2019 publications citing ADF

First author: Wen, M, OBCN isomerization and noble gas insertion compounds of identical valence electron number species: stability and bonding, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 26311, (2019)
Abstract: A series of new noble gas (Ng) insertion compounds of the general type XNgX, XNgY and XNgY(+) has been theoretically studied using ab initio and DFT methods herein. We first studied the isomerization process of the OBCN compound, and then investigated the bonding properties and stability of the compounds formed by inserting Ng into the single bond of the three low energy isomers by high-level ab initio calculations. The OBNgCN compounds are thermochemically stable with respect to all dissociation channels except for the processes of releasing OBCN/OBNC and free Ng. Furthermore, the two dissociation processes OBNgCN -> Ng + OBNC and OBNgNC -> Ng + OBCN are kinetically prohibited by the relatively high free energy barrier ranging from 22.7 to 31.7 kcal mol(-1) except for the OBKrCN and OBKrNC analogues. And the adaptive natural density partitioning (AdNDP) analysis indicated that chemical bonding in OBNgCN compounds is realized via a delocalized 3-center 2-electron (3c-2e) sigma-bond in the B-Ng-C moiety and a totally delocalized 5-center 2-electron (5c-2e) sigma-bond in the whole O-B-Ng-C-N. Natural bond orbital (NBO) theory, atoms-in-molecules (AIM) and energy decomposition analysis (EDA) based on the molecular wavefunction revealed that the B-Ng bond and Ng-C bond have some covalent character in OBNgCN. In addition, the calculation and detailed bonding analysis on a large number of neutral and monocationic compounds with identical valence electron numbers to OBNgCN demonstrate that the two bonds directly linked to the Ng atoms have covalent properties in neutral compounds, whereas Ng forms one typical covalent bond and one partial covalent and partial ionic bond with the neighboring atoms in the monocationic compounds.

First author: Darrnanovic, D, Combined Experimental and Theoretical Investigation of the Origin of Magnetic Anisotropy in Pentagonal Bipyramidal Isothiocyanato Co(II), Ni(II), and Fe(III) Complexes with Quaternary-Ammonium-Functionalized 2,6-Diacetylpyridine Bisacylhydrazone, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 31142, (2019)
Abstract: Magnetic anisotropy in pentagonal bipyramidal complexes of Co(II) (1 and 2), Fe(III) (3 and 4), and Ni(II) (5) with a 2,2′-[2,6-pyridinediylbis(ethylidyne-1-hydrazinyl-2-ylidene)]bis[N,N,N-trimethyl-2-oxoethanaminium] equatorial ligand and isothiocyanato axial ligands has been investigated by magnetic susceptibility measurements, powder X-band electron paramagnetic resonance (EPR) spectroscopy, Mossbauer spectroscopy, ab initio, and ligand-field density functional theory (LFDFT) calculations. The studied complexes display three distinct types of magnetic anisotropy. Co(II) complexes (1 and 2) show an easy plane anisotropy with large and positive D values and negligible rhombicity. The Ni(II) complex (5) has uniaxial magnetic anisotropy with a negative D value. Fe(III) complexes (3 and 4) have small zero-field splitting (ZFS) parameters. Theoretical modeling is used to rationalize the magnetic anisotropy in these systems and to identify the most important excited states that are responsible for the zero-field splitting. These excitations are a consequence of the electronic structure of the central metal ion in ideal pentagonal bipyramidal coordination.

First author: Kim, J, Control of anisotropy of a redox-active molecule-based film leads to non-volatile resistive switching memory, CHEMICAL SCIENCE, 10, 10888, (2019)
Abstract: Control of the pi-pi interaction direction in a redox-active pi-molecule based film led to the formation of new mechanistic nonvolatile resistive switching memory: a redox-active organic molecule, 2,5,8-tri(4-pyridyl)1,3-diazaphenalene, showed non-volatile bistable resistance states with a high on-off ratio, retention, and endurance only when the molecular orientation was anisotropic. Control experiments using redox-active/redox-inert organic molecules with isotropic/anisotropic molecular orientations implied that the formation of conductive oxidized pi-pi stacking layers from non-conductive neutral pi-pi stacking layers is responsible for resistive switching phenomena, indicating new mechanisms such as ReRAM. Our findings will give a comprehensive understanding of electron transport in organic solid materials based on the effects of redox-activity and molecular arrangement, leading to fabrication of a new class of ReRAM based on organic molecules.

First author: Ricci, M, MOLC. A reversible coarse grained approach using anisotropic beads for the modelling of organic functional materials, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 26195, (2019)
Abstract: We describe the development and implementation of a coarse grained (CG) modelling approach where complex organic molecules, and particularly the pi-conjugated ones often employed in organic electronics, are modelled in terms of connected sets of attractive-repulsive biaxial Gay-Berne ellipsoidal beads. The CG model is aimed at reproducing realistically large scale morphologies (e.g. up to 100 nm thick films) for the materials involved, while being able to generate, with a back-mapping procedure, atomistic coordinates suitable, with limited effort, to be applied for charge transport calculations. Detailed methodology and an application to the common hole transporter material alpha-NPD are provided.

First author: Mallick, S, Mediation of Electron Transfer by Quadrupolar Interactions: The Constitutional, Electronic, and Energetic Complementarities in Supramolecular Chemistry, ISCIENCE, 22, 269, (2019)
Abstract: Studies of intermolecular interactions enhance our knowledge of chemistry across molecular and supramolecular levels. Here, we show that host-guest quadrupolar interaction has a profound influence on the molecular system. With covalently bonded dimolybdenum complex units as the electron donor (D) and acceptor (A) and a thienylene group (C4H2S) as the bridge (B), the mixed-valence D-B-A complexes are shaped with clefts in themiddle of the molecule. Interestingly, in aromatic solvents, the D-A electronic coupling constants (H-ab) and electron transfer rates (k(et)) are dramatically reduced. Theoretical computations indicate that an aromatic molecule is encapsulated in the cleft of the D-B-A array; quadrupole-quadrupole interaction between the guest molecule and the C4H2S bridge evokes a charge redistribution, which increases the HOMO-LUMO energy gap, intervening in the throughbond electron transfer. These results demonstrate that a supramolecular system is unified underlying the characteristics of the assembled molecules through constitutional, electronic, and energetic complementarities.

First author: Koenis, MAJ, Analytical chemistry on many-center chiral compounds based on vibrational circular dichroism: Absolute configuration assignments and determination of contaminant levels, ANALYTICA CHIMICA ACTA, 1090, 100, (2019)
Abstract: The absolute configuration of a chiral molecule is key to its biological activity. Being able to find out what this configuration is, is thus crucial for a wide range of applications. The difficulties associated with such a determination steeply rise as the number of chiral centers in a given compound becomes larger. Concurrently, it becomes increasingly more challenging to determine the levels and identity of potential stereochemical contaminants in a given sample with one and the same technique, leading in practice to extensive and laborious efforts employing multiple analytical techniques. Here, experimental and theoretical studies based on Vibrational Circular Dichroism (VCD) are presented for dydrogesterone, a synthetic drug employed in reproductive medicine that is a prototypical example of such a multi-center chiral compound. We show that our approach allows us to distinguish and assign its absolute configuration without prior knowledge to one of the 64 possible stereoisomers associated with the six chiral centers. Studies on mixtures of dydrogesterone and 6-dehydroprogesterone, one of the diastereomers of dydrogesterone and generally the dominant impurity of dehydrogesterone, show that we can identify the presence of both compounds from one single VCD spectrum. Moreover, we find that we can determine diastereomeric contamination levels as low as 5% from the experimental VCD spectra.

First author: Brela, MZ, Comparison of the Hydrogen Bond Interaction Dynamics in the Guanine and Cytosine Crystals: Ab Initio Molecular Dynamics and Spectroscopic Study, JOURNAL OF PHYSICAL CHEMISTRY A, 123, 10757, (2019)
Abstract: In this work, we present the comparison study of guanine and cytosine crystals based on the hydrogen bond (HB) dynamics. The ab initio molecular dynamics gave us a base for detailed analysis. The analysis of the trajectories by power spectrum generation, as well as the fluctuation of the interaction energies, showed large differences between HB networks in the considered crystals. The charge flow is present in the guanine molecule which forms the flat surfaces in the crystals. In the cytosine zigzag structure, the charge flow is blocked. The interaction energy is significantly less stabilizing in the cytosine structure than in the guanine. Finally, the possible influence of charge transfer on the melting temperature has been discussed.

First author: Olejniczak, M, A Topological Data Analysis perspective on noncovalent interactions in relativistic calculations, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 120, 10757, (2020)
Abstract: Topological Data Analysis (TDA) is a powerful mathematical theory, largely unexplored in theoretical chemistry. In this work we demonstrate how TDA provides new insights into topological features of electron densities and reduced density gradients, by investigating the effects of relativity on the bonding of the Au-4-S-C6H4-S ‘-Au ‘(4) molecule. Whereas recent analyses of this species carried out with the Quantum Theory of Atoms-In-Molecules (a previous study) concluded, from the emergence of new topological features in the electron density, that relativistic effects yielded noncovalent interactions between gold and hydrogen atoms, we show from their low persistence values (which decrease with increased basis set size) these features are not significant. Further analysis of the reduced density gradient confirms no relativity-induced noncovalent interactions in Au-4-S-C6H4-S ‘-Au ‘(4). We argue TDA should be integrated into electronic structure analysis methods, and be considered as a basis for the development of new topology-based approaches.

First author: Mecheri, S, Bonding and electronic structures in dinuclear (X)[(Ind)M2L2] complexes (M = Ni, Pd, L = CO, PEt3, X = Cl, Allyl, Ind = indenyl, Cp = cyclopentadienyl): analogy between four-electron donor ligands, THEORETICAL CHEMISTRY ACCOUNTS, 139, 10757, (2019)
Abstract: The calculations of bimetallic complexes of the type (X)[(Ind)M-2(L)(2)] (M = Ni, Pd, L = CO, (PEt3) and X = Allyl, Cp and indenyl) have been done using two DFT functionals, namely BP86 and B3LYP*. The allyl, Cp and indenyl ligands adopt the same eta(3)-coordination mode with a pi bond and can be considered to be isolobal, while the chloride acts as sigma- and pi-donor. The computed structural and energetic parameters and energy decomposition yield chemically useful information. We report that the metal-metal bond distances are slightly sensitive to the electron donation and electron pi-backdonation as the isolobal prediction suggests. Changing the metal from Ni to Pd has the result of increasing the metal-metal bond distance, decreasing the natural population of Pd and the weakness interactions between the X- ligand and the [(Ind)M-2(L)(2)](+) fragment. The results showed that the four ligands behave quite similarly in terms of bonding, coordination mode and donation and pi-backdonation properties highlighted by the orbitals’ populations and the energy decomposition. However, the strength of interactions can be classified as follows: Cl < Cp approximate to Ind < Allyl. In all the complexes studied, the M-2(2+) moiety adopts a single metal-metal bonding attributing the 16-MVE configuration to each M(I) cation.

First author: Carlotto, S, Comparative Experimental and Theoretical Study of the C and O K-Edge X-ray Absorption Spectroscopy in Three Highly Popular, Low Spin Organoiron Complexes: [Fe(CO)(5)], [(eta(5)-C5H5)Fe(CO)(mu-CO)](2), and [(eta(5)-C5H5)(2)Fe], INORGANIC CHEMISTRY, 58, 16411, (2019)
Abstract: The unoccupied electronic structures of three closed-shell, highly popular organoiron complexes ([Fe(CO)(5)], [(eta(5)-C5H5)Fe(CO)(mu-CO)](2), and [(eta(5)-C5H5)(2)Fe]; 0, I, and II, respectively) have been investigated both experimentally and theoretically by combining original gas-phase X-ray absorption spectroscopy (XAS) outcomes recorded at the C and O K-edge with results of scalar relativistic time-dependent density functional calculations carried out within the zeroth order regular approximation. Experimental evidence herein discussed complement the Fe L-2,L-3-edges XAS ones we recently recorded, modeled, and assigned for the same complexes (Carlotto et al. Inorg. Chem. 2019, 58, 5844). The first-principle simulation of the C and O K-edge features allowed us to univocally identify the electronic states associated to the ligand-to-metal charge transfer (LMCT) transitions both in I and in II. At variance to that, LMCT transitions with sizable oscillator strengths do not play any role in determining neither the C nor the O K-edge spectral pattern of 0. The higher pi-acceptor capability of the CO ligand, regardless of its terminal or bridging coordination, with respect to [(eta(5)-C5H5)](-) is herein ultimately confirmed.

First author: Romeo, LJ, Evaluation of the sigma-Donating and pi-Accepting Properties of N-Heterocyclic Boryl Anions, INORGANIC CHEMISTRY, 58, 16500, (2019)
Abstract: The relative a-donating and pi-accepting capacities of a range of synthetically relevant boryl anions have been evaluated by examining the geometric, thermo-chemical, and electronic properties of their adducts to the Li+ cation and Se atom, as compared to the properties of the analogous neutral N-heterocyclic carbenes (NHCs), by theoretical methods. The results indicate that boryl anions have a weaker pi-accepting capability compared to NHCs, but it is still a non-negligible factor in the bonding contributions between boryl and the Se atom. The tunability of the pi-accepting capacity of boryl anions is similar to that of NHCs, indicating a potential for the modification of the electronic properties of metal complexes incorporating either boryl or NHC ligands. In all cases, the boryl ligands were found to be superior sigma-donors to NHCs.

First author: Zhao, ZW, Theoretical Insight into Multiple Charge-Transfer Mechanisms at the P3HT/Nonfullerenes Interface in Organic Solar Cells, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, 7, 19699, (2019)
Abstract: Poly(3-hexylthiophene) (P3HT)-based organic solar cells (OSCs) have been developed in recent years because of their advantages such as easy production, low cost, and large-area manufacture. However, fewer nonfullerene acceptors with higher power conversion efficiency (PCE) than PC61BM have been explored in P3HT-based OSCs. In this contribution, the excited states were in-depth analyzed toward probing the particularities of superior P3HT/nonfullerene systems. Multiple charge-transfer (CT) mechanisms involving intermolecular electric field (IEF), hot CT states, and direct excitation of CT states were found, which suggests that more favorable CT pathways exist at these P3HT/nonfullerene interfaces. Accordingly, the calculations on CT rates of all of the investigated donor/acceptor interfaces further verified the positive effect of multiple CT pathways. In addition, the interesting hybrid Frenkel-CT states were first found to be relevant with the stronger electrostatic surface potential (ESP) differences on the donor and acceptor for these P3HT/nonfullerene systems, which may provide a strategy for the design of high-efficiency OSCs.

First author: Babgi, BA, Exploring DNA-Binding and anticancer properties of benzoimidazolyl-ferrocene dye, JOURNAL OF MOLECULAR STRUCTURE, 1198, 19699, (2019)
Abstract: The synthesis of the benzoimidazolyl-ferrocene containing compound was achieved by Knovenagel condensation of ferrocene-1-carbaldehyde and (2-benzoimidazolyl) acetonitrile. Single crystal structure of the compound showed intramolecular (hydrogen bonding) NH center dot center dot center dot N interactions, forming an infinite 1D-chain that propagate along the [010] direction. The titled compound exhibits two major energy bands around 360 nm and 515 nm in the UV-vis range, that are assigned by TD-DFT calculations for CT (Donor-pi-Acceptor) and MLCT respectively. In acidified solution, the molecule spectrum exhibits a red shift in the lowest energy band associated with a color change from purple to violet when the pH maintained around 5. DNA-binding study showed hypochromic shifts in all the absorption with no red shift in the MLCT which can attributed to the reduced probability of the transitions as the LUMO is strongly involved in the interaction with the ct-DNA. The compound exerts high toxicity against the lung cancer cell line (A549) while the prostate cancer cell line (PC-3) was extremely resistant. Docking study showed that the compound and Erlotinib have similarities in targeting the EGFR. Theoretically, the title compound exhibits physiochemical features, matching those of orally active drugs. Selective cytotoxicity of chemotherapeutic agents is desirable and hence more studies would be undertaken on benzoimidazolyl-ferrocene to understand the mechanism of action on the lung cancer cell line.

First author: Navamani, K, Effect of site energy fluctuation on charge transport in disordered organic molecules, JOURNAL OF CHEMICAL PHYSICS, 151, 19699, (2019)
Abstract: Effect of dynamics of site energy disorder on charge transport in organic molecular semiconductors is not yet well-established. In order to study the relationship between the dynamics of site energy disorder and charge transport, we have performed a multiscale study on dialkyl substituted thienothiophene capped benzobisthiazole (BDHTT-BBT) and methyl-substituted dicyanovinyl-capped quinquethiophene (DCV5T-Me) molecular solids. In this study, we explore the structural dynamics and correlated charge transport by electronic structure calculations, molecular dynamics, and kinetic Monte-Carlo simulations. We have also proposed the differential entropy dependent diffusion and charge density equations to study the electric field drifted diffusion property and carrier density. In this investigation, we have addressed the transformation mechanism from dynamic to static disorder in the extended stacked molecular units. Here, the decrease in the charge transfer rate due to site energy fluctuations reveals the dispersion transport along the extended pi-stacked molecules. Furthermore, the calculated current density for a different set of site energy difference values shows the validity and the limitations of the Einstein relation. Based on the calculated ideality factor, we have classified the charge transport in these molecules as either the Langevin or the Shockley-Read-Hall type mechanism. Through the calculated mobility, current density, and ideality factor analysis, we categorize the applicability of molecules of interest for photovoltaic or light emitting diode applications.

First author: Zhulyaev, NS, Organometallic chemistry of new carbon materials. Structure and dynamic behavior of group 6 metal tricabonyl complexes of graphene and perforated graphene: a DFT study, NEW JOURNAL OF CHEMISTRY, 43, 17991, (2019)
Abstract: The mechanism of inter-ring haptotropic rearrangements (IRHRs) was investigated by DFT for the tricarbonyl eta(6)-complexes of group 6 metals (M = Cr, Mo, W) of coronene (I-M), kekulene (II-M) and a model graphene (III-M). The computed eta(6),eta(6)-IRHR activation barriers in the middle size PAHs I-M and II-M were calculated to be substantially lower than those in the case of complexes of relatively small size PAHs such as naphthalene chromium tricarbonyl (Delta G approximate to 20-25 kcal mol(-1)vs. approximate to 30 kcal mol(-1)). The barrier is further lowered in the case of the model graphene complex III-Cr (Delta G approximate to 13 kcal mol(-1)). An even lower barrier is found for III-Mo (Delta G approximate to 10 kcal mol(-1)), whereas it slightly increases for III-W (Delta G approximate to 14 kcal mol(-1)).

First author: Berezin, AS, Trinuclear copper(ii) bromide complex [C3H5N3Br](2n)[Cu3Br8](n). Structure, magnetic properties and DFT calculations, NEW JOURNAL OF CHEMISTRY, 43, 18203, (2019)
Abstract: Halidocuprates(ii) show unusual magnetic properties and a high degree of structural flexibility. We present the results of crystallographic, electron paramagnetic resonance (EPR) spectroscopic and magnetochemical analyses of a new [HL](2n)[Cu3Br8](n) compound (HL = 3-amino-4-bromopyrazolium) – the first example of an inorganic polymer built from trimeric [Cu3Br8](2-) units with a 5-membered nitrogen-containing heterocycle as an organic counter ion. The EPR spectrum of the polycrystalline sample exhibited a signal at g approximately equal to 2.06 broadened owing to spin-spin interactions between copper ions. The EPR and magnetochemical data indicate a ferromagnetic intertrimer interaction with Theta = 13 K and an antiferromagnetic intratrimer interaction with J = 310 K between the nearest-neighbor copper(ii) ions, which is in agreement with DFT calculations.

First author: Stein, BW, Advancing Chelation Chemistry for Actinium and Other+3 f-Elements, Am, Cm, and La, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 141, 19404, (2019)
Abstract: A major chemical challenge facing implementation of Ac-225 in targeted alpha therapy-an emerging technology that has potential for treatment of disease-is identifying an Ac-225 chelator that is compatible with in vivo applications. It is unclear how to tailor a chelator for Ac binding because Ac coordination chemistry is poorly defined. Most Ac chemistry is inferred from radiochemical experiments carried out on microscopic scales. Of the few Ac compounds that have been characterized spectroscopically, success has only been reported for simple inorganic ligands. Toward advancing understanding in Ac chelation chemistry, we have developed a method for characterizing Ac complexes that contain highly complex chelating agents using small quantities (mu g) of Ac-227. We successfully characterized the chelation of Ac3+ by DOTP8- using EXAFS, NMR, and DFT techniques. To develop confidence and credibility in the Ac results, comparisons with +3 cations (Am, Cm, and La) that could be handled on the mg scale were carried out. We discovered that all M3+ cations (M = Ac, Am, Cm, La) were completely encapsulated within the binding pocket of the DOTP8- macrocycle. The computational results highlighted the stability of the M(DOTP)(5-) complexes.

First author: Vlahovic, F, Density functional approximations for consistent spin and oxidation states of oxoiron complexes, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 141, 19404, (2019)
Abstract: We report here a computational study on a series of Fe-II, Fe-III, and Fe-IV hydroxo/oxoiron complexes with a broad palette of ligands. We are interested in assessing the robustness of widely used density functionals for their prediction and description of structures and spin states for the examined oxoiron complexes. We have used a variety of density functional approximations (S12g, LDA, BP86-D-3, OPBE, SSB-D, B3LYP-D-3, S12h, and MVS), in all cases including solvation and relativistic effects explicitly. One of the main observations of this detailed study is the excellent performance of S12g for both accurate structures and spin state splittings. Moreover, our results show that in general all density functionals can be used as a reliable computational tool for reproducing and predicting geometries, determining the oxidation state of iron, and most are able as well to providing good descriptions of spin state energetics.

First author: Grimmel, SA, Is it worthwhile to go beyond the local-density approximation in subsystem density functional theory?, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 141, 19404, (2019)
Abstract: Frozen density embedding (FDE) theory is one of the major techniques aiming to bring modeling of extended chemical systems into the realm of high accuracy calculations. To improve its accuracy it is of interest to develop kinetic energy density functional approximations specifically for FDE applications. In the study reported here we focused on optimizing parameters of a generalized gradient approximation-like kinetic energy functional with the purpose of better describing electron excitation energies. We found that our optimized parametrizations, named excPBE and excPBE-3 (as these are derived from a Perdew-Burke-Ernzerhof-like parametrization), could not yield improvements over available functionals when applied on a test set of systems designed to probe solvatochromic shifts. Moreover, as several different functionals yielded very similar errors to the simple local-density approximation (LDA), it is questionable whether it is worthwhile to go beyond the LDA in this context.

First author: Rong, MK, Protic NHC Iridium Complexes with beta-H Reactivity-Synthesis, Acetonitrile Insertion, and Oxidative Self-Activation, ORGANOMETALLICS, 38, 4543, (2019)
Abstract: Protic NHC iridium complexes, obtained from the corresponding azido-phenylene-isocyanide precursor complexes, were investigated for ligand-based reactivity. Under redox-neutral conditions, acetonitrile inserts into the N-H bonds to provide kappa(2)-NHC-imidoyl ligand-based complexes, while under reductive conditions the complex also expels one N-H proton to provide the corresponding deprotonated analogues. Using zinc as a reductor activates the NHC-iridium complex to form an asymmetric bimetallic iridium hydrido complex, in which two anionic N-deprotonated NHCs bridge the bimetallic core. X-ray crystal structures are reported for the azido-phenylene-isocyanide precursor complex, the protic NHC complex, and the asymmetric bimetallic iridium hydride complex. Density functional computations and a QTAIM analysis of the bimetallic iridium hydrido complex are provided.

First author: Lenczyk, C, Toward Transition-Metal-Templated Construction of Arylated B-4 Chains by Dihydroborane Dehydrocoupling, CHEMISTRY-A EUROPEAN JOURNAL, 38, 4543, (2019)
Abstract: The reactivity of a diruthenium tetrahydride complex towards three selected dihydroboranes was investigated. The use of [DurBH(2)] (Dur=2,3,5,6-Me4C6H) and [(Me3Si)(2)NBH2] led to the formation of bridging borylene complexes of the form [(Cp*RuH)(2)BR] (Cp*=C5Me5; 1 a: R=Dur; 1 b: R=N(SiMe3)(2)) through oxidative addition of the B-H bonds with concomitant hydrogen liberation. Employing the more electron-deficient dihydroborane [3,5-(CF3)(2)-C6H3BH2] led to the formation of an anionic complex bearing a tetraarylated chain of four boron atoms, namely Li(THF)(4)[(Cp*Ru)(2)B4H5(3,5-(CF3)(2)C6H3)(4)] (4), through an unusual, incomplete threefold dehydrocoupling process. A comparative theoretical investigation of the bonding in a simplified model of 4 and the analogous complex nido-[1,2(Cp*Ru)(2)(mu-H)B4H9] (I) indicates that there appear to be no classical sigma-bonds between the boron atoms in complex I, whereas in the case of 4 the B-4 chain better resembles a network of three B-B sigma bonds, the central bond being significantly weaker than the other two.

First author: Saielli, G, One-bond (1)J((NF)-N-15-F-19) spin-spin coupling constants of cationic fluorinating reagents: Insights from DFT calculations, MAGNETIC RESONANCE IN CHEMISTRY, 38, 4543, (2019)
Abstract: We have investigated, by means of density functional theory protocols, the one-bond (1)J((NF)-N-15-F-19) spin-spin coupling constants in a series of fluorinating reagents, containing the NF bond, recently studied experimentally. The results of the calculations show a very good linear relationship with the experimental values, even though only the M06-2X(PCM)/pcJ-2//B3LYP/6-311G(d,p) level affords a very low mean absolute error. The calculations allow to analyze the various molecular orbitals contributions to the J coupling and to rationalize the observed positive sign, corresponding to a negative sign of the reduced spin-pin coupling constant K(NF). Moreover, of the four Ramsey contributions, only the diamagnetic spin orbit is negligible, whereas the paramagnetic spin orbit and spin dipole terms decrease the magnitude of the Fermi contact (FC) term by an amount that goes from a minimum of 35% up to more than 60% of the FC term itself. Several effects have been investigated, namely, the contribution of the long-range solvent reaction field, relativistic corrections, and conformational and vibrational effects.

First author: Viesser, RV, Counterintuitive deshielding on the C-13 NMR chemical shift for the trifluoromethyl anion, MAGNETIC RESONANCE IN CHEMISTRY, 38, 4543, (2019)
Abstract: The trifluoromethyl anion (CF3-) displays C-13 NMR chemical shift (175.0 ppm) surprisingly larger than neutral (CHF3, 122.2 ppm) and cation (CF3+, 150.7 ppm) compounds. This unexpected deshielding effect for a carbanion is investigated by density functional theory calculations and decomposition analyses of the C-13 shielding tensor into localized molecular orbital contributions. The present work determines the shielding mechanisms involved in the observed behaviour of the fluorinated anion species, shedding light on the experimental NMR data and demystify the classical correlation between electron density and NMR chemical shift. The presence of fluorine atoms induces the carbon lone pair to create a paramagnetic shielding on the carbon nucleus.

First author: Liu, X, A novel storage design for ultrahigh-cell-voltage Al-ion batteries utilizing cation-pi interactionst, CHEMICAL COMMUNICATIONS, 55, 14198, (2019)
Abstract: We propose a novel storage design for ultrahigh-cell-voltage Al-ion battery by utilizing cation-pi interactions by means of density functional theory (DFT) computations. The ultrahigh cell voltage can reach up to similar to 12 V, which is about 6 times that of the cell voltages of current Al-ion batteries; further, the heat loss can be considerably reduced.

First author: Schubert, K, Absorption spectra at the iodine 3d ionisation threshold following the CHxI+ (x=0-3) cation sequence, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 25415, (2019)
Abstract: Yields of atomic iodine Iq+ (q >= 2) fragments resulting from photoexcitation and photoionisation of the target cations CHxI+ (x = 0-3) have been measured in the photon-energy range 610 eV to 670 eV, which comprises the threshold for iodine 3d ionisation. The measured ion-yield spectra show two strong and broad resonance features due to the excitation of the 3d(3/2,5/2) electrons into epsilon f states similar to atomic iodine. In the 3d pre-edge range, electrons are excited into molecular orbitals consisting of iodine, carbon, and hydrogen atomic orbitals. These transitions have been identified by comparison with literature data and by simulations using time-dependent density functional theory (TDDFT) with the KMLYP functional. The ion-yield spectrum for CH3I+ resembles the spectrum of IH+ [Klumpp et al., Phys. Rev. A, 2018, 97, 033401] because the highest occupied molecular orbitals (HOMO) of the H and CH3 fragments both contain a single vacancy, only. For the molecular cations with higher number of vacancies in the valence molecular orbitals CHxI+ (x = 0-2), a stronger hybridisation of the molecular orbitals occurs between the organic fragment and the iodine resulting in a change of bonding from a single sigma bond in CH3I+ to a triple bond including two pi orbitals in CI+. This is reflected in the resonance energies of the observed absorption lines below the iodine 3d excitation threshold.

First author: Brooks, JL, Plasmon-Driven C-N Bond Cleavage Across a Series of Viologen Derivatives, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 29306, (2019)
Abstract: The optical excitation of surface plasmons leads to the generation of highly enhanced nanoscale local fields and an abundance of harvestable hot carriers. When certain analytes are positioned within these unique environments, surface plasmons may be able to induce chemical reactions that are energetically unfavorable under standard conditions. Sometimes, the plasmonic environments can initiate entirely new reaction pathways for the chemical adsorbates. Here, we investigate the nature of plasmon-driven reactions on three viologen derivatives: methyl viologen, ethyl viologen, and benzyl viologen. Viologens have traditionally been employed as excellent redox agents due to their ability to reversibly stabilize additional electrons in their molecular structures. However, by using surface-enhanced Raman spectroscopy, we were able to directly observe a C-N bond cleavage on benzyl and ethyl viologen to form 4,4′-bipyridine on the surface of gold film-over-nanosphere substrates. Surprisingly, methyl viologen does not undergo a similar process. We posit that this differing reactivity may be due to changes in adsorption geometry or in reduction potential. Using both spectroscopic and theoretical methods, we were able to confirm 4,4′-bipyridine as the plasmonmediated photoproduct. This work highlights the novelty of using plasmonic environments to access new chemical reactions and adds to the expanding library of plasmon-mediated chemical reactions.

First author: Wilson, TR, Observing the 3D Chemical Bond and its Energy Distribution in a Projected Space, CHEMPHYSCHEM, 123, 29306, (2019)
Abstract: Our curiosity-driven desire to “see” chemical bonds dates back at least one-hundred years, perhaps to antiquity. Sweeping improvements in the accuracy of measured and predicted electron charge densities, alongside our largely bondcentric understanding of molecules and materials, heighten this desire with means and significance. Here we present a method for analyzing chemical bonds and their energy distributions in a two-dimensional projected space called the condensed charge density. Bond “silhouettes” in the condensed charge density can be reverse-projected to reveal precise three-dimensional bonding regions we call bond bundles. We show that delocalized metallic bonds and organic covalent bonds alike can be objectively analyzed, the formation of bonds observed, and that the crystallographic structure of simple metals can be rationalized in terms of bond bundle structure. Our method also reproduces the expected results of organic chemistry, enabling the recontextualization of existing bond models from a charge density perspective.

First author: Kolivoska, V, Single Molecule Conductance of Electroactive Helquats: Solvent Effect, CHEMELECTROCHEM, 6, 5856, (2019)
Abstract: A series of helquat molecules with increasing number of rings n was studied by electrochemical and break junction methods to provide redox characteristics and single molecule conductance properties. Even though selected species do not contain anchoring groups the molecular junction conductance was observed experimentally and depends strongly on the solvent used. Single molecule conductance G is almost two orders of magnitude higher in water environment compared to mesitylene, whereas the distribution of G values is narrow in water and wide in mesitylene solvent. In the non-polar environment, G increases with increasing n, contrary to generally accepted notion of decreasing tunneling current with increasing molecular length. This behavior is, however, consistent with electrochemical properties, which showed that longer helquats are reduced more easily than the shorter ones. Furthermore, theoretical computations provided most probable molecular junction configurations of helquats in water solvent with excellent agreement between theoretical and experimental G values.

First author: Alkorta, I, Relativistic Effects on NMR Parameters of Halogen-Bonded Complexes, MOLECULES, 24, 5856, (2019)
Abstract: Relativistic effects are found to be important for the estimation of NMR parameters in halogen-bonded complexes, mainly when they involve the heavier elements, iodine and astatine. A detailed study of 60 binary complexes formed between dihalogen molecules (XY with X, Y = F, Cl, Br, I and At) and four Lewis bases (NH3, H2O, PH3 and SH2) was carried out at the MP2/aug-cc-pVTZ/aug-cc-pVTZ-PP computational level to show the extent of these effects. The NMR parameters (shielding and nuclear quadrupolar coupling constants) were computed using the relativistic Hamiltonian ZORA and compared to the values obtained with a non-relativistic Hamiltonian. The results show a mixture of the importance of the relativistic corrections as both the size of the halogen atom and the proximity of this atom to the basic site of the Lewis base increase.

First author: Gunther, F, Experimental and theoretical assessment of the aminolysis of cyclo carbonate to form polyhydroxyurethanes, MATERIALS TODAY COMMUNICATIONS, 21, 5856, (2019)
Abstract: Polyurethanes (PU) is one of the most used polymers and finds its applications in many modern technologies. The use of not-environmental-friendly chemicals in the actual manufacturing process claims for new more sustainable synthetic strategies. One of these novel routes is the aminolysis of cyclic carbonates resulting in so-called polyhydroxyurethanes (PHU). So far, this ring opening polymerisation (ROP) was mainly investigated considering aliphatic amines. In this study, both aromatic and aliphatic amines without additional catalysts are studied and their reaction behaviours are compared. For this aim, the ROP reactions were monitored by FTIR and NMR spectroscopies. It turned out that aromatic amines do not react in opposition to aliphatic ones. To gain a deeper insight on the reactivity parameters related to this different reaction behavior, simple molecular models were studied by density functional theory methods. Aiming to assess the impact of different conformations and to determine a statistical mean value of the reaction energy molecular dynamic (MD) simulations of a large set of different conformations was sampled. Moreover, the detailed consideration of the electronic density, revealed that the lone pair of the amine nitrogen is delocalised along the p-system of the aromatic compounds. This positive mesomerie effect results in a planarisation of the amine group, in higher reaction barriers and, smaller reaction energies.

First author: Li, ZZ, Rg(n)Be(3)B(3)(+): theoretical investigation of Be3B3+ and its rare gas capability, JOURNAL OF MOLECULAR MODELING, 25, 5856, (2019)
Abstract: A series of Be3B3+ and its rare gas (Rg) containing complexes Rg(n)Be(3)B(3)(+) (Rg = He-Rn, n = 1-6) have been predicted theoretically using the B3LYP, MP2, and CCSD(T) methods to explore structures, stability, charge distributions, and nature of bonding. Both Be3B3+ and RgBe(3)B(3)(+) are the global minima on the potential energy surfaces. In the Rg(n)Be(3)B(3)(+) complexes, the dissociation energy drops with the increase in number of Rg. Natural bond orbital (NBO) and topological analysis of the electron density (AIM) show that the Rg-Be bonds for Kr-Rn have some covalent character. The Rg-Be bond is stabilized dominantly by the Rg -> Be3B3+ sigma-donation from the valence p orbital of Rg to the vacant valence LUMO orbital of Rg(n-1)Be(3)B(3)(+). Besides, other two pi-donations also play important roles in stabilizing the Rg-Be bonds.

First author: Toader, AM, Atoms in Generalized Orbital Configurations: Towards Atom-Dedicated Density Functionals, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 20, 5856, (2019)
Abstract: Deriving a practical formula for the atomic body with generalized shell occupations, we perform a detective analysis of the radial distribution in the exchange energy, hinting at ideas about new types of density functionals, dedicated to the specifics of the electronic structure of atoms, exploiting the intrinsic spherical symmetry.

First author: Liu, QL, Computer-aided reaction solvent design considering inertness using group contribution-based reaction thermodynamic model, CHEMICAL ENGINEERING RESEARCH & DESIGN, 152, 123, (2019)
Abstract: Solvents have been widely used in process manufacturing industries. When involved in liquid-phase organic synthesis reactions, solvents can reduce the activation energy of reactions between the reactants and the transition state through solvation effects. However, undesirable side reactions can also be performed between solvents and the reaction system (the reactants and products), which should be avoided for producing unnecessary byproducts in the reaction system. In this paper, an optimization-based methodology is proposed for inert reaction solvent design. In this method, first, a Group Contribution (GC)-based reaction thermodynamic model is developed to quantitatively identify the thermodynamic feasibility of side reactions between solvents and the reaction system. Then, the SMARTS (SMiles Arbitrary Target Specification)-based reaction generation algorithm is employed to generate possible side reactions between solvents and the reaction system, helping to integrate the developed GC-based reaction thermodynamic model with the Computer-Aided Molecular Design (CAMD) problem for designing inert reaction solvents through the formulation and solution of the Mixed-Integer Non-Linear Programming (MINLP) model. Due to the nonlinear equations in the MINLP model, a decomposition-based solution strategy is employed to solve the optimization problem. Finally, two case studies are presented to demonstrate the feasibility and effectiveness of the proposed optimization-based methodology for promising inert reaction solvent design.

First author: Pal, PP, Polarizable Frozen Density Embedding with External Orthogonalization, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 15, 6588, (2019)
Abstract: We report a polarizable subsystem density functional theory to describe electronic properties of molecules embedded on a metal cluster. Interaction between the molecule and metal cluster is described using frozen density embedding (FDE). Substituting the nonadditive kinetic potential (NAKP) by approximate functionals is circumvented by enforcing external orthogonality (EO) through a projection operator. The computationally expensive freeze/thaw (FT) cycles are bypassed by including a polarization term in the embedding operator. Furthermore, the combination of polarization and EO permits supermolecular basis set calculations, which was not possible for strongly interacting systems with existing kinetic energy functionals. To test the method, we described the ground state density of pyridine, water, and benzene on a silver cluster. Performing FT on top of EO results in exact density embedding for this category of systems and is thus used for benchmarking the method. We find that the density is reproduced to within 0.15e, and the dipole and quadrupole moments are within 18% of the reference points for subsystem separations ranging from bonding to noninteracting distances. Additionally, our formalism allows the flexibility of incorporating different density functionals to the molecular and the metallic subsystems reducing the overall computational cost.

First author: Jones, LO, Quantum Interference and Substantial Property Tuning in Conjugated Z-ortho-Regio-Resistive Organic (ZORRO) Junctions, NANO LETTERS, 19, 8956, (2019)
Abstract: Coherence is a significant factor in nanoscale electronic insulator technology and necessitates an understanding of the structure-property relationship between constructive and destructive quantum interference. This is particularly important in organic dielectric circuitry, which is the subject of this work. It is known that molecular wires composed of (i) meta-substituted phenylene rings, (ii) cross-conjugated double bonds (orthogonal to the molecular long axis), and (iii) single bonds can dramatically reduce electrical transmission. Here we add to these tools the use of an unexplored molecular shape to create strong and counter-intuitive interference: a fully conjugated molecular wire with a structure that is forced back on itself in a Z shape, thereby exhibiting remarkably low conductance (G = 0.43 x 10(-9) S) even though the phenylene arrangements are ortho- rather than meta-disposed. We call these Z-shaped molecules having ultralow conduction Z-ortho-regio-resistive organics (ZORROs). Here we analyze a series of ZORRO molecules and find them to have significant insulating properties in the coherent electrontran-sport regime due to interfering transmission pathways in the phenylene rings. Importantly, we find that both electron with-drawing (fluorine) and electron-donating (methoxy) substituents enhance the transmission, which is not desirable. The former is due to the suppression of the destructive quantum interference at the F site, thereby enhancing the overall transmission, much like a Buttiker probe. The latter is due to a methoxy unit resonance additive effect, akin to oxygen doping, and positively contributes to the transmission. We then examine the effects of replacing the phenylene rings with 4,5- and 3,4-disubstituted thiophenes and how this ZORRO modification further reduces the transmission. An ultralow conductance of 0.13 x 10(-9) S and a relatively high dielectric constant (epsilon(r)) of similar to 5 are predicted for the 3,4-thiophene ZORRO derivative, which closely resembles two cross-conjugated units, making it an intriguing candidate for a gate dielectric material.

First author: Chandrasekar, A, On the position of La, Lu, Ac and Lr in the periodic table: a perspective, JOURNAL OF CHEMICAL SCIENCES, 131, 8956, (2019)
Abstract: The periodic table of elements, organised as blocks of elements that contain similar properties, occupies a central role in chemistry. However, the position of some of the elements in the periodic table is a debate that has been ensuing over the past one and a half long centuries. Particularly, the positions of lanthanum (La), lutetium (Lu), actinium (Ac) and lawrencium (Lr) in the periodic table have been quite controversial. Different kinds of studies carried out by various research groups have yet left the fate of these elements undecided as the results of these investigations suggested that these elements could potentially be placed in the d-block, p-block or all four in the f-block. Our recent work looked into this question from a new perspective, involving encapsulation of La, Lu, Ac and Lr into Zintl ion clusters, Pb-12(2-) and Sn-12(2-). These clusters were chosen as they provide a fitting environment for the determination of structural, thermodynamic and electronic properties of the encapsulated species. Various results that have been evaluated and subsequently analysed (Joshi et al. in Phys. Chem. Chem. Phys. 20:15253-15272, 2018) in order to seek out similarities and differences for making justified conclusions about the placement of all these four elements in the periodic table are the subject matter of this review article.

First author: Joy, J, Designing M-bond (X-M center dot center dot center dot Y, M = transition metal): sigma-hole and radial density distribution, JOURNAL OF CHEMICAL SCIENCES, 131, 8956, (2019)
Abstract: Following the ubiquitous H-bond, there is a growing interest in weak non-covalent interactions involving other elements, viz., the Z-bonds (X-Z center dot center dot center dot Y, Z = halogens, chalcogens, etc.). Although almost all the main group elements can act as Z bond donors, the search for a similar role for transition metals in X-M center dot center dot center dot Y, (M = transition metal) interaction, called the Metal-bond, is still in its infancy. This article summarizes our attempts to understand the participation of transition metal elements as electron acceptors in a weak interaction with electron-rich species Y. Cambridge Structural Database analysis revealed that except Group 11 and 12 transition metal complexes (Type-II), electron-saturated (18 electron) metal complexes having partly filled d orbitals (Group 3-10; Type-I) hesitate to form Metal-bonds. This is attributed to the partial sigma-hole screening by core electron density and diminished stabilization from charge polarization in Type I complexes. We also show that Type-I complexes could be forced to form Metal-bonds by employing extreme ligand conditions, thereby opening new areas of research where Metal-bonds can act as emerging non-covalent interaction in designing supramolecular architectures.

First author: Mikhailov, AA, Photoinduced inhibition of DNA repair enzymes and the possible mechanism of photochemical transformations of the ruthenium nitrosyl complex [RuNO(beta-Pic)(2)(NO2)(2)OH], METALLOMICS, 11, 1999, (2019)
Abstract: In this work we have demonstrated that the ruthenium nitrosyl complex [RuNO(beta-Pic)2(NO2)2OH] is suitable for investigation of the inactivation of DNA repair enzymes in vitro. Photoinduced inhibition of DNA glycosylases such as E. coli Endo III, plant NtROS1, mammalian mNEIL1 and hNEIL2 occurs to an extent of Z90% after irradiation with the ruthenium complex. The photophysical and photochemical processes of [RuNO(beta-Pic)(2)(NO2)(2)OH] were investigated using stationary and time-resolved spectroscopy, and mass spectrometry. A possible mechanism of the photo-processes was proposed from the combined spectroscopic study and DTF calculations, which reveal that the photolysis is multistage. The primary and secondary photolysis stages are the photo-induced cleavage of the Ru-NO bond with the formation of a free nitric oxide and RuIII complex followed by ligand exchange with solvent. For E. coli Endo III, covalent interaction with the photolysis product was confirmed by UV-vis and mass spectrometric methods.

First author: Conradie, J, Density functional theory calculated data of different electronic states and bond stretch isomers of tris(trifluoroacetylacetonato)-manganese(III), DATA IN BRIEF, 27, 1999, (2019)
Abstract: In this data article, using density functional theory calculations, it is shown that in the gas phase, free from crystal packing effects, different elongation and compression Jahn-Teller geometries of fac and mer tris(trifluoroacetylacetonato)-manganese(III) are possible. A careful construction of input geometries made it possible to obtain the density functional theory calculated optimized geometries of different elongation and compression Jahn-Teller geometries of fac and mer tris(trifluoroacetylacetonato)-manganese(III). The mer CF3-CF3 elongation isomer has the lowest energy (Fig. 1), while in the solid state a mer CH3-CH3 compression tris(trifluoroacetylacetonato)-manganese(III) isomer is experimentally characterized [1]. The rare experimental example of a compression tris(beta-diketonato)-manganese(III) structure is ascribed to intermolecular F…F and F…H interactions between the tris(trifluoroacetylacetonato)-manganese(III) molecules in the solid crystalline state, contributing to the distortion of the coordination polyhedron of tris(trifluoroacetylacetonato)manganese(III) from the expected elongation Jahn-Teller geometry, to the observed higher energy electronic state with compression Jahn-Teller distortion.

First author: Owczarzak, A, Role of Staple Molecules in the Formation of S center dot center dot center dot S Contact in Thioamides: Experimental Charge Density and Theoretical Studies, CRYSTAL GROWTH & DESIGN, 19, 7324, (2019)
Abstract: The reasons behind the formation of S center dot center dot center dot S contacts in thioamides, the most important compounds with terminal sulfur atoms, were investigated by means of experimental charge density studies and theoretical calculations. As this interaction is to some extent similar to the much better-known halogen bond, geometrical analysis was performed using previously determined halogen bond formation criteria. To investigate the most representative thioamides, three compounds, namely, 6-amintothiouracil hydrate (ATU center dot H2O, 1), 2-imidazolidinethione (IMT, 2), and 2-thiazolidinethione (TT, 3), were selected. In all three structures, relatively short S center dot center dot center dot S contacts displaying different geometries were observed. Furthermore, different symmetry elements (mirror plane in ATU, inversion center in TT, and translation in IMT) determined the mutual orientation of the sulfur atoms in contact. The structural analysis and calculations proved that the isolated S center dot center dot center dot S dimers are unstable and that they are stabilized by “staple” molecules, which are any molecules present in the crystal structure that interact with both molecules forming the S center dot center dot center dot S contact. Several types of staple molecules were identified, differing in the area of interaction with the S center dot center dot center dot S dimer molecule. The analysis of the data in the Cambridge Structural Database showed that the staple structures can be found in 77% of all structures with short S center dot center dot center dot S contacts (shorter than 3.4 angstrom) and in more than half of the structures with the contacts within the van der Waals radius limit. The calculations show that the smaller the distance between sulfur atoms in the S center dot center dot center dot S dimer, the greater the amount of energy needed for dimer stabilization. Consequently, the presence of a staple is essential.

First author: Dulieu, F, Reactivity of coronene with O-atoms, a possible route to ketene in the interstellar medium, MOLECULAR ASTROPHYSICS, 17, 7324, (2019)
Abstract: PAHs are one of the important components of the carbonaceous matter of the Universe. They are not detected in the darkest regions of the Interstellar Medium and one possible reason could be their chemical transformation through gas phase reactions In particular, their oxidation was considered ineffective because the reaction barriers appear to be too high, based on combustion studies conducted at high temperatures. For the first time, we experimentally studied the oxidation of Coronene, a PAH archetype, at low temperature (50 K), as well as the oxidation of hydrogenated Coronenes. It appears that reactivity is higher than expected and that the fragmentation of coronene is a significant channel of the oxidation. Furthermore, hydrogenated coronenes are very reactive to oxygen. To understand the experimental data, DFT calculations were performed. They confirm a low oxidation barrier (0.11 eV) and show that oxygen is preferentially inserted at the periphery of the coronene and propose a reaction mechanism for fragmentation also involving a hydrogen atom. An estimate of the orders of magnitude shows that PAH oxidation may explain part of the decrease in their abundances in warm environments.

First author: Venkataramanan, NS, Unraveling the binding nature of hexane with quinone functionalized pillar[5]quinone: a computational study, JOURNAL OF INCLUSION PHENOMENA AND MACROCYCLIC CHEMISTRY, 95, 307, (2019)
Abstract: The nature of host-guest interactions between the hexane and pillar[5]arene and its quinone modified pillararenes has been studied using dispersion-corrected density functional theory and wave functional methods. The introduction of quinone in pillararene prompted flexibility in structure and the electrophilicity of pillararenes increases with the number of quinone moiety. Thermochemical as well as energetic results indicate that hexane binding is favorable on all studied systems. The presence of quinone reduces the exothermicity, and exergonic nature and the decrease in temperature increases the free energy of formation. Molecular electrostatic potential analysis indicates the existence of charge transfer between the host and guest molecules. Quantum theory of atoms in molecule analysis reveals in the quinone functionalized pillararenes, the number of interactions arising from quinone is less than that on the 1,4-alkoxybenzene unit. Noncovalent interaction analysis shows a larger area of interactions correspond to C-H center dot center dot center dot pi interactions in the encapsulated complexes. EDA results reveal that dispersion Delta E-disp interaction followed by electrostatic attraction Delta E-elstat contributes mainly for the attractive terms. These insights can be used to tune further and improve the binding ability of pillararene guest towards linear host molecules.

First author: Rusakova, IL, On the heavy atom on light atom relativistic effect in the NMR shielding constants of phosphine tellurides, MAGNETIC RESONANCE IN CHEMISTRY, 57, 1071, (2019)
Abstract: The relativistic HALA effect has been shown to depend on the spatial deformation of the lone electron pairs of a heavy atom, as demonstrated for alkyl and alkene phosphine tellurides. It was found that HALA effect on phosphorous nuclear magnetic resonance shielding constant is strongly dependent on the spatial arrangements of light substituents on phosphorus, resulting in the deformation of the lone electron pairs of tellurium.

First author: Benmachiche, A, Coordination and ligands’ effects in trinuclear [Pd-3(COT)(2)(L)](2+) (L = H2O, CO, N-2, HCN, HNC, NH3, PH3, PCl3, PF3, CS, CH2) sandwich complexes of cyclooctatetraene: theoretical investigation, STRUCTURAL CHEMISTRY, 30, 2339, (2019)
Abstract: This paper reports the molecular structure, the electronic structure, and the decomposition energies of the [M-3(COT)(2)(L)](2+) (M = Cr, Fe, Pd, and L = H2O, CO, N-2, HCN, HNC, NH3, PH3, PCl3, PF3, CS, CH2, and COT = C8H8) complexes obtained by means of DFT method using BP86 and PW91 functionals with the TZP basis set. The Pd-L bonding between the Pd-3 moiety and both COT ligands is weakly sensitive to the nature of the ancillary L ligands. In accordance with the coordination modes, the COT behaves as neutral distorted ligand deviating from the planarity. The calculations showed that the various complexes are found to have a low spin ground state. The MO plots and Wiberg bond indices provide further information about the nature of the Pd-Pd bonding. The Ziegler-Rauk energy decomposition analysis scheme was employed to characterize the geometry distortion and steric interaction (electrostatic and Pauli) and orbital interaction terms in the total bonding energy of Pd complexes. The results showed that the interaction terms are governed by one third covalent and two third ionic characters, in agreement with the Delta E-elstat (electrostatic) and Delta E-orb (orbital) contributions, respectively, into the total attractive interaction (Delta E-elstat + Delta E-orb) for the studied complexes except for those of PCl3 and N-2 ligands, which are almost of half covalent and half ionic characters. The sigma -donation and pi -backdonation amounts indicate that the CH2 is the strongest donor ligand; however, the HCN is revealed to be the weakest sigma -donor and pi -acceptor one. The sigma -donation and pi -backdonation are in perfect accord with the natural charges of the interacting fragments.

First author: Zhang, Q, Persulfurated Coronene and Its Chalcogenide Analogues: Insight into Effects of Peripheral Substitution, JOURNAL OF PHYSICAL CHEMISTRY A, 123, 10273, (2019)
Abstract: The density functional theory (DFT) and time-dependent DFT methods have been used to investigate the persulfurated coronene (PSC) and its chalcogenide analogues (POC and PSeC), derived from the substitution of sulfur, oxygen, and selenium for all hydrogen atoms in coronene, respectively. The presence of peripheral S-S in PSC results in a c-type lowest unoccupied molecular orbital and the dark low-lying states (S-1 similar to S-15). The peripheral S-S bond is responsible for its electron capture, which maintains a planar configuration of the singly and doubly negative-charged PSC. POC is predicted to have the most stable saddle-shaped structure with the C=0 group, and its bowl-shaped isomer with the O-O moiety is less stable by 279.2 kcal/mol energetically. PSeC has similar electronic and structural features with PSC, but its dimer is predicted to have much better hole mobility, compared to PSC. The present results indicate that the chalcogenide substitution at the periphery of the polycyclic aromatic hydrocarbons may remarkably change their electronic and spectroscopic properties as well as the carrier transport behavior of their molecular materials.

First author: Weerawardene, KLDM, Luminescence and Electron Dynamics in Atomically Precise Nanoclusters with Eight Superatomic Electrons, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 141, 18715, (2019)
Abstract: The [Au-25(SR)(18)](-) and [Au-13(dppe)(5)Cl-2](3+) [dppe = 1,2-bis-(diphenylphosphino)ethane] nanoclusters both possess a 13-atom icosahedral core with 8 delocalized superatomic electrons (8e), but their emission properties and time-resolved electron dynamics differ significantly. In this work, experimental photoluminescence and photoluminescence decay measurements are combined with time-dependent density functional theory calculations of radiative and nonradiative decay properties and lifetimes to elucidate the similarities and differences in the emission of these two nanoclusters with similar cores. In this work, the photodynamic properties of [Au-13(dppe)(5)Cl-2](3+) are elucidated theoretically for the first time. [Au-13(dppe)(5)Cl-2](3+) exhibits a single strong emission peak compared to the weaker bimodal luminescence of [Au-25(SR)(18)](-) (modeled here as [Au-25(SH)(18)](-)). The strongly emissive state is found to arise from deexcitation out of the S1 state, similar to what is seen for [Au-25(SH)(18)](-). Both theory and experiment exhibit microsecond lifetimes for this state. Transient absorption measurements and theoretical calculations demonstrate that the excited-state lifetimes for higher excited states are typically less than 1 ps. The decay times for the higher excited states of [Au-13(dppe)(5)Cl-2](3+) and its model compound [Au-13(pe)(5)Cl-2](3+) [pe = 1,2-bis(phosphino)ethane] are observed to be shorter than the lifetimes of the corresponding states of [Au-25(SR)(18)](-); this occurs because the energy gap separating degenerate sets of unoccupied orbitals is only similar to 0.2 eV in [Au-13(dppe)(5)Cl-2](3+) compared to a similar to 0.6 eV energy gap in [Au-25(SH)(18)](-).

First author: Namiecinska, E, Anticancer and antimicrobial properties of novel eta(6)-p-cymene ruthenium(II) complexes containing a N,S-type ligand, their structural and theoretical characterization, RSC ADVANCES, 9, 38629, (2019)
Abstract: Ruthenium(II) complexes are lately of great scientific interest due to their chemotherapeutic potential as anticancer and antimicrobial agents. Here we present the synthesis of new pyrazole carbothioamide derivatives and their four arene-ruthenium complexes. The title compounds were characterized with the application of IR, NMR, mass spectrometry, elemental analysis and X-ray diffraction. Additionally, for new complexes DFT calculations were done. Their antimicrobial activity (MIC, MBC/MFC) was examined in vitro against Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, Pseudomonas aeruginosa, Proteus vulgaris and Candida albicans. Their cytotoxic effects, using the MTT assay, against three cancer cell lines: HL-60, NALM-6, WM-115 and normal human foreskin fibroblasts (HFF-1) were also investigated. The influence of the new arene-ruthenium(II) complexes on the DNA structure was also tested. From our results, compound 2d showed higher cytotoxicity against melanoma cell line WM-115 than cisplatin. Strong biostatic and biocidal activity of the tested complexes against Gram-positive bacteria, including S. aureus, S. epidermidis and E. faecalis was demonstrated. The new arene-ruthenium(II) compounds could not only inhibit proliferation of cancer cells, but also protect patients against malignant wound infections.

First author: Cabrera-Trujillo, JJ, Understanding the Reactivity of Neutral Geminal Group 14 Element/Phosphorus Frustrated Lewis Pairs, JOURNAL OF PHYSICAL CHEMISTRY A, 123, 10095, (2019)
Abstract: The influence of the nature of the group 14 elements (E = Si, Ge, Sn) on the reactivity of (F5C2)(3)E-CH2-P(tBu)(2) geminal frustrated Lewis pairs (FLPs) has been computationally explored by means of density functional theory calculations. To this end, the experimentally described activation reactions of CO2 and phenyl isocyanate have been investigated and compared to the analogous processes involving the corresponding B/P geminal FLP. It is found that the reactivity of these species is kinetically enhanced when going down the group 14 (Si < Ge < Sn). This trend of reactivity is quantitatively analyzed in detail by means of the activation strain model of reactivity in combination with the energy decomposition analysis method, which identify the interaction energy between the deformed reactants as the main factor controlling the reactivity of these group 14 containing geminal FLPs.

First author: Paredes-Gil, K, Insights into the role of D-A-pi-A type pro-aromatic organic dyes with thieno[3,4-b]pyrazine as A acceptor group into dye-sensitized solar-cells. A TD-DFT/periodic DFT study, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 123, 10095, (2019)
Abstract: Time-dependent density functional theory (TD-DFT)/periodic DFT calculations were performed to determine the role of pro-aromatic organic D-A-pi-A type dyes (the NL1-NL17 family) with Thieno[3,4-b]pyrazine (Tpy) as A acceptor group into dye-sensitized solar-cells (DSSC). This work presents a discussion of the ground and excited states of these dyes along with the aromaticity analysis and the electron injection step using a dye@(TiO2)(72) model. The results suggest that the pro-aromatic behavior increases from the thiophene ring to the pyrazine when an acceptor pi-bridge such as phenyl is used. This strong pro-aromaticity is also reflected in the electron injection step, studied using a 3×2 3 layer (TiO2)(72) slab model. The resulting adsorption energies (Delta E-ads and Delta G(ads)) and the electron injection (Delta G(inject)) in the stablest coordination mode, Bid_CN_COOH, indicate that the redox reaction (Dye* & x2794; Dye(+) + e(-)) is stronger and more spon than the adsorption reaction (Dye(+) + TiO2 [+e(-)] & x2794; Dye@TiO2) in the electron injection. In this way, the highest efficiency of NL6 and NL12 is a consequence of the more significant pro-aromatic characteristics and the more spontaneous redox process. Finally, these NL dyes are promising in the molecular engineering of D-A-pi-A metal-free types dyes.

First author: Caulfield, KP, Iron(II) Corrole Anions, INORGANIC CHEMISTRY, 58, 15225, (2019)
Abstract: Reduction of [Fe(TPC)(THF)] (TPC = trianion of 5,10,15-triphenylcorrole) with KC8 generates the iron(II) corrole anion, K(THF)(2)[Fe-II(TPC)] (3a). Compound 3a represents the first example of an isolated and crystallographically characterized corrole complex of divalent iron. The compound adopts an intermediate-spin state (S = 1), displaying square-planar geometry about the iron atom. All-electron density functional theory (OLYP and B3LYP) calculations with STO-TZP basis sets indicate two essentially equienergetic d electron configurations, d(xy)(2)d(z)(22)d(xz)(1)d(yz)(1) (occupation 1) and d(xy)(2)d(z)(21)d(xz)(1)d(yz)(2) (occupation 2), as likely contenders for the ground state of [Fe-II(TPC)](-), with the optimized geometry of the former in slightly better agreement with the low-temperature X-ray structure. Solutions of 3a react with carbon monoxide to afford the low-spin (S = 0) complex, [Fe(TPC)(CO)](-), whereas introduction of oxygen at -78 degrees C leads to a putative O-2 adduct, [Fe(TPC)(O-2)](-), which decays rapidly even at low temperatures. Treatment of 3a with organic electrophiles results in formal oxidative addition to give both iron(III) and iron(IV) corrole species. With iodomethane, [Fe(TPC)Me] is produced, illustrating the first instance of alkyl ligand coordination in an iron corrole complex.

First author: Conger, MA, Spectroscopic Evidence for Electronic Control of Heme Hydroxylation by IsdG, INORGANIC CHEMISTRY, 58, 15455, (2019)
Abstract: Staphylococcus aureus IsdG catalyzes a unique trioxygenation of heme to staphylobilin, and the data presented in this article elucidate the mechanism of the novel chemical transformation. More specifically, the roles of the second-sphere Asn and Trp residues in the monooxygenation of ferric-peroxoheme have been clarified via spectroscopic characterization of the ferric-azidoheme analogue. Analysis of UV/vis absorption data quantified the strength of the hydrogen bond that exists between the Asn7 side chain and the azide moiety of ferric-azidoheme. X-band electron paramagnetic resonance data were acquired and analyzed, which revealed that this hydrogen bond weakens the pi-donor strength of the azide, resulting in perturbations of the Fe 3d based orbitals. Finally, nuclear magnetic resonance characterization of C-13-enriched samples demonstrated that the Asn7 center dot center dot center dot N-3 hydrogen bond triggers partial porphyrin to iron electron transfer, resulting in spin density delocalization onto the heme meso carbons. These spectroscopic experiments were complemented by combined quantum mechanics/molecular mechanics computational modeling, which strongly suggested that the electronic structure changes observed for the N7A variant arose from loss of the Asn7 center dot center dot center dot N-3 hydrogen bond as opposed to a decrease in porphyrin ruffling. From these data a fascinating picture emerges where an Asn7 center dot center dot center dot N-3 hydrogen bond is communicated through four bonds, resulting in meso carbons with partial cationic radical character that are poised for hydroxylation. This chemistry is not observed in other heme proteins because Asn7 and Trp67 must work in concert to trigger the requisite electronic structure change.

First author: Ryzhikov, MR, Reduction of carbon and nitrogen centered trigonal prismatic tungsten clusters: Bonding patterns as viewed by ELF and AIM methods, POLYHEDRON, 173, 15455, (2019)
Abstract: W-W and W-X bonds in a series of trigonal prismatic [X@W6Cl18](n) (n = 0, -2, -4 for X = C: n =1, -1, -3 for X = N) clusters were studied using the methods of Electron Localization Function (ELF) and the Atoms In Molecules (AIM) along with the molecular orbital (MO) approach. The [X@W6Cl18](n) clusters contain two {W-3} fragments which form a trigonal prism. Each {W-3} fragment is characterized by a three-center bond and three two-center bonds. The carbon or the nitrogen atom encapsulated in the center of the trigonal prism influence intertriangular W-W bonds. The bonding pattern of {W-3} fragments are preserved even in four-electron reduced clusters. The inter-triangular bonding is mainly due to the interactions of two tungsten atoms with the central C or N atom and is associated with the formation of a heteroatomic three-center bond.

First author: Kuda-Singappulige, GU, Geometrical and Electronic Structure, Stability, and Optical Absorption Spectra Comparisons between Thiolate- and Chloride-Stabilized Gold Nanoclusters, JOURNAL OF PHYSICAL CHEMISTRY A, 123, 9712, (2019)
Abstract: Thiolate-stabilized gold nanoclusters have drawn significant attention for their extraordinary properties and their applications in many fields such as catalysis, sensing, biomedicine, etc. However, due to the size, complexity, and conformational flexibility of thiolate ligands, accurate structure prediction can be a challenge using computational approaches. Substitution of thiolate ligands with chloride ligands provides a possible alternative. In this work, the stabilities of a series of gold thiolate and chloride clusters with 1:1 stoichiometry (AunLn; L = SH, Cl; n = 2-9) and the analogs of some experimentally observed gold nanoclusters (AunLn; L = SH, Cl; n = 18-133) are examined, and binding energies, HOMO-LUMO gaps, and absorption spectra are determined using density functional theory (DFT). We observed that the optimized geometries of gold nanoclusters for both types of ligands converged to the same local minimum structure as the experimentally observed structures. The average binding energy per gold atom in gold clusters converges after Au4L4. The binding energies of chloride-stabilized gold clusters and nanoclusters average 87.5% and 95.7% of the binding energies of thiolate-stabilized systems for the clusters and nanoclusters, respectively. Typically, thiolates are found to be more stable than the chlorides. However, higher HOMO-LUMO gaps in Au2Cl2, Au38Cl24, and Au102Cl44 compared to their thiolate analogs suggest systems of particular interest for investigating the possible existence of chloride-based gold nanoclusters. Absorption spectra are very similar regardless of the ligand used. This study also demonstrates that in theoretical studies on large nanoclusters, complex thiolate ligands can be replaced by Cl ligands to predict structural and electronic properties with reasonable accuracy and reduced computational effort.

First author: Joshi, M, Lanthanide and actinide doped B12H122- and Al12H122- clusters: new magnetic superatoms with f-block elements, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 23720, (2019)
Abstract: In recent years, actinide containing clusters have attracted immense attention because of the distinctive bonding properties of their 5f and 6d electrons. In this context, in the present work, we have studied the isoelectronic series of actinide (An = Np+, Pu2+, Am3+) doped B12H122- and Al12H122- clusters using density functional theory (DFT). Similarly, corresponding isoelectronic lanthanide (Ln = Pm+, Sm2+, Eu3+) doped clusters are also investigated using DFT for comparison. Both exohedral and endohedral metal doped Al12H122- clusters are investigated in various possible spin states, whereas for B12H122- only exohedral metal doped clusters are studied due to its smaller cage diameter. Among all the metal doped clusters, the exohedral metal doped B12H122- and Al12H122- clusters in a septet spin state with retained high spin population on the doped actinide ion, are the most stable, indicating that all these doped clusters are magnetic in nature. The high stability of exohedral clusters is due to small steric repulsion as compared to that in the corresponding endohedral clusters. A prominent charge transfer from cage to metal ion is responsible for the strong interaction of the doped metal ion with the cage atoms. The studied Ln@B12H122- (Ln@Al12H122-) and An@B12H122- (An@Al12H122-) clusters are not only thermodynamically stable, but also kinetically stable. Metal ion encapsulated endohedral Al12H122- clusters are found to satisfy the 32-electron principle corresponding to the completely filled s, p, d and f shells of the central f-block atom. Theoretical predictions of these lanthanide and actinide doped stable B12H122- and Al12H122- clusters could encourage experimentalists for the preparation of these metal-doped clusters. Thus, the present work offers borane and alane clusters as new hosts for encapsulating radioactive actinides. Furthermore, various functional derivatives of these actinide doped B12H122- clusters may find applications in the field of radiation medicine.

First author: Huang, G, A supramolecular chain of dimeric Dy single molecule magnets decorated with azobenzene ligands, DALTON TRANSACTIONS, 48, 16053, (2019)
Abstract: We report the synthesis, ab initio calculations, magnetic and optical characterization of a Dy-III-based dimeric compound named DyAZO. The dimers self-organize into a supramolecular chain decorated with photo-isomerizable azobenzene ligands. DyAZO displays single-molecule magnet (SMM) behavior. However, ab initio calculations highlight a quite strong admixture of M-J states of the H-6(15/2) level of Dy-III ions, the presence of low-lying excited M-J states and antiferromagnetic Dy-Dy dipolar coupling. This favors zero-field fast tunneling. Accordingly the Dy-doped analogue YDyAZO (5.5% Dy doping) displays enhanced magnetic relaxation with a hysteresis that is observed at 0.5 K. The influence of the cis- to trans-isomerization of the decorating azobenzene ligand on magnetic properties has been tested for both solid samples and solutions of DyAZO and YDyAZO. This provides hints for the synthesis of future Dy-based photo-isomerizable molecules.

First author: Alkorta, I, Theoretical calculations of the chemical shifts of cyclo[n]phosphazenes for n=2, 3, 4 and 5 (X2PN)(n) with X = CH3, F, Cl and Br: the effect of relativistic corrections, PHOSPHORUS SULFUR AND SILICON AND THE RELATED ELEMENTS, 195, 307, (2020)
Abstract: Di, tri, tetra and pentacyclophosphazenes substituted on the phosphorus atoms by CH3, F, Cl and Br atoms corresponding to (X2PN)(n) structures have been studied theoretically at the B3LYP/6-311++G(d,p) level. After a brief discussion of their geometries comparing them to those of the conjugated carbocycles, (CH)(n), of the same size, the absolute shieldings calculated with the GIAO and ZORA approximations will be reported. For the Cl and mainly for the Br substituted cyclo[n]-phosphazenes, relativistic corrections are absolutely necessary for P-31 and useful for N-15 chemical shifts.

First author: Alam, M, Spectroscopic Identifications, Molecular Docking, Neuronal Growth and Enzyme Inhibitory Activities of Steroidal Nitro Olefin: Quantum Chemical Study, CHEMISTRYSELECT, 4, 12062, (2019)
Abstract: FT-IR, NMR and ultraviolet spectroscopy by means of DFT / B3LYP-6-311G(d, p), molecular docking and biological activity of 6-nitrocolest-5-en-3-beta-yl acetate (steroid nitro-olefin) was reported in this article. The optimized molecular geometric structure and its associated parameters including vibrational frequencies, carbon and H-1 NMR data of the title compound in ground electronic state was obtained at DFT approach applying B3LYP/6-311G(d,p). The ultraviolet absorbance data is obtained at TDB3LYP/6-311G(d,p) basis set. The present computational data are found in reasonable agreement with the experimental results. Simulated electronic and NMR (H-1 and C-13) spectra have been reported in solution phase. Parameters like thermodynamic quantities, dipole moment, FMO energies, MEP and global reactivity descriptors of steroid nitro olefin were determined at same level of theory. The neuromodulatory effect of the compound on central nervous system development of rat embryonic hippocampal neurons has been studied. Based on the outcome; compound demonstrated suppression activity despite the promotion of neuronal cytoarchitecture leading to a negative effect on hippocampal neurons. The nature of the compound found to be toxic to the cells. Besides, steroid compound is also used to perform inhibitory activity against acetylcholinesterase (AChE) compared to the reference drug i. e. Galanthamine. The molecular docking of the synthesized compound is carried out with the structure of the acetylcholinesterase (PDB: 1DX6) protein to check the mode of interactions.

First author: Keil, H, New Insights in the Catalytic Activity of Cobalt Orthophosphate Co-3(PO4)(2) from Charge Density Analysis, CHEMISTRY-A EUROPEAN JOURNAL, 4, 12062, (2019)
Abstract: An extensive characterization of Co-3(PO4)(2) was performed by topological analysis according to Bader’s Quantum Theory of Atoms in Molecules from the experimentally and theoretically determined electron density. This study sheds light on the reactivity of cobalt orthophosphate as a solid-state heterogeneous oxidative-dehydration and -dehydrogenation catalyst. Various faces of the bulk catalyst were identified as possible reactive sites given their topological properties. The charge accumulations and depletions around the two independent five- and sixfold-coordinated cobalt atoms, found in the topological analysis, are correlated to the orientation and population of the d-orbitals. It is shown that the (011) face has the best structural features for catalysis. Fivefold-coordinated ions in close proximity to advantageously oriented vacant coordination sites and electron depletions suit the oxygen lone pairs of the reactant, mainly for chemisorption. This is confirmed both from the multipole refinement as well as from density functional theory calculations. Nearby basic phosphate ions are readily available for C-H activation.

First author: Alkan, F, Understanding plasmon coupling in nanoparticle dimers using molecular orbitals and configuration interaction, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 23065, (2019)
Abstract: We perform a theoretical investigation of the electronic structure and optical properties of atomic nanowire and nanorod dimers using DFT and TDDFT. In both systems at separation distances larger than 0.75 nm, optical spectra show a single feature that resembles the bonding dipole plasmon (BDP) mode. A configuration interaction (CI) analysis shows that the BDP mode arises from constructive coupling of transitions, whereas the destructive coupling does not produce significant oscillator strength for such separation distances. At shorter separation distances, both constructive and destructive coupling produce oscillator strength due to wave-function overlap, which results in multiple features in the calculated spectra. Our analysis shows that a charge-transfer plasmon (CTP) mode arises from destructive coupling of transitions, whereas the BDP results from constructive coupling of the same transitions at shorter separation distances. Furthermore, the coupling elements between these transitions are shown to depend heavily on the amount of exact Hartree-Fock exchange (HFX) in the functional, which affects the splitting of CTP and BDP modes. With 50% HFX or more, the CTP and BDP modes mainly merge into a single feature in the spectra. These findings suggest that the effects of exact exchange must be assessed during the prediction of CTP modes in plasmonic systems.

First author: Narayanan, R, C-13 and Pb-207 NMR Chemical Shifts of Dirhodio- and Dilithioplumbole Complexes: A Quantum Chemical Assessment, INORGANIC CHEMISTRY, 58, 14708, (2019)
Abstract: Density functional theory (DFT) and zeroth-order regular approximation DFT calculations were performed to investigate the electronic structures and C-13 and Pb-207 nuclear magnetic resonance (NMR) chemical shifts of metal-coordinated plumboles, namely, mono-rhodioplumbole ([Rh-plumbole](-)), dirhodioplumbole (Rh-2-plumbole), and dilithioplumbole (Li-2-plumbole), which have a five-membered ring containing lead. The molecular orbital correlation diagram and extended transition state-natural orbitals for chemical valence analysis of the [Rh-plumbole](-) and Rh-2-plumbole complexes showed that the plumbole is primarily a ir-donor, with Jr-donation being dominant in the Rh-2-plumbole complex. The present calculations show that the Pb-C, internuclear distances are longer in the Rh-2-plumbole complex than in [Rh-plumbole](-)because of the combined effect of strong pi-donation and weak pi-back-donation in the Rh-2-plumbole complex. The calculated Pb-207 and C-13(alpha) NMR chemical shifts agree with the experimental trends reasonably well. The influences of the relativistic effect, role of the functional, effect of the solvent, and dependence of the exact exchange admixture on the calculated Pb-207 and C-13(alpha) NMR chemical shifts were investigated. The NMR chemical shift trend of the Pb-207 atom in the complexes originates from the paramagnetic and spin-orbit contributions. NMR component analysis revealed that the upfield shift of the C-13(alpha) atoms of the [Rh-plumbole](-) and Rh-2-plumbole complexes compared to that of the Li-2-plumbole complex is mainly due to the decrease in the paramagnetic term.

First author: Bai, YY, The Structure-Property Correlations in the Isomerism of Au-21(SR)(15) Nanoclusters by Density Functional Theory Study, CHEMISTRY-AN ASIAN JOURNAL, 58, 14708, (2019)
Abstract: Isomerism of atomically precise noble metal nanoclusters provides an excellent platform to investigate the structure-property correlations of metal nanomaterials. In this study, we performed density functional theory (DFT) and time-dependent (TD-DFT) calculations on two Au-21(SR)(15) nanoclusters, one with a hexagonal closed packed core (denoted as Au-21(hcp)), and the other one with a face-centered cubic core (denoted as Au-21(fcc)). The structural and electronic analysis on the typical Au-Au and Au-S bond distances, bond orders, composition of the frontier orbitals and the origin of optical absorptions shed light on the inherent correlations between these two clusters.

First author: Soldatov, MA, Local Atomic and Electronic Structures of beta-Coooh Nanosheets for the Hydrogen-Release Reaction, JOURNAL OF SURFACE INVESTIGATION, 13, 1028, (2019)
Abstract: The geometric and band structures of cobalt-metahydroxide nanosheets, which are related to a new class of two-dimensional nanocatalysts for the hydrogen-release reaction, are calculated. As a result of improving the procedure, the optimal exchange-correlation functionals, basis sets, and dimensions of the “frozen” core are chosen to calculate the atomic and electronic structures, the density of states, and the width of the forbidden band. The calculated results show a decrease in the forbidden band of the cobalt-metahydroxide nanosheets compared with the crystal phase. The X-ray absorption spectra show a high sensitivity of the method to changes in the local atomic environment, especially in the first coordination sphere of cobalt atoms. The calculated model structure makes it possible to determine the features of the local atomic and electronic structures on a cobalt-metahydrixide nanosheet surface during the hydrogen-release reaction.

First author: Sojka, M, Quantum chemical calculations of P-31 NMR chemical shifts of P-donor ligands in platinum(II) complexes, JOURNAL OF MOLECULAR MODELING, 25, 1028, (2019)
Abstract: This work aims to find the most suitable method that is practically applicable for the calculation of P-31 NMR chemical shifts of Pt(II) complexes. The influence of various all-electron and ECP basis sets, DFT functionals, and solvent effects on the optimized geometry was tested. A variety of combinations of DFT functionals BP86, B3LYP, PBE0, TPSSh, CAM-B3LYP, and omega B97XD with all-electron basis sets 6-31G, 6-31G(d), 6-31G(d,p), 6-311G(d,p), and TZVP and ECP basis sets SDD, LanL2DZ, and CEP-31G were used. Chemical shielding constants were then calculated using BP86, PBE0, and B3LYP functionals in combination with the TZ2P basis. The magnitude of spin-orbit interactions was also evaluated.

First author: Zanchi, C, Evaluation of Molecular Polarizability and of Intensity Carrying Modes Contributions in Circular Dichroism Spectroscopies, APPLIED SCIENCES-BASEL, 9, 1028, (2019)
Abstract: We re-examine the theory of electronic and vibrational circular dichroism spectroscopy in terms of the formalism of frequency-dependent molecular polarizabilities. We show the link between Fermi’s gold rule in circular dichroism and the trace of the complex electric dipole-magnetic dipole polarizability. We introduce the C++ code polar to compute the molecular polarizability complex tensors from quantum chemistry outputs, thus simulating straightforwardly UV-visible absorption (UV-Vis)/electronic circular dichroism (ECD) spectra, and infrared (IR)/vibrational circular dichroism (VCD) spectra. We validate the theory and the code by referring to literature data of a large group of chiral molecules, showing the remarkable accuracy of density functional theory (DFT) methods. We anticipate the application of this methodology to the interpretation of vibrational spectra in various measurement conditions, even in presence of metal surfaces with plasmonic properties. Our theoretical developments aim, in the long run, at embedding the quantum-mechanical details of the chiroptical spectroscopic response of a molecule into the simulation of the electromagnetic field distribution at the surface of plasmonic devices. Such simulations are also instrumental to the interpretation of the experimental spectra measured from devices designed to enhance chiroptical interactions by the surface plasmon resonance of metal nanostructures.

First author: Jung, CK, Grand Canonical ReaxFF Molecular Dynamics Simulations for Catalytic Reactions, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 15, 5810, (2019)
Abstract: In order to study the time-dependent behavior of catalytic systems during operation, we have developed a grand canonical molecular dynamics approach based on the ReaxFF reactive force-field framework. After describing the details of the implementation, the capabilities of this method are demonstrated by studying the gas-phase water formation from oxygen and hydrogen on platinum catalysts during the steady state where we discuss the effects of the surface structure as well as the importance of kinetics. The approach presented here can be extended to other dynamic (catalytic) systems, providing a framework for exploring catalytic and electrocatalytic processes, in particular, allowing studies on the effects of reaction conditions on a system’s behavior, characteristics, and stability.

First author: Galvan, IF, OpenMolcas: From Source Code to Insight, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 15, 5925, (2019)
Abstract: In this Article we describe the OpenMolcas environment and invite the computational chemistry community to collaborate. The open-source project already includes a large number of new developments realized during the transition from the commercial MOLCAS product to the open-source platform. The paper initially describes the technical details of the new software development platform. This is followed by brief presentations of many new methods, implementations, and features of the OpenMolcas program suite. These developments include novel wave function methods such as stochastic complete active space self-consistent field, density matrix renormalization group (DMRG) methods, and hybrid multiconfigurational wave function and density functional theory models. Some of these implementations include an array of additional options and functionalities. The paper proceeds and describes developments related to explorations of potential energy surfaces. Here we present methods for the optimization of conical intersections, the simulation of adiabatic and nonadiabatic molecular dynamics, and interfaces to tools for semiclassical and quantum mechanical nuclear dynamics. Furthermore, the Article describes features unique to simulations of spectroscopic and magnetic phenomena such as the exact semiclassical description of the interaction between light and matter, various X-ray processes, magnetic circular dichroism, and properties. Finally, the paper describes a number of built-in and add-on features to support the OpenMolcas platform with postcalculation analysis and visualization, a multiscale simulation option using frozen-density embedding theory, and new electronic and muonic basis sets.

First author: Chen, FY, Role of Intermolecular Interactions in Molecular Packing of Alkoxy-Substituted Bis-1,3,4-oxadiazole Derivatives, CRYSTAL GROWTH & DESIGN, 19, 6100, (2019)
Abstract: The molecular packing, intermolecular interactions, and electron-transporting and photophysical properties of a series symmetrical alkoxy-substituted bis-1,3,4-oxadiazole derivatives (BOXD-o-OCH3, BOXD-m-OCH3, BOXD-D1, and BOXD-T1) are carefully investigated through a combination of experimental techniques and theoretical calculations here. The single-crystal structure analysis reveals that all these single crystals exhibit similar layer structures, while their molecular structures, displacement of the nearest adjacent molecules in pi-stacking, and molecular packing modes are effectively tuned by changing the positions, amounts, or lengths of alkoxy groups in these compounds. Careful analysis of intermolecular interactions demonstrated that pi-pi intermolecular interactions are the main forces in the formation of single crystal and that C-H center dot center dot center dot O intermolecular interactions have a non-negligible contribution in determining the distinguished packing modes of these single crystals. BOXD-o-OCH3-alpha crystal exhibit a maximum calculated electron mobilities value (5.2 cm(2)V(-1)S(-1)) among these selected crystals. The absorption and emission maxima of these single crystals exhibit different redshifts. In addition, these single crystals also exhibit high fluorescence quantum efficiency. Our investigations would not only provide an effective way to tuning crystal packing but also guide the design of materials with excellent performance in a device.

First author: Sliwa, P, Formation of active species from ruthenium alkylidene catalysts-an insight from computational perspective, JOURNAL OF MOLECULAR MODELING, 25, 6100, (2019)
Abstract: Ruthenium alkylidene complexes are commonly used as olefin metathesis catalysts. Initiation of the catalytic process requires formation of a 14-electron active ruthenium species via dissociation of a respective ligand. In the present work, this initiation step has been computationally studied for the Grubbs-type catalysts (H(2)IMes)(PCy3)(Cl)(2)Ru=CHPh, (H(2)IMes)(PCy3)(Cl)(2)Ru=CH-CH=CMe2 and (H(2)IMes)(3-Br-py)(2)(Cl)(2)Ru=CHPh, and the Hoveyda-Grubbs-type catalysts (H(2)IMes)(Cl)(2)Ru=CH(o-OiPrC(6)H(4)), (H(2)IMes)(Cl)(2)Ru=CH(5-NO2-2-OiPrC(6)H(3)), and (H(2)IMes)(Cl)(2)Ru=CH(2-OiPr-3-PhC6H3), using density functional theory (DFT). Additionally, the extended-transition-state combined with the natural orbitals for the chemical valence (ETS-NOCV) and the interacting quantum atoms (IQA) energy decomposition methods were applied. The computationally determined activity order within both families of the catalysts and the activation parameters are in agreement with reported experimental data. The significance of solvent simulation and the basis set superposition error (BSSE) correction is discussed. ETS-NOCV demonstrates that the bond between the dissociating ligand and the Ru-based fragment is largely ionic followed by the charge delocalizations: sigma(Ru-P) and pi(Ru-P) and the secondary (CHCl)-Cl- horizontal ellipsis , CH horizontal ellipsis pi, and (CHHC)-H- horizontal ellipsis interactions. In the case of transition state structures, the majority of stabilization stems from London dispersion forces exerted by the efficient (CHCl)-Cl- horizontal ellipsis , CH horizontal ellipsis pi, and (CHHC)-H- horizontal ellipsis interactions. Interestingly, the height of the electronic dissociation barriers is, however, directly connected with the prevalent (unfavourable) changes in the electrostatic and orbital interaction contributions despite the favourable relief in Pauli repulsion and geometry reorganization terms during the activation process. According to the IQA results, the isopropoxy group in the Hoveyda-Grubbs-type catalysts is an efficient donor of intra-molecular interactions which are important for the activity of these catalysts.

First author: Zhang, ZH, Interactions of phosphorylated cyclohexapeptides with uranyl: insights from experiments and theoretical calculations, JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY, 322, 677, (2019)
Abstract: Two phosphorylated cyclohexapeptides (CPs) bearing one (CP1) or two phosphates (CP2) were synthesized to explore the interactions between uranyl ions and very small cyclic peptides. According to the results of the ESI-MS and fluorescence titrations, the 1:1 uranyl-CPs complexes are the main products with the affinity constants of 7.3 x 10(4) and 2.0 x 10(5) for CP1 and CP2, respectively. Density functional theory calculations indicate phosphoryl and carboxyl groups coordinate uranyl in mono-dentate and bi-dentate fashions due to steric effects, which is consistent with the results of extended X-ray absorption fine structure spectroscopy.

First author: Xu, Y, LCOFs: Role of the excited state hydrogen bonding in the detection for nitro-explosives, JOURNAL OF LUMINESCENCE, 215, 677, (2019)
Abstract: It is of important theoretical significance to research the mechanism of luminescent covalent organic frameworks (LCOFs) for detecting nitro-explosives. The interaction between LCOF-BTT1 and nitrobenzene has been investigated by DFT and TDDFT methods. By studying electronic configurations and frontier molecular orbitals, the luminescence mechanism of LCOF-BTT1 has changed due to the hydrogen bonding formed between LCOF-BTT1 and nitrobenzene (Complex 1). Further study of electronic transition energies, hydrogen bond lengths, H-1 NMR and IR spectra of Complex 1 reveals that hydrogen bonding is stronger in the excited state than in the ground state, indicating fluorescence quenching. Furthermore, the fluorescence rate coefficient and the internal conversion rate coefficient of Complex 1 are correspondingly decreased and increased, indicating that the increase in the strength of hydrogen bonding in the excited state is beneficial to the non-radiative transition and is not conducive to the radiation transition.

First author: Alkorta, I, Theoretical study of some lambda(5)-phosphinines and their NMR spectra, MAGNETIC RESONANCE IN CHEMISTRY, 57, 975, (2019)
Abstract: It is of important theoretical significance to research the mechanism of luminescent covalent organic frameworks (LCOFs) for detecting nitro-explosives. The interaction between LCOF-BTT1 and nitrobenzene has been investigated by DFT and TDDFT methods. By studying electronic configurations and frontier molecular orbitals, the luminescence mechanism of LCOF-BTT1 has changed due to the hydrogen bonding formed between LCOF-BTT1 and nitrobenzene (Complex 1). Further study of electronic transition energies, hydrogen bond lengths, H-1 NMR and IR spectra of Complex 1 reveals that hydrogen bonding is stronger in the excited state than in the ground state, indicating fluorescence quenching. Furthermore, the fluorescence rate coefficient and the internal conversion rate coefficient of Complex 1 are correspondingly decreased and increased, indicating that the increase in the strength of hydrogen bonding in the excited state is beneficial to the non-radiative transition and is not conducive to the radiation transition.

First author: Rodriguez-Jimenez, JA, Computational study of GanAsm (m plus n=2-9) clusters using DFT calculations, JOURNAL OF NANOPARTICLE RESEARCH, 21, 975, (2019)
Abstract: Gallium arsenide is a semiconductor compound with well-known properties in its bulk phase. Theoretical works explain some of the properties of this material at a cluster scale; nevertheless, more research is required to fully understand these systems. In this work, we used the density functional theory (DFT) formalism, specifically the PBE functional and the TZ2P basis set for the study of structural, electronic, and chemical properties of GanAsm (m + n = 2-9) clusters in the gas phase, for all possible compositions. Our study reveals that the structural and electronic properties in GanAsm clusters present a size and composition dependence, with a size range within 3-10 angstrom. Even/odd behavior is observed in most electronic and chemical properties of the clusters. The even/odd behavior is related to the electronic close shell structure of the system. It is found that the predominance of arsenic atoms in the GanAsm clusters generate comparatively more stable molecules, with lower binding energies per atom, higher hardness values, ionization potentials, and Gap(HOMO-LUMO).

First author: Wilson, TR, Quantum theory of atoms in molecules in condensed charge density space, CANADIAN JOURNAL OF CHEMISTRY, 97, 757, (2019)
Abstract: By leveraging the fundamental doctrine of the quantum theory of atoms in molecules – the partitioning of the electron charge density (rho) into regions bounded by surfaces of zero flux- we map the gradient field of rho onto a two-dimensional space called the gradient bundle condensed charge density (P). The topology of P appears to correlate with regions of chemical significance in rho. The bond wedge is defined as the image in rho of the basin of attraction in P, analogous to the Bader atom, which is the basin of attraction in rho. A bond bundle is defined as the union of bond wedges that share interatomic surfaces. We show that maxima in P typically map to bond paths in rho, though this is not necessarily always true. This observation addresses many of the concerns regarding the chemical significance of bond critical points and bond paths in the quantum theory of atoms in molecules.

First author: Kepenekian, M, Red-NIR luminescence of Mo-6 monolayered assembly directly anchored on Au(001), MATERIALS HORIZONS, 6, 1828, (2019)
Abstract: A tailored near infrared luminescent Mo-6 octahedral cluster bearing thiocyanate (NCS) terminal ligands, [Mo6Br8i(NCS)(6)(a)](2-), has been synthesized to anchor onto a gold substrate. After immobilization, [Mo6Br8i(NCS)(6)(a)](2-) building blocks form a self-assembled monolayer on the Au(001) surface as shown by scanning tunneling microscopy, atomic force microscopy and X-ray photoelectron spectroscopy. Strikingly, the photoluminescence of [Mo6Br8i(NCS)(6)(a)](2-) observed in the powder precursor remains after grafting on Au(001). No quenching effect was observed despite the vicinity of the flat metal surface unlike most of the molecular luminophors. Periodic and molecular computational investigations based on density functional theory show that optical properties originate from the Mo6Br8i core and are protected by the NCS outer sphere, despite the shortness of the anchors.

First author: Laziz, D, Synthesis, structural characterization, DFT calculations and biological properties of mono- and dinuclear nickel complexes with tetradentate transformed ligands by aerobic oxidative-coupling reactions, INORGANICA CHIMICA ACTA, 497, 1828, (2019)
Abstract: Reaction of nickel chloride with acetylacetone bis(salicylhydrazone) (L) (prepared in situ by condensation of acetylacetone with salicylhydrazide) in methanol results in the formation of air-sensitive nickel (II) complex of symmetrical tetradentate Schiff base [Ni-II(L)] (1). Air oxidation of 1 leads to the formation of dinuclear species [Ni-II(L-L)Ni-II] (2) where the ligand (L-L)(4-) is formed by oxidative C-C coupling at the central methylene group of the acetylacetone fragment of (L)(2-). The same reaction in methanol/pyridine solution leads to oxidative C-N coupling forming a mesoionic [Ni-II(L-Py)](3). The use of Nickel acetylacetonate in methanol/pyridine or DMSO solution under aerobic conditions provide [Ni-II(L-O)(py)(2)](4), [Ni-II(L-O)(DMSO)(2)](5). In this case, the ligand (L)(2-) is partially oxidized to form (L-O) which is formed by oxidation of the central methylene group. The molecular structure of 1-5 have been determined by X-ray crystallography. The first three complexes 1, 2 and 3 have a square-planar geometry, while, 4 and 5 adopt octahedral geometry. In vitro antioxidant activities of compounds 1, 4 and 5 were evaluated against DPPH radical and hydrogen peroxide and were compared with standard antioxidant, ascorbic acid. Our results reveal that the three compounds exhibit excellent radical scavenging activities. DFT calculations have been performed on complexes 1-5 using the BP86 and B3LYP functionals to provide a complete rationalization of their structures and to describe their electronic structures elucidating the fundamental spin state and the Metal-Ligand interaction type.

First author: Dheepika, R, Solution-Processable Unsymmetrical Triarylamines: Towards High Mobility and ON/OFF Ratio in Bottom-Gated OFETs, CHEMISTRY-A EUROPEAN JOURNAL, 25, 15155, (2019)
Abstract: Self-assembly of organic small molecules into an ordered thin film has been the key strategy towards efficient charge transport for organic field-effect transistors (OFETs). Solution processing is a feasible and economic way to enhance pi-pi interaction. Herein, nitrile-substituted unsymmetrical triarylamines for OFET applications with high mobility are reported. The compounds were constructed by Suzuki cross-coupling reactions under inert conditions. The HOMO level of about 5.3 eV indicates good hole-transporting ability. OFETs were assembled in bottom-gate, top-contact architecture. Devices fabricated from a binary solvent system exhibited excellent p-channel characteristics, with impressively high charge-carrier mobility of up to 2.58 cm(2) V-1 s(-1) and I-ON/OFF current ratios of 10(6)-10(7). SEM and AFM analysis showed the efficient molecular self-assembly attained by the simple and effective solvent-engineering method. Theoretical insights obtained by DFT calculations supported by single-crystal structures showed that the crystalline nature and packing modes of these compounds ensure high mobility. The results prove that these compounds have great potential for use in numerous electronic applications, such as sensors and logic switches.

First author: Zarate, X, DFT/MRCI assessment of the excited-state interplay in a coumarin-schiff Mg2+ fluorescent sensor, JOURNAL OF COMPUTATIONAL CHEMISTRY, 41, 136, (2020)
Abstract: Fluorescent sensors with selectivity and sensitivity to metal ions are an active field in supramolecular chemistry for biochemical, analytical, and environmental problems. Mg2+ is one of the most abundant divalent ions in the cell, and it plays a critical role in many biological processes. Coumarin-based sensors are widely used as desirable fluorophore and binding moieties showing a remarkable sensitivity and fluorometric enhancement for Mg2+. In this work, density functional theory/multireference configuration interaction (DFT/MRCI) calculations were performed in order to understand the sensing behavior of the organic fluorescent sensor 7-hydroxy-4-methyl-8-((2-(pyridin-2-yl)hydrazono)methyl)-2H-chromen-2-one (PyHC) in ethanol to solvated Mg2+ ions. The computed optical properties reproduce well-reported experimental data. Our results suggest that after photoexcitation of the free PyHC, a photo-induced electron transfer (PET) mechanism may compete with the fluorescence decay to the ground state. In contrast, this PET channel is no longer available in the complex with Mg2+ making the emissive decay more efficient.

First author: Boughlala, Z, Alkali Metal Cation Affinities of Neutral Maingroup-Element Hydrides across the Periodic Table, JOURNAL OF PHYSICAL CHEMISTRY A, 123, 9137, (2019)
Abstract: We have carried out an extensive quantum chemical exploration of gas-phase alkali metal cation affinities (AMCAs) of archetypal neutral bases across the periodic system using relativistic density functional theory. One objective of this work is to provide an intrinsically consistent set of values of the 298 K AMCAs of all neutral maingroup-element hydrides XHn of groups 15-18 along the periods 1-6. Our main purpose is to understand these trends in terms of the underlying bonding mechanism using Kohn-Sham molecular orbital theory together with a canonical energy decomposition analysis (EDA). We compare the trends in XHn AMCAs with the trends in XHn, proton affinities (PAs). We also examine the differences between the trends in AMCAs of the neutral XHn bases with those in the corresponding anionic XHn-1- bases. Furthermore, we analyze how the cation affinity of our neutral Lewis bases changes along the group-1 cations H+, Li+, Na+, K+, Rb+, and Cs+.

First author: Niu, XH, Two-Dimensional Phosphorene, Arsenene, and Antimonene Quantum Dots: Anomalous Size-Dependent Behaviors of Optical Properties, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 25775, (2019)
Abstract: Employing size effect to tailor photoabsorption and photoemission properties of quantum dot (QD) nanostructures is a widely used method for optoelectronic and biomedical applications. In this work, based on time-dependent density functional theory calculations, we systematically research the size-dependent optical absorption and emission properties of two-dimensional phosphorene, arsenene, and antimonene single-element QDs. As expected, the photoabsorption gap is monotonically decreasing with the increase of QD diameter, which is consistent with the well-accepted quantum confinement effect (QCE). Surprisingly, the emission gap increases with the increase of size within similar to 3 nm diameter range. It is revealed that the anomalous phenomenon is derived from the competition between the QCE and excited-state structural rearrangement during the relaxation of the excited state. The smaller two-dimensional QDs is more prone to structural deformation at the excited state accompanied by the greater change of the electronic structure, which prevails over the QCE and reduces the emission gap. The atomic level picture of the anomalous emission phenomenon revealed in our research is valuable for the fundamental understanding of the size effect of QDs as well as for their optical utilization in optoelectronics and biomedical fields.

First author: Fornari, RP, Unexpectedly Large Couplings Between Orthogonal Units in Anthraquinone Polymers, CHEMISTRY-A EUROPEAN JOURNAL, 25, 14651, (2019)
Abstract: The unusual electronic properties of directly linked 1,4-polyanthraquinones (14PAQs) are investigated. The dihedral angle between the molecular planes of anthraquinones (AQs) is found to be close to 90 degrees. Contrary to the prevailing notion that the interaction between orthogonal units is negligible due to broken pi-electron conjugation, the coupling between neighboring AQ units does not have a minimum at 90 degrees and is much larger than that expected. The unexpectedly large electronic coupling between orthogonal AQ units is explained by the interaction between the lone pairs of the carbonyl oxygen and the pi system of the neighboring unit, which allows favorable overlap between frontier molecular orbitals at the orthogonal geometry. It is shown that this effect, which is described computationally for the first time, can be strengthened by adding more quinone units. The effect of thermal fluctuations on the couplings is assessed through ab initio molecular dynamics simulations. The distributions of the couplings reveal that electron transport is resilient to dynamic disorder in all systems considered, whereas the hole couplings are much more sensitive to disorder. Lone pair-pi interactions are described, as a previously largely overlooked conjugation mechanism, for incorporation into a new class of disorder-resilient semiconducting redox polymers.

First author: Quintana, CG, Nature of mercury inclusion in intermediate 6-valence electron [M@Au8Hgx(PPh3)(8)](n+) (M = Au, Pd, Pt; x=0-2) protected gold superatoms: Insights from relativistic density functional theory calculations, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 25, 14651, (2019)
Abstract: Superatomic clusters offer useful templates displaying distinctive physical and chemical characteristics. Here, we explore the [M@Au-8(PPh3)(8)](n+) (M = Au, n = 3; Pd, Pt, n = 2) robust framework to gain an understanding of the nature of the inclusion of mercury atoms at Au-4 faces, leading to [M@Au8Hgx(PPh3)(8)](n+) (x = 1, 2). Our results show a weak interaction of about 25kcalmol(-1) per Hg atom, which is mainly of electrostatic character, followed by orbital and London dispersion-type interactions. This weak interaction can be understood as the formation of host-guest species, for which the inherent electronic and optical properties of the [M@Au-8(PPh3)(8)] cluster along the series do not vary to a large extent. This demonstrates that, in [M@Au8Hgx(PPh3)(8)], each Hg can be considered an inclusion atom rather than a dopant element, where the parent cluster is able to act as a Lewis acid host. Furthermore, the viable formation of such species can serve as useful examples to stimulate future experimental characterization of inclusion complexes involving related superatomic structures with available open faces.

First author: Du, WGH, DFT Fe-a3-O/O-O Vibrational Frequency Calculations over Catalytic Reaction Cycle States in the Dinuclear Center of Cytochrome c Oxidase, INORGANIC CHEMISTRY, 58, 13933, (2019)
Abstract: Density functional vibrational frequency calculations have been performed on eight geometry optimized cytochrome c oxidase (CcO) dinuclear center (DNC) reaction cycle intermediates and on the oxymyoglobin (oxyMb) active site. The calculated Fe-O and O-O stretching modes and their frequency shifts along the reaction cycle have been compared with the available resonance Raman (rR) measurements. The calculations support the proposal that in state A[Fe-a3(3+)-O-2(-center dot)center dot center dot center dot Cu-B(+)] of CcO, O-2 binds with Fe-a3(2+) in a similar bent end-on geometry to that in oxyMb. The calculations show that the observed 20 cm(-1) shift of the Fe-a3-O stretching mode from the P-R to F state is caused by the protonation of the OH- ligand on Cu-B(2+) (P-R[Fe-a3(4+)=O2-center dot center dot center dot HO–Cu-B(2+)] -> F[Fe-a3(4+)=O2-center dot center dot center dot H2O-Cu-B(2+)), and that the H2O ligand is still on the Cu-B(2+) site in the rR identified F[Fe-a3(4+)=O2-center dot center dot center dot H2O-Cu-B(2+)] state. Further, the observed rR band at 356 cm(-1) between states P-R and F is likely an O-Fe-a3-porphyrin bending mode. The observed 450 cm(-1) low Fe-a3-O frequency mode for the O-H active oxidized state has been reproduced by our calculations on a nearly symmetrically bridged Fe-a3(3+)-OH-Cu-B(2+) structure with a relatively long Fea3-O distance near 2 angstrom. Based on Badger’s rule, the calculated Fe-a3-O distances correlate well with the calculated nu(-2.3)(Fe-O) (nu(Fe-O) is the Fe-a3-O stretching frequency) with correlation coefficient R = 0.973.

First author: Ramanantoanina, H, Theoretical insight into the magnetic circular dichroism of uranium N-6,N-7-edge X-ray absorption, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 120, 13933, (2020)
Abstract: We use ligand-field density functional theory to determine the electronic structure and to model magnetic circular dichroism in the X-ray absorption spectroscopy (XAS) of uranium compounds. This study extends earlier work on tetravalent uranium ion, in which a model Hamiltonian was set up in order to study electronic structure with three nonequivalent 4f, 5f, and 6d electrons. In the earlier work, the model Hamiltonian took into consideration the interelectron repulsion, spin-orbit coupling interaction, and ligand-field splitting. Uranium N-6,N-7-edge XAS spectra were calculated on the basis of the 5f(2) -> 4f(13)5f(2)6d(1) electron transition, showing spectral profiles that were mainly dominated by 4f electron spin-orbit coupling, as well as 6d ligand-field splitting. Fine structures were also observed due to the interelectronic repulsion between 4f-5f, 4f-6d, and 5f-6d electrons. Here, the theoretical study is extended to take into consideration the presence of an external magnetic field, incorporating into the model Hamiltonian for three-open-shell electron configuration a term for Zeeman interaction. Therefore, we are able to model spectra with a left-circularly and right-circularly polarized X-ray, demonstrating evidence of X-ray magnetic circular dichroism (XMCD) for a tetravalent U4+ ion in the molecular (U(eta(8)-C8H8)(2)) complex. The XMCD originates from a ground-state electronic structure with open-shell 5f electrons. Furthermore, the present calculation of uranium N-6,N-7-edge XAS and XMCD spectra also enables the ligand-field bonding analysis of the coordination compound.

First author: Liu, XR, Promising hole-transporting materials for perovskite solar cells: Modulation of the electron-deficient units in triphenylamine derivative-based molecules, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 120, 13933, (2020)
Abstract: Modulation of the electron-deficient pi-bridge units in 4-methoxy-N-(4-methoxyphenyl)-N-phenylbenzenamine (MeTPA)-based hole-transporting materials (HTMs) is a significant approach to improve hole mobility of HTMs for perovskite solar cells (PSCs). In this study, a class of simple MeTPA-based HTMs (H1-H4) with different pi-bridged electron-deficient units were designed for the purpose of providing a theoretical model to obtain potential MeTPA-based HTMs. The results indicated that H2 to H4 exhibit better performance, such as larger Stokes shifts, smaller exciton-binding energy, better stability, good solubility, and higher hole mobility, in comparison with the parental material H1. H2 to H4 materials with high hole mobility (5.45 x 10(-4), 2.70 x 10(-1), and 3.99 x 10(-3) cm(2) V-1 second(-1), respectively) may embody promising HTMs to yield good performance in PSCs. Therefore, the useful information obtained regarding control of the electron-deficient pi-bridge units of MeTPA-based HTMs is an effective way to obtain excellent HTMs for PSC applications.

First author: Nagurniak, GR, Double-bond elucidation for arsagermene with a tricoordinate germanium center: a theoretical survey, NEW JOURNAL OF CHEMISTRY, 43, 15681, (2019)
Abstract: Multiple-bonded heteronuclear combinations have recently received great attention because of the first experimental arsagermene (>Ge=As-) synthesis, which is a relevant topic in organometallic chemistry. However, a systematic elucidation of the Ge=As bond still remains necessary. Here, we report a computational investigation, based on second order Moller-Plesset perturbation theory and density functional theory calculations, of arsagermene with a tricoordinate germanium center, to understand the >Ge=As- double bond and the influence of the substituents on the stabilization process. We considered a diversified set of R2GeAsR compounds to understand the nature and magnitude of the arsagermene bond. Geometrically we have obtained an excellent agreement with experimental results, where the Ge=As bond is confirmed to be a double bond, with a theoretical underestimation of 0.05 angstrom in the bond length. After a complete characterization of the substituents, we obtain that they influence the Ge=As formation, mainly through a push-and-pull effect, which comes mainly from the R groups bonded to the Ge species. From the studied topological parameters, a large strength is obtained for the Ge=As bond with electron density accumulation, considering electronegative R groups (e.g., halogens), as well as lone pair groups (hydroxy, methoxy, and amine groups). Finally, from the energy decomposition analysis, we obtained a type of interaction-model and the nature of the Ge=As bond for all compounds, especially for (H3Si)(2)GeAsPh, which is our model of the synthesized arsagermene compound. The >Ge=As- bond was characterized with 52.86% orbital contribution, 44.19% electrostatic interaction, and 2.95% dispersive contribution. The other compounds followed the same trend, helping to complete the picture for the double-bond elucidation for arsagermene.

First author: Alemayehu, AB, Unexpected Molecular Structure of a Putative Rhenium-Dioxo-Benzocarbaporphyrin Complex. Implications for the Highest Transition Metal Valence in a Porphyrin-Type Ligand Environment, CHEMISTRYOPEN, 8, 1298, (2019)
Abstract: A combination of quantum chemical calculations and synthetic studies was used to address the possibility of very high (>6) valence states of transition metals in porphyrin-type complexes. With corrole as a supporting ligand, DFT calculations ruled out Re(VII) and Ir(VII) dioxo complexes as stable species. Attempted rhenium insertion into benzocarbaporphyrin (BCP) ligands on the other hand led to two products with different stoichiometries – Re[BCP]O and Re[BCP]O-2. To our surprise, single-crystal structure determination of one of the complexes of the latter type indicated an (ReO)-O-V center with a second oxygen bridging the Re-C bond. In other words, although the monooxo complexes Re[BCP]O are oxophilic, the BCP ligand cannot sustain a trans-Re-VII(O)(2) center. The search for metal valence states >6 in porphyrin-type ligand environments must therefore continue.

First author: Ungordu, A, Charge transfer properties of Gaq3 and its derivatives: An OLED study, CHEMICAL PHYSICS LETTERS, 733, 1298, (2019)
Abstract: Tris(8-hydroxyquinoline) gallium (Gaq3) is an alternative compound to tris(8-hydroxyquinoline) aluminum (Alq3) which is an organic light emitting diode (OLED) material. The performance of Gaq3 incorporated into OLEDs has been seen to be superior compared to that of Alq3-based ones but the OLED properties of a substituted Gaq3 complex has been not studied yet. For this reason, the OLED performances of Gaq3 and its derivatives were investigated theoretically. Gaq3, functionalized Gaq3 derivatives and their dimers were designed. While monomer calculations were performed on the B3LYP/6-31G(d) level, dimer computations were carried out on the B3LYP/TZP level. The reorganization energies (lambda e and lambda h), ionization potentials and electron affinities (adiabatic and vertical), energy gaps, effective transfer integrals (Je and Jh) and charge transfer rates (Ke and Kh) of the aforementioned molecules were calculated. Based on these parameters, the OLED behaviors of the compounds were estimated.

First author: Lu, YX, 2Ch-2N square and hexagon interactions: a combined crystallographic data analysis and computational study, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 21568, (2019)
Abstract: In recent years, chalcogen bonding (ChB), a typical sigma-hole interaction, has shown great potential as a bottom-up design approach for specific applications. According to our survey of the Cambridge Structural Database (CSD), a large number of crystal structures containing 2Ch-2N square and hexagon interaction motifs were extracted. On the basis of the CSD search results, the 2Ch-2N square interactions in the dimers of 2,1,3-benzochalcogenadiazole 1 and 2,1,3-pyridochalcogenadiazole 2, together with 2Ch-2N hexagon interactions in the dimers of chalcogenazolo-pyridine 3 and triazolo-chalcogenadiazole 4, were firstly studied. Then, substituent effects on these peculiar interactions were thoroughly examined by introducing a diversity of small, non-aromatic substituents at the 4,7-positions of the 1S scaffold and various aryl substituents at the 2-position of the 3Te scaffold. Our calculations showed that the major contribution to the attraction of such bidentate ChB interactions is electrostatics, while the orbital term also plays an important role. Some strong electron-withdrawing substituents, such as NO2, CN, and CF3, tend to enhance square ChB interactions, while C6F5 and CF3 substituents with a strong electron-withdrawing ability strengthen hexagon ChB interactions. Particularly, a good linear correlation has been established between the binding energies of the dimers under study and both the surface electrostatic potential (ESP) maxima for the Ch sigma-holes and the minimum surface ESP of the N atoms, which provides reasonable models to evaluate these interactions. The results reported in this work will provide design guidance for the applications of 2Ch-2N cyclic motifs in materials science and biochemistry.

First author: Shi, RY, Functional Models of the Nickel Pincer Nucleotide Cofactor of Lactate Racemase, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 58, 16869, (2019)
Abstract: A novel nickel pincer cofactor was recently discovered in lactate racemase. Reported here are three synthetic nickel pincer complexes that are both structural and functional models of the pincer cofactor in lactate racemase. DFT computations suggest the ipso-carbon atom of the pyridinium pincer ligands act as a hydride acceptor for lactate isomerization, whereas an organometallic pathway involving nickel-mediated beta-hydride elimination is less favored.

First author: Koca, B, Exploring the Photophysics of Polyfluorinated Phthalocyanine Derivatives as Potential Theranostic Agents, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 24417, (2019)
Abstract: State-of-the-art computational tools were used to investigate the photophysical properties of polyfluorinated phthalocyanines (Pc) to predict their potential use as photo sensitizers in photodynamic therapy. The main factors, such as the identity of the metal ion, the effect of substituents, the environment, and solvent effects that enhance the efficiency of phthalocyanines as photosensitizers, were considered, particularly taking into account their influence on the triplet-state energy and intersystem crossing probability. The population of the triplet state ultimately determines the phthalocyanine’s propensity to activate singlet oxygen, which is responsible for inducing death of the cancer cell. Time-dependent density functional theory was used to elucidate the photophysical properties of pentafluorobenzyloxy-substituted phthalocyanines (R2Pc) as well as their unsubstituted analogues. Vibrational and dynamic effects influencing the absorption and emission spectra were included by sampling the potential energy surfaces via the Wigner distribution approach. Furthermore, the intersystem crossing pathways were analyzed by using the singlet-triplet band gap and the spin-orbit coupling constant. Finally, the singlet oxygen generation capability was experimentally verified for the R-2-ZnPc complex both in DMSO and in different ratios of DMSO/water mixtures. The singlet oxygen quantum yield of R-2-ZnPc in DMSO was also evaluated and compared with that of the unsubstituted ZnPc.

First author: Li, Y, Theoretical study on the excited state decay properties of iron(ii) polypyridine complexes substituted by bromine and chlorine, RSC ADVANCES, 9, 31621, (2019)
Abstract: Transition metal iron(ii) polypyridyl complexes with quintet ground states were deeply investigated by density functional theory (DFT) and time-dependent density functional theory (TDDFT). Compared with the parent complex [Fe(tpy)(2)](2+) (tpy = 2,2 ‘:6 ‘,2 ”-terpyridine), the ground states of the complexes substituted by halogen atoms changed from singlet states to quintet states with rare high spin excited state lifetimes. The substituted complex [Fe(dbtpy)(2)](2+) (1) results in a high spin metal-ligand charge transfer lifetime of 17.4 ps, which is 1.4 ps longer than that of [Fe(dctpy)(2)](2+) (2) with the substitution of chlorine atoms. The reason for this is explored by a combination of electronic structures, absorption spectra, extended transition state coupled with natural orbitals for chemical valence (ETS-NOCV) studies and potential energy curves (PECs). The distortion of 1 in the angles and dihedrals of the ligands is slightly larger than that in 2, although the average metal-ligand bond lengths of the latter are larger. The twisted octahedron decreases the interactions between the d orbitals of iron(ii) and the n/pi orbitals of the ligands. Compared with 2, the enlarged energy gaps among the different PECs of 1 and the increased energy crossing points caused by the larger distortion result in the increase of its excited state lifetime. The different pairwise orbital interaction contributions between the metal center and the ligands in their singlet states are qualitatively estimated by ETS-NOCV. The results show that the substitution of bromine atoms will decrease the electrostatic attraction between the metal and ligands but not significantly impact the orbital interactions.

First author: Schulz, A, Description of intermolecular charge transfer with subsystem density-functional theory, JOURNAL OF CHEMICAL PHYSICS, 151, 31621, (2019)
Abstract: Efficient quantum-chemical methods that are able to describe intermolecular charge transfer are crucial for modeling organic semiconductors. However, the correct description of intermolecular charge transfer with density-functional theory (DFT) is hampered by the fractional charge error of approximate exchange-correlation (xc) functionals. Here, we investigate the charge transfer induced by an external electric field in a tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) complex as a test case. For this seemingly simple model system, a supermolecular DFT treatment fails with most conventional xc functionals. Here, we present an extension of subsystem DFT to subsystems with a fractional number of electrons. We show that within such a framework, it becomes possible to overcome the fractional charge error by enforcing the correct dependence of each subsystem’s total energy on the subsystem’s fractional charge. Such a subsystem DFT approach allows for a correct description of the intermolecular charge transfer in the TTF-TCNQ model complex. The approach presented here can be generalized to larger molecular aggregates and will thus allow for modeling organic semiconductor materials accurately and efficiently.

First author: Yoshimura, T, Synthesis, structures, redox properties, and theoretical calculations of thiohalide capped octahedral hexanuclear technetium(iii) clusters, DALTON TRANSACTIONS, 48, 14085, (2019)
Abstract: The first thiohalide mu(3)-capped octahedral hexanuclear technetium clusters with 24 valence electrons, [Tc-6(mu(3)-S)(8-n)(mu(3)-Br)(n)Br-6](n-4) [n = 1 ([Tc-S7Br](3-)) and n = 2 ([Tc-S6Br2](2-))] and [Tc-6(mu(3)-S)(7)(mu(3)-Cl)Cl-6](3-) ([Tc-S7Cl](3-)), were synthesized and characterized. The structures of [Tc-S7Br](3-), [Tc-S6Br2](2-), and [Tc-S7Cl](3-) were determined by single-crystal X-ray analysis. The Tc-Tc bond distances in [Tc-S7Br](3-), [Tc-S6Br2](2-), and [Tc-S7Cl](3-) are 2.5842(6)-2.6029(6) angstrom (avg. 2.593(2) angstrom), 2.5835(10)-2.6049(10) angstrom (avg. 2.596(1) angstrom), and 2.5829(4)-2.5940(4) angstrom (avg. 2.587(3) angstrom), respectively. The capping halide and sulfide ligands in [Tc-S7Br](3-), [Tc-S6Br2](2-), and [Tc-S7Cl](3-) were disordered in the crystals. The bond distances of Tc-S/Br as a function of the occupancies of the capping bromides for [Tc-S6Br2](2-), [Tc-S7Br](3-), and [Tc-6(mu(3)-S)(8)Br-6](4-) ([Tc-S-8](4-)) showed a linear correlation. The one-electron reduction waves assignable to the TcIII6/Tc(II)TcIII5 [Tc-6(24e/25e)] process were observed for the novel complexes. Density functional theory (DFT) calculations of the hexanuclear technetium complexes showed a smaller energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the hexanuclear technetium complexes compared to those of the rhenium analogues. The electronic transitions of the new technetium complexes shifted to lower energy compared to the isotypic rhenium complexes.

First author: Lehtola, S, A review on non-relativistic, fully numerical electronic structure calculations on atoms and diatomic molecules, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 119, 14085, (2019)
Abstract: The need for accurate calculations on atoms and diatomic molecules is motivated by the opportunities and challenges of such studies. The most commonly used approach for all-electron electronic structure calculations in general-the linear combination of atomic orbitals (LCAO) method-is discussed in combination with Gaussian, Slater a.k.a. exponential, and numerical radial functions. Even though LCAO calculations have major benefits, their shortcomings motivate the need for fully numerical approaches based on, for example, finite differences, finite elements, or the discrete variable representation, which are also briefly introduced. Applications of fully numerical approaches for general molecules are briefly reviewed, and their challenges are discussed. It is pointed out that the high level of symmetry present in atoms and diatomic molecules can be exploited to fashion more efficient fully numerical approaches for these special cases, after which it is possible to routinely perform all-electron Hartree-Fock and density functional calculations directly at the basis set limit on such systems. Applications of fully numerical approaches to calculations on atoms as well as diatomic molecules are reviewed. Finally, a summary and outlook is given.

First author: Kostin, GA, Ruthenium nitrosyl complexes [RuNOL2(NO2)(2)OH] with ethyl isonicotinate and pyrazine: Synthesis, structure and formation of metastable linkage isomers, JOURNAL OF MOLECULAR STRUCTURE, 1193, 334, (2019)
Abstract: New complexes of ruthenium nitrosyl with ethyl isonicotinate and pyrazine were prepared in the reaction of [RuNO(NO2)(2)(H2O)(3)](+) with corresponding ligands. With the ligand excess the reaction results in cis-[RuNOL2(NO2)(2)OH] with good yields (78% for I L = inicEt, 35% for II L = Pyz). The dimeric complex [(RuNO(Pyz)(NO2)(mu-NO2))(2)mu-O] (III) forms in a small yield when less than 2 molar equivalents of pyrazine are taken for the reaction. Crystal structures of all three complexes were determined by single crystal XRD. Upon blue light irradiation complexes I and II undergo isomerization from Ru-NO (ground state, GS) to Ru-ON (metastable state, MS1) group. Reverse thermal transformation MS1 – GS was studied by IR and DSC techniques, activation parameters of MS1 – GS transition are: I – E-a = 53.4(4.0) kJ mol(-1), lg k(0) = 10.6(4); II – E-a = 58.9(4.3) kJ mol(-1), lg( )k(0) = 13.5(0.4).

First author: Douara, B, Experimental and theoretical study of quinoline derivatives obtained by slight modifications of the standard skraup reaction, JOURNAL OF MOLECULAR STRUCTURE, 1193, 416, (2019)
Abstract: In order to explore the role of glycerol in the Skraup reaction, in producing complex structure quinolines, synthesis of some quinoline-5-carboxylic acid glycerol esters from the commercially available anilines (3-aminobenzoic acid derivatives) has been carried out using a slightly modified Skraup reaction. It has been found that the reaction of an excess of glycerol with 3-aminobenzoic acid with I-2 as oxidant in concentrated H2SO4, results in the formation of two acyclic isomers (a, b) of the corresponding glycerol ester, one of them (a) is predominant and a third cyclic isomer (c) obtained in the form of traces. Among the final products, isomer (a) has been purified by flash chromatography and analyzed by IR, H-1 NMR, C-13 NMR and Mass spectroscopy and isomers (b) and (c) (R = OMe, R’ = H) were identified by H-1 NMR. While obtaining the acyclic isomers is quite expected, the cyclic isomer (c), which was previously isolated in traces and characterized, failed to be formed again despite various attempts. To support the experimental results, theoretical computations have been carried out at DFT level and using the B3LYP/6-31++G(d,p) method. Calculations of the activation energies corresponding to the transition states of proposed ways to give isomer (c) show that the formation of this isomer is possible. However, this later is probably obtained from the less predominant isomer (b) which is not an energetically favorable product according to the theoretical calculations. This explains the small amount of isomer (c). Furthermore, the regioselectivity of the esterification reaction has been also assessed by conceptual DFT descriptors.

First author: Ramaraju, P, Enantio- and Diastereoselective Two-Pot Synthesis of Isoquinuclidines from Glutaraldehyde and N-Aryl (mines with DFT Calculations, JOURNAL OF ORGANIC CHEMISTRY, 84, 12408, (2019)
Abstract: A pot-economic method for the enantio- and diastereoselective synthesis of a [2.2.2] azabicyclic isoquinuclidine system is developed. This protocol involves the proline-catalyzed direct Mannich reaction-cyclization/IBX-mediated site-selective oxidation/NaBH4-reduction sequence between glutaraldehyde and imines to generate in situ chiral 1,2-DHPs, followed by the diastereoselective Diels-Alder reaction with N-aryl maleimides furnishing isoquinuclidines in overall five steps. A variety of isoquinuclidines having five-contiguous chiral centers, including an all-carbon quaternary, were prepared with high yields (up to 78%) and excellent stereoselectivity (>50:1 dr, and up to >99:1 er). DFT calculations support the observed high stereoselective reaction outcome.

First author: Ikeda, A, Molecular structure and basic spectroscopic properties of 3-selenocyanatoindole: An important reference compound in organoselenium research, TETRAHEDRON, 75, 12408, (2019)
Abstract: Studies of the molecular structure and the basic spectroscopic properties of 3-selenocyanatoindole, an important reference compound in organoselenium chemistry, were carried out. Single-crystal diffraction analysis revealed that the selenocyanation of indole occurred at 3-position. The characteristic feature of its molecular structure is the perpendicularly connected SeCN group. Theoretical studies indicated that the SeCN group attached to arene rotates freely at room temperature and takes any conformation in the solid state depending on the packing effect. A hitherto unreported Se-77 NMR spectrum of the title compound showed a large upfield shift that suggests the strong electron-donating nature of indole-3-yl.

First author: Chen, LH, Electrically Tunable Electron Transfer and Binding Interaction between Hydrated Ions and Graphene Oxide, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 10, 5735, (2019)
Abstract: Density functional theory simulations were carried out to study the binding interaction between hydrated Na+/Cl- and graphene oxide (GO) under electric fields. External electric fields can modify the binding interactions of the hydrated ions with GO. The field-dependent binding energy is mainly controlled by the orbital interaction driven by the field-dependent electron transfer, in which miscellaneous electron-transfer routes in the interfaces between hydrated ions and GO surface were disclosed. The electric field is able to influence the electron-transfer degree for each route, thereby creating various electron acceptor-donor coupling interactions. Furthermore, we preliminarily explored the effect of the electric field on the interlayer structure of bilayer GO with NaCl and water confined inside. Electric fields can enlarge the interlayer spacing through tuning of the hydrated ion-GO interactions. Our simulations present a new understanding of hydrated ion-GO interactions in the presence of an electric field, which is expected to be valuable in the electrical modulation of GO nanomaterials.

First author: Agostini, A, Similarity and Specificity of Chlorophyll b Triplet State in Comparison to Chlorophyll a as Revealed by EPR/ENDOR and DFT Calculations, JOURNAL OF PHYSICAL CHEMISTRY B, 123, 8232, (2019)
Abstract: An investigation of the photoexcited triplet state of chlorophyll (Chl) b has been carried out by means of electron nuclear double resonance, both in a frozen organic solvent and in a protein environment provided by the water-soluble chlorophyll protein of Lepidium virginicum. Density functional theory calculations have allowed the complete assignment of the observed hyperfine couplings corresponding to the methine protons and the methyl groups, leading to a complete picture of the spin density distribution of the triplet state in the tetrapyrrole macrocycle. The triplet-state properties of Chl b are found to be similar, in many respects, to those previously reported for Chl a, although some specificities have been highlighted. Concerning the spin density distribution, the differences are mainly localized on the carbon atoms close to the formyl group which, in Chl b, replaces the methyl group of Chl a.

First author: Shi, HT, Measuring Local Electric Fields and Local Charge Densities at Electrode Surfaces Using Graphene-Enhanced Raman Spectroscopy (GERS)-Based Stark-Shifts, ACS APPLIED MATERIALS & INTERFACES, 11, 36252, (2019)
Abstract: We report spectroscopic measurements of the local electric fields and local charge densities at electrode surfaces using graphene-enhanced Raman spectroscopy (GERS) based on the Stark-shifts of surface-bound molecules and the G band frequency shift in graphene. Here, monolayer graphene is used as the working electrode in a three-terminal potentiostat while Raman spectra are collected in situ under applied electrochemical potentials using a water immersion lens. First, a thin layer (1 A) of copper(II) phthalocyanine (CuPc) molecules are deposited on monolayer graphene by thermal evaporation. GERS spectra are then taken in an aqueous solution as a function of the applied electrochemical potential. The shifts in vibrational frequencies of the graphene G band and CuPc are obtained simultaneously and correlated. The upshifts in the G band Raman mode are used to determine the free carrier density in the graphene sheet under these applied potentials. Of the three dominant peaks in the Raman spectra of CuPc (i.e., 1531, 1450, and 1340 cm(-1)), only the 1531 cm(-1) peak exhibits Stark-shifts and can, thus, be used to report the local electric field strength at the electrode surface under electrochemical working conditions. Between applied electrochemical potentials from -0.8 V to 0.8 V vs NHE, the free carrier density in the graphene electrode spans a range from -4 x 10(12) cm(-2) to 2 x 10(12) cm(-2). Corresponding Stark-shifts in the CuPc peak around 15(31) cm(-1) are observed up to 1.0 cm(-1) over a range of electric field strengths between -3.78 x 10(6) and 1.85 x 10(6) V/cm. Slightly larger Stark shifts are observed in a 1 M KCl solution, compared to those observed in DI water, as expected based on the higher ion concentration of the electrolyte. Based on our data, we determine the Stark shift tuning rate to be 0.178 cm(-1)/ (10(6) V/cm), which is relatively small due to the planar nature of the CuPc molecule, which largely lies perpendicular to the electric field at this electrode surface. Computational simulations using density functional theory (DFT) predict similar Stark shifts and provide a detailed atomistic picture of the electric field-induced perturbations to the surface-bound CuPc molecules.

Abstract: In order to study the behavior of ethyl esters with 2-hydroxy-benzamide structure in the presence of beta-cyclodextrin (beta-CYD), the [2-(2-bromophenylcarbamoyl)phenoxy]acetic acid ethyl ester was chosen as a representative compound. The evidence of obtaining the inclusion complex in the liquid phase, the 1:1 stoichiometry and the apparent formation constant (K=1211 +/- 111 L/mol) of ethyl ester/beta-CYD inclusion complex was performed using absorbance measurements and the Benesi-Hildebrand equation. A beta-CYD inclusion complex containing the ethyl ester as a guest was prepared using the kneading method and with the aliquot addition of ethanol. The product was characterized by H-1-Nuclear Magnetic Resonance (H-1-NMR), which proves the formation of the inclusion complex where the benzamide part of the ethyl ester has been encapsulated in the hydrophobic cavity of beta-CYD. The inclusion compound’s geometry was established using molecular modeling, which also proved that the ethyl ester is included with the benzamide moiety inside the beta-CYD cavity.

First author: Grabowski, SJ, Bifurcated Triel Bonds-Hydrides and Halides of 1,2-Bis(Dichloroboryl)Benzene and 1,8-Bis(Dichloroboryl)Naphthalene, CRYSTALS, 9, 849, (2019)
Abstract: MP2/aug-cc-pVTZ calculations were performed on hydrides, fluorides, and chlorides of 1,8-bis(dichloroboryl)naphthalene and 1,2-bis(dichloroboryl)benzene. The theoretical analysis of BHB-, BFB-, and BClB- arrangements occurring in these complexes and classified as bifurcated triel bonds was partly based on decomposition of the energy of interaction. The latter was carried out for structures optimized using the DFT method. The complexes analyzed were characterized by a partly covalent character of the links to the hydride and halide anions; these anions strongly influenced the geometry of the complexes. The boron centers’ links for the neutral 1,8-bis(dichloroboryl)naphthalene and 1,2-bis(dichloroboryl)benzene molecules were characterized by approximately trigonal and planar configurations, while for anionic complexes, tetrahedral configurations were observed. The crystal structures of compounds related to species calculated here were found in the Cambridge Structural Database (CSD).

First author: Daniel, C, Structural and Optical Properties of Metal-Nitrosyl Complexes, MOLECULES, 24, 849, (2019)
Abstract: The electronic, structural and optical properties (including Spin-Orbit Coupling) of metal nitrosyl complexes [M(CN)(5)(NO)](2-) (M = Fe, Ru or Os) are investigated by means of Density Functional Theory, TD-DFT and MS-CASPT2 based on an RASSCF wavefunction. The energy profiles connecting the N-bound (eta(1)-N), O-bound (eta(1)-O) and side-on (eta(2)-NO) conformations have been computed at DFT level for the closed shell singlet electronic state. For each structure, the lowest singlet and triplet states have been optimized in order to gain insight into the energy profiles describing the conformational isomerism in excited states. The energetics of the three complexes are similar-with the N-bound structure being the most stable-with one exception, namely the triplet ground state of the O-bound isomer for the iron complex. The conformation isomerism is highly unfavorable in the S-0 electronic state with the occurrence of two energy barriers higher than 2 eV. The lowest bands of the spectra are assigned to MLCTNO/LLCTNO transitions, with an increasing MLCT character going from iron to osmium. Two low-lying triplet states, T1 (MLCTNO/LLCTNO) and T2 (MLCTNO/ILNO), seem to control the lowest energy profile of the excited-state conformational isomerism.

First author: Buta, MC, Molecular and Supramolecular Interactions in Systems with Nitroxide-Based Radicals, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 20, 849, (2019)
Abstract: Nitroxide-based radicals, having the advantage of firm chemical stability, are usable as probes in the detection of nanoscale details in the chemical environment of various multi-component systems, based on subtle variations in their electron paramagnetic resonance spectra. We propose a systematic walk through the vast area of problems and inquires that are implied by the rationalization of solvent effects on the spectral parameters, by first-principle methods of structural chemistry. Our approach consists of using state-of-the-art procedures, like Density Functional Theory (DFT), on properly designed systems, kept at the border of idealization and chemical realism. Thus, we investigate the case of real solvent molecules intervening in different configurations between two radical molecules, in comparison with radicals taken in vacuum or having the solvent that is treated by surrogate models, such as polarization continuum approximation. In this work, we selected the dichloromethane as solvent and the prototype radicals abbreviated TEMPO ((2,2,6,6-Tetramethylpiperidin-1-yl) oxyl). In another branch of the work, we check the interaction of radicals with large toroidal molecules, beta-cyclodextrin, and cucurbit[6]uril, modeling the interaction energy profile at encapsulation. The drawn synoptic view offers valuable rationales for understanding spectroscopy and energetics of nitroxide radicals in various environments, which are specific to soft chemistry.

First author: Conradie, J, Bis(acetylacetonato)copper(II) – structural and electronic data of the neutral, oxidized and reduced forms, DATA IN BRIEF, 26, 849, (2019)
Abstract: Bis(acetylacetonato)copper(II) can be synthesized economically and with ease by the reaction between acetylacetone and a copper salt (Cu(OAc)(2) or CuCl2 center dot 2H(2)O). When used as catalyst, bis(acetylacetonato)copper(II) is sometimes being oxidized to Cu(III) or reduced to Cu(I), although only the structure of the neutral form is known experimentally. The content of this paper provides computational chemistry calculated data of the geometry, electronic structure, spin state and frontier orbitals for the neutral, as well as the oxidized and reduced forms of the bis(acetylacetonato)copper(II) molecule. This data shows that both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the neutral molecule are copper based. The neutral molecule is a spin = 1/2 system. The data shows that the spin state of both the oxidized and reduced molecules is zero.

First author: Keller, M, A Theoretical Multiscale Approach to Study the Initial Steps Involved in the Chemical Reactivity of Soot Precursors, ENERGY & FUELS, 33, 10255, (2019)
Abstract: In the present study, bond formation reactions between soot precursors and their role in the soot inception process are investigated. The soot precursors were generated in macroscopic detailed gas-phase kinetic calculations and according to certain criteria introduced in simulation boxes to model bond formation between soot precursor molecules with reactive force field molecular dynamics modeling. The impacts of temperature, fuel mixture, and equivalence ratio have been investigated on the rate and structure of the newly formed molecules. The resulting structures compare well to previously reported experimental results. Furthermore, the bond formation rate between PAHs is found to be linearly correlated with the temperature at which the PAH precursors are generated, while fuel and equivalence ratio do not have a direct impact on the reaction rate. The generated growth structures are lumped in (1) directly linked, (2) aliphatically linked, and (3) pericondensed polycyclic hydrocarbons. It is found that the amount of aliphatically linked PAH increases with the amount of aliphatic content of the fuel mixture. Finally, a reaction scheme is presented displaying the most representative reaction pathways to form growth structures in each lumping class and their eventual interconversion. The present work-that applies a combined approach of macroscopic gas-phase kinetic calculations and atomistic reactive force field simulations-offers a good alternative to obtain structural differences of nascent soot for a broad range of thermodynamic conditions and detailed reaction mechanisms for the soot inception process.

First author: Pyta, K, Specific Interactions between Rifamycin Antibiotics and Water Influencing Ability To Overcome Natural Cell Barriers and the Range of Antibacterial Potency, ACS INFECTIOUS DISEASES, 5, 1754, (2019)
Abstract: Rifamycins are a group of macrocyclic antibiotics mainly used for the treatment of various bacterial infections including tuberculosis. Spectroscopic studies of rifamycins evidence the formation of temperature- and solvent-dependent equilibria between A-, B-, and C-type conformers in solutions. The B- and C-type conformers of rifamycin antibiotics are exclusively formed in the presence of water molecules. A- and B-type conformers exhibit a hydrophilic and “open” ansa-bridge nature whereas the C type conformer is more lipophilic due to the presence of a “closed” ansa-bridge structure. The involvement of the lactam moiety of the ansa-bridge in intramolecular H-bonds within rifapentine and rifampicin implicates the formation of a more hydrophilic A-type conformer. In contrast to rifampicin and rifapentine, for rifabutin and rifaximin, the “free” lactam group enhances conformational flexibility of the ansa-bridge, thereby enabling interconversion between A- and C-type conformers. In turn, an equilibrium between A- and C-type conformers for rifamycins improves their adaptation to the changing nature of bacteria cell membranes, especially those of Gram-negative strains and/or to efflux pump systems.

First author: Braun, M, Finite element density functional calculations for light molecules using a cusp factor to mitigate the Coulomb potential, EUROPEAN PHYSICAL JOURNAL B, 92, 1754, (2019)
Abstract: Finite element calculations have been performed in Cartesian coordinates using the density functional approach for a number of small molecules. In order to aid convergence of the orbitals and total energies a suitable cusp factor was employed, such that the resulting effective potential is non-singular at all nuclei. The resulting total energies and densities were compared with those obtained using the Gaussian basis set package NWChem [M. Valiev et al., Comput. Phys. Commun. 181, 1477 (2010)] and excellent agreement was found.

First author: Szlag, VM, Optimizing linear polymer affinity agent properties for surface-enhanced Raman scattering detection of aflatoxin B1, MOLECULAR SYSTEMS DESIGN & ENGINEERING, 4, 1019, (2019)
Abstract: A series of poly(N-acryloyl glycinamide) (pNAGA) polymers were synthesized and studied as capture agents for surface-enhanced Raman scattering (SERS) detection of aflatoxin B1 (AFB1), a highly carcinogenic food-borne toxin. Four molecular weights of pNAGA were synthesized by reversible addition-fragmentation chain-transfer (RAFT) polymerization to study the dependence of affinity agent efficacy on chain length for this AFB1 sensing platform. Isothermal titration calorimetry (ITC) was used to verify the sign and magnitude of the enthalpic effects involved in polymer-AFB1 interactions in solution and to understand the effects of pNAGA chain length on AFB1 noncovalent binding. pNAGA-AFB1 interactions were found to be exothermic, and longer pNAGA chains generally resulted in smaller enthalpy decreases per repeat unit. With pNAGA(22) being thermodynamically the strongest affinity agent, we hypothesize that AFB1 affinity is determined by a balance between the configurational restrictions in pNAGA chains and the enthalpic advantage of binding AFB1. SERS spectral changes observed following AFB1 exposure were used to evaluate the influence of polymer molecular weight (2.0-5.2 kDa), order of attachment (pre- vs. post- functionalization of the substrate) and attachment chemistry (thiol vs. trithiocarbonate) on the sensitivity of AFB1 detection. The method by which target, polymer affinity agent, and signal transduction mechanism are combined was found to have significant impacts on the achieved sensitivity. The most effective polymer chain length (pNAGA(22)), anchoring chemistry (thiol), and polymer/toxin assembly scheme (in-solution) allowed detection of 10 ppb AFB1 in water (below the FDA regulatory limit of 20 ppb), a hundred-fold improvement over SERS sensing without the pNAGA affinity agent.

First author: Chong, DP, Computational study of the structures and photoelectron spectra of 12 azabenzenes, CANADIAN JOURNAL OF CHEMISTRY, 97, 697, (2019)
Abstract: The molecular structures of 12 azabenzenes have been optimized with the Gaussian09 package at the level of coupled cluster singles and doubles with the basis set cc-pVTZ. The optimized geometry of each is used in the ADF13 program for the calculation of the vertical ionization energies of all the electrons. For both outer-shell and inner-shell valence electrons, the 2009 method of Delta PBE0(SAOP) is used, whereas the 1999 method of Delta PW86PW91 + C-rel is employed for the core electrons. For degenerate orbitals, the alternative method chosen is to use localized orbitals, keeping the integer number of electrons, while giving up proper symmetry, rather than to keep symmetry with fractional electrons. The success of the computed results of valence ionization potentials of pyridine and the diazabenzenes gives confidence for the predicted values for the higher azabenzenes. The calculated results for core-electron binding energies provide incentive to experimentalists to measure them with X-ray photoelectron spectrometers and (or) synchrotron facilities.

First author: Toyota, S, Nano-Saturn with an Ellipsoidal Body : Anthracene Macrocyclic Ring-C-70 Complex, BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN, 92, 1721, (2019)
Abstract: A macrocyclic compound consisting of six anthracene units formed a Saturn-shaped complex with fullerene C-70 as the ellipsoidal guest. The association constant of the host-guest complex was determined by the NMR titration method to be 4.6 x 10(3) L mol(-1), twice than observed for the C-60 counterpart. X-ray analysis revealed that the guest molecule was included in the center of the cavity in nearly standing orientation, whereas DFT calculations predicted the complexation in various orientations. In any complex structure, CH center dot center dot center dot pi interactions play an important role in forming the ring-body supramolecular system. The intraannular hydrogen atoms in the ring moiety were deshielded upon complexation, and this phenomenon is discussed on the basis of the NMR shielding of C-70 and the calculated structures. In spite of the different relative orientations of C-70, the host-guest formation strength remains similar exposing the great versatility of the host capabilities against non-spherical fullerenes.

First author: Rodriguez, JI, Size evolution study on the electronic and optical properties of gold-cluster complexes Au-4-S-CnH2n-S ‘-Au-4 ” (n=2-5), CHEMICAL PHYSICS LETTERS, 732, 1721, (2019)
Abstract: Relativistic unrestricted time-dependent density functional theory calculations were performed for obtaining the absorption spectra of gold-cluster complexes Au-4 – S – CnH2n – S’- Au-4′ (n = 2-5). The range-separated ex- change-correlation functional CAMYB3LYP was used to properly predict charge transfer excitations. The absorption UV-vis spectrum is not affected by size if structure and metal-molecule bonding remains similar. Changes in the ‘local’ structure and bonding have drastic effects on these systems’ electronic transitions. The HOMO-LUMO gap of the cluster complexes shows a zig-zag behavior typical of gold nanoclusters with respect to the size of the alkanedithiol chain (n).

First author: Guda, AA, Quantitative structural determination of active sites from in situ and operando XANES spectra: From standard ab initio simulations to chemometric and machine learning approaches, CATALYSIS TODAY, 336, 3, (2019)
Abstract: In the last decade the appearance of progressively more sophisticated codes, together with the increased computational capabilities, has made XANES a spectroscopic technique able to quantitatively confirm (or discard) a structural model, thus becoming a new fundamental diagnostic tool in catalysis, where the active species are often diluted metal centers supported on a matrix. After providing a brief historical introduction and the basic insights on the technique, in this review article, we provide a selection of four examples where operando XANES technique has been able to provide capital information on the structure of the active site in catalysts of industrial relevance: (i) Phillips catalyst for ethylene polymerization reaction; (ii) TS-1 catalyst for selective hydrogenation reactions; (iii) carbon supported Pd nanoparticles for hydrogenation reactions; (iv) Cu-CHA zeolite for NH3-assisted selective reduction of NOx and for partial oxidation of methane to methanol. The last example testifies how the multivariate curve resolution supported by the alternating least-squares algorithm applied to a high number of XANES spectra collected under operando conditions allows to quantitatively determine different species in mutual transformation. This approach is particularly powerful in the analysis of experiments where a large number of spectra has been collected, typical of time- or space-resolved experiments. Finally, machine learning approaches (both indirect and direct) have been applied to determine, from the XANES spectra, the structure of CO, CO2 and NO adsorbed on Ni2+ sites of activated CPO-27-Ni metal-organic framework.

First author: Singh, T, Donor -> Acceptor Coordination Interactions in 1,3-bis(NHC)triazenyl Cations: An Electronic Structure Analysis, JOURNAL OF COMPUTATIONAL CHEMISTRY, 40, 2207, (2019)
Abstract: Donor -> acceptor coordination interactions (L -> N) between ligands and nitrogen center as in L -> N-circle plus <- L were reported in the recent past. This article describes the possibility of L -> N coordination interactions in triazenyl cation species L -> N-3(circle plus) <- L. A few 1,3-bis(NHC) triazenyl cation species were experimentally known, the electronic structure analysis reported in this work reveals the presence of L -> N (donor -> acceptor) interactions in these species. Molecular orbital analysis, NBO charge analysis, energy decomposition analysis, and so forth, confirm the possibility of L -> N coordination bond character. Ten molecules with the general formula L -> N-3(circle plus) <- L have been designed carrying L -> N-3(circle plus) <- L interactions.

First author: Sun, XB, PyFrag 2019-Automating the Exploration and Analysis of Reaction Mechanisms, JOURNAL OF COMPUTATIONAL CHEMISTRY, 40, 2227, (2019)
Abstract: We present a substantial update to the PyFrag 2008 program, which was originally designed to perform a fragment-based activation strain analysis along a provided potential energy surface. The original PyFrag 2008 workflow facilitated the characterization of reaction mechanisms in terms of the intrinsic properties, such as strain and interaction, of the reactants. The new PyFrag 2019 program has automated and reduced the time-consuming and laborious task of setting up, running, analyzing, and visualizing computational data from reaction mechanism studies to a single job. PyFrag 2019 resolves three main challenges associated with the automated computational exploration of reaction mechanisms: it (1) computes the reaction path by carrying out multiple parallel calculations using initial coordinates provided by the user; (2) monitors the entire workflow process; and (3) tabulates and visualizes the final data in a clear way. The activation strain and canonical energy decomposition results that are generated relate the characteristics of the reaction profile in terms of intrinsic properties (strain, interaction, orbital overlaps, orbital energies, populations) of the reactant species.

First author: Charistos, ND, Double aromaticity of the B-40 fullerene: induced magnetic field analysis of pi and sigma delocalization in the boron cavernous structure, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 20232, (2019)
Abstract: The induced magnetic field of B-40 was dissected into contributions from pi, sigma and core electrons revealing the origins for the formation of the strong long range shielding response characterizing the spherical aromatic nature of the cavernous D-2d structure. Our analysis showed the complementary role of pi and sigma orbitals for the formation of the global shielding cone, with weak pi contributions at a long range and strong sigma contributions inside the cage, supporting the molecule as double aromatic with weak pi and strong sigma delocalization. Similar local variations of both pi and sigma magnetic responses were identified portraying peripheral diatropic and local paratropic currents. The weak pi aromaticity is explained on the basis of symmetry rules pertaining to its electronic structure which forbid small gap paratropic rotational excitations.

First author: Cornaton, Y, A noncovalent interaction insight onto the concerted metallation deprotonation mechanism, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 20486, (2019)
Abstract: The CMD/AMLA mechanisms of cyclopalladation and the parent fictitious but challenging cyclonickelation of N,N-dimethylbenzylamine have been investigated by joint DFT-D and DLPNO-CCSD(T) methods assisted by QTAIM-based noncovalent interaction plots (NCI plots) and interacting quantum atoms (IQA) analyses, and the local energy decomposition (LED) procedure. Bader charges, NCI plots, IQA and the LED analyses clearly suggest that coulombic interactions play an important role and somewhat govern the whole process that is sensitive to the charge borne by the metal centre. It is found that replacement of acetate by acetamidate used as a ligand and a base significantly lowers the barrier to the formation of the key agostic intermediate. The latter shows a peculiar polarization by its immediate ligand environment where a significant electrostatic CHMIDLINE HORIZONTAL ELLIPSISO interaction with the neighboring carboxylato ligand competes with the strong propensity of the latter to bind the metal center, which is stronger in the agostic intermediate when the carboxylato ligand is the acetate and when the metal is Ni. It is also shown that the hereby idealized cyclonickelation is disfavored as compared to cyclopalladation owing to enhanced electrostatic repulsion in almost all stages of the CMD mechanism.

First author: Franconetti, A, Intramolecular pi-hole interactions with nitro aromatics, CRYSTENGCOMM, 21, 5410, (2019)
Abstract: A thorough evaluation of the CSD and DFT computations were conducted to assess if intramolecular pi-hole interactions can stabilize a conformer of nitro aromatics. It was found that this can only be the case when the nitro N-atom and an interacting electron-rich atom are separated by at least four bonds. Data from the solid state correspond well to the gas phase calculations and stabilizing energies were estimated to be as large as about 2-3 kcal mol(-1), which is in the order of weak hydrogen bonding interactions.

First author: Fang, ZT, Formation of Cerium and Neodymium Isocyanides in the Reactions of Cyanogen with Ce and Nd Atoms in Argon Matrices, JOURNAL OF PHYSICAL CHEMISTRY A, 123, 8208, (2019)
Abstract: Laser ablation of metallic Ce and Nd reacting with cyanogen in excess argon during codeposition at 4 K forms Ce(NC)(x) and Nd(NC)(x) for x = 1-3, which are identified from their matrix infrared spectra using cyanogen substituted with C-13 and N-15. The electronic structure calculations were performed for isocyano and cyano Cd and Nd compounds for up to n = 4. The frequencies were calculated at the density functional theory level with three different functionals as well as correlated molecular orbital theory (MP2) and are consistent with the experimental assignments and the corresponding C-12/C-13 isotopic frequency ratios for the isocyano species. The computed frequencies for the analogous cyanide complexes are significantly higher than those for the isocyano isomers, and they are not observed in the spectra. The high spin isocyano complexes are the lowest energy structures. On the basis of the natural population analysis results, the bonding in (CeNC)-Ce-4 and (NdNC)-Nd-6 is essentially purely ionic with the Ce/Nd in the +I-oxidation state. The bonding for disocyano (Ce-3(NC)(2) and Nd-5(NC)(2)) and triisocyano (Ce-2(NC)(3) and Nd-4(NC)(3)) complexes is still quite ionic with the lanthanide in the +II and +III formal oxidation states, respectively. For Ce-1(NC)(4), the oxidation state is best described as being between +III and +IV. Formation of Nd-5(NC)(4) does not really change the electron configuration on the Nd from that in Nd-4(NC)(3) and the oxidation state on the Nd remains at +III. Although Nd compounds with up to 3 NC- groups have more ionic binding than do the corresponding Ce compounds, Ce(NC)(4) has more ionic binding than does Nd(NC)(4). The ionic nature of isocyano Ce and Nd complexes decreases as the number of isocyano groups increases. The energetics of formation of the isocyano Ce and Nd complexes using cyanogen or CN radicals are calculated to be mostly due to exothermic processes, with the exothermicity decreasing as the number of isocyano groups increases.

First author: Kang, XM, An Ultrastable Matryoshka [Hf-13] Nanocluster as a Luminescent Sensor for Concentrated Alkali and Acid, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 58, 16610, (2019)
Abstract: Stable metal clusters that can resist both highly concentrated acid and alkali are unknown. Herein, we present a discrete neutral cluster, Hf-13(mu(4)-O)(8)(OCH3)(36) (1), which features extraordinary chemical stability by preserving its crystalline state in concentrated aqueous solutions of both acid (10 m HNO3) and alkali (20 m boiling NaOH). Importantly, 1 can serve as a luminescent probe for detecting both concentrated alkali (20 m NaOH) and strong acid (1 m HNO3) with high selectivity and repeatability. DFT studies of the electronic structure and bonding revealed that 1 has an extremely large HOMO-LUMO gap due to strong d pi-p pi bonding that accounts for the ultrahigh stability.

First author: Mucelini, J, Understanding the interplay between pi-pi and cation-pi interactions in [janusene-Ag](+) host-guest systems: a computational approach, DALTON TRANSACTIONS, 48, 13281, (2019)
Abstract: Janusene is a symmetrical molecule that contains four benzene rings, with two of them forced to be in a vertical quasi-parallel face-to-face alignment. The unique physical nature of the transannular interactions and the electronic features of the region between the enforced parallel rings was tested with the complexation of Ag+ ion as a probe to evaluate the interplay between pi-stacking and cation-pi non-bonded interactions. The janusene framework and the [janusene-Ag](+) host-guest (H-G) system were analyzed through the introduction of substituent groups with different chemical natures and in different parts of the host framework. The janusenes were used to tune both pi-stacking and cation-pi interactions. Three modes of substitution (facial, lateral, and facial plus lateral) were explored to gain insight into the effects of such scaffold modifications on the dual non-bonded interactions. Our findings suggest that the eta(2):eta(2) silver coordination is the most stable interaction mode between the silver ion and the janusene parallel rings. The cation-pi interaction in the host structure is stabilized by electron donating groups and destabilized by electron withdrawing groups. The stabilization effect is highlighted with substitutions on the facial and facial plus lateral modes, with the latter being due to additive cooperation between the substituent groups. The bonding analysis indicates that [janusene-Ag](+) complexes containing electron withdrawing groups in the facial and facial plus lateral substitution schemes are more stabilized by orbital interactions. Complexes with electron donating groups and the complexes with substituent groups in the lateral position are mainly stabilized by electrostatic interactions, although in all cases orbital and dispersive interactions are also essential to describe the bonding situation. We envisage that these results will guide the development of new systems with increased cation-pi interaction capability.

First author: Rodrigues, AI, Boron complexes of aromatic 5-substituted iminopyrrolyl ligands: synthesis, structure, and luminescence properties, DALTON TRANSACTIONS, 48, 13337, (2019)
Abstract: A group of new mononuclear boron chelate compounds [BPh2{kappa N-2,N ‘-5-R-NC4H2-2-C(H)-N-Ar}] (R = Ar = C(6)H(5)7; R = C6H5, Ar = 2,6-iPr(2)C(6)H(3)8; R = Anthracen-9-yl (Anthr), Ar = C(6)H(5)9; R = Anthr, Ar = 2,6-iPr(2)C(6)H(3)10) were synthesized via the reaction of B(C6H5)(3) with the corresponding 5-substituted 2-(N-arylformimino)pyrrole ligand precursors 3-6. These complexes were prepared in order to evaluate the luminescence potential derived from the substitution of the position 5 of the pyrrolyl ring with an aromatic group. Compounds 7-10 were photophysically characterized in solution and in the solid state. The 5-phenyl-2-iminopyrrolyl-BPh2 complexes 7 and 8 are blue emitters and have enhanced photoluminescence quantum yields in the solid state (phi(PL)) up to 0.95, whereas the 5-anthracenyl derivatives 9 and 10 have green-bluish fluorescence and a phi(PL) of 0.49 and 0.24, respectively. DFT and TDDFT studies were performed, considering the effect of solvent and dispersion, in order to show how the geometries of compounds 7-10 changed from the ground to the excited state, to assign electronic transitions, and to rationalize the observed luminescence. These materials were applied in organic light-emitting diodes (OLEDs), with various device structures, the best showing an external quantum efficiency of 2.75% together with a high luminance of 23 530 cd m(-2).

First author: Khavasi, HR, Phenomenal Observation of Attractive Intermolecular CHMIDLINE HORIZONTAL ELLIPSISHC Interaction in a Mercury (II) Complex: An Experimental and First-Principles Study, CHEMISTRYSELECT, 4, 10246, (2019)
Abstract: The nature of the attractive intermolecular C-H horizontal ellipsis H-C interaction, which could affect the crystal packing and solid-state molecular structure, is yet unknown. Here, a novel mercury (II) complex including N-(2-biphenyl)pyrazine-2-carboxamide ligand, one such system, has been synthesized and characterized by a single crystal X-ray diffraction. The existence of attractive intermolecular C-HMIDLINE HORIZONTAL ELLIPSISH-C interaction (-2.64 to -9.30 kj/mol depending on computational levels) is a notable feature in the crystal packing of this complex, which is the first observation of intermolecular C-HMIDLINE HORIZONTAL ELLIPSISH-C interaction in a metal complex. From crystallographic data, this contact has a distance of 2.172 angstrom which is 9.5% shorter than the sum of the van der Waals radii of two hydrogen atoms, which is the primary condition of having intermolecular interactions. We study the nature C-H horizontal ellipsis H-C interaction in the synthesized mercury (II) complex using periodic/non-periodic density functional theory in conjunction with quantum theory of atoms in molecules, non-covalent interaction reduced density gradient method, natural bond orbital, and energy decomposition analysis tools. Our results suggest that C-HMIDLINE HORIZONTAL ELLIPSISH-C interaction has closed-shell, donor-acceptor, and van der Waals nature.

First author: Rivier, L, Mechanistic Study on the Photogeneration of Hydrogen by Decamethylruthenocene, CHEMISTRY-A EUROPEAN JOURNAL, 25, 12769, (2019)
Abstract: Detailed studies on hydrogen evolution by decamethylruthenocene ([Cp*Ru-2(II)]) highlighted that metallocenes are capable of photoreducing hydrogen without the need for an additional sensitizer. Electrochemical, gas chromatographic, and spectroscopic (UV/Vis, H-1 and C-13 NMR) measurements corroborated by DFT calculations indicated that the production of hydrogen occurs by a two-step process. First, decamethylruthenocene hydride [Cp*Ru-2(IV)(H)](+) is formed in the presence of an organic acid. Subsequently, [Cp*Ru-2(IV)(H)](+) is reversibly reduced in a heterolytic reaction with one-photon excitation leading to a first release of hydrogen. Thereafter, the resultant decamethylruthenocenium ion [Cp*Ru-2(III)](+) is further reduced with a second release of hydrogen by deprotonation of a methyl group of [Cp*Ru-2(III)](+). Experimental and computational data show spontaneous conversion of [Cp*Ru-2(II)] to [Cp*Ru-2(IV)(H)](+) in the presence of protons. Calculations highlight that the first reduction is endergonic (Delta G(0)=108 kJ mol(-1)) and needs an input of energy by light for the reaction to occur. The hydricity of the methyl protons of [Cp*Ru-2(II)] was also considered.

First author: Pei, H, Selectively Photocatalytic Activity of an Open-Framework Chalcogenide Built from Corner-Sharing T4 Supertetrahedral Clusters, INORGANIC CHEMISTRY, 58, 12011, (2019)
Abstract: The photocatalysis process with high selectivity is a very important research forefront for the semiconductor photocatalytic decomposition of organic pollutants. However, the rational design of efficient photocatalysts with high selectivity is still a challenge. Here, we present an open framework chalcogenide (Heta)(8)[In14Sn2Zn4Se33] (Heta = ethanolamine-H+) (compound 1) constructed from T4 supertetrahedral clusters [In14Sn2Zn4Se35](12-) with visible light-driven selectively photocatalytic degradation activity. Single-crystal XRD analysis shows that compound 1 crystallizes in I4(1)/acd (no. 142) space group, with a = b = 24.3462(2) angstrom, c = 45.0062(9) angstrom, V = 26676.9(7) angstrom(3), and Z = 8. Under visible-light irradiation, the selectively photocatalytic activities of 1 were evaluated by photodegradation of two kinds of cationic dye molecules, i.e., methylene blue (MB) and rhodamine B (RhB), against two anionic dyes, methyl orange (MO) and Kermes red (KR), with different sizes. We show that the adsorption capability and charge-matching between organic dyes and the supertetrahedral cluster together with a suitable band structure make it an excellent and selective photocatalyst. This is the first example of an open-framework chalcogenide based on supertetrahedral T4 for the selectively semiconductor photocatalytic decomposition of organic dyes.

First author: Zhang, FJ, Repurposing DNA-binding agents as H-bonded organic semiconductors, NATURE COMMUNICATIONS, 10, 12011, (2019)
Abstract: Organic semiconductors are usually polycyclic aromatic hydrocarbons and their analogs containing heteroatom substitution. Bioinspired materials chemistry of organic electronics promises new charge transport mechanism and specific molecular recognition with biomolecules. We discover organic semiconductors from deoxyribonucleic acid topoisomerase inhibitors, featuring conjugated backbone decorated with hydrogen-bonding moieties distinct from common organic semiconductors. Using ellipticine as a model compound, we find that hydrogen bonds not only guide polymorph assembly, but are also critical to forming efficient charge transport pathways along pi-conjugated planes when at a low dihedral angle by shortening the end-to-end distance of adjacent pi planes. In the pi-pi stacking and hydrogen-bonding directions, the intrinsic, short-range hole mobilities reach as high as 6.5 cm(2)V(-1)s(-1) and 4.2 cm(2)V(-1)s(-1) measured by microwave conductivity, and the long-range apparent hole mobilities are up to 1.3 x 10(-3) cm(2)V(-1)s(-1) and 0.4 x 10(-3) cm(2)V(-1)s(-1) measured in field-effect transistors. We further demonstrate printed transistor devices and chemical sensors as potential applications.

First author: Borghesi, C, The nature of the lead-iodine bond in PbI2: A case study for the modelling of lead halide perovskites, COMPUTATIONAL AND THEORETICAL CHEMISTRY, 1164, 12011, (2019)
Abstract: A detailed knowledge of the basic electronic interactions in lead halide perovskites components (PbI2 and methylammonium iodide) can possibly drive enhanced solar cell efficiency. We report an extensive investigation on the electronic structure and nature of the chemical bond in the PbI2 perovskite precursor, both in gas and solid state, together with a comparison with available experimental data, which allows to effectively calibrate the computational framework, along with gaining basic understanding on the nature of the Pb-I chemical bond. Inclusion of spin orbit coupling and calibrated HF exchange contribution to the DFT hybrid functional are proved essential for an accurate description of the electronic structure of both molecular and solid state PbI2. Such computational framework, calibrated on the model PbI2 system, can be directly translated to the accurate description of the electronic band structure of the prototypical methylammonium lead-iodide perovskite, setting the basis for the trustful modelling of different lead-halide perovskites.

First author: Kido, K, A noniterative mean-field QM/MM-type approach with a linear response approximation toward an efficient free-energy evaluation, JOURNAL OF COMPUTATIONAL CHEMISTRY, 40, 2072, (2019)
Abstract: Mean-field treatment of solvent provides an efficient technique to investigate chemical processes in solution in quantum mechanics/molecular mechanics (QM/MM) framework. In the algorithm, an iterative calculation is required to obtain the self-consistency between QM and MM regions, which is a time-consuming step. In the present study, we have proposed a noniterative approach by introducing a linear response approximation (LRA) into the solvation term in the one-electron part of Fock matrix in a hybrid approach between molecular-orbital calculations and a three-dimensional (3D) integral equation theory for molecular liquids (multicenter molecular Ornstein-Zernike self-consistent field [MC-MOZ-SCF]; Kido et al., J. Chem. Phys. 2015, 143, 014103). To save the computational time, we have also developed a fast method to generate electrostatic potential map near solute and the solvation term in Fock matrix, using Fourier transformation (FT) and real spherical harmonics expansion (RSHE). To numerically validate the LRA and FT-RSHE method, we applied the present approach to water, carbonic acid, and their ionic species in aqueous solution. Molecular properties of the solutes were evaluated by the present approach with four different types of initial wave functions and compared with those by the original (MC-MOZ-SCF). We found that an initial wave function considering solvation effects is needed to appropriately reproduce the properties by MC-MOZ-SCF. Furthermore, a benchmark test for 32 solute molecules was performed to evaluate the accuracy of the present approach for solvation free energy (SFE) and measure the speedup ratio for MC-MOZ-SCF. The error of SFE for MC-MOZ-SCF does not correlate with the SFE but increases in proportion to the electronic reorganization energy. Similar to water and carbonic acid, an initial wave function with solvation effects is also important to make the error small. From the averaged speed up ratio, the present approach is 13.5 times faster than MC-MOZ-SCF.

First author: Zhang, XR, Highly selective extraction of Pu (IV) and Am (III) by N,N ‘-diethyl-N,N ‘-ditolyl-2,9-diamide-1,10-phenanthroline ligand: An experimental and theoretical study, SEPARATION AND PURIFICATION TECHNOLOGY, 223, 274, (2019)
Abstract: The group actinide extraction ligand, N,N’-diethyl-N,N’-ditolyl-2,9-diarnide-1,10-phenanthroline (Et-Tol-DAPhen) has been successfully developed in our laboratory recently. In this work, the extraction behaviors of the tetradentate Et-Tol-DAPhen toward Am(III) and Pu(IV) by using 1-(trifluoromethyl)-3-nitrobenzene as the diluent were systematically explored. The effects of HNO3 and ligand concentration as well as temperature were studied in detail. In addition, the selectivity of this ligand towards actinides and the stripping performance of the extraction system were also investigated to assess its potential application for group actinide separation over trivalent lanthanides (Ln(III)). According to our results, Et-Tol-DAPhen exhibits large distribution ratios for both Am(III) and Pu(IV) with high separation factors over Pm(III) in a wide range of acidity. Moreover, Am(III) and Pu(IV) can be efficiently stripped into the aqueous phase via three stages of batch back extraction. In addition, density functional theory (DFT) calculations suggest that the ligand selectivity towards actinides over Ln(III) probably results from the higher covalency of An-N bonds. The consistency between calculated thermodynamic parameters and experimental observations demonstrates the reasonability of the proposed extraction mechanism. Our findings afford insightful extraction parameters of Et-Tol-DAPhen towards actinides with different oxidation states and justify its versatile coordination abilities with respect to group actinide separation over lanthanides.

First author: Papai, M, Simulation of ultrafast excited-state dynamics and elastic x-ray scattering by quantum wavepacket dynamics, JOURNAL OF CHEMICAL PHYSICS, 151, 274, (2019)
Abstract: Simulation of the ultrafast excited-state dynamics and elastic X-ray scattering of the [Fe(bmip)(2)](2+) [bmip = 2,6-bis(3-methyl-imidazole-1-ylidine)-4-pyridine] complex is presented and analyzed. We employ quantum wavepacket dynamics simulations on a 5-dimensional potential energy surface (PES) calculated by time-dependent density functional theory with 26 coupled diabatic states. The simulations are initiated by explicit inclusion of a time-dependent electromagnetic field. In the case of resonant excitation into singlet metal-to-ligand charge transfer ((MLCT)-M-1) states, kinetic (exponential) population dynamics are observed with small nuclear motion. In agreement with transient optical absorption spectroscopy experiments, we observe a subpicosecond (MLCT)-M-1 -> (MLCT)-M-3 intersystem crossing and a subsequent decay into triplet metal-centered ((MC)-M-3) states on a picosecond time scale. The simulated time-resolved difference scattering signal is dominated by the (MC)-M-3 component, for which the structural distortions are significant. On the other hand, excitation into (MC)-M-1 states leads to ballistic (nonexponential) population dynamics with strong nuclear motion. The reason for these ballistic dynamics is that in this case, the excitation occurs into a nonequilibrium region, i.e., far from the minimum of the (MC)-M-1 PES. This results in wavepacket dynamics along the principal breathing mode, which is clearly visible in both the population dynamics and difference scattering. Finally, the importance of decomposing the difference scattering into components by electronic states is highlighted, information which is not accessible from elastic X-ray scattering experiments.

First author: Casella, G, New light on an old debate: does the RCN-PtCl2 bond include any back-donation? RCN <- PtCl2 backbonding vs. the IR nu(CN) blue-shift dichotomy in organonitriles-platinum(ii) complexes. A thorough density functional theory – energy decomposition analysis study, DALTON TRANSACTIONS, 48, 12974, (2019)
Abstract: For a series of organonitrile [RCN (R = Me, CF3, Ph, CH3Ph, CF3Ph)] ligands, the nature of the N-Pt bond in the related cis-/trans-(RCN)(2)PtCl2 complexes has been computationally investigated by Density Functional Theory. A fragment based bond analysis has been performed in the canonical Kohn-Sham molecular orbitals framework, and it has been ultimately assessed that this bond is characterized both by N -> Pt sigma and by N <- Pt pi contributions. Voronoi Deformation Density charges further confirms the occurrence of N <- Pt pi interactions. Moreover, the Energy Decomposition Analysis-Natural Orbital for Chemical Valence (EDA-NOCV) method shows that the strength of the N <- Pt pi interaction is not negligible by contributing to about 30-40% of the total orbital interaction. Finally, the well-known nu(CN) blue-shift occurring upon coordination to Pt-II, has been thoroughly investigated by exploiting the EDA-NOCV and by evaluating nu(CN) and force constants. The origin of the nu(CN) blue-shift in these systems has been discussed on the basis of the CN bond polarization. N <- Pt pi backbonding causes only a systematic decrease of the observed nu(CN) blue-shift when compared to the one calculated for RCN-X (X = H+, alkaline, Lewis acids) herein reported (X = purely sigma acceptors).

First author: Guru, MM, B(C6F5)(3)-catalyzed dehydrogenative cyclization of N-tosylhydrazones and anilines via a Lewis adduct: a combined experimental and computational investigation, CHEMICAL SCIENCE, 10, 7964, (2019)
Abstract: Tris(pentafluorophenyl)borane-catalyzed dehydrogenative-cyclization of N-tosylhydrazones with aromatic amines has been disclosed. This metal-free catalytic protocol is compatible with a range of functional groups to provide both symmetrical and unsymmetrical 3,4,5-triaryl-1,2,4-triazoles. Mechanistic experiments and density functional theory (DFT) studies suggest an initial Lewis adduct formation of N-tosylhydrazone with B(C6F5)(3) followed by sequential intermolecular amination of the borane adduct with aniline, intramolecular cyclization and frustrated Lewis pair (FLP)-catalyzed dehydrogenation for the generation of substituted 1,2,4-triazoles.

First author: Sels, A, Vibrational Circular Dichroism of Thiolate-Protected Au-25 Clusters: Accurate Prediction of Spectra and Chirality Transfer within the Mixed Ligand Shell, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 22586, (2019)
Abstract: We have prepared Au-25(PET)(18-2x)((R)-FBI-NAS)(x) (PET = 2-phenylethylthiol, (R)-FBINAS = (R)-5,5′,6,6′,7,7′,8,8′-octafluoro-[1,1′-binaphthalene]-2,2′-dithiol) mixed ligand shell clusters via ligand exchange. Two fractions with different composition of the ligand shell were separated using size-exclusion chromatography and studied by infrared (IR) spectroscopy and vibrational circular dichroism (VCD). Both IR and VCD spectra are dominated by FBINAS vibrations although PET is more abundant on the cluster. Calculated VCD spectra on a model cluster Au-25(SH)(16)(FBINAS)(1) depend on the charge state of the cluster, and the anion is in excellent agreement with the experimental spectra of the Au-25(PET)(18-2x)(FBINAS)(x) samples. Calculations of Au-25(SH)(14)(FBINAS)(2) furthermore show very similar spectra for different adsorption isomers with one exception, where the two ligands share a SR-Au-SR-Au-SR staple motif. Model calculations show that it is not necessary to consider the entire cluster for obtaining reliable VCD and IR spectra, but the staple motifs cannot be neglected. A band that is assigned to PET shows significant vibrational optical activity, and an anisotropy factor that depends on the composition of the ligand shell. This shows that the FBINAS molecules can transfer chirality to achiral PET within the ligand shell of the cluster.

First author: Zhang, YK, Folding and Assembly of Short alpha, beta, gamma-Hybrid Peptides: Minor Variations in Sequence and Drastic Differences in Higher-Level Structures, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 141, 14239, (2019)
Abstract: Multilevel protein structures typically involve polypeptides of sufficient lengths. Here we report the folding and assembly of seven short tetrapeptides sharing the same types of alpha-, beta-, and aromatic gamma-amino acid residues. These are two sets of hybrid peptides, with three members in one set and four in the other, having complementary hydrogen bonding sequences that were hypothesized to pair into linear H-bonded duplexes. However, instead of undergoing the anticipated pairing, the initially examined three oligomers, 1 and 2a or 2b, differing only in their central alpha beta hybrid dipeptide sequence, do not associate with each other and exhibit distinctly different folding behavior. Experiments based on NMR and mass spectrometry, along with computational studies and systematic inference, reveal that oligomer 1 folds into an expanded beta-turn containing an unusual hybrid alpha/beta-amino acid sequence composed of glycine and beta-alanine, two alpha- and beta-amino acid residues that are conformationally most flexible, and peptides 2a and 2b adopt a noncanonical, extended helical conformation and dimerize into double helices undergoing rapid conformational exchange or helix inversion. The different central dipeptide sequences, alpha beta vs beta alpha, result in drastically different intramolecular H-bonding patterns that are responsible for the observed folding behavior of 1 and 2. The revealed turn and double helix have few natural or synthetic counterparts, and provide novel and unique folding prototypes based on which chiral alpha- and beta-amino acids are incorporated. The resultant derivatives 1a, 1b, 2c, and 2d follow the same folding and assembling behavior and demonstrate the generality of this system with the formation of expanded beta-turns and double helices with enhanced folding stabilities, hampered helix inversion, as well as defined and dominant helical sense. This work has demonstrated the unique capability of synthetic foldamers in generating structures with fascinating folding and assembling behavior. The revealed systems offer ample opportunity for further structural optimization and applications.

First author: Gieseking, RLM, Third-Order Nonlinear Optical Properties of Ag Nanoclusters: Connecting Molecule-like and Nanoparticle-like Behavior, CHEMISTRY OF MATERIALS, 31, 6850, (2019)
Abstract: Molecules and materials with negative real parts of third-order nonlinear optical (NLO) polarizability Re(gamma) are rare despite their advantages for applications such as all-optical switching. Although plasmonic metal nanoparticles can have a negative Re(gamma) that increases in magnitude with a decrease in size, these properties are not yet understood from a quantum mechanical perspective. Here, we use quantum chemical approaches to model the NLO properties of prototypical silver nanoclusters. In linear Ag nanowires, the longitudinal excited-state properties are analogous to those of polyenes, leading to a positive Re(gamma) that increases with nanowire length. In contrast, the transverse modes show plasmon-like mixing of excitations in the main one-photon excited state, leading to a negative Re(gamma). The tetrahedral Ag-20 cluster likewise has a negative Re(gamma) due to plasmon-like mixing of excitations. On the basis of these results, we propose a new approach to obtain a large negative Re(gamma) by identifying and tuning the structural features that contribute to plasmon-like mixing of excitations in the absorbing states.

First author: Winkler, C, Understanding the Correlation between Electronic Coupling and Energetic Stability of Molecular Crystal Polymorphs: The Instructive Case of Quinacridone, CHEMISTRY OF MATERIALS, 31, 7054, (2019)
Abstract: A crucial factor determining charge transport in organic semiconductors is the electronic coupling between the molecular constituents, which is heavily influenced by the relative arrangement of the molecules. This renders quinacridone, with its multiple, structurally fundamentally different polymorphs and their diverse intermolecular interactions, an ideal test case for analyzing the correlation between the electronic coupling in a specific configuration and the configuration’s energetic stability. To provide an in-depth analysis of this correlation, starting from the alpha-polymorph of quinacridone, we also construct a coplanar model crystal. This allows us to systematically compare the displacement dependence of the electronic coupling with that of the total energy. In this way, we identify the combination of Pauli repulsion and orbital rehybridization as the driving force steering the system toward a structure in which the electronic coupling is minimal (especially for the valence band and at small displacements). The general nature of this observation is supported by equivalent trends for an analogous pentacene model system. This underlines that the design of high-performance materials cannot rely on the “natural” assembly of the pi-conjugated backbones of organic semiconductors into their most stable configurations. Rather, it must include the incorporation of functional groups that steer crystal packing toward more favorable structures, where aiming for short-axis displacements or realizing comparably large longaxis displacements appear as strategies worthy of exploring.

First author: Li, JB, Homolytic Versus Heterolytic Bond Breaking in Functionalized [R-C20H10](+) Systems, JOURNAL OF COMPUTATIONAL CHEMISTRY, 41, 88, (2020)
Abstract: The comprehensive theoretical investigation of stability of functionalized corannulene cations [R-C20H10](+) with respect to two alternative bond-breaking mechanisms, namely, homolytic or radical ([R-C20H10](+) -> R-center dot + C20H10+center dot) and heterolytic or cationic ([R-C20H10](+) -> R+ + C20H10), was accomplished. The special focus was on the influence of the nature of R-group on the energetics of the bond cleavage. Detailed study of energetics of both mechanisms has revealed that the systems with small alkyl groups such as methyl tend to undergo bond breaking in accordance with homolytic mechanism. Subsequent elongation of the chain of the R-group resulted in shifting the paradigm, making heterolytic path more energetically favorable. Subsequent analysis of different components of the bonding between R-group and corannulene polyaromatic core helped to shed light on trends observed. In both mechanisms, the covalent contribution was found to be dominating, whereas ionic part contributes similar to 25-27%. Two leading components of Delta E-orb, C20H10 -> R and R -> C20H10, were identified with NOCV-EDA approach. While the homolytic pathway is best described as R -> C20H10 process, the heterolytic mechanism shows domination of the C20H10 -> R term. Surprisingly, the preparation energy (Delta E-prep) was identified as a key player in stability tendencies found. In other words, the relative stability of corresponding molecular fragments (here R-groups as the corannulene fragment remains the same for all systems) in their cationic or radical forms determine the preference given to a specific bond breaking path and, as consequence, the total stability of target functionalized cations. These conclusions were further confirmed by extending a set of R-groups to conjugated (allyl, phenyl), bulky (iPr, tBu), beta-silyl (CH2SiH3, CH2SiMe3), and benzyl (CH2Ph) groups.

First author: Senanayake, RD, Theoretical investigation of relaxation dynamics in the Au-18(SH)(14) thiolate-protected gold nanocluster, JOURNAL OF CHEMICAL PHYSICS, 151, 88, (2019)
Abstract: Experimental findings of Au-18(GSH)(14) as a photosensitizer with the highest potential compared to other glutathione-protected clusters demand understanding the photophysics and relaxation dynamics of the Au-18(SR)(14) cluster. To this end, we perform ab initio real-time nonadiabatic molecular dynamics simulations on Au-18(SH)(14) to investigate its relaxation dynamics compared to the well-studied [Au-25(SR)(18)](-1) relaxation dynamics. In this work, the excitations covering up to similar to 2.6 eV in the optical absorption spectrum are analyzed to understand the electronic relaxation process of the Au-18(SH)(14) cluster. The ground state growth times of Au-18(SH)(14) are several orders of magnitude shorter than the growth times observed for the [Au-25(SH)(18)](-1) nanocluster. The S-1 (HOMO-LUMO) state gives the slowest decay time (similar to 11 ps) among all the states (S-1-S-30) considered similar to [Au-25(SH)(18)](-1). However, the S-1 state in Au-18(SH)(14) is a semiring-to-core charge transfer state, whereas S-1 in the [Au-25(SH)(18)](-1) cluster is a core-to-core transition. The remaining higher excited states have very short decay time constants less than 1.4 ps except for S-2 which has the second slowest decay of 6.4 ps. The hole relaxations are faster than the electron relaxations in Au-18(SH)(14) due to the closely packed HOMOs in the electronic structure. Radiative relaxations are also examined using the time-dependent density functional theory method, and the excited state emission energy and lifetime are found to be in good agreement with experiment.

First author: Misturini, A, Tracking the absence of anion-pi interactions in modified [2(3)](1,3,5)cyclophanes: insights from computation, NEW JOURNAL OF CHEMISTRY, 43, 13271, (2019)
Abstract: Using DFT-based computational tools, the capabilities of [2(3)](1,3,5)cyclophanes and their analogs, containing 1,3,5-triazine and 1,3,5-triphosphinine rings, to recognize anions were addressed. The impacts of such chemical modifications in the cyclophane scaffold and how they affect the anion recognition were explored since they are crucial to designing new and more efficient anion receptors. Long-range effects of transition metal coordination on the anion recognition were also investigated by the coordination of [Cr(CO)(3)](0) at the lower ring of cyclophanes leading to the piano-stool complexes. The role of such modifications on the interaction with anions was analyzed in details by considering the interactions between the upper ring of all proposed hosts with anions of different shapes and charges, including Cl-, Br-, NO3-, BF4-, SO42-, and PO43-. The interactions were rationalized in the light of energy decomposition (ETS-NOCV), wavefunction (NBO), and molecular electrostatic potential (MEP) analyses. The main findings reveal that the chemical modifications (substitution of 3 C-H groups at the upper ring by N and P) do not lead to significant changes on the structural features of cage-type cyclophanes, but modify their capabilities to recognize anions in a significant way, since very stable host-guest systems are formed and kept by strong sigma-interactions and hydrogen bonds. The coordination of [Cr(CO)(3)](0) group amplifies such effects noticeably by withdrawing the electronic density from the host scaffold. Our results suggest that tuning the host-guest interaction by modification of the cyclophane structure is an important strategy to the rational design of anion receptors.

First author: Koenis, MAJ, Taming conformational heterogeneity in and with vibrational circular dichroism spectroscopy, CHEMICAL SCIENCE, 10, 7680, (2019)
Abstract: The flexibility of a molecule has important consequences on its function and application. Vibrational Circular Dichroism (VCD) is intrinsically an excellent experimental technique to get a hold on this flexibility as it is highly sensitive to key conformational details and able to distinguish rapidly interconverting conformers. One of the major challenges in analyzing the spectra by comparison to theoretical predictions is the uncertainty in the computed energies of the multitude of conformations. This uncertainty also affects the reliability of the stereochemical assignment it is normally used for. We present here a novel approach that explicitly takes the energy uncertainties into account in a genetic algorithm based method that fits calculated to the experimental spectra. We show that this approach leads to significant improvements over previously used methodologies. Importantly, statistical validation studies provide quantitative measures for the reliability of relevant parameters used such as the energy uncertainty and the extent to which conformational heterogeneity can be determined. Similarly, quantitative measures can be obtained for the possibility that the flexibility that is introduced in the fit might lead to an incorrect assignment of the stereochemistry. These results break new ground for different techniques based on VCD to elucidate conformational flexibility.

First author: Gayfulin, YM, Luminescent twelve-nuclear rhenium clusters, DALTON TRANSACTIONS, 48, 12522, (2019)
Abstract: The first luminescent twelve-nuclear rhenium cluster complexes were obtained. Three new clusters, namely, [Re12CS14(mu-Cl)(3)Cl-6](5-), [Re12CS14(mu-Br)(3)Cl-6](5-) and [Re12CS14(mu-Br)(3)Br-6](5-), were synthesized using the non-isovalent substitution of mu-O ligands within the {Re12CS14(mu-O)(3)}(0) cluster core by halide anions. The geometry of the new clusters was investigated by X-ray structural analysis, and the electronic structures were evaluated by the use of DFT calculations. It was found that compounds based on these anions showed red luminescence in both the solid state and solution that was never observed before for previously studied twelve-nuclear rhenium clusters.

First author: Shao, Y, Photocatalytic Water Splitting Cycle in a Dye-Catalyst Supramolecular Complex: Ab Initio Molecular Dynamics Simulations, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 21403, (2019)
Abstract: A dye-sensitized photoelectrochemical cell (DS-PEC) is a promising device for direct conversion of solar energy into fuel. The basic idea, inspired by natural photosynthesis, is to couple the photoinduced charge separation process to catalytic water splitting. The photo-oxidized dye coupled to a water oxidation catalyst (WOC) should exert a thermodynamic driving force for the catalytic cycle, while water provides the electrons for regenerating the oxidized dye. These conditions impose specific energetic constraints on the molecular components of the photoanode in the DS-PEC. Here, we consider a supramolecular complex integrating a mononuclear Ru-based WOC with a fully organic naphthalene-diimide (NDI) dye that is able to perform fast photo-induced electron injection into the conduction band of the titanium-dioxide semiconductor anode. By means of constrained ab initio molecular dynamics simulations in explicit water solvent, it is shown that the oxidized NDI provides enough driving force for the whole photocatalytic water splitting cycle. The results provide strong evidence for the significant role of spin alignment and solvent rearrangement in facilitating the proton-coupled electron transfer processes. The predicted activation free energy barriers confirm that the O-O bond formation is the rate-limiting step. Our results expand the current understanding of the photocatalytic water oxidation mechanism and provide guidelines for the optimization of high-performance DS-PEC devices.

First author: Ospadov, E, Quantum Monte Carlo assessment of density functionals for pi-electron molecules: ethylene and bifuran, MOLECULAR PHYSICS, 117, 2241, (2019)
Abstract: We perform all-electron, pure-sampling quantum Monte Carlo (QMC) calculations on ethylene and bifuran molecules. The orbitals used for importance sampling with a single Slater determinant are generated from Hartree-Fock and density functional theory (DFT). Their fixed-node energy provides an upper bound to the exact energy. The best performing density functionals for ethylene are BP86 and M06, which account for 99% of the electron correlation energy. Sampling from the pi-electron distribution with these orbitals yields a quadrupole moment comparable to coupled cluster CCSD(T) calculations. However, these, and all other density functionals, fail to agree with CCSD(T) while sampling from electron density in the plane of the molecule. For bifuran, as well as ethylene, a correlation is seen between the fixed-node energy and deviance of the QMC quadrupole moment estimates from those calculated by DFT. This suggests that proximity of DFT and QMC densities correlates with the quality of the exchange nodes of the DFT wave function for both systems.

First author: Del Pezzo, R, Ortho-substituted azobenzene: shedding light on new benefits, PURE AND APPLIED CHEMISTRY, 91, 1533, (2019)
Abstract: Novel functional polymeric microcapsules, based on modified azobenzene moieties, are exhaustively investigated, both from a theoretical and experimental points of view. Theoretical calculations and several measurements demonstrate that visible light can act as a trigger for release of encapsulated material, as a consequence of trans-cis isomerization which modifies microcapsule surface topography and can induce a “squeezing” release mechanism. Interfacial polymerization of an oil-in-water emulsion is performed and leads to core-shell microcapsules which are characterized by means of atomic force microscopy (AFM), optical microscopy (OM), scanning electron microscopy (SEM) and light scattering. These analyses put into evidence that microcapsules’ size and surface morphology are strongly affected by irradiation under visible light: moreover, these changes can be reverted by sample exposure to temperatures around 50 degrees C. This last evidence is also confirmed by NMR kinetic analyses on modified azobenzene moiety. Finally, it is shown that these smart microcapsules can be successfully used to get a controlled release of actives such as fragrancies, as a consequence of visible light irradiation, as confirmed by an olfactive panel.

First author: Michalczyk, M, Theoretical Studies of IR and NMR Spectral Changes Induced by Sigma-Hole Hydrogen, Halogen, Chalcogen, Pnicogen, and Tetrel Bonds in a Model Protein Environment, MOLECULES, 24, 1533, (2019)
Abstract: Various types of sigma-hole bond complexes were formed with FX, HFY, H(2)FZ, and H3FT (X = Cl, Br, I; Y = S, Se, Te; Z = P, As, Sb; T = Si, Ge, Sn) as Lewis acid. In order to examine their interactions with a protein, N-methylacetamide (NMA), a model of the peptide linkage was used as the base. These noncovalent bonds were compared by computational means with H-bonds formed by NMA with XH molecules (X = F, Cl, Br, I). In all cases, the A-F bond, which lies opposite the base and is responsible for the sigma-hole on the A atom (A refers to the bridging atom), elongates and its stretching frequency undergoes a shift to the red with a band intensification, much as what occurs for the X-H bond in a H-bond (HB). Unlike the NMR shielding decrease seen in the bridging proton of a H-bond, the shielding of the bridging A atom is increased. The spectroscopic changes within NMA are similar for H-bonds and the other noncovalent bonds. The C=O bond of the amide is lengthened and its stretching frequency red-shifted and intensified. The amide II band shifts to higher frequency and undergoes a small band weakening. The NMR shielding of the O atom directly involved in the bond rises, whereas the C and N atoms both undergo a shielding decrease. The frequency shifts of the amide I and II bands of the base as well as the shielding changes of the three pertinent NMA atoms correlate well with the strength of the noncovalent bond.

First author: Mooibroek, TJ, Intermolecular Non-Covalent Carbon-Bonding Interactions with Methyl Groups: A CSD, PDB and DFT Study, MOLECULES, 24, 1533, (2019)
Abstract: A systematic evaluation of the CSD and the PDB in conjunction with DFT calculations reveal that non-covalent Carbon-bonding interactions with X-CH3 can be weakly directional in the solid state (P <= 1.5) when X = N or O. This is comparable to very weak CH hydrogen bonding interactions and is in line with the weak interaction energies calculated (<= -1.5 kcalmol(-1)) of typical charge neutral adducts such as [Me3N-CH3OH2] (2a). The interaction energy is enhanced to <=-5 kcalmol(-1) when X is more electron withdrawing such as in [O2N-CH3O=C-dme] (20b) and to <= 18 kcalmol(-1) in cationic species like [Me3O+-CH3OH2](+) (8a).

First author: Geng, N, A First-Principles Exploration of NaxSy Binary Phases at 1 atm and Under Pressure, CRYSTALS, 9, 1533, (2019)
Abstract: Interest in Na-S compounds stems from their use in battery materials at 1 atm, as well as the potential for superconductivity under pressure. Evolutionary structure searches coupled with Density Functional Theory calculations were employed to predict stable and low-lying metastable phases of sodium poor and sodium rich sulfides at 1 atm and within 100-200 GPa. At ambient pressures, four new stable or metastable phases with unbranched sulfur motifs were predicted: Na2S3 with C2/c and Imm2 symmetry, C2-Na2S5 and C2-Na2S8. Van der Waals interactions were shown to affect the energy ordering of various polymorphs. At high pressure, several novel phases that contained a wide variety of zero-, one-, and two-dimensional sulfur motifs were predicted, and their electronic structures and bonding were analyzed. At 200 GPa, P4/mmm-Na2S8 was predicted to become superconducting below 15.5 K, which is close to results previously obtained for the beta-Po phase of elemental sulfur. The structures of the most stable M3S and M4S, M = Na, phases differed from those previously reported for compounds with M = H, Li, K.

First author: Wei, JY, Elucidating the Electronic Structure of the Ligated Cuboctahedral Palladium Cluster [Pd-13(mu(4)-C7H7)(6)](2+), JOURNAL OF CLUSTER SCIENCE, 30, 1227, (2019)
Abstract: The electronic structure of the recently reported cuboctahedral [Pd-13(mu(4)-Tr)(6)](2+) (Tr = C7H7) cluster is analyzed using DFT calculations. Results indicate that the bonding in this cluster can be described from the formal starting point of a [Pd-13](2-) core interacting with a partly reduced [Tr-6](4+) ligand shell. The orbital interactions between the two fragments are strong, owing in particular to the very strong accepting ability of the surrounding ligands. The (moderate) Pd-Pd bonding character is in part due to the occupation of the strongly bonding in-phase combination of the 5s(Pd) orbitals (the 1S jellium level) and for another part from through-bond interactions.

First author: Gil, A, Unraveling the Modulation of the Activity in Drugs Based on Methylated Phenanthroline When Intercalating between DNA Base Pairs, JOURNAL OF CHEMICAL INFORMATION AND MODELING, 59, 3989, (2019)
Abstract: Phenanthroline derivatives intercalate between base pairs of DNA and produce cytotoxic effects against tumoral cells. Nevertheless, modulation of their efficiency by substitution remains unclear in bibliography. In this work, the effects of methylation of phenanthroline, in number and position, when it intercalates between guanine cytosine base pairs (GC/CG), were studied with PM6-DH2 and DFT-D methods including dispersion corrections. An analysis of the geometries, electronic structure, and energetics in the interaction was carried out for the studied systems. Our results were compared to experimental works to gain insight on the relation structure-interaction for the intercalated system with cytotoxicity. The trends are explained including not only intrinsic contributions to energy, Delta E-pauli, Delta E-disp, Delta E-orb, and Delta E-elstat, but also the solvation energy, Delta E-Solv. A subtle balance between the number of stabilizing weak interactions (CH/pi, CH/n, etc.) and steric hindrance seems to be related to the efficiency of such drugs.

First author: Frances-Monerris, A, Toward Luminescent Iron Complexes: Unravelling the Photophysics by Computing Potential Energy Surfaces, CHEMPHOTOCHEM, 3, 666, (2019)
Abstract: Due to its high societal impact, the replacement of precious metals used in technological devices by more abundant and eco-friendly metals, such as iron, has stimulated significant scientific efforts in the last years. In the present review, we focus on different computational strategies and techniques used to characterize the potential energy surfaces (PESs) that govern the photophysical pathways of a wide variety of Fe-II complexes. The different procedures are discussed in terms of accuracy, computational cost and availability of the implementations, and illustrated with specific examples taken from the literature. The determination of minimum energy paths (MEPs) and the optimization of minimum energy crossing points (MECPs) are particularly emphasized since they can be combined to provide connected and optimized PESs independent from any a priori selected coordinate. The use of such computational techniques is exemplified in detail through a recent study on the influence of the facial and meridional isomerism in the triplet PESs of a pyridylcarbene Fe(II) complex, and its implications in the decay mechanism of each isomer.

First author: Zhou, ZB, Revealing the pH-Dependent Photoluminescence Mechanism of Graphitic C3N4 Quantum Dots, ADVANCED THEORY AND SIMULATIONS, 2, 666, (2019)
Abstract: Graphitic C3N4 quantum dots (g-C3N4 QDs), as a kind of widely explored fluorescent materials, show pH-dependent photoluminescence feature. However, opposite variation tendencies on their pH-dependent photoluminescence performance are observed in different experiments and the underlying mechanism remains unclear. Herein, based on time-dependent density functional theory and nonadiabatic molecular dynamics simulations, a synergistic mechanism between light absorption and radiative/nonradiative recombination of g-C3N4 QDs in neutral and acidic conditions is proposed to address the inconformity. Specifically, under weak acidic condition, the strong light absorption and weak nonradiative recombination of g-C3N4 QDs yield strong fluorescence emission. While under strong acidic condition, although the light absorption remains high, the fast nonradiative electron-hole recombination dramatically reduces the population of the excited state and the fluorescence is quenched consequently. The protonation of N atom changes the orbital composition of transition channels and frontier molecular orbital overlap, which consequently modulates the competition between radiative and nonradiative recombination as well as the emission performance. In addition, there is no obvious change in the variation tendency of absorption and emission properties of g-C3N4 QDs with different functional groups, implying the general applicability of understanding.

First author: Rocha, MVJ, Structure and bonding in triorganotin chlorides: a perspective from energy decomposition analysis, JOURNAL OF MOLECULAR MODELING, 25, 666, (2019)
Abstract: The Sn-Cl chemical bond of four organotin halides (Me3SnCl, Et3SnCl, Bu3SnCl, and Ph3SnCl) was studied by using relativistic density functional theory in combination with a quantitative energy decomposition analysis to explain the formation of charged species. The sigma orbital is the dominant contributor to the stabilization of the Sn-Cl bond, and the pi-orbital interactions also have a significant contribution to the stabilization of Ph3Sn+ cation when the aromatic groups are bonded to the tin atom. The aromaticity of the phenyl groups delocalizes the positive charge, donating electrons to tin atom by conjugation. Although Me3SnCl and Ph3SnCl are constituted by groups which the size of the substituents is different, the interaction energies obtained with the energy decomposition analysis present similar values, which also occur with the thermodynamic parameters.

First author: Wang, Y, First-principles calculations of B/N co-doped graphene for sensing NO and NO2 molecules, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 113, 121, (2019)
Abstract: Adsorption of NO and NO2 on the 1N1B/G, 1B2N/G and 1N2B/G are theoretically investigated using firstprinciples method based on density functional theory. The most stable adsorption geometry, adsorption energy, band structure and density of states of these systems are thoroughly discussed. It is found that NO molecule is weakly adsorbed on the 1N1B/G and 1B2N/G but their electronic properties are obviously changed. The adsorption sensitivity of 1N2B/G is lower than 1N1B/G and 1B2N/G to NO molecule. It is found that NO2 molecule is strongly adsorbed on the 1B2N/G but its electronic property is slightly changed. In contrast, the 1N1B/G is more suitable for the detection of NO2 molecule. The results will provide a new direction for the detection of NO and NO2 by introducing B and N doping atoms into graphene.

First author: Lu, H, Theoretical screening of novel electrode materials for lithium-ion batteries from industrial polymers, IONICS, 25, 4161, (2019)
Abstract: Organic polymers have the potential to be electrode materials for lithium-ion batteries due to their lower solubility, lower self-discharge rates, high mechanical strength, greater flexibility, superior thermal stability, and versatility. In this paper, the density functional theory (DFT) was applied to investigate industrial polymers as electrode materials for lithium-ion batteries. The charge/discharge potentials of reported polymer electrode materials for lithium-ion batteries were collected, and the experimental values were fitted linearly with the values of Delta E-poly (as shown in Eq. (2b)) calculated with a single-molecule model to obtain a semi-empirical formula, which was subsequently applied to predict the charge/discharge potentials of industrial polymers. The results showed that 16th (polypyromellitic diphenyl sulfide), 17th (polypyromellitic diphenyl ether imine), and 23rd (polypyromellitic diphenylmethaneimine) materials have better electrochemical performance than the other materials in this paper, and we also find that the material, such as polypyromellitic diphenylmethaneimine, containing low electronegative heteroatom and electron-donating groups, has a low potential value.

First author: Twigge, L, Rh-103 NMR shifts of Rh-I-beta-diketonato and Rh-I-beta-aminoketonato complexes influenced by different substituents, POLYHEDRON, 169, 14, (2019)
Abstract: Rh-103, H-1 and P-31 NMR data of [Rh(beta-diketonato)(CO)(PPh3)], [Rh(CH3COCHC(NR2)CH3)(CO)(PPh3)] and [Rh(beta-diketonato)(COD)] complexes with beta-diketonato = RCOCHCOR1 and R and/or R-1 = H, CH3, ferrocenyl, phenyl, CF3, thienyl and for the beta-aminoketonato R-2 = H or Ph, are reported. The chemical shift values of Rh-103 have been measured by inverse two-dimensional P-31, Rh-103- or H-1, Rh-103 NMR. Values for Rh-103 of [Rh(beta-diketonato)(CO)(PPh3)] and [Rh(CH3COCHC(NR2)CH3)(CO)(PPh3)] varies from 103 to 322 ppm, while Rh-103 values for [Rh(beta-diketonato)(COD)] lies between 1286 and 1327 ppm. The chemical shift values are compared to that of similar Rh-I-beta-diketonato compounds previously reported in literature. It was shown that by changing the electron-density of the beta-diketonato or beta-aminoketonato ligand, a small change in chemical shift was observed, while by changing from the CO and PPh3 ligands to the less pi-acceptor COD ligand, a bigger change in chemical shift occurs.

First author: Haseena, S, Interactions of thiol and alkoxy radical with coinage metal nanoclusters, APPLIED SURFACE SCIENCE, 487, 1409, (2019)
Abstract: Interaction of small neutral coinage metal clusters (M-19 = Ag-19/Au-19) with thiol/alkoxy radical (E = -SCH3, -OCH3, and -OCH2CH3) has been investigated to understand the bonding mechanism in the coinage metal-molecule junctions, which would allow to design biocompatible materials. In this study, structure, reactivity, and energy decomposition analysis (EDA) of M-19-E complexes have been unravelled using density functional theory (DFT) based Perdew, Burke and Ernzerhof (PBE) method. In addition, the theory of “atoms in molecules” (AIM) has also been used characterize the nature of interaction. The calculated reactivity descriptors predict that the vertex atoms (Ag/Au) are the most reactive site for nucleophilic attack. The atoms lying at the center of each face are favourable for an electrophilic attack in both the cases. Geometrical parameters illustrate that the structure of the molecules change significantly before and after interactions. The signatures of del(2)rho(r) and H-c for the anchoring bonds are respectively positive and negative, revealing that these bonds are partially electrostatic and covalent in nature. EDA calculation indicates that the largest contribution to the M-X (X=O/S) bond arise from Delta E-orb and Delta E-elstat contributions. Specifically, contribution from the orbital interaction is higher than the electrostatic contribution, which further confirms the covalent nature of the interaction.

First author: Majid, A, First principles study of transition metals doped SiC for application as counter electrode in DSSC, SURFACE SCIENCE, 687, 41, (2019)
Abstract: The modification in material of counter electrode to improve the performance of dye sensitized solar cell based on first principles calculations is being reported. The slab models of pure SiC and its doping with Pt and Cr were investigated to study the catalytic activity on the basis of adsorption of triiodide and monoiodides as well as charge transfer from the slabs to the adsorbents. The iodide reduction reaction was modeled to study the splitting of tri-iodide into iodine and then into iodide ions which receive negative charge from the slabs. It was found that Cr doped SiC exhibited better activity to split the triiodide but poor action to further split the iodine into monoiodides when compared with pure SiC and Pt doped SiC slabs. The outcomes of this study revealed that TM doped SIC slabs may provide alternate materials to platinum for use as counter electrodes.

First author: Armstrong, A, Al Valence Controls the Coordination and Stability of Cationic Aluminum-Oxygen Clusters in Reactions of Al-n(+) with Oxygen, JOURNAL OF PHYSICAL CHEMISTRY A, 123, 7463, (2019)
Abstract: The reactivity of cationic aluminum clusters with oxygen is studied via a customized time-of-flight mass spectrometer. Unlike the etching effect for anionic aluminum clusters exposed to oxygen, here, the cationic Al-n(+) clusters react and produce a range of small AlnOm+ clusters. Relatively large-mass abundances are found for Al3O4+, Al4O5+, and Al5O7+ at lower O-2 reactivity, while at higher O-2 concentration, oxygen addition leads to Al2O7+, Al3O6,8-10+, and Al4O7,(+)(9), showing relatively high abundance, and Al5O7+ remains as a stable species dominating the Al5Om+ distribution. To understand these results, we have investigated the structures and stabilities of the AlnOm+ clusters. First- I principles theoretical investigations reveal the structures, highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gaps, fragmentation energies, ionization energies, and Hirshfield charge of the AlnOm+ clusters (2 <= n <= 7; 0 <= m <= 10). Energetically, Al3O4+, Al4O5+, and Al5O7+ are calculated to be most stable with high fragmentation energies; however, they still allow for the chemisorption of additional O-2 with large binding energies leading to clusters with higher O/Al ratios. The stability of the species is consistent with Al possessing three valence electrons, while 0 typically accepts two, leading to the expectation that Al3O4+, Al5O7+, and Al7O10+ are reasonably stable. In addition to this, Al3O4+, Al5O3+, and Al7O5+ are found to exhibit large HOMO-LUMO gaps associated with the different oxidation states of Al. The oxygen-rich species such as Al2O7+, Al3O10+, and Al4O9+ all display superoxide structures providing further insights into the oxidation of aluminum clusters.

First author: De, S, Probing the Local Magnetic Structure of the [Fe-III(Tp)(CN)(3)](-) Building Block Via Solid-State NMR Spectroscopy, Polarized Neutron Diffraction, and First-Principle Calculations, CHEMISTRY-A EUROPEAN JOURNAL, 25, 12120, (2019)
Abstract: The local magnetic structure in the [Fe-III(Tp)(CN)(3)](-) building block was investigated by combining paramagnetic Nuclear Magnetic Resonance (pNMR) spectroscopy and polarized neutron diffraction (PND) with first-principle calculations. The use of the pNMR and PND experimental techniques revealed the extension of spin-density from the metal to the ligands, as well as the different spin mechanisms that take place in the cyanido ligands: Spin-polarization on the carbon atoms and spin-delocalization on the nitrogen atoms. The results of our combined density functional theory (DFT) and multireference calculations were found in good agreement with the PND results and the experimental NMR chemical shifts. Moreover, the ab-initio calculations allowed us to connect the experimental spin-density map characterized by PND and the suggested distribution of the spin-density on the ligands observed by NMR spectroscopy. Interestingly, significant differences were observed between the pseudo-contact contributions of the chemical shifts obtained by theoretical calculations and the values derived from NMR spectroscopy using a simple point-dipole model. These discrepancies underline the limitation of the point-dipole model and the need for more elaborate approaches to break down the experimental pNMR chemical shifts into contact and pseudo-contact contributions.

First author: Attia, AAA, Cationic gold clusters with eight valence electrons: possible spherical aromatic systems with Sigma holes, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 17779, (2019)
Abstract: The energetically preferred structures of the gold clusters Au-9(+), Au-11(3+), and Au-12(4+) with eight skeletal electrons have been studied by density functional theory for comparison with the 8-electron Au-10(2+) cluster shown previously to have a highly favored T-d tetracapped octahedral structure. The low-energy structures for the Au-9(+) and Au-11(3+) clusters are found to be similar relatively spherical polyhedra. Such systems can be considered to exhibit spherical aromaticity in accord with their filled 1S(2)1P(6) shells, their diatropic NICS(0) values ranging from -21.4 to -44.3 ppm, and their shielding cone surfaces. However, the preferred spherical polyhedra for Au-9(+) and Au-11(3+) are not the same as the closo deltahedra found in the BnHn2- borane dianions. Instead they have smaller internal cavities formed by capping faces of smaller deltahedra or by formation of internal Au-Au bonds. The lowest energy Au-12(4+) structures are not similar nearly spherical polyhedral structures. Instead they are derived from planar gold subclusters by adding more gold atoms to form tetrahedral Au-4 bubbles. The planar origin of the low-energy Au-12(4+) structures relates to the energetic preference for neutral Au-n((n-8)+) (n = 9 to 12) clusters. The strength of their electrostatic interactions is predicted to increase upon increasing cluster size.

First author: Meng, XX, Theoretical Study on Asymmetric [2+2] Cycloaddition of an Alkynone with a Cyclic Enol Silyl Ether Catalyzed by a Chiral N,N ‘-Dioxide-Zn(II) Complex, ORGANOMETALLICS, 38, 3111, (2019)
Abstract: The reaction mechanism and enantioselectivity of the asymmetric [2 + 2] cycloaddition between an alkynone (R.1) and a cyclic enol silyl ether (R2) were studied theoretically by the DFT method at the B3LYP-D3(BJ)/6-311G**(CH2C12,SMD)//B3LYP-D3(BJ)/def2-SVP(CH2Cl2,SMD) theoretical level. The noncatalytic reaction occurred via a stepwise mechanism. The first C-C bond was constructed by coupling two pseudo radical centers generated at the most nucleophilic C-2 atom in the cyclic enol silyl ether and the most electrophilic terminal C-beta atom in the alkynone, which was responsible for the regioselectivity of the reaction. The counterion NTf2- could stabilize the Zn(II) complex by coordinating to the center metal, forming a high-reactivity hexacoordinate Zn(II)complex intermediate. The bulky CF3 group in the NTf2- ion adjusted the blocking effect of o-iPr in aniline of the ligand toward the reactive site (that is, the C beta atom in the alkynone) and induced the si face of the cyclic enol silyl ether to approach the alkynone from its less hindered re face, achieving a high enanotioselectivity of products. The Pauli repulsion between the Zn(II)-associated moiety and cyclic enol silyl ether fragment was the main contributor to the stereodifference of the two competing pathways in chiral N,N’-dioxide-Zn(II)-catalyzed [2 + 2] cycloaddition. The unfavorable steric repulsion between the o-iPr group of aniline in the ligand and tert-butyldimethylsilyl (TBS) in the cyclic enol silyl ether along the re face path translated into a more destabilizing Delta E-Pauli value, leading to the predominant cycloaddition product (P-RR) observed in experiments. Variation of the linkage and chiral backbone could affect the repulsion among the o-iPr in the ligand, the counterion NTf2-, and substrates, leading to different stereochemical outcomes. These results are in good agreement with experimental observations.

First author: Kharitonov, VB, Fluorene Complexes of Group 9 Metals: Fluorene Effect and Application for Reductive Amination, ORGANOMETALLICS, 38, 3151, (2019)
Abstract: The ri6-fluorene cyclopentadienyl complexes [(eta(5)-C5R5)-M(176-fluorene)](SbF6)2 (1: M = Co, R = Me; 2a: M = Rh, R = H; 2b: M = Ir, R = H) were synthesized by the iodide abstraction from [(175CsR5)MI2] with AgSbF6 in the presence of fluorene. The procedure is also suitable for the synthesis of the indenyl derivatives [(175indenyl)M(176-fluorene)](SbF6)2 (3a: M = Rh; 3b: M = Ir) starting from [(175-indenyl)MI2]. The structures of [1](SbF6)2 and [2b](SbF6)2 were determined by X-ray diffraction. The rhodium complex [2a](SbF6)2 readily undergoes the replacement of the fluorene ligand by mesitylene, being more reactive than the benzene derivative [CpRii()76C6H6)](SbF6)2. According to experimental data and DFT calculations, the fluorene elimination proceeds via a cascade of 176 > 175 > 171 haptotropic rearrangements. The complex [21:](SbF6)2 (at 1 mol % loading) effectively catalyzes the reductive amination reaction between aldehydes (or ketones) and primary aromatic (or secondary aliphatic) amines in the presence of carbon monoxide, giving the corresponding secondary and tertiary amines in the range of yields 59-91%. This protocol uses water as a solvent.

First author: Chi, CX, Octacarbonyl Ion Complexes of Actinides [An(CO)(8)](+/-) (An=Th, U) and the Role of f Orbitals in Metal-Ligand Bonding, CHEMISTRY-A EUROPEAN JOURNAL, 25, 11772, (2019)
Abstract: The octacarbonyl cation and anion complexes of actinide metals [An(CO)(8)](+/-) (An=Th, U) are prepared in the gas phase and are studied by mass-selected infrared photodissociation spectroscopy. Both the octacarbonyl cations and anions have been characterized to be saturated coordinated complexes. Quantum chemical calculations by using density functional theory show that the [Th(CO)(8)](+) and [Th(CO)(8)](-) complexes have a distorted octahedral (D-4h) equilibrium geometry and a doublet electronic ground state. Both the [U(CO)(8)](+) cation and the [U(CO)(8)](-) anion exhibit cubic structures (O-h) with a (6)A(1g) ground state for the cation and a (4)A(1g) ground state for the anion. The neutral species [Th(CO)(8)] (O-h; (1)A(1g)) and [U(CO)(8)] (D-4h; B-5(1u)) have also been calculated. Analysis of their electronic structures with the help on an energy decomposition method reveals that, along with the dominating 6d valence orbitals, there are significant 5f orbital participation in both the [An]<- CO sigma donation and [An]-> CO pi back donation interactions in the cations and anions, for which the electronic reference state of An has both occupied and vacant 5f AOs. The trend of the valence orbital contribution to the metal-CO bonds has the order of 6d>>5f>7s approximate to 7p, with the 5f orbitals of uranium being more important than the 5f orbitals of thorium.

First author: Thornley, W, Photodynamics of [FeFe]-Hydrogenase Model Compounds with Bidentate Heterocyclic Ligands, JOURNAL OF PHYSICAL CHEMISTRY B, 123, 7137, (2019)
Abstract: Two asymmetrically structured model compounds for the hydrogen-generating [Fe-Fe]-hydrogenase active site were investigated to determine the ultrafast photodynamics, structural intermediates, and photo-products compared to more common symmetric di-iron species. The bidentate-ligand-containing compounds studied were Fe-2(mu-S2C3H6)(CO)(4)(bipy), 1, and Fe-2(mu-S2C3H6)(CO)(4)(phen), 2, in dilute room temperature acetonitrile solution and low-temperature 2Me-THF matrix isolation using static FTIR difference and time-resolved infrared spectroscopic methods (TRIR). Ultraviolet-visible spectra were also compared to time-dependent density functional theory (TD-DFT) to ascertain the orbital origins of long wavelength electronic absorption features. The spectroscopic evidence supports the conclusions that only a propyl-bridge flip occurs in low-temperature matrix, while early time CO ejection leads to the formation of solvated isomeric species on the 25 ps time scale in room temperature solution.

First author: Rogers, FJM, Computational Assessment of Verdazyl Derivatives for Electrochemical Generation of Carbon-Centered Radicals, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 20174, (2019)
Abstract: To expand the scope for carbon-centered radical generation by electrochemical activation of adducts based on stable free radicals, a test set of six simple electron-rich Kuhn verdazyl derivatives in conjunction with nine different alkyl leaving groups has been computationally assessed. Like triazinyls, adducts of simple verdazyl derivatives functionalized with electron-donating substituents favor mesolytic cleavage to carbon-centered radicals under mild electrochemical potentials (-0.7 to -0.2 V vs Fc(+)/Fc). Electrochemical oxidation was found to reduce the bond dissociation Gibbs free energy (298 K in acetonitrile) by 70 kJ mol(-1) on average, when comparing the homolytic cleavage pathway of the unoxidized adduct to the preferred mesolytic pathway of the oxidized adduct (i.e., to form either a verdazyl radical and a carbocation or a verdazyl cation and a carbon-centered radical). Considering the full thermochemical cycle, we illustrate that all the relevant free energy changes can be reduced to differences between the oxidation potentials of adducts and radicals, defining a series of criteria that govern the rational design of suitable candidates for oxidative carbon-centered radical cleavage. As a result of a tradeoff between promoting the oxidation of the adduct and enhancing the net reduction in BDFE upon oxidation, the best verdazyl derivatives for carbon-centered radical generation are those substituted with tBu substituents.

First author: Nazari, M, Ultrafast dynamics in polycyclic aromatic hydrocarbons: the key case of conical intersections at higher excited states and their role in the photophysics of phenanthrene monomer, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 16981, (2019)
Abstract: In this study we reveal the detailed photocycle of a phenanthrene monomer. Phenanthrene serves as a popular building block for supramolecular systems and as an archetypal molecule to study the photochemistry of polycyclic aromatic hydrocarbons. By means of femtosecond time-resolved UV-vis transient absorption spectroscopy and molecular modeling, we found that the first bright transition involves the second excited singlet state, which relaxes toward the lowest excited singlet state with a biphasic internal conversion through a conical intersection region: a fast coherent branching followed by an exceptionally slow (similar to ps) incoherent internal conversion. We succeeded to pinpoint the complete relaxation pathways and to extract the relevant parameters, e.g., the branching ratio at the conical intersection and internal conversion rates.

First author: Dumpala, RMR, Reduction in Coordination Number of Eu(III) on Complexation with Pyrazine Mono- and Di-Carboxylates in Aqueous Medium, INORGANIC CHEMISTRY, 58, 11180, (2019)
Abstract: The denticity, flexibility, and steric hindrance of the ligand are key factors in deciding the mode and number of coordination around a metal ion on complex formation. The thermodynamic aspects of lanthanide complexation with various multidentate ligands provides a significant insight into understand the coordination chemistry of lanthanides in framing the relevant metal organic networks for the applications in biological, biochemical and medical aspects. The pyrazine carboxylic acids are known to form many structurally important complexes and further can form chelates with coordination number of eight for europium in which more water molecules can be knocked out from the primary coordination sphere than demanded by denticity of the ligand. The present studies aimed at ESI-MS characterization and determination of the thermodynamic parameters (log beta, Delta G, Delta H, and Delta S), luminescence properties of europium complexes with pyrazine-2-carboxylate and pyrazine-2,3-dicarboxylate in aqueous solutions by experiment as well as theory. Time resolved luminescence spectroscopy supported by DFT calculations are carried out to optimize the stable geometries of the complexes with various modes of binding and coordination. Furthermore, the thermodynamic parameters estimated theoretically have been used to trace the path of complex formation.

First author: Yang, BC, Magnetic Feshbach resonances in ultracold collisions between Cs and Yb atoms, PHYSICAL REVIEW A, 100, 11180, (2019)
Abstract: We investigate magnetically tunable Feshbach resonances in ultracold collisions between ground-state Yb and Cs atoms, using coupled-channel calculations based on an interaction potential recently determined from photoassociation spectroscopy. We predict resonance positions and widths for all stable isotopes of Yb, together with resonance decay parameters where appropriate. The resonance patterns are richer and more complicated for fermionic Yb than for spin-zero isotopes, because there are additional level splittings and couplings due to scalar and tensorial Yb hyperfine interactions. We examine collisions involving Cs atoms in a variety of hyperfine states and identify resonances that appear most promising for experimental observation and for magnetoassociation to form ultracold CsYb molecules.

First author: Velthoen, MEZ, Insights into the activation of silica-supported metallocene olefin polymerization catalysts by methylaluminoxane, CATALYSIS TODAY, 334, 223, (2019)
Abstract: Metallocene-based olefin polymerization catalysts often require large excesses of co-catalyst for optimal catalyst activation. In this work, mechanistic insights into the activation of supported metallocenes by methylaluminoxane as co-catalyst are acquired. UV-vis diffuse reflectance (DR) spectroscopy of five metallocene catalysts with varying co-catalyst loading reveals the presence of different metallocene species on the surface of the catalyst particles. Deconvolution of the obtained spectra, in combination with an extensive TD-DFT study of UV-vis DR spectra of metallocene structures results in a proposed activation mechanism. We find that with increasing MAO loading, more AlMe2+-bound metallocenes are observed with a shift towards the trimethylaluminum-stabilized cationic methylated metallocene compound. This shift can be directly correlated with a higher activity in the olefin polymerization reaction. Based on this finding, we propose a universal metallocene activation mechanism in which the cationic methylated metallocene is the active species. This species is formed through initial interaction with AlMe2+, followed by ligand exchange with MAO and stabilized in complex with trimethylaluminum as a dormant species.

First author: De, S, 6 pi, 8 pi and 10 pi Six Membered Sulfur Nitrogen Compounds: A Comparative Study with Organic Analogues, CHEMISTRYSELECT, 4, 8807, (2019)
Abstract: Benzene has played an important role in the development of the ideas concerning ‘ aromaticity ‘, as much as that benzene and its derivatives are the best examples of aromatic compounds. Although the inorganic aromatic compounds have been found to obey Huckel 4n+2 pi electron rule, they often possess a different number of pi e as compared to their organic analogues. One such system is cyclic compounds of S3N3, where 10 pi aromatic S3N3- and 8 pi S3N3+ are known, but interestingly, a 6 pi benzene-analogue of the sulfur-nitrogen compound is not reported. Hence as a case study, we have undertaken an extensive theoretical investigation of the electronic structure of 6 pi, 8 pi and 10 pi electrons cyclic S3N33+, S3N3+ and S3N3-, based on the Energy Decomposition Analysis (EDA). We have also compared the results with isoelectronic classical C6H6, C6H62- and C6H64-. Our results indicated that the pi-contribution increases and the sigma-contribution decreases, while the contribution from the orbital interaction energy remains nearly similar upon addition of pi electrons to C6H6 and S3N33+. However, the major decrease in the interaction energy is caused by the drastic reduction of the electrostatic component in C6H64- and S3N33+, which can be correlated to the instability of these molecules. Thus, aromatic binary compounds of sulfur and nitrogen are commonly pi-electron rich, while their aromatic hydrocarbon analogues are pi-electron precise.

First author: Castro-Latorre, P, Catalytic activity of iron phthalocyanine for the oxidation of thiocyanate and L-cysteine anchored on Au(111) clusters, MOLECULAR SIMULATION, 45, 1447, (2019)
Abstract: We studied the oxidation reactions of thiocyanate and L-cysteine on iron phthalocyanine (FePc) coupled via a bridging ligand of the 4-mercatopyridine (4MP) type to a gold cluster (Au-26), aiming to simulate a modified gold electrode. Theoretical models have been used based on the framework of density functional theory. Several mechanistic pathways are explored for the study of these reactions, finding that the most favorable mechanism involves an electron transfer process as the rate-determining step. Along the process, the ability of the gold cluster to act as an electron acceptor facilitating the reactions was detected. In addition, the proposed models presented a correlation between the energy obtained for the rate-determining step of the reaction and the experimental oxidation potentials of the thiocyanate and L-cysteine.

First author: Liu, XR, Optimizing electron-rich arylamine derivatives in thiophene-fused derivatives as pi bridge-based hole transporting materials for perovskite solar cells, RSC ADVANCES, 9, 24733, (2019)
Abstract: Based on the observations of thienothiophene derivatives as pi-bridged small molecule hole transporting materials (HTMs), adjusting their electron-rich arylamine derivatives is an effective approach to obtain the alternative HTMs for perovskite solar cells (PSCs). In this work, starting from a new electron-rich arylamine derivative and different pi-bridged units of thienothiophene derivatives, a series of arylamine derivative-based HTMs were designed, and their properties were investigated using density functional theory combined with the Marcus charge transfer theory. Compared with the parental Z26 material, the designed H01-H04 exhibit appropriate frontier molecular orbitals, good optical properties, better solubility, good stability and higher hole mobilities. H01-H04 materials with high hole mobility (similar to x 10(-2)) can serve as promising HTMs for improving the efficiency of PSCs. The results confirm that the design strategy of adjusting the electron-rich arylamine derivatives in thienothiophene derivatives as pi-bridged HTMs is a reliable approach to obtain the promising HTMs for PSC applications.

First author: Gam, F, Stabilizing heteroatom-centered 16-vertex group 11 tetrahedral architectures: Bonding and structural considerations toward versatile endohedral species, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 119, 24733, (2019)
Abstract: Density functional theory (DFT) calculations were carried out on a series of clusters made of a centered tetrahedral 16-atom superatomic cage having 20 or 18 jellium electrons (je) and structurally related to [Au-20], namely [X@M-16] (M = group 11; X = group 2, 4, 12, 14 element). Such species provide further information of how two different electron counts offer a more preferred endohedral situation for specific group elements. Calculations show that the encapsulated atom provides supplementary orbitals to stabilize the bonding M-16 MO’s. Different favored electron counts are found depending on the nature of the encapsulated atom, as observed by the formation of 20-je species when encapsulating a group 14 element and 18-je species when encapsulating a group 2 element. In addition, the capabilities to enable reactive sites along the cage structure are found via the formation of sigma holes at the coinage-metal edges, as shown by their electrostatic potential surface. Such naked species, which constitute an interesting addition to libraries of examples as small models for doped M(111) surfaces of fcc metals, reveal that different superatomic electronic configurations can favor the encapsulation of certain group elements. These results can guide further design of endohedral species.

First author: Martel, L, Local structure and magnetism of LaxEu1-xPO4 solid solutions, PHYSICAL REVIEW B, 100, 24733, (2019)
Abstract: By combining high spinning speed (60 kHz) and low-field (4.7 T) P-31 solid-state NMR with magnetic susceptibility measurements, we experimentally characterized a series of solid solutions belonging to the LaxEu1-xPO4 (0 <= x <= 1) series. Analyses of the magnetic susceptibility data were carried out using the free ion model and crystal field theory calculations allowing to extract the electronic structure. The paramagnetic shifts of the P sites having one Eu3+ cation in their surrounding were predicted by combining the determined crystal field and energy level values with density functional theory (DFT) calculations. For the La0.9Eu0.1PO4 sample, these theoretical shifts gave a very good overall trend allowing the unambiguous attribution of each P site. This study paves the way for the future analysis of both magnetic susceptibility and NMR data for a broad range of materials containing paramagnetic rare-earth cations.

First author: Kundi, V, Predicting Octanol-Water Partition Coefficients: Are Quantum Mechanical Implicit Solvent Models Better than Empirical Fragment-Based Methods?, JOURNAL OF PHYSICAL CHEMISTRY B, 123, 6810, (2019)
Abstract: In this work, we examined the performance of contemporary quantum mechanical implicit solvent models (SMD, SM8, SM12, and ADF-COSMO-RS) and empirical fragment-based methods for predicting octanol-water partition coefficients (log P-ow). Two test sets were chosen: the first is composed of 34 organic molecules from a recent study by Mobley et al. J. Chem. Theory Comput, 2016, 12, 4015-4024, and the second set is based on a collection of 55 fluorinated alkanols and carbohydrates from Linclau et al. Angew. Chem., Int. Ed., 2016,.55, 674-678. Our analysis indicates that the errors in the solvation free energies of implicit models are reasonably systematic in both solvents such that there is substantial cancellation of errors in the calculation of transfer free energies. Overall, implicit solvent models performed very well across the two test sets with mean absolute errors (MAEs) of about 0.6 log unit and are superior to explicit solvent simulations (GAFF and GAFF-DC). Interestingly, the best performers were empirical fragment-based methods, including ALOGP and miLOGP with significantly lower MAEs (0.2 to 0.4 log unit). The ALOGP method was further tested against the recent SAMPL6 log P-ow challenge consisting of 11 drug-like molecules where it obtained an MAE of 0.32 log unit compared to the best-performing COSMOtherm model (0.31 log unit).

First author: Stohr, M, Theory and practice of modeling van der Waals interactions in electronic-structure calculations, CHEMICAL SOCIETY REVIEWS, 48, 4118, (2019)
Abstract: The accurate description of long-range electron correlation, most prominently including van der Waals (vdW) dispersion interactions, represents a particularly challenging task in the modeling of molecules and materials. vdW forces arise from the interaction of quantum-mechanical fluctuations in the electronic charge density. Within (semi-) local density functional approximations or Hartree-Fock theory such interactions are neglected altogether. Non-covalent vdW interactions, however, are ubiquitous in nature and play a key role for the understanding and accurate description of the stability, dynamics, structure, and response properties in a plethora of systems. During the last decade, many promising methods have been developed for modeling vdW interactions in electronic-structure calculations. These methods include vdWinclusive Density Functional Theory and correlated post-Hartree-Fock approaches. Here, we focus on the methods within the framework of Density Functional Theory, including non-local van der Waals density functionals, interatomic dispersion models within many-body and pairwise formulation, and random phase approximation-based approaches. This review aims to guide the reader through the theoretical foundations of these methods in a tutorial-style manner and, in particular, highlight practical aspects such as the applicability and the advantages and shortcomings of current vdW-inclusive approaches. In addition, we give an overview of complementary experimental approaches, and discuss tools for the qualitative understanding of noncovalent interactions as well as energy decomposition techniques. Besides representing a reference for the current state-of-the-art, this work is thus also designed as a concise and detailed introduction to vdW-inclusive electronic structure calculations for a general and broad audience.

First author: Darari, M, Iron(ii) complexes with diazinyl-NHC ligands: impact of pi-deficiency of the azine core on photophysical properties, DALTON TRANSACTIONS, 48, 10915, (2019)
Abstract: Ligand field enhancing N-heterocyclic carbene (NHC) ligands were recently shown to prevent photo-induced spin crossover in Fe(ii) complexes due to their intricate effects on the electronic excited state structure. Due to their pico- to nanosecond lifetimes, these complexes are now good candidates for photo-sensitizing applications. Herein we report the synthesis and photophysical characterization of a new family of homoleptic Fe(ii) complexes with C<^>N<^>C ligands involving diazines as the central N-heteroaromatic ligand. For these four carbene bond complexes, ultrafast transient absorption spectroscopy revealed a significant improvement of the excited-state lifetime. A record 32 ps lifetime was measured for a complex bearing a ligand combining a pi-deficient pyrazine nucleus and a benzimidazolylidene as NHC. When compared to other azine-based ligands investigated, we argue that the lifetimes are modulated by a small excited state barrier expressing the ability of the ligand to reach the Fe-N distance needed for internal conversion to the ground state.

First author: Cammarota, RC, Thermodynamic and kinetic studies of H-2 and N-2 binding to bimetallic nickel-group 13 complexes and neutron structure of a Ni(eta(2)-H-2) adduct, CHEMICAL SCIENCE, 10, 7029, (2019)
Abstract: Understanding H-2 binding and activation is important in the context of designing transition metal catalysts for many processes, including hydrogenation and the interconversion of H-2 with protons and electrons. This work reports the first thermodynamic and kinetic H-2 binding studies for an isostructural series of first-row metal complexes: NiML, where M = Al (1), Ga (2), and In (3), and L = [N(o-((NCH2PPr2)-Pr-i)C6H4)(3)](3-). Thermodynamic free energies (Delta G degrees) and free energies of activation (Delta G(double dagger)) for binding equilibria were obtained via variable-temperature P-31 NMR studies and lineshape analysis. The supporting metal exerts a large influence on the thermodynamic favorability of both H-2 and N-2 binding to Ni, with Delta G degrees values for H-2 binding found to span nearly the entire range of previous reports. The non-classical H-2 adduct, (eta(2)-H-2)NiInL (3-H-2), was structurally characterized by single-crystal neutron diffraction-the first such study for a Ni(eta(2)-H-2) complex or any d(10) M(eta(2)-H-2) complex. UV-Vis studies and TD-DFT calculations identified specific electronic structure perturbations of the supporting metal which poise NiML complexes for small-molecule binding. ETS-NOCV calculations indicate that H-2 binding primarily occurs via H-H sigma-donation to the Ni 4p(z)-based LUMO, which is proposed to become energetically accessible as the Ni(0)-> M(iii) dative interaction increases for the larger M(iii) ions. Linear free-energy relationships are discussed, with the activation barrier for H-2 binding (Delta G(double dagger)) found to decrease proportionally for more thermodynamically favorable equilibria. The Delta G degrees values for H-2 and N-2 binding to NiML complexes were also found to be more exergonic for the larger M(iii) ions.

First author: Ende, EV, Physicochemical Trapping of Neurotransmitters in Polymer-Mediated Gold Nanoparticle Aggregates for Surface-Enhanced Raman Spectroscopy, ANALYTICAL CHEMISTRY, 91, 9554, (2019)
Abstract: Because of the sharp distance dependence of surface-enhanced Raman spectroscopy (SERS), analyte molecules that do not exhibit strong affinity for Au/Ag often elude detection. New methods of integrating such analytes with SERS substrates are required to circumvent this limitation and expand the sensitivity of SERS to new molecules and applications. We communicate here a solution-phase, capture agent-free method of aggregating Au nanospheres in the presence of five neurotransmitters (dopamine, epinephrine, norepinephrine, serotonin, and histamine) and preventing sedimentation by encapsulating the aggregated nanospheres with polyvinylpyrrolidone, thereby trapping the neurotransmitters in close proximity to the Au nanospheres and enabling SER detection. The primary advantages of this physicochemical trapping method, which is generalizable to analytes beyond the scope of this work, are the high signal-to-noise ratio and spectral consistency down to nM levels. Normal Raman spectra and density functional theory calculations corroborate the accuracy of the spectra. Spectra collected over a wide range of concentrations were used to construct adsorption isotherms for all five neurotransmitters, from which adsorption dissociation constants were calculated, spanning from 5.7 X 10(-4) M to 1.7 X 10(-10) M. We expect this method to produce high quality SER spectra of any molecule with an Au affinity known or expected (based on functional groups) to be within that range. Our results have implications for plasmonic detection of these neurotransmitters, particularly for mixtures of those that exhibited disparate Au affinity in our study. We also present evidence that this method produces spectra of sufficient resolution to explore hypotheses related to surface adsorption behavior.

First author: Sadhu, B, Enhancing Actinide(III) over Lanthanide(III) Selectivity through Hard-by-Soft Donor Substitution: Exploitation and Implication of Near-Degeneracy-Driven Covalency, INORGANIC CHEMISTRY, 58, 9738, (2019)
Abstract: Soft donor ligands often provide higher selectivity for actinides(III) over chemically similar lanthanides(III), e.g., in the Am-III-Eu-III pair. Frequently, the origin of such selectivity is associated with an increased covalency in actinide-ligand bonding. However, the relationship between the degree of covalency and ion selectivity has yet to reach general consensus. Further, it is unclear whether the enhanced covalency leads to a thermodynamic stabilization of the complex or not. Using relativistic density functional theory, we have addressed these outstanding issues by analyzing the subtle change of metal-ligand interactions from a hard donor ligand to a mixed soft-hard one. The present comparative study on the structure of and binding in Am3+ and Eu3+ complexes with 3,4,3-LI(1,2-HOPO) (L) and its mixed-donor variant (LS) shows that the introduction of sulfur as a soft donor atom into the metal coordination sphere indeed infuses an Am3+ selectivity into the otherwise nonselective ligand L but also leads to a significant reduction of the metal-binding Gibbs free energies. Natural population analysis, charge decomposition analysis, and its extended version point to the critical role of ligand-to-metal charge transfer in the overall thermodynamic stability of the complexes. A detailed energy decomposition analysis combining the extended transition state with the natural orbitals chemical valence method reveals an enhancement of the covalency upon switching to the soft-hard donor ligand because of the different nature of the metal-ligand interaction. The ligand L predominantly binds the metal via pi donation, whereas the ligand LS prefers sigma donation. Molecular orbital and quantum theory of atoms in molecules analyses as well as a comparison to a simple model system show that the covalency occurs as a result of orbital mixing and is near-degeneracy-driven in nature. This enhanced covalency, however, fails to thermodynamically compensate for the loss of strong electrostatic interaction and thus does not lead to an additional stabilization of the metal-LS complexes.

First author: Pershina, V, Properties and Reactivity of Hydroxides of Group 13 Elements In, Tl, and Nh from Molecular and Periodic DFT Calculations, INORGANIC CHEMISTRY, 58, 9866, (2019)
Abstract: Adsorption energies, E-ads, of gaseous hydroxides of In, Tl, and the superheavy element Nh on surfaces of Teflon and gold are predicted using molecular and periodic relativistic DFT calculations. The ambition of the work is to assist related “one atom at a time” gas-phase chromatography experiments on the volatility of NhOH. The obtained low values of E-ads(MOH), where M = In, Tl, Nh, on Teflon should guarantee easy transportation of the molecules through the Teflon capillaries from the accelerator to the chemistry setup. Straightforward band-structure DFT calculations using the revPBE-D3(BJ) functional have given an E-ads(MOH) value of 161.4 kJ/mol on the Au(111) surface, being indicative of significant molecule-surface interaction. The MOH-gold surface binding is shown to take place via the oxygen atom of the hydroxide, with the oxygen-gold charge density transfer increasing from InOH to NhOH. The trend in E-ads(MOH) is shown to be InOH < TlOH < NhOH, caused by increasing molecular dipole moments and decreasing stability of the hydroxides in this row. A trend in E-ads of the atoms of these elements on gold is, however, opposite, In > Tl > Nh, caused by the increasing relativistic contraction and stabilization of the np(1/2) AO with Z. These opposite trends in E-ads(MOH) and E-ads(M) in group 13 lead to almost equal E-ads(Nh) and E-ads (NhOH) values, making identification of Nh, as a type of species, difficult by measuring its adsorption enthalpy on gold.

First author: Teyar, B, Theoretical Investigation of the Electronic Structure and Magnetic Properties of Oxo-Bridged Uranyl(V) Dinuclear and Trinuclear Complexes, INORGANIC CHEMISTRY, 58, 10097, (2019)
Abstract: The uranyl(V) complexes [UO2(dbm)(2)K(18C6)](2) (dbm = dibenzoylmethanate) and [UO2(L)](3)(L = 2-(4-tolyl)-1,3-bis(quinolyl)malondiiminate), exhibiting diamond-shaped U2O2 and triangular-shaped U3O3 cores respectively with 5f(1)-5f(1 )and 5f(1)-5f(1)-5f(1) configurations, have been investigated using relativistic density functional theory (DFT). The bond order and QTAIM analyses reveal that the covalent contribution to the bonding within the oxo cores is slightly more important for U3O3 than for U2O2, in line with the shorter U-O distances existing in the trinuclear complex in comparison to those in the binuclear complex. Using the broken symmetry (BS) approach combined with the B3LYP functional for the calculation of the magnetic exchange coupling constants (J) between the magnetic centers, the antiferromagnetic (AF) character of these complexes was confirmed, the estimated J values being respectively equal to -24.1 and -7.2 cm(-1) for the dioxo and trioxo species. It was found that the magnetic exchange is more sensitive to small variations of the core geometry of the dioxo species in comparison to the trioxo species. Although the robust AF exchange coupling within the UxOx cores is generally maintained when small variations of the UOU angle are applied, a weak ferromagnetic character appears in the dioxo species when this angle is higher than 114 degrees, its value for the actual structure being equal to 105.9 degrees. The electronic factors driving the magnetic coupling are discussed.

First author: Hu, SX, Destruction of the Uranyl Moiety in a U(V) “Cation-Cation” Interaction, INORGANIC CHEMISTRY, 58, 10148, (2019)
Abstract: A gas-phase uranyl peroxide dimer supported by three 12-crown-4 ether (12C4) ligands, [(UO2)(2)(O-2)-(12C4)(3))](2+) (A), was prepared by electrospray ionization. Density functional theory (DFT) indicates a structure with two terminal 12C4 and the third 12C4 bridging the uranium centers. Collision induced dissociation (CID) of A resulted in elimination of the bridging 12C4 to yield a uranyl peroxide dimer with two terminal donor ligands, [(12C4)(UO2)(2)(O-2)-(UO2)(12C4)](2+) (B). Remarkably, CID of B resulted in elimination of the bridging peroxide concomitant with reduction of U(VI) to U(V) in C, [(12C4)(UO2)(UO2)(12C4)](2+). DFT studies indicate that in C there is direct interaction between the two UO2+ species, which can thus be considered as a so-called cation-cation interaction (CCI). This formal CCI, induced by tetradentate 12C4 ligands, corresponds to destruction of the linear uranyl moieties and creation of bridging U-O-U oxobonds. On the basis of the structural rearrangement to achieve the structurally extreme CCI interaction, it is predicted also to be accessible for PaO2+ but is less feasible for transuranic actinyls.

First author: Zhang, XR, Coordination of Eu(III) with 1,10-Phenanthroline-2,9-dicarboxamide Derivatives: A Combined Study by MS, TRLIF, and DFT, INORGANIC CHEMISTRY, 58, 10239, (2019)
Abstract: Tetradentate 1,10-phenanthroline-2,9-dicarboxamide (PDAM) derivatives have been well documented as effective binding ligands toward MA(III) and Ln(III), while the structural analysis and species determination of the complexes are still limited. Herein, we report a combined study on the coordination of Eu(III) with PDAM derivatives using electrospray ionization mass spectrometry (ESI-MS), time-resolved laser-induced fluorescence (TRLIF), and density functional theory (DFT) calculations. PDAM derivatives here involve N,N’-diethyl-N,N’-diethyl-2,9-diamide-1,10-phenanthroline (Et-Et-DAPhen), N,N’-dibutyl-N,N’-dibutyl-2,9-diamide-1,10-phenanthroline (But-But-DAPhen), and N,N’-dihexyl-N,N’-dihexyl-2,9-diamide-1,10-phenanthroline (Hex-Hex-DAPhen). The collision-induced dissociation (CID) test shows that these alkyl-DAPhen ligands coordinate strongly with Eu(III), given that the coordination moieties remain intact during CID. The 1/2 Eu-III-L species was found to be the dominant component for all three ligands, as evidenced by ESI-MS and fluorescence titration. The fluorescence decay results indicate that the hydration numbers of Eu(III) are reduced from 9 to 1 upon complexation, in agreement with the fact that the 1/2 Eu-III-L species are formed, and eight water molecules are exactly replaced by eight donor atoms of two alkyl-DAPhen ligands. In addition, the DFT calculations suggest that the 1:2 Eu-III-L species is more stable than the 1/1 Eu-III-L species and the Eu-oxygen/nitrogen (Eu-O/N) bonds have a dominant ionic character, with the O atoms having stronger electron-donating abilities toward Eu(III) in comparison to the N atoms.

First author: Li, ZZ, Stability and bonding in rare gas inserted interhalogens FRgXF(n) (X = Br and I, n=0 and 2), INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 119, 10239, (2019)
Abstract: Structures, stabilities, and bonding nature of the Rg inserted interhalogens FRgXF(n) (Rg = Kr, Xe, and Rn, X = Br and I, n = 0 and 2) have been studied using PBE0, MP2, and CCSD(T) methods. In these compounds, the dissociation energy for F-Rg bonds ranging from 160 kcal mol(-1) to 180 kcal mol(-1) could be best described as ionic bonds. Rg-X bonds have some covalent character with lower interaction energies within the range 20-50 kcal mol(-1). NBO, ELF, and EDA calculations were used to further confirm the nature of the Rg inserted compounds and present a clear description of Rg bonding properties.

First author: Muszak, D, The synthesis and characterization of tetramic acid derivatives as Mdm2-p53 inhibitors, JOURNAL OF MOLECULAR STRUCTURE, 1189, 161, (2019)
Abstract: We present syntheses, prediction of tautomer forms and activities of the second generation of the Mdm2-p53 inhibitors that are based on the tetramic acid scaffold. The inhibitors do not contain 6-chloroindole. Binding of these compounds to Mdm2 was checked by two orthogonal methods: the fluorescence polarization and the H-1-N-15 HSQC NMR titration experiments. We discovered that the 3-phenylthio-substituted tetramic acid derivatives exist in solution solely in their enol forms which is in contrast to the similar 3-aliphatic substituted derivatives. The inhibitory (K-i) and dissociation (K-D) constants are in low micromolar ranges with the best binding compound 9a having K-D = 2.9 mu M. Furthermore, our data show that the compounds indeed bind to the p53-binding pocket of Mdm2 and do not cause dimerization of Mdm2. The current work provides solid base for further rational design of the Mdm2/p53 inhibitors.

First author: Liu, PC, Resolving Molecular Structures with High-Resolution Tip-Enhanced Raman Scattering Images, ACS NANO, 13, 9342, (2019)
Abstract: Vibrational modes of a single molecule can be visualized by tip-enhanced Raman spectroscopy with atomic resolution. However, the exact vibrations associated with these Raman scattering images are still in debate due to the lack of theoretical interpretation. In this work, we systematically study the Raman scattering images of a single Co (II)-tetraphenylporphyrin molecule. The stable structure whose Raman scattering images consistently match experimental results is discovered. Furthermore, we elucidate the effects of near-field localizations and field gradient on the resolution in Raman scattering images. The approach of locally integrated Raman polarizability density employed in this work provides an intuitive explanation of the origin of the experimental Raman scattering images.

First author: Szymanski, S, Aromaticity and Electron Density of Hypericin, JOURNAL OF NATURAL PRODUCTS, 82, 2106, (2019)
Abstract: The influence of the substituents on the geometry of the central ring system of hypericin has been analyzed. Substitution that causes flattening of the hypericin central rings is connected with introducing the aromatic character of the empty rings. All the hypericin rings have an aromatic character illustrated by the Harmonic Oscillator Measure of Aromaticity (HOMA), Nucleus Independent Chemical Shift (NICS), Fluctuation Index (FLU), and Ellipticity Index (EL) indices. Quantum Theory of Atoms in Molecules (QTAIM) and Natural Bond Orbital (NBO) analyses performed on 7,14-dihydrophenanthro[1,10,9,8-opqra]perylene, its substituted analogues, and hypericin show an influence of this substitution on electron density of the central rings.

First author: Ahmad, SM, In Silico Acetylene [2+2+2] Cycloadditions Catalyzed by Rh/Cr Indenyl Fragments, CATALYSTS, 9, 2106, (2019)
Abstract: Metal-catalyzed alkyne [2+2+2] cycloadditions provide a variety of substantial aromatic compounds of interest in the chemical and pharmaceutical industries. Herein, the mechanistic aspects of the acetylene [2+2+2] cycloaddition mediated by bimetallic half-sandwich catalysts [Cr(CO)(3)IndRh] (Ind = (C9H7)(-), indenyl anion) are investigated. A detailed exploration of the potential energy surfaces (PESs) was carried out to identify the intermediates and transition states, using a relativistic density functional theory (DFT) approach. For comparison, monometallic parent systems, i.e., CpRh (Cp = (C5H5)(-), cyclopentadienyl anion) and IndRh, were included in the analysis. The active center is the rhodium nucleus, where the [2+2+2] cycloaddition occurs. The coordination of the Cr(CO)(3) group, which may be in syn or anti conformation, affects the energetics of the catalytic cycle as well as the mechanism. The reaction and activation energies and the turnover frequency (TOF) of the catalytic cycles are rationalized, and, in agreement with the experimental findings, our computational analysis reveals that the presence of the second metal favors the catalysis.

Abstract: Keggin heteropolyacids (HPW) supported on niobia have been considered for both homogeneous and heterogeneous catalysis due to its special features, like the strong Bronsted acidity, low volatility, high activity and high selectivity for various reactions in comparison with mineral acids. Literature reports many different preparation methods for these catalysts through the addition of HPW solutions, in either water or acid, over niobia under stirring. However not much is known about the way how HPW interacts with the support, neither how the temperature influences this interaction. In order to contribute to expand the knowledge on this field we report here a new way of preparing HPW supported catalysts over niobia calcined at 500 and 600 degrees C, followed by a theoretical study meant to check the influence of the temperature increase on the adsorption behavior of the catalysts over the support. Our proposed method showed to be an efficient alternative for impregnation of HPW over niobia, while the theoretical results suggest that pseudo-hexagonal and orthorhombic are the most likely crystalline forms for these catalysts.

First author: Zhang, BY, Janus: An Extensible Open-Source Software Package for Adaptive QM/MM Methods, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 15, 4362, (2019)
Abstract: Adaptive quantum mechanics/molecular mechanics (QM/MM) approaches are able to treat systems with dynamic or nonlocalized active centers by allowing for on-the-fly reassignment of the QM region. Although these approaches have been in active development, the inaccessibility of current software has caused slow adoption and limited applications. JANUS seeks to remedy the limitations of current software by providing a free and open-source Python library for adaptive methods that is modular and extensible. Our software has implementations of many existing adaptive methods and a user-friendly input structure that removes the hindrance of complicated setup procedures. A Python API is made available to customize JANUS’s capabilities and implement novel adaptive approaches. JANUS currently interfaces with PSI4 and OPENMM, but its modular infrastructure enables easy extensibility to other molecular codes without major modifications to either code. The software is freely available at https://github.com/CCQC/janus. Our goal is that JANUS will serve as a user-driven platform for adaptive QM/MM methods.

First author: Keskic, T, What Is the Nature of Interactions of BF4-, NO3-, and ClO4- to Cu(II) Complexes with Girard’s T Hydrazine? When Can Binuclear Complexes Be Formed?, CRYSTAL GROWTH & DESIGN, 19, 4810, (2019)
Abstract: In solid-state coordination chemistry, the coordination number of a metal center is not always unambiguously determined, as sometimes from the geometrical parameters it is not clear if ligands are directly bound to the central metal ion or they belong to the outer sphere of a complex. The nature of bonding between Cu(II) and weakly coordinated anions BF4-, NO3-, and ClO4- is investigated by the combined crystallographic and computational study. It is shown that the synergy between the crystal structure determination and computational chemistry allows identification of all interactions present in crystals. Three new complexes, [CuLCl]BF4 (1), [CuLCl]NO3 (2), and [Cu2L2Cl2](BF4)(2) (3) with the same [CuLCl](+) moiety (L = (E)-N,N,N-trimethyl-2-oxo-2-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)ethan-1-amin), were synthesized and characterized by single crystal X-ray diffraction methods and compared to the previously reported [CuLCIIClO4 (4). Energy decomposition analysis, noncovalent interaction index analysis, independent gradient model, and the quantum theory of atoms in molecules are performed on the X-ray structures of these four complexes. The results revealed that in 1, 2, and 4, BF4-, NO3-, and ClO4- are weakly, but directly coordinated to the Cu(II) with bonds having high electrostatic character. In 3, BF4- is the counter-anion, electrostatically bonded to the L. Furthermore, the present analysis rationalized the fact that only complex 3 is binuclear with bridging Cl- ions.

First author: Song, XD, Computational insights into the mechanism of formaldehyde detection by luminescent covalent organic framework, JOURNAL OF MOLECULAR MODELING, 25, 4810, (2019)
Abstract: Luminescent covalent organic frameworks (COFs) as fluorescent sensor materials provide a distinct advantage over other materials. In this work, we investigated the hydrogen bonding between the luminescent COF Ph-An-COF and formaldehyde in its excited electronic state by using density functional theory and time-dependent density functional theory to determine whether this type of COF can be used for formaldehyde detection. Hydrogen bonding significantly changed the nature of the frontier orbital and the luminescent properties. Our study reveals that the hydrogen bonding was strengthened in the excited state and the fluorescence rate coefficient was significantly reduced, which is not favorable for the luminescence of this type of COF and would lead to a luminescence decrease or quenching phenomenon. Therefore, this type of luminescent COF can be used as a potential chemical sensor to detect formaldehyde. This work provides an insight into the design of luminescence covalent organic frameworks.

First author: Fang, T, Equilibrium thallium isotope fractionation and its constraint on Earth’s late veneer, ACTA GEOCHIMICA, 38, 459, (2019)
Abstract: Equilibrium isotope fractionation of thallium (Tl) includes the traditional mass-dependent isotope fractionation effect and the nuclear volume effect (NVE). The NVE dominates the overall isotope fractionation, especially at high temperatures. Heavy Tl isotopes tend to be enriched in oxidized Tl3+-bearing species. Our NVE fractionation results of oxidizing Tl+ to Tl3+ can explain the positive enrichments observed in ferromanganese sediments. Experimental results indicate that there could be 0.2-0.3 epsilon-unit fractionation between sulfides and silicates at 1650 degrees C. It is consistent with our calculation results, which are in the range of 0.17-0.38 epsilon-unit. Importantly, Tl’s concentration in the bulk silicate Earth (BSE) can be used to constrain the amount of materials delivered to Earth during the late veneer accretion stage. Because the Tl concentration in BSE is very low and its Tl isotope composition is similar with that of chondrites, suggesting either no Tl isotope fractionation occurred during numerous evaporation events, or the Tl in current BSE was totally delivered by late veneer. If it is the latter, the Tl-content-based estimation could challenge the magnitude of late veneer which had been constrained by the amount of highly siderophile elements in BSE. Our results show that the late-accreted mass is at least five-times larger than the previously suggested magnitude, i.e., 0.5 wt% of current Earth’s mass. The slightly lighter Tl-205 composition of BSE relative to chondrites is probable a sign of occurrence of Tl-bearing sulfides, which probably were removed from the mantle in the last accretion stage of the Earth.

First author: Zhang, JL, Photoelectron imaging spectroscopic study and chemical-bonding analysis of AgOH and AgSH anions, JOURNAL OF QUANTITATIVE SPECTROSCOPY & RADIATIVE TRANSFER, 233, 52, (2019)
Abstract: The photodetachment spectra of AgOH- and AgSH- have been investigated using photoelectron velocity map imaging (PE-VMI). In combination with the ab intio calculations, vibration-resolved photoelectron spectra yield accurate electron affinities of 1.177(15) eV and 1.193(10) eV for AgOH and AgSH, respectively. Franck-Condon simulations of the ground state transition are performed to assign vibrational structure in the spectra and to assist us in identifying the observed spectral bands. And the frequencies are extracted to be 475(35) cm(-1) for AgOH and 358(30) cm(-1) for AgSH, respectively. A variety of theoretical calculations are analyzed to reveal the chemical bonding characteristics of AgOH-1/0 and AgSH-1/0, which indicates that Ag-X bonding in AgXH-1/0 (X=O and S) species is much more ionic than covalent.

First author: Yan, X, Potential strategy used for controlling the phosphorescent properties in tetradentate Pt(II) complexes: Effect of azole ligand, APPLIED ORGANOMETALLIC CHEMISTRY, 33, 52, (2019)
Abstract: Designing deep-blue phosphorescent materials is vital and essential in the construction of white organic light-emitting diodes. Using density functional theory (DFT) and time-dependent DFT, three tetradentate Pt(II) complexes were investigated in detail to reveal the influence of azole ligand with varying number of N atoms on the emission wavelengths and radiative and non-radiative decay processes. The calculated results indicate that with an increase of N atoms in azole rings, the radiative decay process can be effectively facilitated. Moreover, an increase of N atoms in azole rings could lead to a distinct blue-shift of emission wavelengths from 553 to 470 nm. Also, the non-radiative decay processes, including temperature-independent and temperature-dependent ones, were taken into account. The results may provide some valuable and meaningful information for designing high-performance phosphorescent Pt(II) complexes.

First author: Bae, YJ, Substituent effects on energetics and crystal morphology modulate singlet fission in 9,10-bis(phenylethynyl)anthracenes, JOURNAL OF CHEMICAL PHYSICS, 151, 52, (2019)
Abstract: Singlet fission (SF) converts a singlet exciton into two triplet excitons in two or more electronically coupled organic chromophores, which may then be used to increase solar cell efficiency. Many known SF chromophores are unsuitable for device applications due to chemical instability or low triplet state energies. The results described here show that efficient SF occurs in derivatives of 9,10-bis(phenylethynyl)anthracene (BPEA), which is a highly robust and tunable chromophore. Fluoro and methoxy substituents at the 4- and 4 ‘-positions of the BPEA phenyl groups control the intermolecular packing in the crystal structure, which alters the interchromophore electronic coupling, while also changing the SF energetics. The lowest excited singlet state (S-1) energy of 4,4 ‘-difluoro-BPEA is higher than that of BPEA so that the increased thermodynamic favorability of SF results in a (16 +/- 2 ps)(-1) SF rate and a 180% +/- 16% triplet yield, which is about an order of magnitude faster than BPEA with a comparable triplet yield. By contrast, 4-fluoro-4 ‘-methoxy-BPEA and 4,4 ‘-dimethoxy-BPEA have slower SF rates, (90 +/- 20 ps)(-1) and (120 +/- 10 ps)(-1), and lower triplet yields, (110 +/- 4)% and (168 +/- 7)%, respectively, than 4,4 ‘-difluoro-BPEA. These differences are attributed to changes in the crystal structure controlling interchromophore electronic coupling as well as SF energetics in these polycrystalline solids.

First author: van der Ham, A, Computational and NMR Studies on the Complexation of Lithium Ion to 8-Crown-4, CHEMPHYSCHEM, 20, 2103, (2019)
Abstract: Lithium ion selective crown ethers have been the subject of much research for a multitude of applications. Current research is aimed at structurally rigidifying crown ethers, as restructuring of the crown ether ring upon ion binding is energetically unfavorable. In this work, the lithium ion binding ability of the relatively rigid 8-crown-4 was investigated both computationally by density functional theory calculations and experimentally by H-1 and Li-7 NMR spectroscopy. Although both computational and experimental results showed 8-crown-4 to bind lithium ion, this binding was found to be weak compared to larger crown ethers. The computational analysis revealed that the complexation is driven by enthalpy rather than entropy, illustrating that rigidity is only of nominal importance. To elucidate the origin of the favorable interaction of lithium ion with crown ethers, activation strain analyses and energy decomposition analyses were performed pointing to the favorable interaction being mainly electrostatic in nature. 8-crown-4 presents the smallest crown ether reported to date capable of binding lithium ion, possessing two distinct conformations from which it is able to do so.

First author: Weerawardene, KLDM, Theoretical Investigation of Water Oxidation Mechanism on Pure Manganese and Ca-Doped Bimetal Oxide Complexes, JOURNAL OF PHYSICAL CHEMISTRY A, 123, 6152, (2019)
Abstract: Understanding the role of Ca2+ ion in the oxygen-evolving complex of photosystem II is essential to design commercially viable and efficient water oxidation catalysts. To this end, small pure manganese oxide and calcium-doped manganese oxide model complexes saturated with water-derived ligands are investigated in this work. Density functional theory calculations are performed to investigate the water oxidation process on Mn-2(mu-OH)(mu-O)(H2O)(3)(OH)(5) (Mn2O4 center dot 6H(2)O) and CaMnO(mu-OH)(2)(H2O)(5)(OH)(2)(CaMnO3 center dot 7H(2)O) complexes. Many reaction pathways are considered, and the three lowest energy water oxidation mechanisms on CaMnO3 center dot 7H(2)O have highest reaction energy steps of 1.37, 1.67, and 1.81 eV compared to the highest reaction energy step of 2.25 eV for the lowest energy mechanism of the pure Mn2O center dot 6H(2)O complex. Doping of the manganese dimer complex with calcium decreases the highest reaction energy of the water oxidation process. Consequently, the inclusion of calcium appears to improve the catalyst’s efficiency for water splitting.

First author: Zhai, LH, Uncovering the Networks of Topological Neighborhoods in beta-Strand and Amyloid beta-Sheet Structures, SCIENTIFIC REPORTS, 9, 6152, (2019)
Abstract: Although multiple hydrophobic, aromatic pi-pi, and electrostatic interactions are proposed to be involved in amyloid fibril formation, the precise interactions within amyloid structures remain poorly understood. Here, we carried out detailed quantum theory of atoms-in-molecules (QTAIM) analysis to examine the hydrophobic core of amyloid parallel and antiparallel beta-sheet structures, and found the presence of multiple inter-strand and intra-strand topological neighborhoods, represented by networks of through-space bond paths. Similar bond paths from side chain to side chain and from side chain to main chain were found in a single beta-strand and in di-and tripeptides. Some of these bond-path networks were enhanced upon beta-sheet formation. Overall, our results indicate that the cumulative network of weak interactions, including various types of hydrogen bonding (X-H-Y; X, Y = H, C, O, N, S), as well as non-H-non-H bond paths, is characteristic of amyloid beta-sheet structure. The present study postulated that the presence of multiple through-space bond-paths, which are local and directional, can coincide with the attractive proximity effect in forming peptide assemblies. This is consistent with a new view of the van der Waals (vdW) interactions, one of the origins of hydrophobic interaction, which is updating to be a directional intermolecular force.

First author: Zhao, LL, Chemical Bonding and Bonding Models of Main-Group Compounds, CHEMICAL REVIEWS, 119, 8781, (2019)
Abstract: The focus of this review is the presentation of the most important aspects of chemical bonding in molecules of the main group atoms according to the current state of knowledge. Special attention is given to the difference between the physical mechanism of covalent bond formation and its description with chemical bonding models, which are often confused. This is partly due to historical reasons, since until the development of quantum theory there was no physical basis for understanding the chemical bond. In the absence of such a basis, chemists developed heuristic models that proved extremely valuable for understanding and predicting experimental studies. The great success of these simple models and the associated rules led to the fact that the model conceptions were regarded as real images of physical reality. The complicated world of quantum theory, which eludes human imagination, made it difficult to link heuristic models of chemical bonding with quantum chemical knowledge. In the early days of quantum chemistry, some suggestions were made which have since proved untenable. In recent decades, there has been a stormy development of quantum chemical methods, which are not limited to the quantitative accuracy of the calculated properties. Also, methods have been developed where the experimentally developed models can be quantitatively expressed and visually represented using mathematically well-defined terms that are derived from quantum chemical calculations. The calculated numbers may however not be measurable values. Nevertheless, as orientation data for the interpretation and classification of experimental findings as well as a guideline for new experiments, they form a coordinate system that defines the multidimensional world of chemistry, which corresponds to the Hilbert space formalism of physics. The nonmeasurability of model values is not a weakness of chemistry but a characteristic by which the infinite complexity of the material world becomes scientifically accessible and very useful for chemical research. This review examines the basis of the commonly used quantum chemical methods for calculating molecules and for analyzing their electronic structure. The bonding situation in selected representative molecules of main -group atoms is discussed. The results are compared with textbook knowledge of common chemistry.

First author: Kim, JH, Green-Sensitive Phototransistor Based on Solution-Processed 2D n-Type Organic Single Crystal, ADVANCED ELECTRONIC MATERIALS, 5, 8781, (2019)
Abstract: 2D single crystals of down to two-monolayer thickness are fabricated from a push-pull structure-based green light absorbing organic n-type semiconductor, (2E,2 ‘ E)-3,3 ‘-(2,5-difluoro-1,4-phenylene)bis(2-(5-(4-(trifluoromethyl)phenyl)thiophen-2-yl)acrylonitrile) (2F-4-TFPTA). The 2F-4-TFPTA 2D single crystal exhibits field-effect electron mobility of 0.9 cm(2) V-1 s(-1) in the dark and also decent photoresponsivity of 3.6 x 10(3) A W-1 under green light-emitting diode irradiation, which is noted as the first demonstration of green-sensitive 2D organic phototransistors. Photoresponse time of this 2F-4-TFPTA 2D single-crystal device is as fast as 43 ms for the rise and 85 ms for the decay.

First author: Silva, TC, Methane Activation by CoOmn+ (n=0, 1, 2; m=1, 2): Reactivity Parameters, Electronic Properties and Binding Energy Analysis, CHEMISTRYSELECT, 4, 7912, (2019)
Abstract: The need for renewal and more efficient energy resources has led to a great interest in carrying out studies aiming to find novel sources of energy, which are able to supply the growing global demand, and providing an eco-friendly usage of natural resources. In this context, the usage of methane stands out as a promising energetic alternative, mostly due to vast reserves, low cost and less polluting fuel. Theoretical studies with B3LYP, CCSD (t) and ZORA-B3LYP methods were used to look into the catalytic properties of (CoOmn+ n= 0, 1, 2 and m=1, 2) in the methane C-H bond activation. According to the EDA results, the studied species presented two stabilizing factors for the global interaction energy, being the electrostatic Delta E-elstat and orbital Delta E-orb interactions. The HOMO and LUMO orbitals were also evaluated based on the molecular orbital diagrams for the monoxides and dioxides series. Regarding the oxidative insertion mechanism, the results demonstrate that the initial interaction between oxide and methane is of great relevance in its activation process, in which E-Bonding is benefited by the increasingly charge on the central metal. The high electron density regarding the oxides is meaningful for the reaction kinetics and the oxo ligands influence the thermodynamics of the reaction, becoming the DHA mechanism exergonic. Regarding the OHM mechanism, better kinetic conditions are found for CoO2++ and better thermodynamics for doubly charged cobalt monoxides and dioxides.

First author: Garcia-Rodeja, Y, Impact of C=C/B-N Replacement on the Diels-Alder Reactivity of Curved Polycyclic Aromatic Hydrocarbons, CHEMISTRY-A EUROPEAN JOURNAL, 25, 9771, (2019)
Abstract: The influence of the replacement of C=C bonds by isoelectronic B-N moieties on the reactivity of pi-curved polycyclic aromatic hydrocarbons has been computationally explored by means of density functional theory calculations. To this end, we selected the Diels-Alder cycloaddition reactions of the parent corannulene and its BN-doped counterparts with either cyclopentadiene or maleic anhydride. In addition, the analogous reactions involving larger buckybowls, such as BN-hemifullerene, BN-circumtrindene, and BN-fullerene, have been also considered. It has been found that whereas corannulene behaves as a dienophile, its BN counterpart better acts as a diene. In contrast, the larger BN-curved systems cannot be used as dienes in Diels-Alder reactions, but undergo facile (i.e., low barrier) cycloaddition reactions with cyclopentadiene. The observed trends in reactivity, which cannot be directly explained by using typical frontier molecular orbital arguments, are quantitatively described in detail by means of state-of-the-art computational methods, namely the activation strain model of reactivity combined with the energy decomposition analysis method. The results of our calculations highlight the crucial role of the curvature of the system on the reactivity and its influence on the strength of the orbital interactions between the deformed reactants during their transformations.

First author: Sahnoune, H, 1,4-Dimethoxybutadienediyl-Bridged Diiron Compounds in Three Oxidation States: Evaluation of Delocalization Effects, ORGANOMETALLICS, 38, 2724, (2019)
Abstract: The binuclear iron complexes [Cp*(PMe3)(CO)Fe-C(OCH3)=CH-CH=C(OCH3)-Fe(PMe3)(CO)Cp*] (1meso and 1dl) were prepared by double deprotonation of their known parents [Cp*(PMe3)(CO)Fe=C(OCH3)CH2-CH2-C(OCH3)=Fe(PMe3)-(CO)Cp*](PF6)(2) (Smeso and 5dl) and were isolated in good yield (90%). These complexes were characterized by ESI-mass spectrometry, IR and multinuclear NMR spectroscopy, and cyclic voltammetry. The singly and doubly oxidized forms lmeso(PF6)(n) and 1dl(PF6)(n) (n = 1, 2) were prepared by oxidation of the parent neutral complexes with 1 and 2 equiv of ferrocenium salt (93-100% yield). The related complex [Cp*(dppe)-Fe-C(OCH3)=CH-CH=C(OCH3)-Fe(dppe)Cp*](PF6) (2(PF6)) was obtained by reduction of the known dicationic derivative [Cp*(dppe)Fe-C(OCH3)=CH-CH=C(OCH3)-Fe(dppe)Cp*RPF6) (2-(PF6)(2)) with 1 equiv of cobaltocene (100% yield). Multinuclear NMR spectroscopy allowed us to establish the diiron(II) conjugated mu-bis(carbene) structure for lmeso(PF6)(2) and 1dl(PF6)(2). In the case of the meso derivative, H-1 NMR revealed the presence of E and Z isomers in a 4:1 ratio, confirming the presence of a C=C double bond in the middle of the bridge. The three radicals 1meso(PF6), 1dl(PF6), and 2(PF6), which are thermally stable, were analyzed by IR, MOssbauer, ESR, UV-vis, and NIR spectroscopy. Experimental data, discussed with the support of quantum chemistry calculations performed at the DFT level of theory, indicate that these radical cations exhibit characteristics of oxidation on the butadienediyl bridge rather than on the metal centers.

First author: Guo, FS, Uranocenium: Synthesis, Structure, and Chemical Bonding, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 58, 10163, (2019)
Abstract: ion of iodide from [(eta(5)-(C5Pr5)-Pr-i)(2)UI] (1) produced the cationic uranium(III) metallocene [(eta(5)-(C5Pr5)-Pr-i)(2)U](+) (2) as a salt of [B(C6F5)(4)](-). The structure of 2 consists of unsymmetrically bonded cyclopentadienyl ligands and a bending angle of 167.82 degrees at uranium. Analysis of the bonding in 2 showed that the uranium 5f orbitals are strongly split and mixed with the ligand orbitals, thus leading to non-negligible covalent contributions to the bonding. Investigation of the dynamic magnetic properties of 2 revealed that the 5f covalency leads to partially quenched anisotropy and fast magnetic relaxation in zero applied magnetic field. Application of a magnetic field leads to dominant relaxation by a Raman process.

First author: Oudsen, JPH, Spectroscopic and theoretical investigation of the [Fe-2(bdt)(CO)(6)] hydrogenase mimic and some catalyst intermediates, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 14638, (2019)
Abstract: In [Fe-Fe] hydrogenase mimic systems the ene-1,2-dithiolene ligands play an important role in the stabilisation of the redox-active metal center. This is demonstrated by the benzenedithiolene (bdt) analogue, featuring six terminal carbonyl ligands connected to a di-iron metal center, i.e. [Fe-2(bdt)(CO)(6)]. Here we present a combined experimental and theoretical study that elucidates key intermediates [Fe-2(bdt)(CO)(6)](1-) and [Fe-2(bdt)(m-CO)(CO)(5)](2-) in the electrocatalytic production of dihydrogen. A DFT study shows that [Fe-2(bdt)(CO)(6)](1-) is the kinetic product after the first one electron reduction, while the previously proposed bridging intermediate species [Fe-2(bdt)(m-CO)(CO)(5)](1)- is kinetically inaccessible. The doubly reduced species [Fe-2(bdt)(m-CO)(CO)(5)](2-) was for the first time structurally characterized using EXAFS. XANES analysis confirms the existence of reduced iron zero species and confirms the distorted geometry that was suggested by the DFT calculations. Combining IR, UV-vis and XAS spectroscopic results with TD-DFT and FEFF calculations enabled us to assign the key-intermediate [Fe-2(bdt)(CO)(6)](2-). This study emphasizes the strengths of combining computational chemistry with advanced spectroscopy techniques.

First author: Zhu, ZD, Halogen bonding in differently charged complexes: basic profile, essential interaction terms and intrinsic sigma-hole, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 15106, (2019)
Abstract: Studies on halogen bonds (XB) between organohalogens and their acceptors in crystal structures revealed that the XB donor and acceptor could be differently charged, making it difficult to understand the nature of the interaction, especially the negatively charged donor’s electrophilicity and positively charged acceptor’s nucleophilicity. In this paper, 9 XB systems mimicking all possibly charged halogen bonding interactions were designed and explored computationally. The results revealed that all XBs could be stable, with binding energies after removing background interaction as strong as -1.2, -3.4, and -8.3 kcal mol(-1) for Cl, Br, and I involved XBs respectively. Orbital and dispersion interactions are found to be always attractive while unidirectional intermolecular electron transfer from a XB acceptor to a XB donor occurs in all XB complexes. These observations could be attributed to the intrinsic sigma-hole of the XB donor and the intrinsic electronic properties of the XB acceptor regardless of their charge states. Intramolecular charge redistribution inside both the donor and the acceptor is found to be system-dependent but always leads to a more stable XB. Accordingly, this study demonstrates that the orbital-based origin of halogen bonds could successfully interpret the complicated behaviour of differently charged XB complexes, while electrostatic interaction may dramatically change the overall bonding strength. The results should further promote the application of halogens in all related areas.

First author: Liu, QL, Computer-aided reaction solvent design based on transition state theory and COSMO-SAC, CHEMICAL ENGINEERING SCIENCE, 202, 300, (2019)
Abstract: Solvents have been widely used in chemical manufacturing processes. When involved in liquid homogeneous-phase kinetic reactions, they can have significant impacts on the reaction product yield. In this paper, an optimization-based framework is developed for reaction solvent design. The framework first identifies a reaction kinetic model using a hybrid method consisting of three steps. In step one, a rigorous thermodynamic derivation based on CTST (Conventional Transition State Theory) is performed to formulate a primary reaction kinetic model. In step two, a knowledge-based method is used to select additional solvent properties as supplementary descriptors to account for quantitative correction to the model and thereby improving the prediction accuracy. In step three, model identification is performed to obtain the best regressed reaction kinetic model. This hybrid modelling method is tested through two case studies, namely Diels-Alder and Menschutkin reactions, and an impressive consistency of the results is observed when the infinite dilution activity coefficients (calculated by COSMO-SAC model), hydrogen-bond donor, hydrogen-bond acceptor and solvent surface tension are selected as descriptors in the final reaction kinetic model. The GC-COSMO and GC (Group Contribution) methods are combined for the prediction of these descriptors. Finally, the Computer-Aided Molecular Design (CAMD) technique is integrated with the derived kinetic model for reaction solvent design by formulating and solving a Mixed-Integer Non-Linear Programming (MINLP) model. A decomposition-based solution algorithm is employed to manage the complexity involved with the nonlinear COSMO-SAC equations. Promising reaction solvents are identified and compared with those reported by others, indicating wide applicability and high accuracy of the developed optimization-based framework.

First author: Murugesan, K, Nickel-Catalyzed Stereodivergent Synthesis of E- and Z-Alkenes by Hydrogenation of Alkynes, CHEMSUSCHEM, 12, 3363, (2019)
Abstract: A convenient protocol for stereodivergent hydrogenation of alkynes to E- and Z-alkenes by using nickel catalysts was developed. Simple Ni(NO3)(2).6 H2O as a catalyst precursor formed active nanoparticles, which were effective for the semihydrogenation of several alkynes with high selectivity for the Z-alkene (Z/E>99:1). Upon addition of specific multidentate ligands (triphos, tetraphos), the resulting molecular catalysts were highly selective for the E-alkene products (E/Z>99:1). Mechanistic studies revealed that the Z-alkene-selective catalyst was heterogeneous whereas the E-alkene-selective catalyst was homogeneous. In the latter case, the alkyne was first hydrogenated to a Z-alkene, which was subsequently isomerized to the E-alkene. This proposal was supported by density functional theory calculations. This synthetic methodology was shown to be generally applicable in >40 examples and scalable to multigram-scale experiments.

First author: Artigas, A, Regioselectivity in Diels-Alder Cycloadditions of C-#6094(68) Fullerene with a Triplet Ground State, JOURNAL OF ORGANIC CHEMISTRY, 84, 9017, (2019)
Abstract: To achieve full control on the regioselectivity of chemical additions to fullerenes is a major goal in the field of reactivity of carbon nanostructures. In this work, we computationally analyze the regioselectivity of the Diels-Alder (DA) reaction of cyclopentadiene to the hollow nonisolated pentagon rule (IPR) C-#6094(68) fullerene, which possesses a triplet ground state. Our aim is to check whether the typically favored [6,6]-addition in fullerenes can be shifted to the [5,6] bonds in C-#6094(68) due to the change in the ground state. Our results show that the [5,5] adduct is the thermodynamic reaction product, whereas the kinetic product is the [5,6] bond of type F, adjacent to a pentalene unit. As compared to the singlet state, in the triplet state, the Gibbs barrier for the attack to the [5,6] bond of C-#6094(68) is reduced by about 5 kcal.mol(-1), the DA cycloaddition becoming more regioselective. Our energy decomposition analysis shows that the change of regioselectivity in the DA reaction of hollow fullerenes from the usual [6,6] bond to the [5,6] bond in C-#6094(68) is driven by higher stabilizing orbital interactions in the latter bond favored by the spin density accumulation around the two pentalene units of the cage. The findings of this investigation complement those of earlier studies on regioselectivity of IPR fullerenes and endohedral metallofullerenes.

First author: Werle, C, Effect of Enhanced Electron Withdrawal on the Cohesion of Cr-Pd Hemichelates, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 84, 3301, (2019)
Abstract: Two new trimetallic Cr-Pd hemichelates containing a fluorenyl moiety and two trans arene-bound Cr(CO)(3) moieties were synthesized and fully characterized. Their molecular structures obtained by X-ray diffraction analysis do not show major differences – in interatomic bond lengths within the Pd coordination sphere – when compared to previously reported bimetallic analogues. Theoretical investigations were performed using methods of the Density Functional Theory (ZORA-PBE-D3(BJ)/all electron TZP level, EDA, ETS-NOCV and QTAIM-IQA) to analyse the influence of a second Cr(CO)(3) moiety in the process of formation of the Cr-Pd hemichelate. Theory shows that despite the extensive charge delocalization in the anion of trans-bistricarbonylchromium(fluorene), the formation of a stable hemichelate is still possible albeit requiring a moderate energy payload to funnel charge density towards the formation of the benzylic carbon-palladium bond. IQA analyses of hemichelates show the important role of attractive electrostatic interactions in the dominantly noncovalent Cr(CO)(3)-Pd interactions.

First author: Weng, SY, The Ligand-Exchange Reactions of Rod-Like Au25-nMn (M=Au, Ag, Cu, Pd, Pt) Nanoclusters with Cysteine – A Density Functional Theory Study, CHEMPHYSCHEM, 20, 1822, (2019)
Abstract: The atomic precision of ultrasmall noble-metal nanoclusters (NMNs) is fundamental for elucidating structure-property relationships and probing their practical applications. So far, the atomic structure of NMNs protected by organic ligands has been widely elucidated, whereas the precise atomic structure of NMNs protected by water-soluble ligands (such as peptides and nucleic acid), has been rarely reported. With the concept of “precision to precision”, density functional theory (DFT) calculations were performed to probe the thermodynamic plausibility and inherent determinants for synthesizing atomically precise, water-soluble NMNs via the framework-maintained two-phase ligand-exchange method. A series of rod-like Au25-nMn (M=Au, Ag, Cu, Pd, Pt) NMNs with the same framework but varied ligands and metal compositions was chosen as the modeling reactants, and cysteine was used as the modeling water-soluble ligand. It was found that the acidity of the reaction remarkably affects the thermodynamic facility of the ligand exchange reactions. Ligand effects (structural distortion and acidity) dominate the overall thermodynamic facility of the ligand-exchange reaction, while the number and type of doped metal atom(s) has little influence.

First author: Knitsch, R, Dihydrogen Splitting by Intramolecular Borane-Phosphane Frustrated Lewis Pairs: A Comprehensive Characterization Strategy Using Solid State NMR and DFT Calculations, CHEMPHYSCHEM, 20, 1837, (2019)
Abstract: Four hydrogenated intramolecular phosphane-borane frustrated Lewis pair (B/P FLP) compounds bearing unsaturated cyclic or aromatic carbon backbones have been synthesized and structurally characterized using B-11, P-31, H-1 and H-2 solid-state NMR spectroscopy. A comparison of the spectra with those of the corresponding free B/P FLPs shows that both B-11 isotropic chemical shifts as well as nuclear electric quadrupolar coupling constants decrease significantly upon FLP hydrogenation, revealing the breakage of the partial B-P bond present in the starting materials. Likewise, the P-31 isotropic chemical shift, the chemical shift anisotropy, and the asymmetry parameter decrease significantly upon FLP hydrogenation, reflecting the formation of a more symmetric, C-3v-like local environment. B-11{P-31} rotational echo double resonance (REDOR) experiments can be used to measure the B-P internuclear distance (about 3.2 angstrom) of these compounds. Observation of the hydrogen atoms bound to the Lewis centers is best accomplished via P-31{H-1} and B-11{H-1} cross-polarization-heteronuclear correlation experiments or by direct observation of the H-2 MAS NMR signals on especially prepared FLP-D-2 adducts. For accurately measuring the phosphorus-deuterium distance via P-31{H-2} rotational echo adiabatic passage double resonance (REAPDOR), it is essential to take the secondary dipolar coupling of P-31 with the boron-bonded H-2 nuclei explicitly into consideration, by simulating a H-2(P)-P-31-H-2(B) three-spin system based on structural input. All of the experimental NMR interaction parameters are found in excellent agreement with values calculated by DFT methods, using the geometries obtained either by energy optimization or from single-crystal structures.

First author: Britz, A, Using Ultrafast X-ray Spectroscopy To Address Questions in Ligand-Field Theory: The Excited State Spin and Structure of [Fe(dcpp)(2)](2+), INORGANIC CHEMISTRY, 58, 9341, (2019)
Abstract: We have employed a range of ultrafast X-ray spectroscopies in an effort to characterize the lowest energy excited state of [Fe(dcpp)(2)](2+) (where dcpp is 2,6-(dicarboxypyridyl)pyridine). This compound exhibits an unusually short excited-state lifetime for a low-spin Fe(II) polypyridyl complex of 270 ps in a room-temperature fluid solution, raising questions as to whether the ligand-field strength of dcpp had pushed this system beyond the T-5(2)/T-3(1) crossing point and stabilizing the latter as the lowest energy excited state. K alpha and K beta X-ray emission spectroscopies have been used to unambiguously determine the quintet spin multiplicity of the long-lived excited state, thereby establishing the T-5(2) state as the lowest energy excited state of this compound. Geometric changes associated with the photoinduced ligand-field state conversion have also been monitored with extended X-ray absorption fine structure. The data show the typical average Fe-ligand bond length elongation of similar to 0.18 angstrom for a T-5(2) state and suggest a high anisotropy of the primary coordination sphere around the metal center in the excited T-5(2) state, in stark contrast to the nearly perfect octahedral symmetry that characterizes the low-spin (1)A(1) ground state structure. This study illustrates how the application of time-resolved X-ray techniques can provide insights into the electronic structures of molecules-in particular, transition metal complexes-that are difficult if not impossible to obtain by other means.

First author: Mawale, R, Mass spectrometric investigation of amorphous Ga-Sb-Se thin films, SCIENTIFIC REPORTS, 9, 9341, (2019)
Abstract: Amorphous chalcogenide thin films are widely studied due to their enhanced properties and extensive applications. Here, we have studied amorphous Ga-Sb-Se chalcogenide thin films prepared by magnetron co-sputtering, via laser ablation quadrupole ion trap time-of-flight mass spectrometry. Furthermore, the stoichiometry of the generated clusters was determined which gives information about individual species present in the plasma plume originating from the interaction of amorphous chalcogenides with high energy laser pulses. Seven different compositions of thin films (Ga content 7.6-31.7 at. %, Sb content 5.2-31.2 at. %, Se content 61.2-63.3 at. %) were studied and in each case about -50 different clusters were identified in positive and -20-30 clusters in negative ion mode. Assuming that polymers can influence the laser desorption (laser ablation) process, we have used parafilm as a material to reduce the destruction of the amorphous network structure and/or promote the laser ablation synthesis of heavier species from those of lower mass. In this case, many new and higher mass clusters were identified. The maximum number of (40) new clusters was detected for the Ga-Sb-Se thin film containing the highest amount of antimony (31.2 at. %). This approach opens new possibilities for laser desorption ionization/laser ablation study of other materials. Finally, for selected binary and ternary clusters, their structure was calculated by using density functional theory optimization procedure.

First author: Abadee, ZGN, Removing phenol contaminants from wastewater using graphene nanobuds: DFT and reactive MD simulation investigations, JOURNAL OF MOLECULAR LIQUIDS, 286, 9341, (2019)
Abstract: Phenol and phenolic compounds are extensively found in effluents and are toxic even at low concentrations hence their elimination from aqueous solutions is necessary. In the present work, the interaction of phenol and water molecules with graphene and graphene nanobud (GNB) was investigated using DFT-D3 calculations with revPBE/def2-TZVP model of theory. Various binding sites and ways of approach for phenol/water molecule approaching the selected adsorbents were evaluated. We found that water molecule tends to interact weakly with both graphene and GNB compared with the phenol molecule. The strength of adsorption for GNB at the top of the fullerene cage as well as near the neck site and onto the graphene surface was found to be stronger for phenol rather than water molecule. This can be attributed to the existence of simultaneous pi-pi stacking and electrostatic attractions for phenol/adsorbent system. Our first-principles calculations showed that binding nature of interacting molecules depends strongly on the long-range non-local dispersion forces but slightly to the solvent entity. The obtained binding energies compared with the experimental and highly accurate quantum-mechanical values available in literature for water/benzene adsorbed onto the graphene surface. Moreover, the adsorption ability and capacity of GNB was verified by reactive MD simulation carrying out at ambient condition. The desirable binding strength obtained accompanied with high specific surface area of GNB (due to fastened buckyballs) compared with the graphene lead to practically arrest these novel hybrid nano-materials as superior adsorbents for phenol adsorption and remediation from water-contaminated environment.

First author: Gotz, AW, Van der Waals effects on structure and optical properties in organic photovoltaics, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 119, 9341, (2019)
Abstract: We have recently reported that dispersion forces can have drastic effects on the structure and charge separation in organic photovoltaics (OPVs) (Martinez et al., J. Phys. Chem. C 121, 20 134 [2017]). Here we investigate dimer complexes formed by the polymer P3HT and the fullerene derivative PCBM. We show how van der Waals (vdW) interactions affect the geometrical structure, which has strong effects on the electronic structure and UV-Vis absorption spectrum. Time-dependent density functional theory calculations demonstrate that the experimentally observed blue-shift of the absorption maximum of P3HT/PCBM OPV cells with respect to pure P3HT results mainly from distortions in P3HT due to vdW interactions between donor and acceptor fragments. Reduced absorption in the red region of the UV-Vis spectrum results from distortions of P3HT and small charge transfer between P3HT and PCBM. These results are in qualitative agreement with experiments and recent theoretical results on the corresponding solid-state films.

First author: Majid, A, First-principles study of vibrational properties of TiSiO4 clusters, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 119, 9341, (2019)
Abstract: First-principles calculations were performed to investigate the vibrational properties of monomers and dimers of titania, silica, and titania-silica hybrid clusters. Density functional theory-based formulism was employed to optimize the geometry at the B3LYP level and calculate the infrared and Raman spectra of the clusters by using the GGA-PBE exchange-correlation functional. It was found that the vibrational spectra of Ti2O4, Si2O4, and TiSiO4 hybrid clusters provide fingerprint information about structures and structural transitions during the formation of cluster structures. In the case of Si2O4 the mode at 410 cm(-1) exhibited the largest vibration of Si atoms, whereas in the case of Ti2O4 the mode at 442 cm(-1) exhibited the largest vibration of Ti atoms. The hybrid cluster TiSiO4 was structured using two different methods to explore the effects of starting geometry on the structures and vibrational modes of the clusters. The structural properties of the clusters remained unchanged but vibrational modes were found to be different. It is found that Si shows notable vibrations, but the metal atom Ti merely shows any vibration in the case of TiSiO4 hybrid clusters. The low and intermediate frequency modes were stiffened, whereas the three highest frequency modes were softened when the starting geometry of the hybrid clusters was changed from Si2O4 to Ti2O4.

First author: Kaya, Z, A Comparative Study of Confining Ligands Derived from Methylated Cyclodextrins in Gold-Catalyzed Cycloisomerization of 1,6-Enynes, EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, 2019, 4528, (2019)
Abstract: Gold(I) complexes containing monodentate P-III-ligands built upon methylated alpha-cyclodextrins have been synthesized and assessed in the cycloisomerization of 1,6-enynes, two of the reactions studied involving prochiral substrates. Their performance was compared with that of previously reported mononuclear and dinuclear alpha- and beta-cyclodextrin-based Au-I complexes. Enantiodiscrimination was found to be strongly dependent on the ability of the ligand to position metal-coordinated substrates inside the cyclodextrin core.

First author: Daoudi, S, Electronic structure and optical properties of isolated and TiO2-grafted free base porphyrins for water oxidation: A challenging test case for DFT and TD-DFT, JOURNAL OF COMPUTATIONAL CHEMISTRY, 40, 2530, (2019)
Abstract: Seven free base porphyrins employed in dye-sensitized photoelectrosynthetic cells are investigated with the aim of benchmarking the ability of different density functional theory (DFT) and time-dependent DFT approaches in reproducing their structure, vertical, and E0-0 excitation energies and the energy levels alignment (red-ox properties) at the interface with the TiO2. We find that both vertical and E0-0 excitation energies are accurately reproduced by range-separated functionals, among which the omega B97X-D delivers the lowest absolute deviations from experiments. When the dye/TiO2 interface is modeled, the physical interfacial energetics is only obtained when the B3LYP functional is employed; on the other hand, M06-2X (54% of exchange) and the two long-range corrected approaches tested (CAM-B3LYP and omega B97X-D) excessively destabilize the semiconductor conduction band levels with respect to the dye’s lowest unoccupied molecular orbitals (LUMOs), predicting no pathway for electron injection.

First author: Matxain, JM, Chirality Induced Spin Selectivity of Photoexcited Electrons in Carbon-Sulfur [n]Helicenes, CHEMPHOTOCHEM, 3, 770, (2019)
Abstract: The Chiral-Induced Spin Selectivity effect (CISS) is ordinarily associated with electron transfer, electron transport or bond polarization in chiral molecules. We explore here CISS associated with inter-system crossing (ISC) in helicene molecules. The relative magnitude of both CISS and ISC is controlled by the strength of the spin-orbit coupling (SOC) associated with either the excited singlet-triplet transition or electron transport through the helix. Depending on the time scale, both mechanisms are connected in photo-induced electron transfer, which is assumed to take place through an initial one-photon singlet-singlet excitation process followed by singlet-triplet mixing, which provides the pathway for subsequent spin polarization. We explore this mechanism computationally, and find an estimate of SOC for helicenes that is consistent with the experimental results obtained for the spin polarization power of molecules using conductance and photo-excitation techniques. Our results show a hitherto unexplored dimension of the CISS effect and connect it to the exciting possibilities of spin-dependent chemistry.

First author: Narsaria, AK, Dual Activation of Aromatic Diels-Alder Reactions, CHEMISTRY-A EUROPEAN JOURNAL, 25, 9902, (2019)
Abstract: The unusually fast Diels-Alder reactions of [5]cyclophanes were analyzed by DFT at the BLYP-D3(BJ)/TZ2P level of theory. The computations were guided by an integrated activation-strain and Kohn-Sham molecular orbital analysis. It is revealed why both [5]metacyclophane and [5]paracyclophane exhibit a significant rate enhancement compared to their planar benzene analogue. The activation strain analyses revealed that the enhanced reactivity originates from 1) predistortion of the aromatic core resulting in a reduced activation strain of the aromatic diene, and/or 2) enhanced interaction with the dienophile through a distortion-controlled lowering of the HOMO-LUMO gap within the diene. Both of these physical mechanisms and thus the rate of Diels-Alder cycloaddition can be tuned through different modes of geometrical distortion (meta versus para bridging) and by heteroatom substitution in the aromatic ring. Judicious choice of the bridge and heteroatom in the aromatic core enables effective tuning of the aromatic Diels-Alder reactivity to achieve activation barriers as low as 2 kcal mol(-1), which is an impressive 35 kcal mol(-1) lower than that of benzene.

First author: Bassoli, S, Phosphorescence enhancement by close metal-metal interaction in T-1 excited state in a dinuclear copper(i) complex, DALTON TRANSACTIONS, 48, 9276, (2019)
Abstract: The dinuclear copper(i) complex [Cu-2(mu-dppm)(2)(lact)(mu-lact)] (1) (dppm = bis(diphenylphosphino)methane; lact = l-(+)-lactate) was synthesized and fully characterized both in solution and solid state. Variable temperature NMR experiments (H-1 and P-31), conductivity measurements and infrared spectroscopy, suggest the occurrence of a fluxional behavior in solution involving the lactate anion. The crystal structure shows the presence of both monodentate and bridged lactate in the complex. In the solid state, 1 shows green phosphorescent emission characterized by a very large Stokes shift (161 nm, 1.09 eV) and a good absolute quantum yield (0.43). Calculations performed at the Density Functional Theory level demonstrate that the electronic transition responsible for the emission originates from a triplet excited state where the shortening of the CuCu distance plays a crucial role.

First author: Svatunek, D, autoDIAS: a python tool for an automated distortion/interaction activation strain analysis, JOURNAL OF COMPUTATIONAL CHEMISTRY, 40, 2509, (2019)
Abstract: The distortion/interaction activation strain (DIAS) analysis is a powerful tool for the investigation of energy barriers. However, setup and data analysis of such a calculation can be cumbersome and requires lengthy intervention of the user. We present autoDIAS, a python tool for the automated setup, performance, and data extraction of the DIAS analysis, including automated detection of fragments and relevant geometric parameters.

First author: Kushawaha, RK, Multi-slit-type interference in carbon 2s photoionization of polyatomic molecules: from a fundamental effect to structural parameters, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 13600, (2019)
Abstract: In molecular photoemission, the analogue of the celebrated Young’s double slit experiment is coherent electron emission from two equivalent atomic centers, giving rise to an interference pattern. Here multi-slit interference is investigated in inner-valence photoionization of propane, n-butane, isobutane and methyl peroxide. A more complex pattern is observed due to molecular orbital delocalization in polyatomic molecules, blurring the distinction between interference and diffraction. The potential to extract geometrical information is emphasized, as a more powerful extension of the EXAFS technique. Accurate reproduction of experimental features is obtained by simulations at the static Density Functional Theory level.

First author: Jin, X, Quantum chemical models for the absorption of endohedral clusters on Si(111)-(7 x 7): a subtle balance between W-Si and Si-Si bonding, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 13686, (2019)
Abstract: The link between the intrinsic electronic properties of an endohedral metallo-silicon cluster, W@Si-12, its ability to bind to a Si(111)-(7 x 7) surface and the impact on transmission properties is explored using periodic density functional theory. The W 5d(z)(2) orbital, the LUMO of the isolated cluster, plays a critical role in all aspects, forming a covalent bond between the metal and the silicon surface, and then providing an effective transmission channel that allows current to flow from the surface to STM tip. The STM images therefore provide a very direct probe of the W-Si surface bond.

First author: Charistos, ND, Aromatic character of O-h-C24N24. A cavernous nitride fullerene bearing N-4-macrocycle motifs, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 119, 13686, (2019)
Abstract: Spherical fullerenes offer noteworthy structures usually involving six- and five-membered faces, with application in technological issues. In this sense, cavernous spherical-like structures bearing larger holes provide interesting examples for further understanding of structure-properties relationship. Here, we explored the magnetic response of a proposed cavernous nitride fullerene, C24N24, which has a O-h-symmetry with six N-4-macrocyclic and eight 1,3,5-triazine faces displaying 48-pi electrons. C24N24 exhibits a local aromatic behavior owing to the contrasting antiaromatic response of the N-4-macrocyclic faces and the aromatic character of the 1,3,5-triazine faces. Thus, the overall structure is ascribed as a local aromatic species, where the triazine faces exhibit the characteristic shielding cone for aromatic rings. Furthermore, the constructive combination of local shielding cones in C24N24 delivers a related shielding-cone response, as expected for a perfect aromatic cage. Hence, the local aromatic/nonaromatic/antiaromatic sections exhibit an additive or subtractive interaction, leading to a characteristic response inherent to the nature of the spherical cage. We expect that further study of the interplay between different aromatic and antiaromatic faces in fullerene-like cages can deliver interesting pseudo-aromatic or pseudo-antiaromatic spherical species.

First author: Chen, JB, Are Explicit Solvent Models More Accurate than Implicit Solvent Models? A Case Study on the Menschutkin Reaction, JOURNAL OF PHYSICAL CHEMISTRY A, 123, 5580, (2019)
Abstract: In this work, contemporary quantum mechanical (QM) implicit solvent models (SMD, SM12, and COSMO-RS) and a molecular mechanical (MM) explicit solvent model were used to predict the aqueous free energy barrier of a simple Menschutkin reaction (NH3 + CH3Cl). Surprisingly, the explicit solvent approach performed the worst, while the implicit solvent models yielded reasonably accurate values that are in accord with available experimental data. The origin of the large error in the explicit solvent model was due to the use of a fixed set of Lennard-Jones parameters during the free energy perturbation (FEP) calculations. Further analyses indicate that M06-2X/6-31+G(d,p) yielded solute solvent interaction energies that are in good agreement with bench-mark DLPNO-CCSD(T)/CBS values. When end-state MM to M06-2X/6-31+G(d,p) corrections were added using FEP, it significantly improved the accuracy of the explicit solvent MM result and demonstrated that the accuracy of these models may be systematically improved with end-state corrections based on a validated QM level of theory.

First author: Wang, Q, QM/MM studies on luminescence mechanism of dinuclear copper iodide complexes with thermally activated delayed fluorescence, RSC ADVANCES, 9, 20786, (2019)
Abstract: The QM/MM method is employed to investigate the photophysical mechanism of two dinuclear copper iodide complexes with thermally activated delayed fluorescence (TADF). The S-1-T-1 energy differences (Delta E-ST) in these two complexes are small enough so that repopulating the S-1 state from T-1 becomes energetically allowed. Both forward and reverse intersystem crossing (ISC and rISC) processes are much faster than the corresponding radiative fluorescence and phosphorescence processes [k(ISC) (10(8) s(-1)) > kFr (10(6) s(-1)), k(rISC) (10(5) s(-1)) > kPr (10(3) s(-1))]. The faster rISC process than the phosphorescence emission enables TADF. Moreover, the diphosphine ligands are found to play an important role in regulating the electronic structures and thereto the radiative and nonradiative rate constants. The present work rationalizes experimental phenomena and helps understand the intrinsic luminescence properties. The obtained insights could be useful for tuning the luminescence performance of dicopper-based luminescence materials.

First author: Sorbelli, D, Cationic Gold(I) Diarylallenylidene Complexes: Bonding Features and Ligand Effects, CHEMPHYSCHEM, 20, 1671, (2019)
Abstract: Using computational approaches, we qualitatively and quantitatively assess the bonding components of a series of experimentally characterized Au(I) diarylallenylidene complexes (N.Kim, R.A.Widenhoefer, Angew. Chem. Int. Ed. 2018, 57, 4722-4726). Our results clearly demonstrate that Au(I) engages only weakly in pi-backbonding, which is, however, a tunable bonding component. Computationally identified trends in bonding are clearly correlated with the substitution patterns of the aryl substituents in the Au(I) diarylallenylidene complexes and good agreement is found with the previously reported experimental data, such as IR spectra, C-13 NMR chemical shifts and rates of decomposition together with their corresponding barrier heights, further substantiating the computational findings. The description of the bonding patterns in these complexes allow predictions of their spectroscopic features, their reactivity and stability.

First author: Kuzuhara, D, 2,7,12,17-Tetra(2,5-thienylene)-substituted porphycenes, JOURNAL OF PORPHYRINS AND PHTHALOCYANINES, 23, 898, (2019)
Abstract: We report syntheses of thiophene and dithiophene-substituted porphycenes (ThPc and DThPc) at 2,7,12,17-positions by McMurry coupling. The crystal structure of ThPc revealed that the porphycene plane shows a highly planar structure, and the dihedral angles between the porphycene core and thiophene are relatively small at 21 degrees and 18 degrees. ThPc and DThPc exhibit red-shifted and broadened absorption because of the extension of rc conjugations through porphycene to the substituted thiophenes. We found that introduction of thiophene units onto porphycene results in decreasing the HOMO-LUMO differences effectively.

First author: Kolesnikov, VI, Friction, Wear, and Monitoring of Heavily Loaded Tribosystems: An Innovative Approach to Studying the Processes, JOURNAL OF FRICTION AND WEAR, 40, 297, (2019)
Abstract: This paper focuses on the influence of diffusion and segregation processes on the strength and tribological characteristics of friction units. The application of the quantum chemical method made it possible to reveal that the appearance of segregated atoms at the grain boundaries is the main reason for hardening or destruction of metal surface layers. The proposed approach was also applied to assess the compatibility of various elements consisting of iron and to relate this compatibility to the tribological characteristics. Comparative tests on friction and wear were aimed at investigating initial 38X2\M & x42e;A-SIC nitrated steel, 38X2\M & x42e;A-SIC nitrated steel with a diamond-like coating, and Nb- and Hf-alloyed 38X2\M & x42e;A-SIC nitrated steel with a diamond-like coating. The tribospectral identification method proposed by the authors was used to study the friction processes in heavily loaded friction units using the example of Mi-26 helicopter spline joints.

First author: Huang, YJ, Ferrocenylmethylthio-maleonitrile for selective recognition of Hg(II) ion, INORGANIC CHEMISTRY COMMUNICATIONS, 105, 129, (2019)
Abstract: A new ferrocene based receptor 1,2-bis(ferrocenyhnethylthio)-maleonitrile (FcMNT) was synthesized and characterized by elemental analysis, FTIR, NMR and X-ray single crystal diffraction. The ligand showed a high selection for Hg2+ in DMF or DMF/H2O mixed solution. Upon addition of Hg2+ in DMF, the receptor showed an obvious color change and significant UV vis spectroscopic response. Electrochemical titration revealed that the receptor sensed Hg2+ in high selectivity with an anodic shift of 307 mV. The (CNMR)-C-13 titration confirmed that the Hg2+ interacted with the S atoms of FcMNT when the amount of Hg2+ was under 1.0 equiv.; the Hg2+ interacted with C=C and C N groups when the amount of Hg2+ was above 1.0 equiv.

First author: Fonseca, D, Inhibition of C. albicans Dimorphic Switch by Cobalt(II) Complexes with Ligands Derived from Pyrazoles and Dinitrobenzoate: Synthesis, Characterization and Biological Activity, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 20, 129, (2019)
Abstract: Seven cobalt(II) complexes of pyrazole derivatives and dinitrobenzoate ligands were synthesized and characterized. The single-crystal X-ray diffraction structure was determined for one of the ligands and one of the complexes. The analysis and spectral data showed that all the cobalt complexes had octahedral geometries, which was supported by DFT calculations. The complexes and their free ligands were evaluated against fungal strains of Candida albicans and emerging non-albicans species and epimastigotes of Trypanosoma cruzi. We obtained antifungal activity with a minimum inhibitory concentration (MIC) ranging from 31.3 to 250 mu g mL(-1). The complexes were more active against C. krusei, showing MIC values between 31.25 and 62.5 mu g mL(-1). In addition, some ligands (L1-L6) and complexes (5 and Co(OAc)(2) 4H(2)O) significantly reduced the yeast to hypha transition of C. albicans at 500 mu g mL(-1) (inhibition ranging from 30 to 54%). Finally, the complexes and ligands did not present trypanocidal activity and were not toxic to Vero cells. Our results suggest that complexes of cobalt(II) with ligands derived from pyrazoles and dinitrobenzoate may be an attractive alternative for the treatment of diseases caused by fungi, especially because they target one of the most important virulence factors of C. albicans.

First author: Patwardhan, S, Atomic Layer Deposition Nucleation on Isolated Self-Assembled Monolayer Functional Groups: A Combined DFT and Experimental Study, ACS APPLIED ENERGY MATERIALS, 2, 4618, (2019)
Abstract: We computationally design and experimentally corroborate the atomic layer deposition (ALD) of metal oxides with tailorable nucleation on selected self-assembled monolayers (SAMs) decorated with terminal functional groups. The low-temperature ALD processes for Al2O3, MnO, and especially ZnO are inhibited on nonpolar alkyl-terminated SAMs with high efficacy, in agreement with the thermodynamics calculated for reactivity with the alkyl-terminated SAMs as well as for potentially physisorbed precursors. Functional-SAM surfaces are also considered for the uniform nucleation of ALD oxides, while mixed alkyl-/functional-group-terminated SAMs are considered for the site directed synthesis of metal oxide clusters. Long alkyl-chain SAMs with functional group termination including OH, COOH, and SH are predicted to react exergonically over a variable energy barrier which depends strongly on ALD precursor chemistry as well as functional group density. Experiments confirm that more efficient nucleation may be catalyzed via a single ALD precursor cycle of a more reactive precursor (e.g., trimethylaluminum) followed by growth of targeted metal oxides (ZnOx and MnOx). The computational strategy and experimental approach may be applicable to the selective deposition of technologically important hybrid organic inorganic barrier films as well as catalytically relevant metal oxide and mixed-metal oxide precision few-atom clusters.

First author: Zapata, F, QMflows: A Tool Kit for Interoperable Parallel Workflows in Quantum Chemistry, JOURNAL OF CHEMICAL INFORMATION AND MODELING, 59, 3191, (2019)
Abstract: We present the QMflows Python package for quantum chemistry workflow automatization. QMflows allows users to write complex workflows in terms of simple Python scripts. It supports the development of interoperable workflows involving multiple quantum chemistry codes and executes them efficiently on large scale parallel computers. This open source library provides standardized interfaces to a number of quantum chemistry packages and can be easily extended to accommodate additional codes. QMflows features are described and illustrated with a number of representative applications.

First author: Wu, ZX, Theoretical insight into the photodeactivation pathway of the tetradentate Pt (II) complex with different inductive substituents, APPLIED ORGANOMETALLIC CHEMISTRY, 33, 3191, (2019)
Abstract: Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) both were used to explore the impacts of different inductive substituents on the photophysical properties, radiative/nonradiative processes and photodeactivation mechanism for the Pt (II) complex with novel spiro-arranged tetradentate ligand. Spectrum simulations show that the electron donor methoxyl (-OCH3) group can cause the emission wavelength to red-shift but have little effect on the absorption spectrum. In the simulation of the radiative decay process for the tetradentate Pt (II) complex, the singlet-triplet splitting energy is reduced by the introduction of substituents with strong electron-releasing capability (i.e., from the original trifluoromethyl (-CF3) group to -OCH3 group), accompanied with a lower radiative rate constant (k(r)). The analyses of non-radiative decay processes show that the substitution of -OCH3 group on azole rings reduces the energy barriers of thermally activated non-radiative photodeactivation pathway, which in turn increases the temperature-dependent non-radiative rate constants (k(nr)(T)). In addition, the substitution of -CF3 by -OCH3 group slightly weakens molecular rigidity and enhances the Huang-Rhys factor, but decreases the SOC between the triplex excited (T) state and the ground (S-0) state. Thereby, the two complexes may have the similar temperature-independent non-radiative rate constant (k(nr)’). This work offers theoretical guidance for the design and optimization of the efficient organic light emitting diode (OLED) materials based on the structure of tetradentate Pt (II) complexes.

First author: Shams, M, Influence of functional groups on the degradation of graphene oxide nanomaterials, ENVIRONMENTAL SCIENCE-NANO, 6, 2203, (2019)
Abstract: The influence of functional groups on the degradation of graphene oxide nanomaterials under direct sunlight was investigated by systematically varying the surface chemistry. Using a solvothermal reduction process, graphene nanomaterials with varying oxidation levels, including graphene oxide, partially reduced graphene oxide and fully reduced graphene oxide, were prepared. The physical and chemical properties of the nanomaterials were extensively characterized before and after exposure to simulated sunlight. The degradation of the nanomaterials was determined to be directly related to the functional groups present on the basal plane of the graphene nanomaterials. Specifically, the hydroxyl and epoxy functional groups are the most susceptible to photodegradation. Upon sunlight exposure, the amount of oxygen-containing functional groups on all graphene nanomaterials decreases over time, with fully reduced graphene oxide showing the lowest degradation rate due to the presence of fewer reactive functional groups on the surface. Overall, these results suggest that the oxygen-containing functional groups on the basal plane are the major initiators of the photodegradation of graphene nanomaterials.

First author: Gendron, F, Ab Initio Study of Circular Dichroism and Circularly Polarized Luminescence of Spin-Allowed and Spin-Forbidden Transitions: From Organic Ketones to Lanthanide Complexes, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 15, 4140, (2019)
Abstract: Complete and restricted active space self-consistent field (CAS-/RAS-SCF) wave function methods are applied for the calculation of circular dichroism (CD) and circularly polarized luminescence (CPL) of a series of molecules comprising four organic ketones, the chiral cobalt(III) complex [Co(en)(3)](3+), and the europium(III) complex [Eu(DPA)(3)](3-). The ab initio results are in good agreement with the experimental data and previous results obtained with Kohn-Sham density functional theory in the case of the spin-allowed transitions. CD and CPL properties are calculated ab initio for the spin-forbidden transitions of both a transition metal and a lanthanide complex.

First author: Breton, GW, A Search for X-ray Crystallographic Evidence of n -> pi* Interactions in a Series of Substituted 2-(Dimethylamino)biphenyl-2 ‘-carboxaldehydes, CRYSTAL GROWTH & DESIGN, 19, 3895, (2019)
Abstract: There has recently been greater appreciation for the impact that n -> pi* interactions have on the conformational preferences of molecules in the gas phase, solution, and crystalline form. Earlier studies, both experimental and computational, have demonstrated that suitably placed substituents can affect the extent of these interactions. A thorough understanding of how substituents affect these interactions is necessary for these forces to be potentially utilized as a means of crystal engineering. We synthesized a series of 2-(dimethylamino)biphenyl-2′-carboxaldehydes substituted at the position para to the aldehyde group with substituents ranging in electronic properties from strong electron-withdrawing to strong electron-donating and determined their structures via X-ray crystallography. In all cases, evidence suggests that the conformations adopted in the crystals retained n -> pi* interactions. However, contrary to computational studies conducted in vacuo, the geometries varied not according to the substituents’ electronic properties (as described by Hammett sigma(p) values) as expected but instead according to their steric properties (using Sotomatsu and Fujita’s steric parameters; Sotomatsu and Fujita J. Org. Chem. 1989,.54, 4443; Sotomatsu and Fujita Bull. Chem. Soc. Jpn. 1992, 65, 2343). Calculations on representative molecular clusters demonstrate that the geometries adopted in the crystal form are such that they minimize destabilizing intermolecular steric interactions, while maximizing stabilizing intermolecular dispersive and electrostatic forces. This comes at fairly low energetic cost to the molecules relative to their optimized theoretical in vacuo geometries (generally less than 0.5 kcal/mol) even though it stresses, but does not overwhelm, the intramolecular n -> pi* interactions.

First author: Vasiliu, M, Electronic Structure Predictions of the Energetic Properties of Tellurium Fluorides, INORGANIC CHEMISTRY, 58, 8279, (2019)
Abstract: The heats of formation, bond dissociation energies (BDEs), fluoride affinities (FA), fluorocation affinities (FCA), electron affinities (EA), and ionization energies (IP) of TeFn (n = 1-6) have been predicted using the Feller-Peterson-Dixon (FPD) approach. To benchmark the approach, the bond dissociation energies of Te-2 and TeO, the heats of formation of Te-2, TeH2, TeO, and TeO2, and the electron affinity for TeO and TeO2 were calculated as there are experimental thermodynamic data available for these tellurium compounds, which allow confirmation of the heat of formation of Te gas as Delta H-f,H-0K(Te) = 50.7 +/- 0.6 kcal/mol. Spin-orbit corrections are required for good results and cannot be ignored. A comparison among fluoride affinities, fluorocation affinities, electron affinities, and ionization energies of TeFn and SeFn is reported.

First author: Conradie, J, Theoretical Search for the Highest Valence States of the Coinage Metals: Roentgenium Heptafluoride May Exist, INORGANIC CHEMISTRY, 58, 8735, (2019)
Abstract: We present here a relativistic density functional theory investigation of the penta- and heptavalent states of gold and roentgenium, employing the ZORA (zeroth order regular approximation to the Dirac equation) Hamiltonian, including spin-orbit coupling at the two-component level, and large all-electron relativistic Slater-type quadruple-zeta quadruple polarization (ZORA-STO-QZ4P) basis sets. Unsurprisingly, our calculations confirm the stability of the experimentally known complexes AuF6- and Au2F10 with respect to decomposition to trivalent Au products and F-2. The calculations also predict that RgF(6)(-) and Rg(2)F(10) should be even more stable with respect to an analogous decomposition pathway. Like an earlier DFT study (Inorg. Chem.2007, 46 (13), 5338-5342), our calculations rule out the true heptavalent Au complex AuF7 as a stable species, preferring instead a C-s AuF5 center dot center dot center dot F-2 formulation. Remarkably, our calculations confirm a D-5h pentagonal-bipyramidal structure of RgF(7) as the global minimum, at an energy of approximately half an electron volt below the RgF(5)center dot center dot center dot F-2 form.

First author: Wolanski, L, Beyond Oxides: Nitride as a Ligand in a Neutral (IrNO3)-N-IX Molecule Bearing a Transition Metal at High Oxidation State, CHEMISTRY-A EUROPEAN JOURNAL, 25, 10290, (2019)
Abstract: Theoretical calculations utilizing relativistic ZORA Hamiltonian point to the conceivable existence of an IrNO3 molecule in C-3v geometry. This minimum is shown to correspond to genuine nonavalent iridium nitride trioxide, which is a neutral analogue of cationic [IrO4](+) species detected recently. Despite the presence of nitride anion, the molecule is protected by substantial barriers exceeding 200 kJ mol(-1) against transformations leading, for example, to global minimum (O=)(2)Ir-NO, which contains metal at a lower formal oxidation state.

First author: Engwerda, AHJ, Racemization and Deracemization through Intermolecular Redox Behaviour, CHEMISTRY-A EUROPEAN JOURNAL, 25, 9639, (2019)
Abstract: Chiral molecules exhibiting a quinone and/or hydroquinone moiety are ubiquitous in natural products and small molecule drugs. Herein, we describe a chiral quinone-hydroquinone molecule that racemizes through a reversible redox reaction. Using a combined computational and experimental approach, we show that this racemization proceeds via an intermolecular reaction mechanism. Starting from two achiral reactants, this molecule could be obtained in enantiopure form using Viedma ripening.

First author: Yurenko, Y, Monitoring the formate-NAD interaction during formate oxidation in the active site of Candida boidinii formate dehydrogenase, EUROPEAN BIOPHYSICS JOURNAL WITH BIOPHYSICS LETTERS, 48, S194, (2019)
Abstract: Chiral molecules exhibiting a quinone and/or hydroquinone moiety are ubiquitous in natural products and small molecule drugs. Herein, we describe a chiral quinone-hydroquinone molecule that racemizes through a reversible redox reaction. Using a combined computational and experimental approach, we show that this racemization proceeds via an intermolecular reaction mechanism. Starting from two achiral reactants, this molecule could be obtained in enantiopure form using Viedma ripening.

First author: Huang, JD, Theoretical study of charge-transport and optical properties of organic crystals: 4,5,9,10-pyrenediimides, IUCRJ, 6, 603, (2019)
Abstract: This work presents a systematic study of the conducting and optical properties of a family of aromatic diimides reported recently and discusses the influences of side-chain substitution on the reorganization energies, crystal packing, electronic couplings and charge injection barrier of 4,5,9,10-pyrenediimide (PyDI). Quantum-chemical calculations combined with the Marcus-Hush electron transfer theory revealed that the introduction of a side chain into 4,5,9,10-pyrenediimide increases intermolecular steric interactions and hinders close intermolecular pi-pi stacking, which results in weak electronic couplings and finally causes lower intrinsic hole and electron mobility in t-C-5-PyDI (mu(h) = 0.004 cm(2) V-1 s(-1) and mu(e) = 0.00003 cm(2) V-1 s(-1)) than in the C-5-PyDI crystal (mu(h) = 0.16 cm(2) V-1 s(-1) and mu(e) = 0.08 cm(2) V-1 s(-1)). Furthermore, electronic spectra of C5-PyDI were simulated and time-dependent density functional theory calculation results showed that the predicted fluorescence maximum of t-C-5-PyDI, corresponding to an S-1 -> S-0 transition process, is located at 485 nm, which is close to the experimental value (480 nm).

First author: Deng, TY, TDDFT investigation on the solvent effect of methanol on the electronic structure and luminescence of metal organic framework CdL2, CHEMICAL PHYSICS, 523, 70, (2019)
Abstract: The solvent effect of methanol on the luminescent property of MOF-CdL2 was theoretically investigated by using DFT and TD-DFT methods. The methanol molecule interacts with CdL2 frameworks through intermolecular hydrogen bonding. The frontier MOs analysis revealed that the luminescent mechanisms of the CdL2 motif and the hydrogen-bonded complex are both LLCT. The calculations on geometry, IR, and H-1 NMR demonstrated the strengthening of the intermolecular hydrogen bonds in the S-1 state. Calculated fluorescent lifetime indicated a smaller quantum yield of hydrogen-bonded CdL2-CH3OH comparing to the CdL2. It can be attributed to the strengthening of the intermolecular hydrogen bonds in the S-1 state which increases the non-radiative processes and decreased the fluorescent emission. Thus, it can be speculated that the methanol competes with the gust molecules for the luminescent response of CdL2 through hydrogen bonding to the framework. The solvent methanol plays a negative role in the luminescence of CdL2.

First author: Gloriozov, IP, DFT study of inter- ring haptotropic rearrangement in CpRu+ complexes of polycyclic aromatic ligands, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 889, 9, (2019)
Abstract: Inter-ring haptotropic rearrangements (IRHRs) of different types are well-known phenomena in organometallic and catalytic chemistry. So far, they are reported for transition metal complexes with carbo-and heterocyclic polyaromatic hydrocarbons (PAH) of small and medium size. Here, we report DFT studies of RuCp+ shifts between neighboring six-membered rings (eta(6) reversible arrow eta(6)-IRHR) on an extra-large PAH as a model for graphene and compare it to naphthalene. Our calculations predict that eta(6) reversible arrow eta(6)-IRHRs proceed with much lower activation energy barrier of rearrangement in the case of the RuCp+ complex of eta(6)-graphene model.

First author: Munoz-Castro, A, Single, double, and triple intercluster bonds: analyses of M2Au36(SR)(24) (M = Au, Pd, Pt) as 14-, 12-and 10-ve superatomic molecules, CHEMICAL COMMUNICATIONS, 55, 7307, (2019)
Abstract: The bonding picture of the experimentally characterized species derived from the M2Au36(SR)(24) cluster is discussed to indicate the occurrence of the classical notion of single, double and triple chemical bonds. The bond order can be reversibly controlled by tuning their charge states which is shown to be opportunely extended to clusters in favor of the conception of molecularly structured materials.

First author: Munoz-Castro, A, On the ligand-core interaction in ligand-protected gold superatoms. Insights from Au-25(XR)(18) (X = S, Se, Te) via relativistic DFT calculations, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 13022, (2019)
Abstract: The stabilization of gold nanoparticles by using thiolate-based ligands is a relevant issue in the design of functional nanostructures. Superatomic clusters, through the prominent Au-25(SR)(18) aggregate, offer a prototypical template to deepen the understanding of the different behaviors gained by the inclusion of different chalcogen atoms at the ligand layer. Through the study of [Au-25(XMe)(18)](-) (X = S, Se and Te), our results revealed that the bonding between the formally [Au-13](5+) core and the protecting layer (PL), further involves the unoccupied 1D-, 1F- and 2S-[Au-13] superatomic shells, acting as a charge acceptor in the PL -> Au-13 charge transfer upon formation of the cluster. In addition, the optical properties showed an increase in the Stokes shift between the S-0 -> S-1 excitation, and S-0 <- S-1 emission, going from -SMe to -TeMe, owing to a more distorted core in the excited state for the heavier counterpart. The approach here employed expands the bonding picture between the [Au-13](5+) and the protecting layer between different anchor atoms, in addition to the formal ionic description of an isolated core. These findings seek to enhance our understanding of bonding, and the optical characteristic resulting from the use of heavier chalcogen atoms in the protecting layer, which can be employed as design guidelines to incorporate or modify the molecular properties towards the synthesis of ligand-protected gold clusters.

First author: Lu, SI, Discrete Solvent Reaction Field Calculations for One- and Two-Photon Absorptions of Solution-Phase Dimethylaminonitrostilbene Molecule, JOURNAL OF PHYSICAL CHEMISTRY A, 123, 5334, (2019)
Abstract: Based on the configurations generated by molecular dynamics (MD) simulations using the on-the-fly density-functional tight-bonding (DFTB) force field, we investigated performance of the discrete solvent reaction field (DRF) model coupled to time-dependent density functional theory (TD-DFT) for solvatochromic effect of one- and two-photon absorption phenomena. Dimethylaminonitrostilbene (DANS) molecule solvated in chloroform, dichloromethane, and dimethyl sulfoxide solvents was selected as a model system for our research purpose. For every selected MD/DFTB configuration, within the context of the DRF, solute molecule is represented by TD-DFT and solvent molecules are described by atomic charges and polarizabilities. The calculated one-photon absorption energies reproduce well the positive solvatochromic behavior of solvated DANS and are in good agreement with available experimental data. For the two-photon absorption cross section, even though our approach overshot the experimental data by about 20% in absolute magnitude, experimentally observed solvatochromic change was captured qualitatively in this work. At last, we examined the contributions of atomic charges and polarizabilities of solvent molecules to the solvatochromic shifts of properties of interest.

First author: Sruthi, PK, Elusive hypervalent phosphorus center dot center dot center dot pi interactions: evidence for paradigm transformation from hydrogen to phosphorus bonding at low temperatures, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 12250, (2019)
Abstract: The pi electron systems are the conventional electron donors to the hydrogen acceptors in hydrogen bonding. Apart from the hydrogen atom, halogens, chalcogens, pnicogens and triel/tetrel atoms can also be envisaged as electron acceptors involving p clouds. Markedly, in pnicogen center dot center dot center dot pi interactions, the bonding of the hypervalent (predominantly pentavalent) state of the phosphorus atom with p electron donors is elusive and can be thought of as an intuitive extension to trivalent phosphorus center dot center dot center dot pi interactions. In this work, on the one hand, POCl3 was taken as a prototypical molecule to explore these pentavalent phosphorus interactions and on the other hand, acetylene (C2H2), ethylene (C2H4) and benzene (C6H6), in which phosphorus center dot center dot center dot pi bonding can be expected to compete with hydrogen and halogen bonding interactions, were taken as p electron donors. All three POCl3-C2H2, POCl3-C2H4 and POCl3-C6H6 heterodimers were experimentally generated at low temperatures in Ar and N-2 matrices and were characterized by both infrared spectroscopy and state-of-the-art quantum chemical computations. Though hydrogen bonding dominates in POCl3-C2H2 and POCl3-C2H4 heterodimers, phosphorus bonding plays a definite and non-trivial role in their overall stabilization. An interesting paradigm transformation was noticed in the POCl3-C6H6 system, where pentavalent phosphorus center dot center dot center dot pi bonding was observed to completely influence the hydrogen bonding interaction. To further shed light on these P center dot center dot center dot pi systems, the interaction characteristics were analyzed with the help of electrostatic potential mapping, natural bond orbital and energy decomposition analyses.

First author: Castro, AC, Four-component relativistic P-31 NMR calculations for trans-platinum(II) complexes: importance of the solvent and dynamics in spectral simulations, DALTON TRANSACTIONS, 48, 8076, (2019)
Abstract: We report a combined experimental-theoretical study on the P-31 NMR chemical shift for a number of trans-platinum(II) complexes. Validity and reliability of the P-31 NMR chemical shift calculations are examined by comparing with the experimental data. A successful computational protocol for the accurate prediction of the P-31 NMR chemical shifts was established for trans-[PtCl2(dma)PPh3] (dma = dimethylamine) complexes. The reliability of the computed values is shown to be critically dependent on the level of relativistic effects (two-component vs. four component), choice of density functionals, dynamical averaging, and solvation effects. Snapshots obtained from ab initio molecular dynamics simulations were used to identify those solvent molecules which show the largest interactions with the platinum complex, through inspection by using the non-covalent interaction program. We observe satisfactory accuracy from the full four-component matrix Dirac-Kohn-Sham method (mDKS) based on the Dirac-Coulomb Hamiltonian, in conjunction with the KT2 density functional, and dynamical averaging with explicit solvent molecules.

First author: Yang, YA, A mechanism of the luminescent covalent organic framework for the detection of NH3, NEW JOURNAL OF CHEMISTRY, 43, 9274, (2019)
Abstract: The interaction between a luminescent covalent organic framework (COF) and the indoor pollutant NH3 was investigated based on density functional theory and time-dependent density functional theory. The frontier molecular orbitals and electronic configuration showed that the luminescence mechanism of the COF was strongly affected by the hydrogen bond between the COF and NH3. In addition, the calculated hydrogen bond length, infrared (IR) spectra, and proton nuclear magnetic resonance (H-1 NMR) spectroscopy analysis indicated that the hydrogen bond in the S-1 state was enhanced, which is identical to the calculated results of electronic excitation energies. The fluorescence rate coefficient of the COF was reduced when interacting with NH3. The hydrogen bond between the COF and NH3 in the S-1 state is critical for the COF luminescence properties, which means that the COF shows potential application in the detection of NH3.

First author: Armstrong, A, Multiple-Valence Aluminum and the Electronic and Geometric Structure of AlnOm Clusters, JOURNAL OF PHYSICAL CHEMISTRY A, 123, 5114, (2019)
Abstract: Electronic stability in aluminum clusters is typically associated with either closed electronic shells of delocalized electrons or a +3 oxidation state of aluminum. To investigate whether there are alternative routes toward electronic stability in aluminum oxide clusters, we used theoretical methods to examine the geometric and electronic structure of AlnOm (2 <= n <= 7; 1 <= m <= 10) clusters. Electronically stable clusters with large HOMO-LUMO (highest occupied molecular orbital and lowest unoccupied molecular orbital) gaps were identified and could be grouped into two categories. (1) Al(2)nO(3)n clusters with a +3 oxidation state on the aluminum and (2) planar clusters including Al4O4, Al5O3, Al6O5, and Al6O6. The structures of the planar clusters have external Al atoms bound to a single O atom. Their electronic stability is explained by the multiple-valence Al sites, with the internal Al atoms having an oxidation state of +3, whereas the external Al atoms have an oxidation state of +1.

First author: Weckhuysen, BM, Vibrational Fingerprinting of Defects Sites in Thin Films of Zeolitic Imidazolate Frameworks, CHEMISTRY-A EUROPEAN JOURNAL, 25, 8070, (2019)
Abstract: Surface-mounted metal-organic frameworks (SURMOFs) are crystalline films of MOFs and have garnered a great deal of attention in the past years. So far, thin-film MOF research has been mainly focused on the synthesis and the exploration of potential applications of these materials, while a detailed understanding of their growth is still lacking. In this report evidence is provided for the inter-grown nature of surface-mounted thin films of Zn-ZIF-8 (SURZIF-8; ZIF=zeolitic imidazolate framework). Two distinct SURZIF-8 thin films have been made through layer-by-layer (LBL) growth after applying 20 and 50 LBL cycles. They have been characterized with atomic force microscopy (AFM) and Raman micro-spectroscopy. A detailed analysis of the Raman mapping data, inter alia using principal component analysis (PCA), revealed the existence of phase boundaries within the 20-cycle thin film, while the 50-cycle thin film is chemically more homogeneous. To further analyze these chemical heterogeneities, density functional theory (DFT) calculations were performed of three theoretical models providing spectroscopic fingerprints of the molecular vibrations associated with the Zn-ZIF-8 thin films. Based on these calculations and the experimental data distinct vibrational markers indicative for the presence of defects sites were identified.

First author: Yang, T, Dative versus electron-sharing bonding in N-imides and phosphane imides R3ENX and relative energies of the R2EN(X)R isomers (E = N, P; R = H, Cl, Me, Ph; X = H, F, Cl), MOLECULAR PHYSICS, 117, 1306, (2019)
Abstract: Quantum chemical calculations using density functional theory BP86 and M06-2X functionals in conjunction with def2-TZVPP basis sets have been carried out on the title molecules. The calculation results reveal that the N-imides R3NNX are always clearly higher in energy than the imine isomers R2NN(X)R. In the case of phosphane imides R3PNX and the isomers R2PN(X)R, the substituent R plays a critical role in determining their relative stabilities. When R is hydrogen or phenyl group, R3PNX are always higher in energy than R2PN(X)R but the former are more stable than the latter when R = Cl. Interestingly, the Me3PNX and Me2PN(X)Me are quite close in energy. The energy decomposition analysis suggests that the P-N bond in the phosphane imides R3PNX (R = H, Cl, Me, Ph; X = H, F, Cl) should be described in terms of an electron-sharing single bond between two charged fragments R3P+-NX- that is supported by (R3P)(+)(NX)(-) -backdonation. The -bond contributes 14-21% of the total orbital interactions while the sigma-bond provides 60-68% of E-orb.

First author: Sanchez-Sanz, G, Understanding Regium Bonds and their Competition with Hydrogen Bonds in Au-2:HX Complexes, CHEMPHYSCHEM, 20, 1572, (2019)
Abstract: A theoretical study of the regium and hydrogen bonds (RB and HB, respectively) in Au-2:HX complexes has been carried out by means of CCSD(T) calculations. The theoretical study shows as overall outcome that in all cases the complexes exhibiting RB are more stable that those with HB. The binding energies for RB complexes range between -24 and -180 kJ . mol(-1,) whereas those of the HB complexes are between -6 and -19 kJ . mol(-1). DFT-SAPT also indicated that HB complexes are governed by electrostatics, but RB complexes present larger contribution of the induction term to the total attractive forces. Au-197 chemical shifts have been calculated using the relativistic ZORA Hamiltonian.

First author: Cabrera-Trujillo, JJ, Carbones and Heavier Ylidones (EL2) in Frustrated Lewis Pair Chemistry: Influence of the Nature of EL2 on Dihydrogen Activation, INORGANIC CHEMISTRY, 58, 7828, (2019)
Abstract: The role of carbones (CL2; L = phosphines vs carbenes) as Lewis bases in dihydrogen (H-2) activation reactions in the presence of the Lewis acid B(C6F5)(3) has been computationally explored by means of density functional theory calculations. To this end, the interaction between H-2 and the [carbone center dot center dot center dot B(C6F5)(3)] pair along the reaction coordinate has been quantitatively analyzed in detail and compared to the parent [‘Bu3P center dot center dot center dot B(C6F5)(3)] frustrated Lewis pair. In addition, the influence on the reactivity of both the nature of the central E atom and the surrounding ligands in ylidones (EL2) has also been considered. It is found that the activation barrier of the H-2 activation reaction as well as the geometry of the corresponding transition states strongly depends on the nature of both E and L in the sense that lower barriers are systematically associated with earlier transition states. Our calculations identify heavier EL2 as the most active systems to achieve facile H-2 activation reactions.

First author: Muravieva, VK, Apical Cyanide Ligand Substitution in Heterometallic Clusters [Re(3)Mo(3)Q(8)(CN)(6)](n-) (Q = S, Se), EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 58, 2685, (2019)
Abstract: A number of transition metal cluster compounds can be obtained only in the melt of inorganic cyanides and, therefore, contain terminal cyanide ligands. Substitution of these ligands, which is often necessary to change the physicochemical properties of the clusters, is an urgent problem because of their low reactivity in substitution reactions. In this work, a synthetic approach has been developed for the substitution of CN-ligands in the heterometallic cluster anions [Re(3)Mo(3)Q(8)(CN)(6)](n-) (Q = S, n = 6; Q = Se, n = 5) by the 4-tert-butylpyridine (TBP) molecules. Two new compounds, namely [Re3Mo3S8(TBP)(6)] (1) and [Re3Mo3Se8(TBP)(6)] (2), were obtained with high yields and crystallized under solvothermal conditions. It has been shown that compounds 1 and 2 are based on the paramagnetic cluster cores {Re(3)Mo(3)Q(8)}(0) containing 23 cluster valence electrons (CVE). The geometry of the new compounds has been investigated using X-ray structural analysis. The electronic structure has been analyzed using the DFT calculations showing large distortion of M-6 cluster core.

First author: Aramburu, JA, Explaining the optical spectrum of CrF2 and CuF2 model materials: role of the tetragonal to monoclinic instability, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 11714, (2019)
Abstract: The properties of MF2 (M = Cr, Cu) model compounds are usually interpreted assuming a Jahn-Teller effect leading to elongated MF64- units. By means of the analysis of experimental data and first-principles calculations on both the monoclinic P2(1)/c structure and the parent rutile structure (tetragonal P4(2)/mnm space group), we prove that such an assumption is not correct. It is shown that in MF2 compounds, the MF64- complexes are actually compressed in the parent phase but along a different direction, a situation that is however hidden by an additional orthorhombic instability due to a negative force constant of b(2g) and b(3g) modes of the cell. This distortion plays a key role in understanding the high experimental value of the lowest d-d transition energy, E-1 = 1.23 and 0.93 eV for CrF2 and CuF2, respectively, when compared to the value E-1 = 0.40 eV derived for the Jahn-Teller system of KZnF3:Cu2+. Aside from reproducing reasonably the experimental values of spin allowed d-d transitions of both compounds, our first-principles calculations show the existence of an accidental degeneracy involving the yz and xy levels in the final P2(1)/c structure. Moreover, the internal electric field of CrF2 and CuF2 is found to be much less anisotropic than in layered compounds like K2CuF4 and thus it has little influence on the d-d transition energy. The influence of the (3z(2) – r(2)) – (x(2) – y(2)) hybridization, caused by the orthorhombic distortion, on the electronic density and the magnetic coupling between layers is also briefly discussed. The present results stress that the interpretation of experimental data using simple parameterized models can lead to wrong conclusions.

First author: Ryzhikov, MR, Understanding structural flexibility of the paddle-wheel Zn-SBU motif in MOFs: influence of pillar ligands, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 11977, (2019)
Abstract: Structural parameters and energies of secondary building units (SBUs) in Zn-2(C8H4O4)(2)center dot C6H12N2 have been examined with DFT and CCSD(T) methods. The SBU structure exhibits flexibility due to close energies of formation of its D-4h, D-4, and D-2d forms. The potential energy surfaces (PESs) calculated for these systems testify that the presence of pillar ligands with negatively charged nitrogens (NCH or DABCO) can lead to almost barrier-free transitions between structural SBU forms. The mobility regions of the SBU motif have been determined.

First author: Boda, A, Scalar Relativistic Density Functional Theoretical Investigation of Higher Complexation Ability of Substituted 1,10-Phenanthroline over Bipyridine Towards Am3+/Eu3+ Ions, ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 645, 817, (2019)
Abstract: The better selectivity of Am3+ over Eu3+ ion with N-based CyMe4-BTPhen compared to CyMe4-BTBP for experimentally observed [ML2(NO3)](2+) complexes was demonstrated using scalar relativistic DFT in conjunction with Born-Haber thermodynamic cycle and COSMO solvation model. The calculated free energy of extraction, Delta G(ext) reveals strong dependence on the hydration free energies of Am3+ and Eu3+ ions and week dependence to the difference in Gibbs free energy of solvation of the ligand or metal-ligand complexes. Further, for the first time, we have computed the effect of co-anion species ([M(NO3)(5)](2-)) on Delta G(ext) of Am3+ and Eu3+ ions with CyMe4-BTPhen and CyMe4-BTBP, which adds a positive contribution and thus reduces the Delta G(ext). The calculated values of Delta Delta Delta G(ext) (= Delta Delta G(ext,L1) – Delta Delta G(ext,L2), Delta Delta G(ext) = Delta G(ext,M1) – Delta G(ext,M2)) can be used to avoid the very sensitive metal ion solvation energy, effect of co-anionic species and thus provides a robust approach to determine the selectivity between two metal ions towards different competitive ligands. The natural population analysis (NPA), molecular orbital analysis, Mayer bond order analysis, and bond character analysis using Bader’s quantum theory of atoms in molecules indicates slightly more covalency for complexes of Am3+ ion that are correlated to the experiental selectvity of Am3+ ion over Eu3+ ion and hence might be useful in the design and development of next generation extractants.

First author: Semenov, VA, Computational Multinuclear NMR of Platinum Complexes: A Relativistic Four-Component Study, JOURNAL OF PHYSICAL CHEMISTRY A, 123, 4908, (2019)
Abstract: The structures of 16 derivatives of cisplatin and transplatin were optimized at the DFT/dyall.ae2z levels, and their H-1, N-15, and Pt-195 NMR chemical shifts were evaluated within the nonrelativistic and four-component relativistic approaches. Reliable correlations of calculated NMR chemical shifts with available experimental data were achieved by taking into account relativistic effects, solvent effects, and vibrational corrections.

First author: Mesta, M, A Protocol for Fast Prediction of Electronic and Optical Properties of Donor-Acceptor Polymers Using Density Functional Theory and the Tight-Binding Method, JOURNAL OF PHYSICAL CHEMISTRY A, 123, 4980, (2019)
Abstract: The ability of donor-acceptor (D-A) type polymers to control the positions of the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals makes them a popular choice for organic solar cell applications. The alternating D-A pattern in a monomer leads to a weak electronic coupling between the constituent monomers within the polymer chain. Exploiting the weak electronic coupling characteristics, we developed a method to efficiently calculate (1) the electronic properties and (2) the optical gap of such polymer chains. The electronic properties (HOMO and LUMO energies, ionization potential, electron affinity, and quasiparticle gap of an oligomer of any length up to an infinitely long polymer) of the D-A polymers are predicted by combining density functional theory calculation results and a tight-binding model. The weak electronic coupling implies that the optical gap of the polymer is size-independent, and thus, it can be calculated using a monomer. We validated the methods using a set of 104 polymers by checking the consistency where the electronic gap of a polymer is larger than the optical gap. Furthermore, we establish relationships between the results obtained from more accurate, yet slower methods (i.e., B3LYP functional, singlet-Delta SCF) with those obtained from the faster counterparts (i.e., BLYP functional, triplet-Delta SCF). Leveraging the found relationships, we propose a way in which the electronic and optical properties of the polymers can be calculated efficiently while retaining high accuracy. The use of the tight-binding model combined with the approach to estimate more accurate results based on less expensive simulations is crucial in the applications where a large volume of computations needs to be carried out efficiently with sufficiently high accuracy, such as high-throughput computational screening or training a machine-learning model.

First author: Velardo, A, Disentangling Electronic and Vibrational Effects in the Prediction of Band Shapes for Singlet-Triplet Transitions, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 14173, (2019)
Abstract: The band shape of phosphorescent emission of benzophenone has been computed by using the first order perturbative expansion of singlet and triplet states with the spin-orbit coupling operator as perturbation and by evaluating Franck-Condon integrals with an efficient strategy for handling the whole set of vibrational coordinates. The computed band shape compares well with the experimental one, showing that modern computational tools yield reliable spin-orbit couplings to be used for evaluating the rates of singlet-triplet transitions in modern optoelectronic devices.

First author: Senanayake, RD, Real-Time TDDFT Investigation of Optical Absorption in Gold Nanowires, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 14734, (2019)
Abstract: Using a real-time TDDFT method, a set of linear gold nanowires Au-m (m = 4, 6, 8, 10, 12) are investigated to understand the plasmon-like behavior that results from resonant excitation of a superposition of single-electron transitions. These characteristic excitations of gold nanowires have been previously investigated via linear-response TDDFT calculations, and the results from these two approaches are compared. Real-time TDDFT provides dynamical information about how the electron populations change during excitations in these systems. This study also investigates the relationship between the d-band transitions and the plasmon-like states in gold nanowires. In this work, the longitudinal and transverse absorption peaks are studied after dipolar excitation, and the effects of changing the length of the nanowire are examined. The time evolution of the single-particle transitions and the interplay between different transitions involved in the plasmon-like excitations of model gold nanowires are also investigated. The lowest-energy longitudinal excitation occurs around 1-2 eV in the optical absorption spectra; this peak redshifts with increasing nanowire length. A splitting in the longitudinal peak is present due to the involvement of interband transitions. The frequency of the transverse mode, which lies around 6-7 eV in the absorption spectra, tends to stay constant as the nanowire length increases. The time-dependent occupation numbers and their Fourier transformed spectra reveal that a dominant single-particle transition (Sigma(n) ->Sigma(n+1)) can be identified in the longitudinal peaks, which is coupled with less probable d-band transitions (d -> Sigma). In contrast, the transverse modes are constructed from a coupling of two or more single-particle transitions with a Sigma(n) -> Pi(n) character.

First author: Chen, X, High-resolution tip-enhanced Raman scattering probes sub-molecular density changes, NATURE COMMUNICATIONS, 10, 14734, (2019)
Abstract: Tip-enhanced Raman spectroscopy (TERS) exhibits new selection rule and sub-nanometer spatial resolution, which is attributed to the plasmonic near-field confinement. Despite recent advances in simulations of TERS spectra under highly confined fields, a simply physical mechanism has remained elusive. In this work we show that single-molecule TERS images can be explained by local sub-molecular density changes induced by the confined near-field during the Raman process. The local sub-molecular density changes determine the spatial resolution in TERS and the gradient-based selection rule. Using this approach we find that the four-fold symmetry of meso-tetrakis(3,5-di-tert-butylphenyl)porphyrin (H2TBPP) TERS images observed in experiments arises from the combination of degenerate normal modes localized in the functional side groups rather than the porphyrin ring as previously considered. As an illustration of the potential of the method, we demonstrate how this new theory can be applied to microscopic structure characterization.

First author: Steller, BG, Selective Preparation of Sterically Encumbered Diaryltin Dihalides from Grignard Reagents via Salt Metathesis and Halide Exchange, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 10, 2591, (2019)
Abstract: A general route for the selective preparation of diaryltin dichlorides, dibromides, and diiodides from readily accessible but sterically demanding, 2,6-disubstituted or 2,4,6-trisubstituted aryl Grignard reagents ArylMgBr and tin tetrachloride was developed. During work-up, the initially obtained mixture of halides is converted into a single species. The thus obtained diaryltin dichlorides were reacted to yield the dihydrides Aryl(2)SnH(2). These exhibit high thermal stability and moderate oxygen tolerance.

First author: Price, JS, Manganese Silyl Dihydride Complexes: A Spectroscopic, Crystallographic, and Computational Study of Nonclassical Silicate and Hydrosilane Hydride Isomers, ORGANOMETALLICS, 38, 2347, (2019)
Abstract: Manganese silyl dihydride complexes [(dmpe)(2)MnH2(SiHR2)] {R = Ph (3a), R = Et (3b)} and [(dmpe)(2)MnH2(SiH2R)] {R = Ph (4a), R = Bu-n (4b)} were generated by exposure of silylene hydride complexes [(dmpe)(2)MnH(=SiR2)] (1a: R = Ph, 1b: R = Et) and disilyl hydride complexes [(dmpe)(2)MnH(SiH2R)(2)] (2a: R = Ph, 2b: R = Bu-n), respectively, to H-2 at room temperature. In solution, 3a,b and 4a,b exist as an equilibrium mixture of a central isomer with a meridional H-Si-H arrangement of the silyl and hydride ligands {this isomer may be considered to contain an eta(3)-coordinated silicate (H2SiR3-) anion}, and a transHSi isomer with trans-disposed hydride and nonclassical hydrosilane ligands (the latter is the result of significant but incomplete hydrosilane oxidative addition). Additionally, DFT calculations indicate the thermodynamic accessibility of lateralH(2) and transH(2) isomers with cis- and trans-disposed silyl and dihydrogen ligands, respectively. Compounds 3a and 4a crystallized as the central isomer, whereas 4b crystallized as the transHSi isomer. Bonding in the central and transHSi isomers of 3a,b and 4a,b was further investigated through Si-29_edited H-1-H-1 COSY solution NMR experiments to determine both the sign and magnitude of J(29Si,1H) coupling (negative and positive values of J(29Si,1H) are indicative of dominant 1- and 2-bond coupling, respectively). These experiments afforded J(29Si,1H) coupling constants of -47 Hz for eta(3)-(H2SiR3) in the central isomer of 3b (calcd -40 to -47 for 3a,b and 4a,b), -38 to -54 Hz for eta(2)-(R3Si-H) in the transHSi isomer of 3a,b and 4a,b (calcd -26 to -47 Hz), and 5 to 9 Hz for the terminal manganese hydride ligand in the transHSi isomer of 3b and 4a,b (calcd 12-14 Hz for 3a,b and 4a,b), experimentally supporting the nonclassical nature of bonding in the central and transHSi isomers.

First author: Torubaev, YV, Energy framework approach to the supramolecular reactions: interplay of the secondary bonding interaction in Ph2E2 (E = Se, Te)/p-I-C6F4-I co-crystals, NEW JOURNAL OF CHEMISTRY, 43, 7941, (2019)
Abstract: In the co-crystals of diphenyl dichalcogenides Ph2E2 (E = Se, Te), the E-E and E-p(Ph) chalcogen bonds assemble Ph2E2 molecules into the chains, which imitate the typical packing patterns of the parent Ph2E2 crystals. These co-crystals consist of quite stable tectonic 1D and 2D Ph2E2 chain architectures, which are repeated in the crystals of pure Ph2E2 as well as in their co-crystals with the halogen bond donor molecules. These chains can be clearly visualized as separate parallel 1D and 2D structures in the energy framework diagrams in CrystalExplorer. From this point of view, the supramolecular reaction of Ph2E2 with the halogen bond donor 1,4-diiodotetrafluorobenzene (p-DITFB) can be considered as the insertion of p-DITFB molecules between the Ph2E2 chains in such a way that I-E and I-p(Ph) halogen bonds come in place of E-E and Te-p(Ph) chalcogen bonds, which are responsible for the close packing of these chains in the parent crystal form. Persistent packing patterns found in parent and binary crystals can provide insight into the mechanism of the crystallization process.

First author: Liu, PC, Atomistic Characterization of Plasmonic Dimers in the Quantum Size Regime, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 13900, (2019)
Abstract: Plasmonic dimer systems show great promise in a wide range of applications because of their unique optical and electronic properties that arise from the coupling of monomer plasmons. To determine the origin of each plasmonic mode and understand the plasmon coupling, atomistic quantum mechanical simulations are required. Here, we adopt a Hirshfeld partitioning scheme of atomic charges and polarizabilities within the time-dependent density functional theory framework to study the plasmonic properties of plasmonic dimers. We are able to separate the charge transfer plasmons because of electron tunneling from local resonance plasmons by the partitioned polarizabilities and induced charges. We find that the strength of charge-transfer plasmons is limited by the charge-flow pathways and dependent on the chemical species. New plasmonic modes for a series of tetrahedral dimers are identified by mapping the induced charges. This approach allows for intuitive and consistent characterizations of strongly coupled plasmonic systems.

First author: Krivdin, LB, Computational protocols for calculating C-13 NMR chemical shifts, PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY, 112, 103, (2019)
Abstract: The most recent results dealing with the computation of C-13 NMR chemical shifts in chemistry (small molecules, saturated, unsaturated and aromatic compounds, heterocycles, functional derivatives, coordination complexes, carbocations, and natural products) are reviewed, paying special attention to theoretical background and accuracy, the latter involving solvent effects, vibrational corrections, and relativistic effects.

First author: Deb, AKS, Macrocyclic host appended carbon nanotubes for selective adsorption of metal ions: combined experimental, DFT and MD studies, MOLECULAR SYSTEMS DESIGN & ENGINEERING, 4, 616, (2019)
Abstract: Crown ethers are very useful for metal ion recognition due to their nanocavity based specific ion selectivity, which on functionalization with carbon nanotubes (CNTs) can be employed as specific metal ion filters by exploiting their different interactions with metal ions. The present study focuses on designing new functionalized nanomaterials using density functional theory and molecular dynamics simulations for understanding their interactions with metal ions of interest followed by synthesis and adsorption experiments. From the analysis of computational results, it is seen that the K+ ion binds strongly to the benzo-15-crown-5 (B15C5) ether and B15C5 appended CNT (CNT-B15C5) followed by Na+ and Li+. Both theoretical and experimental results showed that the adsorption capacity of CNT-B15C5 is much higher than that of free CNTs reflecting the cooperative effect of the pi-electron of the CNT along with the dipole of “O” donors of the crown ether. The adsorption ability of the CNT has been enhanced remarkably by more than 7500% for K+ after functionalization with B15C5. The experimental result reveals zero Li+ ion adsorption by CNT-B15C5. Further, MD simulation also confirmed the selective inclusion of the K+ ion within the cavity of the crown ether in the presence of Li+ and Na+ ions. We anticipate that the functionalized CNT-B15C5 can be used for preparing high purity lithium compounds by selectively filtering K+ and Na+ ions and also for other chemically and biologically important ion filter/channels.

First author: Akbari, A, Theoretical study of structural, electronic and vibrational properties of a Ni-salen complex, JOURNAL OF THE INDIAN CHEMICAL SOCIETY, 96, 655, (2019)
Abstract: Density functional theory (DFT) calculations using ADF 2009.01 package was performed for a nickle(n) complex (NiL, H2L = N,N’-ethylenebis(4-hydroxysalicylideneimine)) and compared with the results of complex characterization (UV-Vis and FTIR techniques). Electronic spectrum of the Ni(II) complex is dominated by charge transfer and intraligand bands at lambda < 436 nm. DFT calculations showed that the HOMO with -4.824 eV energy is metal-dominated, with the H -> L+1 (85%) transfer. The magnitude of bond lengths and angles predictedby DFT calculations are comparable to those determined by X-ray crystallography for similar complex which has the same as bonds as mentioned Ni(II) complex.

First author: Ivanova, TM, An X-ray Spectral Study of the Electronic Structure of Non-Innocent Mono- and Binuclear Platinum Complexes with N-Phenyl-o-Benzosemiquinonediimine, JOURNAL OF STRUCTURAL CHEMISTRY, 60, 909, (2019)
Abstract: The electronic structure of mono- and binuclear platinum complexes with N-phenyl-o benzosemiquinondiimine ligands was studied using X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and the density functional theory. The oxidation state of the central platinum ion corresponds to that of Pt(II). Upon the transition from the trans-complex 1 to the cis-complex 2 and to the binuclear complex 3, the electron density on platinum and nitrogen atoms decreases thus testifying the participation of platinum and nitrogen atoms in the oxidation processes and in the formation of binuclear complex 3.

First author: Hermans, JJ, 2D-IR spectroscopy for oil paint conservation: Elucidating the water-sensitive structure of zinc carboxylate clusters in ionomers, SCIENCE ADVANCES, 5, 909, (2019)
Abstract: The molecular structure around metal ions in polymer materials has puzzled researchers for decades. This question has acquired new relevance with the discovery that aged oil paint binders can adopt an ionomer structure when metal ions leached frompigments bind to carboxylate groups on the polymerized oil network. The characteristics of the metal-polymer structure are expected to have important consequences for the rate of oil paint degradation reactions such as metal soap formation and oil hydrolysis. Here, we use two-dimensional infrared (2D-IR) spectroscopy to demonstrate that zinc carboxylates formed in paint films containing zinc white pigment adopt either a coordination chain-or an oxo-type cluster structure. Moreover, it was found that the presence of water governs the relative concentration of these two types of zinc carboxylate coordination. The results pave the way for a molecular approach to paintings conservation and the application of 2D-IR spectroscopy to the study of polymer structure.

First author: Villasenor-Granados, T, Binding of Pb-Melatonin and Pb-(Melatonin-metabolites) complexes with DMT1 and ZIP8: implications for lead detoxification, DARU-JOURNAL OF PHARMACEUTICAL SCIENCES, 27, 137, (2019)
Abstract: We have applied the docking methodology to characterize the binding modes of the divalent metal transporter 1 (DMT1) and the zinc transporter 8 (ZIP8) protein channels with: melatonin, some melatonin metabolites, and a few lead complexes of melatonin and its metabolites, in three different coordination modes (mono-coordinated, bi-coordinated and tri-coordinated). Our results show that bi-coordinated and tri-coordinated lead complexes prefer to bind inside the central region of ZIP8. Moreover, the interaction strength is larger compared with that of the free melatonin and melatonin metabolites. On the other hand, the binding modes with DMT1 of such complexes display lower binding energies, compared with the free melatonin and melatonin metabolites. Our results suggest that ZIP8 plays a major role in the translocation of Pb, bi or tri coordinated, when melatonin metabolites are present. Finally, we have characterized the binding modes responsible for the ZIP8 large affinities, found in bi-coordinated and tri-coordinated lead complexes. Our results show that such interactions are greater, because of an increase of the number of hydrogen bonds, the number and intensity of electrostatic interactions, and the interaction overlay degree in each binding mode. Our results give insight into the importance of the ZIP8 channel on lead transport and a possible elimination mechanism in lead detoxification processes.

First author: Mai, S, The Influence of the Electronic Structure Method on Intersystem Crossing Dynamics. The Case of Thioformaldehyde, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 15, 3470, (2019)
Abstract: The ability of different electronic structure methods to correctly describe intersystem crossing dynamics is evaluated, using thioformaldehyde as a test case. Mischievously, all methods considered-ranging from the multireference methods MRCISD, MS-CASPT2, or SA-CASSCF, to the single-reference methods ADC(2), CC2, and TDDFT in different flavors provide the same state ordering and energies of the low-lying singlet and triplet electronic excited states within an acceptable error of 0.2-0.3 eV. However, the outcome of the nonadiabatic simulations after excitation to the lowest S-1 ((1)n pi*) state are dramatically different. While MS-CASPT2, ADC(2), BP86, and PBE do not transfer population to the triplet states within 500 fs consistent with experimental evidence SA-CASSCF, B3LYP, and BHHLYP predict intersystem crossing yields between 3% and 21% within the same time. The different excited state dynamics can be rationalized by inspecting potential energy profiles along the C-S bond stretch mode and single-triplet energy gaps. It is found that already at a C-S bond length of 1.9 angstrom, all the single-reference methods struggle to describe the correct asymptotic behavior of the potentials. Moreover, some methods, including SA-CASSCF, obtain incorrect (1)n pi*-(3)pi pi* energy gaps, leading to compensation of errors (ADC(2), BP86, PBE), or wrong dynamics (SA-CASSCF, B3LYP, BHHLYP). Only the accurate MRCISD and MS-CASPT2 methods are able to describe the C-S bond correctly and thus able to deliver the correct potential energy surfaces and dynamics for the right reason. A correlation with the amount of Hartree-Fock exchange in the density functional and the ease to access the (3)pi pi* state from the (1)n pi* are able to explain the different behavior observed for GGA and hybrid functionals. It is thus illustrated that even in the case of a simple molecule, like CH2S, the sole assessment of vertical excitation energies as reliability predictors for nonadiabatic dynamics is inadequate. The reason is that ISC does not occur at the FC geometry, but rather at distorted geometries where the singlet triplet gaps become small. Hence, a characterization of the potential energy surfaces beyond the Franck-Condon region is mandatory.

First author: Wodrich, MD, Activity-Based Screening of Homogeneous Catalysts through the Rapid Assessment of Theoretically Derived Turnover Frequencies, ACS CATALYSIS, 9, 5716, (2019)
Abstract: In homogeneous catalysis, the turnover frequency (TOF) and turnover number (TON) are the most commonly used quantities that experimentally describe catalytic activity. Computational studies, on the other hand, generally yield the ubiquitous free energy profile, which only provides the relative heights of different intermediates and transition states for a given reaction mechanism. This information, however, can be converted into a theoretical TOF through use of the energy span model. Clearly, directly computing turnover frequencies not only allows easy comparison of the activity of different catalysts but also provides a means of directly comparing theory and experiment. Nonetheless, obtaining detailed free energy profiles for many catalysts is computationally costly. To overcome this and accelerate the rate at which prospective catalysts can be screened, here we use linear scaling relationships in tandem with the energy span model to create volcano plots that relate an easily and quickly computed energetic descriptor variable with a catalyst’s turnover frequency. As a demonstration of their ability, we use these “TOF volcanoes” to rapidly screen prospective transition metal/pincer-ligand catalysts based on activity in facilitating the hydrogenation of CO2 to formate.

First author: Marin-Luna, M, A theoretical NMR study of polymorphism in crystal structures of azoles and benzazoles, MAGNETIC RESONANCE IN CHEMISTRY, 57, 275, (2019)
Abstract: The NMR chemical shifts of two azoles and one benzazole whose crystal structures present polymorphism have been computed using the GIPAW approach. N-15 and C-13 nuclei have been studied. Statistical analysis of the computed C-13 and N-15 chemical shifts indicates that the GIPAW chemical shifts reproduce with a high degree of accuracy those experimentally reported. This methodology can be used to identify other polymorphic crystal structures.

First author: Borges-Munoz, AC, Silanization of superficially porous silica particles with p-aminophenyltrimethoxysilane, MICROCHEMICAL JOURNAL, 147, 263, (2019)
Abstract: The surface functionalization of silica particles for chromatographic applications is typically achieved by means of silanization reactions. A silane molecule (e.g., chlorosilanes or alkoxysilanes) with a functional group of interest is attached to the silica surface through a siloxane bond. Even though the surface modification via silanization is widely used, how the reaction parameters affect the degree of surface coverage is rarely discussed, particularly when using the less reactive alkoxysilanes reagents. We studied reaction conditions to graft p-aminophenyltrimethoxysilane (p-APTMS) on superficially porous particles. Theoretical calculations predicted that 3 grafts of p-APTMS per nm(2) (similar to 5 mu mol/m(2)) can be accommodated on the silica surface. This value is not achieved unless the reaction conditions are optimized. To maximize the surface coverage of the aminophenyl layer at the silica surface, we investigated the influence of temperature, reaction time, and addition of water to the silanization reaction on the surface coverage. After optimization, it was found that using elevated temperatures (130 degrees C), adding 3.3 equivalents of water per p-APTMS molecule, and reacting for 24 h in decane as the solvent provided a surface coverage as high as 4.5 mu mol/m(2) (2.7 grafts/nm(2)), approaching the limit suggested via theoretical density functional theory calculations.

First author: Zouchoune, B, Electronic structure and UV-Vis spectra simulation of square planar Bis(1-(4-methylphenylazo)-2-naphtol)-Transition metal complexes [M(L)(2)](x) (M=Ni, Pd, Pt, Cu, Ag, and x=-1, 0,+1): DFT and TD-DFT study, STRUCTURAL CHEMISTRY, 30, 691, (2019)
Abstract: DFT/B3LYP calculations with full geometry optimizations have been carried out on 1-phenylazo-2-naphthol and their metal complexes of formula M(MePhNap)(2) (M=Ni, Pd, Pt, Cu, Ag, and MePhNap=1-(-4-methylphenylazo)-2-naphtol) in their neutral, oxidized, and reduced forms. The predicted structures provide to the M(II) metal ions the square planar geometry and distorted azo ligand. The TD-DFT theoretical study performed on the optimized geometry allowed us to predict the UV-Vis spectra and to identify quite clearly the spectral position and the nature of the different electronic transitions according to their molecular orbital localization. Large HOMO-LUMO gaps are calculated for all optimized structures suggesting good chemical stabilities, hence, reproducing the available UV-Vis spectra and compared to that of free ligand. The electronic spectra obtained in DMSO and ethanol polar solvents predict more important red shifts than those obtained in hexane as nonpolar one.

First author: Michalczyk, M, Interactions of (MY)(6) (M = Zn, Cd; Y = O, S, Se) quantum dots with N-bases, STRUCTURAL CHEMISTRY, 30, 1003, (2019)
Abstract: (MY)(6) clusters, with M = Zn and Cd and Y = O, S, Se, form double-layer drum-like structures containing M-Y covalent bonds. The positive regions near the M atoms attract the N atom of both NH3 and NMe3 so as to form a noncovalent MN bond. This bond is quite strong, with interaction energies exceeding 35kcal/mol. The bond strength diminishes with reduced electronegativity of the Y atom (O > S > Se) and is stronger for M = Zn than for Cd. Trimethylation of the base enhances the bond strength. The interaction is dominated by the electrostatic component which accounts for some 60-70% of the total attractive force. The interaction increases the highest occupied molecular orbital-lowest unoccupied molecular orbital gap by between 0.1 and 0.2eV.

First author: Jana, G, Microsolvation of lithium-phosphorus double helix: a DFT study, THEORETICAL CHEMISTRY ACCOUNTS, 138, 1003, (2019)
Abstract: The chemistry of complexes becomes interesting due to their structural diversity in different environments like in aqueous phase, in gas-phase or in the interior of a host. In the last few decades, powerful tools for the determination of gas-phase have been developed. In this context, the microsolvation approach of Li7P7 helix, where the passage from the bare double-strand helix to the hydrated denatured helix, has been addressed through successive attachment of water molecules using density functional theory. The stability of helical structure of the small clusters has been analyzed on the basis of polar bonding interaction between oxygen end of water molecule and Li centers of the Li7P7 helix. The Li7P7 helix is favored when associated with zero to eight water molecules, but the binding of the ninth water molecule brings a drastic change in the structure. Our results suggest that the natural charges on some sites in Li7P7 are large enough to induce partial and eventually total dissociation of water molecules. We shed light on the bonding situation through natural bond orbital, quantum theory of atoms in molecules and energy decomposition analyses which suggest dominant electrostatic interaction between Li centers of Li7P7 and O centers of water molecules (accounting for 60-64% of total bonding attraction). Nevertheless, 31-36% of total attraction is also originated from the orbital interaction. Variation in reactivity on microhydration is also analyzed. In order to check the site selectivity, we have computed conceptual density functional theory-based local reactivity descriptors such as dual descriptor based on the Fukui function, f(r), and multiphilic descriptor based on the philicity, (r).

First author: Zierkiewicz, W, On the ability of pnicogen atoms to engage in both sigma and -hole complexes. Heterodimers of ZF(2)C(6)H(5) (Z=P, As, Sb, Bi) and NH3, JOURNAL OF MOLECULAR MODELING, 25, 1003, (2019)
Abstract: When bound to a pair of F atoms and a phenyl ring, a pyramidal pnicogen (Z) atom can form a pnicogen bond wherein an NH3 base lies opposite one F atom. In addition to this sigma-hole complex, the ZF(2)C(6)H(5) molecule can distort in such a way that the NH3 approaches on the opposite side to the lone pair on Z, where there is a so-called -hole. The interaction energies of these -hole dimers are roughly 30kcal/mol, much larger than the equivalent quantities for the sigma-hole complexes, which are only 4-13kcal/mol. On the other hand, this large interaction energy is countered by the considerable deformation energy required for the Lewis acid to adopt the geometry necessary to form the -hole complex. The overall energetics of the complexation reaction are thus more exothermic for the sigma-hole dimers than for the -hole dimers.

First author: Marri, AR, Pyridinium p-DSSC dyes: An old acceptor learns new tricks, DYES AND PIGMENTS, 165, 508, (2019)
Abstract: A family of six (five new) thiophenyl bridged triarylamine-donor based dyes with pyridine anchoring groups have been synthesized and studied as sensitizers for the p-type dye-sensitized solar cell (p-DSSC). They comprise bis-dicyano acceptor systems with a single pyridyl binder incorporated directly into the triarylamine (1), or separated by a phenyl group (2); a mono-dicyano with two phenyl pyridine binders (3); and respective homologues 4 to 6 with pyridinium acceptors. In all cases, compared to their dicyano counterparts, the pyridinium based dyes have higher extinction coefficients and smaller HOMO-LUMO gaps that give broader spectrum absorption. Thus, despite lower dye uptake, devices based on pyridiniums 4 and 6 have identical power conversion efficiencies (eta) to the equivalent dicyano systems 1 and 3. However, the best performing device (eta = 0.06%) is based on the known bis-acceptor dicyano system 2, as the large size and double positive charge of 5 leads to a substantial disadvantage in loading on NiO. Absorbed-photon-to-current efficiencies for 5 are competitive with or higher than those of 2, implying a better per dye performance consistent with the absorption profile, and DFT calculations suggesting better charge separation. Thus, pyridiniums may provide a new, and easily accessible high performance acceptor for p-DSSC dyes, but are likely better paired with anionic binding groups such as carboxylates.

First author: Jia, XB, Theoretical studies on charge transport and optical properties of diarylmaleic anhydride derivatives as organic light-emitting materials, CHEMICAL PHYSICS LETTERS, 724, 50, (2019)
Abstract: The charge transport and optical properties of aromatic ring substituents symmetrically-substituted diarylmaleic anhydrides is studied based on the Marcus-Hush theory and quantum chemistry calculations. The molecule with benzene substituents (1) exhibits the balanced hole and electron charge transport properties. Among three molecules, molecule with thiophene substituents (2) shows the maximum carrier mobility. The frontier molecular orbitals analysis turned out that molecule with indole substituents (3) is characterized as intramolecular charge transfer. The absorption and emission spectra indicate that the aromatic substituents can affect optical properties of molecules. 2 might be promising luminescent material for organic light-emitting diodes.

First author: Neto, ANC, On the mechanisms of non-radiative energy transfer between lanthanide ions: centrosymmetric systems, JOURNAL OF LUMINESCENCE, 210, 342, (2019)
Abstract: In this work the aim is three-fold: 1) to call attention for shielding effects in the energy transfer rates between lanthanide ions. 2) to use a new model for treating the Judd-Ofelt Omega(K) intensity parameters in centrosymmetric systems by using a thermal root mean squared displacement around each ligating atom (ion) in the analysis of the intensity parameters. This might have an important role in ion-ion energy transfer processes, particularly when the lanthanide ions occupy a center of inversion. 3) To call attention to the fact that the quadrupole-quadrupole mechanism is dominant for ion-ion distances as far as 20 angstrom, provided shielding effects are taken into account. An illustrating comparison with respect to the weak quadrupole mechanism of 4f-4f transition rates is made.

First author: Sagan, F, Kinetic and Potential Energy Contributions to a Chemical Bond from the Charge and Energy Decomposition Scheme of Extended Transition State Natural Orbitals for Chemical Valence, JOURNAL OF PHYSICAL CHEMISTRY A, 123, 4616, (2019)
Abstract: This work provides novel physical insight into the nature of a chemical bond by exploring qualitative and quantitative relations between the natural orbitals for chemical valence (NOCV)-based deformation density bonding channels Delta rho(i) (i = sigma, pi, delta, etc.) and the corresponding kinetic Delta T-i and potential energy Delta V-i contributions within the charge and energy decomposition scheme ETS-NOCV implemented in the Kohn-Sham-based Amsterdam Density Functional (ADF) package. It is determined that interfragment dative and covalent-type electron charge reorganizations upon formation of a series of strong and weak bonds employing main-group elements are due to lowering of the negative kinetic energy contributions, as opposed to the intrafragment polarizations (e.g., hyperconjugations in ethane), which are, in contrary, driven by the potential energy (electrostatic) component. Complementary, formation of pi-contributions in N-2 is accompanied by lowering of both kinetic and potential energy constituents. Remarkably, well-known globally stabilizing back-donation (M -> ligand, where M is a transition metal) and donation (ligand -> M) processes, ubiquitous in organometallic species, have been discovered for the first time to be driven by the opposite Delta T-i/Delta V-i mechanisms, namely, the former contribution is associated with the negative kinetic term (which outweighs the positive potential energy), whereas the latter charge delocalization into electrophilic transition metals leads to an attractive electrostatic stabilization (and positive kinetic energy).

First author: Wysokinski, R, Influence of monomer deformation on the competition between two types of sigma-holes in tetrel bonds, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 10336, (2019)
Abstract: One of several tetrel (T) atoms was covalently attached to three F atoms and a substituted phenyl ring. A NH3 base can form a tetrel bond with TF3C6H2R3 (T = Si, Ge, Sn, Pb; R = H, F, CH3) in a position opposite either an F atom or the ring. The sigma-hole opposite the highly electron-withdrawing F (T-F) is more intense than that opposite the ring (T-C). However, when the Lewis base deforms from a tetrahedral to a trigonal bipyramidal shape so as to accommodate the base, it is the T-C sigma-hole that is more intense. Accordingly, it is the T-C tetrel-bonded complex for which there is a larger interaction energy with NH3, as high as 34 kcal mol(-1). Countering this trend, it requires more energy for the TF3C6H2R3 to deform into the geometry it adopts within the T-C complex than within its T-F counterpart. There is consequently a balance between the overall binding energies of the two competing sites. The smaller tetrel atoms Si and Ge, with their larger deformation energies, show a preference for T-F tetrel binding, while the T-C site is preferred by Pb which suffers from a smaller degree of deformation energy. There is a near balance for T = Sn and the two sites show comparable binding energies.

First author: Habraken, ERM, Parallels between Metal-Ligand Cooperativity and Frustrated Lewis Pairs, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 21, 2436, (2019)
Abstract: Metal ligand cooperativity (MLC) and frustrated Lewis pair (FLP) chemistry both feature the cooperative action of a Lewis acidic and a Lewis basic site on a substrate. A lot of work has been carried out in the field of FLPs to prevent Lewis adduct formation, which often reduces the FLP reactivity. Parallels are drawn between the two systems by looking at their reactivity with CO2, and we explore the role of steric bulk in preventing dimer formation in MLC systems.

First author: Demir, H, Metal-Organic Frameworks with Metal-Catecholates for O-2/N-2 Separation, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 12935, (2019)
Abstract: Oxygen and nitrogen are widely produced feedstocks with diverse fields of applications but are primarily obtained via the energy-intensive cryogenic distillation of air. More energy-efficient processes are desirable, and materials such as zeolites and metal-organic frameworks (MOFs) have been studied for air separation. Inspired by recent theoretical work identifying metal-catecholates for enhancement of O-2 selectivity MOFs, the computation-ready experimental database of MOF structures was screened to identify promising candidates for incorporation of metal-catecholates. On the basis of structural requirements, preliminary Grand-Canonical Monte Carlo simulations, and further constraints to ensure the computational feasibility, over 5000 structures were eliminated and four MOFs (UiO-66(Zr), Ce-UiO-66, MOF-5, and IRMOF-14) were treated with periodic density functional theory (DFT). Metal-catecholates (Mg, Co, Ni, Zn, and Cd) were selected on the basis of cluster DFT calculations and were added to the shortlisted MOFs. Periodic DFT was used to compute O-2 and N-2 binding energies near metal-catecholates. We find that the binding energies are primarily dependent on the metals in the metal-catecholates, all of which bind O-2 quite strongly (80-258 kJ/mol) and have weaker binding for N-2 (3-148 kJ/mol). Of those studied here, Cd-catecholated MOFs are identified as the most promising.

First author: Sun, XB, Understanding the differences between iron and palladium in cross-coupling reactions, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 9651, (2019)
Abstract: We aim at developing design principles, based on quantum chemical analyses, for a novel type of iron-based catalysts that mimic the behavior of their well-known palladium analogs in the bond activation step of cross coupling reactions. To this end, we have systematically explored C-X bond activation via oxidative addition of CH3X substrates (X = H, Cl, CH3) to model catalysts Fe-m(CO)(4)(q) (q = 0, -2; m = singlet, triplet) and, for comparison, Pd(PH3)(2) and Pd(CO)(2), using relativistic density functional theory at the ZORA-OPBE/TZ2P level. We find that the neutral singlet iron catalyst Fe-1(CO)(4) activates all three C-X bonds via barriers that are lower than those for Pd(PH3)(2) and Pd(CO)(2). This is a direct consequence of the capability of the iron complex to engage not only in pi-backdonation, but also in comparably strong s-donation. Interestingly, whereas the palladium complexes favor C-Cl activation, Fe-1(CO)(4) shows a strong preference for activating the C-H bond, with a barrier as low as 10.4 kcal mol(-1). Our results suggest a high potential for iron to feature in palladium-type cross-coupling reactions.

First author: Babazadeh, M, Calculating transition dipole moments of phosphorescent emitters for efficient organic light-emitting diodes, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 9740, (2019)
Abstract: The out-coupling of light from an organic light-emitting diode, and thus its efficiency, strongly depends on the orientation of the transition dipole moment (TDM) of the emitting molecules with respect to the substrate surface. Despite the importance of this quantity, theoretical investigations of the direction of the TDM of phosphorescent emitters based on iridium(III) complexes remain limited. One challenge is to find an appropriate level of theory able to accurately predict the direction of the TDM. Here, we report relativistic time-dependent density functional theory (TDDFT) calculations of the TDM, emission energies and lifetimes for both the ground-state (S-0) and triplet (T-1) excited-state geometries of fac-tris(2-phenylpyridyl)iridium(III) (Ir(ppy)(3)), using the two-component zero-order regular approximation (ZORA) or including spin-orbit coupling (SOC) perturbatively using the simpler one-component (scalar) formulation. We show that the one-and two-component approaches give similar emission energies and overall radiative lifetimes for each individual geometry. Use of the S-0 geometry leads to two of the excited triplet substates being degenerate, with the degeneracy lifted for the T-1 geometry, with the latter matching experiment. Two-component calculations using the T-1 geometry give results for the direction of the TDM more consistent with experiment than calculations using the S-0 geometry. Finally, we show that adding a dielectric medium does not affect the direction of TDM significantly, but leads to better agreement with the experimentally measured radiative lifetime.

First author: Fukal, J, Structural interpretation of the P-31 NMR chemical shifts in thiophosphate and phosphate: key effects due to spin-orbit and explicit solvent, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 9924, (2019)
Abstract: Structural interpretation of the P-31 NMR shifts measured in O,O-diethyl thiophosphate (PT), 5,5-dimethyl-2- mercapto-1,3,2-dioxaphosphorinane 2-oxide (cPT), diethylphosphate (P) and 5,5-dimethyl-2-hydroxy-1,3,2-dioxaphosphinane 2-oxide (cP) was obtained by means of theoretical calculations including the effects of geometry, molecular dynamics, and solvent, relativistic effects and the effect of NMR reference. NMR calculations employed the B3LYP, BP86, BPW91, M06-2X, PBE0, MP2, and HF methods, the Iglo-n (n = II, III), cc-pVnZ (n = D, T, Q, 5), and pcS-n (n = 0, 1, 2, 3, 4) Gaussian-type basis sets and the Slatertype QZ4P atomic basis. Water solvent was described explicitly and/or implicitly. The effects due to molecular dynamics were calculated using molecular dynamics simulations with the GAFF force field and the TIP3P water molecules, and alternatively by means of the zero-point ro-vibrational averaging. Relativistic effects included the spin-orbit calculated within the two-component zero-order relativistic approximation and the effect with the four-component DFT method. Optimal geometries and largeamplitude dynamical motions within the “opened” PT and P molecules contrasted with notably different geometries and confined dynamical motions within the cPT and cP “closed” molecules. These structuredynamical differences together with the different chemical structures of thiophosphate and phosphate due to a non-esterified sulphur or oxygen atom within the group considerably affected the magnitudes of P-31 NMR shifts. The theoretical calculations enabled accurate and reliable structure-dynamical interpretation of the measured P-31 NMR shifts. The effects due to explicit solvent and relativity turned out to be indispensable for obtaining accurate P-31 NMR shifts particularly in the thiophosphates. Replacement of the non-esterified oxygen atom in the phosphate with sulphur makes NMR shielding of the phosphorus atom qualitatively different as compared to the NMR shielding of the phosphorus atom in phosphate, H3PO4 and PH3.

First author: Parasar, D, Carbonyl complexes of copper(I) stabilized by bridging fluorinated pyrazolates and halide ions, DALTON TRANSACTIONS, 48, 6358, (2019)
Abstract: Syntheses of neutral and anionic, di- and tetra-nuclear copper carbon monoxide complexes using binary copper(I) pyrazolate precursors are reported. The reaction of {[3,5-(CF3)(2)Pz]Cu}(3) (2), {[4-Cl-3,5-(CF3)(2)Pz] Cu}(3) (3) or {[3,4,5-(CF3)(3)Pz]Cu}(3) (4) with CO in CH2Cl2 led to copper carbonyl complexes. They however, lose CO quite easily if not kept under a CO atmosphere. Compounds {[3,5-(CF3)(2)Pz]Cu(CO)}(2) (5) and {[3,4,5-(CF3)(3)Pz]Cu(CO)}(2) (7) were characterized by X-ray crystallography. They are dinuclear species with a Cu2N4 core. The reaction of {[3,5-(CF3)(2)Pz]Cu}(3) with CO in the presence of [NEt4]Br or [NEt4][3,5-(CF3)(2)Pz] affords relatively more stable [NEt4][{[3,5-(CF3)(2)Pz] Cu(CO)}(4)(mu(4)-Br)] (8) and [NEt4]{[3,5-(CF3)(2)Pz](3)Cu-2(CO)(2)} (9). The related [NEt4][{[4-Cl-3,5-(CF3)(2)Pz]Cu(CO)}(4)(mu(4)-Br)] (10) and [NEt4][{[4-Cl-3,5-(CF3)(2)Pz] Cu(CO)}(4)(mu(4)-Cl)] (11) can be synthesized using {[4-Cl-3,5-(CF3)(2)Pz]Cu}(3), CO and [NEt4]Br or [NEt4]Cl. The X-ray structures show that 8, 10 and 11 are tetranuclear species with terminal Cu-CO groups and quadruply bridging Cl- and Br- ions. Compound 9 features an anionic cage of nearly D-3h symmetry formed by three bridging [3,5-(CF3)(2)Pz]-ions and two terminal Cu-CO moieties. Theoretical calculations show that bonding in these 16- and 18-electron copper complexes follows Dewar-Chatt-Duncanson (DCD) model, where the CO stretching frequencies correlate well to the orbital interaction energy Delta E-orb. The major Cu-CO interaction however is electrostatic in nature. Further theoretical exploration of the role of the substituent at pyrazolyl ring 4-position between -H, -Cl, and -CF3, shows a slight decrease in covalent character of the Cu-CO interaction and diminished pi-back bonding as pyrazolate groups become more weakly donating with added electron withdrawing substituents.

First author: Lim, H, X-ray Absorption Spectroscopy as a Probe of Ligand Noninnocence in Metallocorroles: The Case of Copper Corroles, INORGANIC CHEMISTRY, 58, 6722, (2019)
Abstract: The question of ligand noninnocence in Cu corroles has long been a topic of discussion. Presented herein is a Cu K-edge X-ray absorption spectroscopy (XAS) study, which provides a direct probe of the metal oxidation state, of three Cu corroles, Cu[TPC], Cu[Br8TPC], and Cu[(CF3)(8)TPC] (TPC = meso-triphenylcorrole), and the analogous Cu(II) porphyrins, Cu[TPP], Cu[Br8TPP], and Cu[(CF3)(8)TPP] (TPP = meso-tetraphenylporphyrin). The Cu K rising-edges of the Cu corroles were found to be about 0-1 eV upshifted relative to the analogous porphyrins, which is substantially lower than the 1-2 eV shifts typically exhibited by authentic Cu(II)/Cu(III) model complex pairs. In an unusual twist, the Cu K pre-edge regions of both the Cu corroles and the Cu porphyrins exhibit two peaks split by 0.8-1.3 eV. Based on time-dependent density functional theory calculations, the lower- and higher-energy peaks were assigned to a Cu 1s -> 3d(x2-y2) transition and a Cu 1s -> corrole/porphyrin pi* transition, respectively. From the Cu(II) porphyrins to the corresponding Cu corroles, the energy of the Cu 1s -> 3d(x2-y2) transition peak was found to upshift by 0.6-0.8 eV. This shift is approximately half that observed between Cu(II) to Cu(III) states for well-defined complexes. The Cu K-edge XAS spectra thus show that although the metal sites in the Cu corroles are more oxidized relative to those in their Cu(II) porphyrin analogues, they are not oxidized to the Cu(III) level, consistent with the notion of a noninnocent corrole. The relative importance of sigma-donation versus corrole pi-radical character is discussed.

First author: Panthi, D, Nitrogen Reduction by Multimetallic trans-Uranium Actinide Complexes: A Theoretical Comparison of Np and Pu to U, INORGANIC CHEMISTRY, 58, 6731, (2019)
Abstract: There is recent interest in organometallic complexes of the trans-uranium elements. However, preparation and characterization of such complexes are hampered by radioactivity and chemotoxicity issues as well as the air-sensitive and poorly understood behavior of existing compounds. As such, there are no examples of small-molecule activation via redox reactivity of organometallic trans-uranium complexes. This contrasts with the situation for uranium. Indeed, a multimetallic uranium(III) nitride complex was recently synthesized, characterized, and shown to be able to capture and functionalize molecular nitrogen (N-2) through a four-electron reduction process, N-2 -> N-2(4-). The bis-uranium nitride, U-N-U core of this complex is held in a potassium siloxide framework. Importantly, the N-2(4-) product could be further functionalized to yield ammonia (NH3) and other desirable species. Using the U-N-U potassium siloxide complex, K3U-N-U, and its cesium analogue, Cs3U-N-U, as starting points, we use scalar-relativistic and spin-orbit coupled density functional theory calculations to shed light on the energetics and mechanism for N-2 capture and functionalization. The N-2 -> N-2(4-) reactivity depends on the redox potentials of the U(III) centers and crucially on the stability of the starting complex with respect to decomposition into the mixed oxidation U(IV)/U(III) K2U-N-U or Cs2U-N-U species. For the trans-uranium, Np and Pu analogues of K3U-N-U, the N-2 -> N-2(4-) process is endoergic and would not occur. Interestingly, modification of the Np-O and Pu-O bonds between the actinide cores and the coordinated siloxide framework to Np-NH, Pu-NH, Np-CH2, and Pu-CH2 bonds drastically improves the reaction free energies. The Np-NH species are stable and can reductively capture and reduce N-2 to N-2(4-). This is supported by analysis of the spin densities, molecular structure, long-range dispersion effects, as well as spin-orbit coupling effects. These findings chart a path for achieving small-molecule activation with organometallic neptunium analogues of existing uranium complexes.

First author: Carey, DM, Evaluation of N-Heterocyclic Carbene Counterparts of Classical Gold Clusters; Bonding Properties of Octahedral CAu6, Icosahedral Au13Cl2, and Bi-icosahedral Au25Cl2 Cores from Relativistic DFT Calculations, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 12466, (2019)
Abstract: Gold clusters are useful templates for nanosized species retaining a distinctive size-dependent behavior. Usually, a ligand-protected shell passivates such clusters, where their properties can be potentially tuned by introduction of versatile ligands. Here, we explored the recent addition to the well-explored gold-phosphine chemistry, introducing N-heterocyclic carbine (NHC) ligands as characterized by the octahedral carbon-centered CAu6 core, in [CAu6(NHC)(6)](2+). Our results show their similar bonding patterns in such discrete clusters, with slight preference for the later ligands, enabling the proposition of medium-sized species featuring the predominant icosahedral Au-13 structure. NHC counterparts for Au13Cl2(dppe) and Au25Cl2(PPh3)(10)(SR)(5) clusters, denoting both icosahedral and bi-icosahedral central cores, where the bonding features patterns and favorable stability, remain similar to that observed for their phosphine parents and [CAu6(NHC)(6)](2+) clusters, shedding light on other feasible members for explorative synthetic efforts. Optical properties are modified when NHC is introduced instead of phosphine ligands, inducing a red-shift for the lowest-energy peak with a highest occupied molecular orbital lowest unoccupied molecular orbital character and a blue-shift for higher energy absorptions. Hence, NHC derivatives as a ligand-protected layer for medium-sized clusters can introduce useful alternatives for ligand-protected shells, which can be further explored owing to their recognition for well-established versatility in organometallic chemistry.

First author: Niu, XH, Greatly Enhanced Photoabsorption and Photothermal Conversion of Antimonene Quantum Dots through Spontaneously Partial Oxidation, ACS APPLIED MATERIALS & INTERFACES, 11, 17987, (2019)
Abstract: Two-dimensional quantum dots (2DQDs), as promising photothermal agents (PTAs) in photothermal therapy (PTT) to malignant tumors, have been widely studied experimentally, whereas the superior photoabsorption and photothermal conversion mechanisms remain unclear. In this work, we present the first excited-state dynamics study on the PTT of 2D antimonene (AM) QDs by employing time-dependent density functional theory and ab initio nonadiabatic molecular dynamics calculations. Surprisingly, pristine AMQDs themselves are not good PTAs due to weak photoabsorption and low photothermal conversion performance. The superior PTT capacity of AMQDs actually derives from the spontaneously partial oxidation. The partial oxidation introduces additional band edge states, which not only broaden the optical absorption range but also strengthen the transition dipole moment. More importantly, the oxidation doubles the nonradiative transition rate arising from the increased nonradiative coupling, which greatly promotes the release of photogenerated electron energy and accelerates the photothermal conversion efficiency. The in-depth insight unveiled here should be of fundamental importance and benefit for efficient utilization of 2DQDs in biomedical field.

First author: Kanouni, KE, Theoretical investigation of the solubility of some antiemetic drugs, JOURNAL OF MOLECULAR LIQUIDS, 282, 626, (2019)
Abstract: A theoretical study using density functional theory (DFT) is carried out to compare and explain the observed solubility of four antiemetic molecules, namely chlorpromazine, haloperidol, ondansetron and metoclopramide.The COSMO-RS (conductor-like screening model for real solvents) method is used to study the interaction between hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs) of the antiemetic drugs, and their molecular interactions with water (dipole moments, interaction and solvation energies). In addition, the AIM (Atoms in Molecules) method is used to deeply study the hydrogen bonding interaction of the antiemetic drug which was found the most soluble in water, namely the metoclopramide. In fact, results show that atom O42 makes two H-bonds with two different water-oxygen atoms (BCP59 and BCP60). One of them, have another H-bond (BCP62) with the hydrogen H27. This study confirms that two of the three H-bonds with water are more stable than the intramolecular interaction between O9 and H27 (BCP1). These H-bonds are likely responsible of the highest solubility of metoclopramide.

First author: Dalla Torre, G, The interaction of aluminum with catecholamine-based neurotransmitters: can the formation of these species be considered a potential risk factor for neurodegenerative diseases?, DALTON TRANSACTIONS, 48, 6003, (2019)
Abstract: The potential neurotoxic role of Al(iii) and its proposed link with the insurgence of Alzheimer’s Disease (AD) have attracted increasing interest towards the determination of the nature of bioligands that are propitious to interact with aluminum. Among them, catecholamine-based neurotransmitters have been proposed to be sensitive to the presence of this non-essential metal ion in the brain. In the present work, we characterize several aluminum-catecholamine complexes in various stoichiometries, determining their structure and thermodynamics of formation. For this purpose, we apply a recently validated computational protocol with results that show a remarkably good agreement with the available experimental data. In particular, we employ Density Functional Theory (DFT) in conjunction with continuum solvation models to calculate complexation energies of aluminum for a set of four important catecholamines: l-DOPA, dopamine, noradrenaline and adrenaline. In addition, by means of the Quantum Theory of Atoms in Molecules (QTAIM) and Energy Decomposition Analysis (EDA) we assessed the nature of the Al-ligand interactions, finding mainly ionic bonds with an important degree of covalent character. Our results point at the possibility of the formation of aluminum-catecholamine complexes with favorable formation energies, even when proton/aluminum competition is taken into account. Indeed, we found that these catecholamines are better aluminum binders than catechol at physiological pH, because of the electron withdrawing effect of the positively-charged amine that decreases their deprotonation penalty with respect to catechol. However, overall, our results show that, in an open biological environment, the formation of Al-catecholamine complexes is not thermodynamically competitive when compared with the formation of other aluminum species in solution such as Al-hydroxide, or when considering other endogenous/exogenous Al(iii) ligands such as citrate, deferiprone and EDTA. In summary, we rule out the possibility, suggested by some authors, that the formation of Al-catecholamine complexes in solution might be behind some of the toxic roles attributed to aluminum in the brain. An up-to-date view of the catecholamine biosynthesis pathway with sites of aluminum interference (according to the current literature) is presented. Alternative mechanisms that might explain the deleterious effects of this metal on the catecholamine route are thoroughly discussed, and new hypotheses that should be investigated in future are proposed.

First author: Mitoraj, MP, Chameleon-like Nature of Anagostic Interactions and Its Impact on Metalloaromaticity in Square-Planar Nickel Complexes, ORGANOMETALLICS, 38, 1973, (2019)
Abstract: Anagostic C-H-M (M = a metal center) intramolecular interactions, one of the most fundamental and elusive forces in organometallic chemistry, are intuitively considered as repulsive and purely electrostatic in nature because of significant metal-hydrogen distances (similar to 2.3-3.0 angstrom). Contrary to the current state of knowledge, it is shown herein by quantum chemical computations based on the case study of new square-planar Ni-II isomers based on N-thiophosphorylated thiourea that despite significant metal hydrogen anagostic distances, the covalent-type charge delocalization contribution [Ni(d(z)(2)) -> sigma*(C-H) and sigma-(CH) -> Ni(d(z)(2))] exists and it covers, together with the London dispersion energy, up to similar to 40% of the overall anagostic stabilization. This charge delocalization component is found to amplify the metalloaromaticity phenomenon although a lack of any stabilizing charge transfer is expected at such long metal hydrogen distances (>3 angstrom). Remarkably, for the relatively short regime (<3 angstrom) of anagostic distances, the electrostatic Coulomb forces are destabilizing, which leads to the repulsive anagostic interactions, whereas, surprisingly, an increase of anagostic distance above 3 angstrom makes anagostic interactions stabilizing mostly because of attractive Coulomb forces. It shows unprecedented agostic (attractive) <-> anagostic (repulsive) transitions in ubiquitous d(8) square-planar Ni-II complexes containing elongated metal-hydrogen distances.

First author: Hussain, M, Excited state intermolecular hydrogen bond’s effect on the luminescent behaviour of the 2D covalent organic framework (PPy-COF): A TDDFT insight, MOLECULAR SIMULATION, 45, 942, (2019)
Abstract: The theoretical investigation of electronically excited stated intermolecular hydrogen bonding dynamics of the 2D luminescent polypyrene covalent organic framework and methanol molecule (PPy-COF-MeOH) was performed using the density functional theory (DFT) and time-dependent (TD-DFT) method. The strengthening of Hydrogen bonds C-H—O-H and B-O—H-O upon photoexcitation was confirmed via comparison of geometric structures, electronic transition energies, H-1-NMR, binding energies, UV-Vis and infrared spectra in S0 and S1 states. Frontier molecular orbitals (MOs) analysis, electronic configuration, Mulliken charge analysis; and the charge density variation in hydrogen bonding proximity demonstrated that the strengthened hydrogen bonds facilitate the nonradiative path which may consequently proceed the luminescence quenching. Hence, the molecular material property prediction package (MOMAP) programme verified the fluorescence quenching because PPy-COF-MeOH complex showed a lower fluorescent rate constant compared to isolated PPy-COF fragment. The S1-T1 energy gap analysis also revealed the possibility of the Intersystem crossing (ISC). Above results significantly highlighted the role of the hydrogen bonding dynamics on luminescence property of the PPy-COF.

First author: Bhaskar, P, Unconventional Thermally Activated Indirect to Direct Radiative Recombination of Electrons and Holes in Tin Disulfide Two-Dimensional van der Waals Material, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 11968, (2019)
Abstract: Tin disulfide (SnS2) is a two-dimensional semiconducting van der Waals material with an indirect band gap. We measured the mobility and recombination dynamics of charge carriers as a function of temperature and charge density. Excess electrons and holes were generated by pulsed irradiation with 3 MeV electrons. The charge carriers were probed by time-resolved microwave conductivity measurements. The mobility and decay pathways of the charge carriers were determined by a global kinetic rate equation model including decay of charges by recombination and trapping. We found high mobilities for electrons and holes near 100 cm(2) V-1 s(-1). The mobility decreases at higher temperature, which is typical for bandlike transport. The second-order recombination rate constant is found to be thermally activated with an activation energy close to the energy difference of the direct and indirect band gap of SnS2. We demonstrate that the radiative recombination is reaction-limited and takes place via the Gamma-point after thermal excitation of electrons from the M-point to the Gamma-point, while a phonon emission-related recombination between the indirect band gap (M-point electrons and Gamma-point holes) has no relevant contribution to the population decay. The observed effects result in an unusual increase of radiative electron-hole recombination constant with temperature.

First author: Carlotto, S, Comparative Experimental and Theoretical Study of the Fe L-2,L-3-Edges X-ray Absorption Spectroscopy in Three Highly Popular, Low-Spin Organoiron Complexes: [Fe(CO)(5)], [(eta(5)-C5H5)Fe(CO)(mu-CO)](2), and [(eta(5)-C5H5)(2)Fe], INORGANIC CHEMISTRY, 58, 5844, (2019)
Abstract: The occupied and unoccupied electronic structures of three highly popular, closed shell organoiron complexes ([Fe(CO)(5)], [(eta(5)-C5H5 )Fe(CO)(mu-CO)](2), and [(eta(5)-C5H5)(2)Fe]) have been theoretically investigated by taking advantage of density functional theory (DFT) calculations coupled to the isolobal analogy (Elian et al. Inorg. Chem. 1976, 15, 1148). The adopted approach allowed us to look into the relative role played by the ligand -> Fe donation and the Fe -> ligand back-donation in title molecules, as well as to investigate how CO- (terminal or bridging) and [(eta(5)-C5H5)](-)-based pi* orbitals compete when these two ligands are simultaneously present as in [(eta(5)-C5H5)Fe(CO)(mu-CO)](2). Insights into the nature and the strength of the bonding between Fe and the C donor atoms have been gained by exploiting the Nalewajski-Mrozek bond multiplicity index (Nalewajski et al. Int. J. Quantum Chem. 1994, 51, 187), which have been found especially sensitive even to tiny bond distance variations. The bonding picture emerging from ground state DFT results proved fruitful to guide the assignment of original, high-resolution, gas-phase L-2,L-3-edges X-ray absorption spectra of the title molecules, which have been modeled by the two-component relativistic time-dependent DFT including spin orbit coupling and correlation effects and taking advantage of the full use of symmetry. Assignments alternative to those reported in the literature for both [Fe(CO)(5)] and [(eta(5)-C5H5)(2)Fe] are herein proposed. Despite the high popularity of the investigated molecules, the complementary use of symmetry, orbital, and spectroscopy allowed us to further look into the metal-ligand symmetry-restricted-covalency and the differential-orbital covalency, which characterize them.

First author: Ghosh, A, Stereochemistry of Transition-Metal Dinitrosyl Complexes. A Molecular Orbital Rationale for the Attracto and Repulso Conformations, INORGANIC CHEMISTRY, 58, 5943, (2019)
Abstract: Transition-metal dinitrosyl complexes constitute a fairly large class of compounds, exemplified by some 500 structures in the Cambridge Structural Database. While many of the complexes exhibit a claw-like cis-attracto conformation, a handful of them exhibit a peculiar repulso conformation, in which the two NO groups are splayed outward and away from each other. Surprisingly, no computational study to date has attempted to explain the existence of these two limiting conformations of cis-dinitrosyl complexes. Careful examination of the large body of structural data and density-functional-theory-based molecular orbital analyses has identified both specific Enemark-Feltham electron counts and metal-ligand orbital interactions as crucial to each of the two conformations. Thus, the common attracto conformation, which is favored by as many as four metal(d)-NO(pi*) orbital interactions, is observed most characteristically in four- and five-coordinate cis-{M(NO)(2)}(8) complexes. The rarer repulso conformation, characterized by an unusually wide NMN’ angle, appears to be typical of pseudotetrahedral {M(NO )(2)}(10) complexes involving 4d and 5d transition metals. These complexes exhibit an a(1)-symmetry (under a C (2v) molecular point group) metal(d)-NO(pi*) orbital interaction that uniquely favors a repulso geometry. This orbital interaction, however, appears to be weaker for 3d orbitals, which are significantly smaller than 4d and 5d orbitals. Pseudotetrahedral {M(NO )(2)}(10)complexes involving a 3d transition metal accordingly thus tend to exhibit an attracto conformation for hard, nitrogen-based supporting ligands but repulso-like/borderline conformations for soft phosphine- and thioether-type supporting ligands.

First author: Vasilchenko, D, Tetraalkylammonium Salts of Platinum Nitrato Complexes: Isolation, Structure, and Relevance to the Preparation of PtOx/CeO2 Catalysts for Low-Temperature CO Oxidation, INORGANIC CHEMISTRY, 58, 6075, (2019)
Abstract: A series of tetraalkylammonium salts with anionic platinum nitrato complexes (Me4N)(2)[Pt-2(mu-OH)(2)(NO3)(8)] (1), (Et4N)(2)[Pt-2(mu-OH)(2)(NO3)(8)] (2), (n-Pr4N)(2) [Pt-2(mu-OH)(2)(NO3)(8)] (3b), (n-Pr4N)(2)[Pt(NO3)(6)] (3a), and (n-Bu4N)(2)[Pt(NO3)(6)] (4) were isolated from nitric acid solutions of [Pt(H2O)(2)(OH)(4)] in high yield. The structures of salts 2, 3a, 3b, and 4, prepared for the first time, were characterized by X-ray diffraction. The sorption of [Pt(NO3)(6)](2-) and [Pt-2(mu-OH)(2)(NO3)(8)](2-) complexes onto the ceria surface from acetone solutions of salts 4 and 1 was examined. The dimeric anion was shown to quickly and irreversibly chemisorb onto the CeO2 carrier, selectively transforming into Pt(II) centers after thermal treatment, becoming active in the low-temperature CO oxidation reaction (T-50% = 110 degrees C at a space velocity of 240 000 h(-1)). By contrast, the homoleptic complex [Pt(NO3)(6)](2-) did not interact with the ceria, which may be attributed to the substitutional inertness of the [Pt(NO3)(6)](2-) anion. We believe that the strategy based on the sorption of polynuclear platinum nitrato complexes is an effective route to prepare ionic platinum species uniformly distributed on an oxide carrier for various catalytic applications.

First author: Rowicki, T, Synthesis, structure of 7-oxa-1-azabicyclo[2.2.1]heptane derivative obtained from sugar nitrone and analysis of its conformational variety, JOURNAL OF MOLECULAR STRUCTURE, 1183, 14, (2019)
Abstract: Dispiro derivative of 7-oxa-1-azabicyclo [2.2.1]heptane 5 was synthesized as a single stereoisomer from N-(5-allyl-spiro [1,3-dioxan-2,1′-cyclohexane]-5-yl)hydroxylamine 2 and protected D-mannose 3, through intramolecular 1,3-dipolar cycloaddition of in situ formed N-(but-3-en-1-yl)nitrone 4. Structure of product 5 was attributed on the basis of NMR and X-ray analyses. In the solid state, three crystallo-graphically independent molecules of 5 were detected, every exhibiting a different orientation of spiro connected rings. Conformational analysis performed by DFT calculations in the gas phase was performed and revealed that the conformations observed in the crystal correspond to the most stable molecular geometries. Two of them were also found to be dominant in solution.

First author: Hamlin, TA, Structural Distortion of Cycloalkynes Influences Cycloaddition Rates both by Strain and Interaction Energies, CHEMISTRY-A EUROPEAN JOURNAL, 25, 6342, (2019)
Abstract: The reactivities of 2-butyne, cycloheptyne, cyclooctyne, and cyclononyne in the 1,3-dipolar cycloaddition reaction with methyl azide were evaluated through DFT calculations at the M06-2X/6-311++ G(d)//M06-2X/6-31+ G(d) level of theory. Computed activation free energies for the cycloadditions of cycloalkynes are 16.5-22.0 kcalmol(-1) lower in energy than that of the acyclic 2-butyne. The strained or predistorted nature of cycloalkynes is often solely used to rationalize this significant rate enhancement. Our distortion/in-teraction-activation strain analysis has been revealed that the degree of geometrical predistortion of the cycloalkyne ground-state geometries acts to enhance reactivity compared with that of acyclic alkynes through three distinct mechanisms, not only due to (i) a reduced strain or distortion energy, but also to (ii) a smaller HOMO-LUMO gap, and (iii) an enhanced orbital overlap, which both contribute to more stabilizing orbital interactions.

First author: Xiang, WT, Quantifying the Bonding Strength of Gold-Chalcogen Bonds in Block Copolymer Systems, CHEMISTRY-AN ASIAN JOURNAL, 14, 1481, (2019)
Abstract: Gold-chalcogen interactions are ubiquitous in gold biological and medicinal systems. Understanding the nature of these interactions can provide the basis for regulating their structures and functionalities, and a reasonable way to interpret the differences in various properties. However, the relative strength of gold-chalcogen bonds remains controversial, and the conclusions of many related works are inconsistent. Thus, in this work, we successfully quantified the relative strength of Au-X (X=S, Se, and Te from chalcogenide-containing A-B-A type block copolymers) interactions at the single-molecule level through single-molecule force spectroscopy (SMFS) from a kinetic point of view and quantum chemical studies from a thermodynamic point of view. Both sets of results suggested that the strength of the Au-X bonds decreases as Au-Te>Au-Se>Au-S. Our findings unveiled the relative strength and nature of gold-chalcogen interactions, which may help expand their application in electronics, catalysis, medicine and many other fields.

First author: Yang, D, Structures and Infrared Spectra of [M(CO2)(7)](+) (M = V, Cr, and Mn) Complexes, JOURNAL OF PHYSICAL CHEMISTRY A, 123, 3703, (2019)
Abstract: Gas-phase infrared photodissociation spectra of [V(CO2)(n)](+) complexes revealed three new vibrational bands at 1140, 1800, and 3008 cm(-1) at n = 7, the features of which are retained in the larger clusters (Ricks, A. M.; Brathwaite, A. D.; Duncan, M. A. J. Phys. Chem. A 2013, 117, 11490-11498). However, structural assignment of this intriguing feature remains open. Herein, quantum chemical calculations on [V(CO2)(7)](+) were carried out to identify the structure of the low-lying isomers and to assign the observed spectral features. The comparison of calculated infrared spectra of [V(CO2)(7)](+) with experimental infrared spectra identified the formation of a bent CO2 species, suggesting the ligand-induced activation of CO, by the vanadium cation. The structures and infrared spectra of [Cr(CO2)(7)](+) and [Mn(CO2)(7)](+) were also predicted and discussed.

First author: Yoo, DH, n-Type Organic Field-Effect Transistors Based on Bisthienoisatin Derivatives, ACS APPLIED ELECTRONIC MATERIALS, 1, 764, (2019)
Abstract: Bisthienoisatins (BT1-R with R = n-propyl, n-hexyl, and 2-ethylhexyl) and the dicyanomethylene derivatives (BTICN-R) are prepared, and the thin-film transistors are investigated. The crystals have uniform stacking structures, but the packing pattern of the stacks varies depending on the alkyl chains, These materials show n-type transistor properties, and BTICNs exhibit greater performance than BTIs in general. In particular, BTICN-EH shows the maximum electron mobility exceeding 0.2 cm(2) V-1 s(-1).

First author: Yurash, B, Photoluminescence Quenching Probes Spin Conversion and Exciton Dynamics in Thermally Activated Delayed Fluorescence Materials, ADVANCED MATERIALS, 31, 764, (2019)
Abstract: Fluorescent materials that efficiently convert triplet excitons into singlets through reverse intersystem crossing (RISC) rival the efficiencies of phosphorescent state-of-the-art organic light-emitting diodes. This upconversion process, a phenomenon known as thermally activated delayed fluorescence (TADF), is dictated by the rate of RISC, a material-dependent property that is challenging to determine experimentally. In this work, a new analytical model is developed which unambiguously determines the magnitude of RISC, as well as several other important photophysical parameters such as exciton diffusion coefficients and lengths, all from straightforward time-resolved photoluminescence measurements. From a detailed investigation of five TADF materials, important structure-property relationships are derived and a brominated derivative of 2,4,5,6-tetrakis(carbazol-9-yl)isophthalonitrile that has an exciton diffusion length of over 40 nm and whose excitons interconvert between the singlet and triplet states approximate to 36 times during one lifetime is identified.

First author: Murugesan, V, Thermally activated nucleation and growth of cobalt and nickel oxide nanoparticles on porous silica, JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A, 37, 764, (2019)
Abstract: Integrating mesoscale to the molecular level understanding of nanoparticle nucleation phenomena can drive the bottom-up synthesis approach for target applications. The authors studied the thermal evolution of binary metal oxide (cobalt and nickel oxides) nanoparticle structural phases on porous silica host from over wide spatial scale using multimodal analysis involving scanning transmission electron microscopy, x-ray absorption near-edge spectroscopy (XANES), and nuclear magnetic resonance (NMR) spectroscopy along with density functional theory (DFT) based calculations. The TEM analysis reveals thermally activated nanoparticle clustering and subsequent interaction with the porous host material. The Co and Ni K-edge XANES spectra revealed the evolution from metal hydroxide to metal oxide and subsequently metal silicate composites with calcination temperature. Si-29 NMR analysis revealed the role of surface functional groups of silica host for silicate composite formation, which is corroborated by DFT studies. Published by the AVS.

First author: Gomez-Torres, A, Small Cage Uranofullerenes: 27 Years after Their First Observation, HELVETICA CHIMICA ACTA, 102, 764, (2019)
Abstract: The tetravalently stabilized fullerene cage of C-28 is historically the most elusive small fullerene cage observed by employing the laser vaporization synthesis methodology. Its first observation reported by Smalley etal. in 1992 suggests that C-28 is potentially the smallest and most stable fullerene ever observed. By using the Kratschmer-Huffman arc discharge synthesis method, we have recently succeeded in synthesizing a series of uranium-endohedral fullerenes which differ from those reported by Smalley and co-workers. Intrigued by this interesting mismatch, we tuned our experimental conditions to favor the formation and detection of these missing species. Experiments done using solvents of varying polarity allowed the observation of several empty and uranofullerenes. Extractions with pyridine and o-DCB allowed for observation of small U@C-2n (2n=28, 60, 66, 68, 70) by high resolution Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS). This is the first time that U@C-28 is observed in soot produced by the Kratschmer-Huffman arc-discharge methodology. Carbon cage selection and spin density distribution on the endohedral metallofullerenes (EMFs) U@C-60, U@C-70, and U@C-72 were studied by means of density functional theory (DFT) calculations. A plausible pathway for the formation of U@D-3h-C-74 from U@D-5h-C-70 through two C-2 insertions and one Stone-Wales rearrangement is proposed.

First author: Rudolph, J, Computational Insights into the Mechanism of the Selective Catalytic Reduction of NOx: Fe-versus Cu-Exchanged Zeolite Catalysts, ACS OMEGA, 4, 7987, (2019)
Abstract: We computationally investigate the mechanism of the reduction half-cycle of the selective catalytic reduction of nitrogen oxides with ammonia. We compare both Fe- and Cu-exchanged zeolite catalysts and aim at exploring all accessible reaction pathways. From our calculations, a comprehensive picture emerges that unifies several previous mechanistic proposals. We find that both for Fe and for Cu catalysts different reaction pathways are feasible but some of the possible reaction pathways differ in these two cases. Our computational results provide a basis for the interpretation of in situ spectroscopic investigations that can possibly distinguish the different mechanistic pathways.

First author: Du, R, Specific ion effects directed noble metal aerogels: Versatile manipulation for electrocatalysis and beyond, SCIENCE ADVANCES, 5, 7987, (2019)
Abstract: Noble metal foams (NMFs) are a new class of functional materials featuring properties of both noble metals and monolithic porous materials, providing impressive prospects in diverse fields. Among reported synthetic methods, the sol-gel approach manifests overwhelming advantages for versatile synthesis of nanostructured NMFs (i.e., noble metal aerogels) under mild conditions. However, limited gelation methods and elusive formation mechanisms retard structure/composition manipulation, hampering on-demand design for practical applications. Here, highly tunable NMFs are fabricated by activating specific ion effects, enabling various single/alloy aerogels with adjustable composition (Au, Ag, Pd, and Pt), ligament sizes (3.1 to 142.0 nm), and special morphologies. Their superior performance in programmable self-propulsion devices and electrocatalytic alcohol oxidation is also demonstrated. This study provides a conceptually new approach to fabricate and manipulate NMFs and an overall framework for understanding the gelation mechanism, paving the way for on-target design of NMFs and investigating structure-performance relationships for versatile applications.

First author: Radicchi, E, Understanding the Solution Chemistry of Lead Halide Perovskites Precursors, ACS APPLIED ENERGY MATERIALS, 2, 3400, (2019)
Abstract: Identifying the composition of the solvated iodoplumbate complexes that are involved in the synthesis of perovskites in different solution environments is of great relevance in order to link the type and quantity of precursors to the final optoelectronic properties of the material. In this paper, we clarify the nature of these species and the involved solution equilibria by combining experimental analysis and high-level theoretical calculations, focusing in particular on the DMSO and DMF solvents, largely employed in the perovskites synthesis. The specific molecular interactions between the iodoplumbate complexes and the solvent molecules were analyzed by identifying the most thermodynamically stable structures in various solvent solutions and characterizing their optical properties trough DFT and TD-DFT calculations. A comparison with the experimental UV-vis absorption spectra allows us to define the number of iodide and solvent ligands bonded to the Pb2+ ion and the complex formation constants of the involved species.

First author: Majid, A, Optical Properties of Titania-Zirconia Clusters: a TD-DFT Study, JOURNAL OF CLUSTER SCIENCE, 30, 707, (2019)
Abstract: Time dependent density functional theory (TD-DFT) study of the optical properties of titania (TiO2), Zirconia (ZrO2) and their hybrid clusters TiZrO4 are reported. The UV-Visible spectra and Circular Dichroism spectra of the clusters were computed to investigate the molecular orbitals, excitation energies, electronic transitions, HOMO-LUMO characters, oscillatory and rotatory strengths of the clusters. The excitation energies of TiZrO4 starting from Zr2O4 appeared in the visible and near UV region whereas the same is found in near UV region when starting geometry was switched to Ti2O4. The findings of this study revealed that the optical properties of the hybrid clusters are strongly influenced from the geometry of starting clusters. Further, the excitation spectra of the hybrid clusters possess the finger prints of the properties of the starting clusters. The optical activity of the hybrid clusters in visible and near UV regions points to potential of the materials for application in photocatalysis. The hybrid material points to possibility of preparation of tunable materials for use in electronic, optoelectronic, electrochemical/photo-catalytic applications and as chiral compounds.

First author: Nhung, NTA, Theoretical assessment of donor-acceptor complexes [X(PPh3)(2)AlH2](+) (X=C-Pb): structures and bonding, THEORETICAL CHEMISTRY ACCOUNTS, 138, 707, (2019)
Abstract: Quantum chemical investigations at the BP86/def2-SVP, BP86/def2-TZVPP and BP86/TZ2P+ levels of theory have been done for the series of AlH2+ complexes that carry carbodiphosphorane and analogues called tetrylones [X(PPh3)(2)-AlH2](+) (Al-XPPh) (X=C-Pb) using charge and partitioning methods. The most stable structures of Al-XPPh have been found for carbone CPPh as a mildly side-on style in carbone complex Al-CPPh, while the heavier tetrylone adducts Al-SiPPh-Al-PbPPh have significantly different side-on fashions SiPPh-PbPPh, which exhibit the more acute bending angles in tilted forms linked to AlH2+ fragment. Bond dissociation energies (BDEs), D-e (kcal/mol), slightly decrease from the strongest bonded carbone, Al-CPPh, to the weaker bonded heavier homologues. The bulky tetrylone ligands XPPh have significantly influenced to the Al-X bond strength in complexes Al-XPPh when calculating BDEs with dispersion interaction. The NBO analysis revealed that the [X(PPh3)(2)AlH2](+) donation comes mainly from the sigma- and -contributions of the ligands. The EDA-NOCV calculations showed that the bond sturdiness of the Al-X bond results from the decrease in [X(PPh3)(2)AlH2](+) donation and electrostatic attraction. The EDA-NOCV data also indicated that AlH2+-tetrylone complexes exhibit not only (PPh3)(2)XAlH2+ strong sigma-donors and weak -donors but also (PPh3)(2)XAlH2+ weak -back donation as – electrons shared in complexes.

First author: Groenewald, F, Computational investigation of Au center dot H hydrogen bonds involving neutral (AuN)-N-I-heterocyclic carbene complexes and amphiprotic binary hydrides, JOURNAL OF MOLECULAR MODELING, 25, 707, (2019)
Abstract: In this computational study, we investigate the ability of various neutral R-Au-I-NHC (NHC=N-heterocyclic carbene) complexes [R=H, CH3, Cl, OH] to form hydrogen bonds with the amphiprotic binary hydrides NH3, H2O and HF. Optimized geometries of the adducts calculated at various levels of theory all exhibit AuHX hydrogen bonds. In adducts of complexes containing NHC ligands with (N)H units, (NH)(carbene)XH interactions also exist, yielding hydrogen-bonded rings with graph-set notation R-2(2)(6) that correspond to pseudo chelates with C-2,H coordination. AIM analysis at the MP2/aug-cc-pVTZ-pp level of theory indicates that the (NH)(carbene)XH hydrogen bonds are generally stronger than the AuHX interactions, except for those involving HF. The AuHX interactions vary with the Lewis basicity of the Au(I) center as a result of the nature of the R ligand, while the (NH)(carbene)XH hydrogen bonds are unaffected by R. Energy decomposition analysis at the BP86/TZP level of theory identifies the origin of this difference as the greater component of polarization involved in AuHX interactions. Replacing the (N)Hs with methyl groups prevents formation of a strong (NH)(carbene)XH interaction, thus reducing the overall stabilization of the adducts. Nevertheless, the AuH interactions remain largely unchanged and are strong enough to sustain the hydrogen-bonded complexes, although weak C-HX interactions are often also present.

First author: Zadlo, A, Photobleaching of pheomelanin increases its phototoxic potential: Physicochemical studies of synthetic pheomelanin subjected to aerobic photolysis, PIGMENT CELL & MELANOMA RESEARCH, 32, 359, (2019)
Abstract: Although melanin is a photoprotective pigment, its elevated photochemical reactivity could lead to various phototoxic processes. Photoreactivity of synthetic pheomelanin, derived from 5-S-cysteinyldopa (5SCD-M) and its photodegradation products obtained by subjecting the melanin to aerobic irradiation with UV-visible light, was examined employing an array of advanced physicochemical methods. Extensive photolysis of 5SCD-M was accompanied by partial bleaching of the melanin, modification of its paramagnetic properties, and significant increase in the ability to photogenerate singlet oxygen. The changes correlated with a substantial decrease in the melanin content of benzothiazine (BT) units and increase of modified benzothiazole (BZ) units. Synthetically prepared BZ exhibited higher efficiency to photogenerate singlet oxygen than the synthetic BT, and the free radical form of BZ, unlike that of BT, did not show measurable spin density on nitrogen atom, which was confirmed by quantum chemical calculations. Formation of modified BZ units in the photobleached 5SCD-M is responsible for the paramagnetic and photochemical changes of the melanin and its elevated phototoxic potential. Given a relatively constant pheomelanineumelanin ratio, such undesirable changes could occur in individual of all skin types.

First author: Gam, F, Potential to stabilize 16-vertex tetrahedral coinage-metal cluster architectures related to Au-20, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 8428, (2019)
Abstract: DFT calculations were carried out on a series of tetrahedral 16-atom superatomic clusters having 20 or 18 jellium electrons (je) and structurally related to Au-20, namely, [M-16](4-/2-) (M = Cu, Ag, and Au) and [M4M12](0/2+) (M = Zn, Cd, Hg; M = Cu, Ag, Au). While the bare homonuclear 20-je species required further stabilization to be isolated, their 18-je counterparts exhibited better stability. Lowering the electron count led to structural modification from a compact structure (20-je) to a hollow sphere (18-je). Such a change could be potentially controlled by tuning redox properties. Among the 20-je heteronuclear [M4M12] neutral series, [Zn4Au12] appeared to meet the best stability criteria, but their 18-je relatives [M4M12](+), in particular [Zn4Cu12](2+) and [Cd4Au12](2+), offered better opportunities for obtaining stable species. Such species exhibit the smallest models for the M(111) surface of fcc metals, which expose designing rules towards novel high-dopant-ratio clusters as building blocks of nanostructured materials.

First author: Mayer, M, Rational design of an argon-binding superelectrophilic anion, PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF, 116, 8167, (2019)
Abstract: Chemically binding to argon (Ar) at room temperature has remained the privilege of the most reactive electrophiles, all of which are cationic (or even dicationic) in nature. Herein, we report a concept for the rational design of anionic superelectrophiles that are composed of a strong electrophilic center firmly embedded in a negatively charged framework of exceptional stability. To validate our concept, we synthesized the percyano-dodecoborate [B-12(CN)(12)](2-) the electronically most stable dianion ever investigated experimentally. It serves as a precursor for the generation of the monoanion [B-12(CN)(11)](-), which indeed spontaneously binds Ar at 298 K. Our mass spectrometric and spectroscopic studies are accompanied by high-level computational investigations including a bonding analysis of the exceptional B-Ar bond. The detection and characterization of this highly reactive, structurally stable anionic superelectrophile starts another chapter in the metal-free activation of particularly inert compounds and elements.

First author: Lei, YQ, Regulating vibrational modes to improve quantum efficiency: insights from theoretical calculations on iridium(iii) complexes bearing tridentate NCN and NNC chelates, DALTON TRANSACTIONS, 48, 5064, (2019)
Abstract: We reported a theoretical study on [(NCN)Ir(iii)(NNC)](+) tridentate Ir(iii) complexes for organic light-emitting diode (OLED) applications. With appropriate chemical modifications onto the NCN ligand of [(NCN)Ir(iii)(NNC)](+), several rotational and stretching vibration modes were weakened or even eliminated, resulting in a weaker vibrational coupling between the emissive state and the ground state, therefore slowing down the non-radiative decay process, ultimately improving the quantum efficiency. We hope that these theoretical studies and the semi-quantitative prediction on phosphorescence efficiency could provide inspiration for the design of highly efficient phosphorescent materials.

First author: Ramler, J, Carbon monoxide insertion at a heavy p-block element: unprecedented formation of a cationic bismuth carbamoyl, CHEMICAL SCIENCE, 10, 4169, (2019)
Abstract: Major advances in the chemistry of 5th and 6th row heavy p-block element compounds have recently uncovered intriguing reactivity patterns towards small molecules such as H-2, CO2, and ethylene. However, well-defined, homogeneous insertion reactions with carbon monoxide, one of the benchmark substrates in this field, have not been reported to date. We demonstrate here, that a cationic bismuth amide undergoes facile insertion of CO into the Bi-N bond under mild conditions. This approach grants direct access to the first cationic bismuth carbamoyl species. Its characterization by NMR, IR, and UV/vis spectroscopy, elemental analysis, single-crystal X-ray analysis, cyclic voltammetry, and DFT calculations revealed intriguing properties, such as a reversible electron transfer at the bismuth center and an absorption feature at 353 nm ascribed to a transition involving sigma- and -type orbitals of the bismuth-carbamoyl functionality. A combined experimental and theoretical approach provided insight into the mechanism of CO insertion. The substrate scope could be extended to isonitriles.

First author: Gali, SM, Impact of structural anisotropy on electro-mechanical response in crystalline organic semiconductors, JOURNAL OF MATERIALS CHEMISTRY C, 7, 4382, (2019)
Abstract: In an effort to gain a fundamental understanding of the electromechanical response in high mobility crystalline organic semiconductors, we have investigated the uniaxial strain-mobility relationships in rubrene and benzothienobenzothiophene crystals. Elastic moduli and Poisson ratios of the materials are evaluated and the strain mobility response of these materials is rationalized using the effective masses and electronic couplings in the framework of hopping and band transport models, giving consistent results. The microscopic origin of the response is investigated in relation to the strain induced variations in the inter- and intra-molecular degrees of freedom. We demonstrate that the strain applied along one of the crystallographic directions in these materials does not only induce mobility variations along the same direction, but also along the other crystallographic directions that are mechanically coupled with large Poisson ratios. A rational design of electronic devices could therefore benefit from the efficient exploitation of this anisotropic strain mobility response in relation to the inherent crystalline anisotropy.

First author: Ramanantoanina, H, Study of electronic structure in the L-edge spectroscopy of actinide materials: UO2 as an example, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 7789, (2019)
Abstract: While the electronic structure calculation for actinide materials, using ligand-field phenomenology in conjunction with density functional theory (LFDFT) treating configurations with single or two open-shells 5f and 6d electrons, is well established and currently practiced, the consideration of the three open-shells electron configurations for LFDFT treatment is a challenging task addressed in the present work. Herein, we report the first-principles method, developed for the first time on the basis of LFDFT, to evaluate the uranium L-3-edge X-ray absorption near-edge structure (XANES), which requires non-equivalent active electrons within the 2p, 5f and 6d orbitals of the uranium ion. The theoretical results, when compared with the experimental XANES data measured from uranium dioxide fresh fuel pellets and rector-exposed spent fuel materials, show good agreement with the experimental findings elucidating the local oxidation in the spent fuel materials. This report is relevant for the commonly used L-edge spectroscopy of actinide isotopes and important for understanding the structural, optical and electronic properties of actinide-based materials.

First author: Yu, Y, Cobalt-catalysed unactivated C(sp(3))-H amination: two-state reactivity and multi-reference electronic character, CATALYSIS SCIENCE & TECHNOLOGY, 9, 1879, (2019)
Abstract: Theoretical calculations have been performed to gain deeper understanding on the mechanism of Cp*Co(iii)-catalysed C(sp(3))-H amination of 8-methylquinoline with phenyl-1,4,2-dioxazol-5-one. The result suggests that the additive AgSbF6 could thermodynamically facilitate the generation of catalytically active species Cp*Co(OPiv)(+). The subsequent catalytic cycle involves sequential external base assisted C(sp(3))-H activation, decarboxylation, nitrene insertion, and protonation. Importantly, a remarkable two-state reactivity scenario was disclosed for this reaction. A distinct multi-reference feature was found in the processes for Co-nitrene radical intermediate and C-N bond formations, which thus greatly enriches the cobalt catalysis chemistry. Such a multi-reference character was the outcome of double excitation from the Co-N -bonding orbital to its antibonding orbital. DFT results indicate that aminating reagents with a rigid structure would be preferred because they form strong orbital interaction with the metal center. In addition, it is theoretically predicted that the Fe(iii) species is a promising candidate for efficient C(sp(3))-H activation and Tp (Tp = hydridotris(pyrazolyl)borate) can serve as a more effective ligand for Co(iii) catalysed C(sp(3))-H activation, thanks to its stronger interaction with the Co center which thus stabilizes the transition state.

First author: Shi, YR, The role of electron-attracting substituents and molecular stacking motifs in the charge transport of tetraazapyrene derivatives, NEW JOURNAL OF CHEMISTRY, 43, 5706, (2019)
Abstract: The charge transport properties of a series of tetraazapyrene derivatives are theoretically investigated by means of quantum chemical calculations based on density functional theory. The effect of modifying the molecular structures on the charge transport properties is explained with quantitative Kohn-Sham molecular orbital analyses and corresponding energy decomposition analyses of the intermolecular interactions. The results reveal that the charge transfer does not depend on the substituent groups, such as the introduction of electron-attracting groups. Nevertheless, there is crucial evidence that the extension of the main chain and the increase in the number of heterocycles strengthen charge transfer in the systems. 3D visual diagrams of the anisotropy of the charge mobility in two different crystalline models of the same molecule are used to estimate the effect of molecular stacking motifs on the charge transfer properties. The maximum mobility is considered to be along the direction that is perpendicular to the molecular – stacking layers with the largest transfer integral values. In addition, spectral analyses of the polyheterocyclic derivatives provide novel conclusions about the effect of the molecular structures on the photophysical properties.

First author: Singh, T, Enols, Diamino Enols, and Breslow Intermediates: A Comparative Quantum Chemical Analysis, EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, 2019, 2481, (2019)
Abstract: Breslow intermediates (BIs) are generally referred as diamino enols, however, there are subtle differences between enols, diamino enols, and Breslow intermediates. Quantum chemical analysis has been carried out to establish the differences among the three classes of compounds. Electronic structure details, charge distribution, bond dissociation energies, etc. were analyzed in a few BIs and compared with that of enols and diamino enols. Energy decomposition analysis has been carried out to establish the variation in the C-C bond character among these systems. There are clear differences among the three classes of the compounds, though there are a few overlaps. A few systems which were earlier considered as BIs do not exhibit the expected characteristics.

First author: Oliveira, JA, Zn-doped Nb2O5 photocatalysts driven by visible-light: An experimental and theoretical study, MATERIALS CHEMISTRY AND PHYSICS, 228, 160, (2019)
Abstract: Zn-doped Nb2O5 are prospective photocatalysts since they can be activated by visible-light. In this context, undoped and Zn-doped Nb2O5 (0.1 and 0.2% mol of Zn) were synthesized by the oxidant peroxide method with crystallization under hydrothermal conditions. All the synthesized materials presented the diffraction pattern of the Nb2O5 orthorhombic-type phase and part of the structure was amorphous. The doped samples presented better crystallinity, high specific surface area and low band gap values, i.e., low content of zinc were able to considerably improve the photocatalytic activity of Nb2O5 under visible irradiation. Furthermore, the as-synthesized samples were versatile photocatalysts since they presented great photoactivity in rhodamine B and caffeic acid degradation. The materials with 0.1% and 0.2% mol of Zn remained degrading about 80% and 87%, respectively of caffeic acid after three consecutive use cycles, proving that the organic compounds were really degraded not just adsorbed. In addition, the computational calculations showed that the presence of Zn leads to a significant decrease of band gap, decreasing the energy required to activate the photocatalyst.

First author: Chen, X, TGMin: An efficient global minimum searching program for free and surface-supported clusters, JOURNAL OF COMPUTATIONAL CHEMISTRY, 40, 1105, (2019)
Abstract: In this article, we introduce an efficient global-minimum structural search program named Tsinghua Global Minimum 2 (TGMin-2), which is the successor of the original TGMin algorithm that was developed in our group in 2011. We have introduced a number of new features and improvements into TGMin-2, including a symmetric structure generation algorithm that can produce good initial seeds for small- and medium-size clusters, the duplicated structure identification algorithm, and the improved structure adaption algorithm that was implemented in the original TGMin code. To predict the simulated photoelectron spectrum (PE spectrum) automatically, we also implemented a standalone program named AutoPES (Auto Photoelectron Spectroscopy), which can be used to simulate PE spectra and compare them with experimental results automatically. We have demonstrated that TGMin-2 and AutoPES are powerful tools for studying free and surface-supported molecules, clusters, and nanoclusters.

First author: Topchiyan, P, New heteroleptic iridium(III) nitro complexes derived from fac-[Ir(NO2)(3)(H2O)(3)], JOURNAL OF MOLECULAR STRUCTURE, 1182, 100, (2019)
Abstract: An aqueous solution of fac-[IrH2O)(3)(NO2)(3)] (1) was utilized as a starting material for preparation of the new heteroleptic iridium complex [Ir(H2O) (bpy) (NO2)(3)] (2). From alkaline solutions of 2, the salt Na [Ir(OH) (NO2)(3) (bpy)]center dot 2H(2)O was isolated and its structure was determined by X-ray structure analysis. Structures of new compounds 2 and 3 as well as the parent complex 1 was characterized using multinuclear magnetic resonance spectroscopy and mass spectrometry. The structures of parent fac-[Ir(H2O)(3)(NO2)(3)] and complexes 2 and 3 were probed by employing density functional theory (DFT) calculations.

First author: Reber, AC, Transforming Redox Properties of Clusters Using Phosphine Ligands, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 8983, (2019)
Abstract: Organic ligands that protect the surfaces of clusters and nanoparticles against reactions and control the rate of growth are generally considered to be inert passive coatings. Here, we demonstrate in a computational study that ligands can also strongly affect redox properties of clusters. Attaching phosphine ligands to simple metal, noble metal, semiconducting, metal-oxide, and metal-chalcogen clusters is shown to severely reduce ionization energies in all classes of clusters. Several of the simple and noble metal-ligated clusters are transformed into super donors with ionization energies nearly half that of cesium atoms and extremely low second and third ionization energies. The reduction in ionization energy can be split into initial and final state effects. The initial state effect derives in part from the surface dipole but primarily through the formation of bonding/antibonding orbitals that shifts the highest occupied molecular orbital. The final state effect derives from the enhanced binding of the donor ligand to the charged cluster. In comparing simple and noble-metal clusters with transition-metal clusters, the strength of the different mechanisms changes in that the initial state effect is smaller in transition-metal clusters, and the final state effect plays a larger role. Ligation is shown to be an outstanding strategy for the formation of multiple electron donors.

First author: Khodabandeh, MH, Influence of Scalar-Relativistic and Spin-Orbit Terms on the Plasmonic Properties of Pure and Silver-Doped Gold Chains, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 9331, (2019)
Abstract: The unique plasmonic character of silver and gold nanoparticles has a wide range of applications, and tailoring this property by changing electronic and geometric structures has received a great deal of attention. Herein, we study the role of the quantum properties in controlling the plasmonic excitations of gold and silver atomic chains and rods. The influence of relativistic effects, scalar as well as spin-orbit, on the intensity and energy of plasmonic excitations is investigated. The intensity quenching and the red shift of energy in the presence of relativistic effects are introduced via the appearance of d orbitals directly in optical excitations in addition to the screening of s-electrons by mixing with the occupied orbitals. For the linear gold system, it will be demonstrated that by increasing the length the relativistic behavior declines and the contribution of d orbitals to the plasmonic excitations evidently decreases. Furthermore, silver atoms are doped in gold chains and rods (with two different arrangements) to realize how gold-silver interactions decrease the relativistic effects and enhance the intensity of collective excitations. Finally, to strengthen the plasmonic behavior of gold, the elongation of chain and doping with suitable atoms such as silver (with the classical plasmonic behavior) can be introduced as the manipulating ways to control the influence of scalar-relativistic and spin-orbit effects and, consequently, reinforce the plasmonic properties.

First author: Alkan, F, Understanding the Effect of Doping on Energetics and Electronic Structure for Au-25, Ag-25, and Au-38 Clusters, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 9516, (2019)
Abstract: We investigate the doping process theoretically for singly doped MAu24, MAg24, and MAu37 (M = Ni, Pd, Pt, Cu, Ag/Au, Zn, Cd, Hg, Ga, In, and Tl) clusters using density functional theory (DFT). For all clusters, the group X dopants (Ni, Pd, and Pt) prefer the central location due to the relative stability of d electrons in the dopant. For dopants in groups XI-XIII, doping on the surface of the core and the ligand shell in MAu24 becomes thermodynamically more preferable as a result of symmetry-dictated coupling between dopant atomic orbitals and superatomic levels as well as because of relativistic contraction of s and p orbitals. The same mechanisms are also found to be responsible for the relative isomer energies in MAu37 clusters. For these clusters, DFT calculations predict that it is unlikely for the dopant atom to occupy the central location. We found similar trends for different dopants across the periodic table in relative isomer energies of MAu24 and MAg24; however, center-doped clusters are somewhat more stable in the case of MAg24 due to the smaller relativistic stabilization of s and p levels in Ag compared to Au. We also found that the metallic radii of the dopant can affect the geometries and relative stabilities of the isomers for the doped clusters significantly.

First author: Ardizzoia, GA, Tuning the Fluorescence Emission and HOMO-LUMO Band Gap in Homoleptic Zinc(II) Complexes with N,O-Bidentate (Imidazo[1,5-a]pyrid-3-yl)phenols, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 123, 1825, (2019)
Abstract: A series of homoleptic zinc(II) complexes of the general formula [Zn(L-R)(2)] (HLR: (imidazo[1,5-a]pyrid-3-yl)phenol; R: para-substituent to the phenol) have been synthesized. The single-crystal X-ray structure analysis of complex [Zn(L-H)(2)] (1) confirmed the expected N,O-bidentate coordination of L-R, via the pyridine-like nitrogen of the imidazo[1,5-a]pyridine skeleton and the phenolate oxygen. The photophysical properties of the complexes have been investigated in dichloromethane solution, showing fluorescence emission when excited with UV light ((exc) = 340-360 nm). The intensity and (max) of the emission are both significantly influenced by the R-substituent, the emission maxima moving from blue (R = CF3, Zn(L-CF3)(2)] (6)) to orange (R = NO2, Zn(L-NO2)(2)] (7). Most of [Zn(L-R)(2)] compounds are characterized by moderate-to-good absolute photoluminescence quantum yields, with a maximum of 0.33 for [Zn(L-H)(2)] (1). Density functional calculations allowed to identify the Natural Transition Orbitals involved in the electronic transitions and define the main transition as being HOMO-LUMO (>95%) in character. A good linear correlation was found between the HOMO energy and the Hammett sigma(p) constants associated to the R-substituent, whereas the fluorescence behavior has been described in terms of HOMO-LUMO band gap.

First author: Shan, NN, Elucidating Molecular Interactions in Glycerol Adsorption at the Metal-Water Interface with Density Functional Theory, LANGMUIR, 35, 4791, (2019)
Abstract: Glycerol is an extremely versatile platform molecule for chemical and fuel production, as evidenced by successful demonstrations in electrochemical and thermochemical processes, where key catalytic chemistries occur at the solid-liquid interface. Despite the remarkable progress made in enriching the first-principles-based computational tool set to reveal and characterize solvent structures in the past decade, techniques for realistic and efficient molecular-level modeling to study aqueous-phase glycerol chemistry are still far from mature. Many aqueous-phase catalytic systems are deemed too complex for routine modeling because of their highly correlated structures at the heterogeneous solid-liquid interface. This invited feature article merges recent developments in quantum mechanical solvation models and oxygenated hydrocarbon conversion chemistry by revisiting the molecular interactions of adsorbed glycerol and its dehydrogenation intermediates at the water-metal interface. Explicit participation of water through the establishment of water-adsorbate, water-water, and water-metal interactions on Pt(111) was investigated using density functional theory. In periodic models, the adsorption favors networklike structures with adsorbates as nodal points linked by coadsorbed water molecules. We also showed that these adsorption patterns actually preserve the original bond-order-based scaling relationship framework established without the consideration of solvent. This behavior can be exploited to improve computational efficiency for future analysis of catalytic polyol conversions in the aqueous-phase environment.

First author: Garcia-Rodeja, Y, Factors Controlling the Reactivity of Strained-Alkyne Embedded Cycloparaphenylenes, JOURNAL OF ORGANIC CHEMISTRY, 84, 4330, (2019)
Abstract: The factors controlling the reactivity of the strained-alkyne embedded cycloparaphenylenes have been computationally explored by means of Density Functional Theory calculations. To this end, the Diels-Alder cycloaddition reaction involving cyclopentadiene and these macro cyclic systems has been selected in order to understand the influence of the strained nature of the alkyne in their structures as well as the size of the system on their reactivity. It is found that the cycloaddition reactions involving those macrocycles having more strained alkynes not only are more exothermic and exhibit lower activation barriers but also are associated with earlier transition states. The combination of the Activation Strain Model of reactivity and the Energy Decomposition Analysis method suggests that the enhanced reactivity of bent alkynes, as compared to linear C C triple bonds, finds its origin not only in the lower deformation energy required to adopt the corresponding transition state structure but also in the stronger interaction energy between the deformed reactants.

First author: Zhang, JM, Ligand-Mediated Reactivity in CO Oxidation of Niobium-Nickel Monoxide Carbonyl Complexes: The Crucial Roles of the Multiple Adsorption of CO Molecules, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 10, 1566, (2019)
Abstract: The heteronuclear metal oxide complexes are of great significance in heterogeneous catalytic oxidation of CO. However, previous studies are mainly focused on the composition of metal oxide, charge state, the support and the active oxygen species, with little attention paid to adsorbed CO ligands. Herein, the ligand-mediated reactivity in CO oxidation of niobium-nickel monoxide carbonyl complexes has been successfully identified. The NbNiO(CO)(n)(-) (n = 5-6) anions are determined to be O-bridged complexes. In contrast, the NbNiO(CO)(n)(-) (n = 7-8) anions are characterized to be eta(2)-CO2-tagged complexes. The crucial roles of the multiply adsorbed CO molecules that can facilitate not only the competitive binding with bridging oxygen atom to the transition metal centers but also the electron accumulation of transition metal atoms have been discovered. The fascinating results are of substantial importance to understand the mechanisms of CO oxidation over heteronuclear metal oxide under CO-rich feed condition.

First author: Michalczyk, M, Hexacoordinated Tetrel-Bonded Complexes between TF4 (T=Si, Ge, Sn, Pb) and NCH: Competition between sigma- and pi-Holes, CHEMPHYSCHEM, 20, 959, (2019)
Abstract: In order to accommodate the approach of two NCH bases, a tetrahedral TF4 molecule (T=Si, Ge, Sn, Pb) distorts into an octahedral structure in which the two bases can be situated either cis or trans to one another. The square planar geometry of TF4, associated with the trans arrangement of the bases, is higher in energy than its see-saw structure that corresponds to the cis trimer. On the other hand, the square geometry offers an unobstructed path of the bases to the pi-holes above and below the tetrel atom and hence enjoys a higher interaction energy than is the case for the sigma-holes approached by the bases in the cis arrangement. When these two effects are combined, the total binding energies are more exothermic for the cis than for the trans complexes. This preference amounts to some 3 kcal mol(-1) for Sn and Pb, but is amplified for the smaller tetrel atoms.

First author: Pogany, L, High-Spin Mononuclear Iron(III) Complexes with Pentadentate Schiff Base Ligands: Structural Analysis and Magnetic Properties, CHEMPLUSCHEM, 84, 358, (2019)
Abstract: Various substituted 2-hydroxybenzophenones were combined with aliphatic linear triamines to form pentadentate Schiff base ligands. Twelve new iron(III) complexes with the general formula [Fe(L-n)X].mCH(3)CN (n=1-10; X=N-3(-), NCS- or NCSe-; m=0-2) have been synthesized, and spectrally as well as structurally characterized. The structural analysis revealed a notable dependence of coordination polyhedra deformation as well as the spatial configuration of donor atoms on the length and symmetry of the Schiff base ligands. The magnetic properties of the compounds were investigated and the permanent high-spin state (S=5/2) for all reported compounds was established, and allowed calculation of zero-field-splitting parameters as well as coupling constants, which were further confirmed with DFT calculations. The solid-state EPR spectra were recorded at 293K and 98K, and in accordance with the magnetic measurements, showed a high-spin state in the measured temperature range.

First author: de Kock, S, Steric and Electronic Effects in Gold N-Heterocyclic Carbene Complexes Revealed by Computational Analysis, CHEMISTRYOPEN, 8, 358, (2019)
Abstract: A computational analysis of a series of cationic and neutral gold imidazolylidene and benzimidizolylidene complexes is reported. The Bond Dissociation Energies of the various ligands in the complexes calculated at the PBE0-D3/def2-TZVP level of theory increase with increasing ligand volume, except for those of complexes containing t-butyl-substituted ligands, which are anomalously low particularly for the benzimidazolylidene species. Atoms in Molecules studies show the presence of a variety of weak intramolecular interactions, characterised by the presence of bond critical points with a range of different properties. Energy Decomposition Analysis and calculation of Electrostatic Surface Potentials indicate that some interactions are weakly attractive dispersion-type interactions, while others are repulsive. The octanol/water partition coefficients (log P values) were calculated as a measure of the lipophilicities of the complexes and were found to increase with increasing volume.

First author: Gordon, CP, Chemical Shift Tensors – Why Should We Care?, CHIMIA, 73, 252, (2019)
Abstract: Chemical shift tensors give valuable insights into the nature and the relative energy of frontier orbitals and their analysis allows for rationalizing the reactivities of molecules. In this article, we point out the principles that allow for the analysis of chemical shift. Through selected, illustrative examples we show how one can relate chemical shift to molecular electronic structure and thus to reactivity.

First author: Bai, HC, Interaction in Li@Fullerenes and Li+@Fullerenes: First Principle Insights to Li-Based Endohedral Fullerenes, NANOMATERIALS, 9, 252, (2019)
Abstract: This work reveals first principle results of the endohedral fullerenes made from neutral or charged single atomic lithium (Li or Li+) encapsulated in fullerenes with various cage sizes. According to the calculated binding energies, it is found that the encapsulation of a single lithium atom is energetically more favorable than that of lithium cation. Lithium, in both atomic and cationic forms, exhibits a clear tendency to depart from the center in large cages. Interaction effects dominate the whole encapsulation process of lithium to carbon cages. Further, the nature of the interaction between Li (or Li+) and carbon cages is discussed based on reduced density gradient, energy decomposition analysis, and charge transfer.

First author: Zhang, JR, Synergistic and diminutive effects between triel bond and regium bond: Attractive interactions between pi-hole and sigma-hole, APPLIED ORGANOMETALLIC CHEMISTRY, 33, 252, (2019)
Abstract: High quantum chemical calculations have been performed for binary complexes of MCN center dot center dot center dot ZX(3) (M = Cu, Ag, Au; Z = B, Al; X = H, F) and C2H4 center dot center dot center dot AlX3. The strength of triel bonding depends on the nature of triel and coin metal atoms as well as the F substituents and electron donors. The molecular electrostatic potential (MEP) analysis confirms a sigma-hole at the M-C bond end of MCN, engaging in a regium bond with C2H4 in an increasing sequence of AgCN < CuCN < AuCN. The complex C-2(CN)(4)center dot center dot center dot AuCN is unstable in view of MEPs, but a big attractive interaction energy (-38 kcal/mol) is produced when both molecules approach, which is mainly caused by polarization including orbital interactions. Both types of interactions are strengthened in ternary complex of C2H4 center dot center dot center dot MCN center dot center dot center dot ZX(3) but are weakened in NCAu center dot center dot center dot C2H4 center dot center dot center dot AlX3 and C-2(CN)(4)center dot center dot center dot AuCN center dot center dot center dot ZH(3). It is found that the variation from synergistic to diminutive effects can be modulated by four CN groups in C-2(CN)(4). Interestingly, the binding distances of both interactions have an unexpected change. The cooperativity of both interactions has been explained with MEP and charge transfer. When C2H4 binds with AlX3 or AuCN, its pi electron density is greatly decreased and even its MEP becomes positive, but it is still able to participate in a regium bond or a triel bond.

First author: Schmidt, N, Comparing the Self-Assembly of Sexiphenyl-Dicarbonitrile on Graphite and Graphene on Cu(111), CHEMISTRY-A EUROPEAN JOURNAL, 25, 5065, (2019)
Abstract: A comparative study on the self-assembly of sexiphenyl-dicarbonitrile on highly oriented pyrolytic graphite and single-layer graphene on Cu(111) is presented. Despite an overall low molecule-substrate interaction, the close-packed structures exhibit a peculiar shift repeating every four to five molecules. This shift has hitherto not been reported for similar systems and is hence a unique feature induced by the graphitic substrates.

First author: Gransbury, GK, DFT Prediction and Experimental Investigation of Valence Tautomerism in Cobalt-Dioxolene Complexes, INORGANIC CHEMISTRY, 58, 4230, (2019)
Abstract: The family of complexes of general formula [Co(Mentpa)(Xdiox)]+ (tpa = tris(2-pyridylmethyl)amine, n = 0-3 corresponds to successive methylation of the 6-position of the pyridine rings; X = Br-4, Cl-4, H-4, 3,5-Me-2, 3,5-tBu(2); diox = dioxolene) was investigated by density functional theory (DFT) calculations to predict the likelihood of valence tautomerism (VT). The OPBE functional with relativistic and solvent corrections allowed accurate reproduction of trends in spin-state energetics, affording the prediction of VT in complex [Co(Me(3)tpa)(Br(4)diox)]+ (1+). One-electron oxidation of neutral precursor [Co-II(Me(3)tpa)(Br(4)cat)] (1) enabled isolation of target compounds 1(PF6) and 1(BPh4). Solution variable-temperature UV-vis absorption and Evans method magnetic susceptibility data confirm DFT predictions that 1+ exists in a temperature-dependent valence tautomeric equilibrium between low-spin Co(III)-catecholate and high-spin Co(II)-semiquinonate forms. The solution VT transition temperature of 1+ is solvent-tunable with critical temperatures in the range of 291-359 K for the solvents measured. Solid-state magnetic susceptibility measurements of 1(PF6) and 1(BPh4) reveal the onset of VT transitions above room temperature.

First author: Chong, DP, Computational study of the structures and photoelectron spectra of gas-phase nitrosamines: Dimethylnitrosamine, N-nitrosopyrrolidine and 1-nitrosoaziridine, JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA, 232, 35, (2019)
Abstract: The structures of three nitrosamines in gas phase are optimized with various levels of theory available in the Gaussian program. For dimethylnitrosamine and N-nitrosopyrrolidine, the reported rotational constants from microwave spectra let us select the best optimized geometry. For 1-nitrosoaziridine, however, we decide to choose the geometry optimized by CCSD/cc-pVTZ method. At these geometries, the photoelectron spectra are calculated with established methods using the Amsterdam Density Functional program. The calculated ionization energies of valence electrons agree well with available experimental data and provide values for the missing photoelectron data. On the other hand, the computed core-electron binding energies of dimethylnitrosamine agree well with the values from 1975 X-ray solid-state photoelectron spectra after adding the work function. The predicted values for N-nitrosopyrrolidine and 1-nitrosoaziridine must wait for experiments for confirmation.

First author: Suvitha, A, Deciphering the nature of interactions in nandrolone/testosterone encapsulated cucurbituril complexes: a computational study, JOURNAL OF INCLUSION PHENOMENA AND MACROCYCLIC CHEMISTRY, 93, 183, (2019)
Abstract: The intention of the study is to find the nature of interactions that exist in inclusion complexes formed between the steroids, nandrolone, and testosterone with cucurbit[n]urnils (n=7 and 8) host, using density functional theory incorporated with empirical dispersion correction. Upon encapsulation, nandrolone caused a larger geometrical distortion in cucurbit[8]uril geometry, while testosterone inclusion complex is formed with a larger number of intermolecular hydrogen bonds. The molecular electrostatic potential examination shows that the positive potential observed on the eight-membered ring in CB7 got reduced upon encapsulation, while on the nandrolone the negative potential on carbonyl unit has increased. AIM analysis shows that in inclusion complexes, the observed electron density are higher for the interactions between the oxygen atoms of carbonyl fringe of cucurbituril molecule and the steroid molecules. The NCI isosurface of nandrolone@CB7 has green patches in between the nandrolone and cucurbituril molecule, evenly distributed. In the testosterone@CB7, along with the green patches, red patches, due to the steric crowding between the testosterone and cucurbit[7]uril, were observed. The energy decomposition analysis parameters show that Pauli’s repulsive term was highest for nandrolone@CB7. When testosterone is the guest, repulsive energy was found to be larger than nandrolone guest. From the above interference, it can be confirmed that the steric hindrance that arises during the interaction of testosterone with CB7 reduces the stability of the complex, and the nandrolone best fit inside the CB7 cavity with the combination of hydrogen bonding and weak van der Waals bonding as intermolecular interactions.

First author: Prabha, S, The structure and stability of CrnTem (1 <= n <= 6, 1 <= m <= 8) clusters, CHEMICAL PHYSICS LETTERS, 720, 76, (2019)
Abstract: First principles studies on the electronic structure, stability, and magnetic properties of CrnTem (1 <= n <= 6, 1 <= m <= 8) clusters have been carried out within a density functional framework. Investigations into the energetic stability indicate that Cr4Te6 and Cr6Te8 are energetically stable species. The Cr4Te6 cluster is found to be nonmagnetic and to have a large HOMO-LUMO gap. Energetic and electronic stability are not always correlated as Cr6Te8 is marked by a much smaller HOMO-LUMO gap, is magnetic, and has a high electron affinity of 3.39 eV. The stability of Cr6Te8 is enhanced by adding charge donating ligands to form stable Cr6Te8(PEt3)(6) clusters.

First author: Sebera, J, Investigation of the charge transport in model single molecule junctions based on expanded bipyridinium molecular conductors, ELECTROCHIMICA ACTA, 301, 267, (2019)
Abstract: In this work the charge transport and energetics of a photochemically addressable single molecule switch based on the expanded bipyridinium core linked to an anchoring group with a controlled torsion angle theta was investigated. Electrochemical and UV-VIS absorption spectroscopy techniques complemented by the analysis based on density functional theory (DFT) show that for selected molecules the energy and shape of the LUMO is insensitive to the value of theta, but the difference in torsion angle theta leads to a sizable shift of the LUMO energy and single molecule conductance value in a metal-molecule-metal junction for these molecules as shown by the combination of experimental single molecule break junction technique and theoretical non-equilibrium Green’s function (NEGF)/DFT approach. The conductance switching ratio calculated from the cos(2) theta law is in a perfect agreement with the value obtained from the NEGF approach. Our combined experimental and theoretical approach paves the way for investigating expanded bipyridinium systems with multiple photochemically addressable units potentially achieving greater conductance switching ratios.

First author: Ning, Y, The oxygen sensing mechanism of a triphenylamine-based cyclometalated platinum(II) complex, JOURNAL OF LUMINESCENCE, 208, 46, (2019)
Abstract: Triphenylamine-based cyclometalated platinum(II) (TCP) emits phosphorescence at room temperature. The phosphorescence was quenched by oxygen molecule, which means that TCP is a good candidate for oxygen molecule recognition and measurement. By the way of quantum chemical calculation, we proposed the quenching mechanism to elucidate the nature of oxygen sensing, which was different from the traditional dynamic collision mechanism. The luminescence mechanism of TCP involves phosphorescent emission, and the TCP-O-2 complex fluorescent emission. By utilizing the density functional theory (DFT) method, we calculated the electron configurations and the frontier molecular orbitals of TCP and the TCP-O-2 complex. Furthermore, applying the time-dependent density functional theory (TDDFT) method, we calculated the geometric optimization and the excitation energies of TCP and the TCP-O-2 complex in the excited state. The results illustrate that the luminescence of TCP stems from localized excitation, while that of the TCP-O-2 complex stems from delocalized excitation. Moreover, we also calculated the radiative and non-radiative rate constants of TCP and the TCP-O-2 complex and clarified the photophysical processes of them. For TCP, first the electron arrived at the T-1 state via intersystem crossing from the initial S-1 state and finally back to the S-0 state via emitting phosphorescence. For the TCP-O-2 complex, with no spin flip, the electron jumped directly from the T-1 to T-0 state via internal conversion.

First author: Bortoli, M, The Te-125 Chemical Shift of Diphenyl Ditelluride: Chasing Conformers over a Flat Energy Surface, MOLECULES, 24, 46, (2019)
Abstract: The interest in diphenyl ditelluride (Ph2Te2) is related to its strict analogy to diphenyl diselenide (Ph2Se2), whose capacity to reduce organic peroxides is largely exploited in catalysis and green chemistry. Since the latter is also a promising candidate as an antioxidant drug and mimic of the ubiquitous enzyme glutathione peroxidase (GPx), the use of organotellurides in medicinal chemistry is gaining importance, despite the fact that tellurium has no recognized biological role and its toxicity must be cautiously pondered. Both Ph2Se2 and Ph2Te2 exhibit significant conformational freedom due to the softness of the inter-chalcogen and carbon-chalcogen bonds, preventing the existence of a unique structure in solution. Therefore, the accurate calculation of the NMR chemical shifts of these flexible molecules is not trivial. In this study, a detailed structural analysis of Ph2Te2 is carried out using a computational approach combining classical molecular dynamics and relativistic density functional theory methods. The goal is to establish how structural changes affect the electronic structure of diphenyl ditelluride, particularly the Te-125 chemical shift.

First author: Cesario, D, The role of the halogen bond in iodothyronine deiodinase: Dependence on chalcogen substitution in naphthyl-based mimetics, JOURNAL OF COMPUTATIONAL CHEMISTRY, 40, 944, (2019)
Abstract: The effects on the activity of thyroxine (T4) due to the chalcogen replacement in a series of peri-substituted naphthalenes mimicking the catalytic function of deiodinase enzymes are computationally examined using density functional theory. In particular, T4 inner-ring deiodination pathways assisted by naphthyl-based models bearing two tellurols and a tellurol-thiol pair in peri-position are explored and compared with the analogous energy profiles for the naphthalene mimic having two selenols. The presence of a halogen bond (XB) in the intermediate formed in the first step and involved in the rate-determining step of the reaction is assumed to facilitate the process increasing the rate of the reaction. The rate-determining step calculated energy barrier heights allow rationalizing the experimentally observed superior catalytic activity of tellurium containing mimics. Charge displacement analysis is used to ascertain the presence and the role of the electron density charge transfer occurring in the rate-determining step of the reaction, suggesting the incipient formation or presence of a XB interaction.

First author: van der Lubbe, SCC, Secondary Electrostatic Interaction Model Revised: Prediction Comes Mainly from Measuring Charge Accumulation in Hydrogen-Bonded Monomers, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 141, 4878, (2019)
Abstract: The secondary electrostatic interaction (SEI) model is often used to predict and explain relative hydrogen bond strengths of self-assembled systems. The SEI model oversimplifies the hydrogen-bonding mechanisms by viewing them as interacting point charges, but nevertheless experimental binding strengths are often in line with the model’s predictions. To understand how this rudimentary model can be predictive, we computationally studied two tautomeric quadruple hydrogen-bonded systems, DDAA-AADD and DADA-ADAD. Our results reveal that when the proton donors D (which are electron-donating) and the proton acceptors A (which are electron-withdrawing) are grouped together as in DDAA, there is a larger accumulation of charge around the frontier atoms than when the proton donor and acceptor groups are alternating as in DADA. This accumulation of charge makes the proton donors more positive and the proton acceptors more negative, which enhances both the electrostatic and covalent interactions in the DDAA dimer. The SEI model is thus predictive because it provides a measure for the charge accumulation in hydrogen-bonded monomers. Our findings can be understood from simple physical organic chemistry principles and provide supramolecular chemists with meaningful understanding for tuning hydrogen bond strengths and thus for controlling the properties of self-assembled systems.

First author: Kang, S, Highly Conductive Paper/Textile Electrodes Using Ligand Exchange Reaction-Induced in Situ Metallic Fusion, ACS APPLIED MATERIALS & INTERFACES, 11, 12032, (2019)
Abstract: Here, we report that metal nanoparticle (NP)-based paper/textile electrodes with bulk metallic conductivity can be prepared via organic linker-modulated ligand exchange reaction and in situ room-temperature metallic fusion without additional chemical or thermal treatments. For this study, amine-functionalized molecule linkers instead of bulky polymer linkers were layer-by-layer (LbL)-assembled with tetraoctylammonium bromide (TOABr)-stabilized Au NPs to form Au NP multilayered films. By conversion of the amine groups of the organic molecule linkers from -NH3+ to the -NH2 groups, as well as by a decrease in the size of the organic linkers, the LbL-assembled Au NPs became highly interconnected and fused during LbL deposition, resulting in Au NP multilayers with adjustable conductivity and transport behavior. These phenomena were also predicted by a density functional theory investigation for the model system. Particularly, LbL-assembled films composed of TOABr-Au NPs and diethylenetriamine (M-w: similar to 104) exhibited a remarkable electrical conductivity of 2.2 x 10(5) S.cm(-1), which was higher than the electrical conductivity of the metal NP-based electrodes as well as the carbon material-based electrodes reported to date. Furthermore, based on our approach, a variety of insulating flexible papers and textiles were successfully converted into real metal-like paper and textile electrodes with high flexibility preserving their highly porous structure. This approach can provide a basis for further improving and controlling the electrical properties of flexible electrodes through the control of organic linkers.

First author: Taylor, JO, Group 6 Metal Complexes as Electrocatalysts of CO2 Reduction: Strong Substituent Control of the Reduction Path of [Mo(eta(3)-allyl)(CO)(2)(x,x ‘-dimethyl-2,2 ‘-bipyridine)(NCS)] (x=4-6), ORGANOMETALLICS, 38, 1372, (2019)
Abstract: A series of complexes [Mo(eta(3)-allyl)(CO)(2))(x,x’-dmbipy)(NCS)] (dmbipy = dimethyl-2,2′-bipyridine; x = 4-6) have been synthesized and their electrochemical reduction investigated using combined cyclic voltammetry (CV) and variable-temperature spectroelectrochemistry (IR/UV-vis SEC) in tetrahydrofuran (THF) and butyronitrile (PrCN), at gold and platinum electrodes. The experimental results, strongly supported by density functional theory (DFT) calculations, indicate that the general cathodic path of these Group 6 organometallic complexes is closely related to that of the intensively studied class of Mn tricarbonyl alpha-diimine complexes, which, themselves, have recently been identified as important smart materials for catalytic CO2 reduction. The dimethyl substitution on the 2,2′-bipyridine ligand backbone has presented new insights into this emerging class of catalysts. For the first time, the 2e(-) reduced 5-coordinate anions [Mo(eta(3)-allyl)(CO)(2))(x,x’-dmbipy)](-) were directly observed with infrared spectroelectrochemistry (IR SEC). The role of steric and electronic effects in determining the reduction-induced reactivity was also investigated. For the 6,6′-dmbipy, the primary 1e(-) reduced radical anions exert unusual stability, radically changing the follow-up cathodic path. The 5-coordinate anion [Mo(eta(3)-allyl)(CO)(2))(6,6′-dmbipy)](-) remains stable at low temperature in strongly coordinating butyronitrile and does not undergo dimerization at elevated temperature, in sharp contrast to reactive [Mo(eta(3)-allyl)(CO)(2)(4,4′-dmbipy)](-) that tends to dimerize in a reaction with the parent complex. The complex with the 5,5′-dmbipy ligand combines both types of reactivity. Under aprotic conditions, the different properties of [Mo(eta(3)-allyl)(CO)(2)(x,x’-dmbipy)](-) are also reflected in their reactivity toward CO2. Preliminary CV and IR SEC results reveal differences in the strength of CO2 coordination at the free axial position. Catalytic waves attributed to the generation of the 5-coordinate anions were observed using CV, but only a modest catalytic performance toward the production of formate was demonstrated by IR SEC. For 6,6′-dmbipy, a stronger catalytic effect was observed for the Au cathode, compared to Pt.

First author: Charistos, ND, The pseudo- model of the induced magnetic field: fast and accurate visualization of shielding and deshielding cones in planar conjugated hydrocarbons and spherical fullerenes, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 6150, (2019)
Abstract: The induced magnetic fields originating from the system of planar conjugated polycyclic hydrocarbons and spherical fullerenes are accurately reproduced by their corresponding hydrogen skeletal models (HSMs). Moreover, the individual contribution per molecular orbital is also reproduced unraveling simple symmetry rules related to canonical molecular orbitals. Hence, fast, handy and accurate 3D visualization of shielding and deshielding cones is realized, enabling the interpretation of global and local aromaticity and antiaromaticity of PAHs and spherical species in a simple and concise manner to facilitate further interpretations of large sized hydrocarbon systems.

First author: Diab, F, Reductive Elimination and Oxidative Addition of Hydrogen at Organostannylium and Organogermylium Cations, CHEMISTRY-A EUROPEAN JOURNAL, 25, 4426, (2019)
Abstract: Bulkily substituted organodihydrogermylium and -stannylium cations [Ar*EH2](+) (E=Ge, Sn; Ar*=2,6-Trip(2)C(6)H(3), Trip=2,4,6-triisopropylphenyl) were characterized as salts of the weakly coordinating perfluorinated alkoxyaluminate anion [Al{OC(CF3)(3)}(4)](-). At room temperature, the stannylium cation liberates hydrogen to generate the low valent organotin cation [Ar*Sn](+). In contrast, the dihydrogermylium cation transfers the hydrogen atoms to an aryl moiety of the terphenyl ligand and oxidatively adds either hydrogen under an atmosphere of hydrogen or a sp(2) CH unit of the 1,2-difluorobenzene solvent.

First author: Zhao, ZW, Terminal Modulation in Search of a Balance between Hole Transport and Electron Transfer at the Interface for BODIPY-Based Organic Solar Cells, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 6407, (2019)
Abstract: Organic solar cells (OSCs) have made rapid advances in power conversion efficiency during the past decades, which is boosted partly by the various designs of new materials, especially in donor materials. However, as one kind of famous fluorescence materials, 4,4′-difluoro-4-bora-3a,4a-diaza-s-indacenes (BODIPY)-based materials are seldom applied in OSCs until its conjugated molecules have been synthesized and designed as donors recently. Here, we designed a series of BODIPY molecules by terminal modulation based on a reported one and probed their potential promising properties for donor materials in OSCs by means of quantum chemical calculations and molecular dynamics simulations. Many important parameters pertaining to short circuit density (J(SC)) such as capability of light absorption, dipole moment transition between the ground and excited states, hole mobility evaluated on the basis of predicted crystal structures, charge-transfer rate (k(inter-CT)), and charge recombination rate (k(inter-CR)) computed based on local interface geometries of donor/fullerene selected from molecular dynamics simulation results except for some elemental properties were investigated in detail from a theoretical perspective. The results reveal that the terminal modulation through increasing pi-conjugation length is feasible. Notably, it is beneficial to balance the ability of hole transport and charge transfer when considering the pi-conjugation length and planarity of donor materials. Finally, we hope that this work can pave the way to the design of potential near-infrared donor materials.

First author: Cabrera-Trujillo, JJ, Understanding exo-selective Diels-Alder reactions involving Fischer-type carbene complexes, ORGANIC & BIOMOLECULAR CHEMISTRY, 17, 2985, (2019)
Abstract: The factors controlling the selectivity of the Diels-Alder cycloaddition reactions involving Fischer-type carbene complexes and cyclopentadiene have been explored computationally by means of density functional theory calculations. To this end, the influence of the substituents directly attached to the carbene ligand on the endo : exo ratio has been compared to the available experimental data and quantitatively analysed in detail by means of the combination of the activation strain model of reactivity and energy decomposition analysis methods. The insight gained in this computational study may be important for the rational design of exo-selective Diels-Alder reactions.

First author: Conradie, J, Norcorrole as a Delocalized, Antiaromatic System, SCIENTIFIC REPORTS, 9, 2985, (2019)
Abstract: Nickel norcorrole provides an unusual example of a molecule that is strongly antiaromatic according to the magnetic criterion, but which exhibits, according to high-quality DFT calculations, a symmetric, delocalized structure with no difference in bond length between adjacent C-meso-C-alpha, bonds. A fragment molecular orbital analysis suggests that these discordant observations are a manifestation of the high stability of the dipyrrin fragments, which retain their electronic and structural integrity even as part of the norcorrole ring system.

First author: Hussain, M, Impact of electronically excited state hydrogen bonding on luminescent covalent organic framework: a TD-DFT investigation, MOLECULAR PHYSICS, 117, 823, (2019)
Abstract: The investigation of intermolecular hydrogen bonding between the luminescent polypyrene covalent organic framework and formaldehyde (PPy-COF-HCHO) was carried out with the density functional theory and time-dependent density functional theory. The strengthening of the photoexcited hydrogen bond C = O—H-C was verified via geometric structures, electronic transition energies, binding energies, UV-Vis and infrared spectra comparison in both ground state and excited state of the PPy-COF’s truncated representative fragment. From the frontier molecular orbitals examination, natural population analysis, and plotted electron density difference map demonstrated that the strengthened hydrogen bond facilitated the rearrangement of electron density between H-donor and H-acceptor moieties which should account for charge transfer and ultimate fluorescence quenching. Interestingly, the energy gap between excited state and triplet state of the hydrogen-bonded complex showed the possibility of the intersystem crossing. The MOMAP programme further confirmed the quenching process because there was a lower fluorescent rate constant for the donor-acceptor PPy-COF-HCHO complex compared to free PPy-COF fragment. Results above significantly highlighted the high sensitivity of the PPy-COF towards organic analyte, i.e. the formaldehyde and can be employed as a sensor.

First author: Karmodak, N, Overlap of Radial Dangling Orbitals Controls the Relative Stabilities of Polyhedral BnHn-x Isomers (n=5-12, x=0 to n-1), INORGANIC CHEMISTRY, 58, 3627, (2019)
Abstract: The removal of H atoms from polyhedral boranes results in the formation of dangling radial orbitals with one electron each. If there is a requirement of electrons for skeletal bonding to meet the Wade’s rule, these are provided from the exohedral orbitals. Additional electrons occupy a linear combination of the dangling orbitals. Stabilization of these molecular orbitals depends on their overlap. The lateral (sideways) overlap of dangling orbitals decreases with the decreasing cluster size from 12 to 5 boron atoms as the orbitals become more and more splayed out. Thus, as the number of dangling orbitals increases, the destabilization of their combinations increases at a higher rate for smaller polyhedral boranes, leading to flat structures with the removal of a fewer number of hydrogens. Though exohedral orbitals form better overlap in larger polyhedral clusters, the increase of electrons with the removal of H atoms results in occupancy of antibonding skeletal orbitals (beyond Wade’s rules) and leads to flat structures. The reverse happens when hydrogens are added to a flat cluster. Substitution of BH by Si does not change structural patterns.

First author: Chandrasekar, A, Uncovering Heavy Actinide Covalency: Implications for Minor Actinide Partitioning, INORGANIC CHEMISTRY, 58, 3744, (2019)
Abstract: Across the actinide period, the stability of the trivalent oxidation state predominates in the heavy actinides, making their chemical nature close to that of rare earth elements. The resemblance in their chemistry poses difficulties in separating heavy actinides from lanthanides, which is a vital separation in the minor actinide partitioning process. Actinide contraction has conventionally implied electrostatic actinide-ligand interactions among the heavy actinides. The present study challenges this conventional understanding and reveals increasing covalency in the actinide-ligand bond across Am to Cf. Complexes of Am, Cm, Bk, and Cf have been examined for their electronic structure with a focus on the nature of their interactions with different ligands within the framework of density functional theory, where the relativistic effects have been incorporated by using zero-order regular approximation and spin-orbit coupling. The choice of ligands selected for this study facilitates the effect of the donor atom as well as denticity to be accounted for. Hence, heavy actinide complexes of the N- and 0-donor ligand dipicolinic acid, S and 0 mixed donor ligands of the Cyanex type, and an octadentate ligand N,N,N’N’-tetrakis[(6-carboxypyridin-2-yl)methyl]ethylenediamine have been optimized and evaluated. In each case energy decomposition analysis has been used to explicitly decompose the metal ligand interaction energy into components which have then been analyzed. Irrespective of the hard soft characteristics of donor atoms or the denticity of the ligands, steadily increased covalency has been observed across Am to Cf. Inspection of the ligand highest energy occupied molecular orbitals and metal orbitals sheds light on the origin of the unexpected covalency. An overall increase in bonding and also the orbital contribution along the Am Cf series is clearly due to the enhancement in covalency, which is complementary to the orbital degeneracy induced covalency proposed very recently by Batista and co-workers.

First author: Sole-Daura, A, How Does the Redox State of Polyoxovanadates Influence the Collective Behavior in Solution? A Case Study with [I@V18O42](q-) (q=3, 5, 7, 11, and 13), INORGANIC CHEMISTRY, 58, 3881, (2019)
Abstract: A series of stable reduction oxidation states of the cage-like [I@V-IV (xV18-xO42)-O-v](5-x) polyoxovanadate (POV) with x = 8, 10, 12, 16, and 18 were studied with density functional theory and molecular dynamics to gain insight into the structural and electron distribution characteristics of these metal oxo clusters and to analyze the charge/redox-dependent assemblage processes in water and acetonitrile (MeCN) solutions. The calculations show that the interplay between the POV redox state (molecular charge) and the solvent polarity, countercation size, and hydrophilicity (or hydrophobicity) controls the POV agglomeration phenomena, which substantially differ between aqueous and MeCN media. In MeCN, agglomeration is more pronounced for intermediate-charged POVs, whereas in water, the lowest-charged POVs and organic countercations tend to agglomerate into a microphase. Tests made on wet MeCN show diminished agglomeration with respect to pure MeCN. Simulations with alkali countercations in water show that only the highest-charged POV can form agglomerates. The herein presented theoretical investigation aims to support experimental studies of POVs in the field of functional nanomaterials and surfaces, where controlled molecular deposition from the liquid phase onto solid substrates requires knowledge about the features of these metal oxo clusters in discrete solutions.

First author: Chiyindiko, E, Redox behaviour of bis(beta-diketonato)copper(II) complexes, JOURNAL OF ELECTROANALYTICAL CHEMISTRY, 837, 76, (2019)
Abstract: In this study for the first time, a comprehensive report was compiled on the electrochemical behavior of a series of eight square planar bis(beta-diketonato)copper(II) complexes, with a variety of substituents R-1 and R-2 on the beta-diketonato ligand ((RCOCHCOR2)-C-1)(-). The character of the observed redox features was determined by computational chemistry calculations of the frontier molecular orbitals involved. The experimentally obtained electrochemically irreversible Cu-II/Cu-I reduction potentials, E-pc(Cu-II/Cu-I), were related to various electronic descriptors (such as electronegativities, Hammett constants and Lever electronic parameters), which describe the electron withdrawing power of the beta-diketonato ligands attached to the copper metal. Linear relationships have also been obtained between E-pc(Cu-II/Cu-I) and computational chemistry calculated energies of the eight bis(beta-diketonato)copper(II) complexes. These linear relationships confirmed good communication between the copper metal and the eight different beta-diketonato ligands attached to it. Furthermore, the experimentally observed electrochemically irreversible Cu-II/Cu-I reduction potentials of those [Cu-II(beta-diketonato)(2)] complexes which are metal based, were also linearly related to the reduction potentials of the uncoordinated free beta-diketones which are ligand based. Furthermore, the DFT calculated LUMO energies reproduce the experimental absolute reduction potential.

First author: Bosmans, V, Probing Through-Space Polar-pi Interactions in 2,6-Diarylphenols, JOURNAL OF ORGANIC CHEMISTRY, 84, 3632, (2019)
Abstract: Although it is well established that the acidity of phenol can be fine-tuned with substituents on its aromatic ring via through-bond effects, the role of through-space effects on the acidity of phenols is presently poorly understood. Here, we present integrated experimental and computational studies on substituted 2,6-diarylphenols that demonstrate the essential contribution from through-space OH-pi interactions and O–pi interactions in the observed trends in proton affinities and acidities of 2,6-diarylphenols.

First author: Mostafa, R, Does the gradient-regulated connection improve the description of correlated metal bond properties?, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 119, 3632, (2019)
Abstract: Gradient-regulated connection (GRAC) is a generalized gradient approximation exchange density functional designed by combining the revPBE and PW91 exchange functionals to impose their behaviors in the slowly- and fast-varying density regions, respectively. Such a construction allows one single density functional to accurately estimate both covalent and weak interactions occurring in main-group-based molecular systems. For the first time, the assessment of the performance of the GRAC exchange functional is extended to the modeling of various metal bond energy and structure properties. This assessment shows that when GRAC is coupled with the Perdew, Burke, Ernzerhof (PBE) correlation, the resulting exchange-correlation density functional is an excellent alternative to global hybrids to model bond dissociation energy, atomic electronic excitation energy, and bond length structure properties of single-reference metal bonds. It also shows that coupling with the Tognetti, Cortona, Adamo (TCA) correlation constitutes a robust approach to tackle energy bond properties of organometallic complexes with multi-reference character.

First author: Mikhailov, AA, Primary and secondary photochemical transformations of biologically active precursor – Nitro-Nitrosyl ruthenium complex, JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, 373, 37, (2019)
Abstract: Photolysis of [Ru(II)NOPy2(NO2)(2)OH] (A) complex was studied under blue light (445 nm) irradiation. The primary photo-process results in the formation of nitric oxide (NO) and a paramagnetic Ru-III compound, the latter was detected by EPR technique. The quantum yield (6-11%) of primary photolytic process was determined from the evolution of UV-vis spectra in different solvents (water, ethanol, dimethyl sulfoxide and acetonitrile). The secondary processes compete with the NO-release and lead to a variety of ruthenium forms including new nitrosyl forms. Namely, processes of hydroxyl protonation, pyridine photocleavage and nitro – nitrito bond isomerization take a place. HPLC combined with IR and N-15 – NMR spectroscopies clarified the composition of the new forms and their transformations during the photolysis. Supporting EPR and IR DFT calculations confirmed the structure of photoproducts. The oxidation of NO in the secondary processes significantly influences on the total amount of nitric oxide release and reaction routes.

First author: Podolska-Serafin, K, Molecular structures of nickel adducts in zeolites – Interpretation of experimental EPR g-tensors guided by DFT calculations, JOURNAL OF MOLECULAR STRUCTURE, 1180, 754, (2019)
Abstract: Computational electron paramagnetic resonance (EPR) spectroscopy is a combination of robust simulation techniques of complex spectra with density functional theory (DFT) calculations of spin Hamiltonian parameters for the adopted models of the investigated paramagnetic species. This approach was used for guiding interpretation of the experimental EPR data of selected adducts of nickel(l) and nickel (II) centers in high-silica zeolites with gas-phase small molecules of environmental significance (CO, NO, C2H2, NH3, O-2). As a result, a quantitative connection between the spectroscopic fingerprints, in particular g-tensors, and structure of the molecular clusters mimicking the real intrazeolitic species was obtained. Possible calculation schemes for assessing g-tensor values were explored. Various levels of relativistic effects (including relativistic corrections to the composition of electronic ground state and spin-orbit approximations) were studied. Selection of a proper exchange-correlation functional was also discussed underlying its influence for the systems for which spin density is delocalized over a metal core and a ligand. The conformation analysis of g-tensor anisotropy for amine adducts in assessing its structure was shown. Finally, molecular interpretation of electronic g-tensor in terms of the magnetic field-induced transitions between involved orbitals was shown taking as an example a diamine Ni(I) adduct.

First author: Zhang, WW, Hydroxide transport and chemical degradation in anion exchange membranes: a combined reactive and non-reactive molecular simulation study, JOURNAL OF MATERIALS CHEMISTRY A, 7, 5442, (2019)
Abstract: Investigating the structural and dynamical properties, charge transport and membrane degradation in anion exchange membranes (AEMs) using atomistic-scale simulations provides a guideline for the design of new high-performance membrane fuel cells. In this work, we demonstrate a multiscale simulation strategy that combines molecular dynamics simulations using non-reactive polarizable (APPLE&P) and reactive (ReaxFF) force fields. From the comparison of APPLE&P and ReaxFF results for four model AEMs with different functional groups, we show the significance of the Grotthuss mechanism for the OH- diffusion, as well as for water self-diffusion in high OH- concentration environments. With the incorporation of proton hopping into ReaxFF, the OH- diffuses much easier through the bottlenecks in the water channels, without losing some coordinating water molecules. Furthermore, investigation of the chemical degradation selectivity in different membranes with ReaxFF indicates that AEMs with cations connected to large hydrophobic groups have better chemical stability. Considering the balance of transport and stability properties of AEMs, we propose a potential candidate for high performance membranes.

First author: Fedkin, MV, Development of the ReaxFF Methodology for Electrolyte-Water Systems, JOURNAL OF PHYSICAL CHEMISTRY A, 123, 2125, (2019)
Abstract: A new ReaxFF reactive force field has been developed for water-electrolyte systems including cations Li+, Na+, K+, and Cs+ and anions F-, Cl-, and I-. The reactive force field parameters have been trained against quantum mechanical (QM) calculations related to water binding energies, hydration energies and energies of proton transfer. The new force field has been validated by applying it to molecular dynamics (MD) simulations of the ionization of different electrolytes in water and comparison of the results with experimental observations and thermodynamics. Radial distribution functions (RDF) determined for most of the atom pairs (cation or anion with oxygen and hydrogen of water) show a good agreement with the RDF values obtained from DFT calculations. On the basis of the applied force field, the ReaxFF simulations have described the diffusion constants for water and electrolyte ions in alkali metal hydroxide and chloride salt solutions as a function of composition and electrolyte concentration. The obtained results open opportunities to advance ReaxFF methodology to a wide range of applications involving electrolyte ions and solutions.

First author: Patrizi, B, Ultrafast Intramolecular and Solvation Dynamics in 4,7-Bis (4,5-dibutylbenzo[1,2-b:4,3-b ‘]bisthiophene[1,2-b:4,3-b ‘]bisthiophen-2-yl)-2,1,3-benzothiadiazole, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 5840, (2019)
Abstract: We report a combined approach of stationary and time resolved fluorescence measurements and ultraviolet-visible (UV-vis) transient absorption spectroscopy (TAS) along with ab initio calculations, which provide an overall picture of the dynamics occurring after excitation in a push-pull molecule, namely, 4,7-bis (4,5-dibutylbenzo-[1,2-b:4,3-b’]bisthiophene[1,2-b:4,3-blbisthiophen-2-y1)-2,1,3-benzo- thiadiazole. The analysis of the emission spectra in solvents-of different polarities reveals the presence of three conformers whose structures differ in the orientation of the 4,5-dibutylbenzo-bisthiophene groups and in their planarity with respect to the benzothiadiazole acceptor group. The Kawski method allows us to estimate the ground- and first-excited state dipole moments (mu(g) and mu(e)) for the three conformers. We find values of mu(e) similar for the three conformers and higher than the relative mu(g) values as can be expected from a push pull molecule undergoing a light-induced charge-transfer (CT) transition. UV-vis TAS in different solvents highlights the instantaneous (within our instrumental resolution) formation of a locally excited S-1 state (accompanied by a big change in the dipole moment with respect to S-0), which undergoes a rapid intramolecular CT (ICT) assisted by molecule planarization [planar ICT (PICT)]. The strong dipole-dipole interactions with the polarized solvent molecules stabilize the S-1 CT state that decays principally through fluorescence emission. Both PICT and solvation dynamics are responsible for the big Stokes’ shift characterizing the molecule, particularly in polar solvents. The fluorescence lifetimes are substantially longer in polar solvents, and also fluorescence quantum yields are higher in polar solvents. We conclude that the radiative relaxation time increases when molecular planarization of the S, emissive state takes place, and this condition is favored in polar solvents where local dipole-dipole interactions support the structural stabilization of the CT emissive state. In the poly(methyl methacrylate) matrix, the structural and solvation dynamics are strongly inhibited, leading to reduction of nonradiative processes and to shortening of the fluorescence relaxation time.

First author: Schira, R, Localized Surface Plasmon Resonance in Free Silver Nanoclusters Ag-n, n=20-147, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 6205, (2019)
Abstract: Absorption spectra of silver nanoclusters, Ag-n with n = 20-147, are investigated in the framework of the time-dependent density functional theory with the use of a range-separated hybrid density functional. Our calculated spectra reproduce well the experimental data. The plasmon-like band energy is situated at about 4 eV for all clusters in the gas phase. A description of the plasmonic behavior is given using analyses and tools derived from ab initio quantum calculations. The plasmon band originates from multiple peaks gathered in a relatively small range of energy. High intensive peaks near the center of the band present a strong plasmonic character which has been characterized in terms of transition density, hole-electron excitation, transition contribution map, and generalized plasmonicity index.

First author: Zhang, SS, [Ag-48(C (CBu)-Bu-t)(20)(CrO4)(7)]: An Atomically Precise Silver Nanocluster Co-protected by Inorganic and Organic Ligands, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 141, 4460, (2019)
Abstract: The elaborate selection of capping ligands is of great importance in the synthesis of atomically precise metal nanoclusters. Organic thiolates, alkynyls, phosphines, and/or their combinations are the ligands most widely utilized to protect metal nanoclusters, while inorganic oxo anions have been almost neglected in this field. Herein, the first CrO42-/(BuC)-Bu-t C- co-capped Ag-48 nanocluster (SD/Ag48, SD = SunDi) was synthesized and structurally characterized by single-crystal X-ray diffraction. The pseudo-5-fold symmetric metal skeleton of SD/Ag48 shows a core shell structure composed of a Ag-23 cylinder encircled by an outer Ag-25 shell. Unprecedentedly, coexistence of inorganic (CrO42-) and organic ((BuC)-Bu-t C-) ligands was observed on the surface of SD/Ag48. The inorganic CrO42- anion plays three important roles in the construction of silver nanoclusters: (i) passivating the Ag-23 kernel; (ii) connecting the core and shell; and (iii) protecting the Ag-25 shell. This nanocluster belongs to a 14e superatom system and exhibits successive molecule-like absorption bands from the visible to the ultraviolet region. This work not only establishes a fresh inorganic ligand strategy in the synthesis of silver nanoclusters but also provides a new insight into the important surface coordination chemistry of CrO42- in the shape control of silver nanoclusters.

First author: Devillard, M, Selective Carbanion-Pyridine Coordination of a Reactive P,N Ligand to Rh-I, CHEMISTRY-A EUROPEAN JOURNAL, 25, 3875, (2019)
Abstract: Ligands with reactive carbon sites in the periphery of a metal center have emerged as a powerful approach for metal-ligand bond activation. These reactive carbon sites are commonly generated by deprotonation strategies. Carbon-silicon bond cleavage is a potential alternative to access such constructs. Herein, the monodesilylation of bis-silyl-substituted P,N scaffold PNSi2 in the coordination sphere of [Rh-I(Cl)(CO)(PNSi2)] (1) with sodium azide is disclosed. This affords a unique dinucleating anionic kappa(2)-C,N-kappa(1)-P ligand with a carbanionic methine carbon atom directly bound to rhodium as part of a four-membered Rh-N-C-C rhodacycle. This dimer undergoes meta-pyridine C-H activation facilitated by weak bases, which leads to a desymmetrization of the system and provides a sigma,pi-bridging 3-pyridyl fragment bound to Rh-I. The facile Si-C cleavage strategy may pave the way to studying the reactivity and functionalization of a variety of kappa(2)-C,N-coordinated pyridine scaffolds for selective transformations.

First author: Muller, C, Synthesis, Structure, and Bonding Analysis of Tin(II) Dihalide and Cyclopentadienyltin(II) Halide (Alkyl)(amino)carbene Complexes, ORGANOMETALLICS, 38, 1052, (2019)
Abstract: Tin(II) dibromide, 2b, and cyclopentadienyltin(II) chloride, 2c, and cyclopentadienyltin(II) bromide, 2d, were reacted with cyclic (alkyl)(amino)carbene (cAAC), 1, to give the corresponding complexes cAAC.SnBr2, 3b, cAAC-SnCpCl, 3c, and cAAC.SnCpBr, 3d, which were studied in solution and in the solid state. Although isolatable as crystalline solids, 3c,d exist in a heteroleptic/homoleptic equilibrium with other tin(II) species, in solution. In addition, the coordination chemistry of 3b was investigated and the corresponding iron tetracarbonyl complex, 5, could be isolated and structurally characterized. Furthermore, the mechanism of the equilibrium reaction observed for 3c,d in solution, as well as the chemical bonding nature of all cAAC complexes were investigated by quantum-chemical calculations within the DFT framework.

First author: Majid, A, First Principles Study of Dendritic Carbazole Photosensitizer Dyes Modified with Different Conjugation Structures, CHEMISTRYSELECT, 4, 2787, (2019)
Abstract: In the pursuit of efficient organic dyes first principles calculations were carried out by using density functional theory (DFT). The electronic and optical properties of D-D-pi-A carbazole dendritic donor and cyanoacrylic acid acceptor conjugated through thiophene and oxadiazole structures are being reported. The findings of this work point to the dependence of the structural modifications especially changes in length of conjugation molecule appeared to notably affect the properties of the dyes. The positions of highest occupied molecular orbital (HOMO) and lowest molecular orbitals (LUMO) energy levels are found suitable for electron reduction and electron injection processes respectively. The addition of another oxadiazole ring as well as replacement of a thiophene ring with existing oxadiazole in the conjugating bridge appeared to reduce the HOMO-LUMO energy gap. TD-DFT excitation spectra calculated at PBE, B3LYP and CAM B3LYP levels of theory are discussed in detail to shed light on charge transfer process in the dye molecules and the calculated results are found consistent with reported experimental work. The changes in length and structure of pi-spacer chain are discussed to analyze the photon to current conversion efficiency.

First author: Radon, M, Benchmarking quantum chemistry methods for spin-state energetics of iron complexes against quantitative experimental data, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 4854, (2019)
Abstract: The accuracy of relative spin-state energetics predicted by selected quantum chemistry methods: coupled cluster theory at the CCSD(T) level, multiconfigurational perturbation theory (CASPT2, NEVPT2), multireference configuration interaction at the MRCISD+Q level, and a number of DFT methods, is quantitatively evaluated by comparison with the experimental data of four octahedral iron complexes. The available experimental data, either spin-forbidden transition energies or spin crossover enthalpies, are corrected for relevant environmental effects in order to derive the quantitative benchmark set of iron spin-state energetics. Comparison of theory predictions with the resulting reference data: (1) validates the high accuracy of the CCSD(T) method, particularly when based on Kohn-Sham orbitals, giving the maximum error below 2 kcal mol(-1) and the mean absolute error (MAE) below 1 kcal mol(-1); (2) corroborates the tendency of CASPT2 to systematically overstabilize higher-spin states by up to 5.5 kcal mol(-1); (3) confirms that the latter problem is partly remedied by the recently proposed CASPT2/CC approach [Phung et al., J. Chem. Theory Comput., 2018, 14, 2446-2455]; (4) demonstrates that NEVPT2 performs worse than CASPT2, by giving errors up to 7 kcal mol(-1); (5) shows that the accuracy of MRCISD+Q spin-state energetics strongly depends on the size-consistency correction: the Davidson-Silver and Pople corrections perform best (MAE < 3 kcal mol(-1)), whereas the standard Davidson correction is not recommended (MAE of 7 kcal mol(-1)). Only a few DFT methods (including the best performing ones identified in this study: B2PLYP-D3 and OPBE) are able to provide a balanced description of the spin-state energetics for all four studied iron complexes simultaneously, corroborating the non-universality problem of approximate density functionals.

First author: Dang, JH, Coordination of Nd(iii) and Eu(iii) with monodentate organophosphorus ligands in ionic liquids: spectroscopy and thermodynamics, NEW JOURNAL OF CHEMISTRY, 43, 3866, (2019)
Abstract: The complexation of two representative trivalent lanthanides, Nd(III) and Eu(III), with three monodentate organophosphorus ligands, tributyl phosphate (TBP), dibutyl butyl phosphonates (DBBP) and tributylphosphine oxide (TBPO) in the ionic liquid (IL) C(4)mimNTf(2) was investigated by absorption spectroscopy, luminescence spectroscopy, and microcalorimetry. The Nd(III) complexes formed in the IL were successfully identified and their corresponding thermodynamic parameters were determined. As the alkoxyl group is gradually replaced by an alkyl group from TBP to TBPO, the stability of the Nd(III) complexes increases significantly. Moreover, the nature of the complexes was further elucidated on the basis of thermodynamic analysis as well as luminescence characterization. The overall endothermic feature of the complexation process indicates that Nd(III) and the ligands form inner-sphere coordination complexes in the ionic liquid, which is further supported by luminescence studies with Eu(III) as the surrogate. Upon introduction of organophosphorus ligands, the symmetry of Eu(III) complexes becomes lower and water molecules in the primary coordination sphere of Eu(III) were gradually replaced by the organophosphorus ligands. The results from this work provide valuable thermodynamic and structural insights into the coordination chemistry of lanthanides in ionic liquids.

First author: Lebedeva, IV, Orbital magneto-optical response of periodic insulators from first principles, NPJ COMPUTATIONAL MATERIALS, 5, 3866, (2019)
Abstract: Magneto-optical response, i.e. optical response in the presence of a magnetic field, is commonly used for characterization of materials and in optical communications. However, quantum mechanical description of electric and magnetic fields in crystals is not straightforward as the position operator is ill defined. We present a reformulation of the density matrix perturbation theory for time-dependent electromagnetic fields under periodic boundary conditions, which allows us to treat the orbital magneto-optical response of solids at the ab initio level. The efficiency of the computational scheme proposed is comparable to standard linear-response calculations of absorption spectra and the results of tests for molecules and solids agree with the available experimental data. A clear signature of the valley Zeeman effect is revealed in the continuum magneto-optical spectrum of a single layer of hexagonal boron nitride. The present formalism opens the path towards the study of magneto-optical effects in strongly driven low-dimensional systems.

First author: Gregori, L, Alkyne Activation with Gold(III) Complexes: A Quantitative Assessment of the Ligand Effect by Charge-Displacement Analysis, INORGANIC CHEMISTRY, 58, 3115, (2019)
Abstract: A quantitative assessment of the DewarChattDuncanson components of the Au(III)-alkyne bond in a series of cationic and dicationic bis- and monocyclometalated gold(III) complexes with 2-butyne via charge-displacement (CD) analysis is reported. Bonding between Au(III) and 2-butyne invariably shows a dominant sigma donation component, a smaller, but significant, pi back-donation, and a remarkable polarization of the alkyne CC triple bond toward the metal fragment. A very large net electron charge transfer from CC triple bond to the metal fragment results, which turns out to be unexpectedly insensitive to the charge of the complex and more strictly related to the nature of the ancillary ligand. The combination of sigma donation, pi back-donation, and polarization effects is in fact modulated by the different ligand frameworks, with ligands bearing atoms different from carbon in trans position with respect to the alkyne emerging as especially interesting for both imparting Au(III)-alkyne bond stability and inducing a more effective alkyne activation. A first attempt to figure out a rationale on the bonding/reactivity relationship for Au(III)-alkyne is made by performing a comparative study in a model nucleophilic attack of water to the alkyne triple bond. Smaller pi back-donation facilitates alkyne slippage in the transition states, which is energetically less demanding for Au(III) than for Au(I), and suggests a greater propensity of Au(III) to facilitate the nucleophilic attack.

First author: Poltarak, PA, New Molecular Niobium(IV) Complexes NbX4(OPPh3)(2) (X = Cl, Br): Synthesis, Crystal and Electronic Structure, JOURNAL OF STRUCTURAL CHEMISTRY, 60, 457, (2019)
Abstract: New molecular niobium(IV) complexes NbCl4(OPPh3)(2)(1) and NbBr4(OPPh3)(2)(2) are synthesized by heating respective niobium pentahalide with a mixture of triphenylphosphine and triphenylphosphine oxide. For the obtained compounds the crystal structure is solved: 1P-1, a = 13.3540(5) , b = 9.4461(3) , c = 9.5635(3) , = 93.084(1)degrees, = 121.263(1)degrees, = 115.058(1)degrees, Z = 1, R-1 = 0.0194; 2P-1, a = 13.308(2) , b = 9.5934(8) , c = 9.5556(9) , = 93.975(3),degrees, = 119.391(4)degrees, = 114.740(4)degrees, Z = 1, R-1 = 0.0184. The unpaired electron is mainly located on the niobium atom, which is supported by quantum chemical calculations and EPR spectroscopic results.

First author: Wang, J, Superatom-assembly induced transition from insulator to semiconductor: A theoretical study, SCIENCE CHINA-MATERIALS, 62, 416, (2019)
Abstract: Assembly is an effective way to realize the functionalization potential of boron-based superatoms. Here we study the interaction between typical boron-based B-40 superatoms using the density functional theory. Our results reveal that different oligomers constructed by modulating the arrangement of two B-40 superatoms still retain some of the superatomic properties associated with their monomeric form despite possessing different electronic structures. While the inner shell superatomic orbitals maintain their electronic localization, the valence shell superatomic orbitals cannot maintain their original shape due to bonding and antibonding hybridization. Furthermore, the decreasing of band gap means that the B-40 oligomers could achieve a transformation from insulators to semiconductors. The decreased band gap is possibly due to the disappearance of the superatomic orbitals with the principal quantum number of two. Our findings highlight that superatom-superatom interactions could induce synergy effects that differ from their monomers. Therefore, this research will aid in the development of new materials and devices that are constructed from superatoms.

First author: Manzetti, S, Methods for dispersing carbon nanotubes for nanotechnology applications: liquid nanocrystals, suspensions, polyelectrolytes, colloids and organization control, INTERNATIONAL NANO LETTERS, 9, 31, (2019)
Abstract: Carbon nanotubes (CNTs) are a central part of advanced nanomaterials and are used in state-of-the-art technologies, based on their high tensile strength, excellent thermal transfer properties, low-band gaps and optimal chemical and physical stability. Carbon nanotubes are also intriguing given their unique -electron-rich structures, which opens a variety of possibilities for modifications and alterations of their chemical and electronic properties. In this review, a comprehensive survey of the methods of solubilization of carbon nanotubes is presented, forming the methodological foundation for synthesis and manufacturing of modified nanomaterials. The methods presented herein show that solubilized carbon nanotubes have a great potential in being applied as reactants and components for advanced solar cell technologies, nanochemical compounds in electronics and as parts in thermal transfer management. An example lies in the preservation of the aromatic chemistry in CNTs and ligation of functional groups to their surfaces, which confers CNTs with an optimal potential as tunable Schottky contacts, or as parts in nanotransistors and nano-resistances. Future nanoelectronic circuits and structures can therefore depend more and more on how carbon nanotubes are modified and functionalized, and for this, solubilization is oftena critical part of their fabrication process. This review is important, is in conjecture with the latest developments in synthesis and modification of CNTs, and provides the know-how for developing new CNT-based state-of-the-art technologies, particularly with emphasis on computing, catalysis, environmental remediation as well as microelectronics.

First author: Pemmaraju, CD, Valence and core excitons in solids from velocity-gauge real-time TDDFT with range-separated hybrid functionals: An LCAO approach, COMPUTATIONAL CONDENSED MATTER, 18, 31, (2019)
Abstract: An atomic-orbital basis set framework is presented for carrying out velocity-gauge real-time timedependent density functional theory (TDDFT) simulations in periodic systems employing range-separated hybrid functionals. Linear optical response obtained from real-time propagation of the time-dependent Kohn-Sham equations including nonlocal exchange is considered in prototypical solid-state materials such as bulk Si, LiF and monolayer hexagonal-BN. Additionally core excitations in monolayer hexagonal-BN at the B and N K-edges are investigated and the role of long-range and short-range nonlocal exchange in capturing valence and core excitonic effects is discussed. Results obtained using this time-domain atomic orbital basis set framework are shown to be consistent with equivalent frequency-domain planewave results in the literature. The developments discussed lead to a time-domain generalized Kohn-Sham TDDFT implementation for the treatment of core and valence electron dynamics and light-matter interaction in periodic solid-state systems.

First author: Cao, GJ, Dinuclear Metal-Mediated Guanine-Uracil Base Pairs: Theoretical Studies of GUM(2)(2+) (M=Cu, Ag, and Au) Ions, JOURNAL OF CLUSTER SCIENCE, 30, 439, (2019)
Abstract: Dinuclear metal-mediated hetero base pairs with the d(10)-d(10) closed-shell interactions have significant stability. It is interesting to identify whether coinage metal-mediated Wobble base pairs are also stable. Geometric and electronic structures of the lowest-lying isomers of GUM(2)(2+) (G=guanine, U=uracil, M=Cu, Ag, and Au) cluster ions were investigated with density functional theory. In the lowest-lying isomers of these dinuclear metal-mediated base pairs, the 2-oxo-4-hydroxy-trans-N1H isomer of uracil is derived from the canonical tautomer of uracil by the hydrogen atom transfer. M-2(2+) cations remain as an unbroken unit and interact with the GU ligand through two sets of closely linear NMO units, while the reciprocal hydrogen bonds between the Wobble base pair (G-U) are entirely substituted by the M-N or M-O interactions in these complexes. The atoms in molecules and EDA-NOCV calculations really reveal that the sigma interactions in GUM(2)(2+) cations are the paramount term of E-Orb. The obtained instantaneous interaction energies E-int and bond dissociation energies of the metal-ligand interactions give the trend of the bond strength as Cu>Au>Ag.

First author: Nemdili, H, Structural, bonding and redox properties of 34-electron bimetallic complexes and their oxidized 32-and 33-electron and reduced 35-and 36-electron derivatives containing the indenyl fused pi-system: A DFT overview, POLYHEDRON, 160, 219, (2019)
Abstract: DFT calculations with the BP86, OPBE and hybrid B3LYP* functionals have been performed on a series of homo- and heterobimetallic compounds of the type [(RuCp)(2)(Ind)](+), [(CoCb)(2)(Ind)](+) and [(RuCp)(CoCb)(Ind)](+) (Ind = indenyl, Cp = cyclopentadienyl and Cb = cyclobutadiene) of 34-TNE (Total number of electrons), their oxidized 32- and 33-TNEs and their reduced 35- and 36-TNEs species. Depending on the ancillary Cp or Cb ligand to the metal, the electronic and molecular structures and the metal-metal bonding of this family of compounds have been analyzed. The syn and anti-configurations are possible for the studied binuclear complexes, which are related to the metal nature, where mostly steric constraints of the Cp or the Cb ligand appear to control its spatial disposition favouring the anti configuration, despite its electronic deficiency for the 32- and 33-TNEs species. The flexibility of the indenyl ligand, which is related to the metal hapticity, favors the possibility of existence of several syn and anti isomers of close energies. This study showed quite similar behaviours of the (RuCp)(+) and (CoCb)(+) fragments of 12-electrons regarding their change or their permutation. The current study shows the ease of reduction with regard to oxidation, particularly that by the loss of two electrons. The used three functionals gave comparable tendencies of the stability sequences between isomers, favouring the low-spin structures, and provided comparable findings regarding the low-spin/high-spin energy splittings.

Abstract: This review outlines the role of hyperconjugative interactions in the structure and reactivity of organic molecules. After defining the common hyperconjugative patterns, we discuss the main factors controlling the magnitude of hyperconjugative effects, including orbital symmetry, energy gap, electronegativity, and polarizability. The danger of underestimating the contribution of hyperconjugative interactions are illustrated by a number of spectroscopic, conformational, and structural effects. The stereoelectronic nature of hyperconjugation offers useful ways for control of molecular stability and reactivity. New manifestations of hyperconjugative effects continue to be uncovered by theory and experiments.

First author: Lai, SK, An efficient optimization algorithm that hybridizes DFTB and DFT theories both operated within the modified basin hopping method, COMPUTER PHYSICS COMMUNICATIONS, 236, 164, (2019)
Abstract: The density functional tight-binding (DFTB) theory and density functional theory (DFT) are separately combined with the modified basin hopping (MBH) method into a two-stage optimization algorithm that is then applied in sequence to find the lowest-energy structures of Au clusters. In the first-stage, the DFTB/MBH is conducted mainly to provide a speedy and yet semi-quantitatively reliable searching of the lowest-energy structures so as to pave the way for the second-stage DFT/MBH for more refined and accurate sorting of them at the DFT level. To ensure high efficiency in searching the minimized energy, we pay more attention to the DFTB theory in particular the repulsive part energy and examine the quality of the DFTB parameters fitted to different sets of reference structures. This parametrization study is physically relevant since the cluster’s structure is basically determined, by and large, by the repulsive potential. To appreciate the nicety of the present method, we apply the latter and two other existing sets of DFTB parameters to perform the first-stage DFTB/MBH but, separately, we continue the second-stage optimization all by the same DFT/MBH method. We found that the lowest-energy geometries of gold clusters obtained are independent of the use of the DFTB theory to calculate the energy function in the first-stage minimization. Only the efficacy of executing the second-stage DFT/MBH which is generally time-consuming differs, however. In general, for duly-fitted DFTB parameters less computer time is required at the second-stage operation. On comparing further our calculated optimized Au structures with other theoretical calculations and existing experimental clusters, the very good agreement among them clearly explains that the present hybridized scheme has greater potential to efficiently perform with less or within affordable computing time the high-level OFT calculation for medium to larger sized clusters.

First author: Zhang, HM, Photophysical and photochemical insights of the photodegradation of norfloxacin: The rate-limiting step and the influence of Ca2+ ion, CHEMOSPHERE, 219, 236, (2019)
Abstract: Photodegradation is one of the major degradation paths for antibiotics as aquatic micropollutants in surface water. The photodegradation involves a number of complicated photophysical and photochemical processes. Exploration for the rate-limiting step among these processes can be essential for the elimination of antibiotics. In this work norfloxacin was selected as a target compound. The rate constants of photophysical transitions and their competitions were discussed under the framework of Fermi Golden rule and time-depended perturbation theory. Using density functional theory, the reaction paths in triplet state were searched. The competitions among the photophysical transitions and photochemical reaction paths indicate the intersystem crossing (ISC) from the S-1 state to T-1 state is the rate-limiting step in the aquatic photodegradation of norfloxacin. Ca2+ ion significantly accelerates this bottleneck by coordinating with the carbonyl and carboxyl groups of norfloxacin. The coordination creates more ISC paths to triplet states and increases the spin-orbit coupling, Huang-Rhys factors, and the vibrational coupling of the ISCs.

First author: Gao, HF, Insights into the non-covalent interaction between modified nucleobases and graphene nanoflake from first-principles, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 107, 73, (2019)
Abstract: The four new modified nucleobases (NBs), 5-mC, 5-hmC, 5-fC and 5-caC, besides the regular adenine, thymine, cytosine, guanine and uracil, are important in expression and regulation of genetic information. These four new major NBs are all derived from base cytosine by adding various functional groups, and their identification from the regular ones are much desired currently. However, the four new major NBs interacted with graphene on its surface have not been well considered, though a number of studies of regular NBs adsorbed on low-dimensional carbon materials are available to identify different NBs. This work reveals the interaction between the four new major NBs and graphene nanoflake substrate by using first-principle calculations based on density functional theory. The structure, energy and non-covalent interaction of the graphene/NBs complex are calculated and explored in details. The energy decomposition analysis, reduced density gradient, charge transfer and projected density of states are also performed to investigate the nature of the interaction between NBs and graphene nanoflake. Electrostatic and orbital interaction are found to be important to stabilize the interaction between NBs and graphene nanoflake, though orbital interaction is less significant It is very noticed that the proportion of dispersion interaction could be more than half of the sum attractive contributions. Thus, dispersion interaction is the most dominating factor in stabilizing graphene/NBs complexes. The results of reduced density gradient further confirm that the interaction between the graphene nanoflake and NBs is mainly the van der Waals type. Besides, much attention is paid to the interaction differences between the four new major NBs and the pristine cytosine, and the impact of the introduced functional groups of the four new major NBs on the structure, energy and interaction is also discussed.

First author: Zhu, YA, Revealing the mechanism of contrasting charge transport properties for phenyl and thienyl substituent organic semiconductors, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 4641, (2019)
Abstract: The aromatic substituents such as phenyl and thienyl have a direct impact on the structure-property relationship of conjugated semiconducting molecules and thus play a significant role in determining the performance of organic thin film transistors (OTFTs). To design a molecule with good charge transport properties, it is essential to understand the charge transfer process. Herein, through the study of two groups of classical OTFT materials with different substituents, we demonstrate the fundamental reasons for the contrasting carrier mobilities between the materials in each group by means of DFT calculations. The results from our theoretical analysis on the two groups of molecules provide very good estimates of their charge transfer properties and the numerical trend from our calculation is consistent with that from the corresponding experimental results. We reveal in detail the impacts of the subtle geometric differences caused by different substituents from two aspects including (i) the significant influence of steric hindrance on reorganization energy and (ii) the overlap of the adjacent molecular orbitals (MOs) on electron coupling. Overall, our systematic investigation into the charge transfer mechanism and geometry effects allows us to employ a reliable theoretical methodology for the prediction of the material performance, which is crucial for the design of high performance OTFT materials.

First author: Spivak, M, Trends in the Bond Multiplicity of Cr-2, Cr-3, and Cr2M (M = Zn, Ni, Fe, Mn) Complexes Extracted from Multiconfigurational Wave Functions, JOURNAL OF PHYSICAL CHEMISTRY A, 123, 1538, (2019)
Abstract: Extended metal atom chains constitute an interesting class of molecules from both theoretical and applied points of view. In the chromium-based series Cr2M(dpa)(4)X-2 (with M = Zn, Ni, Fe, Mn, Cr), the direct metal-metal interactions span a wide range of possibilities and so do their associated properties. The multiplicity and symmetry components of the metal-metal bond are herein analyzed via the effective bond order (EBO) concept using complete active space self-consistent field wave functions and compared with similar bimetallic Cr2L4X2 systems. The bond multiplicity follows a trend dominated by the Cr-Cr distance which, in turn, depends on the nature of the axial ligand (X). Cr2M compounds present asymmetric structures with virtually no interaction between the Cr-2 unit and M, whereas fully symmetric structures with delocalized bonding among the three metals are also possible in Cr-3 complexes. In such cases, a strategy that involves localization of the molecular orbitals into each Cr-Cr pair is applied to quantify the contribution of each pair to the overall metal metal bond multiplicity.

First author: Fan, JX, Theoretical study of synergetic effect between halogenation and pyrazine substitutions on transport properties of silylethynylated pentacene, NEW JOURNAL OF CHEMISTRY, 43, 3583, (2019)
Abstract: Combining quantum-tunneling-effect-enabled hopping theory with kinetic Monte Carlo simulation and dynamic disorder effects, the charge transport properties of a series of N-hetero 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-PEN) derivatives with halogen substitutions were studied. Based on the single molecule and the theoretically predicted crystal structure, the electronic structures and nuclear dynamic disorder effects of halogen and aza systems and their impacts on the charge transport behaviors were expounded. On the one hand, this study revealed the regularity of carrier transport by substitution with one or two pyrazine rings from the external toward the internal for benzene rings in TIPS-PEN, suggesting the substitution of two internal pyrazine rings can sharply shrink the hole transport features. Meanwhile, internal pyrazine rings improve the electron transport performance mainly by enhancing air stability and compacting pi-stacking. On the other hand, the investigation elaborated the delicate tuning effect of chlorination on two kinds of carrier transports based on aza-TIPS-PEN derivatives, indicating chlorination can effectively equilibrate the electron and hole reorganization energies and decrease the slip distances along the molecular long and short axes in favor of the similarity in the hole and electron transfer integral values, thereby yielding increasingly balanced ambipolar transport characteristic. The coordination of monopyrazine substitution and chlorination on the acene is an effective way to acquire ambipolar transport properties. In addition, the nuclear dynamic disorder effect affects the hole transfer integral more than the electron transfer integral. In the case of the comprehensive consideration of both ease of charge injection and intrinsic transport mobility, both 8,9,10,11-tetrafluoro-6,13-bis((triisopropylsilyl)ethynyl)naphtho[2,3-b]phenazine (2b) and tetrachloro-6,13-bis((triisopropylsilyl)ethynyl)quinoxalino[2,3-b]phenazine (3c) exhibited to be electron-dominant materials, while 8,9,10,11-tetrachloro-6,13-bis((triisopropylsilyl)ethynyl)naphtho[2,3-b]phenazine (2c) showed effective ambipolar transport characteristics with average hole/electron mobility of 3.64/2.21 cm(2) V-1 s(-1).

First author: Kim, JH, Structural and Electronic Origin of Bis-Lactam-Based High-Performance Organic Thin-Film Transistors, ACS APPLIED MATERIALS & INTERFACES, 11, 8301, (2019)
Abstract: We describe herein the comprehensive theoretical and experimental studies on the transistor mobility of organic semiconductors by correlating a two-dimensional (2D) intermolecular interaction with thin-film morphology and the electronic coupling structure. We developed a novel bis-lactam-based small molecule, 1,5-dioctyl-3,7-di(thiophen-2-yl)-1,5-naphthyridine-2,6-dione (C8-NTDT), with a 2D-type C-H center dot center dot center dot O=C intermolecular interaction along the in-plane directions of the crystal packing structure, which is characteristically different from the one-dimensional-type intermolecular interaction shown in the typical bis-lactam molecule of 2,5-dioctyl-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4-dione (C8-DPPT). Experimentally and theoretically, C8-NTDT exhibited more favorable thin-film morphology and an electronic coupling structure for charge transport because of its unique 2D intermolecular interactions compared with C8-DPPT. In fact, C8-NTDT exhibited a hole mobility of up to 1.29 cm(2) V-1 s(-1) and an on/off ratio of 10(7) in a vacuum-processed device. Moreover, the high solubility with the 2D electronic coupling structure of C8-NTDT enables versatile solution processing for device fabrication without performance degradation compared to the vacuum-processed device. As an example, we could demonstrate a hole mobility of up to 1.10 cm(2) V-1 s(-1) for the spin-coated devices, which is one of the best performances among the solution-processed organic field-effect transistors based on bis-lactam-containing small molecules.

First author: Wang, M, Genesis and Stability of Hydronium Ions in Zeolite Channels, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 141, 3444, (2019)
Abstract: The catalytic sites of acidic zeolite are profoundly altered by the presence of water changing the nature of the Bronsted acid site. High-resolution solid-state NMR spectroscopy shows water interacting with zeolite Bronsted acid sites, converting them to hydrated hydronium ions over a wide range of temperature and thermodynamic activity of water. A signal at 9 ppm was observed at loadings of 2-9 water molecules per Bronsted acid site and is assigned to hydrated hydronium ions on the basis of the evolution of the signal with increasing water content, chemical shift calculations, and the direct comparison with HClO4 in water. The intensity of H-1-Si-29 cross-polarization signal first increased and then decreased with increasing water chemical potential. This indicates that hydrogen bonds between water molecules and the tetrahedrally coordinated aluminum in the zeolite lattice weaken with the formation of hydronium ion-water clusters and increase the mobility of protons. DFT-based ab initio molecular dynamics studies at multiple temperatures and water concentrations agree well with this interpretation. Above 140 degrees C, however, fast proton exchange between bridging hydroxyl groups and water occurs even in the presence of only one water molecule per acid site.

First author: Vondung, L, Ligands Based on Phosphine-Stabilized Aluminum(I), Boron(I), and Carbon(0), CHEMISTRY-A EUROPEAN JOURNAL, 25, 3068, (2019)
Abstract: A systematic quantum chemical study of the bonding in d(6)-transition-metal complexes, containing phosphine-stabilized, main-group-element fragments, (R3P)(2)E, as ligands (E=AlH, BH, CH+, C), is reported. By using energy decomposition analysis, it is demonstrated that a strong M-E bond is accompanied by weak P-E bonds, and vice versa. Although the Al-M bond is, for example, found to be very strong, the weak Al-P bond suggests that the corresponding metal complexes will not be stable towards phosphine dissociation. The interaction energies for the boron(I)-based ligand are lower, but still higher than those for two-carbon-based ligands. For neutral ligands, electrostatic interactions are the dominating contributions to metal-ligand bonding, whereas for the cationic ligand a significant destabilization, with weak orbital and even weaker electrostatic metal-ligand interactions, is observed. Finally, for iron(II) complexes, it is demonstrated that different reactivity patterns are expected for the four donor groups: the experimentally observed reversible E-H reductive elimination of the borylene-based ligand (E=BH) exhibits significantly higher barriers for the protonated carbodiphosphorane (CDP) ligand (E=CH) and would proceed through different intermediates and transition states. For aluminum, such reaction pathways are not feasible (E=AlH). Moreover, it is demonstrated that the metal hydrido complexes with CDP ligands might not be stable towards reduction and isomerization to a protonated CDP ligand and a reduced metal center.

First author: Niu, SS, Electron-momentum-spectroscopy study on the valence electronic structure of methyl iodide: Electron correlation and relativistic effects, PHYSICAL REVIEW A, 99, 3068, (2019)
Abstract: We report an experimental and theoretical study on the electronic structure of methyl iodide. The binding energy spectrum (BES) and electron-momentum profiles (EMPs) of valence orbitals have been measured using a high-sensitivity electron-momentum spectrometer at the impact energy of 1200 eV plus binding energy. Theoretical calculations considering the relativistic and electron correlation effects are performed to illuminate the measured results. For the two outermost orbitals, the relativistic effects are revealed by the experimental and theoretical EMPs for two spin-orbit splitting components (2e(3/2) and 2e(1/2)) and the C-I bonding orbital (3a(1)). In the inner valence region, satellite structures associated with the ionizations from 2a(1) and 1a(1) orbitals are observed in the BES and the pole strengths for the satellites are determined by comparing the measured EMPs with the calculated ones. Moreover, distinct relativistic and electron correlation effects on the EMPs for the 2a(1) orbital and its satellites have been found.

First author: Huang, XW, Impact of the phenyl thioether contents on the high frequency dielectric loss characteristics of the modified polyimide films, SURFACE & COATINGS TECHNOLOGY, 360, 205, (2019)
Abstract: With the combination of the phenyl thioether group into the molecular chain of polyimide, the high frequency dielectric loss of the modified polyimide film can be effectively reduced, which will avail this insulating material of application in high frequency electrical equipment. In the proposed study, polyimide films containing different proportions of phenyl thioether were prepared via alternating thermal imidization method and the impact of phenyl thioether contents on the high frequency dielectric loss characteristics investigated. Frequency-domain dielectric spectrum analysis indicated that the dielectric loss of the modified films decreased in the first instance and then roared again with increased phenyl thioether content, among which cases the lowest dielectric loss factor (tan delta = 0.000929 at 1 kHz) occurred in the film with phenyl thioether content of 40%. Both X-ray diffraction (XRD) and Ultraviolet-visible spectroscopy (UV-Vis) measurements, with reactive force field-based molecular dynamics simulation, were utilized to further elucidate the influencing mechanism of phenyl thioether content on dielectric loss characteristics. When the content of phenyl thioether was < 40%, the charge transfer effect decreased with the increased phenyl thioether content, gradually reducing the degree of micro-crystallinity in the modified polyimide, and thereby increasing the dispersion of dipole moment that directly led to the reduced dielectric loss. When the phenyl thioether content is higher than 40%, the charge transfer effect reversed, which results in the PI film with increased crystalline region caused by the tighten molecular stacking and has the increased dielectric loss. Synthesis of the low-dielectric-loss polyimide films can be then optimized for high frequency applications.

First author: Ferreira, H, Electrochemical and electronic properties of a series of substituted polypyridine ligands and their Co(II) complexes, INORGANICA CHIMICA ACTA, 486, 26, (2019)
Abstract: DFT calculations show that, due to Jahn-Teller distortion, the d(7) [Co(N,N)(3)](2+) complexes, with S = 1/2 (N,N = bipyridine or substituted bipyridine ligand) have two longer axial and four shorter equatorial Co-N bonds (elongation Jahn-Teller), while [Co(terpyridine)(2)](2+) with S = 1/2, instead has two shorter central (axial) Co-N bonds and four longer distal Co-N bonds (compression Jahn-Teller), since in the latter, the distal Co-N bonds are more flexible than the Co-N axial bonds in the rigid structure of the tridentate terpyridine ligand. The same trend is observed for the related high spin S = 3/2 Co(II) complexes, though less pronounced. The cyclic voltammograms of [Co(terpyridine)(2)](2+) and a series of the [Co(N,N)(3)](2+) complexes show at least three chemically as well as electrochemically reversible redox couples, namely Co-III/III, Co-II/I and a ligand based reduction of the polypyridine-Co(I) complex. The reduction of the uncoordinated free polypyridine ligand is more than 0.5 V more negative than the reduction of the coordinated ligand in the polypyridine-Co(I) complex.

First author: Conradie, J, Jahn-Teller effect in high spin d(4) and d(9) octahedral metal-complexes, INORGANICA CHIMICA ACTA, 486, 193, (2019)
Abstract: The Jahn-Teller effect, which is the geometrical effect on a molecule due to the energy lowering of spatially degenerate electronic ground states, is not determined, as is often perceived, by the shape of the highest occupied molecular orbital (HOMO), or the shape of a singly occupied molecular orbital (SOMO), but is determined rather by the difference in concentration of electron density (before distortion) between the metal and the two ligands on the z-axis, and concentration of electron density between the metal and the four ligands lying in the xy-plane. A higher concentration of electron density between the metal and the two ligands on the z-axis, than between the metal and the four ligands on the xy-plane, will lead to elongation (z-out) Jahn-Teller distortion. Accordingly, high spin, S = 2, d(4) octahedral metal-complexes with a d(z2) HOMO, as well as S =1/2, d(9) octahedral metal-complexes with a d(x2-y2) HOMO, both exhibit elongation (z-out) Jahn-Teller distortion.

First author: Mehlich, F, Synthesis and characterization of copper complexes with a series of tripodal amine ligands, INORGANICA CHIMICA ACTA, 486, 742, (2019)
Abstract: A series of copper complexes with tripodal amine ligands was synthesized and structurally characterized. The copper(I) complexes of this series were investigated in regard to their reactivity towards dioxygen using stoppedflow techniques. For most complexes no “dioxygen adduct” complexes as intermediates could be detected. During the course of our investigations it was observed that the copper(II) complex with the ligand 3,3′-dimethylaminopropyl-(2-methylenpyridyl)-amine (Me-4-p33) crystallized as a dinuclear complex, [Cu(Me-4-p3H3)OH](2)(ClO4)(4), that could be structurally characterized. Interestingly, it turned out that in crystalline form the two bridging hydroxide ions were intact while two of the amine arms of the two ligands were protonated. DFT calculations were performed to get a better understanding of the behavior of this complex system in solution. Further protonation of two more amine ligand arms in solution was possible, still keeping the bridging hydroxide ions in place in the solid state. A related copper(II) complex system could be crystallized that contained a coordinated carbonate anion together with a protonated amine arm.

First author: Szell, PMJ, Halogen bonding as a supramolecular dynamics catalyst, NATURE COMMUNICATIONS, 10, 742, (2019)
Abstract: Dynamic processes have many implications in functional molecules, including catalysts, enzymes, host-guest complexes, and molecular machines. Here, we demonstrate via deuterium NMR relaxation experiments how halogen bonding directly impacts the dynamics in solid 2,3,5,6-tetramethylpyrazine cocrystals, catalyzing the methyl group rotation. On average, we observe a reduction of 56% in the rotational activation energy of the methyl groups in the halogen bonded cocrystals, contrasting the reduction of 36% in the hydrogen bonded cocrystals, with respect to pure 2,3,5,6-tetramethylpyrazine. Density functional theory calculations attribute this superior catalytic ability of the halogen bond to the simultaneous destabilization of the staggered conformation and stabilization of the gauche conformation, overall reducing the rotational energy barrier. Furthermore, the calculations suggest that the catalytic ability of the halogen bond may be tuneable, with stronger halogen bond donors acting as superior dynamics catalysts. Thus, halogen bonding may play a role in both assembly and promoting dynamical processes.

First author: Toffoli, D, Pd doping, conformational, and charge effects on the dichroic response of a monolayer protected Au-38(SR)(24) nanocluster, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 3585, (2019)
Abstract: TDDFT simulations of the absorption and CD spectra of a Pd2Au36(SC2H4Ph)(24) monolayer-protected cluster (MPC) are carried out with the aim of investigating the effects of doping, conformational degrees of freedom of the thiolates’ end-groups, and charge states on the optical and dichroic response of a prototypical MPC species. Clear signatures of Pd doping in both absorption and CD spectra are found to be a consequence of the participation of Pd (4d) states in the ligand-based d-band and on the unoccupied MOs of lower energy. Exploration of conformational space points to a much greater sensitivity of optical rotation to the conformation of the end-groups of the organic monolayer compared to absorption. Finally, the effect of charge is mainly seen as a decreased dependence of the dichroic response on conformation. The agreement between the TDDFT predictions and the available experimental data is good, and enables an assignment of absorption and CD bands to specific classes of one-particle excitations.

First author: Schwarz, C, Isolation of the Metalated Ylides [Ph3P-C-CN]M (M=Li, Na, K): Influence of the Metal Ion on the Structure and Bonding Situation, CHEMISTRY-A EUROPEAN JOURNAL, 25, 2793, (2019)
Abstract: The isolation and structural characterization of the cyanido-substituted metalated ylides [Ph3P-C-CN]M (1-M; M=Li, Na, K) are reported with lithium, sodium, and potassium as metal cations. In the solid-state, most different aggregates could be determined depending on the metal and additional Lewis bases. The crown-ether complexes of sodium (1-Na) and potassium (1-K) exhibited different structures, with sodium preferring coordination to the nitrogen end, whereas potassium binds in an unusual eta(2)-coordination mode to the two central carbon atoms. The formation of the yldiide was accompanied by structural changes leading to shorter C-C and longer C-N bonds. This could be attributed to the delocalization of the free electron pairs at the carbon atom into the antibonding orbitals of the CN moiety, which was confirmed by IR spectroscopy and computational studies. Detailed density functional theory calculations show that the changes in the structure and the bonding situation were most pronounced in the lithium compounds due to the higher covalency.

First author: Marazzi, M, Charge-Transfer versus Charge-Separated Triplet Excited States of [Re-I(dmp)(CO)(3)(His124)(Trp122)](+) in Water and in Modified Pseudomonas aeruginosa Azurin Protein, CHEMISTRY-A EUROPEAN JOURNAL, 25, 2519, (2019)
Abstract: A computational investigation of the triplet excited states of a rhenium complex electronically coupled with a tryptophan side chain and bound to an azurin protein is presented. In particular, by using high-level molecular modeling, evidence is provided for how the electronic properties of the excited-state manifolds strongly depend on coupling with the environment. Indeed, only upon explicitly taking into account the protein environment can two stable triplet states of metal-to-ligand charge transfer or charge-separated nature be recovered. In addition, it is also demonstrated how the rhenium complex plus tryptophan system in an aqueous environment experiences too much flexibility, which prevents the two chromophores from being electronically coupled. This occurrence disables the formation of a charge-separated state. The successful strategy requires a multiscale approach of combining molecular dynamics and quantum chemistry. In this context, the strategy used to parameterize the force fields for the electronic triplet states of the metal complex is also presented.

First author: Anderson, JSM, Molecular QTAIM Topology Is Sensitive to Relativistic Corrections, CHEMISTRY-A EUROPEAN JOURNAL, 25, 2538, (2019)
Abstract: The topology of the molecular electron density of benzene dithiol gold cluster complex Au-4-S-C6H4-S’-Au'(4) changed when relativistic corrections were made and the structure was close to a minimum of the Born-Oppenheimer energy surface. Specifically, new bond paths between hydrogen atoms on the benzene ring and gold atoms appeared, indicating that there is a favorable interaction between these atoms at the relativistic level. This is consistent with the observation that gold becomes a better electron acceptor when relativistic corrections are applied. In addition to relativistic effects, here, we establish the sensitivity of molecular topology to basis sets and convergence thresholds for geometry optimization.

First author: Alemayehu, AB, Relativistic Effects on a Metal-Metal Bond: Osmium Corrole Dimers, INORGANIC CHEMISTRY, 58, 2798, (2019)
Abstract: A series of metal-metal bonded osmium corrole dimers, {Os[TpXPC]}(2), were synthesized in reasonably good yields (35-46%) via the interaction of the corresponding free-base meso-tris(p-X-phenyl)corroles (H-3[TpXPC], X = CF3, H, CH3, and OCH3), Os-3(CO)(12), and potassium carbonate in 1,2,4-trichlorobenzene under an inert atmosphere at 180 degrees C over several hours. The complexes are only the second class of Os corroles reported to date (the first being (OsN)-N-VI corroles) and also the second class of metal-metal bonded metallocorrole dimers (the other being Ru corrole dimers). Comparison of the X-ray structures, redox potentials, and optical spectra of analogous Ru and Os corrole dimers, along with scalar-relativistic DFT calculations, has provided an experimentally calibrated account of relativistic effects in these complexes. Three of the Os corrole dimers (X = CF3, H, and OCH3) were analyzed with single-crystal X-ray diffraction analysis, revealing inversion-related corrole rings with eclipsed Os-N bonds and Os-Os distances of similar to 2.24 angstrom that are similar to 0.06 angstrom longer than the Ru-Ru distances in the analogous Ru corrole dimers. Interestingly, a comparison of scalar-relativistic and nonrelativistic DFT calculations indicates that this difference in metal-metal bond distance does not, in fact, reflect a differential relativistic effect. For a given corrole ligand, the Ru and Os corrole dimers exhibit nearly identical oxidation potentials but dramatically different reduction potentials, with the Os values similar to 0.5 V lower relative to Ru, suggesting that whereas oxidation occurs in a ligand-centered manner, reduction is substantially metal-centered, which indeed was confirmed by scalar-relativistic calculations. The calculations further indicate that approximately a third of the similar to 0.5 V difference in reduction potentials can be ascribed to relativity. The somewhat muted value of this relativistic effect appears to be related to the finding that reduction of an Os corrole dimer is not exclusively metal-based but that a significant amount of spin density is delocalized over to the corrole ligand; in contrast, reduction of an Ru corrole dimer occurs exclusively on the Ru-Ru linkage. For isoelectronic complexes, the Ru and Os corrole dimers exhibit substantially different UV-vis spectra. A key difference is a strong near-UV feature of the Os series, which in energy terms is blue-shifted by similar to 0.55 V relative to the analogous feature of the Ru series. TDDFT calculations suggest that this difference may be related to higher-energy Os(5d)-based LUMOs in the Os case relative to analogous MOs for Ru.

First author: Grabowski, SJ, A-H horizontal ellipsis sigma Hydrogen Bonds: Dihydrogen and Cycloalkanes as Proton Acceptors, CHEMPHYSCHEM, 20, 565, (2019)
Abstract: omega B97XD/aug-cc-pVTZ calculations were performed for complexes of dihydrogen, cyclopropane, cyclobutane and cyclopentane, with simple proton donating species such as hydrogen fluoride, hydrogen chloride, water, hydrogen cyanide and acetylene. Numerous dependencies between geometrical, energetic and topological parameters of complexes considered were found, since various theoretical approaches were applied: Quantum Theory of ‘Atoms in Molecules’ (QTAIM), Natural Bond Orbital (NBO) method and energy decomposition analysis (EDA). It was confirmed that complexes of dihydrogen and cyclopropane are linked through the A-H horizontal ellipsis sigma interactions that may be classified as hydrogen bonds. In the case of complexes of cyclobutane such hydrogen bonds are rather weak. Other type and also weak A-H horizontal ellipsis C hydrogen bonds are formed for complexes with cyclopentane.

First author: Groh, MF, The Intermetalloid Clusters [Ni2Bi12](4+) and [Rh2Bi12](4+) – Ionothermal Synthesis, Crystal Structures, and Chemical Bonding, ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 645, 161, (2019)
Abstract: The intermetalloid clusters [M2Bi12](4+) (M = Ni, Rh) were synthesized as halogenido-aluminates in Lewis-acidic ionic liquids. The reaction of bismuth and NiCl2 in [BMIm]Cl5AlCl(3) (BMIm = 1-butyl-3-methylimidazolium) at 180 degrees C yielded black, triclinic crystals of [Ni2Bi12][AlCl4](3)[Al2Cl7]. Black, monoclinic (P2(1)/m) crystals of [Rh2Bi12][AlBr4](4) precipitated after dissolving the cluster salt Bi12-xRhX13-x (X = Cl, Br; 0 < x < 1) in [BMIm]Br4.1AlBr(3) at 140 degrees C. In the cationic cluster [Ni2Bi12](4+), the nickel atoms center two base-sharing square antiprisms of bismuth atoms (symmetry close to D-4h). The valence-electron-poorer rhodium-containing cluster is a distorted variant of this motif: the terminating Bi-4 rings are folded to bicyclic butterflies and the central square splits into two dumbbells (symmetry close to D-2h). DFT-based calculations and real-space bonding analyses place the intermetalloid units between a triple-decker complex and a conjoined Wade-Mingos cluster.

First author: Ortolan, AO, On the cation- capabilities of small all sp(2)-carbon host structures. Evaluation of [6.8](3)cyclacene from relativistic DFT calculations, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 119, 161, (2019)
Abstract: Cation- interactions are noncovalent forces with essential roles in the stability of protein structures, molecular recognition, and host-guest chemistry. In this work, we discuss the formation of cation- complexes involving one of the smallest characterized nanobelts to date, given [6.8](3)cyclacene, by using relativistic DFT-D calculations. Such nanobelt exhibits a noteworthy all-sp(2) carbon backbone, leading to a rigid and confined host framework. Our results reveal that the inclusion of representative cations, such as Ag+ and Sn2+, appears to be plausible, revealing that it is feasible to obtain these compounds experimentally. Such systems involves two contrasting coordination modes, where the Ag+ cation remains coordinated in the upper face of the nanobelt, whereas the Sn2+ is able to be located at the center of the structure. In addition, the coordination of isoelectronic Cd2+ and In+ was also discussed. Moreover, the bonding characteristics of the resulting cation- interaction show that the -orbitals from the nanobelt 1 are able to moderate the charge transfer, according to the selected cation, which can be seen as an interesting strategy to tune the amount of charge of the -backbone in nanobelts. We envisage that the use of more rigid host in the formation of cation- interactions will be beneficial to gain a better understanding about the metal coordination and also to tune the capabilities of related nanobelts or nanotubes sections.

First author: Lamine, W, Coordination chemistry of Zn2+ with Sal(ph)en ligands: Tetrahedral coordination or penta-coordination? a DFT analysis, JOURNAL OF COMPUTATIONAL CHEMISTRY, 40, 717, (2019)
Abstract: In this article, the Lewis acidic character within a series of Zn-Sal(ph)en complexes is reviewed and revisited. Besides traditional analyses found in the literature, conceptual density functional theory descriptors are used to assess this acidic character. Using these tools, we highlight how the nature of the bridging diamine linker in the Schiff base ligand controls this feature mainly responsible of the coordination geometry of these complexes. This Lewis acidic behavior is addressed first by application of the usual dual descriptor to a prototypical complex, namely ZnCl42-. However, the usual dual descriptor exhibits significant weaknesses to retrieve the electrophilic part on the metal cation of Zn-sal(ph)en complexes. The inclusion of the densities of the electronic excited states through the so-called state-specific dual descriptor allows us to recover successfully the appropriate reactivity of these chosen complexes with different diamine bridges in flexible to semirigid, and then to rigid ranges. The coordination of the Zn2+ is shown to be dictated by the geometry of the sal(ph)en ligand.

First author: Lin, PP, Theoretical study on the charge transport properties of three series of dicyanomethylene quinoidal thiophene derivatives, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 3044, (2019)
Abstract: It is very important to analyse the most advantageous connection style for quinoidal thiophene derivatives, which are used in n-type organic semiconductor transport materials. In the present work, the charge transport properties of three series of quinoidal thiophene derivatives, oligothiophene (series A), thienothiophene (series B) and benzothiophene (series C), are systematically investigated by employing full quantum charge transfer theory combined with kinetic Monte-Carlo simulation. The single crystal structures of the molecules we had constructed were predicted using the USPEX program combined with density functional theory (DFT) and considering the dispersion corrected. Our theoretical results expounded how the different connection styles, including oligo-, thieno-, and benzo-thiophene in the quinoidal thiophenes derivatives, effectively tune their electronic structures, and revealed how their intermolecular interactions affect the molecular packing patterns and hence their charge transport properties by symmetry-adapted perturbation theory (SAPT). In the meantime we also elucidated the role of end-cyano groups in noncovalent interactions. Furthermore, it is clarified that quinoidal thiophene derivatives show excellent carrier transport properties due to their optimal molecular stacking motifs and larger electronic couplings besides their low energy gap. In addition, our theoretical results demonstrate that quinoidal oligothiophene derivatives (n = 3-5) with more thiophene rings will have ambipolar transport properties, so quinoidal thienothiophene and benzothiophene derivatives should be promising alternatives as n-type OSCs. When we focused only on the electronic transport properties in the three series of molecules, quinoidal benzothiophene derivatives were slightly better than quinoidal oligothiophene or thienothiophene derivatives.

First author: Persaud, RR, Potential Energy Surface of Group 11 Trimers (Cu, Ag, Au): Bond Angle Isomerism in Au-3, JOURNAL OF PHYSICAL CHEMISTRY A, 123, 1198, (2019)
Abstract: Potential energy surfaces for the group 11 trimers were generated at various levels of coupled-cluster theory to examine the effects of Jahn-Teller distortions. Our calculations show that the lowest-energy conformer for Cu-3, Ag-3, and Au-3 is the B-2(2) (similar to 65 degrees isomer) without spin-orbit corrections. Spin-orbit corrections have negligible contributions to the relative energies for the angle dependence of the potential energy surfaces for Cu-3 and Ag-3. The inclusion of spin-orbit corrections for Au-3 makes the B-2(2) (similar to 65 degrees) and (2)A(1) (similar to 55 degrees) states approximately degenerate. A novel B-2(2) isomer of Au-3 at an obtuse angle of,similar to 125 degrees was also characterized, providing evidence for bond angle isomerism on the same B-2(2) potential energy surface. Spin-orbit corrections increase the barrier height between the B-2(2) (65) and B-2(2) (125) bond angle isomers of Au-3. The calculated symmetric stretch vibrational frequencies are in good agreement with the available experimental values. All frequencies calculated for the Au-3 B-2(2) (similar to 125 degrees) state are real, and there is at least one bound bending vibration for this state. Jahn-Teller parameters. Ca are also derived for each trimer.

First author: Izquierdo, MA, Theoretical Study of the Charge Transfer Exciton Binding Energy in Semiconductor Materials for Polymer:Fullerene-Based Bulk Heterojunction Solar Cells, JOURNAL OF PHYSICAL CHEMISTRY A, 123, 1233, (2019)
Abstract: Recent efforts and progress in polymer solar cell research have boosted the photovoltaic efficiency of the technology. This efficiency depends not only on the device architecture but also on the material properties. Thus, insight into the design of novel semiconductor materials is vital for the advancement of the field. This paper looks from a theoretical viewpoint into two of the factors for the design of semiconductor materials with applications to bulk heterojunction solar cells: the charge transfer exciton binding energy and the nanoscale arrangement of donor and acceptor molecules in blend systems. Being aware that the exciton dissociation of local excitons in charge transfer states initiates the charge generation process, the excited state properties of four oligomers (one donor-type: PEO-PPV; and three donor- acceptor-types: PTFB, PTB7, and PTB7-Th) and two fullerene derivatives ([60]PCBM and [70]PCBM), previously reported in the literature as having high electrical conductance, are studied. With such a study, the donor molecules, either of donor-type or donor-acceptor type, are screened as candidates for [60]PCBM- and/or [70]PCBM-based bulk heterojunctions. The charge transfer energy and charge transfer exciton binding energy of suitable donor:acceptor bulk heterojunctions, some of them not yet fabricated, are studied. Further, the charge transfer exciton binding energies of [60]PCBM- and [70]PCBM-based blends are compared. A combination of molecular dynamics simulations with calculations based on Kohn-Sham density functional theory (KS-DFT) and its time-dependent extension (KS-TDDFT) is used. An important feature of this work is that it incorporates the effect of the environment of the quantum chemical system in KS-DFT or KS-TDDFT calculations through a polarizable discrete reaction field (DRF). Our predictions in terms of the influence of the nanoscale arrangement of donor and acceptor molecules on the performance of organic solar cells indicate that bulk heterojunction morphologies for donor acceptor-type oligomers lead to their lowest excited states having charge transfer character. Further, we find that in terms of favorable charge transfer exciton binding energy, the PTB7-Th:[70]PCBM blends outperform the other blends.

First author: Chernyshev, AV, Operando XAS and UV-Vis Characterization of the Photodynamic Spiropyran-Zinc Complexes, JOURNAL OF PHYSICAL CHEMISTRY B, 123, 1324, (2019)
Abstract: Thermal and photoinduced processes accompanying complexation of photochromic spiropyrans (SPP) with Zn ions in acetone solution were characterized by means of UV-vis and X-ray absorption spectroscopies in operando regime. SPP ligands are usually transparent at lambda > 350 nm, but after mixing with Zn ions, they produce a stable colored (epsilon = 32 000-38 000 M-1 cm(-1)) complex with maximum absorption at 525 nm, which makes them a powerful tool for monitoring metal-ion concentration in solution. The complex revealed fluorescence and photochromic behavior under static irradiation with visible light with constant photoreaction quantum yield across its characteristic absorption band. Zn K-edge X-ray absorption spectra show prominent changes in Zn local atomic structure between free Zn ions and Zn complex. The pump-flow-probe scheme was adapted to measure operando changes in Zn coordination upon light irradiation. Within experimental time resolution, we have determined that 20 mu s after light irradiation, Zn ion is released out of the complex. This is the first example of the direct spectroscopic probe of the Zn photorelease from the spiropyran complex.

First author: Fantacci, S, Ab Initio Modeling of Solar Cell Dye Sensitizers: The Hunt for Red Photons Continues, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 123, 743, (2019)
Abstract: Despite the swift surge of lead halide perovskites, research in dye-sensitized solar cells (DSCs) has continued over the last few years, with a steady increase in record device efficiencies. A major requisite of an efficient solar cell sensitizer is that of showing an extended UV/Vis absorption spectrum closely matching that of solar radiation. This has given rise to what we call here the hunt for red photons, and ab initio computational modeling plays a major role in designing and screening new dyes with tailored characteristics. In this microreview, we highlight recent developments in modeling transition metal polypyridyl dyes by means of advanced ab initio simulations, including solvation and relativistic effects. We illustrate the molecular design rules that have led to the best performing ruthenium and osmium dyes to date, showing the information which can be extracted from ab initio simulations and how to exploit such information for engineering novel dye candidates.

First author: Galley, SS, Synthesis and Characterization of Tris-chelate Complexes for Understanding f-Orbital Bonding in Later Actinides, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 141, 2356, (2019)
Abstract: An isostructural family off-element compounds (Ce, Nd, Sm, Gd; Am, Bk, Cf) of the redox-active dioxophenoxazine ligand (DOPOq; DOPO = 2,4,6,8-tetra-tert-butyl-1-oxo-1H-phenoxazin-9-olate) was prepared. This family, of the form M(DOPOq)(3), represents the first nonaqueous isostructural series, including the later actinides berkelium and californium. The lanthanide derivatives were fully characterized using H-1 NMR spectroscopy and SQUID magnetometry, while all species were structurally characterized by X-ray crystallography and electronic absorption spectroscopy. In order to probe the electronic structure of this new family, CASSCF calculations were performed and revealed these systems to be largely ionic in contrast to previous studies, where berkelium and californium typically have a small degree of covalent character. To validate the zeroth order regular approximation (ZORA) method, the same CASSCF analysis using experimental structures versus UDFT-ZORA optimized structures does not exhibit sizable changes in bonding patterns. This shows that UDFT-ZORA combined with CASSCF could be a useful first approximation to predict and investigate the structure and electronic properties of actinides and lanthanides that are difficult to synthesize or characterize.

First author: Base, T, Icosahedral Carbaboranes with Peripheral Hydrogen-Chalcogenide Groups: Structures from Gas Electron Diffraction and Chemical Shielding in Solution, CHEMISTRY-A EUROPEAN JOURNAL, 25, 2313, (2019)
Abstract: Carbaboranes 1,2-(EH)(2) -closo-1,2-C2B10H10 (E=S, Se) were prepared, in the case of E= Se for the first time. Their semi-experimental equilibrium molecular structures were established by the concerted use of quantum-chemical calculations and gas electron diffraction. A method was developed and implemented to quantify the contribution of experimental data to each refined structural parameter. The accuracy of the experimental structures and those calculated at the MP2 level of theory were gauged by comparison of`experimental B-11 NMR chemical shifts with quantum-chemically computed values; the inclusion of electron correlation (GIAO-MP2) provided superior results. For the purpose of geometrical prediction, the remaining group 16 elements were considered, and the icosahedral structures for E =O and Te were also computed; for E =O the same theoretical approach was used as for E=S, and for E =Te a description similar to that for E = Se was employed.

First author: Straka, M, Spectroscopic and Computational Evidence of Intramolecular (AuH+)-H-I-N Hydrogen Bonding, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 58, 2011, (2019)
Abstract: Despite substantial evidence of short AuH-X contacts derived from a number of X-ray structures of Au-I compounds, the nature of (AuH)-H-I bonding in these systems has not been clearly understood. Herein, we present the first spectroscopic evidence for an intramolecular (AuH+)-H-I-N hydrogen bond in a [Cl-Au-L](+) complex, where L is a protonated N-heterocyclic carbene. The complex was isolated in the gas phase and characterized with helium-tagging infrared photodissociation (IRPD) spectra, in which H+-N-mode-derived bands evidence the intramolecular (AuH+)-H-I-N bond. Quantum chemical calculations reproduce the experimental IRPD spectra and allow to characterize the intramolecular AuH+-N bonding with a short r(AuH) distance of 2.17 angstrom and an interaction energy of approximately -10kcalmol(-1). Various theoretical descriptors of chemical bonding calculated for the AuH+-N interaction provide strong evidence for a hydrogen bond of moderate strength.

First author: Dong, X, Li2B24: the simplest combination for a three-ring boron tube, NANOSCALE, 11, 2143, (2019)
Abstract: Herein we introduce a strategy employing lithium atoms as a scaffold to stabilize an embryo for boron tubes. The systematical exploration of the potential energy surface via evolutionary algorithms allowed us to find that Li2B24 adopts a tubular structure formed by three stacked rings of eight borons each with two lithium atoms capping the tube. The lithium atoms are essential for stabilization because of the strong electrostatic interaction between the Li cations and the boron framework, and concomitantly, they compensate for the energy cost of distorting a quasi-planar or double ring B-24 cluster.

First author: Leroy, C, Sb-121/123 Nuclear Quadrupole Resonance Spectroscopy: Characterization of Non-Covalent Pnictogen Bonds and NQR Crystallography, JOURNAL OF PHYSICAL CHEMISTRY A, 123, 1030, (2019)
Abstract: Pnictogen (or pnicogen) bonding is an attractive interaction between the electrophilic region of group 15 elements (N, P, As, Sb, Bi) and a nucleophile. This interaction for which unique applications in catalysis have recently been uncovered continues to gain popularity. Here, we investigate a series of pnictogen-bonded cocrystals based on SbF3 and SbCl3, prepared via mechanochemical ball milling, with Sb-121/123 (I = S/2 and 7/2, respectively) nuclear quadrupole resonance (NQR) spectroscopy. Observed NQR frequency shifts upon cocrystallization are on the order of 0.1 to 10 MHz and are clearly diagnostic of the formation of pnictogen bonds to antimony. Further evidence for pnictogen bonding is obtained by complementary C-13 cross-polarization magic-angle spinning solid-state NMR experiments. DFT calculations of NMR parameters as well as natural localized molecular orbital analyses support the experimental findings and elucidate the electronic origins of the experimental NQR frequency shifts. This work provides insights into the changes in the antimony quadrupolar coupling constant upon pnictogen bonding: strikingly, the decreases noted here parallel those known for hydrogen bonds, but contrast with the increases reported for halogen bonds. The utility of the observed antimony nuclear quadrupolar coupling constants in constraining structural models of cocrystals for which diffraction-based structures are unavailable, i.e., a rudimentary implementation of NQR crystallography, is established. Overall, this work offers a new approach to understand emerging classes of electrophilic interactions and to contextualize them in the broader landscape of established chemical bonding paradigms.

First author: Aramburu, JA, Insight into Compounds with Cu(H2O)(6)(2+) Units: New Ideas for Understanding Cu2+ in Tutton Salts, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 3088, (2019)
Abstract: In the last 65 years the properties of Tutton salts containing Cu2+ cations have been interpreted on the basis of elongated complexes induced by a static Jahn-Teller effect (JTE). Through the analysis of experimental data and the results of first-principles calculations, we show here that such an idea, though widely followed, is not correct. By contrast, this work proves that the local geometry of Cu(H2O)(6)(2+) units in Tutton salts actually arises from a compressed octahedron although hidden by an additional orthorhombic instability fully unrelated to the JTE. For understanding this conclusion, it is crucial to consider the effects of the internal electric field, ER(r), created by the rest of the lattice ions on the electrons localized in the Cu(H2O)(6)(2+) unit. Indeed, the E-R(r) field in Tutton salts opens a gap between, similar to x(2)-y(2) and similar to 3z(2)-r(2) antibonding molecular orbitals that favors a hole in -3z(2)-r(2) and triggers an orthorhombic distortion in the XY plane that reasonably explains available experimental data. The conditions responsible for the orthorhombic instability are discussed pointing out the singularity of Cu2+ complexes in the realm of 3d divalent cations. For the sake of completeness the properties of Cu(H2O)(6)(2+) units in trigonal lattices, where a JTE is clearly observed, are analyzed in detail and compared to results of Cu2+ cations in cubic lattices. In the trigonal compounds, the force constant of the Jahn-Teller mode is shown to be smaller than that for hard ligands like O2- or F- but comparable to the softer ligand Cl-. This fact helps to promote the orthorhombic instability in the Cu(H2O)(6)(2+) complex when the hole is no longer in the similar to x(2)-y(2) orbital but in similar to 3z(2)-r(2).

First author: Rusakov, YY, Long-range relativistic heavy atom effect on H-1 NMR chemical shifts of selenium- and tellurium-containing compounds, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 119, 3088, (2019)
Abstract: Previously unknown manifestation of heavy atom effect on the NMR chemical shifts of beta- and gamma-protons initiated by the relativistic effects of the tellurium and selenium atoms has been investigated in the representative series of selenium- and tellurium-containing compounds. To approve the four-component density functional approach to be the appropriate tool for the investigation of the heavy atom on light atom effect (HALA), the benchmark calculations of the proton chemical shifts have been performed at the CCSD level using comprehensively chosen locally dense basis set with taking into account solvent, vibrational, and relativistic corrections. A good agreement with the experimental data was achieved. The magnitudes of the relativistic HALA corrections to beta- and gamma-proton chemical shifts were found to vary in a wide range, namely from -3.08 ppm for the gamma-proton of methyltelluraldehyde to 14.51 ppm for beta-proton in benzotelluraldehyde.

First author: Adams, RD, Multiple Aromatic C-H Bond Activations by an Unsaturated Dirhenium Carbonyl Complex, INORGANIC CHEMISTRY, 58, 2109, (2019)
Abstract: Reactions of Re-2(CO)(8)(mu-C6H5)(mu-H), 1, with naphthalene and anthracene have yielded the first multiply-CH activated arene products through the reductive elimination of benzene from 1 and multiple oxidative-additions of the dirhenium octacarbonyl grouping to these polycyclic aromatic compounds under very mild conditions. In addition, compound 1 was found to react with itself to yield the bis-Re-2-metalated C6H4 bridged compound Re-2(CO)(8)(mu-H)(mu-1,mu-3-C6H4)Re-2(CO)(8)(mu-H), 3. Reaction of 1 with naphthalene yielded two doubly CH activated isomers, Re-2(CO)(8)(mu-H)(mu-eta(2)-1,2-mu-eta(2)-3,4-C10H6)Re-2(CO)(8)(mu-H), 4, 41% yield, and Re-2(CO)(8)(mu-H)(mu-eta(2)-1,2-mu-eta(2)-5,6-C10H6)-Re-2(CO)(8)(mu-H), 5, via the mono CH activated intermediate Re-2(CO)(8)(mu-eta(2)-C10H7)(mu-H), 2. Compound 4 contains two Re-2(CO)(8)(mu-H) groups on one C-6 ring formed by CH activations at the 2- and 4-positions. Compound 5 contains two Re-2(CO)(8)(mu-H) groups; one formed by CH activation at the 2-position on one C-6 ring and the other formed by CH activation at the 6-position (or centrosymmetrically related 2′-position) on the second C-6 ring. The Re-2(CO)(8)(mu-H) groups are coordinated to the C-6 rings by binuclear sigma + pi coordination to two adjacent carbon atoms in the rings. Compound 1 reacts with anthracene to yield the mono-CH activated compound Re-2( CO)(8)(mu-eta(2)-1,2-C14H9) (mu-H), 6, and two doubly CH activated compounds, Re-2(CO)(8)(mu-H)(mu-eta(2)-1,2-mu-eta(2)-3,4-C14H8)Re-2(CO)(8)(mu-H), 7, and Re-2(CO)(8)(mu-H)(mu-eta(2)-1,2-mu-eta(2)-5,6-C14H8)Re-2(CO)(8)(mu-H), 8. Compounds 7 and 8 are isomers that are structurally similar to 4 and 5. Compounds 7 and 8 can also be obtained in good yields from the reaction of 6 with 1. In the presence of a 5/1 ratio of 1/anthracene, a small amount (5% yield) of the tetra-substituted anthracene product [Re-2( CO)(8)(mu-H)](4)(mu-eta(2)-1,2-mu-eta(2)-3,4-mu-eta(2)-5,6-mu-eta(2)-7,8-C14H6), 9, was formed. Compound 9 contains four sigma + pi coordinated Re-2(CO)(8)(mu-H) groups formed by oxidative additions of the CH bonds of anthracene to the Re-2(CO)(8) groups at the 2, 4, 6, and 8 positions of the three ring system. Molecular orbital calculations have been performed for all new compounds in order to develop an understanding of the bonding of the ring systems to the Re-2(CO)(8)(mu-H) groups. All new compounds were characterized by single-crystal X-ray diffraction analyses.

First author: Petelski, AN, Designing Self-Assembled Rosettes: Why Ammeline is a Superior Building Block to Melamine, CHEMISTRYOPEN, 8, 135, (2019)
Abstract: In supramolecular chemistry, the rational design of self-assembled systems remains a challenge. Herein, hydrogen-bonded rosettes of melamine and ammeline have been theoretically examined by using dispersion-corrected density functional theory (DFT-D). Our bonding analyses, based on quantitative Kohn-Sham molecular orbital theory and corresponding energy decomposition analyses (EDA), show that ammeline is a much better building block than melamine for the fabrication of cyclic complexes based on hydrogen bonds. This superior capacity is explained by both stronger hydrogen bonding and the occurrence of a strong synergy.

First author: Dalla Tiezza, M, Half-Sandwich Metal-Catalyzed Alkyne [2+2+2] Cycloadditions and the Slippage Span Model, CHEMISTRYOPEN, 8, 143, (2019)
Abstract: Half-sandwich Rh’ compounds display good catalytic activity toward alkyne [2+2+2) cycloadditions. A peculiar structural feature of these catalysts is the coordination of the metal to an aromatic moiety, typically a cyclopentadienyl anion, and, in particular, the possibility to change the bonding mode easily by the metal slipping over this aromatic moiety. Upon modifying the ancillary ligands, or proceeding along the catalytic cycle, hapticity changes can be observed; it varies from eta(5), if the five metal-carbon distances are identical, through eta(3)+eta(2), in the presence of allylic distortion, and eta(3), in the case of allylic coordination, to eta(1), if a sigma metal-carbon bond forms. In this study, we present the slippage span model, derived with the aim of establishing a relationship between slippage variation during the catalytic cycle, quantified in a novel and rigorous way, and the performance of catalysts in terms of turnover frequency, computed with the energy span model. By collecting and comparing new data and data from the literature, we find that the highest performance is associated with the smallest slippage variation along the cycle.

First author: Monticelli, M, Structural and Luminescent Properties of Homoleptic Silver(I), Gold(I), and Palladium(II) Complexes with nNHC-tzNHC Heteroditopic Carbene Ligands, ACS OMEGA, 4, 4192, (2019)
Abstract: Novel silver(I), gold(I), and palladium(II) complexes were synthesized with bidentate heteroditopic carbene ligands that combine an imidazol-2-ylidene (nNHC) with a 1,2,3-triazol-5-ylidene (tzNHC) connected by a propylene bridge. The silver(I) and gold(I) complexes were dinuclear species, [M-2(nNHC-tzNHC)(2)](PF6)(2) (M = Ag or Au), with the two bidentate ligands bridging the metal centers, whereas in the palladium(II) complex [Pd(nNHC-tzNHC)(2)]-(PF6)(2), the two ligands were chelated on the same metal center. Because of the presence of two different carbene units, isomers were observed for the gold(I) and palladium(II) complexes. The molecular structures of the head-to-tail isomer for gold(I) complexes, with a twisted or folded-syn conformation of the bridge between the carbene units, were determined by X-ray diffraction analysis. The study was completed with a systematic structural investigation through density functional theory (DFT) calculations. For palladium(II) species, the head-to-head form was structurally characterized. The dinuclear gold(I) complexes were emissive in the solid state in the blue region (PLQY up to 8%); time-dependent density functional theory (abbreviated as TD-DFT) calculations disclosed that the absorption bands have metal-to-ligand-charge-transfer character and evidenced that the emission occurs from the T-1 level (phosphorescence).

First author: Shyama, M, C-H center dot center dot center dot O interaction between cation and anion in amino acid-based ionic liquidsA DFT study in gas and solvent phase, STRUCTURAL CHEMISTRY, 30, 185, (2019)
Abstract: The interaction between anions and cations within amino acid-based ionic liquids (AAILs) are studied in the gas phase and in three different solvents (DMSO, water, and formamide). Structural and topological analyses of ion pairs signify that they interact via C-H center dot center dot center dot O hydrogen bond. In gas and solvent phase, the aliphatic amino acids (anions) interact strongly with EMIM (1-ethyl-3-methylimidazolium) and BMIM (1-butyl-3-methylimidazolium) cations. Further, the interaction between amino acid and EMIM cation is stronger due to large charge transfer from the electronegative oxygen atoms (carbonyl group) of the amino acids to the C-H bond of the imidazole ring. All the C-H center dot center dot center dot O bonds observed between the ions are red shifted and strong due to large interaction energy. The major contribution to the interaction energy is from electrostatic and orbital energies. The implicit solvents tend to increase the H center dot center dot center dot O distance of the AAILs. The increase in the chain length of cations irrespective of phase meagerly decreases the interaction between the ions. From the solvation energy, the reaction between solvents and AAILs are exothermic. AAILs possess higher solvation energy in DMSO. Overall, ionic liquids are highly stable in the gas phase and moderately stable in the solvents due to C-H center dot center dot center dot O bonds.

First author: De Oliveira, AZ, Segmented all-electron basis sets of triple zeta quality for the lanthanides: application to structure calculations of lanthanide monoxides, JOURNAL OF MOLECULAR MODELING, 25, 185, (2019)
Abstract: Nonrelativistic and relativistic (Douglas-Kroll-Hess, DKH) segmented all-electron Gaussian basis sets of valence triple zeta quality plus polarization functions (TZP) for the lanthanides were developed. As some atomic and molecular properties depend on a good description of the electrons far from the nuclei, these basis sets are augmented with diffuse functions, giving rise to the augmented TZP (ATZP) and ATZP-DKH basis sets. At the DKH level of theory, the B3LYP hybrid functional in conjunction with the TZP-DKH basis set were used to calculate the atomic charges and valence orbital populations of the lanthanide and oxygen atoms, the bond lengths, and the equilibrium dissociation energies of lanthanide monoxides. The DKH-B3LYP/ATZP-DKH polarizability of Yb and the DKH-M06/TZP-DKH first ionization energies of the lanthanides are also reported. Compared with the values obtained with a larger all-electron basis set, and theoretical and experimental data found in the literature, data obtained by our compact basis sets are verified to be accurate and reliable. Unlike effective core potential valence basis sets, our basis sets can also be employed in molecular property calculations that involve the simultaneous treatment of core and valence electrons.

First author: Levandowski, BJ, Diels-Alder reactivities of cycloalkenediones with tetrazine, JOURNAL OF MOLECULAR MODELING, 25, 185, (2019)
Abstract: Quantum chemical calculations were used to investigate the Diels-Alder reactivities for a series of cycloalkenediones with tetrazine. We find that the reactivity trend of cycloalkenediones toward tetrazine is opposite to cycloalkenes. The electrostatic interactions between the cycloalkenediones and tetrazine become more stabilizing as the ring size of the cycloalkenediones increases, resulting in lower activation energies. The origin of the more favorable electrostatic interactions and the accelerated reactivities of larger cycloalkenediones result from a stabilizing CH/ interaction that is not present in the reaction of the 4-membered cycloalkenedione. The Diels-Alder reactivity trend of cycloalkenediones toward tetrazine is opposite that of cycloalkenes. The increased reactivity of the 5- and 6-membered cycloalkenediones relative to the 4-membered cycloalkenedione is attributed to a stabilizing electrostatic CH/ interaction that is not present in the reaction of the 4-membered cycloalkenedione.

First author: Marchesi, A, Synthesis and emissive properties of a series of tetrahydro (imidazo[1,5-a]pyrid-3-yl)phenols: a new class of large Stokes shift organic dyes, DYES AND PIGMENTS, 161, 457, (2019)
Abstract: A series of 2-(5,6,7,8-tetrahydroimidazo[1,5-a]pyridin-3-yl)phenols with different substituents (R) in the para position with respect to the hydroxyl group, was synthesized. The photophysical properties of these species have been investigated in dichloromethane solution: they displayed intense fluorescence when excited with UV light (310-340 nm), with lambda(max) of emission varying in the range 430-530 nm and lifetime decay of few nanoseconds. A very large Stokes shift (up to 189 nm) and high absolute quantum yields (up to 0.72) were recorded for most of the compounds. Moreover, good tuning of the emission is observed according to the electronic features of the substituent R, and a linear correlation was found between the emission maxima of the compounds and the Hammett sigma(p) constants of R. Two of these (tetrahydroimidazo[1,5-a]pyridin-3-yl)phenols were then chosen for preliminary measurements of their photophysical properties when dispersed in a host polymeric matrix (PMMA).

First author: Papai, M, Theoretical Evidence of Solvent-Mediated Excited-State Dynamics in a Functionalized Iron Sensitizer, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 2056, (2019)
Abstract: The solvent-mediated excited-state dynamics of the COOH-functionalized Fe-carbene photosensitizer [Fe(bmicp)(2)](2+) (bmicp = 2,6-bis(3-methyl-imidazole-1-ylidine)-4-carboxy-pyridine) is studied by time-dependent density functional theory, as well as classical and quantum dynamics simulations. We demonstrate the crucial role of the polar acetonitrile solvent in stabilizing the metal-to-ligand charge transfer (MLCT) states of the investigated molecule using the conductor polarizable continuum model. This leads to dynamics that avoid sub-ps back electron transfer to the metal and an exceptionally long-lived (MLCT)-M-1 state that does not undergo sub-ps (MLCT)-M-1 -> (MLCT)-M-3 intersystem crossing as it is energetically isolated. We identify two components of the excited-state solvent reorganization process: an initial rotation (similar to 300 fs) and diffusional dynamics within the local cage surrounding the rotated solvent molecule (similar to 2 ps). Finally, it is found that the relaxation of the solvent only slightly affects the excited-state population dynamics of [Fe(bmicp)(2)](2+).

First author: Jones, LO, Germanium Fluoride Nanocages as Optically Transparent n-Type Materials and Their Endohedral Metallofullerene Derivatives, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 141, 1672, (2019)
Abstract: Carbon- and silicon-based n-type materials tend to suffer from instability of the corresponding radical anions. With DFT calculations, we explore a promising route to overcome such challenges with molecular nanocages which utilize the heavier element Ge. The addition of fluorine substituents creates large electron affinities in the range 2.5-5.5 eV and HOMO-LUMO gaps between 1.6 and 3.2 eV. The LUMOs envelop the surfaces of these structures, suggesting extensive delocalization of injected electrons, analogous to fullerene acceptors. Moreover, these GenFn inorganic cages are found to be transparent in the UV-visible region as probed with their excited states. Their capacitance, linear polarizabilities, and dielectric constants are computed and found to be on the same order of magnitude as saturated oligomers and some extended pi-organics (azobenzenes). Furthermore, we explore fullerene-type endohedral isomers, i.e., cages with internal substituents or guest atoms, and find them to be more stable than the parent exohedral isomers by up to -206.45 kcal mol(-1). We also consider the addition of Li, He, Cs, and Bi, to probe the utility of the exo/endo cages as host-guest systems. The endohedral He/Li@F-8@ Ge60F52 cages are significantly more stable than their parent exohedral isomers He/Li@Ge60F52 by -182.46 and -49.22 kcal mol(-1), respectively. The energy of formation of endohedral He@F-8@Ge60F52 is exothermic by-10.4 kcal mol(-1), while Cs and Bi guests are too large to be accommodated but are stable in the exohedral parent cages. Conceivable applications of these materials include n-type semiconductors and transparent electrodes, with potential for novel energy storage modalities.

First author: Weiss, S, eta(3)-Allyl Coordination at Pb(II), ORGANOMETALLICS, 38, 417, (2019)
Abstract: Allylmagnesium chloride and methyl-propenyl-magnesium bromide were reacted with bulky substituted organolead and organotin halides (Ar*PbBr)(2), (Ar’PbBr)(2), (Ar*SnCl)(2) (Ar* = 2,6-trip(2)C(6)H(3)-, trip = 2,4,6-triisopropylphenyl, Ar’ = 2,6-mes(2)C(6)H(3)-, mes = 2,4,6-trimethylphenyl). The allyl ligand coordinates in an eta(3)-coordination mode at organoplumbylene fragments. In the solid state as well as in solution, eta(3)-coordination was characterized by crystal structure analysis and Saunders’ isotopic perturbation technique. For the plumbylene Ar*Pb(C3H5), a solid state Pb-207 magic angle spinning (MAS) NMR spectrum could be obtained. The isotropic chemical shift is -435 ppm, and the magnitude of the Pb-207 chemical shift tensor of 7000(500) ppm is among the greatest observed experimentally. The methylallyl ligand coordinated at a plumbylene fragment exhibits two short and one long Pb-C interaction. In reaction with aniline, the allyl ligand reacts as a leaving group to give amidoplumbylenes.

First author: Rogachev, AY, Placing Metal in the Bowl: Does Rim Alkylation Matter?, ORGANOMETALLICS, 38, 552, (2019)
Abstract: In-depth theoretical analysis of the consequences of methylation of the rim sites of corannulene is completed. The full set of derivatives ranging from parent C20H10 to fully substituted C-20(CH3)(10) has been evaluated, revealing consistent trends along the series. The controlled one-electron chemical reduction of selected methylated corannulenes, such as monomethyl- (C20H9(CH3)), sym-pentamethyl- (1,3,5,7,9-C20H5(CH3)(5)), and decamethylcorannulene (C-20(CH3)(10)) has also been investigated. Cesium metal was used as a reducing agent to access endo complexes having cesium ion placed inside the concave cavity of the monoreduced bowls. Two products, [{Cs+(18-crown-6)}{C20H9(CH3)(-)}] (1) and [{Cs+(18-crown-6)}{C20H5(CH3)(5)(-)}] (2), have been crystallized in the presence of 18-crown-6 ether and crystallographically characterized to confirm the concave cesium ion coordination. The direct structural comparison of 1 and 2 with the complex of unsubstituted corannulene, [{Cs+(18-crown-6)}{C20H10-}] (3), has been conducted. Furthermore, the nature and strength of metal binding for the series of concave cesium complexes with methyl-substituted corannulene bowls has been evaluated using different theoretical methods.

First author: Jiang, QW, DFT Insights into the Interfacial Chemical Behavior of Hybrid LDH/GO Nanocomposites, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 1692, (2019)
Abstract: Hybrid layered double hydroxides (LDHs)/graphene oxide (GO) nanocomposites are novel two-dimen-sional (2-D) materials applied in extensive fields, which take advantages of the synergistic effect of LDH and GO at the composite interface. However, the interfacial interaction mechanism determining the LDH/GO nanocomposite properties still remains to be explored. Herein, we used density functional theory to comprehensively illustrate interfacial interactions, as well as structural and electronic properties of Mg/Al LDH/GO nanocomposites. Our results, for the first time, reveal that there exists unique water generated chemical interaction during the LDH/GO combining process. The generated interfacial water molecules play a key role in maintaining the nanocomposites by forming complicated and diverse interfacial hydrogen bond structures. Moreover, the transfer of the hydrogen atom from LDH to the epoxy group resulting in hydroxyl was also observed. The results provide hints for interpreting previous experimental observations. There is interfacial charge transfer from LDH to GO and water molecules. The electrical properties of the LDH component in the composite can be modulated by properly varying the epoxy/ hydroxyl ratio on GO. The current results might prove to be instrumental in the design of 2-D heterostructural LDH/GO composites.

First author: Dutta, S, Strengths of different Lewis bases in stabilizing titanium fluorides: A theoretical insight, INORGANICA CHIMICA ACTA, 485, 162, (2019)
Abstract: Detailed investigations of the electronic structure and bonding scenario in various cis-TiF4D2 and [TiF5D](-) (D = neutral donor ligand) complexes have been presented using computational methods (R-M06-L/6-311++G(d,p)//R-M06-L/6-311 + G(d)). We have also computed the formation energies of these complexes for different reaction routes in the gas phase and acetonitrile solvent medium. The donor-acceptor nature of the TiD1 and TiD2 bonds in the cis-TiF4D2 complexes are confirmed by QTAIM calculations. Moreover, EDA-NOCV analysis was performed to gain better insight into the bonding situation in this class of complexes and also to obtain a relative scale of both intrinsic and overall Lewis basicity for the ligands, considering TiF4 as reference Lewis acid. The calculations reveal that with respect to TiF4, abnormal N-heterocyclic carbene (aNHC) exhibits both overall and intrinsically strongest Lewis basicity, whereas intrinsically and overall weakest Lewis basicity are shown by CO and AsH3, respectively. Furthermore, the isomerism of mixed chloro and fluoro titanium complexes supported by neutral ligands is extensively studied to shed light on the dependence of the relative stabilities of these isomers on intrinsic Lewis base strength of the ligands.

First author: Hamlin, TA, Elucidating the Trends in Reactivity of Aza-1,3-Dipolar Cycloadditions, EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, 2019, 378, (2019)
Abstract: This report describes a density functional theory investigation into the reactivities of a series of aza-1,3-dipoles with ethylene at the BP86/TZ2P level. A benchmark study was carried out using QMflows, a newly developed program for automated workflows of quantum chemical calculations. In total, 24 1,3-dipolar cycloaddition (1,3-DCA) reactions were benchmarked using the highly accurate G3B3 method as a reference. We screened a number of exchange and correlation functionals, including PBE, OLYP, BP86, BLYP, both with and without explicit dispersion corrections, to assess their accuracies and to determine which of these computationally efficient functionals performed the best for calculating the energetics for cycloaddition reactions. The BP86/TZ2P method produced the smallest errors for the activation and reaction enthalpies. Then, to understand the factors controlling the reactivity in these reactions, seven archetypal aza-1,3-dipolar cycloadditions were investigated using the activation strain model and energy decomposition analysis. Our investigations highlight the fact that differences in activation barrier for these 1,3-DCA reactions do not arise from differences in strain energy of the dipole, as previously proposed. Instead, relative reactivities originate from differences in interaction energy. Analysis of the 1,3-dipole-dipolarophile interactions reveals the reactivity trends primarily result from differences in the extent of the primary orbital interactions.

First author: Mitoraj, MP, N-Thiophosphorylthioureas RNHC(S)NHP(S)(OiPr)(2) as an Excellent Platform for Studying the Synergy between Hydrogen-Hydrogen Bonding and Other Families of Non-Covalent Interactions, EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, 2019, 493, (2019)
Abstract: A family of thiourea based derivatives, RNHC(S)NHP(S)(OiPr)(2) [R = Ph (YEZNUN), 2-MeC6H4 (AQOYAH), 2,5-Me2C6H3 (WARREO), 2,6-Me2C6H3 (GUJGUO), 2,4,6-Me3C6H2 (AQOYEL), PhNH (QORXUR), 1-naphthyl (MOWPEU)], has been studied to understand the synergy between dihydrogen and other (non)conventional non-covalent interactions. It was established that all monomers are stabilized through intramolecular dihydrogen C-H H -C interactions. Additionally, C-H interactions are noted in AQOYAH , WARREO, and MOWPEU; N-H O interactions in AQOYAH , and WARREO; C-H S interactions in GUJGUO , YEZNUN, and AQOYEL; N-H S interactions in GUJGUO , AQOYEL, MOWPEU, and YEZNUN; and N-H N interactions in QORXUR . The crystal structures of all the thioureas are further stabilized by the most pronounced intermolecular C-H H -C interactions followed by N-H S and C -H S with the formation of centrosymmetric R-2( 2)(8) dimers. These non-covalent interactions are augmented by the stacking in YEZNUN and MOWPEU ; C-H in WARREO , GUJGUO, AQOYEL and MOWPEU; N-H in QORXUR . The synergy between intra- and intermolecular C-H H -C and other types of non-covalent interactions lead to the extraordinary stability of these systems as indicated by the ETS-NOCV Scheme Although the London dispersion forces cover approximate to 70-80% of the overall C-H H -C stabilization, the covalent-like charge delocalization based on depletion of electron charge from the sigma(C-H) orbitals to the inter-atomic H H region contributes notably up to 15%.

First author: Tian, JN, Theoretical investigation of U(I) arene complexes: is the elusive monovalent oxidation state accessible?, NEW JOURNAL OF CHEMISTRY, 43, 1469, (2019)
Abstract: Commonly accepted uranium oxidation states in molecular complexes are III+ to VI+. Recently, this has been extended experimentally by the synthesis of seminal U(II) complexes, Y center dot[U(Cp’)(3)] and Y center dot[URE] (Y = K+(2.2.2-cryptand), Cp’ = C5H4SiMe3, H3RE = ((ArOH)-Ar-Ad,Me)(3)mesitylene and Ad = adamantyl). Relativistic density functional theory has been applied to explore whether the uranium oxidation state (+I) is possibly accessible. Calculations show that the U() complex of a heterocalix[4]arene (H2L) is energetically stable. It features a 5f(5)-dominated electronic configuration, four delta(U-Ar)-bond orbitals and a moderate U-II/U-I reduction potential. Its stability and structural/bonding/energetic properties were corroborated by comparisons with theoretically designed complexes [U-I(Cp)(3)](2-) and [(URE)-R-I](2-).

First author: Vorobyev, V, Infrared Detection with Temperature Sweep for Stability Determination of Ru-ON Metastable States, INORGANIC CHEMISTRY, 58, 1007, (2019)
Abstract: A novel method is proposed for studying the thermal decay of the oxygen-coordinated nitrosyl metastable states. Having examined 18 different ruthenium nitrosyl complexes, we observed that, upon photoinduced rotation from Ru-NO to Ru-ON coordination, the frequency of the nitrosyl valence bands shifts, on average, by 126 +/- 15 cm(-1). The thermal stability of the product Ru-ON state is qualitatively characterized (decay temperature, Arrhenius activation energy, and pre-exponential factor) using infrared absorption of the NO group, in comparison with the reference complex(es), which are all heated in the same KBr disk during temperature sweep.

First author: Anderson, CM, Competitive Intramolecular Amination as a Clock for Iron-Catalyzed Nitrene Transfer, INORGANIC CHEMISTRY, 58, 1107, (2019)
Abstract: Reaction of the complex [(Tp(Ph,Me))Fe-II(NCMe)(3)]BF4, where Tp(Ph,Me) = hydrotris(3-phenyl,5-methyl-1-pyrazolyl)borate, with the iodonium heteroylide PhI=NTs (1.5 equiv) is proposed to result in the insertion of N-tosylnitrene into one C-H bond at the ortho ring position of a 3-pyrazole phenyl substituent; subsequent deprotonation of the nascent aniline and one-electron oxidation of iron forms TsNH2 (0.5 equiv) as a coproduct. The covalent ligand modification and oxidation results in an intense purple-brown anilinato-iron(III) LMCT chromophore. This intramolecular reaction is utilized as a consistent clock to determine relative rates of competitive intermolecular nitrene transfer to added substrates, specifically to para-substituted styrenes and thioanisoles. Prior addition of substrate to the reaction of PhI=NTs with the iron(II) complex attenuates the CT absorbance of the equilibrium solution. Fitting of the concentration dependent absorption data gives the ratio of intra-versus intermolecular nitrene transfer. Because the former is independent of substrate, ratios for various substrates are directly comparable, and this approach enables acquisition of data for a single substrate under nearly stoichiometric, as opposed to competitive catalytic, conditions. Hammett analyses of such data are consistent with an electrophilic intermediate consistent with known or suspected imidoiron(IV) complexes. Because this intermediate was not observed directly, plausible geometric and electronic structures were modeled and assessed using density functional theory.

First author: Bi, YT, Heterobimetallic Uranium-Nickel/Palladium/Platinum Complexes of Phosphinoaryl Oxide Ligands: A Theoretical Probe for Metal-Metal Bonding and Electronic Spectroscopy, INORGANIC CHEMISTRY, 58, 1290, (2019)
Abstract: Heterobimetallic uranium-transition metal (UTM) complexes have abundant active centers (two metals and several ancillary ligands with various donor atoms) and possible metal-metal bonding interaction, leading to diversified electronic structures and rather complicated electronic transition types. In this regard, a comprehensive and systematic theoretical study is highly desired although challenging. In the work, density functional theory (DFT) was utilized to examine a series of uranium-group 10 metal complexes supported by bidentate phosphinoaryl oxide ligands (labeled as L). TM (Ni, Pd, and Pt), uranium oxidation state (IV and III) and axial donor (I, Br, Cl, F, Me3SiO, and vacant) were varied. Calculations demonstrate an intrinsic TM -> U dative bond. The order of bond strength of U-Ni > U-Pt > U-Pd is suggested by the formal shortness ratios, quantum theory of atoms in molecule (QTAIM) data, interaction energy (E-int), and bond orders calculated at various levels of theory. It is further evidenced by relativistic effects of heavy metal, natural orbital population and electronic spectroscopy. Regarding U-Ni complexes with different axial donors, metal-metal distances are found to be linearly correlated with QTAIM data/E-int/bond orders. Experimental UV-vis-NIR spectra were well reproduced by time-dependent DFT calculations. Complicated visible-light absorption bands, whose understanding remains unclear for many experimentally known heterobimetallic complexes, were rationalized in the work, along with NIR bands assigned as 5f -> 5f transitions.

First author: Butova, VV, Partial and Complete Substitution of the 1,4-Benzenedicarboxylate Linker in UiO-66 with 1,4-Naphthalenedicarboxylate: Synthesis, Characterization, and H-2-Adsorption Properties, INORGANIC CHEMISTRY, 58, 1607, (2019)
Abstract: We describe the synthesis and corresponding full characterization of the set of UiO-66 metalorganic frameworks (MOFs) with 1,4-benzenedicarboxylate (C6H4(COOH)(2), hereafter H2BDC) and 1,4-naphthalenedicarboxylate (C10H6(COOH)(2), hereafter H2NDC) mixed linkers with NDC contents of 0, 25, 50, and 100%. Their structural (powder X-ray diffraction, PXRD), adsorptive (N-2, H-2, and CO2), vibrational (IR/Raman), and thermal stability (thermogravimetric analysis, TGA) properties quantitatively correlate with the NDC content in the material. The UiO-66 phase topology is conserved at all relative fractions of BDC/NDC. The comparison between the synchrotron radiation PXRD and 77 K N-2-adsorption isotherms obtained on the 50:50 BDC/NDC sample and on a mechanical mixture of the pure BDC and NDC samples univocally proves that in the mixed linkers of the MOFs the BDC and NDC linkers are shared in each MOF crystal, discarding the hypothesis of two independent phases, where each crystal contains only BDC or NDC linkers. The careful tuning of the NDC content opens a way for controlled alteration of the sorption properties of the resulting material as testified by the H-2-adsorption experiments, showing that the relative ranking of the materials in H-2 adsorption is different in different equilibrium-pressure ranges: at low pressures, 100NDC is the most efficient sample, while with increasing pressure, its relative performance progressively declines; at high pressures, the ranking follows the BDC content, reflecting the larger internal pore volume available in the MOFs with a higher fraction of smaller linkers. The H-2-adsorption isotherms normalized by the sample BrunauerEmmettTeller specific surface area show, in the whole pressure range, that the surface-area-specific H-2-adsorption capabilities in UiO-66 MOFs increase progressively with increasing NDC content. Density functional theory calculations, using the hybrid B3LYP exchange correlation functional and quadruple-zeta with four polarization functions (QZ4P) basis set, show that the interaction of H-2 with the H2NDC linker results in an adsorption energy larger by about 15% with respect to that calculated for adsorption on the H2BDC linker.

First author: Deng, JD, Exploring the electrochemical properties of hole transporting materials from first-principles calculations: an efficient strategy to improve the performance of perovskite solar cells, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 1235, (2019)
Abstract: Perovskite solar cells (PSCs) have been achieved with impressively dynamic improvement in power conversion efficiency (PCE), becoming the hottest topic in photovoltaics. One of the hot topics is to develop inexpensive and efficient hole transporting materials (HTMs). In the present work, we systematically investigated the impact of different atoms in the heteromerous structure on the performance of perovskite solar cells. In addition, the influence of the structural modification of the HTM molecular building blocks was also revealed. To further understand the relationship between the charge-transport properties and the structural modification, the electronic properties, reorganization energy, and hole transporting properties of a series of organic hole transporting materials were investigated using first-principles calculations combined with Marcus theory. Moreover, the orientation function (phi) (V, , r, , ; phi) was applied to quantitatively evaluate the overall carrier mobility of HTMs in PSCs. It is revealed that this model predicts the hole mobility of HTMs correctly. The calculated results indicate that hole transporting materials with heteroatoms and larger dimensional structures show higher hole mobility, which may significantly improve the photovoltaic performance of PSCs.

First author: Venkataramanan, NS, Structure, stability, and nature of bonding between high energy water clusters confined inside cucurbituril: A computational study, COMPUTATIONAL AND THEORETICAL CHEMISTRY, 1148, 44, (2019)
Abstract: The structure and stability of the high energy water molecules inside the CB7 cavity was studied using the dispersion corrected density functional theory (DFT) and molecular dynamics (MD). The intermolecular distance between the O and H in the water molecule was found to decrease upon the encapsulation of water molecules inside the cavity, indicating the increase in the stability of water clusters. The computed binding energies were found to be sensitive to the choice of functional. Energy decomposition analysis (EDA) shows that the repulsive Pauli interaction decides the stability of the water complex. In all the encapsulated systems, except the eight water clusters, the electrostatic interactions have supremacy over the dispersive term, due to the large polarization induced by the water clusters. Molecular electrostatic potentials of entrapped systems show the charge distribution between CB7 and water clusters. QTAIM analysis indicates the existence of noncovalent intramolecular interactions between CB7 and water clusters and ellipticity values to be least for 8H(2)O@CB7. The topological of p(r) fields at the undo nitrogen plane in CB7, proves the stronger bonding with water molecules. Thus, entrapped water molecules are not electronically innocent inside the cage and have noncovalent interaction with hydrophobic part of CB7 molecule. Atom centered Density Matrix Propagation (ADMP) molecular dynamic studies shows that the water clusters are stable with respect to their isolated cluster geometry, inside the cucurbituril and the change in potential energy surface is due to the distortion in the geometry of the CB7 unit.

First author: Humphries, ME, Weak acids with super-electron-donor dimetal complexes: Synergy in bifunctional activity, POLYHEDRON, 158, 471, (2019)
Abstract: Dimetal paddlewheel complexes with bicyclic guanidine ligands are extremely strong thermodynamic electron donors. As a probe of the chemical potential and sites for chemical reactivity of these complexes, the interaction of Mo-2(TEhpp)(4) with weak acids was investigated (TEhpp is the anion of the bicyclic guanidine 3,3,9,9-tetraethyl-1,5,7-triazabicyclo[4.4.0.]dec-4-ene). Mo-2(TEhpp)(4) is readily protonated by acetic acid and trifluoroacetic acid as expected, but surprisingly by a mechanism that is more complicated than a simple acid-base proton exchange. Electrochemistry measurements of the shifts in potentials with successive additions of acid reveals that the conjugate base of the acid plays a critical role throughout the reaction. Computations indicate that initially the acid hydrogen bonds to a TEhpp nitrogen atom bound to the metal, and then a facile rearrangement of the conjugate base toward the axial site of the Mo-Mo bond concomitantly results in protonation of the nitrogen atom. Interestingly, the dimetal complex is bifunctional in this process, acting as a nucleophile at the nitrogen atoms of the TEhpp ligands, and as an electrophile at the Mo-Mo axial bond sites. The protonation requires a novel synergism of these disparate bonding interactions, in which protonation is not favored without enhancement by the coordinated base, and coordination of the base is enhanced by the protonation.

First author: Hernandez-Esparza, R, GPUs as boosters to analyze scalar and vector fields in quantum chemistry, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 119, 471, (2019)
Abstract: The analysis of scalar and vector fields in quantum chemistry is an essential task for the computational chemistry community, where such quantities must be evaluated rapidly to perform a particular study. For example, the atoms in molecules approach proposed by Bader has become popular; however, this method demands significant computational resources to compute the involved tasks in short times. In this article, we discuss the importance of graphics processing units (GPU) to analyze electron density, and related fields, implementing several scalar, and vector fields within the graphics processing units for atoms and molecules (GPUAM) code developed by a group of the Universidad Autonoma Metropolitana in Mexico City. With this application, the quantum chemistry community can perform demanding computational tasks on a desktop, where CPUs and GPUs are used to their maximum capabilities. The performance of GPUAM is tested in several systems and over different GPUs, where a GPU installed in a workstation converts it to a robust high-performance computing system.

First author: Svatunek, D, Chemoselectivity of Tertiary Azides in Strain-Promoted Alkyne-Azide Cycloadditions, CHEMISTRY-A EUROPEAN JOURNAL, 25, 754, (2019)
Abstract: The strain-promoted alkyne-azide cycloaddition (SPAAC) is the most commonly employed bioorthogonal reaction with applications in a broad range of fields. Over the years, several different cyclooctyne derivatives have been developed and investigated in regard to their reactivity in SPAAC reactions with azides. However, only a few studies examined the influence of structurally diverse azides on reaction kinetics. Herein, we report our investigations of the reactivity of primary, secondary, and tertiary azides with the cyclooctynes BCN and ADIBO applying experimental and computational methods. All azides show similar reaction rates with the sterically non-demanding cyclooctyne BCN. However, due to the increased steric demand of the dibenzocyclooctyne ADIBO, the reactivity of tertiary azides drops by several orders of magnitude in comparison to primary and secondary azides. We show that this chemoselective behavior of tertiary azides can be exploited to achieve semiorthogonal dual-labeling without the need for any catalyst using SPAAC exclusively.

First author: Coubrough, HM, Supramolecular Self-Sorting Networks using Hydrogen-Bonding Motifs, CHEMISTRY-A EUROPEAN JOURNAL, 25, 785, (2019)
Abstract: A current objective in supramolecular chemistry is to mimic the transitions between complex self-sorted systems that represent a hallmark of regulatory function in nature. In this work, a self-sorting network, comprising linear hydrogen motifs, was created. Selecting six hydrogen-bonding motifs capable of both high-fidelity and promiscuous molecular recognition gave rise to a complex self-sorting system, which included motifs capable of both narcissistic and social self-sorting. Examination of the interactions between individual components, experimentally and computationally, provided a rationale for the product distribution during each phase of a cascade. This reasoning holds through up to five sequential additions of six building blocks, resulting in the construction of a biomimetic network in which the presence or absence of different components provides multiple unique pathways to distinct self-sorted configurations.

First author: Iype, E, Machine learning model for non-equilibrium structures and energies of simple molecules, JOURNAL OF CHEMICAL PHYSICS, 150, 785, (2019)
Abstract: Predicting molecular properties using a Machine Learning (ML) method is gaining interest among research as it offers quantum chemical accuracy at molecular mechanics speed. This prediction is performed by training an ML model using a set of reference data [mostly Density Functional Theory (DFT)] and then using it to predict properties. In this work, kernel based ML models are trained (using Bag of Bonds as well as many body tensor representation) against datasets containing non-equilibrium structures of six molecules (water, methane, ethane, propane, butane, and pentane) to predict their atomization energies and to perform a Metropolis Monte Carlo (MMC) run with simulated annealing to optimize molecular structures. The optimized structures and energies of the molecules are found to be comparable with DFT optimized structures, energies, and forces. Thus, this method offers the possibility to use a trained ML model to perform a classical simulation such as MMC without using any force field, thereby improving the accuracy of the simulation at low computational cost.

First author: Xie, JX, Promoted cobalt metal catalysts suitable for the production of lower olefins from natural gas, NATURE COMMUNICATIONS, 10, 785, (2019)
Abstract: Due to the surge of natural gas production, feedstocks for chemicals shift towards lighter hydrocarbons, particularly methane. The success of a Gas-to-Chemicals process via synthesis gas (CO and H-2) depends on the ability of catalysts to suppress methane and carbon dioxide formation. We designed a Co/Mn/Na/S catalyst, which gives rise to negligible Water-Gas-Shift activity and a hydrocarbon product spectrum deviating from the Anderson-Schulz-Flory distribution. At 240 degrees C and 1 bar, it shows a C-2-C-4 olefins selectivity of 54%. At 10 bar, it displays 30% and 59% selectivities towards lower olefins and fuels, respectively. The spent catalyst consists of 10 nm Co nanoparticles with hcp Co metal phase. We propose a synergistic effect of Na plus S, which act as electronic promoters on the Co surface, thus improving selectivities towards lower olefins and fuels while largely reducing methane and carbon dioxide formation.

First author: Inan, D, Tailoring Photophysical Processes of Perylene-Based Light Harvesting Antenna Systems with Molecular Structure and Solvent Polarity, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 36, (2019)
Abstract: The excited-state dynamics of perylene-based bichromophoric light harvesting antenna systems has been tailored by systematic modification of the molecular structure and by using solvents of increasing polarity in the series toluene, chloroform, and benzonitrile. The antenna systems consist of blue light absorbing naphthalene monoimide (NMI) energy donors (D1, D2, and D3) and the perylene derived green light absorbing energy acceptor moieties, 1,7-perylene-3,4,9,10-tetracarboxylic tetrabutylester (A1), 1,7-perylene-3,4,9,10-tetracarboxylic monoimide dibutylester (A2), and 1,7-perylene-3,4,9,10-tetracarboxylic bisimide (A3). The design of these antenna systems is such that all exhibit ultrafast excitation energy transfer (EET) from the excited donor to the acceptor, due to the effective matching of optical properties of the constituent chromophores. At the same time, electron transfer from the donor to the excited acceptor unit has been limited by the use of a rigid and nonconjugated phenoxy bridge to link the donor and acceptor components. The antenna molecules D1A1, D1A2, and D1A3, which bear the least electron-rich energy donor, isopentylthio-substituted NMI D1, exhibited ultrafast EET (tau(EET) similar to 1 ps) but no charge transfer and, resultantly, emitted a strong yellow-orange acceptor fluorescence upon excitation of the donor. The other antenna molecules D2A2, D2A3, and D3A3, which bear electron-rich energy donors, the amino-substituted NMIs D2 and D3, exhibited ultrafast energy transfer that was followed by a slower (ca. 20-2000 ps) electron transfer from the donor to the excited acceptor. This charge transfer quenched the acceptor fluorescence to an extent determined by molecular structure and solvent polarity. These antenna systems mimic the primary events occurring in the natural photosynthesis, i.e., energy capture, efficient energy funneling toward the central chromophore, and finally charge separation, and are suitable building blocks for achieving artificial photosynthesis, because of their robustness and favorable and tunable photophysical properties.

First author: Ai, PF, Dual Emission of a Cyclic Hexanuclear Gold(I) Complex. Interplay between Au-3 and Au-2 Ligand-Supported Luminophores, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 915, (2019)
Abstract: Finding diverse and tunable molecular structures is relevant toward the design of functional nanostructures. The photoluminescence of complex [Au2Cl(mu-P-C-kappa P,kappa C,kappa N)](3) (1), featuring a ligand-supported hexanuclear Au(I) framework compromising a triangular Au-3 core of which each apex is connected to an external Au(I) center, has revealed a remarkable dual emission at room temperature. The emission bands display maxima centered at lambda(em) = 512 and 694 nm with Stokes shifts of 19 530 and 14 410 cm(-1) and are attributed to the radiative relaxation of two excited-states centered on the central Au-6 skeleton arising from Sd sigma* -> 6p sigma excitation. As suggested by the strikingly different dioxygen dependency of the relative intensity of the two emission bands, the observed dual emission can be tentatively attributed to the incomplete equilibration between two close-lying-emissive excited states with singlet and triplet characters, most likely because of the slow intersystem crossing process, yielding green fluorescence and red phosphorescence, respectively; this phenomenon is rarely observed in heavy element compounds. Based on theoretical calculations, these excited states originated from two different substructure luminophores of the molecular skeleton, mainly (i) the Au-3 core and (ii) one specific Au-2 unit. Thus, the dual luminescence of 1 originates from the noteworthy inclusion of two luminophores within the overall molecular structure. Both solution and solid-state emission spectra show similar characteristics owing to the intramolecular nature of the suggested luminescence mechanism. Such luminophores can be envisaged as novel metalloligands to be incorporated in larger gold nanoclusters toward the development of intense luminescent molecular devices.

First author: Buettner, CS, Mechanistic investigation into the C( sp3)- H acetoxylation of morpholinones, CHEMICAL SCIENCE, 10, 83, (2019)
Abstract: The study of a selective palladium(ii)-catalyzed C(sp(3))-H acetoxylation reaction on a class of cyclic alkyl amines is reported. Computational modelling and kinetic studies were used to provide support for a mechanism involving selective C-O bond formation from a -aminoalkyl-Pd(iv) intermediate. The C-O bond forming step was computed to occur by a dissociative ionization mechanism followed by an S(N)2 process involving external acetate attack at the C-Pd(iv) bond. This pathway was computed to be of lowest energy with no competing C-N products observed. Additionally, with a few modifications to reaction conditions, preliminary studies showed that this process could be rendered enantioselective in the presence of a non-racemic BINOL-phosphoric acid.

First author: Ariai, J, “Through-Space” Relativistic Effects on NMR Chemical Shifts of Pyridinium Halide Ionic Liquids, CHEMPHYSCHEM, 20, 108, (2019)
Abstract: We have investigated, using two-component relativistic density functional theory (DFT) at ZORA-SO-BP86 and ZORA-SO-PBE0 level, the occurrence of relativistic effects on the H-1, C-13, and N-15 NMR chemical shifts of 1-methylpyridinium halides [MP][X] and 1-butyl-3-methylpyridinium trihalides [BMP][X-3] ionic liquids (ILs) (X=Cl, Br, I) as a result of a non-covalent interaction with the heavy anions. Our results indicate a sizeable deshielding effect in ion pairs when the anion is I- and I-3(-). A smaller, though nonzero, effect is observed also with bromine while chlorine based anions do not produce an appreciable relativistic shift. The chemical shift of the carbon atoms of the aromatic ring shows an inverse halogen dependence that has been rationalized based on the little C-2s orbital contribution to the sigma-type interaction between the cation and anion. This is the first detailed account and systematic theoretical investigation of a relativistic heavy atom effect on the NMR chemical shifts of light atoms in the absence of covalent bonds. Our work paves the way and suggests the direction for an experimental investigation of such elusive signatures of ion pairing in ILs.

First author: Chen, X, Lanthanides with Unusually Low Oxidation States in the PrB3- and PrB4- Boride Clusters, INORGANIC CHEMISTRY, 58, 411, (2019)
Abstract: Lanthanide elements typically exhibit a +III oxidation state (OS) in chemical compounds with a few in +IV or even +V OS. Although lanthanides with +II OS have been observed recently in organometallic compounds, +I OS is extremely rare. Using a joint photoelectron spectroscopy and quantum theoretical study, we have found two low OS lanthanides in doped boron clusters, PrB3- and PrB4-. These two clusters are shown to have planar structures, in which the Pr atom is bonded to the aromatic boron clusters via two Pr-B sigma bonds. Chemical bonding and electronic structure analyses reveal that the Pr atom is in a very low OS in the two boride clusters: +II in PrB3- and +I in PrB4-. The current finding suggests that there should exist a whole class of boride complexes featuring rather low-valent lanthanides and expands the frontier of lanthanide chemistry.

First author: Gendron, F, Magnetic Coupling in the Ce(III) Dimer Ce-2(COT)(3), INORGANIC CHEMISTRY, 58, 581, (2019)
Abstract: The monomer [Ce(COT)(2)](-) and the dimer [Ce-2(COT)(3)], with Ce(III) and COT = 1,3,5,7-cyclooctatetraenide, are studied by quantum chemistry calculations. Due to the large spin-orbit coupling, the ground state of the monomer is a strong mixing of sigma and pi states. The experimental isotropic coupling in the dimer was evaluated by Walter et al. to be J = 7 cm(-1) (with a Heisenberg Hamiltonian (H) over cap (S) = J (S) over cap (A)center dot(S) over cap (B)) with a small anisotropic coupling of 0.02 cm(-1). The coupling between the two Ce(III) in the dimer is calculated using CI methods. The low energy part of the spectra are modeled by spin Hamiltonians. All spin Hamiltonians parameters are deduced from ab initio calculations. g factors are calculated for both the pseudodoublet of the monomer and the pseudotriplet of the dimer and their sign have been determined. The magnetic coupling in the dimer is rationalized by a model based on crystal field theory. The kinetic and exchange contributions arising from the different configurations to the isotropic and anisotropic couplings are evaluated. It is shown that the main contribution to isotropic coupling is kinetic and originates from the f(sigma)-f(sigma) interaction due to the large transfer integral between those orbitals. However, the f(pi)-f(pi) interaction plays a non-negligible role. The anisotropic coupling originates from the difference of exchange energy of states arising from the f(sigma)-f(pi) configuration and is, in no matter, related to the anisotropy of the local magnetic moments as already pointed by van Vleck for a fictitious s-p system. The analysis of the natural orbitals evidences a superexchange mechanism through a sigma(CH)* orbital of the bridging cycle favored by a local 4f(sigma)/5d(sigma) hybridization and that the delta type orbitals, both the HOMOs of the ligands and the virtual f(delta) orbitals of the cerium atoms play an important polarization role, and to a less extend the pi type orbitals, the HOMOs-1 of the ligands, and the metal f(pi) orbitals.

First author: Zheng, M, Accessibility of Uranyl-Plutonium Complex Supported by a Polypyrrolic Macrocycle: An Implication for Experimental Synthesis, INORGANIC CHEMISTRY, 58, 950, (2019)
Abstract: The reaction of (THF)(H2L)((UO2)-O-VI) (L is a tetra-anion of polypyrrolic macrocycle) with An(III)Cp(3) (Cp = cyclopentadienyl) afforded two intriguing cation-cation interaction (CCI) complexes (i.e., uranyl-Np and -U), but did not yield the uranyl-Pu analogue. To complement and extend experimental results, a scalar relativistic density functional theory has been performed on the formation reactions and various relevant properties of (THF)(A(2)L)(OUO)-An(CpX)(3) (A = Li and H; An = Pu, Np, and U; X = Me, H, Cl, and SiMe3). Inspired by a strategy that improves uranyl precursor reactivity, we utilized (THF)-(Li2L)((UO2)-O-VI) instead to gain a uranyl-Pu complex. Reaction free energy is reduced even to be negative (i.e., undergoing an exergonic process), which provides the thermodynamic possibility for experimental synthesis. This manner is further rationalized by the lithiated precursor showing the increased Li-O-endo bond, uranium oxidation ability (VI -> V), and exo-oxo basicity, as well as the lithiated uranyl-Pu product having more amount of electron transfer and a stronger O-exo-Pu bond (i.e., representing the CCI). Electronic structures and electron-transfer analyses reveal a U-V-Pu-IV oxidation state for the new complex. Applying the more reactive lithiated precursor also decreases the formation reaction energies of uranyl-An (An = Np and U) complexes. The second strategy via exploiting substituted Cp to raise the reactivity of the plutonium reactant does not work well.

First author: Tolle, J, Charged-cell periodic DFT simulations via an impurity model based on density embedding: Application to the ionization potential of liquid water, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 119, 950, (2019)
Abstract: Calculations of charged systems in periodic boundary conditions (PBC) are problematic because there are spurious interactions between the charges in different periodic images that can affect the physical picture. In addition, the intuitive limit of Coulomb interactions decaying to zero as the interacting charges are placed at infinite separation no longer applies, and for example total energies become undefined. Leveraging subsystem density functional theory (also known as density embedding) we define an impurity model that embeds a finite neutral or charged subsystem within an extended (infinite) surrounding subsystem. The combination of the impurity model and a consistent choice of the Coulomb reference provides us with an algorithm for evaluating the ionization potential (IP) in extended systems. We demonstrate our approach in a pilot calculation of the IP of liquid water, based on a configuration from a prior ab initio molecular dynamics (AIMD) simulation of liquid water (Genova et al., J. Chem. Phys. 2016, 144, 234105). The calculations with the impurity model capture the broadening on the ionization energies introduced by the interactions between the water molecules. Furthermore, the calculated average IP value (10.5 eV) compare favorably to experiments (9.9-10.06 eV) and very recent simulations based on the GW approximation (10.55 eV), while at the same time outperforming density embedding calculations carried out with a naive handling of the electrostatic interactions (about 7 eV).

First author: Jerabek, P, Dative and Electron-Sharing Bonding in Transition Metal Compounds, JOURNAL OF COMPUTATIONAL CHEMISTRY, 40, 247, (2019)
Abstract: Quantum chemical calculations using density functional theory at the BP86-D3(BJ)/def2-TZVPP level of theory are reported for transition metal compounds [TM]-L in high and low oxidation states involving carbene, carbyne, alkene, and alkyne ligands L. The nature of the [TM]-L bond is analyzed with the energy decomposition analysis – natural orbitals for chemical valence (EDA-NOCV) method. The calculations reveal that transition metal compounds with ligands, that are typically classified as donor-acceptor complexes possessing dative bonds (Fischer-type carbenes and carbynes, alkene, and alkyne complexes) or as TM compounds with electron-sharing bonds (Schrock-type carbenes and carbynes, metallacyclopropanes, and metallacyclopropenes), exhibit significant differences between the orbital interactions when closed-shell or open shell fragments are used. Fischer-type carbene complexes have much lower orbital interaction (Delta E-orb) values when singlet fragments are employed compared to triplet fragments. In contrast, singlet and triplet fragments of Schrock-type carbene complexes give similar Delta E-orb values. The best description for Fischer-type carbyne complexes is found for neutral fragments in their electronic doublet state, which engage in a mixture of dative bonding (sigma donation and pi backdonation) and one electron-sharing pi bond. The EDA-NOCV calculations of Schrock-type carbynes using openshell species in their quartet electronic state give similar Delta E-orb values as neutral fragments in their electronic doublet state. Alkene and alkyne complexes, but also metallacyclic species, are best described with singlet fragments, but the difference between the Delta E-orb values for dative bonding and electron-sharing bonding using triplet fragments becomes much smaller for molecules that are considered as metallacycles.

First author: Mondal, T, Computational Exploration of Mechanistic Avenues in C-H Activation Assisted Pd-Catalyzed Carbonylative Coupling, JOURNAL OF ORGANIC CHEMISTRY, 84, 257, (2019)
Abstract: The detailed mechanism of the intermolecular Pd-catalyzed carbonylative coupling reaction between aryl bromides and polyfluoroarenes relying on C(sp(2))-H activation was investigated using state-of-the-art computational methods (SMD-B3LYP-D3(BJ)/BS2//B3LYP-D3/BS1). The mechanism unveils the necessary and important roles of a slight excess of carbon monoxide: acting as a ligand in the active catalyst state, participating as a reactant in the carbonylation process, and accelerating the final reductive elimination event. Importantly, the desired carbonylative coupling route follows the rate-limiting C-H activation process via the concerted metalation-deprotonation pathway, which is slightly more feasible than the decarboxylative route leading to byproduct formation by 1.2 kcal/mol. The analyses of the free energies indicate that the choice of base has a significant effect on the reaction mechanism and its energetics. The Cs2CO3 base guides the reaction toward the coupling route, whereas carbonate bases such as K2CO3 and Na2CO3 switch toward an undesired decarboxylative path. However, K3PO4 significantly reduces the C-H activation barrier over the decarboxylation reaction barrier and can act as a potential alternative base. The positional influence of a methoxy substituent in bromoanisole and different substituent effects in polyfluoroarenes were also considered. Our results show that different substituents impose significant impact on the desired carbonylative product formation energetics. Considering the influence of several ligands leads to the conclusion that other phosphine and N-heterocyclic carbene, such as P(n)BuAd(2) and IMes, can be used as an efficient alternative than the experimentally reported (PBu3)-Bu-l ligand exhibiting a clear preference for C-H activation (Delta Delta double dagger G(L)(s)) by 7.1 and 10.9 kcal/mol, respectively. We have also utilized the energetic span model to interpret the experimental results. Moreover, to elucidate the origin of activation barriers, energy decomposition analysis calculations were accomplished for the critical transition states populating the energy profiles.

First author: Lisac, K, Halogen-bonded cocrystallization with phosphorus, arsenic and antimony acceptors, NATURE COMMUNICATIONS, 10, 257, (2019)
Abstract: The formation of non-covalent directional interactions, such as hydrogen or halogen bonds, is a central concept of materials design, which hinges on using small compact atoms of the 2nd period, notably nitrogen and oxygen, as acceptors. Heavier atoms are much less prominent in that context, and mostly limited to sulfur. Here, we report the experimental observation and theoretical study of halogen bonds to phosphorus, arsenic and antimony in the solid state. Combining 1,3,5-trifluoro-2,4,6-triiodobenzene with triphenylphosphine, -arsine, and -stibine provides cocrystals based on I center dot center dot center dot P, I center dot center dot center dot As and I center dot center dot center dot Sb halogen bonds. The demonstration that increasingly metallic pnictogens form halogen bonds sufficiently strong to enable cocrystal formation is an advance in supramolecular chemistry which opens up opportunities in materials science, as shown by colossal thermal expansion of the cocrystal involving I center dot center dot center dot Sb halogen bonds.

First author: Zierkiewicz, W, Dual Geometry Schemes in Tetrel Bonds: Complexes between TF4 (T = Si, Ge, Sn) and Pyridine Derivatives, MOLECULES, 24, 257, (2019)
Abstract: When an N-base approaches the tetrel atom of TF4 (T = Si, Ge, Sn) the latter molecule deforms from a tetrahedral structure in the monomer to a trigonal bipyramid. The base can situate itself at either an axial or equatorial position, leading to two different equilibrium geometries. The interaction energies are considerably larger for the equatorial structures, up around 50 kcal/mol, which also have a shorter R(TN) separation. On the other hand, the energy needed to deform the tetrahedral monomer into the equatorial structure is much higher than the equivalent deformation energy in the axial dimer. When these two opposite trends are combined, it is the axial geometry which is somewhat more stable than the equatorial, yielding binding energies in the 8-34 kcal/mol range. There is a clear trend of increasing interaction energy as the tetrel atom grows larger: Si < Ge < Sn, a pattern which is accentuated for the binding energies.

First author: Zhou, Q, Microscopic Mechanism of Cellulose Bond Breaking and Bonding Based on Molecular Dynamics Simulation, IEEE ACCESS, 7, 186193, (2019)
Abstract: The ReaxFF molecular dynamics simulation and Monte Carlo method were adopted to analyze the pyrolysis process of cellulose in insulating papers from the perspective of microscopic atom. Molecular dynamics failed to continuously describe the motion behavior of an atom. According to this principle, the system can only calculate the atomic state on the node and then move the atom by a time step to continue calculating the atom. This paper would put forward the optimal step setting method of cellulose thermal decomposition in insulating paper: setting one step every other 0.1 fs. Specifically, for small molecules with a simple structure, such as H2O, the step size was set to 0.4 fs or less, while the step size of macromolecules with complex structures (CH2O2) should be set to 0.2 fs or less. In addition, the relationship between the step size and the temperature to which the system was heated was given as well in this paper. In previous literatures, empirical values were used to set the step size. This study would not only provide a theoretical basis for the study on the bond formation and fracture process of cellulose pyrolysis products, but also offer the data and guidance for related fields in the future, thus rendering an efficient simulation process.u

First author: Jin, X, Structure and bonding in endohedral transition metal clusters, COMPUTATIONAL CHEMISTRY, 73, 265, (2019)
Abstract: Endohedral clusters of the tetrel elements, M@En, provide a diverse platform for exploring chemical bonding, simply because the cluster does not necessarily depend on strong M-E bonding for its integrity. The interaction between the metal and the cluster can therefore range from strongly covalent all the way to cases where the metal is simply trapped inside the cage by virtue of the strong E-E bonds, with little or no direct bonding. This spectrum of bond types leads to unusual structural, spectroscopic and magnetic properties that we seek to rationalize in this review. The clusters of interest are drawn from the field of Zintl-ion chemistry, typically containing the heavier tetrels, and also from the gas-phase spectroscopy of metal-silicon clusters. By highlighting the close relationships between the molecules studied in these two rather different disciplines, we establish a continuum framework that places all of the available experimental data in context.

First author: Lei, ZC, Conformation Analysis of Environmentally Friendly Insulating Gas C5-PFK, IEEE ACCESS, 7, 92724, (2019)
Abstract: The environmentally friendly insulating gas C5-PFK has the potential to replace SF6 in medium and low voltage gas insulated electrical equipment due to its good environmental performance and insulation strength. However, since C5-PFK molecule has rotatable C-C single bonds, the geometry will change when collided with each other or obtained external energy, which may have an impact on the stability and reactivity of C5-PFK molecule. In this paper, the geometry of C5-PFK molecule is optimized by the density functional theory-B3LYP-D3(BJ) method under the triple-zeta polarization basis set and high convergence criterion. The two C-C bonds connected with the carbonyl group (-C = O-) in C5-PFK molecule are rotated to scan its potential energy surface. Then, we obtained four possible conformers that might exist in C5-PFK molecule. The molecule structure, molecule energy, Mayer bond order, and energy levels (HOMO, LUMO orbital included) of frontier molecular orbital were analyzed to study the four conformers’ stability and reactivity, which will pave the way for follow-up research work such as thermostability, transition state, reaction pathways, and adsorption behavior of C5-PFK.

First author: Zafar, MN, Synthesis, Characterization, and Catalytic Activity of Heteroleptic Rhodium Complex for C-N Couplings, RUSSIAN JOURNAL OF COORDINATION CHEMISTRY, 45, 62, (2019)
Abstract: We have reported synthesis of complex [Rh(COD)(L{Me})Cl] (III), where L{Me} (II) is N-(1-methylpyridin-4(1H)-ylidene)benzamide and COD is 1,5-cyclooctadiene. Monodentate ligand L{Me} was synthesized by deprotonation of [HL{Me}][OTf] (I) with sodium hydride. [HL{Me}][OTf] was synthesised by methylation of N-(pyridin-4-yl)benzamide (HL) with methyl triflate. All the three synthesized compounds were characterized by FT-IR, NMR (H-1 and C-13), elemental and MS analyses. The structure of complex I was further explored with single crystal XRD and computational studies. Complex I was found as a good catalyst for C-N coupling reactions. Molecular docking revealed strong binding of rhodium complex with myoglobin.

First author: Chu, YH, MoDoop: An Automated Computational Approach for COSMO-RS Prediction of Biopolymer Solubilities in Ionic Liquids, ACS OMEGA, 4, 2337, (2019)
Abstract: An automated computational framework (MoDoop) was developed to predict the biopolymer solubilities in ionic liquids (ILs) on the basis of conductor-like screening model for real solvents calculations of two thermodynamic properties: logarithmic activity coefficient (ln.) at infinite dilution and excess enthalpy (HE) of mixture. The calculation was based on the optimized two-dimensional structures of biopolymer models and ILs by searching the lowest-energy conformer and optimizing molecular geometry. Three lignin models together with one IL dataset were used to evaluate the prediction ability of the developed method. The evaluation results show that ln. is a more reliable property to predict lignin solubilities in ILs and the p-coumaryl alcohol model is considered as the best model to represent lignin molecules. The developed MoDoop approach is efficient for rapid in silico screening of suitable ionic liquids to dissolve biopolymers.

First author: Majid, A, First principles investigations of vibrational properties of titania and zirconia clusters, JOURNAL OF NANOPARTICLE RESEARCH, 21, 2337, (2019)
Abstract: Clusters are considered as ultrafine particles at microscopic scale and present the distinctive chemical and physical characteristics. In this paper, we described the structural and vibrational characteristics of titania and zirconia clusters calculated using density functional theory. The investigated clusters include monomers TiO2 and ZrO2, dimmers Ti2O4 and Zr2O4; and the hybrid TiZrO4 clusters. The hybrid cluster was prepared from two routes: first from titania and second from zirconia as starting material. The hybrid clusters are structural isomers of the same cluster and are named as trans-TiZrO4 and cis-TiZrO4, respectively. The geometries of the clusters were optimized at B3LYP level of theory and the structural properties including bond length, bond angle, and dipole moment, and Hirshfeld charges were studied. The vibrational properties of the clusters were predicted by calculating the Raman and infrared spectra. In case of monomers, the results indicated the presence of 3 Raman and 3 IR active modes. Whereas for dimmers, 12 modes of vibration were found which were simultaneously Raman and IR active. The hybrid clusters exhibited 12 Raman and IR active modes which are described in details. The formation of the trans-TiZrO4 is energetically cheaper than that of cis-TiZrO4 by an amount of 0.25eV. The various parameters such as intensities, linear depolarization factors, and vibrations in route for preparation of the hybrid clusters are discussed. The studied Raman and IR properties shed light on the characteristics of the clusters which will be helpful to explore the applications of the materials. The calculated thermodynamic properties of the clusters are also given and discussed in detail.

First author: Xiao, YL, Fabrication of mesoporous SiO2@SLS composite to remove organic pollutants: hydrogen bond-induced intriguing changes of solubility, JOURNAL OF NANOPARTICLE RESEARCH, 21, 2337, (2019)
Abstract: Because biomass lignin shows good adsorption activity, its derivatives such as alkali lignin and kraft lignin have been applied in water treatment; however, sodium lignosulfonate (SLS), mainly limited by its high water solubility, is not applicable in this respect. In this work, we fabricated SiO2@SLS mesoporous adsorbent using a facile solution coating method by one step. SLS coating SiO2 enables the former to be separated from water, accomplishing the soluble to insoluble conversion. This change makes the composite more suitable and efficient to remove organic pollutants from water than the SLS precursor. It is found that interfacial hydrogen bonds play a significant role in the conversion, which is further corroborated by density functional theory calculations. Various characterizations show that SiO2@SLS is composed of uniform particles around 80nm in size. Abundant mesopores with diameters ranging from 2 to 3nm are found on the surface of SiO2@SLS nanoparticles. The specific surface areas of SiO2@SLS were measured between 293.4 and 33.2m(2)g(-1), depending on the SLS amount used in the preparing process. Originating from the bio-adsorbent lignin precursor, the SiO2@SLS composite shows excellent adsorption property. Representatively, SiO2@SLS-0.6 is able to efficiently remove methylene blue (MB), almost twice as much as SiO2-0 does; its adsorption capacity (Q(m)) reaches 206.2mgg(-1) according to the Langmuir model fitting; notably, SiO2@SLS-0.6 works very well even in a high-concentration MB solution (50mgL(-1)), showing removal efficiencies at 90.0% (within 1h) and 99.9% (720h, i.e., 30days). Plus having remarkable adsorption stability, our composite SiO2@SLS is anticipated to be promising in application of polluted water treatment.

First author: Parreira, RLT, Evaluation of Lignans from Piper cubeba against Schistosoma mansoni Adult Worms: A Combined Experimental and Theoretical Study, CHEMISTRY & BIODIVERSITY, 16, 2337, (2019)
Abstract: Six dibenzylbutyrolactonic lignans ((-)-hinokinin (1), (-)-cubebin (2), (-)-yatein (3), (-)-5-methoxyyatein (4), dihydrocubebin (5) and dihydroclusin (6)) were isolated from Piper cubeba seed extract and evaluated against Schistosoma mansoni. All lignans, except 5, were able to separate the adult worm pairs and reduce the egg numbers during 24 h of incubation. Lignans 1, 3 and 4 (containing a lactone ring) were the most efficient concerning antiparasitary activity. Comparing structures 3 and 4, the presence of the methoxy group at position 5 appears to be important for this activity. Considering 1 and 3, it is possible to see that the substitution pattern change (methylenedioxy or methoxy groups) in positions 3 ‘ and 4 ‘ alter the biological response, with 1 being the second most active compound. Computational calculations suggest that the activity of compound 4 can be correlated with the largest lipophilicity value.

First author: Philips, A, Quadrupolar N-14 NMR Relaxation from Force-Field and Ab Initio Molecular Dynamics in Different Solvents, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 15, 509, (2019)
Abstract: Quadrupolar NMR spin relaxation rates and corresponding line widths were computed for the quadrupolar nucleus N-14 for neat acetonitrile as well as for 1-methyl-1,3-imidazole and 1-methyl-1,3,4-triazole in different solvents. Molecular dynamics (MD) was performed with forces from the Kohn-Sham (KS) theory (ab initio MD) and force-field molecular mechanics (classical MD), followed by KS electric field gradient (EFG) calculations. For acetonitrile the agreement of the N-14 line width with experiment is very good. Relative line widths for the azole nitrogens are improved over simpler approximations used previously in conjunction with single-point calculations at the multiconfigurational self-consistent field level. Overall, the NMR line widths are computed within a factor of 2 of the experimental values, giving access to reasonable estimates both of the dynamic EFG variance in the solvated systems as well as the associated correlation times that determine the relaxation rates.

First author: Bircher, MP, Shedding Light on the Basis Set Dependence of the Minnesota Functionals: Differences Between Plane Waves, Slater Functions, and Gaussians, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 15, 557, (2019)
Abstract: The Minnesota family of exchange-correlation (xc) functionals are among the most popular, accurate, and abundantly used functionals available to date. However, their use in plane-wave based first-principles MD has been limited by their sparse availability. Here, we present an implementation of the MOS, M06, and M11 families of xc functionals within a plane wave/pseudopotential framework allowing for a comprehensive analysis of their basis set dependence. While it has been reported that in Gaussian bases some members of the Minnesota family only converge slowly to the basis set limit,(1) we show that converged energies can be conveniently obtained from plane waves if sufficiently dense integration meshes are used. Based on the HC7/11 database, we assess the influence of basis set type on the calculation of reaction enthalpies and show that complete basis set values obtained in plane waves may occasionally differ notably from their atom-centered counterparts. We provide an analysis of the origin of these differences and discuss implications on practical usage.

First author: Tabrizi, L, Experimental and theoretical investigation of cyclometallated platinum(ii) complex containing adamantanemethylcyanamide and 1,4-naphthoquinone derivative as ligands: synthesis, characterization, interacting with guanine and cytotoxic activity, RSC ADVANCES, 9, 287, (2019)
Abstract: A new cyclometallated platinum(ii) complex with 1-adamantanemethylcyanamide (1-ADpcydH) and 2-[amino(2-phenylpyridine)]-1,4-naphthoquinone (1,4-NQ) ligands with the formula cis-Pt(1,4-NQ)(1-ADpcyd)(H2O) was synthesized and fully characterized. Cellular uptake, DNA platination, and cytotoxicity against human MCF-7 breast, HepG-2 liver hepatocellular carcinoma, and HT-29 colon cancer cell lines were evaluated. The interaction of guanine (G) with cis-Pt(1,4-NQ)(1-ADpcyd)(H2O) was studied by Pt-195 NMR and mass spectroscopy. Furthermore, DFT calculations were performed on the complexes cis-Pt(1,4-NQ)(1-ADpcyd)(H2O) 1 and cis-Pt(1,4-NQ)(1-ADpcyd)(G) 2 using the BP86-D and B3LYP functionals, in order to gain deeper insights into the molecular and electronic structures. Decomposition energy analysis gave a clear understanding of the bonding within both complexes, showing that the interactions were governed by two-third ionic and one-third covalent characters, which were stronger between the guanine and the Pt(ii) center than those between water and the Pt(ii).

First author: Liu, CY, Impact of a Single Hydrogen Substitution by Fluorine on the Molecular Interaction and Miscibility between Sorafenib and Polymers, MOLECULAR PHARMACEUTICS, 16, 318, (2019)
Abstract: We aim to understand the potential impact of a modest chemical modification of a drug molecule on the downstream design of its amorphous solid dispersion (ASD) formulation. To this end, we used sorafenib (SOR) and its fluorinated form, regorafenib (REG), as model drugs, to assess the impact of a single hydrogen substitution by fluorine on the molecular interaction and miscibility between drug and PVP or PVP-VA, two commonly used polymers for ASDs. In this study, we observed that the T-g values of PVP or PVP-VA based ASDs of SOR deviated positively from the Gordon-Taylor prediction, which assumes ideal mixing, yet the T-g of REG ASDs deviated negatively from or matched well with the ideal mixing model, suggesting much stronger drug-polymer interactions in SOR ASDs compared with the REG ASDs. Using solution NMR and computational methods, we proved that a six-member-ring formed between the carbonyl groups on the polymers and the uramido hydrogen of SOR or REG, through intermolecular hydrogen bonding. However, steric hindrance resulting from fluorination in REG caused weaker interaction between REG-polymer than SOR-polymer. To further confirm this mechanism, we investigated the molecular interactions of other two uramido-containing model compounds, triclocarban (TCC) and gliclazide (GCZ), with PVP. We found that TCC but not GCZ formed a hexatomic ring with PVP. We concluded that PVP based polymers can easily interact with N,N’-disubstituted urea compounds with a trans-trans structure in the form of hexatomic rings, and the interaction strength of the hexatomic ring largely depended on the chemistry of drug molecules. This study illustrated that even a slight chemical modification on drug molecules could result in substantial difference in drug-polymer interactions, thus significantly impacting polymer selection and pharmaceutical performance of their ASD formulations.

First author: Yu, X, Hole accumulation effect on Laser-assisted field evaporation of insulators, ULTRAMICROSCOPY, 196, 121, (2019)
Abstract: Current issues associated with laser-assisted atom probe tomography of insulators are addressed by investigating laser-induced carrier dynamics and field evaporation kinetics. It is shown that for typical insulators with slow carrier recombination compared to the sub-picosecond laser pulse, hole accumulation at the surface plays a key role. By carrying out density functional theory calculations on a MgO cluster, it is found that the critical evaporation field strength decreases linearly as the surface hole density increases. This phenomenon can be explained by the hole-induced electric field. The evaporation of neutral oxygen is enhanced at low electrostatic field strength and high laser intensity. Theoretical insight is also provided for the non-stoichiometry problem in the mass spectra measured in atom probe tomography of compounds.

First author: Majid, A, Effects of thermal annealing on structural and magnetic properties of Mn ions implanted AlInN/GaN films, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 469, 618, (2019)
Abstract: In the search of functional diluted magnetic semiconductors, a study of effects of Mn ions implantation on structural and magnetic properties of AlInN/GaN/sapphire films is reported. Mn ions at 200 keV were implanted into the layers at three doses 5 x 10(14) cm(-2), 5 x 10(15) cm(-2) and 5×10(16) cm(-2). The as-implanted samples were thermally annealed and investigated by using X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS) and vibrating sample magnetometry (VSM). The structural analysis of the samples indicated that the sample implanted at dose of 5 x 10(14) cm(-2) and thermally annealed at 750 degrees C exhibited good crystalline recovery. The ferromagnetism of the samples was investigated by recording magnetization as a function of applied magnetic field. The magnetic characterizations exhibited well shaped hysteresis at room temperature which indicates presence of high temperature ferromagnetism in the samples. The findings of this work pointed out that AlInN/GaN samples implanted with Mn ions at dose of 5 x 10(16) cm(-2) and annealing at 750 degrees C exhibited maximum magnetization. On the basis of first principles calculations, it is predicted that p-d interaction is the mechanism of ferromagnetic ordering in the material.