation causes the anti-centrosymmetric structure of Au(13)Cu(4)clusters with near-infrared emission,
NANOSCALE, 12, 14801, (2020)
Abstract: We synthesized an [Au13Cu4(PPh3)(4)(SPy)(8)](+)nanocluster co-capped by phosphine and thiolate ligands. Interestingly, this Au(13)Cu(4)cluster corresponds to an anti-centrosymmetric structure with the four copper atoms coordinated to the mixed ligands on the same side of the Au(13)icosahedron, which is in sharp contrast to the [Au13Cu4(PPh2Py)(4)(SPhtBu)(8)](+)and [Au13Cu2(PPh3)(6)(SPy)(6)](+)clusters which possess highly symmetric structures with well-separated Cu adatoms. Both [Au13Cu4(PPh3)(4)(SPy)(8)](+)and [Au13Cu2(PPh3)(6)(SPy)(6)](+)clusters correspond to 8 valence electron superatoms with large HOMO-LUMO gaps, respectively. The difference in structure is rooted in the nature of the mixed ligands, with the bidentate SPy binding strongly to Cu on both binding sites (-N-Cu and Au-SR-Cu) leading to the co-linking of adjacent Cu atoms, while the bidentate PPh2Py binds Cu on one site and Au on the other giving rise to a separation of the Cu atoms even in the presence of relatively higher monomer concentration. Both [Au13Cu4(PPh3)(4)(SPy)(8)](+)and [Au13Cu2(PPh3)(6)(SPy)(6)](+)display emissions in the near-IR regions. TD-DFT calculations reproduce the spectroscopic results with specified excited states, shedding light on the geometric and electronic behaviors of the ligand-protected Au(13)M(x)clusters.
First author: Orenha, RP, Tracking the role oftrans-ligands in ruthenium-NO bond lability: computational insight,
NEW JOURNAL OF CHEMISTRY, 44, 11448, (2020)
Abstract: Nitric oxide (NO) is an important endogenously produced molecule. Ruthenium-NO tetraamine complexes appear as model structures to investigate the control of nitric oxide bioavailability. NO release typically occurs through thetrans-[Ru-II(NH3)(4)L-trans(NO+)](3+/2+)+ e(-)-> trans-[Ru-II(NH3)(4)L-trans(NO0)](2+/+)reduction reaction, followed by thetrans-[Ru-II(NH3)(4)L-trans(NO0)](2+/+)+ H2O -> trans-[Ru-II(NH3)(4)L-trans(H2O)](2+/+)+ NO(0)hydrolysis reaction. The choice of the NOtransligand, L-trans, is fundamental to control the Ru-NO bond stability. Here, the nature and charge influences of L(trans)were evaluated considering the following ligands L-trans= sigma-donors (NH(3)and H-), pi-donors (H2O and NH2-), and pi-donors and pi-acceptors (CO and CN-) through the ZORA-BP86/TZ2P computational model. Energy Decomposition Analysis in conjunction with the Natural Orbitals for Chemical Valence methodology (EDA-NOCV) showed that molecules with L-trans= H2O and NH(2)(-)promoted larger Ru-NO stabilization than complexes with L-trans= NH(3)and H-, respectively, mainly due to the interaction orbital energy (Delta E-oi). The opposite trend was observed in compounds with L-trans= CO and CN(-)compared to structures with L-trans= H2O and NH2-. The study of the charge distribution, performed using the Voronoi Deformation Density (VDD) method, and the topological analysis of the electron density, realized using the Quantum Theory of Atoms in Molecules (QTAIM), on the investigated complexes indicated that L(trans)with negative charge promoted, in general, predominantly a decrease of the electron flux in the L-trans(sigma) -> Ru(d(sigma)*) <- NO(sigma) process.
First author: Niu, S, Redox and structural properties of accessible actinide(ii) metallocalixarenes (Ac to Pu): a relativistic DFT study,
RSC ADVANCES, 10, 26880, (2020)
Abstract: The redox properties of actinides play a significant role in manipulating organometallic chemistry and energy/environment science, for being involved in fundamental concepts (oxidation state, bonding and reactivity), nuclear fuel cycles and contamination remediation. Herein, a series oftrans-calix[2]pyrrole[2]benzene (H2L2) actinide complexes (An = Ac-Pu, and oxidation states of +II and +III) have been studied by relativistic density functional theory. Reduction potentials (E-0) of [AnL(2)](+)/[AnL(2)] were computed within -2.45 and -1.64 VversusFc(+)/Fc in THF, comparable to experimental values of -2.50 V for [UL1e]/[UL1e](-)(H3L1e= ((ArOH)-Ar-Ad,Me)(3)mesitylene and Ad = adamantyl) and -2.35 V for [U(Cp-iPr)(2)](+)/[U(Cp-iPr)(2)] (Cp-iPr= (C5Pr5)-Pr-i). TheE(0)values show an overall increasing trend from Ac to Pu but a break point at Np being lower than adjacent elements. The arene/actinide mixed reduction mechanism is proposed, showing arenes predominant in Ac-Pa complexes but diverting to metal-centered domination in U-Pu ones. Besides being consistent with previously reported those of An(III)/An(II)couples, the changing trend of our reduction potentials is corroborated by geometric data, topological analysis of bonds and electronic structures as well as additional calculations on actinide complexes ligated by tris(alkyloxide)arene, silyl-cyclopentadiene and octadentate Schiff-base polypyrrole in terms of electron affinity. The regularity would help to explore synthesis and property of novel actinide(ii) complex.
First author: Deng, GH, Filling a Gap: The Coordinatively Saturated Group 4 Carbonyl Complexes TM(CO)(8) (TM=Zr, Hf) and Ti(CO)(7),
CHEMISTRY-A EUROPEAN JOURNAL, 26, 10487, (2020)
Abstract: Homoleptic Group 4 metal carbonyl cation and neutral complexes were prepared in the gas phase and/or in solid neon matrix. Infrared spectroscopy studies reveal that both zirconium and hafnium form eight-coordinate carbonyl neutral and cation complexes. In contrast, titanium forms only the six-coordinate Ti(CO)(6)(+) and seven-coordinate Ti(CO)(7). Titanium octacarbonyl Ti(CO)(8) is unstable as a result of steric repulsion between the CO ligands. The 20-electron Zr(CO)(8) and Hf(CO)(8) complexes represent the first experimentally observed homoleptic octacarbonyl neutral complexes of transition metals. The molecules still fulfill the 18-electron rule, because one doubly occupied valence orbital does not mix with any of the metal valence atomic orbitals. Zr(CO)(8) and Hf(CO)(8) are stable against the loss of one CO because the CO ligands encounter less steric repulsion than Zr(CO)(7) and Hf(CO)(7). The heptacarbonyl complexes have shorter metal-CO bonds than that of the octacarbonyl complexes due to stronger electrostatic and covalent bonding, but the significantly smaller repulsive Pauli term makes the octacarbonyl complexes stable.
First author: Roeleveld, JJ, Engineering Crystals Using sp(3)-C Centred Tetrel Bonding Interactions,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 10126, (2020)
Abstract: 1,1,2,2-Tetracyanocyclopropane derivatives1and2were designed and synthesized to probe the utility of sp(3)-C centred tetrel bonding interactions in crystal engineering. The crystal packing of1and2and their 1,4-dioxane cocrystals is dominated by sp(3)-C(CN)(2)…O interactions, has significant C…O van der Waals overlap (<= 0.266 angstrom) and DFT calculations indicate interaction energies of up to -11.0 kcal mol(-1). A cocrystal of2with 1,4-thioxane reveals that the cyclopropane synthon prefers interacting with O over S. Computational analyses revealed that the electropositive C-2(CN)(4)pocket in1and2can be seen as a strongly directional ‘tetrel-bond donor’, similar to halogen bond or hydrogen bond donors. This disclosure is expected to have implications for the utility of such ‘tetrel bond donors’ in molecular disciplines such as crystal engineering, supramolecular chemistry, molecular recognition and medicinal chemistry.
First author: Kotyk, CM, Luminescence of Lanthanide Complexes with Perfluorinated Alkoxide Ligands,
INORGANIC CHEMISTRY, 59, 9807, (2020)
Abstract: Four groups of rare-earth complexes, comprising 11 new compounds, with fluorinated O-donor ligands ([K(THF)(6)]-[Ln(OC4F9)(4)(THF)(2)] (1-Ln; Ln = Ce, Nd), [K](THF)(x)[Ln-(OC4F9)(4) (THF)(y)] (2-Ln; Ln = Eu, Gd, Dy), [K(THF)(2)][Ln-(pin(F))(2)(THF)(3)] (3-Ln; Ln = Ce, Nd), and [K(THF)(2)][Ln-(pin(F))(2)(THF)(2)] (4-Ln; Ln = Eu, Gd, Dy, Y) have been synthesized and characterized. Single-crystal X-ray diffraction data were collected for all compounds except 2-Ln. Species 1-Ln, 3-Ln, and 4-Ln are uncommon examples of six-coordinate (Eu, Gd, Dy, and Y) and seven-coordinate (Ce and Nd) Ln(III) centers in all-O-donor environments. Species 1-Ln, 2-Ln, 3-Ln, and 4-Ln are all luminescent (except where Ln = Gd and Y), with the solid-state emission of 1-Ce being exceptionally blue-shifted for a Ce complex. The emission spectra of the six Nd, Eu, and Dy complexes do not show large differences based on the ligand and are generally consistent with the well-known free-ion spectra. Time-dependent density functional theory results show that 1-Ce and 3-Ce undergo allowed 5f -> 4d excitations, consistent with luminescence lifetime measurements in the nanosecond range. Eu-containing 2-Eu and 4-Eu, however, were found to have luminescence lifetimes in the millisecond range, indicating phosphorescence rather than fluorescence. The performance of a pair of multireference models for prediction of the Ln = Nd, Eu, and Dy absorption spectra was assessed. It was found that spectroscopy-oriented configuration interaction as applied to a simplified model in which the free-ion lanthanide was embedded in ligand-centered Lowdin point charges performed as well (Nd) or better (Eu and Dy) than canonical NEVPT2 calculations, when the ligand orbitals were included in the treatment.
First author: Ishihara, K, Synthesis of Dinuclear Mo-Fe Hydride Complexes and Catalytic Silylation of N-2,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 9537, (2020)
Abstract: Two transition-metal atoms bridged by hydrides may represent a useful structural motif for N(2)activation by molecular complexes and the enzyme active site. In this study, dinuclear Mo-IV-Fe(II)complexes with bridging hydrides, Cp (R) Mo(PMe3)(H)(mu-H)(3)FeCp* (2 a; Cp (R)=Cp*=C5Me5,2 b; Cp (R)=C5Me4H), were synthesized via deprotonation of Cp (R) Mo(PMe3)H-5(1 a; Cp (R)=Cp*,1 b; Cp (R)=C5Me4H) by Cp*FeN(SiMe3)(2), and they were characterized by spectroscopy and crystallography. These Mo-Fe complexes reveal the shortest Mo-Fe distances ever reported (2.4005(3) angstrom for2 aand 2.3952(3) angstrom for2 b), and the Mo-Fe interactions were analyzed by computational studies. Removal of the terminal Mo-H hydride in2 a-2 bby [Ph3C] +in THF led to the formation of cationic THF adducts [Cp (R) Mo(PMe3)(THF)(mu-H)(3)FeCp*] + (3 a; Cp (R)=Cp*,3 b; Cp (R)=C5Me4H). Further reaction of3 awith LiPPh(2)gave rise to a phosphido-bridged complex Cp*Mo(PMe3)(mu-H)(mu-PPh2)FeCp* (4). A series of Mo-Fe complexes were subjected to catalytic silylation of N(2)in the presence of Na and Me3SiCl, furnishing up to 129 +/- 20 equiv of N(SiMe3)(3)per molecule of2 b. Mechanism of the catalytic cycle was analyzed by DFT calculations.
First author: Gomez-Alcocer, F, Neutral Hexacoordinate Tin(IV) Halide Complexes with 4,4′-Dimethy-2,2′-bipyridine,
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 646, 1274, (2020)
Abstract: A series of three neutral, hexacoordinate tin(IV) complexes were synthesized by the reaction of 4,4′-dimethyl-2,2′-bipyridine (DMB) with SnX4, X = Cl, Br, and I, as starting materials. The complexes (DMB)SnX(4)were characterized in solution by(1)H,C-13, and(119)Sn NMR spectroscopy, and in the solid-state by(119)Sn MAS NMR spectroscopy. In addition, single-crystal X-ray diffraction and elemental analysis were used to confirm the molecular structures. In these complexes, the tin atom adopts a distorted octahedral arrangement and the DMB acts as a bidentateN,N’-chelate ligand. Computational DFT methods were also employed to gain more insight into the nature of the bonding in these complexes, including the hypothetical complexes (DMB)SnX4(X = F, At). Additionally, the validity and reliability of the(119)Sn NMR chemical shifts were examined. The calculated values were compared with the experimental signals and the effects of structure and solvent are discussed. Finally, all of the complexes (DMB)SnX(4)were successfully tested for the ring-opening polymerization (ROP) of bulk epsilon-caprolactone under non-dried and aerobic conditions as precatalyst.
First author: Gallardo-Fuentes, S, Unraveling the Selectivity Patterns in Phosphine-Catalyzed Annulations of Azomethine Imines and Allenoates,
JOURNAL OF ORGANIC CHEMISTRY, 85, 9272, (2020)
Abstract: The mechanism and selectivity of phosphine-catalyzed [3 + 2] and [3 + 3] annulations of azomethine imines and allenoates have been computationally studied. Exploration of the potential energy surface reveals that the cyclization step is a key step controlling the selectivity of the process. This contrasts with previous studies on related transformations where the initial nucleophilic addition involving the activated allenoate was found to exclusively control the regioselectivity of the transformation. Among the possible reaction pathways, the energetically low-lying reaction channel involves an intramolecular Michael addition leading to the experimentally observed [3 + 2] product. The factors controlling the observed regioselectivity have been quantitatively rationalized by means of state-of-the-art computational methods, namely, the activation strain model of reactivity in combination with the energy decomposition analysis.
First author: Ha, M, Phase Evolution in Methylammonium Tin Halide Perovskites with Variable Temperature Solid-State Sn-119 NMR Spectroscopy,
JOURNAL OF PHYSICAL CHEMISTRY C, 124, 15015, (2020)
Abstract: Hybrid organic-inorganic metal-halide perovskite materials are an emerging class of materials that could profoundly change the optoelectronic and solar absorber research fields and have far-reaching applications. Unfortunately, the leading solar-absorbing candidates are lead-containing materials and suffer from chemical instability, eventually decomposing, resulting in detrimental long-term environmental concerns. A series of nontoxic group 14 Sn(II)-based hybrid organic-inorganic metal-halide perovskites is investigated using variable-temperature solid-state nuclear magnetic resonance (NMR) spectroscopy to examine their unique phases that appear between 150 and 540 K. Each phase of the MASnX(3) (MA(+) = CH3NH3+ and X- = Cl-, Br-, or I-) series is identified and compared to results from quantum chemical calculations of anionic polyhedron clusters. The analysis of the polyhedra about the Sn center is further related to the measured chemical shift anisotropy present when Sn deviates from octahedral symmetry. We also discuss the rapid degradation of pristine MASnI(3) over 2 days studied using in situ Sn-119 NMR spectroscopy. Finally, we report on the H-1, C-13, Sn-119, and Pb-207 NMR structural properties of a Sn/Pb mixed B-site (MASn(0.5)Pb(0.5)I(3)) perovskite, demonstrating the sensitivity of the chemical shift to B-site substitution.
First author: Kim, CL, Dual Mode Radiative Transition from a Phenoselenazine Derivative and Electrical Switching of the Emission Mechanism,
JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 11, 5591, (2020)
Abstract: Dual emission featuring both thermally activated delayed fluorescence (TADF) and phosphorescence was engineered into a single metal-free molecule, phenyl(10-phenyl-10H-phenoselenazin-3-yl)methanone. Selenium incorporated into the molecule increases the spin-orbit coupling to facilitate both TADF and phosphorescence, whereas donor-acceptor units promote TADF emission. The relative contribution of the green TADF and yellow phosphorescence can be controlled by the driving voltage of the devices. At low voltage, phosphorescence emission dominates the electroluminescence, whereas TADF is the major component at high voltages. The mechanism of dual emission was explored using experimental and theoretical methods.
First author: Gebers, J, Crystallization and Organic Field-Effect Transistor Performance of a Hydrogen-Bonded Quaterthiophene,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 10265, (2020)
Abstract: Crystalline thin films of pi-conjugated molecules are relevant as the active layers in organic electronic devices. Therefore, materials with enhanced control over the supramolecular arrangement, crystallinity, and thin-film morphology are desirable. Herein, it is reported that hydrogen-bonded substituents serve as additional structure-directing elements that positively affect crystallization, thin-film morphology, and device performance of p-type organic semiconductors. It is observed that a quaterthiophene diacetamide exhibits a denser packing than that of other quaterthiophenes in the single-crystal structure and, as a result, displays enhanced intermolecular electronic interactions. This feature was preserved in crystalline thin films that exhibited a layer-by-layer morphology, with large domain sizes and high internal order. As a result, organic field-effect transistors of these polycrystalline thin films showed mobilities in the range of the best mobility values reported for single-crystalline quaterthiophenes. The use of hydrogen-bonded groups may, thus, provide an avenue for organic semiconducting materials with improved morphology and performance.
First author: Zouchoune, B, How the ascorbic acid and hesperidin do improve the biological activities of the cinnamon: theoretical investigation,
STRUCTURAL CHEMISTRY, 31, 2333, (2020)
Abstract: DFT/B3LYP calculations have been performed on series of molecules of natural products containing cinnamon and citrus, namely, cinnamic aldehyd, ascorbic acid and hesperidin. This theoretical investigation predicts the biological activities of mixtures between cinnamon and ascorbic acid and between cinnamon and hesperidin based on already proven values for these molecules. The strength of the intermolecular interactions is evaluated in term of energy decomposition of the total interaction energy Delta E(int)between molecules, which are mainly governed by electrostatic interactions. The HOMO-LUMO gaps explain that the possible charge transfer interactions that take place within the molecules are responsible for the molecular reactivity of the studied molecules. The chemical hardness, the chemical potential and the electrophilicity indexes are good indicators for biological activities showing their improvement to that of cinnamon itself. The mixture of hesperidin and cinnamon could be an excellent blood thinner with the regard to its polarity’s enhancement.
First author: Latsch, L, Electronegativity and location of anionic ligands drive yttrium NMR for molecular, surface and solid-state structures,
CHEMICAL SCIENCE, 11, 6724, (2020)
Abstract: Yttrium is present in various forms in molecular compounds and solid-state structures; it typically provides specific mechanical and optical properties. Hence, yttrium containing compounds are used in a broad range of applications such as catalysis, lasers and optical devices. Obtaining descriptors that can provide access to a detailed structure-property relationship would therefore be a strong base for the rational design of such applications. Towards this goal,Y-89 (100% abundant spin 1/2 nucleus), is associated with a broad range of NMR chemical shifts that greatly depend on the coordination environment of Y, rendering(89)Y NMR an attractive method for the characterization of yttrium containing compounds. However, to date, it has been difficult to obtain a direct relationship between(89)Y chemical shifts and its coordination environment. Here, we use computational chemistry to model the chemical shift of a broad range of Y(iii) molecular compounds with the goal to reveal the underlying factors that determine the(89)Y chemical shift. We show through natural chemical shift (NCS)-analysis that isotropic chemical shifts can easily help to distinguish between different types of ligands solely based on the electronegativity of the central atom of the anionic ligands directly bound to Y(iii). NCS-analysis further demonstrates that the second most important parameter is the degree of pyramidalization of the three anionic ligands imposed by additional neutral ligands. While isotropic chemical shifts can be similar due to compensating effects, investigation of the chemical shift anisotropy (CSA) enables discriminating between the coordination environment of Y.
First author: Deb, AKS, DFT and MD simulation supplemented experiments for isotopic fractionation of zinc compounds using a macrocyclic crown ether appended polymeric resin,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 14682, (2020)
Abstract: Isotope effect is a quantum mechanical phenomenon and thus poses a challenge for the separation of isotopes of an element of interest, especially for heavy elements. Isotopic fractionation of zinc is also quite difficult and challenging but is necessitated due to various applications of its isotopes ranging from nuclear medicine to nuclear power reactors. Here, we developed the dibenzo-18-crown-6 (DB18C6) ether-functionalized poly(methacrylic acid) (PMA) resin by exploiting the ion and isotope recognition ability of the crown ether using DFT/MD simulations followed by experiments for isotopic fractionation of zinc. The PMADB18C6 adsorbent was prepared and suitably characterized. Both computational and experimental findings demonstrate that the adsorption and isotope separation of zinc with PMADB18C6 are due to the molecular recognition effect of the “O” dipole of the crown ether. Furthermore, both MD simulations and experiments suggest Langmuir type adsorption isotherms. The adsorption of Zn(2+)ions on the PMA resin is predicted to be endothermic, whereas it is exothermic on the PMADB18C6 resin, as revealed from the experimentally observed enthalpy change. A small scale fixed bed column study was demonstrated to test the scale-up application. The values of the experimental separation factors: 1.0013 for 66/64 and 1.0027 for 68/64 confirm the computationally predicted results of 1.00088 and 1.0010, respectively, thus establishing the combined strength of the theory and experiments for the identification of efficient fractionating agents for a complex quantum isotope effect which eventually helps in planning further experiments in view of medicinal and technological applications of zinc isotopes.
First author: Shu, CC, A family of lead clusters with precious metal cores,
NATURE COMMUNICATIONS, 11, 14682, (2020)
Abstract: Gold nanoparticles have been used for centuries, both for decoration and in medical applications. More recently, many of the major advances in cluster chemistry have involved well-defined clusters containing tens or hundreds of atoms, either with or without a ligand shell. In this paper we report the synthesis of two gold/lead clusters, [Au8Pb33](6-) and [Au12Pb44](8-), both of which contain nido [Au@Pb-11](3-) icosahedra surrounding a core of Au atoms. Analogues of these large clusters are not found in the corresponding Ag chemistry: instead, the Ag-centered nido icosahedron, [Ag@Pb-11](3-), is the only isolated product. The structural chemistry, along with the mass spectrometry which shows the existence of [Au2Pb11](2-) but not [Ag2Pb11](2-), leads us to propose that the former species is the key intermediate in the growth of the larger clusters. Density functional theory indicates that secondary -type interactions between the [Au@Pb-11](3-) ligands and the gold core play a significant part in stabilizing the larger clusters. p id=Par Many Zintl ions with a single endohedrally encapsulated transition metal ion are known, but relatively few where clusters of two or more metals are present. Here, the authors report the synthesis and characterization of two clusters, [Au8Pb33](6-) and [Au12Pb44](12-), which contain Au-8 and Au-12 cores surrounded by Pb shells.
First author: Gholamian, F, Influence of high-electronegativity atoms on the Be-7 decay rate,
PHYSICAL REVIEW C, 102, 14682, (2020)
Abstract: First-principle calculations within the density-functional theory framework are used to study the effect of high electronegativity atoms on decay rate of the Be-7 nucleus. In this study, the electron-capture decay rate of the Be-7 nucleus is investigated in Be(OH)(2), BeF2, BeF3, BeF4, BeCl2, BeCl3, BeCl4, C-36, and C-60 species. It was found that the more decrease of the Be-7 decay rate was estimated in the BeF4 (2.04%) and BeCl4 (1.99%) relative to the Be metal. Furthermore, the half-life of 7Be is different in various positions within C-36 and C-60. The Be-7 half-life in Be-7@C-36 is greater than that in other fullerene compounds investigated, while the Be-7 half-life inside C-60 is smaller.
First author: Bernes, E, S 2p and P 2p Core Level Spectroscopy of PPT Ambipolar Material and Its Building Block Moieties,
JOURNAL OF PHYSICAL CHEMISTRY C, 124, 14510, (2020)
Abstract: The near-edge X-ray absorption fine structure (NEXAFS and X-ray photoelectron (XP) spectra of gas-phase 2,8-bis-(diphenylphosphoryl)dibenzo[b,d]thiophene (PPT) and triphenylphosphine oxide (TPPO) have been measured at the S and P L-II,L-III-edge regions. The time-dependent density functional theory (TDDFT) based on the relativistic two-component zeroth-order regular approximation approach has been used to provide an assignment of the experimental spectra, giving the contribution of the spin-orbit splitting and of the molecular-field splitting to the sulfur and phosphor binding energies. Computed XP and NEXAFS spectra agree well with the experimental measurements. In going from dibenzothiophene and TPPO to PPT, the nature of the most intense S 2p and P 2p NEXAFS features are preserved; this trend suggests that the electronic and geometric behaviors of the S and P atoms in the two building block moieties are conserved in the more complex system of PPT. This work enables us to shed some light onto the structure of the P-O bond, a still highly debated topic in the chemical literature. Since the S 2p and P 2p NEXAFS intensities provide specific information on the higher-lying localized sigma*(C-S) and sigma*(P-O) virtual MOs, we have concluded that P 3d AOs are not involved in the formation of the P-O bond. Moreover, the results support the mechanism of negative hyperconjugation, by showing that transitions toward sigma*(P-O) states occur at lower energies with respect to those toward it pi*(P-O) states.
First author: Herritsch, J, Influence of Ring Contraction on the Electronic Structure of Nickel Tetrapyrrole Complexes: Corrole vs Porphyrin,
ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY, 9, 14510, (2020)
Abstract: The influence of the contracted corrole macrocycle, in comparison to the larger porphyrin macrocycle, on the electronic structure of nickel was studied with X-ray and ultraviolet photoelectron spectroscopy (XPS, UPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Synthesis and in situ characterization of the Ni complexes of octaethylporphyrin (NiOEP) and hexaethyldimethylcorrole (NiHEDMC) were performed in ultra-high vacuum. XPS and NEXAFS spectra reveal a +2 oxidation state and a low-spin d(8)electron configuration of Ni in both complexes, despite the formal trianionic nature of the corrole ligand. UPS, in combination with density functional theory (DFT) calculations, support the electronic structure of a Ni(II) corrole with a pi-radical character of the ligand. The NEXAFS spectra also reveal differences in the valence electronic structure, which are attributed to the size mismatch between the small Ni(II) center and the larger central cavity of NiOEP. Analysis of the gas-phase structures shows that the Ni-N bonds in NiOEP are 4%-6% longer than those in NiHEDMC, even when NiOEP adopts a ruffled conformation. The individual interactions that constitute the Ni-ligand bond are altogether stronger in the corrole complex, according to bonding analysis within the energy decomposition analysis and the natural orbitals for chemical valence theory (EDA-NOCV).
First author: Ghosh, A, Anomaly in the stability of the hydroxides of icosagens (B and Al) and their noble gas (Xe and Rn) derivatives: a comparative study,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 14109, (2020)
Abstract: Motivated by the discovery of neutral noble gas hydrides, herein, we have explored the possibility of the existence of a novel class of neutral noble gas compounds, HNgBO, HNgOB, HNgAlO and HNgOAl (Ng = Xe and Rn), through the insertion of a Ng atom into the hydroxides of icosagens and their isomers, namely, HBO, HOB, HAlO and HOAl. Second-order Moller-Plesset perturbation theory (MP2), density functional theory (DFT), and coupled-cluster theory (CCSD(T))-based methods have been employed to investigate the structures, stabilities, energetics, harmonic vibrational frequencies, and charge distribution of the predicted molecules. The HXeBO, HXeOAl, HRnBO, HRnAlO and HRnOAl molecules are found to be thermodynamically stable with respect to all plausible 2-body and 3-body dissociation channels except the 2-body dissociation pathway, leading to the formation of global minimum products (Ng + HBO), (Ng + HOAl) and (Ng + HAlO). However, the very large activation energy barrier heights provide enough kinetic stability to the predicted metastable molecules, which in turn can prevent them from dissociating into the global minimum products. Between the HNgBO-HNgOB isomers, HNgBO is found to be more stable, where both HNgBO and the precursor molecule HBO are linear. On the other hand, HNgOAl is more stable between the HNgAlO-HNgOAl isomers, where the precursor molecule HOAl is bent and HNgOAl is linear in contradiction and in agreement with Walsh’s rule, respectively. Moreover, in contrast to the more stable HNgBO case, where the Ng atom is bonded with the icosagen atom, in the more stable HNgOAl, the Ng atom is connected to the chalcogen atom. All the detailed aforementioned analyses concerning the predicted molecules clearly indicate that a strong covalent bond exists between the H and Ng atoms, while an ionic interaction is found between the Ng and B atoms in HNgBO and Ng and O atoms in the HNgOAl molecules. In addition, the charge distribution and atoms-in-molecules (AIM) analyses are in agreement with the above-mentioned conclusion and also suggest that the predicted metastable HNgBO and HNgOAl molecules should essentially exist in the form of [HNg](+)[BO](-)and [HNg](+)[OAl](-), respectively. All the calculated results reported in this work indicate that it might be possible to prepare and characterize the predicted moleculesviasuitable experimental technique(s) under cryogenic conditions.
First author: Juwita, R, Osmium sensitizer with enhanced spin-orbit coupling for panchromatic dye-sensitized solar cells,
JOURNAL OF MATERIALS CHEMISTRY A, 8, 12361, (2020)
Abstract: Low-lying triplet metal-to-ligand charge transfer ((MLCT)-M-3) transitions of osmium complexes induced by spin-orbit coupling (SOC) are promising for extending the photocurrent response in dye-sensitized solar cells. In this study, we present a new osmium complex (CYC-33O), incorporating a 2-thiohexyl-3,4-ethylenedioxythiophene functionalized bipyridyl ancillary ligand to red-shift the absorption and enhance the absorbance of singlet and triplet metal-to-ligand charge transfer (1MLCT and (MLCT)-M-3) transitions. Time-dependent density functional theory (TDDFT) calculations show that the reinforced (MLCT)-M-1 and (MLCT)-M-3 transitions of CYC-33O are mainly from osmium to the 4,4′,4 ”-tricarboxy-2,’:6′,2 ”-terpyridine anchoring ligand, increasing the heterogeneous electron transfer between CYC-33O and TiO2. The device sensitized with CYC-33O exhibits panchromatic conversion beyond 1000 nm, yielding a photocurrent density of 19.38 mA cm(-2), which is much higher than those of the cells based on the ruthenium analogue (CYC-33R) and model osmium complex (Os-3) sensitizers.
First author: Du, WGH, A Water Molecule Residing in the Fe-a3(3+)center dot center dot center dot Cu-B(2+) Dinuclear Center of the Resting Oxidized as-Isolated Cytochrome c Oxidase: A Density Functional Study,
INORGANIC CHEMISTRY, 59, 8906, (2020)
Abstract: Although the dinuclear center (DNC) of the resting oxidized “as-isolated” cytochrome c oxidase (CcO) is not a catalytically active state, its detailed structure, especially the nature of the bridging species between the Fe-a3(3+) and Cu-B(2)+ metal sites, is still both relevant and unsolved. Recent crystallographic work has shown an extended electron density for a peroxide type dioxygen species (O1-O2) bridging the Fe-a3 and Cu-B centers. In this paper, our density functional theory (DFT) calculations show that the observed peroxide type electron density between the two metal centers is most likely a mistaken analysis due to overlap of the electron density of a water molecule located at different positions between apparent O1 and O2 sites in DNCs of different CcO molecules with almost the same energy. Because the diffraction pattern and the resulting electron density map represent the effective long-range order averaged over many molecules and unit cells in the X-ray structure, this averaging can lead to an apparent observed superposition of different water positions between the Fe-a3(3+) and Cu-B(2+) metal sites.
First author: Schutz, M, Contrasting Structure and Bonding of a Copper-Rich and a Zinc-Rich Intermetalloid Cu/Zn Cluster,
INORGANIC CHEMISTRY, 59, 9077, (2020)
Abstract: Reaction of the Cu(I) sources, [Cu-5](Mes) 5 and [((i)Dipp)CuOtBu] (Mes = mesityl; (i)Dipp = 1,3-bis(2,6-diisopropylphenyl)-1H-imidazol-2-ylidene) with the Zn(I) complex [Zn-2](Cp*)(2) leads to a mixture of intermetallic Cu/Zn clusters with a distribution of species that is dependent on the stoichiometric ratio of the reactants, the reaction time, as well as the temperature. Systematic and careful investigation of the product mixtures rendered the isolation of two new clusters possible, i.e., the Znrich, red cluster 1, [CuZn10](Cp*)(7) = [Cu(ZnZnCp*)(3)(ZnCp*)(4)], as well as the Cu-rich, dark-green cluster 2 [Cu10Zn2](Mes)(6)(Cp*)(2). Structure and bonding of these two species was rationalized with the help of density functional theory calculations. Whereas 1 can be viewed as an 18-electron Cu center coordinated to four ZnCp* and three ZnZnCp* one-electron ligands (with some interligand bonding interaction), compound 2 is better to be described as a six-electron superatom cluster. This unusual electron count is associated with a prolate distortion from a spherical superatom structure. This unexpected situation is likely to be associated with the ZnCp* capping units that offer the possibility to strongly bind to the top and the bottom of the cluster in addition to the bridging mesityl ligands stabilizing the Cu core of the cluster.
First author: Jung, CK, Properties and Structural Arrangements of the Electrode Material CuDEPP during Energy Storage,
ENERGY TECHNOLOGY, 8, 9077, (2020)
Abstract: Devices for electrical energy storage need to provide high energy yields and output power, guaranteeing at the same time safety, low costs, and long operation times. The porphyrin CuDEPP [5,15-bis(ethynyl)-10,20-diphenylporphinato] copper(II) is a promising electrode material for various battery systems both as anode and cathode. While its functionality has been demonstrated experimentally, there is no atomistic information as to why CuDEPP expresses these interesting properties or how the incorporation of ions affects its structure so far. To answer these questions, CuDEPP is investigated using density functional theory (DFT). Starting with the smallest possible unit (i.e., a single molecule), the spatial dimensionality of the structure is successively increased by studying: 1) di- and trimers, 2) molecular stacking in a 1D chain, 3) extending these chains to planar CuDEPP sheets, and finally 4) a three-dimensionally extended polymer structure. Having thoroughly investigated the isolated properties of the CuDEPP material itself, afterward the insertion (or intercalation) of different ions (including Li, Mg, and Na) is studied, to understand the energetics, diffusion barriers, and structural changes (e.g., volume expansion) within the CuDEPP host material.
First author: Li, M, Changes in Structure and Reactivity of Ng(2)Encapsulated in Fullerenes: A Density Functional Theory Study,
FRONTIERS IN CHEMISTRY, 8, 9077, (2020)
Abstract: Noble gas can be no noble in certain situations from the perspective of structure, bonding, and reactivity. These situations could be extreme experimental conditions or others. In this contribution, we systematically investigate the impact of fullerene encapsulation on molecular structure and chemical reactivity of noble gas dimers (Ng(2)) in a few fullerene molecules. To that end, we consider He-2, Ne-2, and Ar(2)dimers encapsulated in C-50, C-60, and C(70)fullerenes. We unveil that bond distances of Ng(2)inside fullerene become substantially smaller and noble gas atoms become more electrophilic. In return, these noble gas dimers make fullerene molecules more nucleophilic. Using analytical tools from density functional theory, conceptual density functional theory, and information-theoretic approach, we appreciate the nature and origin of these structure and reactivity changes. The results and conclusions from this work should provide more new insights from the viewpoint of changing the perspectives of noble gas reactivity.
First author: Gruden, M, What is the nature of bonding in [Fe(CO)(3)(NO)](-)and [Fe(CO)(4)](2-)?,
THEORETICAL CHEMISTRY ACCOUNTS, 139, 9077, (2020)
Abstract: To shed new light on the electronic structure of [Fe(CO)(3)(NO)] over bar complex ion, DFT-based analysis of the nature of chemical bonding has been performed. For this purpose, the extended transition state energy decomposition analysis alongside the natural orbitals for chemical valence has been used and results are compared to the nature and the strength of the interactions in isoelectronic [Fe(CO)(4)](2-)complex ion. Based on orbital contribution to the interaction energy and charge flow between the fragments, the ground state can be best described as an open-shell singlet with zero formal oxidation state on iron and negative charge on the nitrosyl ligand. It is in agreement with the different nature of interactions when NO(+)and CO ligands are bonded to Fe(-II).
First author: Shapovalov, VV, Metal Plating of Friction Surfaces of the “Wheel-Rail” Pair,
JOURNAL OF FRICTION AND WEAR, 41, 338, (2020)
Abstract: It is shown that in conditions of significant increase of railway transport speeds, requirements for the safety of the friction-mechanical “wheel-rail” subsystem are increased. In order to solve the above problem, a method is proposed for metal plating “wheel-rail” friction surfaces by applying thin films of soft metal, for example, aluminum, with different values of hardness, on surfaces of rolling wheels and wheel ridges of locomotives. On the basis of quantum-chemical calculations, it has been proved that metal plating of the friction surfaces of the “wheel-rail” system provides a chemical bond between wheel steel and aluminum and the formation of a strong protective film. The performed bench tests of the “wheel-rail” model friction subsystem by methods of tribospectration identification of friction processes and dynamic monitoring of changes in elastic-dissipative bonds confirmed the formation of stable dynamic bonds in friction contact. The results of the research formed the basis of the creation of the algorithm of axial control of “wheel-rail” interaction processes at realization of forces of longitudinal and transverse creep, as well as at optimization of modes of vibrodynamic metal plating working surfaces of other tribosystems, of vehicles operating in heavy load-speed conditions of operation.
First author: Grabowski, SJ, Molecular Hydrogen as a Lewis Base in Hydrogen Bonds and Other Interactions,
MOLECULES, 25, 338, (2020)
Abstract: The second-order Moller-Plesset perturbation theory calculations with the aug-cc-pVTZ basis set were performed for complexes of molecular hydrogen. These complexes are connected by various types of interactions, the hydrogen bonds and halogen bonds are most often represented in the sample of species analysed; most interactions can be classified as sigma-hole and pi-hole bonds. Different theoretical approaches were applied to describe these interactions: Quantum Theory of ‘Atoms in Molecules’, Natural Bond Orbital method, or the decomposition of the energy of interaction. The energetic, geometrical, and topological parameters are analysed and spectroscopic properties are discussed. The stretching frequency of the H-H bond of molecular hydrogen involved in intermolecular interactions is considered as a parameter expressing the strength of interaction.
First author: Sarmah, A, Mechanical force-induced manipulation of electronic conductance in a spin-crossover complex: a simple approach to molecular electronics,
NANOSCALE ADVANCES, 2, 2907, (2020)
Abstract: The atomic-scale technological sophistication from the last half-decade provides new avenues for the atom-by-atom fabrication of nanostructures with extraordinary precision. This urges the appraisal of the fabrication scheme layout for a modular nanoelectronic device based on an individual molecular complex. The mechanical force-induced distortion to the metal coordination sphere triggers a low-spin (LS) to high-spin (HS) electronic transition in the complex. The controlled structural distortions (relative to a specific bond-angle) are deemed to be the switching parameter for the observed spin-transitions. Mechanical stretching is the key to engineering a spin-state switch in the proposed molecular device. The spin-dependent reversible variation in the electronic conductance concurrent to the unique spin-states can be understood from the state-of-the-art Nonequilibrium Green’s Function (NEGF) calculations. Combined with NEGF calculations, the DFT study further provides a qualitative perception of the electronic conductance in the two-terminal device architecture. From the transport calculations, there is also evidence of considerable fluctuation in the spin-dependent electronic conductance at the molecular junction with relative variations in the scattering limit. Subsequently, the present study shows significant advances in the transmission probabilities for the high-spin state of the Fe(ii) complex. The results empower the progress of nanoelectronics at the single molecule level.
First author: Toikka, YN, Cyanamides as pi-Hole Donor Components of Structure-Directing (Cyanamide)…Arene Noncovalent Interactions,
CRYSTAL GROWTH & DESIGN, 20, 4783, (2020)
Abstract: Crystallization of newly prepared copper(II) clusters [Cu4X6O(NCNMe2)(4)] (X = Cl 1 or Br 2) from toluene and styrene solutions afforded crystalline adducts 1.4PhMe, 1.4PhCH=CH2, 2.4PhMe, and 2.4PhCH=CH2, which were characterized by physicochemical methods including single-crystal X-ray diffraction. Inspection of the X-ray structures of (1-2).4(arene) and the appropriate Hirshfeld molecular surface analysis allowed the recognition of the previously unreported p-hole…arene interactions involving the cyanamide ligands. The presence of these interactions and their structure-directing character was confirmed theoretically by density functional theory calculations including molecular electrostatic potential, energy decomposition, and atoms-in-molecules analyses. The observed pi-hole…pi interaction between coordinated cyanamide and arene moieties in the adducts exhibits a contribution of pi-hole…sigma(C-H-aryl) interaction. Analysis of the Cambridge Structure Database revealed that the cyanamide center dot center dot center dot arene separations in the [Cu4X6O(NCNMe2)(4)].4(arene) systems are among the shortest found for all reported cyanamide structures.
First author: Zhang, YY, Theoretical study of the effect on halogen-substitution and molecular torsion angle on transport properties of pi Stack Hexabenzoperylenes and its derivatives,
SYNTHETIC METALS, 265, 4783, (2020)
Abstract: The halogen-substituted derivatives and the hexabenzoperylenes in organic semiconductors are theoretically studied using density functional theory. The effects of halogen-substitution on intramolecular energy-level transition and intermolecular stacking patterns are discussed by studying the charge transfer and spectral characteristics. The results show that halogen atom can effectively lower the frontier molecule orbitals energy and enhance the molecular stability. Not only the plane characteristics of the molecular structure been controlled, but also the semiconductors can be converted from p-type to n-type by changing the number and position of halogen-substituted atoms. The studies reveal that the molecular torsion angle can been used to effectively predict the transport level of molecules, and the halogen-substitution play an important part in the photochemical properties of molecules.
First author: Abo-Amer, A, Push-pull ligands and the oxidation of monomethylplatinum(II) complexes with oxygen or hydrogen peroxide,
INORGANICA CHIMICA ACTA, 507, 4783, (2020)
Abstract: A rare example of the oxidation of a monomethylplatinum(II) complex with dioxygen is reported, aided by an appended phenol group. The ligands X-2-HO-C6H3CH2N(CH2-2-C5H4N) 2 (L1, X = H; L2, X = 5-Cl; L3, X = 5-NO2; L4, X = 4-Me) react with [PtClMe(SMe2)2] to give the corresponding complexes [PtMe(kappa(3)-N,N’,N ”-L)]Cl in which L acts as a tridentate pincer ligand, binding through all three nitrogen donors with the phenol group not coordinated. When L = L1 – L3, the complexes react rapidly with hydrogen peroxide and slowly with dioxygen from air to give the corresponding platinum(IV) complexes [Pt(OH)Me(kappa(4)-N,N’,N ”,O-L-H)]Cl, in which the deprotonated phenol group is coordinated trans to the hydroxo ligand. The structures of three of these complexes are determined and all are shown to self-assemble with water molecules to form hydrogen-bonded supramolecular polymers. The mechanisms of the oxidation reactions are discussed.
First author: Das, P, Encapsulation of Mg-2 inside a C-60 cage forms an electride,
JOURNAL OF COMPUTATIONAL CHEMISTRY, 41, 1645, (2020)
Abstract: Density functional theory (DFT) based calculations have been carried out for the endohedral encapsulation of magnesium dimer inside fullerene, that is, Mg-2@C-60. It is observed that the minimum energy structure of the Mg-2@C-60 system is C-2h symmetry. The MgMg bond distance in the Mg-2@C-60 system is much shorter than that in the free Mg-2 and Mg-2(2+) ion. The formation of the endohedral Mg-2@C-60 system is thermochemically spontaneous in nature. The natural bond orbital (NBO) analysis showed the presence of an Mg-2(2+) fragment with an MgMg bond inside the C-60 cage. The electron density descriptors have identified the covalency in the MgMg bond. A non-nuclear attractor (NNA) is present in the middle of the two Mg-atoms. The bonding interaction between the Mg-2 and C-60 fragments is ionic in nature and the [Mg-2(2+)] and [C-60(2-)] represent the bonding pattern in the Mg-2@C-60 system. The designed endohedrally encapsulated system behaves as an electride.
First author: Usta, H, A hybridized local and charge transfer excited state for solution-processed non-doped green electroluminescence based on oligo(p-phenyleneethynylene),
JOURNAL OF MATERIALS CHEMISTRY C, 8, 8047, (2020)
Abstract: We herein report a new highly efficient green emissive hot-exciton molecule, 1,4-bis((4′-diphenylamino3-cyano-[1,1′-biphenyl]-4-yl)ethynyl)-2,5-bis(2-ethylhexyloxy)benzene (2EHO-TPA-CNPE) that consists of an extended D’-pi’-A-pi-D-pi-A-pi’-D’ molecular p-system with diphenylamino end units (D’) and ethynylene/phenylene spacers (pi/pi’). The new molecule exhibits high photoluminescence (PL) quantum efficiencies (Phi(PL) = 0.95 (solution) and 0.45 (spin-coated neat thin-film)), and a strong PL solvatochromic behavior revealing significant changes in excited state energies/characteristics (locally excited (LE) -> hybridized local and charge transfer (HLCT) – charge-transfer (CT)) depending on solvent polarity. Highly efficient (radiative exciton yield (eta(r)) = 50-59% >> 25%) green-emitting OLEDs were fabricated in a conventional device architecture by employing (non-)doped thin-films reaching a maximum current efficiency (CEmax) of 12.0 cd A(-1) and a maximum external quantum efficiency (EQE(max)) of 5.5%. The emission profile of the non-doped OLED has CIE 1976 (u’, v’) chromaticity coordinates of (0.10, 0.55) corresponding to a night vision imaging system (NVIS) compatible Green A region. 2EHO-TPA-CNPE-based OLED devices of industrial relevance were also fabricated by ink-jet printing the emissive layer and by fabricating an inverted architecture, which possessed respectable device performances of 2.4-6.1 cd A(-1). The solid-state solvation effect in OLED devices yields HLCT electronic behavior resulting in high Zr’s, which is confirmed by TDDFT to originate from energetically/spatially favorable reverse intersystem crossings (RISCs) (T-2/3 -> S-1). As a unique observation, delayed fluorescence due to this RISC was evident in the PL decay lifetime measurement with a ns-scale lifetime of similar to 10 ns. These results clearly allow a better understanding of the structure-photophysical property-electroluminescence relationships in this new class of oligo(p-phenyleneethynylene)-based hot-exciton molecules, and it could open up new opportunities for high-performance solution-processed optoelectronic/sensing applications.
First author: Komorovsky, S, NMR Spin-Spin Coupling Constants Derived from Relativistic Four-Component DFT Theory-Analysis and Visualization,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 5157, (2020)
Abstract: An unambiguous assignment of coupling pathways plays an important role in the description and rationalization of NMR indirect spin-spin coupling constants (SSCCs). Unfortunately, the SSCC analysis and visualization tools currently available to quantum chemists are restricted to nonrelativistic theory. Here, we present the theoretical foundation for novel relativistic SSCC visualization techniques based on analysis of the SSCC densities and the first-order current densities induced by the nuclear magnetic dipole moments. Details of the implementation of these techniques in the ReSpect program package are discussed. Numerical assessments are performed on through-space SSCCs, and we choose as our examples the heavy-atom Se-Se, Se-Te, and Te-Te coupling constants in three similar molecules for which experimental data are available. SSCCs were calculated at the nonrelativistic, scalar relativistic, and four-component relativistic density functional levels of theory. Furthermore, with the aid of different visualization methods, we discuss the interpretation of the relativistic effects, which are sizable for Se-Se, very significant for Se-Te, and cannot be neglected for Te-Te couplings. A substantial improvement of the theoretical SSCC values is obtained by also considering the molecular properties of a second conformation.
First author: Tholen, P, Semiconductive microporous hydrogen-bonded organophosphonic acid frameworks,
NATURE COMMUNICATIONS, 11, 5157, (2020)
Abstract: Herein, we report a semiconductive, proton-conductive, microporous hydrogen-bonded organic framework (HOF) derived from phenylphosphonic acid and 5,10,15,20-tetrakis[p-phenylphosphonic acid] porphyrin (GTUB5). The structure of GTUB5 was characterized using single crystal X-ray diffraction. A narrow band gap of 1.56eV was extracted from a UV-Vis spectrum of pure GTUB5 crystals, in excellent agreement with the 1.65eV band gap obtained from DFT calculations. The same band gap was also measured for GTUB5 in DMSO. The proton conductivity of GTUB5 was measured to be 3.00×10(-6)Scm(-1) at 75 degrees C and 75% relative humidity. The surface area was estimated to be 422m(2)g(-1) from grand canonical Monte Carlo simulations. XRD showed that GTUB5 is thermally stable under relative humidities of up to 90% at 90 degrees C. These findings pave the way for a new family of organic, microporous, and semiconducting materials with high surface areas and high thermal stabilities. Research in hydrogen-bonded organic frameworks (HOFs) has gained interest in recent years due to their facile design and synthesis but no semiconducting HOF has been reported to date. Here the authors report a thermally stable and proton-conductive organic semiconductor based on a porphyrin HOF.
First author: Li, XB, Theoretical study on structures of Am(III) carbonate complexes,
JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY, 325, 527, (2020)
Abstract: In order to elucidate the coordination structure and bonding properties between Am(III) and carbonate ion (CO32-), the geometric and electronic structures of the Am(III) carbonate complexes were systematically studied by scalar-relativistic density function theory. The bonding nature between Am atom and ligands was explored by the analyses of the natural bond orbital, quantum theory of atoms-in-molecules and electron localization function. These results indicate that the Am-O(c)bonds are sigma character with ionic interaction. Thermodynamic analysis shows that [Am(CO3)(3)(H2O)(2)](3-)was the most stable complex. This work can provide insight into the coordination and bonding nature of the Am(III) carbonate complexes.
First author: Hansen, T, Regioselectivity of Epoxide Ring-Openings via S(N)2 Reactions Under Basic and Acidic Conditions,
EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, 2020, 3822, (2020)
Abstract: We have quantum chemically analyzed the ring-opening reaction of the model non-symmetrical epoxide 2,2-dimethyloxirane under basic and acidic conditions using density functional theory at OLYP/TZ2P. For the first time, our combined activation strain and Kohn-Sham molecular orbital analysis approach have revealed the interplay of physical factors that control the regioselectivity of these chemical reactions. Ring-opening under basic conditions occurs in a regime of strong interaction between the nucleophile (OH-) and the epoxide and the interaction is governed by the steric (Pauli) repulsion. The latter steers the attack preferentially towards the sterically less encumbered C-beta. Under acidic conditions, the interaction between the nucleophile (H2O) and the epoxide is weak and, now, the regioselectivity is governed by the activation strain. Protonation of the epoxide induces elongation of the weaker (CH3)(2)C-alpha-O bond, and effectively predistorts the substrate for the attack at the sterically more hindered side, which goes with a less destabilizing overall strain energy. Our quantitative analysis significantly builds on the widely accepted rationales behind the regioselectivity of these ring-opening reactions and provide a concrete framework for understanding these indispensable textbook reactions.
First author: Ozawa, Y, Tetra- and hexanuclear copper(I) iminothiolate complexes: synthesis, structures, and solid-state thermochromic dual emission in visible and near-infrared regions,
CHEMICAL PAPERS, 74, 3717, (2020)
Abstract: Two new photoluminescent multinuclear Cu(I) cluster complexes supported by monoanionic bidentate ligandN-methylbenzimidazolethiolate (Me-bimt(-)), [Cu-n(Me-bimt)(n)] withn = 4 (1) and 6 (2), have been synthesized and structurally characterized by single-crystal X-ray diffraction analysis. For1and2, the Cu(I) ions and the Me-bimt(-)ligands construct a cubane-type {Cu4S4} and a hexagonal-prism {Cu6S6} frameworks, respectively. In the crystalline state, complexes1and2exhibit green (lambda(em) = 500 nm) and near-infrared (lambda(em) = 876 nm) emission, respectively, under UV irradiation (lambda(ex) = 365 nm) at room temperature. Both crystals reveal temperature-dependent dual emission below 200 K: complex1emits in the visible wavelength region (lambda(em) = 493 and 542 nm) and complex2in the visible to near-infrared wavelength region (lambda(em) = 752 and 973 nm) which are attributed to multiple photoexcited states at the cluster frameworks with distinct metal nuclearity.
First author: Berezin, AS, A copper(i) bromide organic-inorganic zwitterionic coordination compound with a new type of core: structure, luminescence properties, and DFT calculations,
NEW JOURNAL OF CHEMISTRY, 44, 9858, (2020)
Abstract: A new organic-inorganic Cu(i) bromide complex based on triple protonated tris(2-pyridyl)phosphine (HPy)(3)P, [(HPy)(3)PCu2Br5] (1), has been synthesized by a straightforward reaction in solution or by modification of the [Cu2Br2(Py3P)(2)] complex using hydrobromic acid. At 77 K, the solid complex1exhibits near infra-red photoluminescence with lambda(max)= 680 nm related to(3)(M + X)LCT. The emission of1rapidly decreases with increasing temperature and is absent at 200 K due to thermal quenching with a small energy barrier Delta E approximate to 590 cm(-1). The photophysical results are in good agreement with the TD-DFT calculations showing that in the ground state the cuprophilic interaction between copper ions is absent in spite of the short CuMIDLINE HORIZONTAL ELLIPSISCu distance. After annealing of complex1at 120 degrees C, photoluminescence occurred with lambda(max)= 640 nm at 300 K. Complex1exhibits a luminescence response in ammonia gas consisting of the appearance of luminescence with lambda(max)= 520 nm followed by the gradual enhancement of the luminescence intensity.
First author: Huang, LJ, DFT study of gas adsorbing and electronic properties of unsaturated nanoporous graphene,
MOLECULAR SIMULATION, 46, 853, (2020)
Abstract: The interaction sensitivity of unsaturated nanoporous graphene toward a series of gas molecules (O-2, NO, NO(2)and CO) was investigated by the first-principle calculation based on density functional theory. The most stable geometry configuration, adsorption energy, charge transfer, and electronic density of states of the complexes were thoroughly investigated, in which the gases were adsorbed on the unsaturated nanoporous graphene. It was found that all the gas molecules are strongly chemisorbed on the unsaturated nanoporous graphene. The enhanced adsorption energy and large charge transfer demonstrated a strong chemical adsorption interaction of gas molecules with the nanoporous graphene sheet. However, the electronic properties of the unsaturated nanoporous graphene are not very sensitive to all the gas molecules. It is suggested that the unsaturated nanoporous graphene might be suitable for sensing O(2)and CO, while it could not be used for the NO and NO2.
First author: Scheiner, S, Pnicogen Bonds Pairing Anionic Lewis Acid with Neutral and Anionic Bases,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 4998, (2020)
Abstract: The complexation process between anionic ZCl(4)(-) (Z = P, As, Sb) and neutral NCH and pyridine, as well as the CN- anion, is studied in both the gas phase and aqueous solution by high-level ab initio calculations. Despite the absence of a positively charged sigma-hole on ZCl(4)(-), a pnicogen bond (ZB) holds all of these complexes together. The dimerization induces the ZCl(4)(-) to rearrange internally from a see-saw to a square geometry. The complexation process is endothermic for both HCN and CN- in the gas phase but for different reasons. The approach of CN- to ZCl(4)(-) must overcome anion-anion Coulomb repulsion, while HCN is a much weaker base. The intermediate nucleophilicity of pyridine leads to an exothermic dimerization reaction despite the deformation of the ZCl(4)(-) structure. The dimers must traverse an energy barrier in order to dissociate. Formation of the dianionic -NC center dot center dot center dot ZCl(4)(-) complex becomes exothermic in aqueous solution. Complexation with HCN remains endothermic in water, although less so, and the exothermicity of ZB formation with pyridine is enhanced by solvation.
First author: Pandeya, P, Theoretical Analysis of Optical Absorption Spectra of Parallel Nanowire Dimers and Dolmen Trimers,
JOURNAL OF PHYSICAL CHEMISTRY C, 124, 13495, (2020)
Abstract: Plasmonic nanoparticles are well-known for their properties of electromagnetic field enhancement and surface spectroscopy enhancement. We used the plasmon hybridization method and group theory to study parallel dimers and dolmen trimers of Ag-n (n = 4, 6, and 10) nanoparticles. Interactions between the plasmon modes were studied with decreasing interparticle separation distances. Time-dependent density functional calculations are performed on the structures using the BP86/DZ level of theory. In dimers, the decrease of the interparticle separation blue-shifts the longitudinal peak, but the transverse peak position is not affected significantly. In trimers, a new peak is also observed as a shoulder of the longitudinal peak. When the interparticle separation reduces to 0.6 nm in dimers and trimers, a new peak emerges between the longitudinal and transverse peaks. This new peak red-shifts and increases in intensity upon further decreasing the interparticle separation. Analysis of the transition densities and symmetries for the respective peaks shows that the new peak arises from a charge transfer excitation.
First author: Szatylowicz, H, Substituted adenine quartets: interplay between substituent effect, hydrogen bonding, and aromaticity,
RSC ADVANCES, 10, 23350, (2020)
Abstract: Adenine, one of the components of DNA/RNA helices, has the ability to form self-organizing structures with cyclic hydrogen bonds (A(4)), similar to guanine quartets. Here, we report a computational investigation of the effect of substituents (X = NO2, Cl, F, H, Me, and NH2) on the electronic structure of 9H-adenine and its quartets (A(4)-N1, A(4)-N3, and A(4)-N7). DFT calculations were used to show the relationships between the electronic nature of the substituents, strength of H-bonds in the quartets, and aromaticity of five- and six-membered rings of adenine. We demonstrated how the remote substituent X modifies the proton-donating properties of the NH(2)group involved in the H-bonds within quartets and how the position of the substituent and its electronic nature affect the stability of the quartets. We also showed the possible changes in electronic properties of the substituent and aromaticity of adenine rings caused by tetramer formation. The results indicate that the observed relationships depend on the A(4)type. Moreover, the same substituent can both strengthen and weaken intermolecular interactions, depending on the substitution position.
First author: Bauer, S, Oxidation State Assignments in the Organoplatinum One-Electron Redox Series [(N boolean AND N)PtMes(2)](n),n= +,0, -,2-,
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 2020, 2435, (2020)
Abstract: The neutral complexes [((NN)-N-<^>)PtMes(2)], (NN)-N-<^>= bis(1-methyl-2-imidazolyl)ketone (bik) or N,N’-disubstituted 1,2-bis-iminoacenaphthenes (R-BIAN), Mes = mesityl, were obtained and characterized as Pt(II)species with planar N(2)PtC(2)configuration and charge transfer transitions in the visible. Reversible one-electron reduction produces radical anion complexes with the spin predominantly localized in the (NN)-N-<^> ligand, according to EPR, UV/Vis-IR spectroelectrochemistry, DFT and TD-DFT studies. Reversible one-electron oxidation was also possible, attributed to the steric and electronic influence from the mesityl ligands. The EPR silent cation [(bik)PtMes(2)](+)was characterized by UV/Vis-NIR spectroscopy and TD-DFT calculations as a system with spin density contributions from Pt (31 %) and two mesityl groups (69 %).
First author: Kang, GJ, Efficient structural modification of electron-withdrawing substituents on Pt(II) complexes for red emitters: A theoretical study,
APPLIED ORGANOMETALLIC CHEMISTRY, 34, 2435, (2020)
Abstract: In this study, the electronic structures and optical properties of a cyclometalated Pt(II) complex (M1) and a series of derivatives (M1-F, M1-CF3, and M1-CN) with electron-withdrawing substituents (-F, -CF3, and -CN) at the carbazole moiety were theoretically investigated by density functional theory and time-dependent density functional theory. The calculation results reveal that these Pt complexes display deep red phosphorescence emission above?= 640 nm. When the(3)MLCT/pi -> pi* to triplet metal-centered(3)MC/d-d state decay mechanism is taken into consideration, the nonradiative decay rate constant (k(nr)) decreased in the order M1 > M1-CF3> M1-F > M1-CN. The and kr values of M1-F are similar with those of M1, however the Knr rate ofM1-F is larger than that of M1. M1-F is expected to have improved quantum yields. Moreover, through the analyses of the HOMO/LUMO level and triplet energy, it is found that the introduction of -F and -CN substituents in M1 results in efficient energy transfer from the host material 4,4 ‘-N,N ‘-dicarbazole-biphenyl to these complexes. In view of the electroluminescent applications in organic light-emitting diodes, M1-F can serve as efficient deep-red guest materials with improved electron injection and transport ability.
First author: Mokrane, Z, Coordination’s preference and electronic structure of N-heterocyclic carbene-monometallic complexes: DFT evaluation of sigma-bonding and pi-backbonding interactions,
THEORETICAL CHEMISTRY ACCOUNTS, 139, 2435, (2020)
Abstract: The geometrical parameters, the electronic structures and the nature of the chemical bonding for complexes of the type (NqMes)M[Cl(CO)(2)] (NqMes=naphtoquinone-annulated NHC ligand and M=V, Mn, Re, Co, Rh, Cu) which possess even electron counts have been investigated at the BP86 and B3LYP levels of theory using orbital molecular and energy decomposition analyses. The coordination of the six-membered ring is strongly disfavoured (structures A), while the structures B1 and B2 which differ by the orientation of the M[Cl(CO)(2)] unit are in competition with regard to the metal’s nature and the spin state. The carbene-metal bonds are governed chiefly by electrostatic attractions contributing 65-75% of the bonding attractive interactions. The carbene-metal bonds are strong in electron-moderately rich Re element and weak in electron-rich Cu metal. In the most cases, orbital interactions are more important in symmetrical species than in the unsymmetrical ones, which are mainly described by sigma -bonding with the pi -backbonding part less than 20%.
First author: Parida, R, Unique magnetic shielding and bonding in Pnicogen nortricyclane Zintl clusters,
CHEMICAL PHYSICS LETTERS, 749, 2435, (2020)
Abstract: Using first principle calculations, in-depth bonding and aromaticity pattern of bare anionic nortricyclane, E-7(3-)(E = P, As, Sb, and Bi) Zintl clusters have been explored. A detailed topological analysis reveals that every cluster comprises of nine 2c-2e sigma-bond with an occupation number of 1.96-1.99 vertical bar e vertical bar. We find an impressive covalence in the E-7(3-) cluster which decreases down the group from P-7(3-) to Bi-7(3-). The nucleus independent chemical shift (NICS) foretell about the aromatic property of the Zintl cluster which is also decreasing along the group. In addition, the response with respect to external magnetic field of the nucleus independent shielding tensor was obtained to explore the possible formation of the shielding cone behavior.
First author: Petrus, E, Unveiling a Photoinduced Hydrogen Evolution Reaction Mechanism via the Concerted Formation of Uranyl Peroxide,
INORGANIC CHEMISTRY, 59, 8353, (2020)
Abstract: We present a density functional theory study for the photochemical water oxidation reaction promoted by uranyl nitrate upon sunlight radiation. First, we explored the most stable uranyl complex in the absence of light. The reaction in a dark environmen proceeds through the condensation of uranyl monomers to form dimeric hydroxo-bridged species, which is the first step toward a hydrogen evolution reaction (HER). We found a triplet-state-driven mechanism that leads to the formation of uranyl peroxide and hydrogen gas. To describe in detail this reaction path, we characterized the singlet and triplet low-lying states of the dimeric hydroxo-bridged species, including minima, transition states, minimal energy crossing points, and adiabatic energies. Our computational results provide mechanistic insights that are in good agreement with the experimental data available.
First author: Bacha, RUS, Actinyl-Modified g-C3N4 as CO2 Activation Materials for Chemical Conversion and Environmental Remedy via an Artificial Photosynthetic Route,
INORGANIC CHEMISTRY, 59, 8369, (2020)
Abstract: With the reported CO2 activation for the oxidation of benzene to phenol (-ENE -> -OL) by the graphitic carbon nitride g-C3N4 (CN) via an artificial photosynthetic route as inspiration, high-valent actinyls (An(m)O(2))(n+) (An = U, Np, Pu; m = VI, V; n = 2, 1) have been introduced for its further modification. Our calculations indicate thermodynamic spontaneity in the feasibility of g-C3N4-(An(m)O(2))(n+) (CN-An(m)) formation. The magnificent structural and electronic properties of CN-An(m) are utilized for CO2 activation in terms of the rarely studied -ENE -> -OL conversion. The calculated free energies show that most steps of the catalytic cycle are favored by CN-An(m) complexes. The first step (carbamate formation) is slightly endothermic in all cases, where CN-U is 0.51 eV higher than CN and CN-Pu is -0.01 eV lower. All benzene addition reactions release energy, with that for CN-U being the lowest. The phenolate formation is favored by some actinyl complexes over CN, and CN-U is only 0.23 eV higher. The phenol release (resulting in formamide complexes) and CO desorption are exothermic for all CN-An(m). The overall process suggests the improved catalytic performance of actinyl-modified CN materials, and the slightly depleted uranyl-carbon nitride could be one of the promising catalysts.
First author: Sebesta, F, QM and QM/MM umbrella sampling MD study of the formation of Hg(II)-thymine bond: Model for evaluation of the reaction energy profiles in solutions with constant pH,
JOURNAL OF COMPUTATIONAL CHEMISTRY, 41, 1509, (2020)
Abstract: The formation of the Hg-N3(T) bond between the 1-methylthymine (T) molecule and the hydrated Hg2+ cation was explored with the combined quantum mechanics/molecular mechanics (QM/MM) method including Free Energy Perturbation corrections. The thermodynamic properties were determined in the whole pH range, when these systems were explicitly investigated and considered as the QM part: (1) T + [Hg(H2O)(6)](2+), (2) T + [Hg(H2O)(5)(OH)](+), (3) T + Hg(H2O)(4)(OH)(2), and (4) N3-deprotonated T + Hg(H2O)(4)(OH)(2). The MM part contained only solvent molecules and counterions. As a result, the dependence of Gibbs-Alberty reaction free energy on pH was obtained along the reaction coordinate. We found that an endoergic reaction in acidic condition up to pH < 4-5 becomes exoergic for a higher pH corresponding to neutral and basic solutions. The migration of the Hg2+ cation between N3 and O4/2 positions in dependence on pH is discussed as well. For the verification, DFT calculations of stationary points were performed confirming the qualitative trends of QM/MM MD simulations and NMR parameters were determined for them.
First author: Wang, JN, Wide band gap pyromellitic diimides for photo stable n-channel thin film transistors,
JOURNAL OF MATERIALS CHEMISTRY C, 8, 7344, (2020)
Abstract: This study reports two novel n-channel pyromellitic diimide (PyDI) derivatives, PyDI-BOCF(3)and PyDI-BSCF3, with particularly wide energy gaps of 3.56 eV and 3.49 eV in the solid state, respectively, which induce the investigations of their charge transport properties, photostabilities and thin-film transparency of organic field-effect transistors (OFETs) in this work. Although PyDI-BOCF(3)and PyDI-BSCF(3)exhibit similar two-dimensional (2D) lamellar packing motifs, PyDI-BSCF(3)demonstrates stronger electronic couplings than those of PyDI-BSCF3, suggesting it may show better electrical performance in OFETs. As predicted, PyDI-BSCF(3)shows an electron mobility of 0.09 cm(2)V(-1)s(-1)at a deposition temperature of 70 degrees C in ambient air, which is higher than the electron mobility of 0.058 cm(2)V(-1)s(-1), obtained for PyDI-BOCF3. In contrast, PyDI-BOCF(3)exhibits better thermal stability of mobility, which was maintained at similar to 0.056 cm(2)V(-1)s(-1)after increasing the deposition temperature from room temperature (RT) to 70 degrees C. More importantly, it is worth mentioning that the wide energy gaps of PyDI-BOCF(3)and PyDI-BSCF(3)lead to excellent photostability in OFETs at illumination conditions and optical transparency in the visible range even better than that of DPh-BTBT thin films on transparent glass and flexible PET substrates.
First author: Bista, D, A ligand-induced homojunction between aluminum-based superatomic clusters,
NANOSCALE, 12, 12046, (2020)
Abstract: A superatomic molecule formed by joining two metallic clusters linked by an organometallic bridge can behave like a semiconductor and the addition of ligands can induce a significant energy level shift across an inter-cluster homojunction. This shift is induced by theN-ethyl-2-pyrrolidone ligands, and the placement of the ligands strongly affects the direction of the dipole moment, including the case where the dipole moment is parallel to the cluster interface. This computational study provides an alternative strategy for constructing nanometer-scale electronic interfaces between clusters mimicking semiconductor motifs. The semiconducting features in the PAl(12)clusters emerge from the grouping of the quantum states in a confined nearly free electron gas that creates a substantial energy gap. An organometallic Ge(CH3)(2)(CH2)(2)bridge links the clusters while maintaining the cluster’s electronic shell structure. The amount of level shifting between the bridged clusters can be changed by controlling the number of ligands. Attaching multiple ligands can result in a broken gap energy alignment in which the HOMO level of one cluster is aligned with the LUMO level of the other bridged cluster. Furthermore, the singly ligated bridged superatomic molecule is found to exhibit promising features to separate the electron-hole pairs for photovoltaic applications.
First author: Jian, JW, Proton affinities of pertechnetate (TcO4-) and perrhenate (ReO4-),
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 12403, (2020)
Abstract: The anions pertechnetate, TcO4-, and perrhenate, ReO4-, exhibit very similar chemical and physical properties. Revealing and understanding disparities between them enhances fundamental understanding of both. Electrospray ionization generated the gas-phase proton bound dimer (TcO4-)(H+)(ReO4-). Collision induced dissociation of the dimer yielded predominantly HTcO(4)and ReO4-, which according to Cooks’ kinetic method indicates that the proton affinity (PA) of TcO(4)(-)is greater than that of ReO4-. Density functional theory computations agree with the experimental observation, providing PA[TcO4-] = 300.1 kcal mol(-1)and PA[ReO4-] = 297.2 kcal mol(-1). Attempts to rationalize these relative PAs based on elementary molecular parameters such as atomic charges indicate that the entirety of bond formation and concomitant bond disruption needs to be considered to understand the energies associated with such protonation processes. Although in both the gas and solution phases, TcO(4)(-)is a stronger base than ReO4-, it is noted that the significance of even such qualitative accordance is tempered by the very different natures of the underlying phenomena.
First author: Ferraro, F, Relativistic effects on the energetic stability of Pb-5 clusters,
THEORETICAL CHEMISTRY ACCOUNTS, 139, 12403, (2020)
Abstract: In this work, we study isomers of small lead clusters with five atoms, Pb-5, at different levels of approximation namely Scalar-Relativistic (SR), Scalar-Relativistic plus Spin-Orbit coupling interaction (SR + SO) and four-component DiracHartree-Fock (4c-DHF), in order to analyze the effects of relativity in these heavy molecular systems. The exploration of potential energy surface (PES) with a genetic algorithm produces four possible equilibrium structures, and we find that when Relativity is included at a major level in calculations, the global minimum energy structure changes from S4 isomer with D 3h symmetry at SR level to S1 isomer with C-2 symmetry at 4c-DHF level; this change is related to modifications in the electronic structure and geometric parameters. We explain this significant result using two methodologies in order to analyze the electronic structure and strength of chemical bonds, like energy decomposition analysis (EDA) and Quantum Theory Atoms In Molecules (QTAIM). On the one hand, in the framework of EDA, results at SR + SO level show significant differences on the steric and orbital interactions compared with SR ones, with which the S1 isomer is more stable than S4; this means that SO effects stabilize the interactions on S1 isomer more than S4. The HOMO-LUMO gap also shows a drastic reduction due to the SO effects on S4 isomer, while for the other systems remains unchanged. This result can be associated with the lower stability of S4 isomer with respect to the others when Relativity is included at a major level. On the other hand, in the framework of QTAIM, calculations with SR + SO scheme show the formation of two new critical points compared with SR for S1 isomer, which is reflected in a greater stability of this system.
First author: Gordon, MS, Novel Computer Architectures and Quantum Chemistry,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 4557, (2020)
Abstract: Electronic structure theory (especially quantum chemistry) has thrived and has become increasingly relevant to a broad spectrum of scientific endeavors as the sophistication of both computer architectures and software engineering has advanced. This article provides a brief history of advances in both hardware and software, from the early days of IBM mainframes to the current emphasis on accelerators and modern programming practices.
First author: Xiong, XG, Anion Photoelectron Spectroscopy and Theoretical Study of HAuCN and [HAuCN](-): Spin-Orbit Coupling and Low-Lying Excited States,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 4712, (2020)
Abstract: We report a study of the electronic structures and chemical bonding of gaseous [HAuCN](-) and the corresponding neutral molecule using photoelectron spectroscopy and relativistic quantum chemistry calculations. The electron affinity of the neutral HAuCN is reported to be 4.75 eV for the first time. The low-lying excited states of neutral molecule are observed and assigned according to the calculations utilizing a sophisticated electron correlation method incorporating both the scalar and spin-orbit relativistic effects. Our theoretical calculations suggest the geometry will be distorted from linear structure to the bent during the process of detaching one electron from the anion. Various chemical bonding analyses based on theoretical calculations have been performed for the titled complexes, and the apparent covalent natures of interactions between gold and the studied ligands have been verified.
First author: Linnebank, PR, Regioselective Hydroformylation of Internal and Terminal Alkenes via Remote Supramolecular Control,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 8214, (2020)
Abstract: Regioselective catalytic transformations using supramolecular directing groups are increasingly popular as it allows for control over challenging reactions that may otherwise be impossible. In most examples the reactive group and the directing group are close to each other and/or the linker between the directing group is very rigid. Achieving control over the regioselectivity using a remote directing group with a flexible linker is significantly more challenging due to the large conformational freedom of such substrates. Herein, we report the redesign of a supramolecular Rh-bisphosphite hydroformylation catalyst containing a neutral carboxylate receptor (DIM pocket) with a larger distance between the phosphite metal binding moieties and the DIM pocket. For the first time regioselective conversion of internal and terminal alkenes containing a remote carboxylate directing group is demonstrated. For carboxylate substrates that possess an internal double bond at the Delta-9 position regioselectivity is observed. As such, the catalyst was used to hydroformylate natural monounsaturated fatty acids (MUFAs) in a regioselective fashion, forming of an excess of the 10-formyl product (10-formyl/9-formyl product ratio of 2.51), which is the first report of a regioselective hydroformylation reaction of such substrates.
First author: Chen, TT, Observation of Transition-Metal-Boron Triple Bonds in IrB2O- and ReB2O-,
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 59, 15260, (2020)
Abstract: Multiple bonds between boron and transition metals are known in many borylene (:BR) complexes via metal d(pi)-> BR back-donation, despite the electron deficiency of boron. An electron-precise metal-boron triple bond was first observed in BiB2O- [Bi equivalent to B-B equivalent to O](-) in which both boron atoms can be viewed as sp-hybridized and the [B-BO](-) fragment is isoelectronic to a carbyne (CR). To search for the first electron-precise transition-metal-boron triple-bond species, we have produced IrB2O- and ReB2O- and investigated them by photoelectron spectroscopy and quantum-chemical calculations. The results allow to elucidate the structures and bonding in the two clusters. We find IrB2O- has a closed-shell bent structure (C-s, (1)A ‘) with BO- coordinated to an Ir equivalent to B unit, (-OB)Ir equivalent to B, whereas ReB2O- is linear (C-infinity v, (3)sigma(-)) with an electron-precise Re equivalent to B triple bond, [Re equivalent to B-B equivalent to O](-). The results suggest the intriguing possibility of synthesizing compounds with electron-precise M equivalent to B triple bonds analogous to classical carbyne systems.
First author: Li, N, Mechanistic Insights into Ni-Catalyzed Difunctionalization of Alkenes Using Organoboronic Acids and Organic Halides: Understanding Remarkable Substrate-Dependent Regioselectivity,
ORGANOMETALLICS, 39, 2057, (2020)
Abstract: Transition metal catalyzed difunctionalization reactions of alkenes using simple chemical feedstocks are powerful strategies for the synthesis of valuable compounds and materials. Density functional theory (DFT) calculations reported in the present paper reveal detailed mechanistic insight and the origin of the substrate-dependent regioselectivity in the titled reactions. Computational results demonstrate that these reactions are generally composed of several steps including oxidative addition, carbonickelation, H-shift/transmetalation, and reductive elimination. Among these steps, the key one responsible for the regioselectivity depends upon the organic halides utilized. Natural bond orbital (NBO) analysis, energy decomposition analysis (EDA), and buried volume calculations indicate that steric effect is a common contributor of the regioselectivity, while other energy terms, such as electrostatic interaction, have significant and even dominant effects on the specific regioselectivity. Furthermore, the key reason for successfully suppressing Heck and/or Suzuki products lies in that the formation of Heck and/or Suzuki products is thermodynamically less favorable. Comparison of the total reaction barriers of the rate-limiting step (combined transmetalation and reductive elimination processes) demonstrates that the electron-induced effect of various organic halides significantly causes the different bonding ability between Ni atom and allyl moiety. As a result, transmetalation and reductive elimination processes made distinct contributions to reducing the total activation free energy of the rate-limiting step of various difunctionalized reactions.
First author: Huaulme, Q, Photochromic dye-sensitized solar cells with light-driven adjustable optical transmission and power conversion efficiency,
NATURE ENERGY, 5, 468, (2020)
Abstract: Semi-transparent photovoltaics only allow for the fabrication of solar cells with an optical transmission that is fixed during their manufacturing resulting in a trade-off between transparency and efficiency. For the integration of semi-transparent devices in buildings, ideally solar cells should generate electricity while offering the comfort for users to self-adjust their light transmission with the intensity of the daylight. Here we report photochromic dye-sensitized solar cells (DSSCs) based on dyes with a donor-pi-conjugated-bridge-acceptor structure where the pi-conjugated bridge is substituted by a diphenyl-naphthopyran photochromic unit. DSSCs show change in colour and self-adjustable light transmittance when irradiated and demonstrate a power conversion efficiency up to 4.17%. The colouration-decolouration process is reversible and these DSSCs are stable over 50 days. We also report semi-transparent photo-chromo-voltaic mini-modules (active area of 14 cm(2)) exhibiting a maximum power output of 32.5 mW after colouration.
First author: Yu, R, Structure and bonding of molecular stirrers with formula B7M2- and B8M2 (M = Zn, Cd, Hg),
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 12312, (2020)
Abstract: In this work, we systematically explored clusters with formula B7M2- and B8M2 (M = Zn, Cd, Hg). The putative global minima are formed by an M-2 dimer and a disk-shaped boron wheel. Moreover, the chemical bonding analysis revealed that charge transfer from the metal atoms to the boron motifs resulted in (B-7)(3-)(M-2)(2+) and (B-8)(2-)(M-2)(2+) complexes with double (sigma + pi) aromatic boron wheels and a single bond for the metallic dimer. Above all, the computed rotational barriers of the M-M fragment with respect to the boron disk and molecular dynamics simulations indicate a virtually barrierless spin, resembling a magnetic stirrer on a baseplate.
First author: Blanco, M, Tuning on and off chemical- and photo-activity of exfoliated MoSe2 nanosheets through morphologically selective “soft” covalent functionalization with porphyrins,
JOURNAL OF MATERIALS CHEMISTRY A, 8, 11019, (2020)
Abstract: The covalent functionalization of 2D transition metal dichalcogenides (TMDCs) with organic molecules exploiting the thiol conjugation approach is still a very controversial topic. We have synthesized thiolated tetraphenyl porphyrins, with and without hydroxyl groups in the phenyl substituents, which have been covalently attached to chemically exfoliated MoSe2 (ce-MoSe2) nanosheets. XPS and FTIR have revealed the formation of sulfo-selenide bridges, specifically on the edges of the ce-MoSe2, as confirmed by first principles calculations. The electrocatalytic activity of TMDCs in the hydrogen evolution reaction (HER) has been investigated after conjugation with the organic molecules. The HER activity is suppressed or enhanced according to the presence of mildly acidic hydroxyl groups in the attached molecules, since they provide a local proton relay boosting the production of H-2, especially under mildly acidic conditions (pH = 4.3). Moreover, the well-known light-harvesting properties of porphyrins have been exploited to improve significantly the light-assisted HER activity. Due to the formation of a type II heterojunction or Schottky contact between the molecules and the 2H and 1T MoSe2 nanosheets respectively, the hybrid materials show an improvement of the HER onset potential under illumination compared to the pristine material, without activity loss for more than 16 h.
First author: Sarkar, S, Computational and experimental evidence of N-H center dot center dot center dot pi and cooperative pi(N)center dot center dot center dot pi* interactions in pyrrole center dot center dot center dot benzene and pyrrole center dot center dot center dot ethylene heterodimers at low temperatures,
JOURNAL OF MOLECULAR STRUCTURE, 1209, 11019, (2020)
Abstract: The interaction between pyrrole with benzene and ethylene was investigated using matrix isolation infrared spectroscopy and ab initio computations. Computations indicated the global minimum structure of pyrrole-benzene and pyrrole-ethylene heterodimers are stabilized by pi center dot center dot center dot sigma* (N-H center dot center dot center dot pi) and a cooperative pi(N)center dot center dot center dot pi* interactions. The present work for the first time, reports that pyrrole benzene hetero- dimer is stabilized by both N-H center dot center dot center dot pi and pi(N)center dot center dot center dot pi* interactions, where the latter induces a partial stacking in contrast to the T-shaped structure predicted by previous experimental and theoretical reports. To provide experimental proof, the heterodimers were trapped in N-2 and Ar matrixes, and probed through infrared spectroscopy. Natural bond orbital (NBO) and energy decomposition (ED) analyses revealed that the heterodimers were stabilized by charge-transfer, electrostatic and dispersion interactions. To further understand and delineate the existence of pi(N)center dot center dot center dot pi* interaction (which results from partial pi-stacking), computations were performed on the heterodimers of pyrrole with several acyclic and cyclic pi-donors.
First author: Narsaria, AK, Performance of TDDFT Vertical Excitation Energies of Core-Substituted Naphthalene Diimides,
JOURNAL OF COMPUTATIONAL CHEMISTRY, 41, 1448, (2020)
Abstract: We have evaluated the performance of various density functionals, covering generalized gradient approximation (GGA), global hybrid (GH) and range-separated hybrid (RSH), using time dependent density functional theory (TDDFT) for computing vertical excitation energies against experimental absorption maximum (lambda(max)) for a set of 10 different core-substituted naphthalene diimides (cNDI) recorded in dichloromethane. The computed excitation in case of GH PBE0 is most accurate while the trend is most systematic with RSH LCY-BLYP compared to lambda(max). We highlight the importance of including solvent effects for optimal agreement with the lambda(max). Increasing the basis set size from TZ2P to QZ4P has a negligible influence on the computed excitation energies. Notably, RSH CAMY-B3LYP gave the least error for charge-transfer excitation. The poorest agreement with lambda(max) is obtained with semi-local GGA functionals. Use of the optimally-tuned RSH LCY-BLYP* is not recommended because of the high computational cost and marginal improvement in results.
First author: Ma, H, PyCDFT: A Python package for constrained density functional theory,
JOURNAL OF COMPUTATIONAL CHEMISTRY, 41, 1859, (2020)
Abstract: We present PyCDFT, a Python package to compute diabatic states using constrained density functional theory (CDFT). PyCDFT provides an object-oriented, customizable implementation of CDFT, and allows for both single-point self-consistent-field calculations and geometry optimizations. PyCDFT is designed to interface with existing density functional theory (DFT) codes to perform CDFT calculations where constraint potentials are added to the Kohn-Sham Hamiltonian. Here, we demonstrate the use of PyCDFT by performing calculations with a massively parallel first-principles molecular dynamics code, Qbox, and we benchmark its accuracy by computing the electronic coupling between diabatic states for a set of organic molecules. We show that PyCDFT yields results in agreement with existing implementations and is a robust and flexible package for performing CDFT calculations. The program is available at .
First author: Grabowski, SJ, The Nature of Triel Bonds, a Case of B and Al Centres Bonded with Electron Rich Sites,
MOLECULES, 25, 1859, (2020)
Abstract: The second-order MOller-Plesset perturbation theory calculations with the aug-cc-pVTZ basis set were performed on complexes of triel species: BCl3, BH3, AlCl3, and AlH3 acting as Lewis acids through the B or Al centre with Lewis base units: NCH, N-2, NH3, and Cl- anion. These complexes are linked by triel bonds: B/Al…N or B/Al…Cl. The Quantum Theory of ‘ Atoms in Molecules ‘ approach, Natural Bond Orbital method, and the decomposition of energy of interaction were applied to characterise the latter links. The majority of complexes are connected through strong interactions possessing features of covalent bonds and characterised by short intermolecular distances, often below 2 angstrom. The BCl3 center dot center dot center dot N-2 complex is linked by a weak interaction corresponding to the B…N distance of similar to 3 angstrom. For the BCl3 center dot center dot center dot NCH complex, two configurations corresponding to local energetic minima are observed, one characterised by a short B…N distance and a strong interaction and another one characterised by a longer B center dot center dot center dot N distance and a weak triel bond. The tetrahedral triel structure is observed for complexes linked by strong triel bonds, while, for complexes connected by weak interactions, the structure is close to the trigonal pyramid, particularly observed for the BCl3…N-2 complex.
First author: Miranda-Rojas, S, Exploration of the Interaction Strength at the Interface of Anionic Chalcogen Anchors and Gold (111)-Based Nanomaterials,
NANOMATERIALS, 10, 1859, (2020)
Abstract: Nowadays, the use of sulfur-based ligands to modify gold-based materials has become a common trend. Here, we present a theoretical exploration of the modulation of the chalcogenides-gold interaction strength, using sulfur, selenium, and tellurium as anchor atoms. To characterize the chalcogenide-gold interaction, we designed a nanocluster of 42 gold atoms (Au-42) to model a gold surface (111) and a series of 60 functionalized phenyl-chalcogenolate ligands to determine the ability of electron-donor and -withdrawing groups to modulate the interaction. The analysis of the interaction was performed by using energy decomposition analysis (EDA), non-covalent interactions index (NCI), and natural population analysis (NPA) to describe the charge transfer processes and to determine data correlation analyses. The results revealed that the magnitudes of the interaction energies increase following the order S < Se < Te, where this interaction strength can be augmented by electron-donor groups, under the donor-acceptor character the chalcogen-gold interaction. We also found that the functionalization inmetaposition leads to better control of the interaction strength than theorthosubstitution due to the steric and inductive effects involved when functionalized in this position.
First author: Taping, JJE, Influence of Varying Functionalization on the Peroxidase Activity of Nickel(II)-Pyridine Macrocycle Catalysts: Mechanistic Insights from Density Functional Theory,
COMPUTATION, 8, 1859, (2020)
Abstract: Nickel(II) complexes of mono-functionalized pyridine-tetraazamacrocycles (PyMACs) are a new class of catalysts that possess promising activity similar to biological peroxidases. Experimental studies with ABTS (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), substrate) and H2O2(oxidant) proposed that hydrogen-bonding and proton-transfer reactions facilitated by their pendant arm were responsible for their catalytic activity. In this work, density functional theory calculations were performed to unravel the influence of pendant arm functionalization on the catalytic performance of Ni(II)-PyMACs. Generated frontier orbitals suggested that Ni(II)-PyMACs activate H(2)O(2)by satisfying two requirements: (1) the deprotonation of H(2)O(2)to form the highly nucleophilic HOO-, and (2) the generation of low-spin, singlet state Ni(II)-PyMACs to allow the binding of HOO-. COSMO solvation-based energies revealed that the O-O Ni(II)-hydroperoxo bond, regardless of pendant arm type, ruptures favorably via heterolysis to produce high-spin (S= 1) [(L)Ni3+-O center dot](2+)and HO-. Aqueous solvation was found crucial in the stabilization of charged species, thereby favoring the heterolytic process over homolytic. The redox reaction of [(L)Ni3+-O center dot](2+)with ABTS obeyed a 1:2 stoichiometric ratio, followed by proton transfer to produce the final intermediate. The regeneration of Ni(II)-PyMACs at the final step involved the liberation of HO-, which was highly favorable when protons were readily available or when the pK(a)of the pendant arm was low.
First author: Cuevas-Flores, MD, Interaction and Reactivity of Cisplatin Physisorbed on Graphene Oxide Nano-Prototypes,
NANOMATERIALS, 10, 1859, (2020)
Abstract: The physical adsorption of cisplatin (CP) on graphene oxide (GO) and reduced graphene oxide (rGO) is investigated at the DFT level of theory by exploiting suitable molecular prototypes representing the most probable adsorbing regions of GO and rGO nano-structures. The results show that the CP binding energy is enhanced with respect to that for the interaction with pristine graphene. This is due to the preferential adsorption of the drug in correspondence of the epoxy and hydroxy groups located on GO basal plane: an energy decomposition analysis of the corresponding binding energy reveals that the most attractive contribution comes from the electrostatic attraction between the -NH3 ends of CP and the oxygen groups on (r)GO, which can be associated with hydrogen bonding effects. Moreover, it is found that the reactivity of the physically adsorbed CP is practically unaltered being the free energy variation of the first hydrolysis reaction almost matching that of its free (unadsorbed drug) counterpart. The reported results suggest that the CP physical adsorption on GO and rGO carriers is overall feasible being an exergonic process in aqueous solution. The CP adsorption could facilitate its solubility and transport in water solutions, exploiting the high hydrophilicity of the peripheral carboxylic groups located on the edge of the GO and rGO nano-structures. Moreover, the the higher affinity of CP with respect to the oxidized sites suggests a possible dependence of drug loading and release on pH conditions, which would highly facilitate its specific delivery.
First author: Aray, Y, Exploring the nature of the interactions between the molecules of the sodium dodecyl sulfate and water in crystal phases and in the water/vacuum interface,
HELIYON, 6, 1859, (2020)
Abstract: The nature of the interaction between the molecules of the sodium dodecyl sulfate surfactant forming two crystal phases, one anhydrous, NaC12H25O4S and the other, NaC12H25O4S center dot H2O, hydrated with one water molecule for unit cell, has been studied in detail using the quantum theory of atoms in molecules and a localized electron detector function. It was found that for the anhydrous crystal, the head groups of the surfactant molecules are linked into a head-to-head pattern, by a bond path network of Na-O ionic bonds, where each Na+ atom is attached to four SO4- groups. For the hydrated crystal, in addition to these four bonds for Na+, two additional ones appear with the oxygen atoms of the water molecules, forming a bond paths network of ionic Na-O bonds, that link the Na+ atoms with the SO4- groups and the H2O molecules. Each H2O molecule is bonded to two SO4- groups via hydrogen bonds, while the SO4- groups are linked to a maximum of four Na+ atoms. The phenomenon of ag- gregation of the sodium dodecyl sulfate molecules at the liquid water/vacuum interface was studied using NVT molecular dynamics simulations. We have found that for surfactant aggregates, the Na+ ions are linked to a maximum of three SO4- groups and three water molecules that form Na-O bonds. Unlike hydrated crystal, each of the O atoms that make these Na-O bonds is linked to only one Na+ ion. Despite these differences, like the crystal phases, the surfactant molecules tend to form a head-to-head network pattern of ionic Na-O bonds that link their heads. The present results indicate that the clustering of anionic surfactant at the water/vacuum interface is a consequence of the electrostatic alignment of the cationic and anionic groups as occurs in the crystalline phases of sodium dodecyl sulfate.
First author: Orozco-Ic, M, Delocalization in Substituted Benzene Dications: A Magnetic Point of View,
CHEMISTRYOPEN, 9, 657, (2020)
Abstract: In this work, the induced magnetic field is analyzed for a series of substituted benzenes dications with formula C6R62+(R=I, At, SeH, SeCH3, TeH, TeCH3), presumably exhibiting concentric aromaticity. Previous studies concluded that in the carbon skeleton, just pi-electrons are delocalized. However, our results support that both the sigma- and pi-electrons are delocalized in the carbon skeleton, combined with a sigma-delocalization in the external ring. The role of the relativistic effects in these dications is discussed in detail.
First author: Conradie, J, Computational DFT data related to the redox behaviour of tris(beta-diketonato)ruthenium(III) compounds,
DATA IN BRIEF, 30, 657, (2020)
Abstract: The data presented in this paper are related to the research article titled “Redox Behaviour of [Ru(beta-diketonato)(3)] Compounds”[1]. This paperpresents structuraland energydata obtained from the density functional theory (DFT) computations. The energy data is related to experimentally obtained redox potential values. Various relationships are presented for the Ru-III/II and Ru-III/IV redox couples, involving both their experimental redox data as well as DFT calculated data, such as frontier orbital energies (E-HOMO and E-LUMO) and calculated Mulliken electronegativity values.
First author: Pieters, BJGE, Mechanism of biomolecular recognition of trimethyllysine by the fluorinated aromatic cage of KDM5A PHD3 finger,
COMMUNICATIONS CHEMISTRY, 3, 657, (2020)
Abstract: The understanding of biomolecular recognition of posttranslationally modified histone proteins is centrally important to the histone code hypothesis. Despite extensive binding and structural studies on the readout of histones, the molecular language by which posttranslational modifications on histone proteins are read remains poorly understood. Here we report physical-organic chemistry studies on the recognition of the positively charged trimethyllysine by the electron-rich aromatic cage containing PHD3 finger of KDM5A. The aromatic character of two tryptophan residues that solely constitute the aromatic cage of KDM5A was fine-tuned by the incorporation of fluorine substituents. Our thermodynamic analyses reveal that the wild-type and fluorinated KDM5A PHD3 fingers associate equally well with trimethyllysine. This work demonstrates that the biomolecular recognition of trimethyllysine by fluorinated aromatic cages is associated with weaker cation-pi interactions that are compensated by the energetically more favourable trimethyllysine-mediated release of high-energy water molecules that occupy the aromatic cage.
First author: Baskaran, S, Catalytic mechanism and bonding analyses of Au-Pd single atom alloy (SAA): CO oxidation reaction,
SCIENCE CHINA-MATERIALS, 63, 993, (2020)
Abstract: Single-atom catalysts (SACs), including metal-metal-bonded bimetallic ones named single-atom alloys (SAAs), have aroused significant interest in catalysis. In this article, the catalytic mechanism and bonding analysis of CO oxidation reaction on bimetallic gold-palladium (Au-Pd) model of single atom alloy Au37Pd1 are investigated by using quantum chemical calculations. The molecular geometries and adsorbate/substrate binding energies of CO@Au-Pd, O-2@Au-Pd and CO/O-2@Au-Pd configurations are identified. The core-shell structure is confirmed to be the most stable structure for Au-Pd SAA, where the Pd atom prefers to situate at the core site. Charge transfer from the Pd atom to the Au atoms has been confirmed to stabilize the structure. According to the binding energy and chemical bonding analysis, both CO and O-2 prefer to bind to the Pd atom at the hex site with low coordination number. The formation of new co-adsorption species is identified, in which vertical and parallel bridging adsorptions of CO and O-2 on the Au-Pd bonds are observed. CO oxidation on Au-Pd SAA is found to be feasible with low energy barriers and follows the Langmuir-Hinshewood (L-H) mechanism. Our work offers insights into the significant role of single atom of the SAAs in catalytic reactions and can provide evidence for designing new SAAs with high-performance catalytic activities.
First author: Shreiber, ST, Syntheses, solution behavior, and computational bond length analyses of trifluoromethyl and perfluoroethyl cuprate salts,
JOURNAL OF FLUORINE CHEMISTRY, 234, 993, (2020)
Abstract: Heteroleptic cuprate salts of the form [X-Cu-Y][(SIMes)(2)Cu] (SIMes = 1,3-dimesitylimidazolin-2-ylidene, X and Y = permutations of Cl, CF3, C2F5) were generated by equilibrating mixtures of [(SIMes)Cu-X] and [(SIMes)CuY] in CD2Cl2 solvent. The solubility features of the cuprates relative to the neutral species permitted the structural characterizations of new cuprates, including the first example of a mixed fluoroalkylated cuprate [(CF3)Cu(C2F5)][(SIMes)(2)Cu]. Computational studies (DFT and CCSD(T)) of fluoroalkylated cuprates generate Cu-C distances that are shorter than those in hydrocarbon analogues – a trend that in some cases may conflict with crystallographically determined values.
First author: Swarts, PJ, Solvent and substituent effect on electrochemistry of ferrocenylcarboxylic acids,
JOURNAL OF ELECTROANALYTICAL CHEMISTRY, 866, 993, (2020)
Abstract: The redox properties of six ferrocenyl carboxylic acids (1-6) in dichloromethane and acetonitrile are compared. The fonnal reduction potential of Fe of the ferrocenyl group in these carboxylic acids occur ca. 0.1 V more positive in DCM than in CH3CN. The carboxylic group is directly connected to ferrocenyl, or by an ethene group, or by an alkyl chain of varying length. The length of the alkyl chain separating the two groups affected the formal reduction potential of Fe of the ferrocenyl group. The formal reduction potential was also affected by the electron-withdrawing carbonyl group. The extent of the effect depended on whether the carbonyl group was directly bound to a ferrocenyl moiety or, isolated by an se hybridized carbon atom backbone (-CH2-CH2-) or a non-isolated sp(3) hybridized carbon atom backbone (-CH = CH-). The results obtained were further validated by density functional theory (DFT) calculations on ferrocenyl carboxylic acids (1-6) as well as selected substituted ferrocenyl compounds from literature. A linear relationship between the fonnal reduction potential of substituted ferrocenes and DFT calculated HOMO energies were obtained.
First author: Shen, L, A study on the modification of azole rings to regulate the transition dipole moment, MLCT and T-1 structural distortion of 2-pyridyl-azole copper (I) complexes for high phosphorescence performance,
ORGANIC ELECTRONICS, 81, 993, (2020)
Abstract: Heterocyclic ligands based on 2-pyridyl-azole, have become some of the ideal ligands for metal complexes due to their flexible structure and wide wavelength tunability. In this paper, a series of Cu((NN)-N-boolean AND) ((PP)-P-boolean AND) complexes are studied by density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The results indicate that the combination of incorporation of N atoms and substitution of electron donor-acceptor groups can effectively control the type and the proportion of the lowest triplet states (T-1) phosphorescent transition. A higher matching degree between the effective spin-orbit coupling (SOC) matrix elements and the transition dipole moments (The S-n state has both effective SOC and large transition dipole moments of S-n -> S-0 transition) brings about a larger transition dipole moment M-T(a) of T-1(a) -> S-0 transition, and further results in the fastest radiative decay rate (k(r)) for complex 2, although the main transition of which is internal-ligand charge transfer (ILCT). In addition, the non-radiative decay rate (k(nr)) of complex 2 is lower than other complexes of series 3 (the reorganization energy produced by in-plane bending vibration of C-H bond in six-membered ring is larger than complex 2), so this complex has the highest quantum yield. Overall, the above analyses illustrate that despite the participation of Cu(I) in transition as an indispensable factor for the radiative transition, the higher component ratio does not necessarily lead to a faster k(r). In addition, it is also essential to have a well-matched large transition dipole moments of the singlet states S-n -> S-0 transition involved in the effective SOC. Consequently, in the development of the 2-pyridyl-azole Cu(I) luminescent materials, the high quantum yield materials can be designed by adjusting the substituent at C-3 position and the strength of electron donor-acceptor groups at C-5 position to balance the charge transfer transition modes.
First author: Dumpala, RMR, Aquatic interaction of uranium with two naturally ubiquitous pyrazine compounds: Speciation studies by experiment and theory,
CHEMOSPHERE, 249, 993, (2020)
Abstract: The present studies interpret the speciation of uranyl (UO22+) with the most ubiquitous class of natural species named pyrazines in terms of stability, speciation and its identification, thermodynamics, spectral properties determined by a range of experimental techniques and further evidenced by theoretical insights. UO22+ forms ML and ML2 kind of species with a qualitative detection of ML3 species, while the ESI-MS identified the formation of all the complexes including ML3. Both the ligands act as bidentate chelators with a difference in ring size and coordinating atoms in the complex formed. The ML3 complexes involve the third ligand participation as monodentate via carboxylate only due to the restricted coordination number and space around the UO22+ ion to accommodate three ligand molecules in its primary coordination sphere. All the complexes are found to be endothermic and purely entropy driven formations. The complex formations showed redshift in the absorption spectra and the shift was further enhanced from ML to ML2 formation. The UO22+ ion redox properties are used to explore the redox potential and heterogeneous electron-transfer kinetic parameters as a function of pH and concentration of UO22+ in presence of pyrazine carboxylates. Interestingly, the cyclic voltammograms identified the ligands also as redox sensitive. The theoretical calculation gave inputs to understand the complex formation at the molecular level with major emphasis on geometry optimization, energetics, bonding parameters, molecular orbital diagrams and bond critical point analyses. The experimental observations in combination with theoretical addendum provided detailed knowledge on the interaction of UO22+ with pyrazine-2-carboxylate and pyrazine-2,3-dicarboxylates.
First author: Pustula, K, Oxetan-3-one pyrolysis from the perspective of multireference approaches,
COMPUTATIONAL AND THEORETICAL CHEMISTRY, 1179, 993, (2020)
Abstract: The objective of this research is to provide a theoretical explanation of the thermal decomposition of the oxetan3-one molecule. This process may proceed via at least two distinctive reaction pathways. One of them leads to the formation of ketene and formaldehyde and the other to oxirane and carbon monoxide. We examined, on the basis of multireference approaches, the reaction profiles of oxetan-3-one pyrolysis in terms of Gibb’s free energy. The geometries and thermodynamical parameters of the transition states were obtained and compared to the known experimental facts and calculations. We also show that as some transition states have broken spinsymmetry character in DFT calculations, incorporating multireference approaches seems to be necessary. On the basis of CASPT2 modelling we were able to explain the fundamental experimental finding that the reaction leading to oxirane and carbon monoxide becomes more and more pronounced in higher temperatures and rationalized in terms of entropic contributions.
First author: Li, YC, The differences and cooperativity between Ge (Sn)center dot center dot center dot O tetrel bonds and X (X = F, Cl, Br, and I)center dot center dot center dot O halogen bonds,
CHEMICAL PHYSICS, 534, 993, (2020)
Abstract: In recent years, intermolecular weak interactions especially tetrel bond and halogen bond have aroused widespread concern. However, as far as we know, the intermolecular weak interactions composed of TF3X (T = Ge, Sn; X = F, Cl, Br, and I) and H2O molecules are rarely studied. What’s interesting is that TF3X molecule as Lewis acid can form tetrel and halogen bonding with H2O molecule, respectively. In this paper, a theoretical study of the complexes formed by TF3X and H2O molecules has been performed at the MP2/aug-cc-pVTZ (PP) level. The results show that SnF3X molecule can form a stronger tetrel bond than that of GeF3X molecule, both SnF3X and GeF3X molecules form the halogen bond with similar strength. Energy decomposition indicates that these studied T (T = Ge, Sn)center dot center dot center dot O tetrel bonds and X (X = F, Cl, Br, and I)center dot center dot center dot O halogen bonds are connected by electrostatic interactions. In ternary systems, T center dot center dot center dot O tetrel bond and X center dot center dot center dot O halogen bond show anti-cooperativity.
First author: Majid, A, First principles study of structural, electronic and magnetic properties of transition metals doped SiC monolayers for applications in spintronics,
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 503, 993, (2020)
Abstract: First principles investigations were carried out to explore the prospects of using silicon carbide (SiC) monolayers in spintronics. The structural, electronic and magnetic properties of Ti, V, Cr, Mn and Fe doped SiC monolayers were studied in detail in framework of density functional theory (DFT). These dopants changed the band structure of SiC by introducing gap states and thus altered the electronic and magnetic character of the host. The results indicated that Ti did not produce any magnetic state whereas Mn and Cr exhibited ferromagnetism (FM), and V as well as Fe displayed anti-ferromagnetism (AFM) as stable configurations in the matrix. The calculated values of magnetic moments are 0 mu(B), 1.24 mu(B), 2.37 mu(B), 3.01 mu(B), and 2.21 mu(B )for dopants Ti, V, Cr, Mn and Fe respectively in the host. The dopants reveal 3d-2p hybridization with exchange interactions taking place through charge hopping. The analysis indicated that magnetic exchange takes place in Mn:SiC and Fe:SiC via superexchange whereas in Cr:SiC via double exchange interactions. The Mn doped SiC monolayer appeared to offer highest Curie temperatures with half metallic nature and highest magnetic moment which points to its suitability as potential diluted magnetic semiconductor for different spintronic applications.
First author: Majid, A, Theoretical study of (TM)FeO3 (TM=3d transition metals) molecular clusters,
JOURNAL OF NANOPARTICLE RESEARCH, 22, 993, (2020)
Abstract: Time-dependent density functional theory-based calculations were carried out to comprehensively investigate the structural, electronic, and optoelectronic properties of series of molecular clusters (TM)FeO3 (with TM = 3d elements). The structures were studied at different levels of theory to explore the electronic energy levels, charge transfer analysis, and UV-Vis excitation spectra. In order to predict viable charge states and ordering of TM moments, the calculations were performed at different spin values to consider low-spin and high-spin configurations. The magnetic moments of the series of clusters in most stable configuration increased for the clusters with Sc to Fe and then decreased to Zn. The calculated values of magnetic moment and binding energy of the clusters show nearly a reciprocal trend. The substitution of TM, in order of increasing atom number from Sc to Zn, appeared to modify the optical response and shifted the absorption features of the clusters from ultraviolet to the visible region. The clusters CoFeO3, NiFeO3, CuFeO3, and ZnFeO3 are found suitable for coating on TiO2 and ZnO to increase light absorption in visible region. Owing to the findings of this study, the series of the clusters are predicted to be used in photocatalytic water splitting, photoanode material in dye-sensitized solar cell, supercapacitors, and electrode materials.
First author: Zhang, J, Porphyrin dyes bearing heterocyclic anchoring groups for dye-sensitized solar cells with enhanced efficiency and long-term stability: Further optimization of champion porphyrin dye SM315,
APPLIED SURFACE SCIENCE, 513, 993, (2020)
Abstract: In order to further enhance the long-term stability of porphyrin-based dye- sensitized solar cells (DSSCs) without losing their high efficiency, a serious of porphyrin sensitizers based on the champion dye SM315 but differing in the anchoring groups were theoretically investigated. Compared with SM315 with carboxylic acid anchoring groups, our results demonstrate that porphyrin dyes with hydantoin and barbituric acid anchoring groups exhibit stronger adsorption stability because of the larger orbital interactions between the dye and the semiconductor surface, according to the energy decomposition analysis. Furthermore, porphyrin dyes with these two heterocyclic anchoring groups can also display a superior or comparable charge separation and injection, light harvesting ability and conduction band energy shift, which are the key factors that affect the performance of DSSCs. These results highlight the great potential hydantoin and barbituric acid anchoring groups possess as effective alternatives to carboxylic acid anchoring groups for porphyrin dyes, which could yield an enhanced efficiency and long-term stability and worthy of being experimentally synthesized.
First author: Dasgupta, N, ReaxFF molecular dynamics simulations of electrolyte-water systems at supercritical temperature,
JOURNAL OF CHEMICAL PHYSICS, 152, 993, (2020)
Abstract: We have performed ReaxFF molecular dynamics simulations of alkali metal-chlorine pairs in different water densities at supercritical temperature (700 K) to elucidate the structural and dynamical properties of the system. The radial distribution function and the angular distribution function explain the inter-ionic structural and orientational arrangements of atoms during the simulation. The coordination number of water molecules in the solvation shell of ions increases with an increase in the radius of ions. We find that the self-diffusion coefficient of metal ions increases with a decrease in density under supercritical conditions due to the formation of voids within the system. The hydrogen bond dynamics has been interpreted by the residence time distribution of various ions, which shows Li+ having the highest water retaining capability. The void distribution within the system has been analyzed by using the Voronoi polyhedra algorithm providing an estimation of void formation within the system at high temperatures. We observe the formation of salt clusters of Na+ and K+ at low densities due to the loss of dielectric constants of ions. The diffusion of ions gets altered dramatically due to the formation of voids and nucleation of ions in the system.
First author: Heywood, VL, Observations of tetrel bonding between sp(3)-carbon and THF,
CHEMICAL SCIENCE, 11, 5289, (2020)
Abstract: We report the direct observation of tetrel bonding interactions between sp(3)-carbons of the supramolecular synthon 3,3-dimethyl-tetracyanocyclopropane (1) and tetrahydrofuran in the gas and crystalline phase. The intermolecular contact is established via sigma-holes and is driven mainly by electrostatic forces. The complex manifests distinct binding geometries when captured in the crystalline phase and in the gas phase. We elucidate these binding trends using complementary gas phase quantum chemical calculations and find a total binding energy of -11.2 kcal mol(-1) for the adduct. Our observations pave the way for novel strategies to engineer sp(3)-C centred non-covalent bonding schemes for supramolecular chemistry.
First author: Tosato, M, Toward novel sulphur-containing derivatives of tetraazacyclododecane: synthesis, acid-base properties, spectroscopic characterization, DFT calculations, and cadmium(ii) complex formation in aqueous solution,
NEW JOURNAL OF CHEMISTRY, 44, 8337, (2020)
Abstract: Macrocyclic ligands obtained by N-functionalization of 1,4,7,10-tetraazacyclododecane (cyclen) have been widely studied due to their remarkable complexing properties toward a variety of transition metals and lanthanides. Despite a plethora of cyclen-based molecules described in the literature, ones bearing sulphur-containing functional groups have been almost ignored. Herein, a novel series of derivatives with hanging sulphide side-arms have been investigated: 1,4,7,10-tetrakis[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane (DO4S), 1,4,7,tris[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane (DO3S), 1,4,7,tris[2-(methylsulfanyl)ethyl]-10-methylacetamido-1,4,7,10-tetraazacyclododecane (DO3SAm), and 1,7,bis[2-(methylsulfanyl)ethyl]-4,10-diacetic-1,4,7,10-tetraazacyclododecane (DO2A2S). 1,4,7,10-Tetra-n-buthyl-1,4,7,10-tetraazacyclododecane (DOT-n-Bu) was included as well in this study for comparison purposes. These compounds have been synthesized and then experimentally and theoretically characterized. Their protonation constants (pK(a)) have been determined at 25 degrees C in 0.15 M aqueous NaNO3 and in 0.15 M aqueous tetramethylammonium chloride by potentiometric titrations and partly by UV-vis spectrophotometric measurements. Density functional theory (DFT) calculations have been performed for cyclen, DO4S, and DO3S to investigate the conformations, the thermodynamics of protonation equilibria and to rationalize the relevant electronic transitions. Stability constants of the Na+ complexes (log beta(Na)) were computed for DO4S, DO3S, DO3SAm, and DO2A2S. For all compounds, the monodimensional H-1-NMR and bidimensional (COSY, NOESY, and HMQC) spectra have been obtained in D2O as a function of pD. Results indicate that sulphur-containing pendant arms induce partly unpredictable pK(a), NMR, UV-Vis, and log beta(Na) properties on the molecules, and that these properties significantly differ from those of the corresponding compounds without sulphur (e.g. cyclen and DOT-n-Bu). Furthermore, potentiometric and H-1 NMR titrations were performed in order to evaluate the complexation ability of DO4S, DO3S and DO2A2S toward Cd2+ as a case-example of soft metal ions. The obtained complexes show remarkable stability and are stronger than those formed with cyclen and its most common derivative DOTA especially at acidic pH, thus demonstrating that these compounds can be promising chelators of soft metal ions.
First author: Makhoul, R, 1,4-Diethynylbenzene-Bridged [Cp*(dppe)Fe](n+) Units: Effect of 2,5-Ethynyl Groups on the Chemical and Electronic Properties,
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 2020, 2624, (2020)
Abstract: The bis(ironvinylidene) complex [1,4-{Cp*(dppe)Fe=C=CH}(2)-2,5-(C equivalent to CH)(2)-C6H2](PF6)(2) ([2-2H](PF6)(2)) was prepared from 1,2,4,5-tetraethynylbenzene and two equiv. of Cp*(dppe)FeCl in 87 % yield. The reaction is very selective and [2-2H](PF6)(2) is the unique organoiron species to be formed. Deprotonation of [2-2H](PF6)(2) provided the target complex 2 (66 % yield) and subsequent oxidation gave the monocationic and dicationic complexes 2(PF6) and 2(PF6)(2). The new complexes were characterized by ESI-mass spectrometry, IR, multinuclear NMR, ESR and Mossbauer spectroscopy, and XRD analyses on single crystals for [2-2H](PF6)(2) and 2(PF6)(2). The magnetic properties of 2(PF6)(2) were investigated by VT H-1 NMR. The data were analyzed with the support of quantum chemistry calculations. The terminal ethynyl groups on the aromatic ring of the bridge modify the population of the bridge-oxidized state, weaken the electronic communication (H-ab approximate to 601 cm(-1)) and strengthen magnetic coupling interactions (J = -530 cm(-1)) compared to the unsubstituted species (H-ab = 1700 cm(-1) and J = -340 cm(-1), respectively).
First author: Joost, M, Synthesis, Structures, and Electronic Properties of O- and S-Heterocyclic Carbene Complexes of Iridium, Copper, Silver, and Gold,
ORGANOMETALLICS, 39, 1762, (2020)
Abstract: O- and S-heterocyclic carbenes (OHCs, SHCs) are shown experimentally and computationally to be stronger pi acceptors than NHCs and lack, of course, substituents at the heteroatoms. These different electronic and steric characteristics make OHCs and SHCs interesting ligands for coordination chemistry. Convenient synthetic routes are presented to access their iridium(I), iridium(III), and coinage-metal(I) (Cu, Ag, Au) complexes in good yields by means of dissociation of olefins, deprotonation of precursor salts, and transmetalation from a silver carbene complex Molecular structures and detailed bonding analyses of these complexes are presented.
First author: Boronski, JT, Synthesis and Characterization of an Oxo-Centered Homotrimetallic Uranium(IV)-Cyclobutadienyl Dianion Complex,
ORGANOMETALLICS, 39, 1824, (2020)
Abstract: Reaction of [Li-2{C-4(SiMe3)(4)}(THF)(2)] (1) with [U(eta(5)-C5Me5)I-2(THF)] (2) produced the oxo-centered homotrimetallic uranium-pentamethylcyclopentadienyl complex [{U(eta(5)-C5Me5)(mu-I)(2)}(3){mu(3)-O}{Li(THF)(3)}(0)(.5)](2) [Li(THF)(4)] (3) as the only isolable product in a very low yield. In contrast, reaction of 2 with [Mg{C-4(SiMe3)(4)}(THF)(3)] (4) produced the oxo-centered homotrimetallic uranium(IV)-cyclobutadienyl complex [{U(C-4[SiMe3](4))(mu-I)(2)}(3){mu(3)-O}] [Mg(THF)(6)] (5). The solid state structure of 5 reveals average U-C and U-C-4 centroid distances of 2.574(7) and 2.355(7) angstrom, respectively, and displacements of the silicon atoms from the C-4 plane ranging from 0.478(13) to 0.6528(12) angstrom. Variable-temperature magnetic susceptibility measurements on powdered 5 confirm the exclusively uranium(IV) formulation with no evidence found for any uranium center dot center dot center dot uranium magnetic coupling. Quantum chemical calculations suggest polarized uranium-cyclobutadienyl bonding interactions but underscore the essentially exclusive pi-bonding nature of these linkages with no delta-bonding component. This pi-bonding also accounts for the displacements of the silyl groups from the C-4 plane, which maximizes U-C-4 orbital overlap. The compounds reported here have been variously characterized by single-crystal X-ray diffraction, ATR-IR spectroscopy, elemental analysis, SQUID magnetometry, and quantum chemical calculations.
First author: Dvorackova, O, Tuning the Reactivity and Bonding Properties of Metal Square-Planar Complexes by the Substitution(s) on the Trans-Coordinated Pyridine Ring,
ACS OMEGA, 5, 11768, (2020)
Abstract: The kinetics of the hydration reaction on trans-[Pt(NH3)(2)(pyrX)Cl](+) (pyr = pyridine) complexes (X = OH-, Cl-, F-, Br-, NO2-, NH2, SH-, CH3, C CH, and DMA) was studied by density functional theory calculations in the gas phase and in water solution described by the implicit polarizable continuum model method. All possible positions ortho, meta, and para of the substituent X in the pyridine ring were considered. The substitution of the pyr ligand by electron-donating X’s led to the strengthening of the Pt-N1(pyrX) (Pt-N-pyrX) bond and the weakening of the trans Pt-Cl or Pt-O-w bonds. The electron-withdrawing X’s have exactly the opposite effect. The strengths of these bonds can be predicted from the basicity of sigma electrons on the N-pyrX atom determined on the isolated pyrX ligand. As the pyrX ring was oriented perpendicularly with respect to the plane of the complex, the nature of the X center dot center dot center dot Cl electrostatic interaction was the decisive factor for the transition-state (TS) stabilization which resulted in the highest selectivity of ortho-substituted systems with respect to the reaction rate. Because of a smaller size of X’s, the steric effects influenced less importantly the values of activation Gibbs energies Delta G(double dagger) but caused geometry changes such as the elongation of the Pt-NpyrX bonds. Substitution in the meta position led to the highest Delta G(double dagger) values for most of the X’s. The changes of Delta G(double dagger) because of electronic effects were the same in the gas phase and the water solvent. However, as the water solvent dampened electrostatic interactions, 2200 and 150 times differences in the reaction rate were observed between the most and the least reactive mono-substituted complexes in the gas phase and the water solvent, respectively. An additional NO2 substitution of the pyrNO(2) ligand further decelerated the rate of the hydration reaction, but on the other hand, the poly-NH2 complexes were no more reactive than the fastest o-NH2 system. In the gas phase, the poly-X complexes showed the additivity of the substituent effects with respect to the Pt-ligand bond strengths and the ligand charges.
First author: Li, SJ, Organoboron-Functionalization Enables the Hierarchical Assembly of Giant Polyoxometalate Nanocapsules,
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 59, 8537, (2020)
Abstract: Giant nanocapsules with dimensions of up to 4 nm and a molecular weight of 57 kDa were obtained from Dawson-type polyoxometalates functionalized with aromatic boronic acids, as reported by Z. Zheng, C. Streb, X. Chen, et al. in their Communication (DOI: 10.1002/anie.202003550). A “lock-and-key” organofunctionalization route was used for the regiospecific attachment of the boronic acids to pre-functionalized sites within the Dawson anions. This results in the aggregation of closed capsules rather than infinite networks.
First author: Ramakrishna, K, An efficient method to prepare sulfoxonium ylides and their reactivity studies using copper powder and Sc(III) as catalysts: Molecular and electronic structure analysis,
APPLIED ORGANOMETALLIC CHEMISTRY, 34, 8537, (2020)
Abstract: Sulfoxonium ylides are the viable alternatives for diazo compounds as carbene precursors. Unlike diazo compounds, these are bench-stable and crystalline solids. However, the existing methods for the synthesis of sulfoxonium ylides have disadvantages related to the yields, substrate scope, and usage of expensive catalysts. Therefore, it is necessary to develop efficient and competitive protocols for the preparation of sulfoxonium ylides. In this study, we developed an economically affordable protocol for the synthesis of sulfoxonium ylides from diazo compounds using copper powder as a catalyst. This protocol leads to the efficient multigram-scale synthesis of a wide range of sulfoxonium ylides in good yields. Further, we demonstrated scandium triflate-catalyzed carbene insertion into the N-H bond from sulfoxonium ylide. A variety of anilines and sulfoxonium ylides with various functional groups reacted well and produced the corresponding alpha-amino esters in good yields. All the synthesized compounds were characterized using various standard spectroscopic and analytical techniques. We also used computational methods to understand the electronic structure of all the sulfoxonium ylides using geometry optimization, frequency calculation, molecular orbital and natural bond orbital analysis, and energy decomposition analysis. Our computational results revealed that the interaction between carbene and dimethyl sulfoxide is covalent in nature and stable enough to handle in the absence of any catalyst.
First author: Morales-Bayuelo, A, Molecular quantum similarity studies and molecular properties of the tungsten intermediates [W6I14](2-) clusters,
JOURNAL OF MATHEMATICAL CHEMISTRY, 58, 1409, (2020)
Abstract: The relativistic density functional calculations including scalar and spin-orbit effects via the ZORA approximation and including solvent effects were carried out on the Tungsten intermediates [W6I14](2-) clusters. In addition, these considerations were supported by molecular quantum similarity studies using four similarity descriptors such as overlap and coulomb indices, and their euclidean distances. The current calculations also indicate that the electronic similarities of the lowest excited states of the intermediates clusters and molecular quantum similarity with the strongly luminescent W6I14 cluster, suggest that these intermediates metal clusters (W3I9, W3I9_I-1, W4I11, W4I11_I-2, W5I13, W6I14) could be luminescent. This would imply that the luminescence property is evident from the W3I9 unit, this unit being the minimum necessary to present this property.
First author: Pomogaev, V, Computational Investigation on the Photophysical Properties of Halogenated Tetraphenyl BODIPY,
JOURNAL OF PHYSICAL CHEMISTRY C, 124, 11100, (2020)
Abstract: The electronic structure, transition probabilities, and corresponding quantum yields of fluorescence in a family of dihalogen-tetraphenyl-aza-BODIPY were calculated at the Time-Dependent Density Functional and post-Hartree-Fock levels of theory. Excellent agreement between theoretical and experimental spectral-luminescent data was achieved with the HSE06 functional and the 6-311G* basis set. Because the fluorescence can be quenched through nonradiative intersystem spin crossing transitions from the lowest photoactive singlet state to triplet excited states, spin-orbit coupling matrix elements were calculated and applied along with Marcus-Levich-Jortner theory, leading to satisfactory agreement for the lifetimes in comparison with available experimental data. The anomalous dependence of the fluorescence efficiency on the atomic number of the halogen congeners was elucidated and shown to be due to an inversion between the fluorescent and the nearest triplet states in the iodinated compounds. The high rate of fluorescence quenching by intersystem crossings and the probability of collisions in a solvent between oxygen molecules and the molecules studied show that these molecules can provide efficient triplet sensitization. The most preferable sites for such interactions were predicted using electrostatic potential mapping at the extreme positive and negative charge points.
First author: Tecmer, P, Mixed uranyl and neptunyl cation-cation interaction-driven clusters: structures, energetic stability, and nuclear quadrupole interactions,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 10845, (2020)
Abstract: We present a state-of-the-art quantum chemical study of mixed cation-cation interaction (CCI) driven complexes composed of uranyl and neptunyl units. Specifically, we consider the stability of the D-shaped and T-shaped structural rearrangements in CCIs, various oxidation states of the uranium and neptunium atom (v and vi), as well as a different number of unpaired electrons. Furthermore, we scrutinize the nuclear quadrupole interactions of the bare actinyl subunits and the most stable mixed CCI clusters. The electric field gradients (and nuclear quadrupole coupling constants) of neptunyls are reported for the first time. The characteristic features of the nuclear quadrupole interactions for the bare neptunyl ions are very similar to those predicted for uranyls. When the CCI clusters are formed, a considerable asymmetry is introduced compared to the bare actinyl cations. Most importantly, we are able to distinguish different types of CCIs with respect to their structural arrangement and their total charge by analyzing the electric field gradients at the uranium and neptunium nuclei.
First author: Sa’adeh, H, Experimental and Theoretical Soft X-ray Study of Nicotine and Related Compounds,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 4025, (2020)
Abstract: The valence and core electronic structure of nicotine, nicotinic acid, and nicotinamide have been studied by photoelectron and soft X-ray absorption spectroscopy, supported by theoretical calculations, which take into account conformational isomerism. The core-level photoionization spectra of all molecules have been assigned, and theory indicates that the effects of conformational differences are small, generally less than the natural line widths of the core ionic states. However, in the case of nicotinamide, the theoretical valence ionization potentials of cis and trans conformers differ significantly in the outer valence space, and the experimental spectrum is in agreement with the calculated outer valence cis conformer spectrum. In addition, the C, N, and O K edge near-edge absorption fine structure spectra are reported and interpreted by comparison with reference compounds. We find evidence at the N and O K edges of interaction between the delocalized orbitals of the pyridine ring and the substituents for nicotinic acid and nicotinamide. The strength of the interaction varies because the first is planar, while the second is twisted, reducing the extent of orbital mixing.
First author: Cheng, CY, Evolutionary chemical space exploration for functional materials: computational organic semiconductor discovery,
CHEMICAL SCIENCE, 11, 4922, (2020)
Abstract: Computational methods, including crystal structure and property prediction, have the potential to accelerate the materials discovery process by enabling structure prediction and screening of possible molecular building blocks prior to their synthesis. However, the discovery of new functional molecular materials is still limited by the need to identify promising molecules from a vast chemical space. We describe an evolutionary method which explores a user specified region of chemical space to identify promising molecules, which are subsequently evaluated using crystal structure prediction. We demonstrate the methods for the exploration of aza-substituted pentacenes with the aim of finding small molecule organic semiconductors with high charge carrier mobilities, where the space of possible substitution patterns is too large to exhaustively search using a high throughput approach. The method efficiently explores this large space, typically requiring calculations on only similar to 1% of molecules during a search. The results reveal two promising structural motifs: aza-substituted naphtho[1,2-a]anthracenes with reorganisation energies as low as pentacene and a series of pyridazine-based molecules having both low reorganisation energies and high electron affinities.
First author: Li, Y, Comparative study on the photophysical properties between carbene-based Fe (II) and Ru (II) complexes,
APPLIED ORGANOMETALLIC CHEMISTRY, 34, 4922, (2020)
Abstract: The comparative study on the photophysical properties between cheap metal Fe (II) complexes and noble metal Ru (II) complexes with identical ligand coordination is performed by the combination of density functional theory (DFT) and time-dependent density functional theory (TDDFT) to evaluate the potential alternative applications of Fe (II) complexes. RuBIP (BIP = 2,6-bis (imidazol-2- ylidene)pyridine) is theoretically established that the radiative lifetime of the second lowest triplet state is more consistence with experimental value. However, FeBIP retains nonluminous because of low-lying (MC)-M-3 originated from weak d orbital splitting. FeBIPC (FeBIP with carboxylic acid groups) has twice longer lifetime than its parent complex FeBIP due to the great decrease of the energy gap between (MLCT)-M-3 and (MC)-M-3. What’s more, the lifetimes of Fe (II) complexes detected in the experiments are more accessible to nonradiative decay lifetimes of (MC)-M-3. The carboxylic acid groups are beneficial for the improvement of luminescent possibility and controllability of Fe (II) complexes, while there is still a huge challenge for effective material replacement comparing with Ru (II) complexes.
First author: Shillito, GE, Excited-State Switching Frustrates the Tuning of Properties in Triphenylamine-Donor-Ligand Rhenium(I) and Platinum(II) Complexes,
INORGANIC CHEMISTRY, 59, 6736, (2020)
Abstract: The photophysical properties of a series of rhenium(I) tricarbonyl and platinum(II) bis(acetylide) complexes containing a triphenylamine (TPA)-substituted 1,10-phenanthro-line ligand have been examined. The complexes possess both metal-to-ligand charge-transfer (MLCT) and intraligand charge-transfer (ILCT) transitions that absorb in the visible region. The relative energies and ordering of the absorbing CT states have been successfully controlled by changing the metal center and modulating the donating ability of the TPA group through the addition of electron-donating methoxy and electron-withdrawing cyano groups. The ground-state properties behave in a predictable manner as a function of the TPA substituent and are characterized with a suite of techniques including electronic absorption spectroscopy, resonance Raman spectroscopy, electrochemistry, and time-dependent density functional theory calculations. However, systematic control over the ground-state properties of the complexes does not extend to their excited-state behavior. Unexpectedly, despite variation of both the MLCT and ILCT state energies, all of the luminescent complexes displayed near-isoenergetic emission at 298 K, yet the emissive lifetimes of the complexes vary from 290 ns to 3.9 mu s. Excited-state techniques including transient absorption and transient resonance Raman, combined with a suite of quantum-chemical calculations, including scalar relativistic effects to elucidate competitive excited-state relaxation pathways, have been utilized to aid in assignment of the long-lived state in the complexes, which was shown to possess differing (MLCT)-M-3 and (ILCT)-I-3 contributions across the series.
First author: Singh, SK, Correlating Electronic Structure and Magnetic Anisotropy in Actinide Complexes [An(COT)(2)], An(III/IV) = U, Np, and Pu,
INORGANIC CHEMISTRY, 59, 6815, (2020)
Abstract: The electronic structures and magnetic anisotropies for compounds [An(COT)(2)] (An = U-III/U-IV, Np-III/Np-IV and Pu-III/Pu-IV, COT = cyclooctatetraene) are characterized using scalar relativistic density functional theory calculations and second-order perturbation theory based on a complete active space self-consistent field reference including spin-orbit coupling. The degree of participation of 5f orbitals in actinide-ligand bonding and the associated metal-ligand covalency is found to trend as U > Np >= Pu for both the tetra-positive and tripositive An complexes. A spin-Hamiltonian analysis indicates only weak single-molecule magnet (SMM) characteristics for [U(COT)(2)](-) and [Np(COT)(2)] complexes and no significant SMM behavior for the other complexes. The weak SMM behavior in [U(COT)(2)](-) and [Np(COT)(2)] is attributed to a subtle interplay between local symmetry and ligand-field splitting. Such a result suggests that magnetic anisotropy in Sf(3) ions can be modulated in general by electrostatic ligand field design. In particular, sigma-donor ligands oriented 180 degrees relative to one another will have a maximal influence on the 5f-orbital ligand field splitting, while pi donors like cyclopentadiene and COT generate ligand field influences that have more acute angles associated with corresponding atoms on the individual ligands. These observations rationalize the differences in SMM characteristics for [U(Bc(Me) )(3)] (Bp(Me-) = dihydrobis(methylimidazolyl)borate) and [U(Bp(Me))(3)] (Bp(Me-) = dihydrobis(methylpyrazolyl)borate) and indicate strategies to design new actinide-based SMMs with high magnetic relaxation barriers.
First author: Ribaudo, G, Fluoxetine scaffold to design tandem molecular antioxidants and green catalysts,
RSC ADVANCES, 10, 18583, (2020)
Abstract: Fluoxetine finds application in the treatment of depression and mood disorders. This selective serotonin-reuptake inhibitor (SSRI) also contrasts oxidative stress by direct ROS scavenging, modulation of the endogenous antioxidant defense system, and/or enhancement of the serotonin antioxidant capacity. We synthesised some fluoxetine analogues incorporating a selenium nucleus, thus expanding its antioxidant potential by enabling a hydroperoxides-inactivating, glutathione peroxidase (GPx)-like activity. Radical scavenging and peroxidatic activity were combined in a water-soluble, drug-like, tandem antioxidant molecule. Selenofluoxetine derivatives were reacted with H2O2 in water, and the mechanistic details of the reaction were unravelled combining nuclear magnetic resonance (NMR), electrospray ionisation-mass spectrometry (ESI-MS) and quantum chemistry calculations. The observed oxidation-elimination process led to the formation of seleninic acid and cinnamylamine in a trans-selective manner. This mechanism is likely to be extended to other substrates for the preparation of unsaturated cinnamylamines.
First author: Fu, XJ, Boron -based metallocene-like molecules and nanowires: A computational study,
CHEMICAL PHYSICS LETTERS, 747, 18583, (2020)
Abstract: The Lewis base stabilized borylenes and boryls are used to construct one dimension nanowires. Using the Lewis base (L) to coordinate sp(2) borons, we constructed B5L5- cyclic compounds with six pi-electrons. Then, using B5L5 and transition metals as building units, we further constructed half-sandwich and sandwich compounds. We found that the B-5(CO)(5) is the eta(5)-ligand with stronger bonding affinity with Mn and Fe than the traditional cyclopentadiene. The calculated electronic band structures suggested that the constructed nanowire [VB5(CO)(5)FeB5(CO)(5)](infinity) is an organic half-metal. The results may cast light on the future synthesis of boronbased metallocene-like molecules.
First author: Liu, WJ, Essentials of relativistic quantum chemistry,
JOURNAL OF CHEMICAL PHYSICS, 152, 18583, (2020)
Abstract: Relativistic quantum chemistry has evolved into a fertile and large field and is now becoming an integrated part of mainstream chemistry. Yet, given the much-involved physics and mathematics (as compared with nonrelativistic quantum chemistry), it is still necessary to clean up the essentials underlying the relativistic electronic structure theories and methodologies (such that uninitiated readers can pick up quickly the right ideas and tools for further development or application) and meanwhile pinpoint future directions of the field. To this end, the three aspects of electronic structure calculations, i.e., relativity, correlation, and QED, will be highlighted.
First author: Li, XB, Theoretical Study on the Reduction Mechanism of Np(VI) by Hydrazine Derivatives,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 3720, (2020)
Abstract: The key to effective separation of neptunium from the spent fuel reprocessing process is to adjust and control its valence state. Hydrazine and its derivatives have been experimentally confirmed to be effective salt-free reductants for reducing Np(VI) to Np(V). We theoretically studied the reduction reactions of Np(VI) with three hydrazine derivatives (2-hydroxyethyl hydrazine (HOC2H4N2H3), methyl hydrazine (CH3N2H3), and formyl hydrazide (CHON2H3)) and obtained the free radical ion mechanism and the free radical mechanism. Their potential energy profiles (PEPs) suggest that the free radical mechanism is the most probable reaction. Based on the energy barrier of the free radical ion mechanism, the trend of the reduction ability of the three hydrazine derivatives is HOC2H4N2H3 > CH3N2H3 > CHON2H3, which is in excellent agreement with the experimental results. Lastly, the analyses of natural bond orbitals (NBOs), quantum theory of atoms-in-molecules (QTAIM), and electron localization function (ELF) have been carried out to explore the bonding evolution of the structures along the reaction pathways. This work provides an insight into the reduction mechanism of Np(VI) with hydrazine derivatives from the theoretical perspective and helps to design more effective reductants for the separation of U/Np and Np/Pu in spent fuel reprocessing.
First author: Frati, F, Oxygen K-edge X-ray Absorption Spectra,
CHEMICAL REVIEWS, 120, 4056, (2020)
Abstract: We review oxygen K-edge X-ray absorption spectra of both molecules and solids. We start with an overview of the main experimental aspects of oxygen K-edge X-ray absorption measurements including X-ray sources, monochromators, and detection schemes. Many recent oxygen K-edge studies combine X-ray absorption with time and spatially resolved measurements and/or operando conditions. The main theoretical and conceptual approximations for the simulation of oxygen K-edges are discussed in the Theory section. We subsequently discuss oxygen atoms and ions, binary molecules, water, and larger molecules containing oxygen, including biomolecular systems. The largest part of the review deals with the experimental results for solid oxides, starting from s- and p-electron oxides. Examples of theoretical simulations for these oxides are introduced in order to show how accurate a DFT description can be in the case of s and p electron overlap. We discuss the general analysis of the 3d transition metal oxides including discussions of the crystal field effect and the effects and trends in oxidation state and covalency. In addition to the general concepts, we give a systematic overview of the oxygen K-edges element by element, for the s-, p-, d-, and f-electron systems.
First author: Jian, J, Through-Space Polar-pi Interactions in 2,6-Diarylthiophenols,
CHEMPHYSCHEM, 21, 1092, (2020)
Abstract: Molecular recognition between polar groups and aromatic molecules is fundamentally important to rational drug design. Although it has been well established that many polar functionalities interact with electron-rich aromatic residues through energetically favorable polar-pi interactions, there is a limited understanding of the association between thiols and aromatic systems. Herein we report physical-organic chemistry studies on 2,6-diarylthiophenols that possess the central thiophenol ring and two flanking aromatic rings with tunable electronic properties caused by substituents at distant para position. Hammett analysis revealed that pK(a) values and proton affinities correlate well with Hammett sigma values of substituents. Additional energy decomposition analysis supported the conclusion that both through-space SH-pi interactions and S–pi interactions contribute to intramolecular stabilization of 2,6-diarylthiophenols.
First author: Neto, ANC, Theoretical and Experimental Investigation of the Tb3+ -> Eu3+ Energy Transfer Mechanisms in Cubic A(3)Tb(0.90)Eu(0.10)(PO4)(3 )(A = Sr, Ba) Materials,
JOURNAL OF PHYSICAL CHEMISTRY C, 124, 10105, (2020)
Abstract: In this study the optical spectroscopy, the excited state dynamics, and in particular the Tb3+ -> Eu3+ energy transfer, have been investigated in detail both from the theoretical and experimental point of view in eulytite double phosphate hosts A(3)Tb(PO4)(3) (A = Sr, Ba) doped with Eu3+. It has been found that the energy transfer is strongly assisted by fast migration in the donor Tb3+ subset. Moreover, the transfer rates and efficiencies depend significantly on the nature of the divalent elements present in the structure and hence on the distances between Tb3+-Eu3+ nearest neighbors. It is shown that the competition between quadrupole-quadrupole and exchange interaction is crucial in accounting for the transfer rates.
First author: Bortoli, M, Sequential oxidations of phenylchalcogenides by H2O2: insights into the redox behavior of selenium via DFT analysis,
NEW JOURNAL OF CHEMISTRY, 44, 6724, (2020)
Abstract: The biological activity of sulfur and selenium, despite their similarity, shows some remarkable differences that have been recognized in many different scenarios. However, the underlying cause has not been completely clarified yet. The difference in the redox behavior of these two chalcogens has lately been addressed as justification of the presence of selenium in some essential biological systems. In particular, selenium is found in some peroxidases, i.e. glutathione peroxidases (GPx), whose redox activity relies on a fast-reacting selenocysteine and is fundamental in metabolizing harmful peroxides. In this work, a systematic in silico investigation on model systems, i.e. phenylchalcogenides, containing sulfur, selenium and tellurium is presented. Sequential oxidation reactions of these chalcogen-based substrates by hydrogen peroxide are carried out spanning the range of the biologically relevant chalcogen oxidation numbers [Advances in Molecular Toxicology, ed. J. C. Fishbein, Elsevier, 2010, vol. 4, pp. 183-222.] (2-, 0, 2+ and 4+) and analyzed through the calculation of intrinsic reaction coordinate paths and the application of the activation strain model. The results allowed us to highlight the different behaviors of S, Se and Te in highly oxidizing environments.
First author: Sarkar, S, Strong proton-shared hydrogen bonding in a methyl imidazoleMIDLINE HORIZONTAL ELLIPSISHCl complex: evidence from matrix isolation infrared spectroscopy and ab initio computations,
NEW JOURNAL OF CHEMISTRY, 44, 7116, (2020)
Abstract: Methyl imidazole (M-Imid)MIDLINE HORIZONTAL ELLIPSISHCl (1 : 1) complexes were studied using matrix isolation infrared spectroscopy and ab initio computations. Computations using the MP2 level of theory with the aug-cc-pVDZ basis set predicted three complexes, where the global minimum had a strong hydrogen-bonded NMIDLINE HORIZONTAL ELLIPSISHMIDLINE HORIZONTAL ELLIPSISCl interaction with a binding energy of similar to 12 kcal mol(-1) (complex A). The first local minimum had an HMIDLINE HORIZONTAL ELLIPSIS pi interaction (complex B) and the second local minimum (complex C) was stabilized through combined hydrogen, halogen and pnicogen bonding (with a nitrogen atom as the pnicogen) interactions. Of the three complexes, the hydrogen-bonded complex A alone possesses experimental significance. Experiments were performed by co-depositing M-Imid and HCl separately in an N-2 matrix at a low temperature of similar to 12 K. The annealing of the low temperature matrix encouraged the formation of M-Imid-HCl complex A, which was subsequently probed using infrared spectroscopy. Experimentally, the vibrational shift of similar to 1720 cm(-1) was observed for the N-2 matrix, while harmonic frequency calculations indicated a shift of 1063 cm(-1) in the H-Cl stretching region of the strong hydrogen-bonded complex A. The inclusion of anharmonicity in the calculations red-shifted the H-Cl stretching frequency further down to 1650 cm(-1), which was almost close to the experimental value. It is inferred from this large experimental red-shift of the stretching frequency of the proton donor that proton-shared hydrogen bonding is facilitated in the M-Imid-HCl system experimentally. Using atoms in molecules, energy decomposition and natural bond orbital analyses, the uniqueness of this strong proton-shared hydrogen bonding is established with respect to conventional hydrogen bonding.
First author: Charistos, ND, Induced magnetic field in sp-hybridized carbon rings: analysis of double aromaticity and antiaromaticity in cyclo[2N]carbon allotropes,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 9240, (2020)
Abstract: The induced magnetic field of C-2N (N = 3-14) carbon rings was dissected to contributions from out-of-plane and in-plane pi orbitals revealing two concurrent long range shielding or deshielding cones as a manifestation of the dual aromatic and antiaromatic character of C4n+2 and of C-4n rings respectively. Aromaticity based on the magnetic criterion was evaluated with regard to the bonding pattern and geometrical characteristics that elucidate the influence of bond length and bond angle alteration on out-of-plane and in-plane magnetic responses. Ground state polyynic geometries of C4n+2 rings exhibit comparable shielding cones to annulenes, decreasing the magnetic response with regard to the ring size and similar pi(out) and pi(in) diatropicity. Transition state cumulenic rings display increased aromaticity expressed by a very strong constant magnetic response and augmented pi(out) diatropicity with regard to pi(in). The variations of the induced magnetic field are explained on the basis of frontier orbital interactions through rotational excitations, which enable further rationalization of the aromatic/antiaromatic behavior.
First author: Gao, ST, Theoretical understanding of the electrochemical reaction barrier: a kinetic study of CO2 reduction reaction on copper electrodes,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 9607, (2020)
Abstract: The electrochemical reduction of CO2 is a promising route for converting intermittent renewable energy into storable fuels and useful chemical products. A theoretical investigation of the reaction mechanism and kinetics is beneficial for understanding the electrocatalytic activity and selectivity. In this report, a kinetic model based on Marcus theory is developed to compute the potential-dependent reaction barrier of the elementary concerted proton-electron transfer steps of electrochemical CO2 reduction reactions, different from the previous hydrogen atom transfer model. It is found that the onset potentials and rate-determining steps for CO and CH4 formation are determined by the first and third concerted proton-electron transfer steps C1 and C3. The influence of binding energy, electrode potential, and reorganization energy on the computed reaction barriers of the C1 and C3 reactions is discussed. In general, the calculated reaction barrier shows a quadratic relationship with the applied electrode potential. Specifically, the reaction barrier is merely determined by the reorganization energy at equilibrium potential. The present kinetic model is applied to compare the electrocatalytic activities in the electrochemical reduction of CO2 on various copper crystal surfaces. Among the four studied copper single-crystal surfaces, Cu(211) exhibits the best electrocatalytic activity for CO formation and CH4 formation due to its low onset potential and overpotential.
First author: Roznowska, A, Theoretical study on preference of open polymer vs. cyclic products in CO2/epoxide copolymerization with cobalt(III)-salen bifunctional catalysts,
JOURNAL OF MOLECULAR MODELING, 26, 9607, (2020)
Abstract: The preference of open chain of growing macromolecule vs. possible cyclic form was examined for the bifunctional cobalt(III)-salen catalyst for the copolymerization of CO2 with epoxides. A variety of possible isomers was considered (resulting from trans/cis-beta salen arrangement, different mutual orientation of quaternary ammonium-chains, and possible binding modes). To explore the conformational space, a combined approach was applied, utilizing semiempirical (PM7) MD and the DFT calculations. The preference of the open and cyclic macromolecules attached to the metal center was compared with the corresponding results for isolated model macromolecules, and the systems built of the macromolecule interacting with the tetra-butyl ammonium cation. Result shows that the cyclic structures are strongly preferred for isolated ions, with relatively low cyclization barriers. In the field of positive point charge, the open structures are strongly preferred. For the ions interacting with tetrabutyl ammonium cation, the cyclic structures are preferred, due to delocalization of the positive charge in the cation. For the complexes involving model and “real” Co(III)-salen catalysts, the open structures are strongly preferred. The possible cyclization by dissociation of alkoxide and its transfer to the neighborhood of quaternary ammonium cation is characterized by high activation barriers. Further, the transfer of alkoxide from the metal center to the cation is less likely than the transfer of carbonate, since the metal-alkoxide bond-energy energy is much stronger than energy of metal-carbonate bonding, as shown by ETS-NOCV results. The conclusions are in qualitative agreement with experimental data showing high selectivity towards copolymer formation in the copolymerization processes catalyzed by bifunctional Co(III) salen-complexes.
First author: Zierkiewicz, W, On the Stability of Interactions between Pairs of Anions – Complexes of MCl3- (M=Be, Mg, Ca, Sr, Ba) with Pyridine and CN-,
CHEMPHYSCHEM, 21, 870, (2020)
Abstract: The ability of the central M atom of the MCl3- anion, with M=Be, Mg, Ca, Sr, Ba, to engage in a noncovalent bond with an approaching nucleophile is gauged by ab initio methods. The N atom of pyridine forms a M…N bond with an interaction energy between 12 and 21 kcal mol(-1), even though the pi-hole above the M atom is not necessarily positive in sign. Despite a strong Coulombic repulsion between two anions, CN- is also able to approach the M atom so as to engage in a metastable complex that is higher in energy than the individual anions. The energy barrier separating this complex from its constituent anion pair is roughly 20 kcal mol(-1). Despite the endothermic formation reaction energy of the CN-…MCl3- complex, the electron topology signals a strong interaction, more so than in pyridine…MCl3- with its exothermic binding energy. The dianionic complex is held together largely on the strength of interorbital interactions, thereby overcoming a repulsive electrostatic component. The latter is partially alleviated by the pyramidalization of the MCl3 unit which makes its pi-hole more positive. The complex sinks below the separate monomers in energy when the system is immersed in an aqueous medium, with a binding energy that varies from as much as 20 kcal mol(-1) for Be down to 1.2 kcal mol(-1) for Ba.
First author: Wysokinski, R, Anion center dot center dot center dot Anion Attraction in Complexes of MCl3- (M=Zn, Cd, Hg) with CN-,
CHEMPHYSCHEM, 21, 1119, (2020)
Abstract: High-level ab initio calculations show that the MCl3- anions comprising Group 2B M atoms Zn, Cd, and Hg form a stable complex with the CN- anion, despite the like charge of the two ions. The complexation occurs despite a negative pi-hole region above the M atom of MCl3-. The dimerization distorts the planar geometry of MCl3- into a pyramidal shape which reduces the negative potential above the M atom, facilitating a close approach of the two anions, with R(M…C)similar to 2 angstrom, and an overall attractive electrostatic attraction within the dimer. In the gas phase, this dimer is less stable than the pair of separated ions by some 30 kcal/mol. However, the dissociation must surmount an energy barrier of roughly 25 kcal/mol which occurs at an intermolecular distance of 4 angstrom. In aqueous solution, the dimerization process is exothermic and barrier-free, with a binding energy in the 11-18 kcal/mol range.
First author: Xia, MR, Stronger Hydration of Eu(III) Impedes Its Competition against Am(III) in Binding with N-donor Extractants,
INORGANIC CHEMISTRY, 59, 6267, (2020)
Abstract: The significance of understanding the interaction between actinide(III)/lanthanide(III) (An(III)/Ln(III)) and N-donor extractants lies in the importance of efficient An(3+)/Ln(3+) separation in advanced nuclear fuel cycles and the high expectation of the application of N-donor extractants. This work reports a density functional theory study aiming at a plausible explanation of the origin of the selectivity of the ligands in An(3+)/Ln(3+) separation and an evaluation of the influence of the bridging groups of typical N-donor extractants. Five bis(triazine) N-donor ligands were considered, differing in their denticity dictated by their bridging groups and in the flexibility of these bridging groups. The results showed much stronger hydration of Eu(III) in comparison to Am(III) in the ligand exchange of aqua ligands by N-donor ligands, while there was a moderate difference in their interaction strengths with the N-donor ligands. This implicated that the distinct difficulty in desolvating Eu(III) and Am(III) may govern their selectivity in liquid-liquid extraction. The analysis of the role of the bridging groups of the ligands confirmed the importance of a ligand to be equipped with preorganized binding sites to minimize the perturbation of entropy. We tentatively propose that this conclusion may hold in the explanation of the low selectivity of oxygenated extractants and the high selectivity of extractants with soft donors in An(3+)/Ln(3+) separation.
First author: Hu, SX, Theoretical Insight into Coordination Chemistry of Am(VI) and Am(V) with Phenanthroline Ligand: Implications for High Oxidation State Based Minor Actinide Separation,
INORGANIC CHEMISTRY, 59, 6338, (2020)
Abstract: Despite continuing and burgeoning interest in americium (Am) coordination chemistry in recent years, investigations of the electronic structures and bonding chemistry of high oxidation state americium complexes and their implications for minor actinide separation remain relatively less explored to date. Here, we used density functional theory (DFT) to create high oxidation states of americium but experimentally feasible models of Am(V) and Am(VI) complexes of phenanthroline ligand (DAPhen) as [AmO2(L)](1+/2+) and [AmO3(L)](1+) (L = 2,9-bis[(N,N-dimethyl)-carbonyl]-1,10-phenanthroline (oxo-DAPhen, L-O) and 2,9-bis[(N,N-dimethyl)-thio-carbonyl]-1,10-phenanthroline (thio-DAPhen, L-S)), meanwhile comparing these with [UO2(L)](2+). On the basis of the calculations, the Am(V) and Am(VI) oxidation state are thermodynamically feasible and can be stabilized by DAPhen ligands. From a comparative study, the strength of thio-DAPhen in the separation of high oxidation state Am emerges better than does oxo-DAPhen, which relates to the nature, energy level, and spatial arrangement of their frontier orbitals. This study provides fundamental knowledge toward understanding the transuranic separations processes, which has implications in designing new, more selective extraction processes for the separation of Am from curium (Cm) as well as lanthanide.
First author: Bobo, MV, Bis-Cyclometalated Iridium Complexes Containing 4,4 ‘-Bis(phosphonomethyl)-2,2 ‘-bipyridine Ligands: Photophysics, Electrochemistry, and High-Voltage Dye-Sensitized Solar Cells,
INORGANIC CHEMISTRY, 59, 6351, (2020)
Abstract: In this report, the synthesis and characterization of two bis-cyclometalated iridium(III) complexes are presented. Single-crystal X-ray diffraction shows that [Ir(ppy)(2)(4,4′-bis-diethylphosphonomethyl)-2,2′-bipyridine)]PF6 adopts a pseudooc-tahedral geometry. The complexes have an absorption feature in the near-visible-UV region and emit green light with excited-state lifetimes in hundreds of nanoseconds. The redox properties of these complexes show reversible behavior for both oxidative and reductive events. [Ir(ppy)(2)(4,4′-bis(phosphonomethyl)-2,2′-bipyridine)]PF6 readily binds to metal oxide supports, like nanostructured Se-doped In2O3 and TiO2, while still retaining reversible redox chemistry. When incorporated as the photoanode in dye-sensitized solar cells, the devices exhibit open-circuit voltages of >1 V, which is a testament to their strength of these iridium(III) complexes as photochemical oxidants.
First author: Ulantikov, AA, Soluble Molecular Rhenium Cluster Complexes Exhibiting Multistage Terminal Ligands Reduction,
INORGANIC CHEMISTRY, 59, 6460, (2020)
Abstract: Substitution of terminal halide ligands of octahedral rhenium cluster complexes [Re(6)Q(8)X(6)](4-) in a melt of 4,4′-bipyridine (bpy) led to us obtaining four new compounds with the general formula trans-[Re(6)Q(8)(bpy)(4)X-2] (Q= S or Se; X = Cl or Br) in high yield. In contrast to most of the known molecular rhenium cluster complexes with heteroaromatic terminal ligands, compounds 1-4 are soluble in organic solvents. This made it possible to carry out a detailed characterization of the new compounds both in solids and in solutions. In particular, it was shown that compounds 1-4 in the DMSO solution exhibit four reversible reduction processes. A comparison of the obtained data with the results of DFT calculations of the electronic structure suggests that these processes correspond to two-electron reduction of all four bpy ligands. The reduction potentials are shifted to the positive region compared with the potential of free bipyridine, and the value of the shift depends on the composition of the cluster core. The presence of four transitions also suggests that electronic exchange between terminal ligands in the cis-position is possible. The study of the luminescence of the compounds showed that emission maxima of selenide clusters almost coincide with those of sulfide ones, while luminescence spectra of the complexes with chloride terminal ligands (1 and 3) are slightly blue-shifted relative to the spectra of the complexes with bromide ligands (2 and 4).
First author: Alvarado-Soto, L, Relativistic Structure-Activity Relationship of Cisplatin(II) Complexes,
JOURNAL OF STRUCTURAL CHEMISTRY, 61, 688, (2020)
Abstract: Cytotoxic activities of cisplatin(II) complexes against cancer cell lines are studied using the relativistic structure-activity relationship analysis. Global reactivity descriptors based on the relativistic density functional theory are used. This work demonstrates the usefulness of the relativistic reactivity descriptors to predict the biological activity of the complexes studied.
First author: Pirone, D, Contrasting Photo-Switching Rates in Azobenzene Derivatives: How the Nature of the Substituent Plays a Role,
POLYMERS, 12, 688, (2020)
Abstract: A molecular design approach was used to create asymmetrical visible light-triggered azo-derivatives that can be good candidates for polymer functionalization. The specific electron-donor substituted molecules were characterized and studied by means of NMR analyses and UV-visible spectroscopy, comparing the results with Time Dependent Density Functional (TD-DFT) calculations. A slow rate of isomerization (k(i) = 1.5 x 10(-4) s(-1)) was discovered for 4-((2-hydroxy-5methylphenyl) diazenyl)-3-methoxybenzoic acid (AZO1). By methylating this moiety, it was possible to unlock the isomerization mechanism for the second molecule, methyl 3-methoxy-4-((2-methoxy-5-methylphenyl) diazenyl)benzoate (AZO2), reaching promising isomerization rates with visible light irradiation in different solvents. It was discovered that this rate was heightened by one order of magnitude (k(i) = 3.1 x 10(-3) s(-1)) for AZO2. A computational analysis using density functional (DFT/PBE0) and wavefunction (QD-NEVPT2) methodologies provided insight into the photodynamics of these systems. Both molecules require excitation to the second (S-2) excited state situated in the visible region to initiate the isomerization. Two classic mechanisms were considered, namely rotation and inversion, with the former being energetically more favorable. These azo-derivatives show potential that paves the way for future applications as building blocks of functional polymers. Likewise, they could be really effective for the modification of existing commercial polymers, thus transferring their stimuli responsive properties to polymeric bulky structures, converting them into smart materials.
First author: Yuan, LP, Phosphorus-doping activates carbon nanotubes for efficient electroreduction of nitrogen to ammonia,
NANO RESEARCH, 13, 1376, (2020)
Abstract: The electrochemical nitrogen reduction reaction (NRR) as an energy-efficient approach for ammonia synthesis is hampered by the low ammonia yield and ambiguous reaction mechanism. Herein, phosphorus-doped carbon nanotube (P-CNTs) is developed as an efficient metal-free electrocatalyst for NRR with a remarkable NH3 yield of 24.4 mu g center dot h(-1)center dot mg(cat.)(-1) and partial current density of 0.61 mA center dot cm(-2). Such superior activity is found to be from P doping and highly conjugated CNTs substrate. Experimental and theoretical investigations discover that the electron-deficient phosphorus sites with Lewis acidity should be genuine active sites and NRR on P-CNTs follows the distal pathway. These findings provide insightful understanding on NRR processes on P-CNTs, opening up opportunities for the rational design of highly-active cost-effective metal-free catalysts for electrochemical ammonia synthesis.
First author: Kasprzycka, E, How minor structural changes generate major consequences in photophysical properties of RE coordination compounds; resonance effect, LMCT state,
JOURNAL OF RARE EARTHS, 38, 552, (2020)
Abstract: Lanthanide coordination compounds of the formula Na[Ln(L)(4)] (1Ln), where Ln = La3+, Eu3+, Gd3+, Tb3+, L = [L](-) and HL= dimethyl(4-methylphenylsulfonyl)amidophosphate, were synthesized. Their structural and spectroscopic properties were discussed in detail based on X-ray diffraction measurements, IR spectroscopy, absorption and emission spectroscopy at 293 and 77 K and theoretical calculations of the intramolecular energy transfer (IET) rates. DFT calculations were used to investigate the 1Ln electronic properties required to calculate the transition rates. 30 and 22 pathways of intramolecular nonradiative energy transfer were examined in the case of 1Eu and 1Tb, respectively. It is shown that the main pathway for sensitization of the lanthanide emission is either the triplet (1Eu) or singlet (1Tb) transfer, occurring mainly through the exchange mechanism. The energy rates for energy transfer from S(1 )and T-1 equal W-s = 1.53 x 10(5) s(-1) (1Eu), W-T = 5.14 x 10(6)s(-1) (1Eu) and W-s = 4.09 x 10(7)s(-1) (1Tb), W-T = 6.88 x 10(5)s(-1) (1Tb). The crucial role of the (7)F(5 )level in the energy transfer process of 1Tb and the participation of the LMCT state in the depopulation of the ligand singlet state of 1Eu were demonstrated. The influence of the resonance effect on the splitting of the F-7(1) level in 1Eu was analyzed. By comparing the properties of 1Ln with the properties of 2Ln coordination compounds, sharing the same ligand and crystallizing in the same crystallographic system (monoclinic), but with a different space group, it is demonstrated how slight structural changes can affect the photophysical properties of Ln compounds.
First author: Martini, A, PyFitit: The software for quantitative analysis of XANES spectra using machine-learning algorithms,
COMPUTER PHYSICS COMMUNICATIONS, 250, 552, (2020)
Abstract: X-ray absorption near-edge spectroscopy (XANES) is becoming an extremely popular tool for material science thanks to the development of new synchrotron radiation light sources. It provides information about charge state and local geometry around atoms of interest in operando and extreme conditions. However, in contrast to X-ray diffraction, a quantitative analysis of XANES spectra is rarely performed in the research papers. The reason must be found in the larger amount of time required for the calculation of a single spectrum compared to a diffractogram. For such time-consuming calculations, in the space of several structural parameters, we developed an interpolation approach proposed originally by Smolentsev and Soldatov (2007). The current version of this software, named PyFitIt, is a major upgrade version of FitIt and it is based on machine learning algorithms. We have chosen Jupyter Notebook framework to be friendly for users and at the same time being available for remastering. The analytical work is divided into two steps. First, the series of experimental spectra are analyzed statistically and decomposed into principal components. Second, pure spectral profiles, recovered by principal components, are fitted by theoretical interpolated spectra. We implemented different schemes of choice of nodes for approximation and learning algorithms including Gradient Boosting of Random Trees, Radial Basis Functions and Neural Networks. The fitting procedure can be performed both for a XANES spectrum or for a difference spectrum, thus minimizing the systematic errors of theoretical simulations. The problem of several local minima is addressed in the framework of direct and indirect approaches.
First author: Ghorai, S, Structures and bonding in [L]M(mu-CCR)(2)M[L] and [L]M(mu-RC4R)M[L]: requirements for C-C coupling,
DALTON TRANSACTIONS, 49, 5157, (2020)
Abstract: A theoretical analysis of [L]M(mu-CCR)(2)M[L] and [L]M(mu-RC4R)M[L], where M represents the selected elements from the main group, transition metals, lanthanides and actinides, shows how the central (mu-CCR)(2) and (mu-RC4R) units reorganize as M traverses across the periodic table. In this context transition metal and actinide complexes are similar in nature, while lanthanide and main group complexes show similarity. The ground state electronic configuration and thus the metal oxidation state control these striking differences. An effective way to stabilize the (iii) oxidation state of thorium in a metallacycle complex is shown for the first time. A strategy is proposed to make a cross-connection between the two sets. The approach used here lends itself to obvious extensions.
First author: Balmohammadi, Y, Existence of untypical halogen-involving interactions in crystal packings: a statistical and first-principles study,
CRYSTENGCOMM, 22, 2756, (2020)
Abstract: There is a common perception by the scientific community that a halogen-involving interaction forms when the distance between the donor atom and the acceptor atom is less than the sum of their van der Waals (vdW) radii. Our previous work, some theoretical predictions and a search in the Cambridge Structural Database (CSD) for crystalline solids with halogen-involving interactions cast doubt on this common perception and lead us to express a challenging question: do halogen-involving interactions exist above the sum of the vdW radii of the atoms in contact? To address this question, we chose 21 couples with similar structures where the main difference between them is the distance between the atoms in contact involved in halogen interactions. To characterize halogen-involving interactions, we resort to (i) periodic and non-periodic density functional theory (DFT) calculations, (ii) quantum theory of atoms in molecules (OTAIM), and (iii) energy decomposition analysis (EDA). In contrast to the common perception, our results indicate that halogen-involving interactions do exist at distances up to 20.74% above the sum of the vdW radii of the atoms in contact which shows the same trend as theoretical predictions. Our results modify the current picture of crystal packing which contains halogen-involving interactions, leading to new approaches in designing and engineering crystals for applications.
First author: Becker, P, Approaching Dissolved Species in Ammonoacidic GaN Crystal Growth: A Combined Solution NMR and Computational Study,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 7008, (2020)
Abstract: Solutions of gallium trihalides GaX3 (X=F, Cl, Br, I) and their ammoniates in liquid ammonia were studied at ambient temperature under autogenous pressure by multinuclear (Ga-71, Cl-35, Br-81) NMR spectroscopy. To unravel the role of pH, the analyses were done both in absence and in presence of ammonium halides, which are employed as mineralizers during ammonoacidic gallium nitride crystal growth. While gallium trifluoride and its ammoniate were found to be too sparingly soluble to give rise to a NMR signal, the spectra of solutions of the heavier halides reveal the presence of a single gallium-containing species in all cases. DFT calculations and molecular dynamics simulations suggest the identification of this species as consisting of a [Ga(NH3)(6)](3+) cation and up to six surrounding halide anions, resulting in an overall trend towards negative complex charge. Quantitative Ga-71 NMR studies on saturated solutions of GaCl3 containing various amounts of additional NH4Cl revealed a near linear increase of GaCl3 solubility with mineralizer concentration of about 0.023 mol GaCl3 per mol NH4Cl at room temperature. These findings reflect the importance of Coulombic shielding for the inhibition of oligomerization and precipitation processes and help to rationalize both the low solubility of gallium halides in neutral ammonia solution and, in turn, the proliferating effect of the mineralizer during ammonoacidic gallium nitride formation.
First author: Kryuchkova, NA, Interatomic Interactions in Heterometallic Cubane-Type Clusters with {Mo3S4M ‘} (M ‘ = Cu, Ni, Pd) Core,
JOURNAL OF CLUSTER SCIENCE, 32, 415, (2021)
Abstract: The electronic structure of heterometallic cubane-type clusters with core {Mo3S4M ‘} (M ‘ = Cu+, Ni-0, Pd-0) was investigated by the Atoms in Molecules and Electron Localization Function topological methods as well as Energy Decomposition Analysis. It was found that {Mo3S4Cu} and {Mo3S4M ‘} (M ‘= Ni, Pd) clusters have a different interaction between molybdenum and heterometallic atoms. In case of the complexes with Ni/Pd atom, the disynaptic basins on the Mo-M ‘ bonds were observed in contrast to the Cu containing complex. The complex formation between heterometallic fragments and trinuclear molybdenum complex {Mo3S4} were found to be hindered due to steric interactions. Nevertheless, the formation of the heterometallic cubane-type clusters occurs due to the multicenter and pair covalent interactions between Mo and M ‘ atoms.
First author: Li, QJ, Theoretical study of surface-enhanced Raman scattering mechanism of scandium-doped copper/silver clusters,
NANOTECHNOLOGY, 31, 415, (2020)
Abstract: Rare earth metals exhibit strong chemical activity and have many unique properties in the aspects of magnetic susceptibility, photo-absorption, catalytic activity and electrical property. Precious metals have strong chemical stability and great surface-enhanced Raman scattering (SERS) enhancing activity, providing a good platform for detecting SERS signals from molecules. Combining precious metals with rare earth metals could form new composite materials, providing more possibilities for SERS substrates. In this work, the SERS and absorption spectra of the probe molecule adsorbed on scandium-doped silver/copper clusters are theoretically simulated by time-dependent density functional theory. The contributions of charge-transfer (CT) enhancement and electromagnetic enhancement are treated uniformly in calculations based on a short-time approximation for the Raman scattering cross-section, and distinguished by using visualization of electron transitions. The largest Raman enhancement factor of the probe molecule adsorbed on Sc@Cu-7 and Sc@Ag-7 alloy clusters could reach the order of 10(5), due to the enhancement of resonance excitation to the CT transition. The factors influencing SERS are systematically investigated, including the composition of the substrate, local chemical environment of the binding site, form of electron transition, oscillator strength of excitation and excitation wavelength.
First author: Wang, CL, Structure-Property Study of Homoleptic Zinc(II) Complexes of Di(arylethynyl) Azadipyrromethene as Nonfullerene Acceptors for Organic Photovoltaics: Effect of the Aryl Group,
JOURNAL OF PHYSICAL CHEMISTRY C, 124, 8541, (2020)
Abstract: Azadipyrromethene-based zinc(II) complexes were demonstrated to be promising molecular organic semiconductors for electronic applications due to their easy preparation, tunable structures, and high electron affinity. The first successful such complex incorporated phenylethynyl groups at the pyrrolic positions, which red-shifted the absorption spectra of zinc(II) bis(tetraphenyl azadipyrromethene) and improved the morphology in blends with poly(3-hexylthiophene) (P3HT). We recently discovered that replacing the phenyl group in the pyrrolic positions with the larger 1-naphthyl group [Zn(L2)(2)] increases the crystallinity and improves the organic photovoltaic (OPV) performance. In this work, two more aryl groups were explored to further investigate the relationship between the aryl groups in the pyrrolic position and electronic properties: naphthyl with a different anchoring site, 2-naphthyl [Zn(L3)(2)], and a larger aryl group, 9-phenanthrenyl [Zn(L4)(2)]. The larger aryl group slightly improved the absorptivity, red-shifted the absorption spectra, and led to different packing modes in crystals with most intermolecular pi-pi stacking interactions being of T-shaped-type involving the pyrrolic aryl group of one complex. Of the series, 1-naphthyl gave the highest crystallinity. The organic photovoltaic (OPV) power conversion efficiency (PCE) of Zn(L3)(2) and Zn(L4)(2) when blended with P3HT was 3.7 and 3.4%, respectively, both lower than that of Zn(L2)(2) (PCE of 5.5%) due to the higher trap-assisted recombination and less favorable morphology. The charge carrier mobility in these complexes was also relatively low, also limiting the performance. Single-point energy calculations point to low overlap integrals as a cause for the low mobility. The aryl group anchoring position and size, therefore, have a large effect on the properties in these systems, but do not appear to significantly enhance intermolecular interactions.
First author: Albrecht-Schmitt, TE, Theoretical examination of covalency in berkelium(IV) carbonate complexes,
INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 120, 8541, (2020)
Abstract: Experimental studies on the speciation of berkelium in carbonate media have shown that complexation of berkelium(III) by carbonate results in spontaneous oxidation to berkelium(IV) and that multiple species can be present in solution. We studied two proposed structures present in solution based on theoretical comparisons with spectroscopic data previously reported for Bk(IV) carbonate solutions. The multiconfigurational character of the ground and low-lying excited states in both complexes is demonstrated to result from the strong spin-orbit coupling. Although bonding in Bk(IV) carbonate and carbonate-hydroxide complexes is dominated by strong Coulombic forces, the presence of non-negligible covalent character is supported by ligand-field theory, natural localized orbitals, topological studies of the electron density, and energy transition state natural orbitals for chemical valence. Bond orders based on natural localized molecular orbitals show that Bk-OH bonds possess enhanced orbital overlap, which is reflected in the bond strength. This is also observed in the decomposition of the orbital interaction energy into individual deformation density pairs.
First author: Sanchez-Movellan, I, Local structure and excitations in systems with CuF64- units: lack of Jahn-Teller effect in the low symmetry compound Na2CuF4,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 7875, (2020)
Abstract: This work attempts to unveil the similarities and differences between Jahn-Teller (JT) and non-JT systems involving CuF64- units. For achieving this goal, we firstly explore Na2CuF4 and NaF:Cu2+ systems through first principles calculations and pay particular attention to the links between JT and non-JT systems looking at the electronic density of the hole. The results on Na2CuF4 in the monoclinic P2(1)/c space group and also in the parent Pbam structure reveal that the local geometry can be understood as an initial tetragonally compressed CuF64- unit, followed by an additional orthorhombic instability that excludes the JT effect as the origin. Although the present results on NaF:Cu2+ underpin an elongated equilibrium geometry such as that measured for Cu2+ ions in the cubic perovskite KZnF3, the force constant for NaF:Cu2+ is half that for KZnF3:Cu2+. This crucial fact is direct proof of the elastic decoupling of CuF64- from the NaF lattice leading to a JT energy, E-JT, which is twice that found for KZnF3:Cu2+. However, both systems have practically the same linear electron-vibration coupling constant, V-1e, a relevant fact whose origin is discussed. The final aim of this work concerns the influence of tetragonal and orthorhombic distortions as well as the internal electric field on the A(1g)-B-1g energy gap, Delta, of a variety of systems with CuF64- complexes. Interestingly, it is shown that compounds with orthorhombic instability and an internal electric field can have a Delta value comparable to the JT system NaF:Cu2+. Accordingly, explanations for optical spectra of transition metal compounds based on simple parameterized models can be meaningless. The present study shows that properties displayed by d(9) compounds in low symmetry lattices can hardly stem from a static JT effect.
First author: Ji, Y, DFT-Calculated IR Spectrum Amide I, II, and III Band Contributions of N-Methylacetamide Fine Components,
ACS OMEGA, 5, 8572, (2020)
Abstract: The infrared spectrum (IR) characteristic peaks of amide I, amide II, and amide III bands are marked as amide or peptide characteristic peaks. Through the nuclear magnetic resonance study, N-methylacetamide has been determined to have six fine components, which include protonation, hydration, and hydroxy structures. Then the independent IR spectrum of every component in N-methylacetamide is calculated by using the density functional theory quantum chemistry method, and the contribution of each component to amide I, II, and III bands is analyzed. The results of this research can help to explain the formation of the amide infrared spectrum, which has positive significance in organic chemistry, analytical chemistry, and chemical biology.
First author: Morales-Bayuelo, A, A conceptual DFT analysis of the plausible mechanism of some pericyclic reactions,
STRUCTURAL CHEMISTRY, 31, 1745, (2020)
Abstract: Out of several pericyclic reactions, Diels-Alder (DA) reaction is one of the most widely used synthetic processes. In the present work, several models and methodologies have been used to determine and to analyze the plausible mechanism of some representative DA cycloaddition reactions. A comparison between the dual descriptor and the bond reactivity indices corresponding to the natural bond orbital of the reagents is included, which provides a complete description of the plausible reaction mechanism. In the next step, two very recent models are used to determine the local electronic density transfer and redistribution between the reactants involved. The description of the local electronic density transfer has been made in two stages; first, the variation in the net charge on the atoms is obtained, and then, the electronic density transfer between the natural bond orbitals is calculated. The values obtained using the two models are correlated with the experimental rate constants of the reactions. Finally, the natural bond orbitals are obtained at several steps along the reaction path and the variation in their partial occupation is compared with the corresponding electron density transfer among these orbitals. Furthermore, frontier molecular orbital (FMO) approach has been employed to understand the more feasible way of interaction between the DA pair. Relative electrophilicity descriptors like net electrophilicity (increment omega(+/-)), net reactivity index (NRI, Delta omega R +/-), and electrophilicity difference (increment omega) between DA pairs have also been employed to describe the studied reaction mechanisms especially whether they follow non-polar-concerted/polar-stepwise pathway along with their classification in terms of normal or inverse electron demand. Furthermore, adaptive natural density partitioning method (AdNDP) and energy decomposition analyses (EDA) in conjunction with natural orbital for chemical valence (NOCV) have been made use of in order to analyze the actual bonding situation in the transition state (TS).
First author: Thomas, KE, Free-base porphyrins with localized NH protons. Can substituents alone stabilize the elusive cis tautomer?,
ORGANIC & BIOMOLECULAR CHEMISTRY, 18, 2861, (2020)
Abstract: The elusive cis tautomer of free-base porphyrins has recently been isolated and structurally characterized in the form of a supramolecular complex. The question as to whether a suitable set of peripheral substituents might lead to a stable cis tautomer in the absence of supramolecular interactions, however, remains unanswered and is one we have attempted to address here by means of density functional theory calculations. The fact that many antipodally beta-tetrasubstituted tetraphenylporphyrin derivatives exhibit localized central protons attached to the beta-unsubstituted pyrrole rings led us to surmise that beta-tetrasubstitution of adjacent pyrrole rings might lead to a porphyrin cis tautomer, an idea that proved fruitful. Indeed, for the “adjacently” substituted tetraphenylporphyrin derivative H-2[adj-(CF3)(4)(CH3)(4)TPP], the global energy minimum proved to be a highly saddled cis tautomer, with the trans tautomer about 0.07 eV higher in energy. It is important to underscore, however, that the asymmetric beta-substitution pattern is far from the only factor contributing to the stability of the cis tautomer for this porphyrin. A strongly saddled conformation resulting from meso-beta steric interactions also helps alleviate the repulsion between the two central NH protons, thereby stabilizing the cis tautomer relative to the trans.
First author: Nagata, K, Synthesis, Structures, and Photoluminescent Properties of Tricyanidonitridorhenium(V) Complexes with Bipyridine-Type Ligands,
INORGANIC CHEMISTRY, 59, 5497, (2020)
Abstract: Tricyanidonitridorhenium(V) complexes with 2,2′-bipyridine (bpy) derivatives in which the 4 and 4′ positions were substituted by X, [ReN(CN)(3)(X(2)bpy)](-) (X = NMe2, NH2, OMe, Me, Cl, and Br), were newly synthesized and characterized. The structures of the new complexes were determined by single-crystal X-ray analysis. UV-vis spectra of the complexes in dimethyl sulfoxide (DMSO) showed that the peak maximum wavelengths of rhenium-to-pi* bpy-type-ligand charge transfer were in the range of 474-542 nm. Cyclic voltammograms in n-(C4H9)(4)NPF6-DMSO showed one-electron oxidation and reduction waves corresponding to the Re(VI/V) and X(2)bpy(0/-) processes, respectively. The new complexes and [ReN(CN)(3)bpy](-) showed photoluminescence in the crystalline phase at 295 and 80 K and in DMSO at 295 K. The origin of the emission in DMSO was attributed to the triplet nature of the rhenium-to-pi* bpy-type-ligand charge-transfer transition. Density functional theory calculations showed that the highest occupied and lowest unoccupied molecular orbitals were primarily localized on the d(xy) orbital of the rhenium and pi* orbitals of the bpy-type ligand, respectively.
First author: Barnett, KL, Experimental and Computational Study of the Structure, Steric Properties, and Binding Equilibria of Neopentylphosphine Palladium Complexes,
INORGANIC CHEMISTRY, 59, 5579, (2020)
Abstract: Steric properties of crystallographically and computationally determined structures of linear palladium(0) and square planar palladium(II) complexes of di(tert-butyl)neopentylphosphine (P(t-Bu)(2)Np), tert-butyldineopentylphosphine (P(t-Bu)Np-2), and trineopen-tylphosphine (PNR,) have been determined. Structures of linear palladium(0) complexes show that steric demand increases as tertbutyl groups are replaced with neopentyl groups (P(t-Bu)(2)Np < P(tBu)Np-2< PNp3). In square planar palladium(II) complexes, PNp3 gives the smallest steric parameters, whereas P(t-Bu)Np-2 has the largest steric demand. The change in the steric demand of PNp3 compared to P(tBu)(2)Np and P(t-Bu)Np-2 results from a significant conformational change in PNp3 depending on the coordination number of the metal. The steric properties of these ligands were also probed by measuring the equilibrium constant for coordination of free phosphine to dimeric [(R3P)Pd(mu-Cl)Cl](2) complexes. Binding equilibria follow the same trend as the steric parameters for square planar complexes with PNp3 having the highest binding constant. In contrast to the normal trend, the neopentylphosphines show increased pyramidalization at phosphorus with increasing steric demand. We hypothesize that this unusual dependence reflects the low back side strain of the neopentyl group, which allows the ligand to be more pyramidalized while still exerting a significant front side steric demand.
First author: Noland, WE, Diels-Alder/Ene Reactivities of 2-(1 ‘-Cycloalkenyl)thiophenes and 2-(1 ‘-Cycloalkenyl)benzo[b]thiophenes with N-Phenylmaleimides: Role of Cycloalkene Ring Size on Benzothiophene and Dibenzothiophene Product Distributions,
JOURNAL OF ORGANIC CHEMISTRY, 85, 5265, (2020)
Abstract: Scaffolds of thiophene and benzothiophene are the important class of bioactive compounds found abundant in nature. The Diels-Alder reactions of 2-(1′-cycloalkenyl)thiophenes and 2(1′-cycloalkenyl)benzo[b] thiophenes having the alkene groups present in five-, six-, seven-, eight-, and twelve-membered rings with substituted N-phenylmaleimides are characterized. The size of the cycloalkene rings plays a critical role in dictating the product distributions of expected and isomerized Diels-Alder adducts. 2D NMR studies indicate that the isolated isomers for 2-(1′-cycloalkenyl)thiophenes having five-, six-, and seven-membered rings are aromatized benzothiophene products, whereas eight- and twelve-membered rings are un-rearranged adducts. In addition, the product of subsequent ene-reaction with the N-phenylmaleimide is isolated for the five- and six-membered ring cases. Interestingly, in the 2-(1’cycloalkenyl)benzo[b]thiophene having five-, six-, seven-, eight-, and twelve-membered rings, the un-rearranged dibenzothiophene Diels-Alder adduct is isolated in every instance. Molecular mechanics and density functional theory (M06-2X and PBE0-D3) calculations are performed to understand the differential reactivity of the various dienes for both the initial Diels-Alder reaction and a possible, subsequent ene reaction.
First author: Gryl, M, Unveiling the Impact of Aggregation on Optical Anisotropy of Triazaacephenanthrylene Single Crystals. A Combined Quantum Crystallography and Conceptual Density Functional Theory Approach,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 2931, (2020)
Abstract: Triazaacephenanthrylene (TARP) triclinic single crystals show substantial optical anisotropy of absorption and fluorescence. The maximum effect can be correlated with the direction perpendicular to the plane of chromophores connected in a head-to-tail manner via weak dispersive interactions. This phenomenon is uncommon as usually the existence of postulated pi center dot center dot center dot pi interactions between the molecules forming dimers or stacks cause quenching of fluorescence. Herein we present a comprehensive study of inter- and intramolecular interactions in the crystal of TAAP enriched with the investigation of aromaticity. Our results show that intramolecular interactions stabilize the overall conformation of the molecule whereas dispersive forces determine the aggregation between TAAP molecules. In fact, there is no conventional pi center dot center dot center dot pi interaction between the molecules in the dimer. Instead, we observed a close contact between the lone pair of the bridgehead N10B atom and pi-deficient pyrazine ring from an adjacent molecule. Optical anisotropy in TAAP crystals was directly correlated with the alignment of the molecular transition dipole moments caused by specific molecular self-assembly.
First author: Forster, A, Double hybrid DFT calculations with Slater type orbitals,
JOURNAL OF COMPUTATIONAL CHEMISTRY, 41, 1660, (2020)
Abstract: On a comprehensive database with 1,644 datapoints, covering several aspects of main-group as well as of transition metal chemistry, we assess the performance of 60 density functional approximations (DFA), among them 36 double hybrids (DH). All calculations are performed using a Slater type orbital (STO) basis set of triple-zeta (TZ) quality and the highly efficient pair atomic resolution of the identity approach for the exchange- and Coulomb-term of the KS matrix (PARI-K and PARI-J, respectively) and for the evaluation of the MP2 energy correction (PARI-MP2). Employing the quadratic scaling SOS-AO-PARI-MP2 algorithm, DHs based on the spin-opposite-scaled (SOS) MP2 approximation are benchmarked against a database of large molecules. We evaluate the accuracy of STO/PARI calculations for B3LYP as well as for the DH B2GP-PLYP and show that the combined basis set and PARI-error is comparable to the one obtained using the well-known def2-TZVPP Gaussian-type basis set in conjunction with global density fitting. While quadruple-zeta (QZ) calculations are currently not feasible for PARI-MP2 due to numerical issues, we show that, on the TZ level, Jacob’s ladder for classifying DFAs is reproduced. However, while the best DHs are more accurate than the best hybrids, the improvements are less pronounced than the ones commonly found on the QZ level. For conformers of organic molecules and noncovalent interactions where very high accuracy is required for qualitatively correct results, DHs provide only small improvements over hybrids, while they still excel in thermochemistry, kinetics, transition metal chemistry and the description of strained organic systems.
First author: Carvalho, J, Nonrelativistic protocol for calculating the (1)J((195) Pt-N-15) coupling constant in Pt(II)-complexes using all-electron Gaussian basis-set,
CHEMICAL PHYSICS LETTERS, 745, 1660, (2020)
Abstract: We present a computational protocol for predicting the (1)J((195) Pt-N-15) coupling constant in Pt(II) complexes. The procedure included a working set of 82 coupling constants for 57Pt(II) complexes. Furthermore, it was applied for a testing set of 16 coupling constants in 14Pt(II) complexes. The protocol was based on nonrelativistic calculations at PBEPBE/NMR-DKH level where the all-electron NMR-DKH basis set was previously proposed for calculation of Pt-195 chemical shift (J. Comput. Chem. 37 (2016) 2360-2373). The MAD was 36 Hz corresponding to the MRD of 10.4%, considering all 98 coupling constants for 71Pt(II) complexes studied in the present work.
First author: Hong, YM, Metalloids as halogen bond acceptors: A combined crystallographic data and theoretical investigation,
CHEMICAL PHYSICS LETTERS, 745, 1660, (2020)
Abstract: According to our search of the Cambridge Structural Database (CSD), a number of crystal structures containing Groups 15 and 16 metalloids as halogen bond acceptors have been extracted. On the basis of the CSD survey results, triphenyl-pnictogen (Ph(3)Pn) and diphenyl-chalcogen (Ph(2)Ch) molecules, together with benzimidazole-2chalcogenones (PhN2C=Ch) and triatomic pseudohalide anions (PnCCh(-)), were selected as acceptors to study. Our calculations showed that the chalcogenone compounds PhN2C=Ch serve as better halogen bond acceptors in comparison with the chalcogenide species Ph(2)Ch. Particularly, the properties of halogen bonds formed by both the Ph and Ch ends in PnCCh(-) were characterized.
First author: Wo, XC, Bonding properties of a superatom system with high-Z elements: insights from energy decomposition analysis,
RSC ADVANCES, 10, 14482, (2020)
Abstract: Superatoms with high-Z elements have novel physicochemical properties, and a comprehensive and thorough view of their bonding properties plays a crucial role in the design of superatoms. Now, energy decomposition analysis shows increasingly prominent performance for understanding inter- and intra-molecular interactions, so the bonding properties of typical superatoms with high-Z elements, Th@Au-14, have been investigated here. It is found that under different electron occupation types of the fragments, the electrostatic interaction energy, polarization, and exchange repulsion energy change significantly in their intramolecular interaction energy components, resulting in quantitative or even qualitative differences in their main interaction energy. This indicates that the bonding properties of fragments are related to their electronic structures, and even has extraordinary reference value for the future regulation and control of interactions in superatoms with high-Z elements, which has great significance for superatom development.
First author: Poor Kalhor, M, Dimethyl Carbonate Synthesis from CO2 and Dimethoxytin(IV) Complexes: The Anatomy of the Alkylation Step Viewed from DFT Modeling,
INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 59, 6867, (2020)
Abstract: In line with promoting environmentally acceptable chemical processes, the direct catalytic conversion of CO2 and methanol into dimethyl carbonate (DMC) is a target of current industrial interest. Despite breakthroughs to master thermodynamic limitations, the reaction mechanisms are not well understood for providing keys to boost rate and selectivity. Specifically, the pathways releasing DMC and regenerating the reactive alkoxy moiety are poorly justified. We herein address these steps by density functional theory modeling (DFT) with (CH3)(2)Sn(OCH3)(2). The study complements our kinetics experiments and end-products characterization obtained from Bu2Sn(OCH3)(2) counterpart. Indeed, DMC formation by an intermolecular process between two monomeric stannanes is preferred to that previously reported with the dimer. A following multistep process with methanol is advanced to regenerate the stannanes along with water, thereby promoting a catalytic cycle. Accordingly, dialkyltin(IV) organometallics are unique to promote such a sequence giving opportunity in reactor design to overcome catalyst poisoning as well as thermodynamics limitations.
First author: Wakasugi, C, Bright Luminescent Platinum(II)-Biaryl Emitters Synthesized Without Air-Sensitive Reagents,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 5449, (2020)
Abstract: Transition-metal complexes bearing biaryl-2,2 ‘-diyl ligands tend to show intense luminescence. However, difficulties in synthesis have prevented their further functionalization and practical applications. Herein, a series of platinum(II) complexes bearing biaryl-2,2 ‘-diyl ligands, which have never been prepared in air, were synthesized through transmetalation and successive cyclometalation of biarylboronic acids. This approach does not require any air- or moisture-sensitive reagents and features a simple synthesis even in air. The resulting (Et4N)(2)[Pt(m,n-F(2)bph)(CN)(2)] (m,n-F(2)bph=m,n-difluorobiphenyl-2,2 ‘-diyl) complexes exhibit intense green emissions with high quantum efficiencies of up to 0.80 at 298 K. The emission spectral fitting and variable-temperature emission lifetime measurements indicate that the high quantum efficiency was achieved because of the tight packing structure and strong sigma-donating ability of bph.
First author: Wei, JY, Theoretical Analysis of the Mackay Icosahedral Cluster Pd-55(PiPr(3))(12)(mu(3)-CO)(20): An Open-Shell 20-Electron Superatom,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 5508, (2020)
Abstract: The electronic structure of the spherical Mackay icosahedral nanosized cluster Pd-55(PiPr(3))(12)(mu(3)-CO)(20) is analyzed by using DFT calculations. Results reveal that it can be considered as a regular superatom with a “magic” electron count of 20, characterized by a 1S(2) 1P(6) 1D(10) 2S(2) jellium configuration. Its open shell nature is associated with partial occupation of non-jellium, 4d-type, levels located on the interior of the Pd-55 kernel. This shows that the superatom model can be used to rationalize the bonding and stability of spherical ligated group 10 clusters, despite their apparent 0-electron count.
First author: Pracht, P, Automated exploration of the low-energy chemical space with fast quantum chemical methods,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 7169, (2020)
Abstract: We propose and discuss an efficient scheme for the in silico sampling for parts of the molecular chemical space by semiempirical tight-binding methods combined with a meta-dynamics driven search algorithm. The focus of this work is set on the generation of proper thermodynamic ensembles at a quantum chemical level for conformers, but similar procedures for protonation states, tautomerism and non-covalent complex geometries are also discussed. The conformational ensembles consisting of all significantly populated minimum energy structures normally form the basis of further, mostly DFT computational work, such as the calculation of spectra or macroscopic properties. By using basic quantum chemical methods, electronic effects or possible bond breaking/formation are accounted for and a very reasonable initial energetic ranking of the candidate structures is obtained. Due to the huge computational speedup gained by the fast low-cost quantum chemical methods, overall short computation times even for systems with hundreds of atoms (typically drug-sized molecules) are achieved. Furthermore, specialized applications, such as sampling with implicit solvation models or constrained conformational sampling for transition-states, metal-, surface-, or noncovalently bound complexes are discussed, opening many possible applications in modern computational chemistry and drug discovery. The procedures have been implemented in a freely available computer code called CREST, that makes use of the fast and reliable GFNn-xTB methods.
First author: Orenha, RP, The anionic recognition mechanism based on polyol and boronic acid receptors,
NEW JOURNAL OF CHEMISTRY, 44, 5564, (2020)
Abstract: Anion selective recognition plays pivotal roles in the environmental field. The polyol and boronic acid receptor classes are investigated here to recognize the chloride (Cl-); fluoride (F-); dihydrogen phosphate (H2PO4-); acetate (AcO-); bromide (Br-); and hydrogen sulfate (HSO4-) anions. Energy Decomposition Analysis (EDA) shows that the anion-receptor interactions are predominantly electrostatic. Interestingly, the increase of the number of -CF3 groups or of the carbonic chain in the polyol structure favors Cl- recognition. The polyol-Cl- interactions are more attractive than the boronic acid-Cl- bond. Boronic acid recognizes F- and H2PO4- with the most attractive energies. The Quantum Theory of Atoms in Molecules (QTAIM) method elucidated that the recognition of AcO-, Cl-, Br-, and HSO4- by the receptors is maintained through hydrogen bonds, while the recognition of F- and H2PO4- by boronic acid involves BMIDLINE HORIZONTAL ELLIPSISF- and BMIDLINE HORIZONTAL ELLIPSISO–P bonds, respectively, showing a larger covalent character compared to other boronic acid-anion bonds, but with a primarily electrostatic nature.
First author: Kosicki, MB, Product-state distribution after isotopic substitution in ultracold atom-molecule collisions,
JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, 53, 5564, (2020)
Abstract: We theoretically investigate the isotopic substitution reactions in gaseous samples at ultracold temperature (T MUCH LESS-THAN 1 K) during atom-molecule collisions where one of the constituent atoms of the molecule is replaced by its isotope. We focus on molecular species that can be created experimentally in this range. We show that the molecular products are translationally cold, which could allow their trapping and thus their detection in order to shed new light on ultracold molecular collisions. We also demonstrate that in a few cases, the molecular products may occupy only the lowest rotational states. We discuss the possibility of controlling the kinetic energy release of such chemical reactions by an external electric field.
First author: Jaegers, NR, Thermal perturbation of NMR properties in small polar and non-polar molecules,
SCIENTIFIC REPORTS, 10, 5564, (2020)
Abstract: Water is an important constituent in an abundant number of chemical systems; however, its presence complicates the analysis of in situ(1)H MAS NMR investigations due to water’s ease of solidification and vaporization, the large changes in mobility, affinity for hydrogen bonding interactions, etc., that are reflected by dramatic changes in temperature-dependent chemical shielding. To understand the evolution of the signatures of water and other small molecules in complex environments, this work explores the thermally-perturbed NMR properties of water in detail by in situ MAS NMR over a wide temperature range. Our results substantially extend the previously published temperature-dependent H-1 and O-17 chemical shifts, linewidths, and spin-lattice relaxation times over a much wider range of temperatures and with significantly enhanced thermal resolution. The following major results are obtained: Hydrogen bonding is clearly shown to weaken at elevated temperatures in both H-1 and O-17 spectra, reflected by an increase in chemical shielding. At low temperatures, transient tetrahedral domains of H-bonding networks are evidenced and the observation of the transition between solid ice and liquid is made with quantitative considerations to the phase change. The H-1 chemical shift properties in other small polar and non-polar molecules have also been described over a range of temperatures, showing the dramatic effect hydrogen bonding perturbation on polar species. Gas phase species are observed and chemical exchange between gas and liquid phases is shown to play an important role on the observed NMR shifts. The results disclosed herein lay the foundation for a clear interpretation of complex systems during the increasingly popular in situ NMR characterization at elevated temperatures and pressures for studying chemical systems.
First author: Coimbra, DF, Shedding light on the bonding situation of triangular and square heterometallic clusters: computational insight,
NEW JOURNAL OF CHEMISTRY, 44, 5079, (2020)
Abstract: The motivation of this paper is to provide a comprehensive computational study of a series of heterometallic clusters (1a-3e) [MMoCp(CO)(3)](n) (M = Cu+, Ag+ or Au+, n = 3 or 4); (Cp = eta(5)-C5H5), seeking to clarify the effect of the coinage metal employed on the nuclearity observed, as well as to examine the role of metallophilicity in the cluster stability. A DFT benchmark revealed that the best results are obtained by using the D3ECP model, more specifically with the B3PW91-D3 functional. The calculated structures reproduce the experimentally observed distortion of the Ag-4 core adequately, with bond lengths close to experimental values. Energy decomposition analysis, employing three different fragmentation schemes, revealed that the bonding situation is mainly modulated by electrostatic interactions, followed by orbital contributions, while the presence of dispersion is small, but not negligible. The EDA results for FSIII reveal that for the copper complexes the interaction energies are very similar for both the triangular and square cores, while for the complexes containing square metallic cores of silver or gold, they are much more stabilizing than for the triangular analogues. The density flow channels indicated that the orbital stabilization in the gold complexes is mainly from 4d(Mo) + pi(CO) -> 6s(Au) donations and 5d(Au) -> pi*(CO) + 4d(Mo) + sigma(CH) back-donations. The inner-fragment polarization also contributes to the bonding stabilization.
First author: Izquierdo, MA, Orbital Decomposition of the Carbon Chemical Shielding Tensor in Gold(I) N-Heterocyclic Carbene Complexes,
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 2020, 1177, (2020)
Abstract: The good performance of N-heterocyclic carbenes (NHCs), in terms of versatility and selectivity, has called the attention of experimentalists and theoreticians attempting to understand their electronic properties. Analyses of the Au(I)-C bond in [(NHC)AuL](+/0) (L stands for a neutral or negatively charged ligand), through the Dewar-Chatt-Duncanson model and the charge displacement function, have revealed that NHC is not purely a sigma-donor but may have a significant pi-acceptor character. It turns out, however, that only the sigma-donation bonding component strongly correlates with one specific component of the chemical shielding tensor. Here, in extension to earlier works, a current density analysis, based on the continuous transformation of the current density diamagnetic zero approach, along a series of [(NHC)AuL](+/0) complexes is presented. The shielding tensor is decomposed into orbital contributions using symmetry considerations together with a spectral analysis in terms of occupied to virtual orbital transitions. Analysis of the orbital transitions shows that the induced current density is largely influenced by rotational transitions. The orbital decomposition of the shielding tensor leads to a deeper understanding of the ligand effect on the magnetic response properties and the electronic structure of (NHC)-Au fragments. Such an orbital decomposition scheme may be extended to other magnetic properties and/or substrate-metal complexes.
First author: Schmitt-Monreal, D, Frozen-density embedding-based many-body expansions,
INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 120, 1177, (2020)
Abstract: Fragmentation methods allow for the accurate quantum chemical (QC) treatment of large molecular clusters and materials. Here we explore the combination of two complementary approaches to the development of such fragmentation methods: the many-body expansion (MBE) on the one hand, and subsystem density-functional theory (DFT) or frozen-density embedding (FDE) theory on the other hand. First, we assess potential benefits of using FDE to account for the environment in the subsystem calculations performed within the MBE. Second, we use subsystem DFT to derive a density-based MBE, in which a many-body expansion of the electron density is used to calculate the system’s total energy. This provides a correction to the energies calculated with a conventional energy-based MBE that depends only on the subsystem’s electron densities. For the test case of clusters of water and of aspirin, we show that such a density-based MBE converges faster than the conventional energy-based MBE. For our test cases, truncation errors in the interaction energies are below chemical accuracy already with a two-body expansion. The density-based MBE thus provides a promising avenue for accurate QC calculation of molecular clusters and materials.
First author: Vasiliu, M, A Computational Assessment of Actinide Dioxide Cations AnO(2)(2+) for An = U to Lr: The Limited Stability Range of the Hexavalent Actinyl Moiety, [O=An=O](2+),
INORGANIC CHEMISTRY, 59, 4554, (2020)
Abstract: The isolated gas-phase actinide dioxide dications, AnO(2)(2+) , were evaluated by DFT and coupled cluster CCSD(T) calculations for 12 actinides, An = U-Lr. CASSCF calculations were used to define the orbitals for the CCSD(T) calculations. The characteristic linear [O=An=O](2+) hexavalent actinyl(VI) was found to be the lowest energy structure for An = U, Np, and Pu, which also form stable actinyl(VI) species in solution and possibly for Am when spin-orbit effects are included. For Am, there is a divalent [An(II)(O-2)](2+) structure where the dioxygen is an end-on physisorbed eta(1)-O-3(2) kcal/mol above the actinyl when spin-orbit effects are included which lower the energy of the actinyl structure. For An = Cm, Bk, and Lr, the lowest energy structure is trivalent [An(III)(O-2(-))](2+) where the dioxygen is a side-on superoxide, eta(2)-O-2(-). For Cm, the actinyl is close in energy to the ground state when spin-orbit effects are included. For An = Cf, Es, Fm, Md, and No, the lowest energy structure is divalent [An(II)(O-2)](2+) where the dioxygen is an end-on physisorbed eta(1)-O-3(2). The relative energies suggest that curyl(VI) and berkelyl(VI), like well-known americyl(VI), might be stabilized by coordinating ligands in condensed phases. The results further indicate that for californyl and beyond, the actinyl(VI) moieties will probably be elusive even using strong donor ligands. The prevalence of low oxidation states (OSs) An(II) and An(III) for transplutonium actinides reflects stabilization of the 5f orbitals and validates established trends, including the remarkably high stability of divalent No. Bond distances and other parameters suggest maximum bond covalency around plutonyl(VI), with a particularly substantial decrease in bond strength between americyl(VI) and curyl(VI).
First author: Chai, SY, A grand product design model for crystallization solvent design,
COMPUTERS & CHEMICAL ENGINEERING, 135, 4554, (2020)
Abstract: Solvents play an important role in crystallization processes. The screening/design of solvents for crystallization (crystallization solvents) is still of great concern in research and development. At present, most of the design/screening methods of crystallization solvents are still based on the trial-and-error approach. Even though some computer-aided design methods have been proposed, the process model as well as economic/environmental/health issues have not been fully established for a wide application range. In this paper, the Grand Product Design (GPD) model is applied for the screening/design of crystallization solvents. The GPD-model includes process sub-model, property sub-model, quality sub-model, cost sub-model, pricing sub-model, economic sub-model and environmental sub-model as well as other factors such as company strategy, government policies and regulations. The general equations of the GPD-model for crystallization solvent screening/design are presented in this paper. Solution strategies are given for three cases: solvent design for a fixed process, process design for a fixed solvent and simultaneous design of solvent and process. Taking 2-Mercapotobenzothiazole (MBT) as an example, the solvent design for a fixed (existing) process design is carried out by using the problem specific GPD-model, in which the GPD-model is formulated as Mixed-Integer Non-Linear Programming (MINLP) model with objective function, process sub-model, property sub-model, quality sub-model, pricing sub-model, cost sub-model, economic sub-model and environmental sub-model. The established MINLP model is then solved by the decomposition-based approach. Experiments are carried out to verify the candidate solvents, which is found to perform better in terms of product purity and recovery than the best-known solvents in use.
First author: Hintzen, JCJ, Comparison of Molecular Recognition of Trimethyllysine and Trimethylthialysine by Epigenetic Reader Proteins,
MOLECULES, 25, 4554, (2020)
Abstract: Gaining a fundamental insight into the biomolecular recognition of posttranslationally modified histones by epigenetic reader proteins is of crucial importance to understanding the regulation of the activity of human genes. Here, we seek to establish whether trimethylthialysine, a simple trimethyllysine analogue generated through cysteine alkylation, is a good trimethyllysine mimic for studies on molecular recognition by reader proteins. Histone peptides bearing trimethylthialysine and trimethyllysine were examined for binding with five human reader proteins employing a combination of thermodynamic analyses, molecular dynamics simulations and quantum chemical analyses. Collectively, our experimental and computational findings reveal that trimethylthialysine and trimethyllysine exhibit very similar binding characteristics for the association with human reader proteins, thereby justifying the use of trimethylthialysine for studies aimed at dissecting the origin of biomolecular recognition in epigenetic processes that play important roles in human health and disease.
First author: Mato, J, Accuracy of the PM6 and PM7 Methods on Bare and Thiolate-Protected Gold Nanoclusters,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 2601, (2020)
Abstract: Semiempirical quantum mechanical (SEQM) methods offer an attractive middle ground between fully ab initio quantum chemistry and force-field simulations, allowing for a quantum mechanical treatment of the system at a relatively low computational cost. However, SEQM methods have not been frequently utilized in the study of transition metal systems, mostly due to the difficulty in obtaining reliable parameters. This paper examines the accuracy of the PM6 and PM7 semiempirical methods to predict geometries, ionization potentials, and HOMO-LUMO energy gaps of several bare gold clusters (Au-n) and thiolate-protected gold nanoclusters (AuSNCs). Contrary to PM6, the PM7 method can predict qualitatively correct geometries and ionization potentials when compared to DFT. PM6 fails to predict the characteristic gold core and gold-sulfur ligand shell (staple motifs) of the AuSNC structures. Both the PM6 and PM7 methods overestimate the HOMO-LUMO gaps. Overall, PM7 provides a more accurate description of bare gold and gold-thiolate nanoclusters than PM6. Nevertheless, refining the gold parameters could help achieve better quantitative accuracy.
First author: Du, QY, Structure Evolution of Transition Metal-doped Gold Clusters M@Au-12 (M=3d-5d): Across the Periodic Table,
JOURNAL OF PHYSICAL CHEMISTRY C, 124, 7449, (2020)
Abstract: The comprehensive genetic algorithm (CGA) incorporated with density functional theory (DFT) calculations were used for a global search of the potential energy surfaces of M@Au-12 (M = 3d-5d) clusters. The feasibility of the revTPSS functional was confirmed by comparison between experimental and calculated data such as bond lengths and vibrational frequencies of transition metal dimers. We found the ground state structures of Mo/W@Au-12 clusters to be the perfect icosahedron cage. The V/Nb/Ta/Tc/Re@Au-12 clusters were found to have the distorted icosahedron cages owing to Jahn-Teller effects. The lowest energy structures of Sc/Ti/Cr/Mn/Fe/Co/Ru/Rh/Ir@Au-12 have the perfect or distorted magnetic cuboctahedron cages, which can be explained by a 14-electron rule in a cuboctahedral ligand field (M2+@Au-12(2-)). Y/Zr/La/Hf@Au-12 clusters have the half-cage ground states, while Ni/Cu/Zn/Pt/Ag/Cd/Pd/Au/HgAu12 clusters have oblate ground states. The scalar relativistic X2C method combined with revTPSS/TZP were used to calculate the energy difference between the magnetic cuboctahedron ground state and the icosahedron isomers of Cr@Au-12 using energy decomposition analysis-natural orbitals for chemical valence. The magnetic M2+@Au-12(2-) model was found to significantly enhance the d orbital interactions of transition metal atoms and reduce Pauli repulsion, resulting in magnetic cuboctahedra as the more stable structures.
First author: Sebera, J, Interstrand Charge Transport within Metallo-DNA: the Effect Due to Hg(II)- and Ag(I)-Mediated Base Pairs,
JOURNAL OF PHYSICAL CHEMISTRY C, 124, 7477, (2020)
Abstract: Metallo-DNA is considered promising in regard to functional molecular electronic elements. From this perspective, the longitudinal charge transport within metallo-DNA is usually studied. By contrast, this work was aimed at the transversal conductance of metallo-DNA, particularly at the effect of Hg and Ag metals on the conductance of base pairs. The charge transport through metal-mediated base pairs involving Hg(II) and Ag(I) metals, deoxythymidine (T) and 4-deoxythiothymidine (Ts), was studied by means of density functional theory (DFT) calculations employing the non-equilibrium Green’s function (NEGF) method and electronic coupling calculations. The calculations showed that the conductance along the base-to-base charge transport pathway was significantly enhanced mainly due to the Hg(II)-mediated linkage. This work further showed that not only the metals within the metallo-base pair but also the substitution of the O4 atom in deoxythymidine by sulfur (the Ts nucleoside) enhanced molecular conductance as in the case of Ts-Ag(I)(2)-Ts. The bias charge transport for T-Ag(I)(2)-T was less effective than the transport for a TT mismatched base pair. The Ag orbitals participated in the highest occupied molecular orbital (HOMO) of T-Ag(I)(2)-T and Ts-Ag(I)(2)-Ts in contrast to negligible participation of Hg orbitals in the HOMO of T-Hg(II)-T. Therefore, a Coulomb blockade effect can be assumed particularly for Ag-mediated base pairs as was apparent from the plateau obtained for the calculated I/V dependencies. The Ag-mediated base pairs can, thus, be potentially utilized as molecular transistors. In addition, the metallo-base pairs anchored to gold electrodes mediated by sulfur preferred hole transport against the electron transport mechanism. This work highlighted the importance of electronic compatibility between the organic DNA scaffold and a particular metal that is essential for effective charge transport through metallo-base pairs (M-base pairs).
First author: Confer, MP, Direct fluorination of tetrafluoroethylene at low temperatures,
JOURNAL OF FLUORINE CHEMISTRY, 232, 7477, (2020)
Abstract: Mechanisms for the processes of direct fluorination of tetrafluoroethylene (TFE) in matrices of TFE, hexafluoropropylene (HFP), and dimers and trimers of HFP ((HFP)(2) and (HFP)(3)) from 77 K to 300 K have been developed. Electronic structure calculations at the composite correlated G3(MP2) and G4 molecular orbital theory levels of the energetics of a range of reactions involving TFE and fluorine are presented to aid in the development of these mechanisms. The equilibrium products of the direct fluorination of TFE in the gas phase at varied temperature and initial composition was determined by Gibbs free energy minimization. Spontaneous reactions (explosions) were observed for the fluorination of pure crystalline TFE and HFP. Fluorination of TFE can be performed without explosion in glassy matrixes of (HFP)(2) or (HFP)(3) at low temperatures. The explosive nature of the reaction decreases in the matrix order TFE > (HFP)(2) > (HFP)(3). The fluorination of TFE begins at the phase transition temperature of the matrix, i.e., after the transition of devitrified (HFP)(2) and (HPF)(3) into the supercooled liquid state at 110 K and 150 K, respectively. The experiments show that either the presence of a branched structure (C9F20, the saturated analog of (HFP)(3)) or the presence of unsaturated bonds (perfluorotoluene) separately cannot provide a medium for the safe fluorination of TFE as the direct fluorination of TFE in these matrices led to an explosion. HFP oligomers provide an effective environment for TFE fluorination because of the presence of double bonds surrounded by the branched perfluorinated groups. The unsaturated bonds of the HFP oligomers are an active participant in the chemical processes involved in the safe, direct fluorination of TFE.
First author: Sidorov, AI, Raman spectroscopic investigations on UV irradiated phosphate glasses with high content of silver or sodium,
OPTICAL MATERIALS, 102, 7477, (2020)
Abstract: The influence of UV radiation on structural properties of phosphate glasses, with addition of high concentration of silver or sodium was studied by Raman spectroscopy. It is shown that glass synthesis conditions (reducing or oxidizing) influences considerably on glass structure reaction on UV irradiation. The role of additions (silver or sodium) is also studied. It is shown that structural changes in sodium-containing glass after UV irradiation are more manifested, than in silver-containing glasses. The destruction of subnanosized neutral silver molecular clusters under UV irradiation is also observed. The results, obtained for all types of glasses are compared and discussed. For the definition of the influence of silver and sodium atoms on chemical bonds in glass structural units, computer simulation, using density functional theory, was performed.
First author: Gordon, CP, Probing the Electronic Structure of Spectator Oxo Ligands by O-17 NMR Spectroscopy,
CHIMIA, 74, 225, (2020)
Abstract: Spectator oxo ligands are ubiquitous in catalysis, in particular in olefin epoxidation and olefin metathesis. Here we use computationally derived O-17 NMR parameters to probe the electronic structure of spectator oxo ligands in these two reactions. We show that O-17 NMR parameters allow to distinguish between doubly-bonded and triply-bonded oxo ligands, giving detailed insights into the frontier molecular orbitals involved in the metal-oxo bonds along the reaction pathway. On the one hand, our study shows that in olefin epoxidation catalysed by methyltrioxorhenium (MTO), the oxo ligand significantly changes its bonding mode upon formation of the oxygen-transferring Re-oxo-bisperoxo-species, changing its nature from a doubly bonded to a triply bonded oxo ligand. On the other hand, only minor changes in the binding mode are found along the olefin metathesis reaction pathway with Mo- and W-based oxo-alkylidene species, in which the oxo ligand behaves as a triply bonded ligand throughout the reaction. This finding contrasts earlier studies that proposed that the change of binding mode of the oxo ligand was key to metallacyclobutane formation.
First author: Yan, X, Effects of intramolecular hydrogen bonds on phosphorescence emission: A theoretical perspective,
APPLIED ORGANOMETALLIC CHEMISTRY, 34, 225, (2020)
Abstract: Importing intramolecular hydrogen bond in phosphorescent transition metal complexes has been considered one of the excellent approaches to improve the electroluminescence performance of organic light-emitting diodes in real applications. However, the relationships between such H-bond structure and phosphorescent properties have not been theoretically revealed yet. In this study, two types of intramolecular hydrogen bonds are introduced into the two classes of traditional materials, that is, Pt(II) and Ir(III) complexes (1a and 2a) to completely elucidate their influence on the structures and properties by comparing with the original phosphors (1b and 2b) using density functional theory/time-dependent density functional theory for the first time. A comprehensive analysis of the geometric structures, molecular orbitals, and luminescence properties (including phosphorescence emission wavelengths and radiative and nonradiative decay processes) has been carried out. Our theoretical model highlights that complexes 1a and 2a embedded with H-bonds significantly promote the phosphorescence emission band blue-shifted and restrict molecular deformations compared with the corresponding 1b and 2b, which can provide helpful guidance to regulate and design several aspects of highly efficient blue phosphorescent emitters.
First author: Chatterjee, S, Solvatochromism of a Novel Ruthenium Complex, [Ru(acac)(2)(N-(2-Methylsulfonylphenyl)formamido)]: A Correlation between the Electronic Structure and Spectroscopic Properties,
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A, 94, 789, (2020)
Abstract: Solvatochromism is commonly used in many fields of chemical and biological research to study bulk and local polarity in macro systems (membranes, etc.), or even the conformation and binding of proteins. Despite its wide use, solvatochromism still remains a largely unknown phenomenon due to the extremely complex coupling of many different interactions and dynamical processes which characterize it. In this work the spectroscopic characterization of the Ru(acac)(2)(L) complex (1) [HL = N-(2-methylsulfonyl-phenyl)formamide] are presented. Gas- and solution-phase structural and electronic features of (acac)(2)Ru(L) have been investigated using density functional theory. The molecular structure underscores the flexibility of the formyl fragment in the metal complex. Time-dependent density functional theory has been used to investigate the excited states and solvatochromic properties of Ru(acac)(2)(L). The calculated vertical excitation energies in solution are consistent with the experimental data, showing that the ligand-to-metal charge-transfer transitions, in both the visible and UV regions, dominate over the ligand based pi-pi* transitions.
First author: Vermeeren, P, How Alkali Cations Catalyze Aromatic Diels-Alder Reactions,
CHEMISTRY-AN ASIAN JOURNAL, 15, 1167, (2020)
Abstract: We have quantum chemically studied alkali cation-catalyzed aromatic Diels-Alder reactions between benzene and acetylene forming barrelene using relativistic, dispersion-corrected density functional theory. The alkali cation-catalyzed aromatic Diels-Alder reactions are accelerated by up to 5 orders of magnitude relative to the uncatalyzed reaction and the reaction barrier increases along the series Li+ < Na+ < K+ < Rb+ < Cs+ < none. Our detailed activation strain and molecular-orbital bonding analyses reveal that the alkali cations lower the aromatic Diels-Alder reaction barrier by reducing the Pauli repulsion between the closed-shell filled orbitals of the dienophile and the aromatic diene. We argue that such Pauli mechanism behind Lewis-acid catalysis is a more general phenomenon. Also, our results may be of direct importance for a more complete understanding of the network of competing mechanisms towards the formation of polycyclic aromatic hydrocarbons (PAHs) in an astrochemical context.
First author: Kharitonov, VB, Mononuclear (C5R5)Ir-complexes with pi-linked biaryls: Stability and fluorescence quenching,
JOURNAL OF ORGANOMETALLIC CHEMISTRY, 911, 1167, (2020)
Abstract: The arene iridium complexes [(eta(5)-C5R5)M(eta(6)-PhX)](SbF6)(2) (1a: R = H, X = CH=CHPh; 1b: R = Me, X = CH=CHPh; 2: R = Me, X = C=CPh; 3: R = Me, X = 4-Me-1H-isochromen-1-one) were synthesized by the reactions of the halides [CpIrI2]n or [Cp*IrCl2](2) with trans-stilbene, tolan and 3-phenyl-4-methyl-1H-isochromen-1-one in the presence of AgSbF6. They have proved to be stable towards the arene replacement with nucleophiles (such as acetonitrile, water and KI). The structures of 1b(SbF6)(2) and 3(SbF6)(2) were determined by X-ray diffraction. The experimental and DFT calculation data showed that the coordination of trans-stilbene and 3-phenyl-4-methyl-1H-isochromen-1-one with the Cp*Ir-moiety leads to the fluorescence quenching due to the intramolecular charge transfer from the ligand to iridium.
First author: Ali, E, Improved theoretical calculations for electron-impact ionization of DNA analogue molecules,
JOURNAL OF CHEMICAL PHYSICS, 152, 1167, (2020)
Abstract: Ionizing interactions between charged particles and molecules of biological relevance have attracted considerable interest in the last decade due to its importance in medical radiation therapy. We have previously calculated triply differential cross sections for five biomolecules in collaboration with experimental groups. We used the molecular 3-body distorted wave approximation for these calculations. For ionization of biomolecules, experimentalists are unable to determine the orientation of the molecule at the time of ionization, which means that the calculated cross sections need to be averaged over all molecular orientations. At the time the calculations were performed, it was not numerically feasible for us to perform proper averaging over orientations, so we introduced the orientation averaged molecular orbital approximation to make the calculations possible. We now have the computational capability to properly perform this average, so, here, we present new results with a proper average over orientations and compare with the previous calculations and experiment. Since the original calculations, results from two different distorted-wave models have also been published and the new results will also be compared with those calculations. Overall, the new results are in better agreement with the experiment.
First author: Shaik, S, Two-state Reactivity: Personal Recounting of Its Conception and Future Prospects,
ISRAEL JOURNAL OF CHEMISTRY, 60, 938, (2020)
Abstract: This essay tells the story of the conception of the Two-State Reactivity (TSR) notion. Since scientific career is part of life’s flow, the story blends sub-stories of scientific colleagues and events. This is also a story of a beguiling paradigm, which has started from a puzzling reactivity of the diatomic oxidant FeO+, has continued to larger oxidants, like the active species of Cytochrome P450 and of nonheme enzymes, and its extension to reductive processes. Finally, the essay discusses prospects of experimental probing of the reactive spin-state, and of the transition state constitution for these reactions by means of tunneling-augmented kinetic isotope effects.
First author: Zhao, SW, Construction of heterostructured g-C3N4/ZnO/cellulose and its antibacterial activity: experimental and theoretical investigations,
DALTON TRANSACTIONS, 49, 3723, (2020)
Abstract: A g-C3N4/ZnO/cellulose ternary composite (labeled as CNZCel) with an ordered structure and excellent antibacterial properties has been successfully synthesized via a facile method. Its morphology, microstructure and components have been analyzed by using XRD, SEM, TEM and EDS, and the results corroborate the co-existence of three components in the ternary composite. It is revealed that ZnO particles are connected to the layered g-C3N4 and simultaneously attached to the cellulose substrate. This microstructural feature is also borne out by the relativistic density functional study of a finite g-C3N4-ZnO-cellulose cluster. Both experimental and theoretical results unravel that the interfacial bonding interactions in the ternary composite improve electron transfer among components and enable high-efficiency spatial separation of photogenerated electrons and holes. Consequently, good antibacterial performance of the composite has been found in tests. This study provides the prospect of preparing low-cost and environment-friendly food packaging materials, which are also endowed with excellent antibacterial activity.
First author: Alkan, M, Coupling of two curved polyaromatic radical-anions: stabilization of dimers by counterions,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 6716, (2020)
Abstract: In this study, a comprehensive theoretical investigation of both kinetic and thermodynamic stabilities was performed for dimeric dianionic systems (C20H10)(2)(2-) and (C28H14)(2)(2-), neutralized by two alkali metal cations. The influence of the counterions was of primary interest. The impact of the additional/spectator ligand(s) was elucidated by considering adducts with four molecules of diglyme or two molecules of 18-crown-6 ether. Importantly, both types of systems – in the form of contact-ion pair (CIP) and solvent-separated ion pair (SSIP) – were considered. The SSIP set was augmented by the adduct, in which the dimeric dianionic species were neutralized with purely organic cations N(CH3)(4)(+) and P(CH3)(4)(+). Detailed analysis of the bonding revealed that the presence of the counterions made these systems thermodynamically stable. This finding is in sharp contrast with results obtained for isolated (PAH)(2)(2-) systems, which were previously found to be thermodynamically unstable, but kinetically persistent. The introduction of the alkali metal cations to the system significantly increases the ionic term (Delta E-elstat), whereas the repulsive Delta E-Pauli one was found to be substantially reduced. Considering that the orbital component (Delta E-orb) exhibited only a moderate decrease and the preparation energy (Delta E-prep) showed no changes, the above-mentioned changes in Delta E-elstat and Delta E-Pauli provided a clear explanation for the increase of the thermodynamic stability of the target species. Importantly, a clear correlation between the size of the alkali metal cation and stability of the target dimeric product was established. Thermodynamic stability of the system rises with a decrease in the size of M+ due to enlargement of the Delta E-orb. Evaluated energy barriers (as spin-crossing points between singlet and triplet energy surfaces) were found to be equal to +15.85 kcal mol(-1) and +18.5 kcal mol(-1) for [(Cs+)(2){(C20H10)(2)(2-)}] and [(Cs+)(2){(C28H14)(2)(2-)}], respectively, which is substantially higher than those calculated for isolated (PAH)(2)(2-) systems (+10.00 kcal mol(-1) for (C20H10)(2)(2-) and +12.35 kcal mol(-1) for (C28H14)(2)(2-)). Thus, this study identified the presence of counterions as the key factor, which have a dramatic influence on the thermodynamic and kinetic stabilities of the aimed dianionic dimeric systems, which are formed by two curved polyaromatic monoanion-radicals.
First author: Vorobyev, V, Tuning the structure and photoinduced linkage isomerism of tetrapyridine nitrosyl ruthenium(ii) complexes by changing the trans-to-NO coordinated ligand,
NEW JOURNAL OF CHEMISTRY, 44, 4762, (2020)
Abstract: The perchlorate series of nitrosyl ruthenium tetrapyridine-cations trans-[RuNOPy4X](n+) (where X = OH, Cl, and H2O) were synthesized. The exchange of the anion in an excess of sodium perchlorate results in the formation of the hydroxo complex, with perchlorate as a counter-anion. The protonation of the coordinated hydroxyl resulted in the formation of the aqua complex in acidic media. The outcome of the protonation depends on the choice of the acid. The use of non-coordinating perchloric acid leads to the aqua complex as the product. The ruthenium nitrosyl complex with a coordinated chloride anion was a result of the interaction of the hydroxo complex with concentrated hydrochloric acid. The crystal structures were determined using X-ray single crystal analysis. The 445 nm irradiation promotes electron transfer from the metal orbital to the antibonding orbital of the nitrosyl group. In the solid phase, this metal-to-ligand charge transfer results in the formation of the metastable states with Ru-ON coordination. These photoinduced linkage isomers for each complex were monitored by IR-spectra and their stability was measured using the temperature sweep method described in an earlier study.
First author: Kelley, MP, delta and phi back-donation in An(IV) metallacycles,
NATURE COMMUNICATIONS, 11, 4762, (2020)
Abstract: In all known examples of metal-ligand (M-L) delta and bonds, the metal orbitals are aligned to the ligand orbitals in a “head-to-head” or “side-to-head” fashion. Here, we report two fundamentally new types of M-L delta and phi interactions; “head-to-side” delta and “side-to-side” phi back-bonding, found in complexes of metallacyclopropenes and metallacyclocumulenes of actinides (Pa-Pu) that makes them distinct from their corresponding Group 4 analogues. In addition to the known Th and U complexes, our calculations include complexes of Pa, Np, and Pu. In contrast with conventional An-C bond decreasing, due to the actinide contraction, the An-C distance increases from Pa to Pu. We demonstrate that the direct L-An sigma and pi donations combined with the An-L delta or phi back-donations are crucial in explaining this non-classical trend of the An-L bond lengths in both series, underscoring the significance of these delta/phi back-donation interactions, and their importance for complexes of Pa and U in particular. p id= Par Metal-ligand delta and phi interactions, though considered weak, may be necessary for fully describing the electronic and geometric structures of certain compounds. Here, in actinide metallacycles, the authors discover two new types of M-L delta and phi back-bonds that contribute substantially to their unusual chemical behavior.
First author: Margiotta, E, Halogen Bonds in Ligand-Protein Systems: Molecular Orbital Theory for Drug Design,
JOURNAL OF CHEMICAL INFORMATION AND MODELING, 60, 1317, (2020)
Abstract: Halogen bonds are highly important in medicinal chemistry as halogenation of drugs, generally, improves both selectivity and efficacy toward protein active sites. However, accurate modeling of halogen bond interactions remains a challenge, since a thorough theoretical investigation of the bonding mechanism, focusing on the realistic complexity of drug-receptor systems, is lacking. Our systematic quantum-chemical study on ligand/peptide-like systems reveals that halogen bonding is driven by the same bonding interactions as hydrogen bonding. Besides the electrostatic and the dispersion interactions, our bonding analyses, based on quantitative Kohn-Sham molecular orbital theory together with energy decomposition analysis, reveal that donor-acceptor interactions and steric repulsion between the occupied orbitals of the halogenated ligand and the protein need to be considered more carefully within the drug design process.
First author: Majid, A, DFTB Investigations on Transition Metals Doped TiO2 Quantum Dots,
JOURNAL OF ELECTRONIC MATERIALS, 49, 3659, (2020)
Abstract: The structural, optical and electronic properties of different-sized pure as well as transition metals doped TiO2 quantum dots were investigated using density functional tight binding (DFTB) methods. The self-consistent charge density functional tight binding theory (SCC-DFTB) was used to model the TiO2 quantum dots (QDs) of increasing size up to 3.03 nm. The size dependence of density of states, position of molecular orbitals, and gap between highest orbital molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) of the QDs were studied. It appeared that, when the size of QDs approaches 3.03 nm, the energy gap narrowed down due to quantum confinement effects. The QD Ti27O54 was doped with 3d transition metals to further explore the possibility of tailoring the properties. The dopants introduced 3d impurity gap states which opens the opportunity to modify the band gap or positions of principal bands. The position of a shifted Fermi level was monitored to explore the changes in conductivity and n- or p-type behaviors of the doped QDs. It was observed that TiO2 QDs doped with V and Cr showed the n-type behavior while those doped with Sc, Mn and Fe showed p-type behavior. The findings are helpful to enhance the photocurrent efficiency of dye-sensitized solar cells and use the materials in electronic and optoelectronic properties.
First author: Conradie, J, Redox behaviour of [Ru(beta-diketonato)(3)] compounds,
ELECTROCHIMICA ACTA, 337, 3659, (2020)
Abstract: The reduction potentials of the Ru-III/II and the Ru-III/IV redox couples of fourteen [Ru(beta-diketonato)(3)] compounds are related both to electronic descriptors that describe the electron donating or withdrawing properties of the R and R’ groups on the beta-diketonato ligand (RCOCHCOR’)(-), as well as to their density functional theory (DFT) calculated energies. Most of these linear relationships have a R-2 value of above 0.90. The relationship between the experimental reduction potential of both the Ru-III/II and the Ru-IV/III redox couples and their calculated HOMO and LUMO energy values respectively, the latter directly obtainable from the DFT computed output files, can conveniently be used to theoretically predict the redox potentials of related customized [Ru(beta-diketonato)(3)] compounds, prior to synthesis of such compounds.
First author: Zhang, JX, Aggregation-Induced Intersystem Crossing: Rational Design for Phosphorescence Manipulation,
JOURNAL OF PHYSICAL CHEMISTRY B, 124, 2238, (2020)
Abstract: Phosphorescence of organic molecules has drawn extensive attention due to its potential applications in energy and life science. However, typically intersystem crossing (ISC) in organic molecules is slow due to the small spin-orbit couplings (SOC) and large energy gaps (Delta ES-T) between different multiplicities. Molecular aggregation offers a practical strategy to manipulate phosphorescent characteristics. In this work, the impact of aggregation on the luminescence properties of pi-conjugated benzophenone luminophore 1-dibenzo[b,d]thiophen-2-yl(phenyl)methanone (BDBT) are investigated theoretically using density functional theory (DFT) and time-dependent DFT. Molecular aggregation results in substantial energy splitting and variation of SOC, eventually changing the ISC rate. This is known as the “aggregation-induced intersystem crossing” (AI-ISC) mechanism. Different types of electron donating and withdrawing functional groups are further introduced into BDBT molecular system to tailor the phosphorescent efficiency. We find that functional groups can influence the SOC and energy gaps and further manipulate the phosphorescence efficiency. Molecular systems with donating functional groups have faster ISC rates, and dimers exhibit the best electronic luminescence due to the relatively large SOC and small Delta ES-T. The AI-ISC mechanism accompanied by group functionalization provides a practical platform for phosphorescence enhancement.
First author: Smith, AD, Femtosecond Soft-X-ray Absorption Spectroscopy of Liquids with a Water-Window High-Harmonic Source,
JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 11, 1981, (2020)
Abstract: Femtosecond X-ray absorption spectroscopy (XAS) is a powerful method to investigate the dynamical behavior of a system after photoabsorption in real time. So far, the application of this technique has remained limited to large-scale facilities, such as femtosliced synchrotrons and free-electron lasers (FEL). In this work, we demonstrate femtosecond time-resolved soft-X-ray absorption spectroscopy of liquid samples by combining a sub-micrometer-thin flat liquid jet with a high-harmonic tabletop source covering the entire water-window range (284-538 eV). Our work represents the first extension of tabletop XAS to the oxygen edge of a chemical sample in the liquid phase. In the time domain, our measurements resolve the gradual appearance of absorption features below the carbon K-edge of ethanol and methanol during strong-field ionization and trace the valence-shell ionization dynamics of the liquid alcohols with a temporal resolution of similar to 30 fs. This technique opens unique opportunities to study molecular dynamics of chemical systems in the liquid phase with elemental, orbital, and site sensitivity.
First author: Pakhira, S, Quantum Nature in the Interaction of Molecular Hydrogen with Porous Materials: Implications for Practical Hydrogen Storage,
JOURNAL OF PHYSICAL CHEMISTRY C, 124, 6454, (2020)
Abstract: The storage of hydrogen (H-2) is of economic and ecological relevance, because it could potentially replace petroleum-based fuels. However, H-2 storage at mild condition remains one of the bottlenecks for its widespread usage. In order to devise successful H-2 storage strategies, there is a need for a fundamental understanding of the weak and elusive hydrogen interactions at the quantum mechanical level. One of the most promising strategies for storage at mild pressure and temperature is physisorption. Porous materials are specially effective at physisorption, however the process at the quantum level has been under-studied. Here, we present quantum calculations to study the interaction of H-2 with building units of porous materials. We report 240 H-2 complexes made of different transition metal (Tm) atoms, chelating ligands, spins, oxidation states, and geometrical configurations. We found that both the dispersion and electrostatics interactions are the major contributors to the interaction energy between H-2 and the transition metal complexes. The binding energy for some of these complexes is in the range of at least 10 kJ/mol for many interactions sites, which is one of these main requirements for practical H-2 storage. Thus, these results are of a fundamental nature for practical H-2 storage in porous materials.
First author: Sarkar, S, Experimental evidence of N-H center dot center dot center dot N hydrogen bonding in the heterodimers of pyrrole with nitrogen bases,
JOURNAL OF MOLECULAR STRUCTURE, 1204, 6454, (2020)
Abstract: ( )The hydrogen bonded heterodimers of pyrrole (C4H5N) with nitrogen bases, ammonia (NH3), pyridine (C5H5N) and quinoline (C9H7N) have been studied in Ar and N-2 matrices at low temperatures. The heterodimers were characterized using infrared spectroscopy. To account for the possible structures of the heterodimers, quantum chemical calculation at MP2/aug-cc-pVDZ level of theory was performed which indicated five, four and three minima for the 1:1 C4H5N-NH3, C4H5N-C5H5N and C4H5N-C9H7N heterodimers, respectively. The global minimum heterodimer in each of the systems studied are stabilized by a robust N-H center dot center dot center dot N bonding between the weak proton donor C4H5N, and the strong proton acceptors viz. NH3, C5H5N and C9H7N. The experimental evidence for the formation of the heterodimers was observed in the N-H stretching and bending, C-H bending modes of C4H5N and N-H bending modes of NH3. Since, NH3 is a small molecule, the possibility of forming a vivid range of higher clusters with C4H5N was explored by computational and experimental methods. NBO and ED analyses were performed to understand the nature of the interactions prevailing in the heterodimers.
First author: Cabrera-Trujillo, JJ, Understanding the role of frustrated Lewis pairs as ligands in transition metal-catalyzed reactions,
DALTON TRANSACTIONS, 49, 3129, (2020)
Abstract: The role of frustrated Lewis pairs (FLPs) as ligands in gold(I) catalyzed-reactions has been computationally investigated by using state-of-the-art density functional theory calculations. To this end, the nature of (P,B)-FLP-transition metal interactions in different gold(I)-complexes has been first explored in detail with the help of the energy decomposition analysis method, which allowed us to accurately quantify the so far poorly understood AuB interactions present in these species. The impact of such interactions on the catalytic activity of gold(I)-complexes has been then evaluated by performing the Au(I)-catalyzed hydroarylation reaction of phenylacetylene with mesitylene. With the help of the activation strain model of reactivity, the factors governing the higher activity of Au(I)-complexes having a FLP as a ligand as compared to that of the parent PPh3 system have also been quantitatively identified.
First author: Windorff, CJ, Probing a variation of the inverse-trans-influence in americium and lanthanide tribromide tris(tricyclohexylphosphine oxide) complexes,
CHEMICAL SCIENCE, 11, 2770, (2020)
Abstract: The synthesis, characterization, and theoretical analysis of meridional americium tribromide tris(tricyclohexylphosphine oxide), mer-AmBr3(OPcy(3))(3), has been achieved and is compared with its early lanthanide (La to Nd) analogs. The data show that homo trans ligands display significantly shorter bonds than the cis or hetero trans ligands. This is particularly pronounced in the americium compound. DFT along with multiconfigurational CASSCF calculations show that the contraction of the bonds relates qualitatively with overall covalency, i.e. americium shows the most covalent interactions compared to lanthanides. However, the involvement of the 5p and 6p shells in bonding follows a different order, namely cerium > neodymium similar to americium. This study provides further insight into the mechanisms by which ITI operates in low-valent f-block complexes.
First author: Kumar, V, Double Chalcogen Bonds: Crystal Engineering Stratagems via Diffraction and Multinuclear Solid-State Magnetic Resonance Spectroscopy,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 3275, (2020)
Abstract: Group 16 chalcogens potentially provide Lewis-acidic sigma-holes, which are able to form attractive supramolecular interactions with electron rich partners through chalcogen bonds. Here, a multifaceted experimental and computational study of a large series of novel chalcogen-bonded cocrystals, prepared using the principles of crystal engineering, is presented. Single-crystal X-ray diffraction studies reveal that dicyanoselenadiazole and dicyanotelluradiazole derivatives work as promising supramolecular synthons with the ability to form double chalcogen bonds with a wide range of electron donors including halides and oxygen- and nitrogen-containing heterocycles. Extensive Se-77 and Te-125 solid-state nuclear magnetic resonance spectroscopic investigations of cocrystals establish correlations between the NMR parameters of selenium and tellurium and the local chalcogen bonding geometry. The relationships between the electronic environment of the chalcogen bond and the Se-77 and Te-125 chemical shift tensors were elucidated through a natural localized molecular orbital density functional theory analysis. This systematic study of chalcogen-bond-based crystal engineering lays the foundations for the preparation of the various multicomponent systems and establishes solid-state NMR protocols to detect these interactions in powdered materials.
First author: Cavo, S, Accurate optical spectra of solids from pure time-dependent density functional theory,
PHYSICAL REVIEW B, 101, 3275, (2020)
Abstract: We present accurate optical spectra of semiconductors and insulators within a pure Kohn-Sham time-dependent density functional approach. In particular, we show that the onset of the absorption is well reproduced when comparing to experiment. No empirical information nor a theory beyond Kohn-Sham density functional theory, such as GW, is invoked to correct the Kohn-Sham gap. Our approach relies on the link between the exchange-correlation kernel of time-dependent density functional theory and the derivative discontinuity of ground-state density functional theory. We show explicitly how to relate these two quantities. We illustrate the accuracy and simplicity of our approach by applying it to various semiconductors (Si, GaP, GaAs) and wide-gap insulators (C, LiF, Ar).
First author: Senanayake, RD, Electronic relaxation dynamics in [Au-25(SR)(18)](-1) (R = CH3, C2H5, C3H7, MPA, PET) thiolate-protected nanoclusters,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 5272, (2020)
Abstract: We investigate the excited electron dynamics in [Au-25(SR)(18)](-1) (R = CH3, C2H5, C3H7, MPA, PET) [MPA = mercaptopropanoic acid, PET = phenylethylthiol] nanoparticles to understand how different ligands affect the excited state dynamics in this system. The population dynamics of the core and higher excited states lying in the energy range 0.00-2.20 eV are studied using a surface hopping method with decoherence correction in a real-time DFT approach. All of the ligated clusters follow a similar trend in decay for the core states (S-1-S-6). The observed time constants are on the picosecond time scale (2-19 ps), which agrees with the experimental time scale, and this study confirms that the time constants observed experimentally could originate from core-to-core transitions and not from core-to-semiring transitions. In the presence of higher excited states, R = H, CH3, C2H5, C3H7, and PET demonstrate similar relaxations trends whereas R = MPA shows slightly different relaxation of the core states due to a smaller gap between the LUMO+1 and LUMO+2 gap in its electronic structure. The S-1 (HOMO -> LUMO) state gives the slowest decay in all ligated clusters, while S-7 has a relatively long decay. Furthermore, separate electron and hole relaxations were performed on the [Au-25(SCH3)(18)](-1) nanocluster to understand how independent electron and hole relaxations contribute to the overall relaxation dynamics.
First author: Syatunek, D, Concerted [4+2] and Stepwise (2+2) Cycloadditions of Tetrafluoroethylene with Butadiene: DFT and DLPNO-UCCSD(T) Explorations,
JOURNAL OF ORGANIC CHEMISTRY, 85, 3858, (2020)
Abstract: Tetrafluoroethylene and butadiene form the 2 + 2 cycloadduct under kinetic control, but the Diels-Alder cycloadduct is formed under thermodynamic control. Borden and Getty showed that the preference for 2 + 2 cycloaddition is due to the necessity for syn-pyramidalization of the two CF2 groups in the 4 + 2 transition state. We have explored the full potential energy surface for the concerted and stepwise reactions of tetrafluoroethylene and butadiene with density functional theory, DFT (B3LYP and M06-2X), DLPNO-UCCSD(T), and CASSCF-NEVPT2 methods and with the distortion/interaction-activation strain model to explain the energetics of different pathways. The 2 + 2 cycloadduct is formed by an anti-transition state followed by two rotations and a final bond formation transition state. Energetics are compared to the reaction of maleic anhydride and ethylene.
First author: Koenis, MAJ, Analysis of Vibrational Circular Dichroism Spectra of Peptides: A Generalized Coupled Oscillator Approach of a Small Peptide Model Using VCDtools,
JOURNAL OF PHYSICAL CHEMISTRY B, 124, 1665, (2020)
Abstract: Vibrational circular dichroism (VCD) is one of the major spectroscopic tools to study peptides. Nevertheless, a full understanding of what determines the signs and intensities of VCD bands of these compounds in the amide I and amide II spectral regions is still far from complete. In the present work, we study the origin of these VCD signals using the general coupled oscillator (GCO) analysis, a novel approach that has I recently been developed. We apply this approach to the ForVa1NHMe model peptide in both alpha-helix and beta-sheet configurations. We show that the intense VCD signals observed in the amide I and amide II spectral regions essentially have the same underlying mechanism, namely, the through-space coupling of electric dipoles. The crucial role played by intramolecular hydrogen bonds in determining VCD intensities is also illustrated. Moreover, we find that the contributions to the rotational strengths, considered to be insignificant in standard VCD models, may have sizable magnitudes and can thus not always be neglected. In addition, the VCD robustness of the amide I and II modes has been investigated by monitoring the variation of the rotational strength and its contributing terms during linear transit scans and by performing calculations with different computational parameters. From these studies-and in particular, the decomposition of the rotational strength made possible by the GCO analysis-it becomes clear that one should be cautious when employing measures of robustness as proposed previously.
First author: Chen, Y, Probing Conformational Evolution and Associated Dynamics of Mg(N(SO2CF3)(2))(2)center dot Dimethoxyethane Adduct Using Solid-State F-19 and H-1 NMR,
JOURNAL OF PHYSICAL CHEMISTRY C, 124, 4999, (2020)
Abstract: Bis(trifluoromethanesulfonimide) or TFSI is widely used as a counter anion in electrolyte design due to its structural flexibility and chemical stability. We studied the conformational variations and associated dynamics of TFSI in adduct of Mg(TFSI)(2) with dimethoxyethane (DME), a solvate crystalline material using solid-state H-1 and F-19 NMR. TFSI molecular motion in this solvate structure falls within the timescale of the F-19 NMR experiment, yielding spectroscopic signatures for unique TFSI conformers under the coordination environment of Mg2+ cation. Within the temperature range of -5 to 82 degrees C, we observe nine distinct TFSI sites in both crystalline and disordered regions using F-19 NMR, reflecting complexity of structural and dynamics of TFS1 anions within solvate structure. The four distinguishable sites in the disordered region for the two CF3 groups of the same TFSI molecule are identified using chemical shift analysis. The exchange rate constants from site to site are calculated through variable temperature F-19 NMR and twodimensional (2D) exchange spectroscopy (EXSY) experiments, along with respective activation enthalpies using Eyring’s formulation. The flip rate of CF3 around the S-C bond is estimated as similar to 15 s(-1) at 8 degrees C with Delta H-not equal similar to 22 kJ/mol, but the rotation of the entire TFSI is 4.8 s(-1) at 8 degrees C with a significantly greater Delta H-not equal = 98 +/- 10 kJ/mol. Furthermore, the slow conversion of trans to cis conformers at a lower temperature (T <= 1 degrees C) in the crystalline region is monitored, with a conversion rate of similar to 2 x 10(-5) s(-1) at -5 degrees C. Density functional theory (DFT)-based calculations were performed to support further the assignment of experimental chemical shifts, and the activation energy E-a = 21.1 kJ/mol obtained for the cis to trans transition is consistent with experimental values. The combined set of F-19 and H-1 under both one-dimensional (1D) and 2D NMR methods demonstrated here can be further used for examining electrode-electrolyte interfaces to probe the motions of various constituents that can enable detailed studies of interfacial processes and dynamics. Ultimately, such studies will aid in the design and discovery of interfacial constructs in which directed defect chemistry, chemical moiety distribution, and nanostructure are employed to drive efficient charge transport.
First author: Persaud, RR, Prediction of Structures and Atomization Energies of Coinage Metals, (M)(n), n < 20: Extrapolation of Normalized Clustering Energies to Predict the Cohesive Energy,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 1775, (2020)
Abstract: The geometries of the group 11 coinage metals (n = 2-20) were optimized to determine the lowest energy isomers for each cluster size, singlets for even numbers and doublets for odd numbers. For copper and silver, 2-D (planar) geometries were favored up to n = 6. For gold, 2D (planar) geometries were favored up to n = 13. Normalized clustering energies were plotted as a function of cluster size (n(-1/3), for n = 4-20) with various DFT functionals and the CCSD(T)-F12b method and were extrapolated to predict the bulk cohesive energy. In the case of copper and silver, there is excellent agreement between the cohesive energies predicted at the CCSD(T)-F12b level of theory and the experimental values. For gold, the CCSD(T)-F12b values needed to be corrected for spin-orbit relativistic effects to obtain good agreement with experiment. Electronic properties including the HOMO-LUMO gaps for the even clusters and the spin densities for the odd clusters were calculated. The lowest gap is predicted to occur for n = 16 where the HOMO and LUMO are very similar in shape.
First author: Muller, FMA, Conformational preference of nitroformazans: A computational study,
JOURNAL OF MOLECULAR STRUCTURE, 1203, 1775, (2020)
Abstract: A conformation analysis of all possible isomers of 22 differently substituted 1,5-bis(phenyl)-3-nitroformazans is presented. Results clearly showed that, except for 1,5-bis(m-OPh-phenyl)-3-nitroformazan, the closed ring trans-syn, s-cis isomer (DD) is preferred. This result agrees with available experimental structures of differently substituted 1,5-bis(phenyl)-3-nitroformazans that all exhibit the closed ring trans-syn, s-cis conformation. The preference for the closed ring trans-syn, s-cis conformation was further explored by natural bond orbital and quantum theory of atoms in molecules analysis. It was hereby shown that the donor-acceptor interaction and electron density of the bond path related to the intramolecular N-H center dot center dot center dot N hydrogen bond in the closed ring trans-syn, s-cis isomer (DD) is stronger and larger respectively than in other isomeric forms such as the open trans-syn, s-trans (UD and DU) and linear trans-anti, s-trans (UU) configurations.
First author: Truscott, JC, Synthesis, structure and DFT study of novel Ga(III) complexes containing a tetradentate ligand,
JOURNAL OF MOLECULAR STRUCTURE, 1203, 1775, (2020)
Abstract: The synthesis, structure and density functional theory (DFT) calculations of two novel Ga(III) complexes, the first containing a tetradentate Schiff base ligand (L1) and the second containing a tetradentate carboxamide ligand (L2), are presented. The complexes are isolated as octahedral complexes with two water molecules attached to the axial positions. Both experimental and DFT calculations show that when [Ga(L1)(H2O)(2)]center dot NO3 is dissolved in dimethyl sulfoxide (DMSO), spontaneous substitution of axial water groups by DMSO occur to form [Ga(L1)(DMSO)(2)]center dot NO3.
First author: Bettens, T, Ambident Nucleophilic Substitution: Understanding Non-HSAB Behavior through Activation Strain and Conceptual DFT Analyses,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 3884, (2020)
Abstract: The ability to understand and predict ambident reactivity is key to the rational design of organic syntheses. An approach to understand trends in ambident reactivity is the hard and soft acids and bases (HSAB) principle. The recent controversy over the general validity of this principle prompted us to investigate the competing gas-phase S(N)2 reaction channels of archetypal ambident nucleophiles CN-, OCN-, and SCN- with CH3Cl (S(N)2@C) and SiH3Cl (S(N)2@Si), using DFT calculations. Our combined analyses highlight the inability of the HSAB principle to correctly predict the reactivity trends of these simple, model reactions. Instead, we have successfully traced reactivity trends to the canonical orbital-interaction mechanism and the resulting nucleophile-substrate interaction energy. The HOMO-LUMO orbital interactions set the trend in both S(N)2@C and S(N)2@Si reactions. We provide simple rules for predicting the ambident reactivity of nucleophiles based on our Kohn-Sham molecular orbital analysis.
First author: Sadhu, B, Periodic trends and complexation chemistry of tetravalent actinide ions with a potential actinide decorporation agent 5-LIO(Me-3,2-HOPO): A relativistic density functional theory exploration,
JOURNAL OF COMPUTATIONAL CHEMISTRY, 41, 1427, (2020)
Abstract: A relativistic density functional theory (DFT) study is reported which aims to understand the complexation chemistry of An(4+) ions (An = Th, U, Np, and Pu) with a potential decorporation agent, 5-LIO(Me-3,2-HOPO). The calculations show that the periodic change of the metal binding free energy has an excellent correlation with the ionic radii and such change of ionic radii also leads to the structural modulation of actinide-ligand complexes. The calculated structural and binding parameters agree well with the available experimental data. Atomic charges derived from quantum theory of atoms in molecules (QTAIM) and natural bond order (NBO) analysis shows the major role of ligand-to-metal charge transfer in the stability of the complexes. Energy decomposition analysis, QTAIM, and electron localization function (ELF) predict that the actinide-ligand bond is dominantly ionic, but the contribution of orbital interaction is considerable and increases from Th4+ to Pu4+. A decomposition of orbital contributions applying the extended transition state-natural orbital chemical valence method points out the significant pi-donation from the oxygen donor centers to the electron-poor actinide ion. Molecular orbital analysis suggests an increasing trend of orbital mixing in the context of 5f orbital participation across the tetravalent An series (Th-Pu). However, the corresponding overlap integral is found to be smaller than in the case of 6d orbital participation. An analysis of the results from the aforementioned electronic structure methods indicates that such orbital participation possibly arises due to the energy matching of ligand and metal orbitals and carries the signature of near-degeneracy driven covalency.
First author: Adeyiga, O, Activating Water and Hydrogen by Ligand-Modified Uranium and Neptunium Complexes: A Density Functional Theory Study,
INORGANIC CHEMISTRY, 59, 3102, (2020)
Abstract: Organometallic uranium complexes that can activate small molecules are well-known. In contrast, there are no known organometallic trans-uranium species capable of small-molecule transformations. Using density functional theory, we previously showed that changing actinide-ligand bonds from U-O groups to Np-N- (amide/imido) bonds makes redox small-molecule activation more energetically favorable for Np species. Here, we determine how general this ligand-modulation strategy is for affecting small-molecule activation in Np species. We focus on two reactions, one involving redox transformation of the actinide(s) and the other involving no change in the oxidation state of the actinide(s). Specifically, we considered the hydrogen evolution reaction (HER) from H2O by actinide tris-aryloxide species. We also considered H-2 capture and hydride transfer by actinide siloxide and silylamide complexes. For the HER, the barriers for Np(III) systems are much higher than those of U(III). The overall reaction energies are also much worse. An-O -> An-N substitutions marginally improve the barriers by 1-4 kcal/mol and more substantially improve the reaction energies by 9-15 kcal/mol. For H-2 capture and hydride transfer, the reaction energies for the U and Np species are similar. For both actinides, like-for-like An-O -> An-N substitutions lead to improved reaction energies. Interestingly, in a recent report, it seemingly appears that U-O (siloxide) -> U-N (silylamide) leads to complete shutdown of reactivity for H-2 capture and hydride transfer. This observation is reproduced and explained with calculations. The ligand environments of the siloxide and silylamide that were compared are vastly different. The steric environment of the siloxide is conducive for reactivity while the particular silylamide is not. We conclude that small-molecule activation with organometallic neptunium species is achievable with a guided choice of ligands. Additional emphasis should be placed on ligands that can allow for improved transition state barriers.
First author: Chen, YM, Theoretical Insights into Modification of Nitrogen-Donor Ligands to Improve Performance on Am(III)/Eu(III) Separation,
INORGANIC CHEMISTRY, 59, 3221, (2020)
Abstract: Nitrogen-donor ligands have been considered to be promising agents for separating trivalent actinides (An(III)) from lanthanides (Ln(III)). Thereinto, how to decorate these ligands for better extraction performance is urgent to design “perfect” separating extractants. In this work, we systematically explored a series of heterocyclic N-donor ligands (L-1 = dipyridazino[4,3-c:3′,4′-h]acridine, L-2 = dipyridazino[3,4-a:4′,3′-j]phenazine, L-3 = 2,6-di(cinnolin-3-yl)pyridine)), as well as their substituted derivatives, and compared their extraction and complexation ability toward An(III) and Ln(III) ions by using quasi-relativistic density functional theory (DFT). We found that the pyridazine N atoms probably play a notable role in electron donation to metal cations by molecular orbital (MO) and bond order analyses. Besides, the calculated results clearly verified that these N-donor ligands possess higher coordination affinity toward Am(III) over Eu(III). The rigid ligands (L-1 and L-2) exhibit higher selective abilities for the Am(III)/Eu(III) separation compared with that of the flexible ligand (L-3). For each ligand, the 1:2 (metal/ligand) extraction reaction is predicted to be most probable in the separation process. The introduction of an alkyl group on the lateral chain or an electron-donating group on the main chain gives rise to a better extraction performance of the ligands, and the CyMe4 or MeO substituted ligands show higher extraction and separation ability. Simultaneous introduction of CyMe4 and MeO groups can enhance the extraction ability of the ligand to metal ions, but the separating ability depends on the differences of the extraction capacity of An(III) and Ln(III). This work can help to gain a more in-depth understanding the selectivity differences of similar N-donor ligands and provide more theoretical insights into the design of novel extractants for An(III)/Ln(III) separation.
First author: Rahman, MH, Infrared Spectroelectrochemistry of Iron-Nitrosyl Triarylcorroles. Implications for Ligand Noninnocence,
INORGANIC CHEMISTRY, 59, 3232, (2020)
Abstract: Recent DFT calculations have suggested that iron nitrosyl triarylcorrole complexes have substantial {FeNO}(7)-corrole(center dot 2-) character. With this formulation, reduction of Fe(C)(NO) complexes, where C = triarylcorrole, should be centered on the corrole macrocycle rather than on the {FeNO}(7) moiety. To verify this proposition, visible and infrared spectroelectrochemical studies of Fe(C)(NO) were carried out and the results were interpreted using DFT (B3LYP/STO-TZP) calculations. The first reduction of Fe(C)(NO) led to significant changes in the Soret and Q-band regions of the visible spectrum as well as to a significant downshift in the nu(NO) and changes in the corrole vibrational frequencies. DFT calculations, which showed that the electron was mostly added to the corrole ligand (85%), were also able to predict the observed shifts in the v No and corrole bands upon reduction. These results underscore the importance of monitoring both the corrole and nitrosyl vibrations in ascertaining the site of reduction. By contrast, the visible spectroelectrochemistry of the second reduction revealed only minor changes in the Soret band upon reduction, consistent with the reduction of the FeNO moiety.
First author: Banibairami, T, Sensing Behavior of Hexagonal-Aluminum Nitride to Phosgene Molecule Based on Van der Waals-Density Functional Theory and Molecular Dynamic Simulation,
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A, 94, 581, (2020)
Abstract: In this paper, we evaluated adsorption of phosgene gas molecule (COCl2), on the hexagonal-aluminum nitride (h-AlN) nanosheet by using first-principles van der Waals density functional theory calculations (vdW-DF) method. The nature of interaction between the phosgene molecule and h-AlN is discovered by geometries, adsorption energies, Mulliken, Hirshfeld as well as Voronoi charges analyses. The density of states (DOS) was calculated and the results show that HOMO/LUMO energy gap of h-AlN is significantly reduced upon the COCl2 adsorption. The projected density of states (PDOS) of the adsorption systems suggested that the enhancement of adsorption was owing to the hybridization between Al atom of h-AlN sheet and the O atom of phosgene molecule. Interestingly, the results reveal that the E-g of h-AlN is very sensitive to the presence of COCl2 molecule as its value reduces from 3.337 eV in pure h-AlN to 1.966 eV (41.08% change) after the COCl2 adsorption which would result in electrical conductance increment. Global reactivity descriptor values such as electronegativity (chi), global hardness (eta), global softness (S), electronic chemical potential (mu), electrophilicity index (omega), and electro accepting power (omega(+)) were calculated. Additionally, the stability of the most stable phosgene/h-AlN complex was evaluated by means of DFT molecular dynamics (MD) simulation at room temperature under constant volume and temperature conditions with PBE method. Based on the DFT calculation results, the h-AlN nano sheet is expected to be potential novel sensor for detecting the presence of COCl2 gas.
First author: Dohm, S, Semiautomated Transition State Localization for Organometallic Complexes with Semiempirical Quantum Chemical Methods,
JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 16, 2002, (2020)
Abstract: We present an efficient computational protocol for robust transition state localization that can be routinely applied to complex (organometallic) reactions. The capabilities of the combination of extended tight-binding semiempirical methods (GFNn-xTB) with a state-of-the-art transition state localization algorithm (mGSM) is demonstrated on a modified version of the MOBH35 benchmark set, consisting of 29 organometallic reactions and transition states. Furthermore, for three examples we demonstrate how error-prone the conventional (manual) approach based on chemical intuition can be and how errors are avoided by a semiautomated generation of reaction profiles. The performance of the GFNn-xTB methods is carefully assessed and compared with that of the widely used PM6-D3H4 and PM7 semiempirical methods. The GFNn-xTB methods show much higher success rates of 89.7% (GFN1-xTB) and 86.2% (GFN2-xTB) compared with 72.4% for PM6-D3H4 and 69.0% for PM7. The barrier heights and reaction energies are computed with much better accuracy at reduced computational cost for the GFNn-xTB methods compared with the PMx methods, allowing a semiquantitative assessment of possible reaction pathways already at a semiempirical level. The mean error of GFN2-xTB for the barrier heights (8.2 kcal mol(-1)) is close to what low-cost density functional approximations provide and substantially smaller than the corresponding error of the competitor methods.
First author: Bacha, RUS, Graphdiyne-actinyl complexes as potential catalytic materials: A DFT perspective from their structural, bonding, electronic and redox properties,
ARABIAN JOURNAL OF CHEMISTRY, 13, 4564, (2020)
Abstract: Versatile graphdiyne (GDY) substrate has been modified by numerous transition metals and resulting composites showed excellent photo/electro-catalytic performance. However, GDY materials modified by actinides that are stockpiled waste product due to large-scale use in nuclear industry, are particularly scarce and remains great challenge. To deeply understand the structural properties, GDY complexating actinyl (An(m)O(2))(n+) (An = U, Np, Pu; m = VI, V) species with its atomistic pore was investigated by relativistic density functional theory (DFT). The GDY pore was found suitable to hold actinyl species, by forming organometallic An-C dative bonds. This chemical coupling interaction was further confirmed by quantum theory of atoms-in-molecule and electronic structure calculations. The GDY-uranyl(V), for instance, shows a pi(U-C) bonding HOMO, which is anticipated to improve electron transfer between ligand and metal. Orbital structures and compositions of complexes suggest their implication towards catalysis, which were further corroborated by calculations on redox potentials of GDY-actinyl complexes. Hence, our results show the potential applications of GDY complexating actinyl species towards novel catalytic surfaces.
First author: Kang, S, The key role of acceptor moieties on the structural and the electronic properties of thermally activated delayed fluorescence emitters in excited states: A computational study,
ORGANIC ELECTRONICS, 78, 4564, (2020)
Abstract: The insight into understanding the effect of acceptor moieties with phenoxazine (PXD) donor and bridging phenyl (Ph) spacer on structural and electronic properties of excited state was theoretically investigated through density functional theory simulations. Di-phenyltriazine (DPhTRZ), di-phenyl pyrimidine (DPhPyM), and dipyridyl pyrimidine (DPyPyM) were chosen as acceptor moieties for thermally activated delayed fluorescence (TADF) emitters. It was found that planar structure between phenyl spacer and DPhTRZ/DPyPyM was dominantly determined by intramolecular H-bonds at inner side of acceptor moiety. Depending on the acceptor moieties, the adiabatic excitation energy in singlet and triplet state is shifted to higher energies in order: DPyPyM (blue) > DPhPyM (greenish-blue) > DPhTRZ (green). In the perspective of spin conversion, the exact spin flip barrier, defined as total energy barrier for triplet-to-singlet transition, is in order of DPhTRZ < DPyPyM < DPhPyM. The calculated spin-orbit coupling matrix element with DPyPyM is relatively larger than that with DPhTRZ and DPhPyM. The calculated reverse intersystem crossing rate for triplet conversion is the largest with DPhTRZ and the smallest with DPhPyM. The comprehensive analyses conclusively suggest that DPyPyM acceptor moiety can be utilized for blue TADF emitters with superb structural rigidity, large spin conversion rate and low spin flip barrier.
First author: Majid, A, Assessment of 2H-SiC based intercalation compound for use as anode in lithium ion batteries,
CERAMICS INTERNATIONAL, 46, 5297, (2020)
Abstract: The improvement in electrode materials to upgrade lithium ion battery (LIB) is at heart of research related to energy devices. Herein, we report on the prospects of using 2H-SiC as an anode material in LIB on the basis of first principles based theoretical predictions. The energy profiling of high symmetry structural sites pointed out that the site T-c related to tetrahedral configuration with carbon is favorable intercalation site in the host. The reaction of Li with stoichiometric as well as non-stoichiometric 2H-SiC are found endothermic which points to their unsuitability for lithiation process in LIBs. However, Li intercalation into the host in presence of Si monovacancy appeared an exothermic process which motivated us to study this system in detail. The Li atom after intercalation into the host is found ionized thereby donating its 2s electron to carbon atoms. The average value of the lithium insertion voltage and theoretical capacity are calculated as 1.87 V and 85 mA h/g respectively for the host simulated in the form of supercell LixSi15C16. The diffusion barrier faced by lithium atom while moving along crystalline a-axis is minimum (among all the paths considered here) when it follows a path that links hexagonal rings while passing carbon atoms. On the other hand, in case of motion along c-axis, similar results are found for minimum energy path that is along Tc site. The low diffusion barrier will facilitate the lithium ion to move quickly that points to fast charging capability of the battery.
First author: Ponce, S, First-principles calculations of charge carrier mobility and conductivity in bulk semiconductors and two-dimensional materials,
REPORTS ON PROGRESS IN PHYSICS, 83, 5297, (2020)
Abstract: One of the fundamental properties of semiconductors is their ability to support highly tunable electric currents in the presence of electric fields or carrier concentration gradients. These properties are described by transport coefficients such as electron and hole mobilities. Over the last decades, our understanding of carrier mobilities has largely been shaped by experimental investigations and empirical models. Recently, advances in electronic structure methods for real materials have made it possible to study these properties with predictive accuracy and without resorting to empirical parameters. These new developments are unlocking exciting new opportunities, from exploring carrier transport in quantum matter to in silico designing new semiconductors with tailored transport properties. In this article, we review the most recent developments in the area of ab initio calculations of carrier mobilities of semiconductors. Our aim is threefold: to make this rapidly-growing research area accessible to a broad community of condensed-matter theorists and materials scientists; to identify key challenges that need to be addressed in order to increase the predictive power of these methods; and to identify new opportunities for increasing the impact of these computational methods on the science and technology of advanced materials. The review is organized in three parts. In the first part, we offer a brief historical overview of approaches to the calculation of carrier mobilities, and we establish the conceptual framework underlying modern ab initio approaches. We summarize the Boltzmann theory of carrier transport and we discuss its scope of applicability, merits, and limitations in the broader context of many-body Green’s function approaches. We discuss recent implementations of the Boltzmann formalism within the context of density functional theory and many-body perturbation theory calculations, placing an emphasis on the key computational challenges and suggested solutions. In the second part of the article, we review applications of these methods to materials of current interest, from three-dimensional semiconductors to layered and two-dimensional materials. In particular, we discuss in detail recent investigations of classic materials such as silicon, diamond, gallium arsenide, gallium nitride, gallium oxide, and lead halide perovskites as well as low-dimensional semiconductors such as graphene, silicene, phosphorene, molybdenum disulfide, and indium selenide. We also review recent efforts toward high-throughput calculations of carrier transport. In the last part, we identify important classes of materials for which an ab initio study of carrier mobilities is warranted. We discuss the extension of the methodology to study topological quantum matter and materials for spintronics and we comment on the possibility of incorporating Berry-phase effects and many-body correlations beyond the standard Boltzmann formalism.
First author: Lima, GBV, Novel trivalent europium beta-diketonate complexes with N-(pyridine-2-yl)amides and N-(pyrimidine-2-yl)amides as ancillary ligands: Photophysical properties and theoretical structural modeling,
JOURNAL OF LUMINESCENCE, 219, 5297, (2020)
Abstract: Eighteen new Eu3+ complexes and their Gd3+ analogues with 1,3-diketonate as main ligands and N-(pyridine-2-yl)amides or N-(pyrimidine-2-yl)amides as ancillary ligands were synthesized. The replacement of water molecules by those amides in the Eu3+ complexes increase the intrinsic quantum yields of luminescence, making them comparable or even more efficient than Eu3+ complexes with standard ancillary ligands such as 2,2′-bipyridine. The luminescence spectra of Gd3+ complexes in comparison with the Eu3+ ones show that efficient ligand-tometal intramolecular energy transfer processes take place. In most cases the experimental Judd-Ofelt intensity parameters (Omega(2) and Omega(4)) for the Eu3+ complexes show variations as a function of the temperature (77 and 300K) that overall apparently does not follow clearly any trend. For this reason, geometric variations (on the azimuthal angle phi and ancillary ligands distances) were carried out in the coordination polyhedron for simulating thermally induced structural changes. It has been observed that, in this way, the Omega(2) and Omega(4) can be satisfactorily reproduced by in silica experiments. It was concluded that, at low-temperature, the ancillary ligands become closer to the Eu3+ ion and the angular variations affect more Omega(2) than Omega(4), in agreement to the theoretical calculations. The use of N-(pyridine-2-yl)amides or N-(pyrimidine-2-yl)amides as ancillary ligands in Eu3+ 1,3-diketonates looks to be a good strategy for obtaining highly luminescent complexes.
First author: Marazzi, M, Trans-to-cis photoisomerization of cyclocurcumin in different environments rationalized by computational photochemistry,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 4749, (2020)
Abstract: Cyclocurcumin is a turmeric component that has attracted much less attention compared to the well-known curcumin. In spite of the less deep characterization of its properties, cyclocurcumin has shown promising anticancer effects when used in combination with curcumin. Especially, due to its peculiar molecular structure, cyclocurcumin can be regarded as an almost ideal photoswitch, whose capabilities can also be exploited for relevant biological applications. Here, by means of state-of-the-art computational methods for electronic excited-state calculations (TD-DFT, MS-CASPT2, and XMS-CASPT2), we analyze in detail the absorption and photoisomerization pathways leading from the more stable trans isomer to the cis one. The different molecular surroundings, taken into account by means of the electrostatic solvent effect and compared with available experimental data, have been found to be critical in describing the fate of irradiated cyclocurcumin: when in non-polar environments, an excited state barrier prevents photoisomerization and favours fluorescence, whereas in polar solvents, an almost barrierless path results in a striking decrease of fluorescence, opening the way toward a crossing region with the ground state and thus funneling the photoproduction of the cis isomer.
First author: Plasser, F, TheoDORE: A toolbox for a detailed and automated analysis of electronic excited state computations,
JOURNAL OF CHEMICAL PHYSICS, 152, 4749, (2020)
Abstract: The advent of ever more powerful excited-state electronic structure methods has led to a tremendous increase in the predictive power of computation, but it has also rendered the analysis of these computations much more challenging and time-consuming. TheoDORE tackles this problem through providing tools for post-processing excited-state computations, which automate repetitive tasks and provide rigorous and reproducible descriptors. Interfaces are available for ten different quantum chemistry codes and a range of excited-state methods implemented therein. This article provides an overview of three popular functionalities within TheoDORE, a fragment-based analysis for assigning state character, the computation of exciton sizes for measuring charge transfer, and the natural transition orbitals used not only for visualization but also for quantifying multiconfigurational character. Using the examples of an organic push-pull chromophore and a transition metal complex, it is shown how these tools can be used for a rigorous and automated assignment of excited-state character. In the case of a conjugated polymer, we venture beyond the limits of the traditional molecular orbital picture to uncover spatial correlation effects using electron-hole correlation plots and conditional densities. Published under license by AIP Publishing.
First author: Eng, J, Competition between the heavy atom effect and vibronic coupling in donor-bridge-acceptor organometallics,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 4659, (2020)
Abstract: The excited state properties and intersystem crossing dynamics of a series of donor-bridge-acceptor carbene metal-amides based upon the coinage metals Cu, Ag, Au, are investigated using quantum dynamics simulations and supported by photophysical characterisation. The simulated intersystem rates are consistent with experimental observations making it possible to provide a detailed interpretation of the excited state dynamics which ultimately control their functional properties. It is demonstrated that for all complexes there is a competition between the direct intersystem crossing occurring between the (CT)-C-1 and (CT)-C-3 states and indirect pathways which couple to an intermediate locally excited pi pi* triplet state ((LE)-L-3) on either the donor or acceptor ligands. The energy of the (LE)-L-3 states decreases as the size of the metal decreases meaning that the indirect pathway plays an increasingly important role for the lighter metals. Importantly whenever the direct pathway is efficient, the presence of indirect pathways is detrimental to the overall rate of ISC as they provide a slower alternative pathway. Our results provide a detailed insight into the mechanism of intersystem crossing in these complexes and will greatly facilitate the design of new higher performing molecules.
First author: Grover, P, Adsorption of Actinide (U-Pu) Complexes on the Silicene and Germanene Surface: A Theoretical Study,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 1522, (2020)
Abstract: Adsorption of actinide (Ac = U, Np, Pu) complexes with environmentally relevant ligands on silicene and germanene surfaces has been investigated using density functional theory to determine the geometrical, energetic, and electronic properties. Three types of ligands for each central metal atom are considered: OH-, NO3-, and CO32- with common oxo ligands in all cases. Among these, carbonate complexes show the strongest adsorption followed by hydroxide and nitrate. Two types of model, cluster and periodic models, have been considered to include the short- and long-range effects. The cluster and periodic models are complementary, although the former has not yet been widely used for studies of 2D materials. Two cluster sizes have been investigated to check size dependency. Calculations were performed in the gas phase and water solvent. On the basis of the adsorption energy, for the CO32- and OH- ligands, the bond position between two Si atoms in the silicene sheet is the most strongly adsorbed site in the cluster model for silicene whereas in the periodic model these complexes exhibit strong binding on the Si atom of the silicene surface. The Ac complexes with the NO3- ligand show strong affinity at the hollow space at the center of a hexagonal ring of silicene in both models. The H site is most favorable for the binding of complexes on the germanene cluster whereas these sites vary in the periodic model. Electronic structure calculations have been performed that show a bandgap range from 0.130 to 0.300 eV for the adsorption of actinide complexes on silicene that can be traced to charge transfer. Density of states calculations show that the contribution of the nitrate complexes is small near the Fermi level, but it is larger for the carbonate complexes in the silicene case. Strong interactions between Ac complexes and silicene are due to the formation of strong Si-O bonds upon adsorption which results in reduction of the actinide atom. Such bonding is lacking in germanene.
First author: Chang, CK, Improved Prediction of Phase Behaviors of Ionic Liquid Solutions with the Consideration of Directional Hydrogen Bonding Interactions,
INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 59, 3550, (2020)
Abstract: The consideration of directional hydrogen bonding in the COSMO-SAC model based on the minima in the molecular electrostatic potential has been shown to significantly improve the description of solvation properties of a wide variety of associating fluids containing nonionic species. In this work, we report the use of this method for the prediction of thermodynamic properties and phase equilibria of ionic liquid solutions, including infinite dilution activity coefficients (IDAC), osmotic coefficients (phi), liquid- liquid equilibria (LLE), and vapor-liquid equilibria (VLE). When compared to the previous version of the COSMO-SAC model without the consideration of directional hydrogen bonding, the new method, which has a tendency giving more polar sigma-profiles, improves the prediction of osmotic coefficients and VLE by 10% (26% AARD, 1372 data points) and 5% (32% AARD, 1645 data points), respectively. Comparable results are observed from the two methods in LLE [0.2 and 0.1 root mean square (rms) error for ionic liquid-rich and solvent-rich regions, respectively, with 2876 data points] and IDAC (0.71 rms error with 3555 data points) predictions.
First author: Danes, S, Bonding Situation in Stannocene and Plumbocene N-Heterocyclic Carbene Complexes,
ORGANOMETALLICS, 39, 516, (2020)
Abstract: A detailed experimental and computational study of a series of stannocene and plumbocene N-heterocyclic carbene complexes is presented. This unique class of group 14 Lewis acid-base adducts was obtained from reactions of the corresponding metallocenes and N-heterocyclic carbenes (NHC) and was structurally characterized by single-crystal X-ray diffraction. The obtained structures show a perpendicular pose of the NHC with respect to the metallocene, hence precluding the maximum interaction between the moieties. The nature of the Sn-C-NHC and Pb-C-NHC bonds has been investigated by applying natural bond orbital (NBO) analysis and energy decomposition analysis (EDA-NOCV). For the sake of comparison, known stannocene and plumbocene Lewis base complexes have been included in the series. The attractive chemical bonding interactions are around 50% electrostatic, 30% covalent, and 20% dispersion. Indeed, dispersion interactions play a determining role the larger the substituents become. The covalent interactions derive from the donation of the carbene ligand into the empty p orbital of the metallocene.
First author: Benti, NE, The effect of CO2 contamination in rechargeable non-aqueous sodium-air batteries,
JOURNAL OF CHEMICAL PHYSICS, 152, 516, (2020)
Abstract: Metal-air batteries have higher theoretical specific energies than existing rechargeable batteries including Li-ion batteries. Among metal-air batteries, the Na-O-2 battery has gained much attention due to its low discharge/charge overpotentials (100 mV) at relatively high current densities (0.2 mA/cm2), high electrical energy efficiency (90%), high theoretical energy density, and low cost. However, there is no information reported regarding the effect of CO2 contamination in non-aqueous Na-air batteries. Density functional theory has, here, been applied to study the effect of low concentrations of CO2 contamination on NaO2 and Na2O2 growth/depletion reaction pathways and overpotentials. This was done on step surfaces of discharge products in non-aqueous Na-air batteries. Adsorption energies of CO2 at various nucleation sites for both step surfaces were determined, and results revealed that CO2 preferentially binds at the step valley sites of (001) NaO2 and (1100) Na2O2 surfaces with binding energies of -0.65 eV and -2.67 eV, respectively. CO2 blocks the step nucleation site and influences the reaction pathways and overpotentials due to carbonate formation. The discharge electrochemical overpotential increases remarkably from 0.14 V to 0.30 V and from 0.69 V to 1.26 V for NaO2 and Na2O2 surfaces, respectively. CO2 contamination is thus drastically impeding the growth/depletion mechanism pathways and increases the overpotentials of the surface reaction mechanism, hampering the performance of the battery. Avoiding CO2 contamination from intake of gas and electrolyte decomposition is thus critical in development of Na-air batteries.
First author: Moustafa, ME, Photoswitchable organoplatinum complexes with an azobenzene derivative of di-2-pyridylamine,
NEW JOURNAL OF CHEMISTRY, 44, 2882, (2020)
Abstract: A new di-2-pyridylamine ligand with an appended azobenzene group (2-C5H4N)(2)N-4-C6H4-N & xe001;N-Ph, dpaa, is reported. This ligand readily forms the platinum(ii) complexes [PtMe2(dpaa)], 1, and [PtCl2(dpaa)], 2. Complex 1 is electron-rich and it undergoes oxidative addition with I-2, MeI or PhCH2Br to give the corresponding organoplatinum(iv) complexes [PtI2Me2(dpaa)], [PtIMe3(dpaa)] or [PtBrMe2(CH2Ph)(dpaa)]. Both the ligand dpaa and its platinum complexes undergo photoswitching by trans-cis isomerization about the N & xe001;N linkage.
First author: Bergmann, TG, Towards theoretical spectroscopy with error bars: systematic quantification of the structural sensitivity of calculated spectra,
CHEMICAL SCIENCE, 11, 1862, (2020)
Abstract: Molecular spectra calculated with quantum-chemical methods are subject to a number of uncertainties (e.g., errors introduced by the computational methodology) that hamper the direct comparison of experiment and computation. Judging these uncertainties is crucial for drawing reliable conclusions from the interplay of experimental and theoretical spectroscopy, but largely relies on subjective judgment. Here, we explore the application of methods from uncertainty quantification to theoretical spectroscopy, with the ultimate goal of providing systematic error bars for calculated spectra. As a first target, we consider distortions of the underlying molecular structure as one important source of uncertainty. We show that by performing a principal component analysis, the most influential collective distortions can be identified, which allows for the construction of surrogate models that are amenable to a statistical analysis of the propagation of uncertainties in the molecular structure to uncertainties in the calculated spectrum. This is applied to the calculation of X-ray emission spectra of iron carbonyl complexes, of the electronic excitation spectrum of a coumarin dye, and of the infrared spectrum of alanine. We show that with our approach it becomes possible to obtain error bars for calculated spectra that account for uncertainties in the molecular structure. This is an important first step towards systematically quantifying other relevant sources of uncertainty in theoretical spectroscopy.
First author: Dutta, S, Cooperative Donor-Acceptor Interactions in Stabilizing Carbene-Borane and Carbene-Alane Compounds: A Theoretical Insight,
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 2020, 638, (2020)
Abstract: Density functional theory calculations have been performed to elucidate the electronic structure and bonding scenario in various carbene-borane (L-BX & x2083;) and carbene-alane (L-AlX & x2083;) compounds (X = -H, -Me, -Cl, -Ph, -C6F5). We have performed extended transition state (ETS) analysis to reveal the nature of the donor-acceptor bonds (C (c)(arb)-E; E = B, Al) and also for the assessment of the intrinsic donor-acceptor strength in this class of compounds. Our computations suggest that the C (c)(arb)-Al bonds in all the L-AlX & x2083; adducts have substantially higher electrostatic nature than covalent character. Conversely, the nature of the C (c)(arb)-B bonds in L-BX & x2083; have a strong dependence on the electronic nature of both carbene and borane. Moreover, unlike alanes in L-AlX & x2083;, the intrinsic Lewis acid strength of the boranes in L-BX & x2083; has a strong dependence on the electronic nature of the carbenes. We have also explored the correlation of the interaction energies (Delta E-int) with various bonding parameters i.e., geometrical and Natural bond orbital (NBO) parameters of L-EH & x2083;. Furthermore, natural orbital for chemical valence (NOCV) calculations are performed to have a qualitative understanding of the relative sigma-donating and pi-accepting abilities of the carbenes in L-EH & x2083;. Additionally, we have investigated the abilities of carbenes to activate the B-H bonds in BH3 and pinacolborane. ETS analysis shows a strong dependence of the B-H activation barriers on the distortion energies of both carbene and borane fragments.
First author: Reber, AC, Superatomic molecules with internal electric fields for light harvesting,
NANOSCALE, 12, 4736, (2020)
Abstract: Traditional p-n junctions used for photovoltaics require an interface where a light induced electron-hole pair is separated by an electric field. Developing alternative strategies for forming strong internal electric fields for electron-hole pair separation offers the possibility for better performance. We demonstrate that fusing two superatomic clusters with donor/acceptor ligands on opposite sides of the cluster leads to such a strong internal electric field. In two fused metal-chalcogenide Re6S8Cl2(L)(4) clusters with donor PMe3 ligands and acceptor CO ligands on the opposite sides of the fused clusters, the electronic levels undergo shifts analogous to band bending in traditional p-n junctions. The fused cluster has a large dipole moment, and an optical spectrum that strongly absorbs excitation above the HOMO-LUMO gap of the fused clusters, but is optically very weak for the lowest energy excitation that can lead to electron-hole pair recombination. This is because the electron is localized on the CO portion of the fused cluster, while the electron-hole pair is localized on the PMe3 side of the cluster. It is shown that the electronic states localized on each side of the cluster can be aligned/misaligned by applying a voltage in different directions, offering diode like characteristics.
First author: Dasgupta, S, Using Atomic Confining Potentials for Geometry Optimization and Vibrational Frequency Calculations in Quantum-Chemical Models of Enzyme Active Sites,
JOURNAL OF PHYSICAL CHEMISTRY B, 124, 1137, (2020)
Abstract: Quantum-chemical studies of enzymatic reaction mechanisms sometimes use truncated active-site models as simplified alternatives to mixed quantum mechanics molecular mechanics (QM/MM) procedures. Eliminating the MM degrees of freedom reduces the complexity of the sampling problem, but the trade-off is the need to introduce geometric constraints in order to prevent structural collapse of the model system during geometry optimizations that do not contain a full protein backbone. These constraints may impair the efficiency of the optimization, and care must be taken to avoid artifacts such as imaginary vibrational frequencies. We introduce a simple alternative in which terminal atoms of the model system are placed in soft harmonic confining potentials rather than being rigidly constrained. This modification is simple to implement and straightforward to use in vibrational frequency calculations, unlike iterative constraint-satisfaction algorithms, and allows the optimization to proceed without constraint even though the practical result is to fix the anchor atoms in space. The new approach is more efficient for optimizing minima and transition states, as compared to the use of fixed-atom constraints, and also more robust against unwanted imaginary frequencies. We illustrate the method by application to several enzymatic reaction pathways where entropy makes a significant contribution to the relevant reaction barriers. The use of confining potentials correctly describes reaction paths and facilitates calculation of both vibrational zero-point and finite-temperature entropic corrections to barrier heights.
First author: Jones, LO, Embedding Methods for Quantum Chemistry: Applications from Materials to Life Sciences,
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 142, 3281, (2020)
Abstract: Quantum mechanical embedding methods hold the promise to transform not just the way calculations are performed, but to significantly reduce computational costs and improve scaling for macro-molecular systems containing hundreds if not thousands of atoms. The field of embedding has grown increasingly broad with many approaches of different intersecting flavors. In this perspective, we lay out the methods into two streams: QM:MM and QM:QM, showcasing the advantages and disadvantages of both. We provide a review of the literature, the underpinning theories including our contributions, and we highlight current applications with select examples spanning both materials and life sciences. We conclude with prospects and future outlook on embedding, and our view on the use of universal test case scenarios for cross-comparisons of the many available (and future) embedding theories.
First author: Ricciarelli, D, Spin-Forbidden Reactivity of Transition Metal Oxo Species: Exploring the Potential Energy Surfaces,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 3080, (2020)
Abstract: Spin-forbidden reactions are frequently encountered when transition metal oxo species are involved, particularly in oxygen transfer reactivity. The computational study of such reactions is challenging, because reactants and products are located on different spin potential energy surfaces (PESs). One possible approach to describe these reactions is the so-called minimum energy crossing point (MECP) between the diabatic reactants and products PESs. Alternatively, inclusion of spin-orbit coupling (SOC) effects allows to locate a saddle point on a single adiabatic PES (TS SOC). The TS SOC approach is rarely applied because of its high computational cost. Recently evidence for a TS SOC impact on significantly lowering the activation barrier in dioxygen addition to a carbene-gold(I)-hydride complex reaction (Chem. Sci. 2016, 7, 7034-7039) or even on predicting a qualitatively different reaction mechanism in mercury methylation by cobalt corrinoid (Angew. Chem. Int. Ed. 2016, 55, 11503-11506) has been put forward. Using MECP and TS SOC approaches a systematic analysis is provided here of three prototypical transition metal oxo spin-forbidden processes to investigate their implications on reactivity. Cycloaddition of ethylene to chromyl chloride (CrO2Cl2+C2H4), iron oxide cation insertion into the hydrogen molecule (FeO++H-2) and H-abstraction from toluene by a Mn-V-oxo-porphyrin cation (MnOP(H2O)(+)+C6H5CH3) are case studies. For all these processes the MECP and TS SOC results are compared, which show that the spin-forbidden reactivity of transition metal oxo species can be safely described by a MECP approach, at least for the first-row transition metals investigated here, where the spin-orbit coupling is relatively weak. However, for the Mn-oxo reactivity, the MECP and TS SOC have been found to be crucial for a correct description of the reaction mechanism. In particular, the TS SOC approach allows to straightforwardly explore detailed features of the adiabatic potential energy surface which in principle could affect the overall reaction rate in cases where the involved diabatic PESs are tricky.
First author: Dash, C, Organic Azide and Auxiliary-Ligand-Free Complexes of Coinage Metals Supported by N-Heterocyclic Carbenes,
INORGANIC CHEMISTRY, 59, 2188, (2020)
Abstract: Organic azide complexes of copper(I) and silver(I), [(SIPr)CuN(1-Ad)NN][SbF6] [(SIPr)CuN(2-Ad)-NN][SbF6], [(SIPr)CuN(Cy)NN][SbF6], and [(SIPr)AgN(1-Ad)NN][SbF6] have been synthesized by using Ag[SbF6] and the corresponding organic azides with (SIPr)CuBr and (SIPr)AgCl (SIPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene). The copper and silver organic azide complexes were characterized by various spectroscopic techniques and X-ray crystallography. Group trends of isoleptic Cu(I), Ag(I), and Au(I) organic azide complexes are presented on the basis of experimental data and a detailed computational study. The nu(asym) (N-3) values of the metal-bound 1-AdNNN in [(SIPr)-MN(1-Ad)NN](+) follow the order Ag < Cu < Au. DFT calculations show that gold(I) forms the strongest bond with 1-AdNNN in this series, while silver has the weakest interaction. Furthermore, auxiliary ligand free coinage metal N-heterocyclic carbene complexes, [(SIPr)M][SbF6], have been synthesized via metathesis reactions of (SIPr)MCl (M = Cu, Ag, Au) with Ag[SbF6]. X-ray crystal structures of dinuclear [(SIPr)Ag](2) [SbF6](2) and [(SIPr)Au](2)[SbF6](2) are also reported. They show close metallophilic contacts. [(SIPr)Au](2)[SbF6](2) reacts with OEt2, SMe2, and (CNBu)-Bu-t to afford [(SIPr)Au(OEt2)][SbF6], [(SIPr)Au(SMe2)][SbF6], and [(SIPr)An((CNBu)-Bu-t)]-[SbF6] adducts, respectively.
First author: Baghdasaryan, A, Thiolato Protected Copper Sulfide Cluster with the Tentative Composition Cu74S15(2-PET)(45),
INORGANIC CHEMISTRY, 59, 2200, (2020)
Abstract: Ligand protected copper nanoclusters with precise compositions have attracted considerable attention due to their unique photoluminescent properties. However, the acquisition of structural information, knowledge of the factors affecting the stability, and high quantum yields are prerequisites for assessing their applications in biomedicine as fluorescent contrast agents, biosensors, and probes for cells. Despite all the effort, only finite examples of single crystal structures of CuNCs are reported. Herein, we report the phosphine-free synthesis and structure determination of 2-PET protected CuNCs. The structure analysis established by single crystal X-ray diffraction reveals the formation of binary Cu74S15(2-PET)(45) sulfide cluster. A similar phenomenon has been observed for several other chalcogenide-bridged copper clusters. The synthesized cluster possesses a rod-like structure, protected with 45 thiol ligands on the surface. Fifteen independent bridged-sulfur atoms couple to the copper atoms inside the core. Calculations for both a neutral and negatively charged cluster showed no major differences in their geometrical structures. Further analysis of frontier MO levels of the closed-shell anion predicts the HOMO-LUMO transition to be intramolecular L7 -> L1 charge transfer, where “L7” and “L1” abbreviations refer to the corresponding sulfur layer in the structure. For the neutral cluster, the calculated spin density is delocalized over the two moieties. On the basis of TDDFT+TB calculations, the onset of the measured absorption spectrum could be satisfactorily reproduced.
First author: Realista, S, Structural and electronic properties in asymmetric binuclear Zn(II) amphiphilic compounds,
JOURNAL OF COORDINATION CHEMISTRY, 73, 634, (2020)
Abstract: A new type of asymmetric binuclear Zn(II) complex was synthesized from a suitable mononuclear precursor. One Zn(II) was coordinated to a salphen ligand (salphen = N,N ‘-disalicylidene-1,2-phenylenediamine) and the other to a modified salphen bearing OC12H25 chain in the 4,4’ positions, the two being joined by phenylene rings. The molecular structure, determined by DFT calculations (ADF/BP86(COSMO:THF)/TZ2P), showed the non-planarity of each of the two complexes, the dihedral angle at the junction being similar to 36 degrees. The absorption spectra of 2 and its precursor 1 in DMSO showed a strong band in the visible at 427 and 408 nm, respectively, assigned based on TDDFT calculations mainly to intra- and interligand pi ->pi* transitions. Complex 2 displayed emission at 531 nm in DMSO and 534 nm in other solvents. The long alkyl chain of its substituents promoted self-assembly of these amphiphilic molecules. No gels were formed in DMSO, but several bands (420, 418 and 480 nm) and shoulders appeared in other solvents, and gels were detected when increasing concentration. The formation of aggregates was studied by scanning electron microscopy and atomic force microscopy, and the images found in the three solvents reflected different supramolecular arrangements. These studies revealed that the binuclear compound formed stable gels above 8.88 mM for tetrahydrofuran and 13.3 mM for toluene and chloroform.
First author: Lachmanova, SN, Electrochemical characterization of the artificial metalloenzyme papain-[(eta(6)-arene)Ru(1,10-phenanthroline)Cl](+),
JOURNAL OF ELECTROANALYTICAL CHEMISTRY, 859, 634, (2020)
Abstract: Electrochemical properties were studied for [(eta(6)-arene)Ru(1,10-phenanthroline)Cl]Cl (arene = C6H5(CH2)(2)NHCOCH2Cl) organometallic complex 1, protein Papain PAP and its conjugate with organometallic complex 1 PAP. The latter can serve as an artificial metalloenzyme with catalytic activity in transfer hydrogenation. This work demonstrates that AC voltammetry and electrochemical impedance spectroscopy can be used as fast tools to screen the catalytic ability of 1-PAP electrochemically by studies of the catalytic hydrogen evolution reaction (HER). Proteins are known to catalyze this process, but we have shown that additional HER signal associated with the catalytic activity of 1 is observed for its conjugate with Papain 1-PAP.
First author: Kong, XH, Coordination behavior of uranyl with PDAM derivatives in solution: Combined study with ESI-MS and DFT,
JOURNAL OF MOLECULAR LIQUIDS, 300, 634, (2020)
Abstract: Although the extraction behaviors of the tetradentate 1,10-phenanthroline-2,9-dicarboxamide (PDAM, L) derivative ligands toward actinide and lanthanide ions have been reported, the coordination structures and species determination of the complexes are still involved and are also of great significance. To reveal the coordination structure of U(VI) ion and three PDAM derivative ligands with different alkyl chain, electrospray ionization mass spectrometry (ESI-MS) combined with density functional theory (OFT) calculations were carried out. The [UO2L(NO3)](+) complexes are the dominant species for the three PDAM derivative ligands based on the ESI-MS spectra. Collision-induced dissociation (CID) results further show that the U(VI) ions strongly bind with the phenanthroline fragment, while the amine groups and the alkyl moieties are apt to lost. Furthermore, DFT calculations further confirm that three PDAM derivative ligands can be well combined with uranyl, and [UO2L(NO3)](+) species are more stable than [UO2L(OH)center dot H2O](+) one. The length of the alkyl chain has little effect on the coordination structure of uranyl complexes, but affects their thermodynamic behaviors due to the steric hindrance effect. Therefore, the studies on the coordination chemistry of uranyl with three PDAM derivative ligands at the molecular level provide basic information for efficient actinides separation in spent fuel reprocessing.
First author: Szczepanska, M, Electronic excited states and luminescence properties of palladium(II)corrin complex,
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, 389, 634, (2020)
Abstract: The DFT and TD-DFT calculations were performed for palladium(II)1,2,2,7,12,12-heptamethylo-15-cyanocorrin complex aPd(II)HM-CN-corr](+)). Experimentally [Pd(II)HM-CN-corr](+) exhibits a weak fluorescence and strong phosphorescence. For the [Pd(II)HM-CN-corr](+) complex the electronic spectrum was calculated using the BP86 and B3LYP functionals. The results shows that BP86 gives electronic transition energies in good agreement with the experiment, while B3LYP overestimates the calculated transition energies, which can be related to the order and energy of molecular orbitals. Therefore, the BP86 functional was used in further calculations. The presence of the solvent was taken into account by the use of the COSMO model. The spin-orbit (SO) states were calculated along the PEC determined by N-Pd-N bending angle active coordinate in the S-1 using the ZORA method. The rate constants of fluorescence, phosphorescence and intersystem crossing processes were determined. Based on calculations the photophysical processes occurring in [Pd(II)HM-CN-corr](+) can be explained. After light absorption there is excitation to the S-1 or S-2 states and then the internal conversion to S-1 state from S-2. Comparison of the calculated rate constants of fluorescence (3.3.10(7)S(-1)) and ISC to the close lying T-2 state (8.5.10(10)s(-1)) in the S-1 minimum shows that the ISC is more probable. This is an explanation why fluorescence in [Pd(II)HM-CN-corr](+) is weak. The vibrationally resolved fluorescence and phosphorescence band shapes were determined using the Franck-Condon approximation. The obtained band profiles agree qualitatively with the experimental ones. The most important molecular vibrations contributing to vibrational bands were determined. The calculated rate constants values and the obtained picture of photophysical processes agree qualitatively with the experimental data.
First author: Gildeh, SFG, Experimental and theoretical probing of the physicochemical properties of ionic liquids composed of [Bn-DBU](+) cation and various anions,
JOURNAL OF MOLECULAR STRUCTURE, 1202, 634, (2020)
Abstract: The experimental approaches coupled with computational methods are powerful tools to understand the physicochemical properties of ionic liquids. The 1,8-diazobicyclo[5.4.0]undec-7-ene-8-benzylium ([BnDBU](+)) cation is a N-substituted DBU cation that was joined with various anions for production of [BnDBU][Y1-8], (Y1- 8 = CH3CO2-, PhSO2-, PhSO3-, HCO3-, HSO4-, CF3CO2-, BF4-, and SCN-) ionic liquids (ILs). In this study, at first, several aprotic ionic liquids composed of [Bn-DBU](+) cation and various anions were synthesized and characterized experimentally by the combined of (HNMR)-H-1 and FTIR spectroscopies, and thermogravimetric analysis (TGA). Then, density functional theory (DFT) at M06-2X/6-311++G(d,p) level of theory was used for calculation of the molecular electrostatic potential (MESP), interaction energies, structural parameters, vibrational frequencies, topological properties, charge transfer (CT) values and non-covalent interaction index.
First author: Tanaka, S, DNP NMR spectroscopy of cross-linked organic polymers: rational guidelines towards optimal sample preparation,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 3184, (2020)
Abstract: Cross-linked polystyrenes (PS) are an important class of polymers, whose properties are strongly dependent on incorporated functionalities, for which detailed understanding of their structure remains a challenge. Here, we develop a rational guideline for dynamic nuclear polarization (DNP) sample formulation for cross-linked PS to interrogate their structure. We show that the DNP enhancement on a series of cross-linked PS bearing alkylammonium groups as prototypical organic polymers correlates with the polymer swelling properties in both apolar and polar formulations (TEKPol/1,1,2,2-tetrachloroethane and AMUPol/dimethyl sulfoxide). This work provides guidelines to easily optimize DNP formulation using a simple swelling test and enables natural abundance N-15 NMR to be recorded on a series of PS-supported quaternary alkylammonium salts, allowing a detailed structural analysis.
First author: Khan, MI, A DFT study on a borophene/boron nitride interface for its application as an electrode,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 3304, (2020)
Abstract: In order to search for a new anode material for lithium-ion batteries (LIBs), a borophene/boron nitride (B/BN) interface was investigated in detail using density functional theory. Borophene is an excellent two-dimensional (2D) anode material that offers high charging capacity and a low energy barrier, but it suffers from stability issues when it is used in its free-standing form. The findings of this work indicate that the thermal and mechanical stabilities of the borophene epilayer are notably increased by preparing its interface with a boron nitride substrate. The electronic properties of the lithiated and delithiated interface exhibited metallic behavior, whereas the mechanical stiffness of the interface increased three times when compared with that of the pristine borophene. The thermal stability was calculated by molecular dynamics and indicated a six times increase in its value for the interface. The interface exhibited a specific charging capacity of 1698 mA h g(-1), which is higher than that of bare borophene and several other 2D materials. Furthermore, nudged elastic band (NEB) calculations indicated a low energy barrier to diffusion of Li in the interface. These advantages of the B/BN interface make it an excellent choice as an anode material for LIBs.
First author: Campeggio, J, Multiscale modeling of reaction rates: application to archetypal S(N)2 nucleophilic substitutions,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 3455, (2020)
Abstract: We propose an approach to the evaluation of kinetic rates of elementary chemical reactions within Kramers’ theory based on the definition of the reaction coordinate as a linear combination of natural, pseudo Z-matrix, internal coordinates of the system. The element of novelty is the possibility to evaluate the friction along the reaction coordinate, within a hydrodynamic framework developed recently [J. Campeggio et al., J. Comput. Chem. 2019, 40, 679-705]. This, in turn, allows to keep into account barrier recrossing, i.e. the transmission coefficient that is employed in correcting transition state theory evaluations. To test the capabilities and the flaws of the approach we use as case studies two archetypal S(N)2 reactions. First, we consider to the standard substitution of chloride ion to bromomethane. The rate constant at 295.15 K is evaluated to k/c(circle minus) = 2.7 x 10(-6) s(-1) (with c(circle minus) = 1 M), which compares well to the experimental value of 3.3 x 10(-6) s(-1) [R. H. Bathgate and E. A. Melwyn-Hughes, J. Chem. Soc 1959, 2642-2648]. Then, the method is applied to the SN2 reaction of methylthiolate to dimethyl disulfide in water. In biology, such an interconversion of thiols and disulfides is an important metabolic topic still not entirely rationalized. The predicted rate constant is k/c(circle minus) = 7.7 x 10(3) s(-1). No experimental data is available for such a reaction, but it is in accord with the fact that the alkyl thiolates to dialkyl disulfides substitutions in water have been found to be fast reactions.
First author: Zhang, Y, BDF: A relativistic electronic structure program package,
JOURNAL OF CHEMICAL PHYSICS, 152, 3455, (2020)
Abstract: The BDF (Beijing Density Functional) program package is in the first place a platform for theoretical and methodological developments, standing out particularly in relativistic quantum chemical methods for chemistry and physics of atoms, molecules, and periodic solids containing heavy elements. These include the whole spectrum of relativistic Hamiltonians and their combinations with density functional theory for the electronic structure of ground states as well as time-dependent and static density functional linear response theories for electronically excited states and electric/magnetic properties. However, not to be confused by its name, BDF nowadays comprises also of standard and novel wave function-based correlation methods for the ground and excited states of strongly correlated systems of electrons [e.g., multireference configuration interaction, static-dynamic-static configuration interaction, static-dynamic-static second-order perturbation theory, n-electron valence second-order perturbation theory, iterative configuration interaction (iCI), iCI with selection plus PT2, and equation-of-motion coupled-cluster]. Additional features of BDF include a maximum occupation method for finding excited states of Hartree-Fock/Kohn-Sham (HF/KS) equations, a very efficient localization of HF/KS and complete active space self-consistent field orbitals, and a unique solver for exterior and interior roots of large matrix eigenvalue problems.
First author: Choudhary, S, Sequential multicomponent site-selective synthesis of 4-iodo and 5-iodopyrrole-3-carboxaldehydes from a common set of starting materials by tuning the conditions,
ORGANIC & BIOMOLECULAR CHEMISTRY, 18, 1155, (2020)
Abstract: A simple and straightforward method for the synthesis of 4-iodo and 5-iodopyrrole-3-carboxaldehydes is developed from a common set of starting materials by tuning the reaction conditions. This sequential multicomponent protocol involves I-2-mediated regioselective C4-iodination and aromatization of intermediate dihydropyrrole, generated through proline-catalyzed direct Mannich reaction-cyclization sequence between succinaldehyde and imines, to access 4-iodopyrroles. While aerobic oxidative aromatization of dihydropyrrole to pyrrole followed by NIS-mediated regioselective iodination furnished 5-iodopyrroles in a two-pot fashion. A series of site-selective C4/C5-iodopyrroles have been synthesized in good to high yields (up to 78%) and DFT calculations of these compounds were also performed.
First author: Fu, MX, Bonding Analysis of the Shortest Bond between Two Atoms Heavier than Hydrogen and Helium: O-2(2+),
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 1087, (2020)
Abstract: Quantum chemical calculations using ab initio methods at the CCSD(T) level with large basis sets and DFT calculations using the BP86 functional have been carried out for O-2(2+) and N An energy decomposition analysis of the chemical bonds suggests that the shorter bond in O-2(2+) compared with isoelectronic N-2 is due to the weaker Pauli repulsion in the dication, which overcompensates the weakening of attractive interactions that are operative in N-2. At the equilibrium distance of N-2, the orbital (covalent) bonding in O-2(2+) is weaker than in N-2, and the attractive Coulomb interactions in the neutral diatomic system become repulsive in the dication, but the weakening of the Pauli repulsion caused by the shrinking of the orbitals in O-2(2+) compensates for these forces and leads to a shortening of the bond. The results also show that the bond dissociation energy is not a reliable indicator for the strength of bond, which is more faithfully given by the (local) force constant.
First author: Narsaria, AK, Distortion-Controlled Redshift of Organic Dye Molecules,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 2080, (2020)
Abstract: It is shown, quantum chemically, how structural distortion of an aromatic dye molecule can be leveraged to rationally tune its optoelectronic properties. By using a quantitative Kohn-Sham molecular orbital (KS-MO) approach, in combination with time-dependent DFT (TD-DFT), the influence of various structural and electronic tuning parameters on the HOMO-LUMO gap of a benzenoid model dye have been investigated. These parameters include 1) out-of-plane bending of the aromatic core, 2) bending of the bridge with respect to the core, 3) the nature of the bridge itself, and 4) a-a stacking. The study reveals the coupling of multiple structural distortions as a function of bridge length and number of bridges in benzene to be chiefly responsible for a decreased HOMO-LUMO gap, and consequently, red-shifting of the absorption wavelength associated with the lowest singlet excitation (lambda approximate to 560 nm) in the model cyclophane systems. These physical insights together with a rational approach for tuning the oscillator strength were leveraged for the proof-of-concept design of an intense near-infrared (NIR) absorbing cyclophane dye at lambda = 785 nm. This design may contribute to a new class of distortion-controlled NIR absorbing organic dye molecules.
First author: Berkefeld, A, C-P vs C-H Bond Cleavage of Triphenylphosphine at Platinum(0): Mechanism of Formation, Reactivity, Redox Chemistry, and NMR Chemical Shift Calculations of a mu-Phosphanido Diplatinum(II) Platform,
ORGANOMETALLICS, 39, 443, (2020)
Abstract: Transition-metal phosphanides M-PR2 are key intermediates in catalytic C-P bond functionalization. M-PR2 formation from tertiary phosphines through P-C bond cleavage widens the scope beyond P-H functionalized substrates, but mechanistic understanding of this reaction still is fragmentary. Starting from a defined coordination complex has allowed monitoring the reaction of a Pt-PPh3 moiety and Pt(0) by NMR spectroscopy. Initial Pt(0) transfer is rate-limiting and leads to products from PPh3-borne ortho-C-H and C-P bond cleavage along kinetically distinct pathways. Albeit kinetically favored, the reversibility of C-H bond cleavage eventually leads to thermodynamically preferred C-P bond scission. This pathway affords a robust [Pt(mu-PPh2)Pt] core structure whose redox chemistry and reactivity toward external ligands are reported. Organometallic products have been substantiated by a combination of magnetic resonance and absorption spectroscopies, X-ray diffraction, and DFT computations.
First author: Tang, Q, Reverse Turn Foldamers: An Expanded beta-Turn Motif Reinforced by Double Hydrogen Bonds,
ORGANIC LETTERS, 22, 1003, (2020)
Abstract: Hybrid tetrapeptides sharing a backbone with a central alpha/beta-dipeptide segment flanked by aromatic gamma-amino acid residues fold into the same hairpin conformation with an expanded beta-turn. This hairpin/beta-turn motif is general for accommodating different alpha- and beta-amino acid residues. Replacing glycine with other alpha-amino acid residues has an insignificant influence on or slightly decreases the stabilities of the folded conformations; substituting beta-alanine with other beta-amino acid residues enhances the stabilities of the folded structures.
First author: Domanski, MA, The high covalence of metal-ligand bonds as stability limiting factor: the case of Rh(IX)O-4(+) and Rh(IX)NO3,
JOURNAL OF MOLECULAR MODELING, 26, 1003, (2020)
Abstract: Rhodium, a 4d transition metal and a lighter analogue of iridium, is known to exhibit its highest VIth oxidation state in RhF6 molecule. In this report, the stability and decomposition pathways of two species containing rhodium at a potentially formal +IX oxidation state, [RhO4](+) and RhNO3, have been investigated theoretically within the framework of the relativistic two-component Hamiltonian calculations. Possible rearrangement into isomers featuring lower formal oxidation numbers has been explored. We found that both species studied are metastable with respect to elimination of O-2 or NO. However, the local minima containing Rh(IX) are protected by sufficient energy barriers on the decomposition pathway, and they could in principle be prepared. The analysis of a broader set of compounds containing group 8 and 9 metals in high formal oxidation states that correspond to the group number showed that, in contrast to a standard trend, the limits of formally attainable oxidation state correlate with high level of covalent bonding character in the complexes studied.
First author: Mobley, TA, Relativistic DFT Calculations of (1)J(WH) and (1)J(WC) Provide Detailed Structural Insight of Cyclopentadienyl Binding in Cp2WH2,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 966, (2020)
Abstract: Experimental measurements of the one-bond scalar coupling of Cp2WH2 in tetrahydrofuran ((1)J(WH) = 73.4 Hz and (1)J(WC) = 4.8 Hz) are compared to density functional theory calculations of the same based upon geometries minimized utilizing a variety of approximate functionals typically utilized to calculate organometallic geometries. One difference between the various functionals is the Cp-W distance, and d(CpW) is linearly correlated to the calculated values for both (1)J(WH) and (1)J(WC). Differences in the structures of the Cp2WH2 reported in the literature are compared to the calculated geometries, utilizing calculated values of (1)J(WH) to provide insight into the differences. The distance between the tungsten and attached hydride as well as the angle of the cyclopentadienyl plane with respect to the tungsten cyclopentadienyl centroid vector also have a strong effect on (1)J(WH). A natural bond orbital (NBO) analysis of the orbital origins of (1)J(WH) indicates that the W-H sigma-bonding orbital is the primary contributor to the coupling constant.
First author: Gieseking, RLM, Analytical Approaches To Identify Plasmon-like Excited States in Bare and Ligand-Protected Metal Nanoclusters,
JOURNAL OF PHYSICAL CHEMISTRY C, 124, 3260, (2020)
Abstract: Noble metal nanoclusters containing dozens to hundreds of metal atoms are of great interest because of their unique optical properties. Classical electrodynamics fails to describe the optical properties of clusters smaller than a few nanometers, so quantum-mechanical models are needed to describe these clusters. However, it is challenging to identify which features of the computed excited states indicate plasmon-like character, particularly in a way that is generalizable to the ligand-protected clusters that are commonly studied in experiments. We present an analytical method to identify plasmon-like excited states using three quantifiable indicators that must be considered in combination: (1) large superatomic character, (2) large collectivity among single-particle excitations, and (3) large additivity of contributions of these single-particle excitations to the transition dipole moment. Visualizing these three indicators on a single plot enables rapid classification of hundreds of excited states into plasmon-like, collective, single-particle, or interband categories or as intermediate between these categories. This method is used to identify excited states with plasmon-like character in both bare and ligand-protected Ag clusters at the TDDFT level. Using these three nearly orthogonal indicators in combination provides more information than any one criterion can provide.
First author: Petelski, AN, Hydrogen-Bonded Rosettes of Aminotriazines for Selective-Ion Recognition,
JOURNAL OF PHYSICAL CHEMISTRY C, 124, 3352, (2020)
Abstract: Ion recognition is still an emerging topic in supramolecular chemistry and has aroused great attention in the last few years. In this work, we have examined the assemblies of selected hexameric rosettes of melamine and ammeline and their capacities to host halide and alkali ions in the gas phase and in water. Using relativistic dispersion-corrected density functional theory (DFT-D), we first studied the stability and the effect of introducing monovalent anions (Cl-, Br-, and I-) and cations (Na+, K+, and Rb+) in the center of the rosette’s cavity. Finally, we explored the interactions in two stacked rosettes with an interlayer ion. Our computations reveal that amine-substituted triazines are promising candidates for anion and cation recognition either in self-assembled monolayers or pillar array structures. The anion recognition process is governed by both the electrostatic and charge-transfer (donor-acceptor) interactions, while the cation recognition is governed by electrostatic and polarization. In addition, melamine and ammeline could constitute a potent mixture for dual-ion recognition strategies.
First author: Alkorta, I, An experimental and computational NMR study of organometallic nine-membered rings: Trinuclear silver(I) complexes of pyrazolate ligands,
MAGNETIC RESONANCE IN CHEMISTRY, 58, 319, (2020)
Abstract: This work reports the calculation of the nuclear magnetic resonance (NMR) chemical shifts of eight trinuclear Ag(I) complexes of pyrazolate ligands using the relativistic program ZORA. The data from the literature concern exclusively H-1, C-13, and F-19 nuclei. For this reason, one of the complexes that is derived from 3,5-bis-trifluoromethyl-1H-pyrazole has been studied anew, and the N-15 and Ag-109 chemical shifts determined for the first time in solution. Solid-state NMR data of this compound have been obtained for some nuclei (H-1, C-13, and F-19) but not for others (N-14, N-15, and Ag-109).
First author: Gostynski, R, X-ray diffraction and QTAIM calculations of the non-covalent intermolecular fluorine-fluorine interactions in tris(trifluoroacetylacetonato)-manganese(III),
JOURNAL OF MOLECULAR STRUCTURE, 1201, 319, (2020)
Abstract: An X-ray study was conducted on tris(trifluoroacetylacetonato)-manganese(III). The two different molecules in the unit cell exhibit a distorted octahedral geometry and moderate compression Jahn-Teller distortion respectively. A number of F center dot center dot center dot H and F center dot center dot center dot F intermolecular interactions were observed in the packing of the crystals in the solid state. The crystal packing effects could lead to the observed compressed Jahn-Teller distortion, instead of the expected elongation Jahn-Teller distortion. A Quantum Theory of Atoms in Molecules (QTAIM) study on selected molecular pairs identified intermolecular bond paths (BP) between fluorine atoms with bond critical points (BCP) which have positive electron density (rho) and Laplacian of electron density (del(2)rho) values, which are indicative of weak F center dot center dot center dot F non-covalent bonding interactions.
First author: Sergeieva, T, Ligand-Mediated Regioselective Rhodium-Catalyzed Benzotriazole-Allene Coupling: Mechanistic Exploration and Quantum Chemical Analysis,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 2342, (2020)
Abstract: The ligand-controlled rhodium-catalyzed regioselective coupling of 1,2,3-benzotriazoles and allenes was investigated by DFT calculations. Because allylation can occur at either the N1 or N2 position of the 1,2,3-benzotriazole, the complete Gibbs free energy profiles for both pathways were computed. A kinetic preference emerged for the experimentally observed N1 allylation with the JoSPOphos ligand, whereas N2 allylation was favored with DPEphos. Analysis of the regiodetermining oxidative addition step by using the activation strain model in conjunction with a matching energy decomposition analysis has revealed that the unprecedented N2 reaction regioselectivity is dictated by the strength of the electrostatic interactions between the 1,2,3-benzotriazole and the rhodium catalyst. The nature of the electrostatic interaction was rationalized by analysis of the electrostatic potential maps and Hirshfeld charges: a stabilizing electrostatic interaction was found between the key atoms involved in the oxidative addition for the N2 pathway, analogous interactions are weaker in the N1 case.
First author: Gupta, M, Metal-Organic Frameworks of Cu(II) Constructed from Functionalized Ligands for High Capacity H-2 and CO2 Gas Adsorption and Catalytic Studies,
INORGANIC CHEMISTRY, 59, 1810, (2020)
Abstract: Two Cu(II)-based metal-organic frameworks (MOFs) having paddle-wheel secondary building units (SBUs), namely, 1(Me) and 1(ip)(r) were synthesized solvothermally using two new bent di-isophthalate ligands incorporating different substituents. The MOFs showed high porosity (BET surface area, 2191 m(2)/g for 1(Me) and 1402 m(2)/g for For 1(Me), very high CO2 adsorption (98.5 wt % at 195 K, 42.9 wt % at 273 K, 23.3 wt % at 298 K) at 1 bar was found, while for 1(ipr) it was significantly less (14.3 wt % at 298 K and 1 bar, 54.4 wt % at 298 K at 50 bar). 1(Me) exhibited H-2 uptake of 3.2 wt % at 77 K and 1 bar of pressure, which compares well with other benchmark MOFs. For 1(Me), the H-2 uptake was found to be 2.54 wt % under similar experimental conditions. The significant adsorption of H-2 and CO2 for 1(Me) could be due to the presence of micropores as well as unsaturated metal sites in these MOFs besides the presence of substituents that interact with the gas molecules. The experimental adsorption behavior of the MOFs could be justified by theoretical calculations. Additionally, catalytic conversions of CO2 and CS2 into useful chemicals like cyclic carbonates, cyclic trithiocarbonates, and cyclic dithiocarbonates could be achieved.
First author: Ciancaleoni, G, Disentanglement of orthogonal hydrogen and halogen bonds via natural orbital for chemical valence: A charge displacement analysis,
JOURNAL OF COMPUTATIONAL CHEMISTRY, 41, 1185, (2020)
Abstract: As known, the electron density of covalently bound halogen atoms is anisotropically distributed, making them potentially able to establish many weak interactions, acting at the same time as halogen bond donors and hydrogen bond acceptors. Indeed, there are many examples in which the halogen and hydrogen bond coexist in the same structure and, if a correct bond analysis is required, their separation is mandatory. Here, the advantages and limitations of coupling the charge displacement analysis with natural orbital for chemical valence method (NOCV-CD) to separately analyze orthogonal weak interactions are shown, for both symmetric and asymmetric adducts. The methodology gives optimal results with intermolecular adducts but, in the presence of an organometallic complex, also intramolecular interactions can be correctly analyzed. Beyond the methodological aspects, it is shown that correctly separate and quantify the interactions can give interesting chemical insights about the systems.
First author: Meleti, VR, (+/-)-Licarin A and its semi-synthetic derivatives: In vitro and in silico evaluation of trypanocidal and schistosomicidal activities,
ACTA TROPICA, 202, 1185, (2020)
Abstract: This paper reports the synthesis of (+/-)-licarin A 1, a dihydrobenzofuran neolignan, resultant of an oxidative coupling reaction of isoeugenol and horseradish peroxidase (HRP) enzyme. Following, three semi-synthetic derivatives from this compound were obtained: benzylated (+/-)-licarin A 2, methylated (+/-)-licarin A 3 and acetylated (+/-)-licarin A 4. After structural elucidation and assignment by Nuclear Magnetic Resonance of H-1, C-13 and DEPT, all compounds were evaluated in vitro against Trypomastigote forms of Trypanosoma cruzi (T. cruzi), the etiologic agent of Chagas disease, and Schistosoma mansoni (S. mansoni) worms, the etiologic agent of schistosomiasis. Compound (4) was the most active against S. mansoni adult worms, displaying worm viability reduction at 25 mu M and mortality of all worms at 100 and 200 mu M within 24 h. Compound 1 was the second most active, showing worm viability reduction at 50 mu M and mortality of 25% and 100% of worms in 24h at concentrations of 100 and 200 mu M, respectively. In addition, theoretical calculations aiming at finding molecular properties that showed the correlation for schistosomicidal and trypanocidal activities of (+/-)-licarin A and three of its semi-synthetic derivatives were also performed.
First author: Conradie, J, Tris(beta-ketoiminato)ruthenium(III) – Structural and electronic data of the neutral, oxidized and reduced forms,
DATA IN BRIEF, 28, 1185, (2020)
Abstract: In this data article, density functional theory (DFT) calculated data for the optimized geometries and electronic structure data of the neutral, oxidized and reduced forms of the fac and mer isomers of tris(amino-pent-3-en-2-onato-N,O)ruthenium(III) as representative example of tris(beta-ketoiminato)ruthenium(III) complexes is provided. Energy-level diagrams of the neutral, oxidized and reduced molecules, show the effect on the molecular energy levels and the electron occupation of the frontier orbitals, when the neutral complex is oxidized or reduced. The DFT calculated data also confirms the spin state of the molecules and show that the fac and mer isomers of tris(amino-pent-3-en-2-onato-N,O)ruthenium(III) are equi-energetic.
First author: Cao, MJ, Theoretical Study on Electronic Structural Properties of Catalytically Reactive Metalloporphyrin Intermediates,
CATALYSTS, 10, 1185, (2020)
Abstract: Metalloporphyrins have attracted great attention in the potential application of biomimetic catalysis. Especially, they were widely investigated as green catalysts in the chemical oxidation of various hydrocarbons through the catalytic activation of molecular oxygen. The structural properties of active central metal ions were reported to play a decisive role in catalytic activity. However, those delicate structural changes are difficult to be experimentally captured or elucidated in detail. Herein, we explored the electronic structural properties of metalloporphyrins (metal porphyrin (PMII, (PMCl)-Cl-III)) and their corresponding catalytically active intermediates (metal(III)-peroxo(PMIII-O-2), metal(III)-hydroperoxo(PMIII-OH), and metal(IV)-oxo(PMIV =O), (M=Fe, Mn, and Co)) through the density functional theory method. The ground states of these intermediates were determined based on the assessment of relative energy and the corresponding geometric structures of ground states also further confirmed the stability of energy. Furthermore, our analyses of Mulliken charges and frontier molecular orbitals revealed the potential catalytic behavior of reactive metalloporphyrin intermediates.
First author: Alkorta, I, Regium Bonds between Silver(I) Pyrazolates Dinuclear Complexes and Lewis Bases (N-2, OH2, NCH, SH2, NH3, PH3, CO and CNH),
CRYSTALS, 10, 1185, (2020)
Abstract: A theoretical study and Cambridge Structural Database (CSD) search of dinuclear Ag(I) pyrazolates interactions with Lewis bases were carried out and the effect of the substituents and ligands on the structure and on the aromaticity were analyzed. A relationship between the intramolecular Ag-Ag distance and stability was found in the unsubstituted system, which indicates a destabilization at longer distances compensated by ligands upon complexation. It was also observed that the asymmetrical interaction with phosphines as ligands increases the Ag-Ag distance. This increase is dramatically higher when two simultaneous PH3 ligands are taken into account. The calculated Ag-109 chemical shielding shows variation up to 1200 ppm due to the complexation. Calculations showed that six-membered rings possessed non-aromatic character while pyrazole rings do not change their aromatic character significantly upon complexation.
First author: Lefeuvre, B, Redox-Modulations of Photophysical and Single-molecule Magnet Properties in Ytterbium Complexes Involving Extended-TTF Triads,
MOLECULES, 25, 1185, (2020)
Abstract: The reaction between the 2,2′-benzene-1,4-diylbis(6-hydroxy-4,7-di-tert-butyl-1,3-benzodithiol-2-ylium-5-olate triad (H(2)SQ) and the metallo-precursor [Yb(hfac)(3)].2H(2)O led to the formation of a dinuclear coordination complex of formula [Yb-2(hfac)(6)(H(2)SQ)].0.5CH(2)Cl(2) (H(2)SQ-Yb). After chemical oxidation of H(2)SQ in 2,2′-cyclohexa-2,5-diene-1,4-diylidenebis(4,7-di-tert-butyl-1,3-benzodithiole-5,6-dione (Q), the latter triad reacted with the [Yb(hfac)(3)].2H(2)O precursor to give the dinuclear complex of formula [Yb-2(hfac)(6)(Q)] (Q-Yb). Both dinuclear compounds have been characterized by X-ray diffraction, DFT optimized structure and electronic absorption spectra. They behaved as field-induced Single-Molecule Magnets (SMMs) nevertheless the chemical oxidation of the semiquinone to quinone moieties accelerated by a factor of five the relaxation time of the magnetization of Q-Yb compared to the one for H(2)SQ-Yb. The H(2)SQ triad efficiently sensitized the Yb-III luminescence while the chemical oxidation of H(2)SQ into Q induced strong modification of the absorption properties and thus a quenching of the Yb-III luminescence for Q-Yb. In other words, both magnetic modulation and luminescence quenching are reached by the oxidation of the protonated semiquinone into quinone.
First author: Zierkiewicz, W, Competition between Intra and Intermolecular Triel Bonds. Complexes between Naphthalene Derivatives and Neutral or Anionic Lewis Bases,
MOLECULES, 25, 1185, (2020)
Abstract: A TrF2 group (Tr = B, Al, Ga, In, Tl) is placed on one of the alpha positions of naphthalene, and its ability to engage in a triel bond (TrB) with a weak (NCH) and strong (NC-) nucleophile is assessed by ab initio calculations. As a competitor, an NH2 group is placed on the neighboring C-alpha, from which point it forms an intramolecular TrB with the TrF2 group. The latter internal TrB reduces the intensity of the pi-hole on the Tr atom, decreasing its ability to engage in a second external TrB. The intermolecular TrB is weakened by a factor of about two for the smaller Tr atoms but is less severe for the larger Tl. The external TrB can be quite strong nonetheless; it varies from a minimum of 8 kcal/mol for the weak NCH base, up to as much as 70 kcal/mol for CN-. Likewise, the appearance of an external TrB to a strong base like CN- lessens the ability of the Tr to engage in an internal TrB, to the point where such an intramolecular TrB becomes questionable.
First author: Chen, YM, Complexation of trivalent lanthanides and actinides with diethylenetriaminepentaacetic acid: Theoretical unraveling of bond covalency,
JOURNAL OF MOLECULAR LIQUIDS, 299, 1185, (2020)
Abstract: Separation of trivalent actinides (An(III)) and lanthanides (Ln(III)) is a pivotal step with respect to the treatment of nuclear waste based on the partitioning and transmutation (P&T) strategy, which is also extraordinarily challenging due to their similar coordination chemistry. The diethylenetriaminepentaacetate (DTPA) ligand has been demonstrated to possess selective separation ability toward An(III) over Ln(III) in aqueous media. Nevertheless, the extracted complexes of An(III)/Ln(III) with DTPA, and the origin of selectivity for An(III) are still not well deciphered. In this work, from theoretical perspective and at the molecular level, the geometrical structures, bonding nature as well as thermodynamic behaviors of possible complexes of An(III) (An = Am, Cm, Cf) and Ln(III) (Ln = Nd, Eu) with DTPA in the aqueous phase have been systematically studied using scalar relativistic density functional theory (DFT). All bonding analyses indicate that the metal-ligand bonds possess weak but non-negligible covalent interactions, and An(III)-DTPA species demonstrate more covalency compared to Ln(III) analogues. In addition, the covalency of the metal-ligand bonding of An(III)-DTPA increases across the actinide series from Am to Cf, which stems from the increased orbital degeneracy of the 5f orbitals of actinides and the 2p orbitals of the ligands. According to thermodynamic analysis, the anhydrous species [Cf(HDTPA)](-) is the most likely species for Cf(III) in acidic solution, whereas [M(HDTPA)(H2O)](-) are more favorable for Am(III) and Cm (III), probably due to the different bonding nature of the transplutonium series. This work affords new theoretical insights into the coordination chemistry of An(III)/Ln(III)-DTPA complexes, and paves the way to further design efficient DTPA-based ligands for An(III)/Ln(III) separation. Moreover, the DTPA ligand may also be applied for in-group separation of trivalent actinides, which is quite meaningful for the extraction of Cf(III).
First author: Forster, A, A Quadratic Pair Atomic Resolution of the Identity Based SOS-AO-MP2 Algorithm Using Slater Type Orbitals,
JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 16, 875, (2020)
Abstract: We report a production level implementation of pair atomic resolution of the identity (PARI) based second-order Moller-Plesset perturbation theory (MP2) in the Slater type orbital (STO) based Amsterdam Density Functional (ADF) code. As demonstrated by systematic benchmarks, dimerization and isomerization energies obtained with our code using STO basis sets of triple-zeta-quality show mean absolute deviations from Gaussian type orbital, canonical, basis set limit extrapolated, global density fitting (DF)-MP2 results of less than 1 kcal/mol. Furthermore, we introduce a quadratic scaling atomic orbital based spin-opposite-scaled (SOS)-MP2 approach with a very small prefactor. Due to a worst-case scaling of O(N-3), our implementation is very fast already for small systems and shows an exceptionally early crossover to canonical SOS-PARI-MP2. We report computational wall time results for linear as well as for realistic three-dimensional molecules and show that triple-zeta quality calculations on molecules of several hundreds of atoms are only a matter of a few hours on a single compute node, the bottleneck of the computations being the SCF rather than the post-SCF energy correction.
First author: Majerz, I, Substituent effect on inter-ring interaction in paracyclophanes,
MOLECULAR DIVERSITY, 24, 11, (2020)
Abstract: The theoretical calculations, namely multipole-derived charge analysis, quantum theory of atom in molecules, and non-bonding interaction (NCI), were performed for [2.2]paracyclophanes, [2.2]paracyclophane-7,9-dienes, and [3.3]paracyclophanes optimized at B3LYP/6-311++G** level, including dispersion correction. The substituent effect of the electron donor N(Me)(2) and electron acceptor NO2 group and the influence of the length of bridges joining the aromatic ring on aromatic ring interaction energy (AIE) and strain energy were discussed. The local and electrostatic character of the substituent effect in paracyclophanes was shown. The presence of the weak orbital through-space C center dot center dot center dot C interaction between the [3.3]paracyclophane ring and weak CH center dot center dot center dot O hydrogen bonds between the substituents in the different rings was shown.
First author: Hoffmann, JM, pi-Hole Interactions with Various Nitro Compounds Relevant for Medicine: DFT Calculations and Surveys of the Cambridge Structural Database (CSD) and the Protein Data Bank (PDB),
SYNTHESIS-STUTTGART, 52, 521, (2020)
Abstract: Model DFT computations and a thorough evaluation of the Cambridge structural database (CSD) and the protein data bank (PDB) were conducted to assess the occurrence and significance of intermolecular pi-hole interactions with various nitro compounds relevant to medicine. DFT calculations indicate interaction energies between -3.9 to -6.5 kcal.mol(-1), which is in the order of typical hydrogen- and halogen-bonding interactions. Ample structural evidence for the occurrence of nitro pi-hole interactions was found within the CSD and the PDB.
First author: Hughes, HJ, The orientation of a membrane probe from structural analysis by enhanced Raman scattering,
BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES, 1862, 521, (2020)
Abstract: Small fluorescent molecules are widely used as probes of biomembranes. Different probes optically indicate membrane properties such as the lipid phase, thickness, viscosity, and electrical potential. The detailed molecular mechanisms behind probe signals are not well understood, in part due to the lack of tools to determine probe position and orientation in the membrane. Optical measurements on aligned biomembranes and lipid bilayers provide some degree of orientational information based on anisotropy in absorption, fluorescence, or nonlinear optical properties. These methods typically find the polar tilt angle between the membrane normal and the long axis of the molecule. Here we show that solution-phase surface enhanced Raman scattering (SERS) spectra of lipid membranes on gold nanorods can be used to determine molecular orientation of molecules within the membrane. The voltage sensitive dye 4-(2-(6-(dibutylamino)-2-naphthalenypetheny1)-1-(3-sulfopropyl)-hydroxide, known as di-4-ANEPPS, is studied. Through the analysis of several peaks in the SERS spectrum, the polar angle from the membrane normal is found to be 66 degrees, and the roll angle around the long axis of the molecule to be 305 degrees from the original orientation. This structural analysis method could help elucidate the meaning of fluorescent membrane probe signals, and how they are affected by different lipid compositions.
First author: Zhang, HZ, Highly efficient blue-emitting of bis-cyclometalated tetravalent platinum (IV) complexes: A theoretical study,
INORGANICA CHIMICA ACTA, 501, 521, (2020)
Abstract: Pt(IV) complexes bespeak the prospect as phosphorescent materials because of their excellent properties, whereas the reports of excavating potential properties for Pt (IV) complexes in phosphorescence are limited. To address this issue, a DFT/TDDFT calculation has been applied on two series of biscyclometalated Pt(IV) complexes ([Pt(ppy)(2)XCl], where X = -CH3(1-Me); -CF3(1a-CF3); -CN(1a-CN), -(CH3)(3) (1b-tBu); -CH2NH2(1b-AMe); -C6H5(2-Ph); -C6F5(2a-C-6 F-5) and -2,4,6-(CH3)(3) C6H5 (2b-Mes)) to shed light on the effects of systematic single monodentate ancillary ligand modifications on structure and photophysical properties. The calculated results confirm that all complexes displayed blue emission in dichloromethane solution with varying emission efficiencies that were found to be influenced by the electronic nature of the ancillary ligand. The stronger the electron-releasing ability and the smaller degree of extended conjugation in the monodentate ancillary ligand can give rise to intensive the radiative decay. Regardless of whether pi conjugation exists or not, increasing electron-withdrawing character in ancillary ligand of parent complexes 1-Me ([Pt(ppy)(2)CH3Cl]) or 2-Ph ([Pt(ppy)(2)C6H5Cl]) can be unbeneficial for the nonradiative decay process. In addition, the results demonstrate that complexes 1a-CN ([Pt(ppy)(2)CNCl]) exhibits a better blue phosphorescent material with a higher quantum yield.
First author: Dasgupta, N, ReaxFF molecular dynamics simulations on the structure and dynamics of electrolyte water systems at ambient temperature,
COMPUTATIONAL MATERIALS SCIENCE, 172, 521, (2020)
Abstract: ReaxFF molecular dynamics simulations have been performed to study the effect of cations Li+, Na+ and K+ and anion Cl- on the structural and dynamical properties of water, using the force field recently developed by Fedkin and co-workers. The structural relationship of ion and water has been analyzed from the radial distribution function and angular distribution. Comparisons of ReaxFF angle variation of ions and water within the first solvation shell were made and found to be in good agreement with literature. The disruption of hydrogen bond network of water by ions is elucidated by ion-water residence times, water-water hydrogen bond dynamics and reorientational dynamics. ReaxFF diffusion coefficient and residence times of electrolyte water system were compared with ab initio and non-reactive potentials to analyze the difference in dynamics. We gained insight into the ion interaction with water and how it can accelerate or decelerate water dynamics. ReaxFF outlines the formation and dissolution of metal hydroxides and metal chlorides over the course of simulation to explain the diffusion dynamics of water in salt solutions, allowing us to elucidate the impact of concentration on the self-diffusivity of water and ions in solutions, and to reveal that this effect always decreases the mobility and is not at all ion-specific. The obtained results have opened new opportunities to extend the ReaxFF methodology towards systems involving electrolytes.
First author: Mavrommati, SA, Initial-state preparation effects in time-resolved electron paramagnetic resonance experiments,
JOURNAL OF CHEMICAL PHYSICS, 152, 521, (2020)
Abstract: We explain a recent experimental observation that the time-resolved electron paramagnetic resonance spectra of an organic molecule for optical excitation within a highly absorbing region of the molecule has similar intensities to the spectra for optical excitation in a nonabsorbing region [D. L. Meyer et al., J. Phys. Chem. Lett. 8, 1677 (2017)]. We demonstrate that this phenomenon is due to an initial-state preparation effect of photoexcitation that leads to similar initial populations of triplet states for both optical excitation regions. Due to the low intersystem crossing rates, the initial triplet populations are not perturbed on the time scale of the experiment, so they determine the relative intensities of the paramagnetic resonance spectra. The effect is surprising given the weak spin-orbit interactions of organic molecules. Such initial-state preparation effects are likely to occur in systems where the intersystem crossing time scales are long compared to the time scale of the experiment. Published under license by AIP Publishing.
First author: Geerlings, P, Conceptual density functional theory: status, prospects, issues,
THEORETICAL CHEMISTRY ACCOUNTS, 139, 521, (2020)
Abstract: This paper results from a round table discussion at the CCTC2018 Conference in Changsha City, Hunan, China, in December 2018. It presents a report on the status, prospects, and issues of conceptual density functional theory (CDFT). After a short exposition on the history of CDFT, its fundamentals, philosophy, and successes are highlighted. Then ten issues for reflection on the future of conceptual DFT are formulated and discussed, ending with one or more summarizing statements on the present status of various concepts/principles/practices and proposed directions for future research. The issues include the further analysis of the energy functional, E[N,v], extended to include effects of temperature, solvent, and mechanical forces, basic requirements for physically acceptable response functions as reactivity descriptors, the use of the grand canonical ensemble, the relevance of CDFT for chemical kinetics and thermodynamics, the domain of validity of CDFT-based principles, the combination of CDFT with reaction path calculations, information-theoretic descriptors, and the treatment of excited states and time dependence. The final issue advocates the transition of CDFT from an interpretative to a predictive mode; we believe this is of utmost importance for promoting CDFT as a viable alternative to wave function-based methods for the practicing chemist, a separate issue treated in the final section.
First author: Pietrasiak, E, Understanding Te-125 NMR chemical shifts in disymmetric organo-telluride compounds from natural chemical shift analysis,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 2319, (2020)
Abstract: Organotellurium compounds of general formula X-Te-R display a broad range of chemical shifts that are very sensitive to the X and R substituents. In order to link the Te-125 chemical shift of a series of perfluoroalkyl aryl tellurides to their electronic structure, the chemical shielding tensors of the Te-125 nuclei were calculated by density functional theory (DFT) and further analyzed by a decomposition into contributions of natural localized molecular orbitals (NLMOs). The analysis indicated that the variation in Te-125 chemical shifts in molecules 1-13 is mainly due to the magnetic coupling of the tellurium p-character lone pair with antibonding orbitals perpendicular to it {sigma*(Te-X) and sigma*(Te-C(Ar))} upon action of an external magnetic field. The strength of the coupling is affected by electronic properties of the X-substituents, polarization of the antibonding orbitals and presence of secondary interactions perturbing the energy of these orbitals. The lower in energy and the more polarized towards tellurium the antibonding orbitals are, the stronger is the coupling and the more deshielded the tellurium nucleus.
First author: Lehtola, S, Fully numerical calculations on atoms with fractional occupations and range-separated exchange functionals,
PHYSICAL REVIEW A, 101, 2319, (2020)
Abstract: recently developed finite-element approach for fully numerical atomic structure calculations [S. Lehtola, Int. J. Quantum Chem. 119, e25945 (2019)] is extended to the description of atoms with spherically symmetric densities via fractionally occupied orbitals. Specialized versions of Hartree-Fock as well as local density and generalized gradient approximation density functionals are developed, allowing extremely rapid calculations at the basis-set limit on the ground and low-lying excited states, even for heavy atoms. The implementation of range separation based on the Yukawa or complementary error function (erfc) kernels is also described, allowing complete basis-set benchmarks of modern range-separated hybrid functionals with either integer or fractional occupation numbers. Finally, the computation of atomic effective potentials at the local density or generalized gradient approximation levels for the superposition of atomic potentials (SAP) approach [S. Lehtola, J. Chem. Theory Comput. 15, 1593 (2019)] that has been shown to be a simple and efficient way to initialize electronic structure calculations is described. The present numerical approach is shown to afford beyond micro-Hartree accuracy with a small number of numerical basis functions, and to reproduce the literature results for the ground states of atoms and their cations for 1 <= Z <= 86. Our results indicate that the literature values deviate by up to 10 mu E-h from the complete basis-set limit. The numerical scheme for the erfc kernel is shown to work by comparison to results from large Gaussian basis-set calculations from the literature. Spin-restricted ground states are reported for Hartree-Fock and Hartree-Fock-Slater calculations with fractional occupations for 1 <= Z <= 118.
First author: Castro, AC, Computational NMR Spectra of o-Benzyne and Stable Guests and Their Hemicarceplexes,
CHEMISTRY-A EUROPEAN JOURNAL, 26, 2626, (2020)
Abstract: The incarceration of o-benzyne and 27 other guest molecules within hemicarcerand 1, as reported experimentally by Warmuth, and Cram and co-workers, has been studied by density functional theory (DFT). The H-1 NMR chemical shifts, rotational mobility, and conformational preference of the guests within the supramolecular cage were determined, which showed intriguing correlations of the chemical shifts with structural parameters of the host-guest system. Furthermore, based on the computed chemical shifts reassignments of some NMR signals are proposed. This affects, in particular, the putative characterization of the volatile benzyne molecule inside a hemicarcerand, for which our CCSD(T) and KT2 results indicate that the experimentally observed signals are most likely not resulting from an isolated o-benzyne within the supramolecular host. Instead, it is shown that the guest reacted with an aromatic ring of the host, and this adduct is responsible for the experimentally observed signals.
First author: Pratik, SM, Boosting Photoelectric Conductivity in Porphyrin-Based MOFs Incorporating C-60,
JOURNAL OF PHYSICAL CHEMISTRY C, 124, 1878, (2020)
Abstract: Electronic structure calculations show that guest C-60 in the porphyrin-containing metal organic frameworks Zn-2(TCPB)(DA-ZnP) (DA-MOF; H4TCPB = 1,2,4,5-tetrakis (4-carboxyphenyl)benzene, DA-ZnP = [ 5, 15-bis [(4-pyridyl)ethynyl]-10,20-diphenylporphinato]zinc(II)) and Zn-2(TCPB)(F-ZnP) (F-MOF; F-ZnP = [5,15-di(4-pyridyl)-10,20-bis (p entafluorophenyl)porphinato] zinc (II) ) engenders high photoelectrical conductivity due to efficient donor-acceptor charge-transfer (CT) interactions. Structural modifications at the meso position of the porphyrin influence the preferred positions of C-60 within the frameworks, giving rise to host-guest interactions with different anisotropic structural, electronic, and optoelectronic properties. A preferred slipped-parallel pi-stacked interaction of C-60 that is predicted for NH2-substituted DA-MOF and F-MOF fosters strong CT transitions and lowers band gaps by similar to 1.0 eV compared to the pristine DA-MOF and F-MOF. Hopping rates computed using Marcus theory are found to be anisotropic and accelerated by multiple orders of magnitude across pi-stacked interfaces created by C-60 incorporation, a consequence of strong electronic coupling between initial and final diabatic states. Calculations indicate that photoinduced electron transfer, as well as direct CT from porphyrin to C-60 upon irradiation, triggers a charge separation process that leads to the formation of what should be long-lived electron-trapped states at the heterojunctions. Design principles revealed here for the control of photophysical and electron-transfer processes will be useful for constructing new MOF-derived visible- and infrared-based optoelectronics.
First author: Oschinski, H, Structures and Thermodynamics of MgO/SiO Interfaces,
JOURNAL OF PHYSICAL CHEMISTRY C, 124, 1923, (2020)
Abstract: Silicon monoxide is a complex material which tends to form atomic and nanoscale amorphous structures. The question is in which ways can the stability of SiO on suitable carriers or interfaces be enhanced. This was investigated by statistical thermodynamics based on density functional theory calculations on SiO layers on and in-between MgO(100) model surfaces. Furthermore, the stability of ordered close-packed SiO layers and their relaxation into amorphous structures were studied. Some selected SiO structures between thin MgO sheets were investigated and their interface energies are discussed. The results for the interface tensions can be understood by a strong lateral repulsion between atoms in ordered close-packed SiO layers on MgO(100). The SiO layer can thereby induce stress on the MgO sheets.
First author: Dong, QB, Accelerated C2H2/CO2 Separation by a Se-Functionalized Porous Coordination Polymer with Low Binding Energy,
ACS APPLIED MATERIALS & INTERFACES, 12, 3764, (2020)
Abstract: High-quality pure acetylene (C2H2) is a kind of crucial starting material for various value-added products. However, selective capture of C2H2 from the main impurity of CO, via porous absorbents is a great challenge, as they possess extremely similar kinetic diameters and boiling points, as well as the explosive and reactive properties of C2H2. Herein, we report a porous coordination polymer (PCP), (NTU-55), which assembled from the coordination between a Cu dimer and a newly designed ligand with a nonmetal selenium (Se) site. Static single-component adsorption and dynamic breakthrough experiments reveal that desolvated NTU-55 can completely adsorb C2H2 from the C2H2/CO2 mixture (1/4, v/v) at 298 K, along with higher C2H2 capacity and much lower binding energy. The origin of this separation, as comprehensively revealed by density functional theory (DFT) calculations, is derived from the interaction discriminatory of C2H2 and CO, toward accessible Se and Cu adsorption sites. To the best of our knowledge, this is the first time to find the positive effect of nonmetal Se sites for selective C2H2 capture.
First author: Vorobyev, V, Synthesis of the Ruthenium Nitrosyl Complex with Coordinated Ammonia and Pyridine at Room Temperature,
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 646, 58, (2020)
Abstract: The reaction of nitrate ruthenium complex, fac-[RuNO(NH3)(2)(NO3)(3)], with pyridine resulted in cis-[RuNO(NH3)(2)Py-2(NO3)](NO3)(2)center dot H2O with 84 % yield of the product at room temperature. Addition of any solvent leads to the reaction failure; the excess of pyridine fulfilled the role of a solvent. The DFT simulation of the dissociative mechanism reveals that the nitrate loss from cis-position to NO occurs more easily than for trans-coordinated nitrate. This conclusion is in agreement with the X-ray determined structure of the product. In the solid state, the nitrosyl groups of two neighboring complexes are closely positioned to each other. The small available volume around the nitrosyl group, ca. 0.5 angstrom(3), leads to the enhanced stability of the photoinduced metastable state. The Ru-ON isomer converts back to the ground N-coordinated state with 0.001 s(-1) rate constant at 257 K. This O-coordinated isomer of the studied complex is one of the ten known most stable Ru-ON isomers ranked by the “decay” temperature.
First author: Barbon, A, Comprehensive investigation of the triplet state electronic structure of free-base 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin by a combined advanced EPR and theoretical approach,
JOURNAL OF CHEMICAL PHYSICS, 152, 58, (2020)
Abstract: The nature of the photoexcited triplet state of free-base 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (H2TPPS4-) has been investigated by advanced Electron Paramagnetic Resonance (EPR) techniques combined with quantum chemical calculations. The zero-field splitting (ZFS) parameters, D and E, the orientation of the transition dipole moment in the ZFS tensor frame, and the proton hyperfine couplings have been determined by magnetophotoselection-EPR and pulse electron-nuclear double resonance spectroscopy. Both time-resolved and pulse experiments exploit the electron spin polarization of the photoexcited triplet state. Comparison of the magnetic observables with computational results, including CASSCF calculations of the ZFS interaction tensor, provides an accurate picture of the triplet-state electronic structure. The theoretical investigation has been integrated with a systematic analysis on the parent free-base porphyrin molecule to assess the effect of the sulfonatophenyl substituents on the magnetic tensors. Additionally, the magnetophotoselection effects are discussed in terms of tautomerization in the excited singlet state of H2TPPS4-.
First author: Munoz-Castro, A, Triple 1D equivalent to 1D superatomic bonding. Au-22(dppo)(6) as a pi(4)- and Delta(2)-triply bonded cluster based on Au-11 assembled units,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 1422, (2020)
Abstract: delta-Bonds have been intimately related to metal-metal bonds of d-elements since the archetypal d(4)-d(4) [Re2Cl8](2-) ion with a sigma(2)pi(4)delta(2) bond. Currently, the notion of multiple superatom arrangements as initial steps toward molecular materials within the building-up approach is dominated by P-shell characteristics, as given in the well-described Au-25(SR)(18) ligand protected cluster. In this work we rationalize the Au-22(dppo)(6) cluster as a triple-bonded 22-valence electron (ve) supermolecule, featuring a bonding scheme based on 1D + 1D shell combinations, which largely contrasts with the 14-ve Au-38(SR)(24) with mainly 1P + 1P patterns mimicking a F-2 molecule. The resulting pi(4)Delta(2)-bonding pattern shows an unprecedented superatomic counterpart of a d-shell based bond inherently related to transition-metal dimers, adding useful key aspects to the understanding of species based on cluster-assembly.
First author: Cailler, LP, Comparative Study of the Electronic Structures of mu-Oxo, mu-Nitrido, and mu-Carbido Diiron Octapropylporphyrazine Complexes and Their Catalytic Activity in Cyclopropanation of Olefins,
INORGANIC CHEMISTRY, 59, 1104, (2020)
Abstract: The electronic structure of three single-atom bridged diiron octapropylporphyrazine complexes (FePzPr(8))(2)X having Fe(III)-O-Fe(III), Fe(III)-N-Fe(IV) and Fe(IV)-C-Fe(IV) structural units was investigated by Mossbauer spectroscopy and density functional theory (DFT) calculations. In this series, the isomer shift values decrease, whereas the values of quadrupole splitting become progressively greater indicating the increase of covalency of Fe-X bond in the mu-oxo, mu-nitrido, mu-carbido row. The Mossbauer data point to low-spin systems for the three complexes, and calculated data with B3LYP-D3 show a singlet state for mu-oxo and mu-carbido and a doublet state for mu-nitrido complexes. An excellent agreement was obtained between B3LYP-D3 optimized geometries and X-ray structural data. Among (FePzPr(8))(2)X complexes, mu-oxo diiron species showed a higher reactivity in the cyclopropanation of styrene by ethyl diazoacetate to afford a 95% product yield with 0.1 mol % catalyst loading. A detailed DFT study allowed to get insight into electronic structure of binuclear carbene species and to confirm their involvement into carbene transfer reactions.
First author: Pirillo, J, Trans Influence across a Metal-Metal Bond of a Paddle-Wheel Unit on Interaction with Gases in a Metal-Organic Framework,
INORGANIC CHEMISTRY, 59, 1193, (2020)
Abstract: Metal-organic frameworks (MOFs) are known as promising adsorbent materials that can recognize gases specifically. In the frameworks, gases favor interacting with specific binding sites such as open metal sites (OMSs), which can consist of various metals and show characteristic adsorption properties. A recently reported framework possessing OMSs of rhodium paddle-wheel (Rh-PW) showed distinct adsorption properties between NO and CO. We investigated theoretically the reasons for stronger NO binding to the Rh-PW and different adsorption amounts between NO and CO using Rh-PW cluster models, as well as the frequently reported Cu-PW for comparison. We also analyzed the cases of CO2 and N-2, which are often used to probe functions of MOFs. We observed an increase in binding energy of NO at the second adduction of NO. On the basis of energy decomposition analysis, we found that Rh-NO bond formation inducing a trans influence is important for the stronger binding than with CO. Furthermore, we proposed a reason for twice the adsorption amount of NO than CO. The results are consistent with experimental observations, giving us insight into design functions of MOFs by selecting metal species.
First author: Leygue, N, Tripyridinophane Platform Containing Three Acetate Pendant Arms: An Attractive Structural Entry for the Development of Neutral Eu(III) and Tb(III) Complexes in Aqueous Solution,
INORGANIC CHEMISTRY, 59, 1496, (2020)
Abstract: We report a detailed characterization of Eu3+ and Tb3+ complexes derived from a tripyridinophane macro cycle bearing three acetate side arms (H(3)tpptac). Tpptac(3-) displays an overall basicity (Sigma log K-i(H)) of 24.5, provides the formation of mononuclear ML species, and shows a good binding affinity for Ln(3+) (log K-LnL = 17.5-18.7). These complexes are also thermodynamically stable at physiological pH (pEu = 18.6, pTb = 18.0). It should be noted that the pGd value of Gd-tpptac (18.4) is only slightly lower than that of commercially available MRI contrast agents such as Gd-dota (pGd = 19.2). Moreover, a very good selectivity for these ions over the endogenous cations (log K-CuL = 14.4, log K-ZnL = 12.9, and log K-CaL = 9.3) is observed. The X-ray structure of the terbium complex shows the metal coordinated by the nine N6O3 donor set of the ligand and one inner-sphere water molecule. DFT calculations result in two Eu-tpptac structures with similar bond energies (Delta E = 0.145 eV): one structure in which the water is coordinated to the metal ion and one structure in which the water molecule is farther away from the ion, bound to the ligand with an OH-pi bond. By detailed luminescence experiments, we demonstrate that the europium complex in aqueous solution presents a hydration equilibrium between nine-coordinate, dehydrated [Eu-tpptac](0) and ten-coordinate, monohydrated [Eu-tpptac(H2O)](0) species. A similar trend is observed for the terbium complex. Despite the presence of this hydration equilibrium, the H(3)tpptac ligand sensitizes Eu3+ and Tb3+ luminescence efficiently in buffered water at physiological pH. Particularly, the terbium complex displays a long excited-state lifetime of 2.24 ms and an overall quantum yield of 33% with a brightness of 3600 M-1 cm(-1). Such features of Ln(3+) complexes of H(3)tpptac indicate that this platform appears to be particularly appealing for the further development of luminescent lanthanide labels.
First author: Tsoureas, N, Uranium(iv) cyclobutadienyl sandwich compounds: synthesis, structure and chemical bonding,
CHEMICAL COMMUNICATIONS, 56, 944, (2020)
Abstract: The 1:1 reactions of uranium(iv) tetrakis(borohydride) with the sodium and potassium salts of the cyclobutadienyl anion [C-4(SiMe3)(4)](2-) (Cb ””) produce the half-sandwich complexes [Na(12-crown-4)(2)][U(eta(4)-Cb ””)(BH4)(3)] and [U(eta(4)-Cb ””)(mu-BH4)(3){K(THF)(2)}](2). In the 1:2 reaction of U(BH4)(4) with Na2Cb ””, formation of [U(eta(4)-Cb ””)(eta(3)-C4H(SiMe3)(3)-kappa-(CH2SiMe2)(BH4))](-) reveals that a Cb ”” ligand undergoes an intramolecular deprotonation, resulting in an allyl/tuck-in bonding mode. A computational study reveals that the uranium-Cb ”” bonding has an appreciable covalent component with contributions from the uranium 5f and 6d orbitals.
First author: Tanriver, G, Keteniminium Salts: Reactivity and Propensity toward Electrocyclization Reactions,
JOURNAL OF ORGANIC CHEMISTRY, 85, 449, (2020)
Abstract: A predictive computational study was conducted in order to assess the efficiency of electrocyclization reactions of keteniminium salts, in an effort to form a variety of heterocyclic systems, namely, 3-amino(benzo)thiophenes, 3-amino(benzo)furans, 3-aminopyrroles, as well as 3-amino-indoles. A density functional theory (DFT) approach was utilized and the effect of heteroatoms (NMe, O, S) was thoroughly investigated by means of population analysis, QTAIM, NICS, ACID, and local reactivity descriptors (Parr and Fukui functions). The electrocyclization of enamines leading to 3-aminopyrroles was shown to be both kinetically and thermodynamically most favorable. Moreover, the pericyclic nature of the electrocyclizations was confirmed using FMO, QTAIM, NICS, and ACID methods. Additionally, substituent effects were investigated in order to give further insight on the reactivity of heteroatom containing keteniminium systems toward electrocyclization reactions. Finally, computational predictions were experimentally confirmed for a selection of keteniminium systems.
First author: Reese, HR, Peptide science: A “rule model” for new generations of peptidomimetics,
ACTA BIOMATERIALIA, 102, 35, (2020)
Abstract: Peptides have been heavily investigated for their biocompatible and bioactive properties. Though a wide array of functionalities can be introduced by varying the amino acid sequence or by structural constraints, properties such as proteolytic stability, catalytic activity, and phase behavior in solution are difficult or impossible to impart upon naturally occurring alpha-L-peptides. To this end, sequence-controlled peptidomimetics exhibit new folds, morphologies, and chemical modifications that create new structures and functions. The study of these new classes of polymers, especially alpha-peptoids, has been highly influenced by the analysis, computational, and design techniques developed for peptides. This review examines techniques to determine primary, secondary, and tertiary structure of peptides, and how they have been adapted to investigate peptoid structure. Computational models developed for peptides have been modified to predict the morphologies of peptoids and have increased in accuracy in recent years. The combination of in vitro and in silico techniques have led to secondary and tertiary structure design principles that mirror those for peptides. We then examine several important developments in peptoid applications inspired by peptides such as pharmaceuticals, catalysis, and protein-binding. A brief survey of alternative backbone structures and research investigating these peptidomimetics shows how the advancement of peptide and peptoid science has influenced the growth of numerous fields of study. As peptide, peptoid, and other peptidomimetic studies continue to advance, we will expect to see higher throughput structural analyses, greater computational accuracy and functionality, and wider application space that can improve human health, solve environmental challenges, and meet industrial needs.
First author: Wang, J, Electronic Transport Inhibiting of Carbon Nanotubes by 5f Elements,
ADVANCED THEORY AND SIMULATIONS, 3, 35, (2020)
Abstract: Based on the combination of the non-equilibrium Green’s function and density functional theory, a theoretical method for studying the transport behavior of high angular momentum 5f electrons is developed and the transport properties of the structure for actinide atoms embedded in carbon nanotubes (An@CNTs, An = Ac, Th, Pa and U) is reported. Results show that An@CNTs have lower transmission coefficients than that of CNTs. Furthermore, electrical bias to the U@(4, 4)/(5, 5) CNTs induces an additional transition spectral peak, which demonstrates that the U@(4, 4)/(5, 5) CNTs has a lower resistance. Therefore, 5f electrons of actinide atoms inhibit the electronic transport of CNTs. These findings may provide fresh insight into the transport properties of systems having higher angular momentum electrons.
First author: Chen, R, Interpreting the chemical mechanism in SERS using a Raman bond model,
JOURNAL OF CHEMICAL PHYSICS, 152, 35, (2020)
Abstract: We present a first-principles model that partitions Raman intensities to atomic and bond contributions. This framework allows us to interpret the chemical mechanism in surface-enhanced Raman scattering (SERS) as interatom charge flow modulations, which we define as Raman bonds. Hirshfeld partitioning and charge density localization are applied to express polarizability derivatives as charge flow modulations. Model systems consisting of pyridines, thiols, and carbenes interacting with metal clusters are studied using time-dependent density functional theory. We demonstrate that the mode-specific enhancements can be explained as Raman bonds conjugated across the molecule-metal interface. We also illustrate that the changes in Raman intensities induced by electric fields or chemical substitutions can generally be interpreted as changes of charge flows. The model is shown to work consistently for different types of molecule-metal bonds. Furthermore, our work shows that increasing the Raman bond conjugation across the interface leads to stronger chemical enhancements. The Raman bond model developed in this work provides a quantitative and intuitive interpretation of the chemical mechanism in SERS.
First author: De, S, Molecular mechanism of Be2+-ion binding to HLA-DP2: tetrahedral coordination, conformational changes and multi-ion binding,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 799, (2020)
Abstract: The chemistry of beryllium is rather unusual, however, less explored as compared to other main group elements. This is mainly attributed to the high toxicity of beryllium, leading to chronic granulomatous pneumonitis, called chronic beryllium disease (CBD). It has been reported that Be2+-ion binding to the human leukocyte antigen protein (HLA-DP2) and peptide (M2) results in favorable interaction with the T-cell receptor protein (TCR), which initiates immune-mediated toxicity. We have carried out molecular dynamics (MD) simulations combined with quantum mechanical/molecular mechanical (QM/MM) studies to explore the binding nature of Be2+ with a HLA-DP2 protein and M2 peptide. The interaction between the negatively charged M2 peptide and the negatively charged binding cleft of HLA-DP2 is unfavorable. However, this interaction is stabilized by one Be2+ and two Na+-ions bridged by negatively charged carboxyl groups of glutamate residues (beta 26E and beta 69E) of the beta-chain of HLA-DP2 and one glutamate (p7E) and one aspartate residue (p4D) of the M2 peptide. This multi-ion cavity consists of tetrahedrally coordinated static Be2+ and Na+-ions, as well as one dynamically exchangeable Na+-ion. The smaller size and higher charge of the Be2+-ion as compared to the Na+-ion reduce the distance between the M2 peptide and the beta-chain of HLA-DP2, which results in conformational change suitable for TCR binding. However, the replacement of the Be2+ by the Na+-ion could not generate a suitable binding site for TCR.
First author: Ramanathan, N, Prototypical cyclohexane dimers: spectroscopic evidence for sigma stacking at low temperatures,
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 905, (2020)
Abstract: Owing to the fact that sigma stacking is as important as pi stacking in determining the structural motifs of aliphatic saturated cyclic hydrocarbons, in this work we have provided the first unambiguous spectroscopic evidence for the existence of sigma stacking interactions in cyclohexane dimers at low temperatures. Molecular beam experiments performed using effusive nozzle and supersonic jet sources on cyclohexane in an N-2 matrix generated cyclohexane dimers stabilized through sigma stacking and the dimers were characterized by infrared spectroscopy. The ab initio computations carried out on cyclohexane dimers identified eclipsed (face-to-face), parallel displaced and T-shaped structures, which are predominantly stabilized by sigma stacking interactions. While natural bond orbital analysis substantiated a significant amount of sigma -> sigma* interactions involved in the stabilization, the Atoms in Molecules analysis indicated that the stacking is induced by a plausible ‘dihydrogen bonding’ interaction. Energy decomposition analysis disclosed that a large measure of dispersion interactions effectively contributes for the overall stability of cyclohexane dimers.
First author: Prasad, S, Hop-Skip-Jump: Monovalent Metals on the Surface of the Phenalenyl Radical,
ORGANOMETALLICS, 39, 34, (2020)
Abstract: The phenalenyl radical (P) and its relatively stable cation and anion are of interest for applications in areas spanning magnetic materials and ligand development for reaction catalysis. We report on a broad investigation of the bonding, thermochemistry, and kinetics of PM complexes where M is a group 1 or 11 metal atom. The PM species that are considered in this work afford a simplified picture of the behavior of metal adatoms on hydrogen terminated graphene fragments, and, more crucially, we expand a still nascent understanding of the organometallic chemistry of P. The exceptional fluxionality of group 1 metals on the phenalenyl surface is predicted, the associated energy barriers are quantified, and the major role of relativistic effects in restricting the fluxionality of Au on the surface is demonstrated. Although relativistic effects swell the barriers to isomerization, we find that orbital size and energies, even in the absence of relativistic effects, dictate different path preferences for the motion of Au on the surface of the radical compared to Cu and Ag.
First author: Maria, L, CO2 conversion to phenyl isocyanates by uranium(vi) bis(imido) complexes,
CHEMICAL COMMUNICATIONS, 56, 431, (2020)
Abstract: Uranium(vi) trans-bis(imido) complexes [U(kappa(4)-{((2ArO)-Ar-tBu)(2)Me-2-cyclam})(NPh)(NPh (R))] react with CO2 to eliminate phenyl isocyanates and afford uranium(vi) trans-[O=U=NR](2+) complexes, including [U(kappa(4)-{((2ArO)-Ar-tBu)(2)Me-2-cyclam})(NPh)(O)] that was crystallographically characterized. DFT studies indicate that the reaction proceeds by endergonic formation of a cycloaddition intermediate; the secondary reaction to form a dioxo uranyl complex is both thermodynamically and kinetically hindered.
First author: Vermeeren, P, Understanding chemical reactivity using the activation strain model,
NATURE PROTOCOLS, 15, 649, (2020)
Abstract: This analysis of chemical reaction mechanisms is based on the activation strain model of reactivity. The PyFrag 2019 program is used to perform activation strain and energy decomposition analysis on each point along the energy profile.
First author: Kukulka, M, Substituent Effect on Conformational Preferences in Ground and Excited States of Selected Schiff Bases: An Insight from Theoretical Calculations,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 63, (2020)
Abstract: 2-Hydroxy aromatic Schiff bases that exhibit ESIPT (excited state intramolecular proton transfer) or TICT (twisted intramolecular charge transfer) photodeactivation pathways emerge as promising candidates for fluorescent sensors. In this computational work the influence of various substituents, differing in the electronic properties, on conformational preferences in the ground and S-1 excited state for a series of 2-hydroxy-1-naphthylmethylene-hydrazine-based ligands is systematically studied using (TD)DFT calculations. In order to shed light on physical factors which might determine the obtained conformational preferences, extensive bonding analyses are performed. The results highlight the crucial role of a substituent’s ability to form not only well-established intramolecular hydrogen bonds (e.g., O-H center dot center dot center dot N) but also unintuitive nonclassic weak interactions (e.g., C-H center dot center dot center dot O, C-H center dot center dot center dot N, and C-H center dot center dot center dot H-C) in the modulation of the equilibrium between naphthol-imine and keto-amine forms, and planar or twisted conformations, and, thus, in determination of photophysical properties of the considered bases.
First author: Ponzi, A, Photoionization of C-60: Effects of Correlation on Cross Sections and Angular Distributions of Valence Subshells,
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 108, (2020)
Abstract: Calculations of the photoionization cross section and asymmetry parameter, beta, are performed at the density functional theory (DFT) and time-dependent density functional theory (TDDFT) levels for all 32 valence levels of C-60. Accurate numerical results are obtained for the isolated molecule in icosahedral symmetry. A detailed analysis based on the comparison between the DFT and TDDFT results allows the identification of four types of resonances: the well-known confinement resonances of mainly geometrical origin, shape resonances native to the ionization channel, induced shape resonances, and autoionization resonances brought about by interchannel coupling, as well as their different prominence in cross section or asymmetry parameter. Generally, cross sections are enhanced at the TDDFT level, which includes contribution from the bound-state excitations from closed channels, neglected at the DFT level, and the effect persists even well above the highest ionization threshold. This effect is best seen in the total cross section, although not as dramatic as found from simpler models, probably due to the stiffer electronic structure inherent in the full molecular description. The effects of interchannel coupling on individual native resonances are rather less predictable, leading to both enhancement and decreases and often altering the details of the structure significantly. A comparison with the previous accurate total cross-sectional calculations, as well as with the available experimental data, is very good for cross sections but slightly inferior for beta’s. The results reported can serve as a reference to compare the effects of different environments on C-60, as well as chemical substitution, notably endohedral fullerenes.
First author: Ramanantoanina, H, Electronic Structure and Photoluminescence Properties of EU(eta(9)-C9H9)(2),
JOURNAL OF PHYSICAL CHEMISTRY A, 124, 152, (2020)
Abstract: The electronic structure of Eu2+ compounds results from a complex combination of strongly correlated electrons and relativistic effects as well as weak ligand-field interaction. There is tremendous interest in calculating the electronic structure as nowadays the Eu2+ ion is becoming more and more crucial, for instance, in lighting technologies. Recently, interest in semiempirical methods to qualitatively evaluate the electronic structure and to model the optical spectra has gained popularity, although the theoretical methods strongly rely upon empirical inputs, hindering their prediction capabilities. Besides, ab initio multireference models are computationally heavy and demand very elaborative theoretical background. Herein, application of the ligand-field density functional theory (LFDFT) method that is recently available in the Amsterdam Modeling Suite is shown: (i) to elucidate the electronic structure properties on the basis of the multiplet energy levels of Eu configurations 4f(7) and 4f(6)5d(1) and (ii) to model the optical spectra quite accurately if compared to the conventional time-dependent density functional theory tool. We present a theoretical study of the molecular Eu(eta(9)-C9H9)(2) complex and its underlying photoluminescence properties with respect to the Eu 4f-5d electron transitions. We model the excitation and emission spectra with good agreement with the experiments, opening up the possibility of modeling lanthanides in complex environment like nanomaterials by means of LFDFT at much-reduced computational resources and cost.
First author: Wen, J, Electronic States of 2,3-Diamino-1,4-naphthoquinone and Its N-Alkylated Derivatives,
JOURNAL OF PHYSICAL CHEMISTRY C, 124, 60, (2020)
Abstract: Diaminoquinones with a captodatively stabilized biradicaloid structure are candidates for singlet fission, but few such compounds are known. We report the solution spectroscopy and photophysics of 1,2,2,3-tetramethy1-2,3-dihydro-1H-naphtho[2,3-d]-imidazole-4,9-dione (1): its steady-state and transient UV-visible absorption, linear dichroism in stretched poly(vinyl alcohol), and magnetic circular dichroism. We also describe the absorption spectra of the stable radical ions 1(center dot+) and 1(center dot-) and of two parent structures, 2,3-diamino-1,4-naphthoquinone (2) and 2,3-bis(methylamino)-1,4-naphthoquinone (3). The spectra are interpreted and electronic transitions are assigned by comparison with the results of density functional theory and MS-CASPT2 calculations.
First author: Oudsen, JPH, Electronic characterization of redox (non)-innocent Fe2S2 reference systems: a multi K-edge X-ray spectroscopic study,
RSC ADVANCES, 10, 729, (2020)
Abstract: Di-iron dithiolate hydrogenase model complexes are promising systems for electrocatalytic production of dihydrogen and have therefore been spectroscopically and theoretically investigated in this study. The direct effect of ligand substitution on the redox activity of the complex is examined. In order to understand and eventually optimize such systems, we characterised both metal and ligand in detail, using element specific X-ray absorption Fe- and S-K edge XAS. The (electronic) structure of three different [Fe2S2] hydrogenase systems in their non-reduced state was investigated. The effect of one- and two-electron reduction on the (electronic) structure was subsequently investigated. The S K-edge XAS spectra proved to be sensitive to delocalization of the electron density into the aromatic ring. The earlier postulated charge and spin localization in these complexes could now be measured directly using XANES. Moreover, the electron density (from S K-edge XANES) could be directly correlated to the Fe-CO bond length (from Fe K-edge EXAFS), which are in turn both related to the reported catalytic activity of these complexes. The delocalization of the electron density into the conjugated pi-system of the aromatic moieties lowers the basicity of the diiron core and since protonation occurs at the diiron (as a rate determining step), lowering the basicity decreases the extent of protonation and consequently the catalytic activity.
First author: Bonde, NA, Importance of Axial Symmetry in Elucidating Lanthanide-Transition Metal Interactions,
INORGANIC CHEMISTRY, 59, 235, (2020)
Abstract: In this paper, we experimentally study and model the electron donating character of an axial diamagnetic Pd2+ ion in four metalloligated lanthanide complexes of formula [PPh4] [Ln-{Pd(SAc)(4)}(2)] (SAC(-) = thioacetate, Ln = Tb, Dy, Ho, and Er). A global model encompassing inelastic neutron scattering, torque magnetometry, and dc magnetometry allows to precisely determine the energy level structure of the complexes. Solid state nuclear magnetic resonance reveals a less donating character of Pd2+ compared to the previously reported isostructural Pt2+ based complexes. Consequently, all complexes invariably show a lower crystal field strength compared to their Pt2+-analogues. The dynamic properties show an enhanced single molecule magnet behavior due to the suppression of quantum tunneling, in agreement with our model.
First author: Heiss, P, Combined Experimental and Theoretical Study on Hampered Phosphine Dissociation in Heteroleptic Ni/Zn Complexes,
INORGANIC CHEMISTRY, 59, 514, (2020)
Abstract: Heterometallic Ni/Zn complexes can serve as molecular models for the semihydrogenation of acetylene catalyzed by heterogeneous Ni/Zn phases. Pursuing this target, we present the synthesis of the series [Ni(ZnCp*)(n)(ZnMe)(n)(PEt3)(4-n) (n = 1-3; 1, 2, 3) which is obtained via E/Zn exchange from [Ni(ECp*)(n)(PEt3)(4-n)](n = 1-3, E = Al, Ga; P1, P2, P3). The isolation of the intermediate compound [Ni(GaCp*)(ZnCp*) isolation of the intermediate compound [Ni(GaCp*)(ZnCp*)-ZnMe)(PEt3)(2)] (2a) supports the assumption of a stepwise Ga/Zn exchange in the formation of 3. The dissociation behavior of PEt3 in 2 and 3 was investigated experimentally using variable temperature VT) UV-vis spectroscopy indicating suppressed phosphine dissociation in both cases. For comparison, the absorption spectra of the saturated and unsaturated compounds were calculated using time dependent DFT calculations (TDDFT). Energy decomposition analysis with the natural orbital for chemical valence extension (EDA NOCV) calculations shows a bond strengthening of the Ni-P bond by successive substitution of the phosphines with (ZnR)(2) units. The influence of different phosphines (PMe3, PEt3, PPh3, P(OEt)(3)) on Ni-P bond length and on Zn-Zn interactions in [Ni(ZnR)(2n)(PR’)(4-n)] (R = Cp*, Me; R’ = Me, Et, Ph, OEt) was also studied by DFT calculations. A correlation of increasing sterical demand of the phosphine ligand and a shortening of the Zn-Zn distances is observed.
First author: Aramburu, JA, Ground State and Optical Excitations in Compounds with Tetragonal CuF64- Units: Insight into KAlCuF6 and CuFAsF6,
INORGANIC CHEMISTRY, 59, 539, (2020)
Abstract: It has been argued that AAlCuF(6) (A = K, Cs) and CuFAsF6 are the only known crystals that exhibit compressed CuF64- units due to the Jahn-Teller effect. However, no grounds for this singular behavior have yet been reported. By means of first-principles calculations on such compounds and the isomorphous compounds involving Zn2+ ions instead of Cu2+, we prove that neither the ground state nor the equilibrium geometry of CuF64- complexes in KAlCuF6 and CuFAsF6 is the result of a Jahn-Teller effect. In contrast, it is shown that the internal electric field, E-R(r), created by the rest of the lattice ions upon the localized electrons in the complex, plays an important role in understanding this matter as well as the d-d transitions of these two compounds. The energy of an optical transition is shown to involve two contributions: the intrinsic contribution derived for the isolated CuF64- unit at equilibrium and the extrinsic contribution coming from the E-R(r) field. Aside from reproduction of the experimental d-d transitions observed for KAlCuF6, it is found that in CuFAsF6 the b(1g) (x(2) – y(2)) -> a(1g) (3z(2) – r(2)) transition is not the lowest one due to the stronger effects from the internal field. Interestingly, the intrinsic contribution corresponding to that transition can simply be written as beta(R-eq – R-ax) where R-eq and R-ax are the equatorial and axial Cu2+-F- distances and beta = 2.7 eV/angstrom is the same for all systems involving tetragonal CuF64- units and an average metal-ligand distance close to 2.03 angstrom. This shows the existence of a common point shared by the Jahn-Teller system KZnF3:Cu2+ and other non-Jahn-Teller systems such as KAlCuF6, CuFAsF6, K2ZnE4:Cu2+, and Ba2ZnF6:Cu2+. Although most Jahn-Teller systems display an elongated geometry, there are however many Cu’ compounds with a compressed geometry but hidden by an additional orthorhombic instability. The lack of that instability in KAlCuF6 and CuFAsF6 is also discussed.
First author: Kaiukov, R, Cs3Cu4In2Cl13 Nanocrystals: A Perovskite-Related Structure with Inorganic Clusters at A Sites,
INORGANIC CHEMISTRY, 59, 548, (2020)
Abstract: An effort to synthesize the Cu(I) variant of a lead-free double perovskite isostructural with Cs2AgInCl6 resulted in the formation of Cs3Cu4In2Cl13 nanocrystals with an unusual structure, as revealed by single-nanocrystal three-dimensional electron diffraction. These nanocrystals adopt a A(2)BX(6) structure (K2PtCl6 type, termed vacancy ordered perovskite) with tetrahedrally coordinated Cu(I) ions. In the structure, 25% of the A sites are occupied by [Cu4Cl](3+) clusters (75% by Cs+), and the B sites are occupied by In3+. Such a Cs3Cu4In2Cl13 compound prepared at the nanoscale is not known in the bulk and is an example of a multinary metal halide with inorganic cluster cations residing in A sites. The stability of the compound was supported by density functional theory calculations that also revealed that its bandgap is direct but parity forbidden. The existence of the Cs3Cu4In2Cl13 structure demonstrates that small inorganic cluster cations can occupy A sites in multinary metal halides.
First author: Hussain, M, TD-DFT insights into the sensing potential of the luminescent covalent organic framework for indoor pollutant formaldehyde,
SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY, 224, 548, (2020)
Abstract: This paper investigates the sensitivity of the luminescent thieno[2,3-b]thiophene-based covalent organic framework (TT-COF) towards the formaldehyde using the density functional theory and time-dependent method. The hydrogen bonding dynamics is explored by comparison of geometries, electronic transition energies, binding energies, UV-vis, and infrared spectra. Frontier molecular orbitals examination, natural population analysis, and plotted electron density difference map describe the quenching process explicitly via electron density distribution. The MOMAP program illuminates the quenching owing to TT-COF-HCHO complex radiative rate constant. Furthermore, the S1-T1 energy gap describes the facilitation of the luminescence quenching through the intersystem crossing. Above all results elaborate the TT-COF’s potential to detect the formaldehyde.
First author: Keskic, T, Synthesis, X-ray structure and DFT calculation of magnetic properties of binuclear Ni(II) complex with tridentate hydrazone-based ligand,
JOURNAL OF THE SERBIAN CHEMICAL SOCIETY, 85, 1279, (2020)
Abstract: Binuclear double end-on azido bridged Ni(II) complex (1) with composition [Ni2L2(mu-(1,1)-N-3)(2)(N-3)(2)]center dot 6H(2)O, (L = (E)-N,N,N-trimethyl-2-oxo-2-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)ethan-1-amin) was synthesized and characterized by single-crystal X-ray diffraction method. Ni(II) ions are hexacoordinated with the tridentate heteroaromatic hydrazone-based ligand and three azido ligands (one terminal and two are end-on bridges). DFT calculations revealed that coupling between two Ni(II) centers is ferromagnetic in agreement with binuclear Ni(II) complexes with similar structures.
First author: Toman, P, Charge Transport in pi-Conjugated Polymer Semiconductors,
CHEMICKE LISTY, 114, 729, (2020)
Abstract: The charge carrier transport in linear conjugated polymer semiconductors, used in printed organic electronics for construction of solar cells, light emitting diodes, transistors, sensors and other devices, significantly differs from the charge transport in inorganic materials. This article shows a possible theoretical approach to the modelling of the charge transport, which considers different nature of interactions present within the polymer chain and between chains in the amorphous and crystalline phases. The onchain charge carrier states and distributions of molecular parameters influencing the transport are solved by means of the quantum chemical methods. Semi-classical description of the interchain charge hopping includes the charge carrier thermalization, complying with Pauli’s exclusion principle. Numerical calculations, performed for poly(3-hexylthiophene-2,5-diyl), show that, depending on the value of the energetic and structural disorder, the charge mobility significantly increases with the charge concentration, which may be explained by trap filling. After the traps are completely filled, the effect of the disorder disappears and the mobility decreases due to the lower density of unoccupied states available for the hopping transport. This phenomenon is related to the experimentally observed mobility degradation in organic field-effect transistors at high gate voltage.
First author: Cox, CS, Mixed Ramp-Gaussian Basis Sets for Core-Dependent Properties: STO-RG and STO-R2G for Li-Ne,
AUSTRALIAN JOURNAL OF CHEMISTRY, 73, 911, (2020)
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First author: Pino-Rios, R, B12N12 cluster as a collector of noble gases: A quantum chemical study,
PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 115, 911, (2020)
Abstract: Systematic analysis of the noble gas (Ng = He – Rn) trapping capacity of the B12N12 cluster were performed at the PBE0-D3/def2-TZVP level by means of thermochemical data, topological analysis of the electron density (QTAIM), non-covalent interactions index (NCI), and energy decomposition analysis (EDA). The results indicate that the Ng(n)B(12)N(12) (n = 1, 12) cluster can be obtained below room temperature. Additionally, it was found that this cluster can trap up to 12 noble gas atoms without losing stability, Finally, the effect of an applied electric field has been analysed, showing that the interaction energy can be improved through this strategy.
First author: Kravtsova, AN, Synchrotron-Based X-Ray Absorption Spectroscopy for the Study of Geological Materials,
JOURNAL OF SURFACE INVESTIGATION, 14, 135, (2020)
Abstract: X-ray absorption spectroscopy (XAS) is a new highly effective nondestructive technique for diagnostics of the local atomic and electronic structure of materials, including those that do not have long-range order in their atomic arrangement. In particular, X-ray absorption near edge structure (XANES) spectroscopy makes it possible to identify materials, to assess the oxidation states of atoms, and to find the parameters of the full 3D local structure around absorbing atoms with a high degree of accuracy, up to 1 pm for bond lengths and several degrees for bond angles. This review describes the current state and capabilities of XAS spectroscopy and, in particular, XANES in studying terrestrial and extraterrestrial natural materials. Modern synchrotron centers allow the acquisition of XAS spectra of materials with high energy and time resolutions, with microfocusing and nanofocusing, and spectral measurements under real conditions (for example, directly under high pressures and temperatures). These broad possibilities make X-ray absorption spectroscopy a unique highly effective technique for the diagnostics of geological materials.
First author: Backler, F, Switching On/Off the Intramolecular Hydrogen Bonding of 2-Methoxyphenol Conformers: An NMR Study,
AUSTRALIAN JOURNAL OF CHEMISTRY, 73, 222, (2020)
Abstract: Intramolecular hydrogen bonding of 2-methoxyphenol (2-MP, guaiacol) is studied using NMR spectroscopy combined with quantum mechanical density functional theory (DFT) calculations. The hydrogen bonding of OHO and HOH is switched on in the conformers of anti-syn (AS, 99.64% dominance) and anti-gauche (AG), respectively, with respect to the anti-anti (AA) conformer (without either such hydrogen bonding interactions). It confirms that the 13 C and 1 H NMR chemical shift of AS dominates the measured NMR spectra, as the AS conformer reproduces the measurements in CDCl3 solvent (RMSD of 1.86 ppm for 13 CNMRand of 0.27 ppm for 1 H NMR). The chemical shift of hydroxylH(1) at 5.66 pm is identified as the fingerprint of theOH(1)OCH3 hydrogen bonding in AS, as it exhibits a significant deshielding fromH(1) ofAA(4.24 ppm) andH(1) ofAG (4.38 ppm) without suchOH(1)OCH3 hydrogen bonding. TheAGconformer (C1 point group symmetry) possesses a less strong hydrogen bonding of HOHCH2O, with the methoxyl group out of the aromatic phenol plane. The substituent effect of AG due to the resonance interaction of methoxyl being out of plane in a concentrated solution shifts the ortho-and para-aromatic carbons, C(3)/C(5), of the AG to,125.05/125.44 ppm from the corresponding carbons in AS at 108.81/121.60 ppm. The hydrogen bonding exhibits inwards reduction of IR frequency regions of AS and AG from AA. Finally, energy decomposition analysis (EDA) indicates that there is a steric energy of 45.01 kcal mol1 between the AS and AG when different intramolecular hydrogen bonding is switched on.
First author: Spiegelman, F, Density-functional tight-binding: basic concepts and applications to molecules and clusters,
ADVANCES IN PHYSICS-X, 5, 222, (2020)
Abstract: The scope of this article is to present an overview of the Density Functional based Tight Binding (DFTB) method and its applications. The paper introduces the basics of DFTB and its standard formulation up to second order. It also addresses methodological developments such as third order expansion, inclusion of non-covalent interactions, schemes to solve the self-interaction error, implementation of long-range short-range separation, treatment of excited states via the time-dependent DFTB scheme, inclusion of DFTB in hybrid high-level/low level schemes (DFT/DFTB or DFTB/MM), fragment decomposition of large systems, large scale potential energy landscape exploration with molecular dynamics in ground or excited states, non-adiabatic dynamics. A number of applications are reviewed, focusing on -(i)- the variety of systems that have been studied such as small molecules, large molecules and biomolecules, bare or functionalized clusters, supported or embedded systems, and -(ii)- properties and processes, such as vibrational spectroscopy, collisions, fragmentation, thermodynamics or non-adiabatic dynamics. Finally outlines and perspectives are given.
First author: Toader, AM, The Structural Details of Aspirin Molecules and Crystals,
CURRENT MEDICINAL CHEMISTRY, 27, 99, (2020)
Abstract: We revisit, in the key of structural chemistry, one of the most known and important drugs: the aspirin. Although apparently simple, the factors detennining the molecular structure and supramolecular association in crystals are not trivial. We addressed the problem from experimental and theoretical sides, considering issues from X-ray measurements and results of first-principle reconstruction of molecule and lattices by ab initio calculations. Some puzzling problems can give headaches to specialists and intrigue the general public. Thus, the reported polymorphism of aspirin is disputed, a so-called form II being alleged as a result of misinterpretation. At the same time, were presented evidences that the structure of common form I can he disrupted by domains where the regular packing is changed to the pattern of form IL The problems appear even at the level of independent molecule: the most stable conformation computed by various techniques of electronic structure differs from those encountered in crystals. Because the energy difference between the related conformational isomers (computed as most stable vs. the experimental structure) is small, about 1 kcal/moll, comprised in the error bars of used methods, the unrest Mg question is whether the modelling is imprecise, or the supramolecular factors are Imitating the conformational preferences. By a detective following of the issue, the intermolecular effects were made responsible for the conformation of the molecule in crystal. The presented problems were gathered from literature results, debates, glued with modelling and analysis redone by ourselves. in order to secure the unitary view of the considered prototypic topic.
First author: Lu, L, Pnictogen, chalcogen, and halogen bonds in catalytic systems: theoretical study and detailed comparison,
JOURNAL OF MOLECULAR MODELING, 26, 99, (2020)
Abstract: Although halogen bond (XB), a typical sigma-hole noncovalent interaction, has been widely exploited in organocatalysis within the last two decades, only very recently has its sister sigma-hole interactions, such as chalcogen bond (ChB) and pnictogen bond (PnB), begun to be explored for potential applications in catalysis. Herein, a detailed comparison investigation of PnB, ChB, and XB interactions in catalytic systems was performed from a theoretical point of view. Owing to the excellent properties of the pentafluorophenyl moiety (C6F5) in catalysis, the complexes of (C6F5)(3)Pn, (C6F5)(2)Ch, and C6F5X with chloride ion were firstly studied. Then, we successively substituted C6F5 by phenyl groups, to examine the influence of substituents on the characteristics of such interactions. In addition, several halogen-bonded complexes between the donor 1,3,5-trifluoro-2,4,6-triiodobenzene (C6F3I3) and heavier Pn and Ch species as acceptors were also investigated. Our calculations showed that the interactions become gradually stronger upon going from row 3 to 5 and from main group VII to V, which correlates well with the experimental observations. As the strength of the interactions enhances, the contribution of electrostatics to the attraction increases, while the orbital term contribution becomes smaller. Particularly, the significant differences between the three types of sigma-hole interactions found in catalysis and anion transport were clarified.
First author: Amati, M, The Electron Affinity as the Highest Occupied Anion Orbital Energy with a Sufficiently Accurate Approximation of the Exact Kohn-Sham Potential,
JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 16, 443, (2020)
Abstract: Negative ions are not accurately represented in density functional approximations (DFAs) such as (semi)local density functionals (LDA or GGA or meta-GGA). This is caused by the much too high orbital energies (not negative enough) with these DFAs compared to the exact Kohn-Sham values. Negative ions very often have positive DFA HOMO energies, hence they are unstable. These problems do not occur with the exact Kohn-Sham potential, the anion HOMO energy then being equal to minus the electron affinity. It is therefore desirable to develop sufficiently accurate approximations to the exact Kohn-Sham potential. There are further beneficial effects on the orbital shapes and the density of using a good approximation to the exact KS potential. Notably the unoccupied orbitals are not unduly diffuse, as they are in the Hartree-Fock model, with hybrid functionals, and even with (semi)local density functional approximations (LDFAs). We show that the recently developed B-GLLB-VWN approximation [Gritsenko et al. J. Chem. Phys. 2016, 144, 204114] to the exact KS potential affords stable negative ions with HOMO orbital energy close to minus the electron affinity.
First author: Thomas, KE, Gold dipyrrin-bisphenolates: a combined experimental and DFT study of metal-ligand interactions,
RSC ADVANCES, 10, 533, (2020)
Abstract: Given that noninnocent and metalloradical-type electronic structures are ubiquitous among dipyrrin-bisphenolate (DPP) complexes, we synthesized the gold(iii) derivatives as potentially innocent paradigms against which the properties of other metallo-DPP derivatives can be evaluated. Electronic absorption spectra, electrochemical studies, a single-crystal X-ray structure, and DFT calculations all suggest that the ground states of the new complexes indeed correspond to an innocent Au-III-DPP3-, paralleling a similar description noted for Au corroles. Interestingly, while DFT calculations indicate purely ligand-centered oxidations, reduction of AuDPP is predicted to occur across both the metal and the ligand.
First author: Pal, R, Ligand stabilized transient “MNC” and its influence on MNC -> MCN isomerization process: a computational study (M = Cu, Ag, and Au),
THEORETICAL CHEMISTRY ACCOUNTS, 139, 533, (2020)
Abstract: A theoretical investigation of the binding ability of different ligands [L = CO, H2O, H2S, N-2, NH3, 1,3-dimethylimidazole (DMI), C2H2 and C2H4] with metal isocyanide and cyanide (MNC and MCN; M = Cu, Ag, Au) compounds has been carried out using quantum chemical computations. In order to analyze the thermochemical stability of these complexes, we have calculated the changes in the related dissociation energies and free energies by considering different possible dissociation pathways (four two-body and one three-body) such as (a) LMCN(/NC) = L + MCN(/NC); (b) LMCN = LM + CN; (c) LMCN = L + M + CN; (d) LMCN = LM+ + CN-; and (e) LMCN = L- + MCN+. The possible dissociation processes are endothermic in nature at room temperature suggesting non-spontaneity at 298 K. Our inspection suggests that MNC have higher binding ability than the MCN compounds in all of the L-bonding cases and both of them follow similar trends as Au > Cu > Ag. The natural bond orbital analysis, topological analysis of the electron density from atoms in molecules technique, and energy decomposition analysis have been carried out to characterize the nature of interaction between L and MCN which shows that the L-M bonds acquire some degree of covalent character. Furthermore, in order to check the validity of the conceptual DFT-based electronic structure principles like maximum hardness and minimum electrophilicity principles, the change in the relevant global reactivity descriptors like chemical hardness (eta), chemical potential (mu), and electrophilicity index (omega) is also studied along the isomerization path, LMNC -> LMCN.
First author: Lamine, W, Relaxation of Kohn-Sham orbitals of organometallic complexes during the approach of a nucleophilic reactant (or an electron approach): the case of [sal(ph)en](2) Zn complexes,
THEORETICAL CHEMISTRY ACCOUNTS, 139, 533, (2020)
Abstract: In a recent paper, the Lewis acidic character of a series of Zn-Sal(ph)en complexes was reviewed, using conceptual density functional theory descriptors to assess the acidic character. It was shown that the nature of the bridging diamine link in the Schiff base ligand controls this character that is mainly responsible for the coordination of the Zn2+, hence for the geometry of these complexes. However, the usual dual descriptor did exhibit significant weaknesses to retrieve the electrophilic part on the metal cation of the Zn-sal(ph)en complexes. Indeed, it is necessary to include the densities of the electronic excited states through the so-called state-specific dual descriptor. This procedure will allow us to recover successfully the appropriate reactivity of the studied complexes holding diamine bridges differing by flexible to semi-rigid and to rigid ranges. Nevertheless, the selection of the excited state allowing a meaningful description of the Lewis acidic is not a priori obtained from a direct identification of the Kohn-Sham (KS) orbitals involved in the excitation. The present work reports an analysis of the relaxation of the KS orbitals when a fraction of charge is added to a virtual orbital, and when an excitation is considered, while a fractional charge is transferred from an occupied orbital toward a virtual orbital.
First author: Miao, SS, DFT study of non-covalent interaction mechanisms of solvents with GO surfaces and the solvent-mediated GO interaction,
APPLIED SURFACE SCIENCE, 499, 533, (2020)
Abstract: Understanding the non-covalent interaction between solvent and graphene oxide (GO) is of significance to the application of GOs. Herein, the adsorption interactions of several typical solvents with GO surfaces were studied by density functional theory, in which non(less)-polar, protic polar, and aprotic polar solvents were included. The interaction energies, geometrical characteristics, and bonding natures have been characterized. The atomsin-molecule theory and the natural orbitals for chemical valence analysis reveal that miscellaneous non-covalent interaction mechanisms appear between solvent molecules and GO surfaces, covering a change from vdW (pi-pi) interaction for non(less)-polar solvents to moderate and strong hydrogen bonding interactions for polar solvents. There exists an approximately linear correlation between the interaction energies and the interfacial electron density topological parameters. The orbital interaction mechanisms and charge transfer performances have also been disclosed. We further attempt to establish a correlation between the GO-GO interaction free energies in solvents and the solvent-GO interactions, which illustrates that increasing the solvent-GO interaction can weaken the aggregative degree of GOs in the solvent media. Our simulation results not only are valuable to the solventphase processing of GOs, but also provide new binding mechanisms on GO surfaces, which lays a foundation on the functional modification of GO nanomaterials.
First author: Tabrizi, L, Theoretical and experimental study of gold(III), palladium(II), and platinum (II) complexes with 3-((4-nitrophenyl)thio)phenylcyanamide and 2,2 ‘-bipyridine ligands: Cytotoxic activity and interaction with 9-methylguanine,
INORGANICA CHIMICA ACTA, 499, 533, (2020)
Abstract: The new gold(III), palladium(II), and platinum(II) complexes with 3-((4-nitrophenyl)thio)phenylcyanamide (HL) and 2,2′-bipyridine (bpy) ligands of formula [M(bpy)LCl] (M = Pd(II),1, Pt(II), 2) or [Au(bpy)LCl]Cl, 3, have been synthesized and fully characterized. The cytotoxicity of free ligands and complexes 1-3 were evaluated against HT-29 (colorectal adenocarcinoma), MCF-7 (breast), and HeLa (human squamous cervical adenocarcinoma) cancer cell lines along with MRC-5 non-tumorigenic cells (human lung fibroblasts) and their activity has been compared to the familiar platinum-based anticancer agent cisplatin. The free ligands bpy and HL were ineffective against the cancer cell lines. However, the complexes 1-3 showed a significant in vitro antitumor activity with IC50 values in the low micromolar. The complexes 1-3 were revealed to produce cellular reactive oxygen species (ROS). The most potent ROS producer, complex 3, also elicited the highest cytotoxicity. The interaction of 9-methylguanine (9-MeG-N7) with complexes 1-3 was studied by H-1 NMR and mass spectroscopy. Furthermore, DFT calculations have been performed on complexes 1-3 and also [M(bpy)(L)(9-MeG-N7)](NO3) (M = Pd(II), 4, Pt(II), 5) or [Au(bpy)(L)(9-MeG-N7)](NO3)(2), 6, using the BP86-D and B3LYP* functionals to provide a complete rationalization of their structures and to describe their electronic structures. The energy decomposition analysis (EDA) gave a clear understanding of the bonding for all complexes 1-6 showing that the interactions are mostly governed by electrostatic ones. Strong interactions occurred between the chlorine anion and the metallic fragment, but weakened between 9-methylguanine and the metallic fragment, in agreement with the electron transfers and the interaction energies.
First author: Villagomez, CJ, A first-principles DFT dispersion-corrected C-60/Au(111) Raman study,
COMPUTATIONAL MATERIALS SCIENCE, 171, 533, (2020)
Abstract: We present an extensive density functional theory (DFT) study on the interaction of C-60 molecules with Au(111), involving both periodic metal surfaces and clusters. The aim of this work is 2-fold: First, to quantify the adsorption energies per molecule (E-ads) of the C-60/Au(111) system from periodic calculations using a dispersion-corrected functional (DFT-D3). Secondly, to determine the effect of the metal substrate on the adsorbed C-60 molecule via calculated non-resonant Raman vibrational frequencies. Using a commensurate (2 root 3×2 root 3) R30 degrees phase – as proposed by experimental work as a stable C-60/Au(111) monolayer – our DFT-D3 periodic calculations show a slight C-60 molecule preference to adsorb on its hexagonal facet, with a calculated adsorption energy value of 2.40 eV. Our DFT-D3 calculations further reveal an energetic gain when the C-60 molecule is adsorbed on an HCP surface (2.40 eV) site compared to an FCC one (2.31 eV). Using a variety of finite-size, slab-type Au clusters (e.g.Au-24, Au-32 and Au-50), our DFT-D3 calculated Raman intensity profile shows a strong interaction between the C-60 fullerene molecule and the gold substrate. This influences new vibrational modes over a wide range of frequencies, compared to those active modes for the isolated C-60 gas-phase single molecule, and an overall shift of frequencies and symmetries. The DFT-D3 calculated Raman spectra of the C-60 molecule supported on Au clusters are in good agreement when confronted to those recently obtained experimentally under ultra-high vacuum (UHV) conditions using tip-enhanced Raman spectroscopy (TERS).
First author: Pietrzyk, P, Redox states of nickel in zeolites and molecular account into binding of N-2 to nickel(I) centers – IR, EPR and DFT study,
MICROPOROUS AND MESOPOROUS MATERIALS, 291, 533, (2020)
Abstract: Redox chemistry of nickel centers in high-silica ZSM-5 and BEA zeolites was investigated by a combined use of temperature-programmed reduction (TPR), electron paramagnetic resonance (EPR), and infrared (FTIR) spectroscopic techniques supported by quantum chemistry methods. The isolated nickel and nickel-oxo centers were identified and quantified by means of EPR using CO and NO probes and by IR using CO as a probe molecule. The nickel-oxo species gave rise to the nickel(I) centers upon reduction in CO. Their interaction with N-2 under low temperature led to the formation of nickel(I)-dinitrogen adducts. Attribution of the IR bands and identification of the structures of dinitrogen adducts were based on the coadsorption experiments of N-14(2) and N-15(2) isotopes and complementary density functional theory (DFT) calculations. Because of the presence of a mixed ligand ((N2N2)-N-14-N-15) adduct, a structural dichotomy of possible formation of the geminal Ni(I)-(N-2)(2) and two coupled vicinal mono-adducts N-2-Ni(I)center dot center dot center dot Ni(I)-N-2 was resolved. The isolated Ni(I)-N-2 and geminal Ni(I)-(N-2)(2) adducts were identified with confidence. A mechanism of N-2 bonding was accounted for by natural orbitals for chemical valence (NOCV) population analysis. Charge flow molecular channels due to the a donation and pi back-donation effects were established in a quantitative way. This allowed for unraveling the molecular background of the observed bathochromic shift of the stretching vibrations of all dinitrogen adducts.