2020 publications citing ADF

First author: Majid, A, First principles study of structural, electronic and magnetic properties of transition metals doped SiC monolayers for applications in spintronics, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 503, , (2020)
Abstract: First principles investigations were carried out to explore the prospects of using silicon carbide (SiC) monolayers in spintronics. The structural, electronic and magnetic properties of Ti, V, Cr, Mn and Fe doped SiC monolayers were studied in detail in framework of density functional theory (DFT). These dopants changed the band structure of SiC by introducing gap states and thus altered the electronic and magnetic character of the host. The results indicated that Ti did not produce any magnetic state whereas Mn and Cr exhibited ferromagnetism (FM), and V as well as Fe displayed anti-ferromagnetism (AFM) as stable configurations in the matrix. The calculated values of magnetic moments are 0 mu(B), 1.24 mu(B), 2.37 mu(B), 3.01 mu(B), and 2.21 mu(B )for dopants Ti, V, Cr, Mn and Fe respectively in the host. The dopants reveal 3d-2p hybridization with exchange interactions taking place through charge hopping. The analysis indicated that magnetic exchange takes place in Mn:SiC and Fe:SiC via superexchange whereas in Cr:SiC via double exchange interactions. The Mn doped SiC monolayer appeared to offer highest Curie temperatures with half metallic nature and highest magnetic moment which points to its suitability as potential diluted magnetic semiconductor for different spintronic applications.

First author: Zhang, J, Porphyrin dyes bearing heterocyclic anchoring groups for dye-sensitized solar cells with enhanced efficiency and long-term stability: Further optimization of champion porphyrin dye SM315, APPLIED SURFACE SCIENCE, 513, , (2020)
Abstract: In order to further enhance the long-term stability of porphyrin-based dye- sensitized solar cells (DSSCs) without losing their high efficiency, a serious of porphyrin sensitizers based on the champion dye SM315 but differing in the anchoring groups were theoretically investigated. Compared with SM315 with carboxylic acid anchoring groups, our results demonstrate that porphyrin dyes with hydantoin and barbituric acid anchoring groups exhibit stronger adsorption stability because of the larger orbital interactions between the dye and the semiconductor surface, according to the energy decomposition analysis. Furthermore, porphyrin dyes with these two heterocyclic anchoring groups can also display a superior or comparable charge separation and injection, light harvesting ability and conduction band energy shift, which are the key factors that affect the performance of DSSCs. These results highlight the great potential hydantoin and barbituric acid anchoring groups possess as effective alternatives to carboxylic acid anchoring groups for porphyrin dyes, which could yield an enhanced efficiency and long-term stability and worthy of being experimentally synthesized.

First author: Carvalho, J, Nonrelativistic protocol for calculating the (1)J((195) Pt-N-15) coupling constant in Pt(II)-complexes using all-electron Gaussian basis-set, CHEMICAL PHYSICS LETTERS, 745, , (2020)
Abstract: We present a computational protocol for predicting the (1)J((195) Pt-N-15) coupling constant in Pt(II) complexes. The procedure included a working set of 82 coupling constants for 57Pt(II) complexes. Furthermore, it was applied for a testing set of 16 coupling constants in 14Pt(II) complexes. The protocol was based on nonrelativistic calculations at PBEPBE/NMR-DKH level where the all-electron NMR-DKH basis set was previously proposed for calculation of Pt-195 chemical shift (J. Comput. Chem. 37 (2016) 2360-2373). The MAD was 36 Hz corresponding to the MRD of 10.4%, considering all 98 coupling constants for 71Pt(II) complexes studied in the present work.

First author: Hong, YM, Metalloids as halogen bond acceptors: A combined crystallographic data and theoretical investigation, CHEMICAL PHYSICS LETTERS, 745, , (2020)
Abstract: According to our search of the Cambridge Structural Database (CSD), a number of crystal structures containing Groups 15 and 16 metalloids as halogen bond acceptors have been extracted. On the basis of the CSD survey results, triphenyl-pnictogen (Ph(3)Pn) and diphenyl-chalcogen (Ph(2)Ch) molecules, together with benzimidazole-2chalcogenones (PhN2C=Ch) and triatomic pseudohalide anions (PnCCh(-)), were selected as acceptors to study. Our calculations showed that the chalcogenone compounds PhN2C=Ch serve as better halogen bond acceptors in comparison with the chalcogenide species Ph(2)Ch. Particularly, the properties of halogen bonds formed by both the Ph and Ch ends in PnCCh(-) were characterized.

First author: Kosicki, MB, Product-state distribution after isotopic substitution in ultracold atom-molecule collisions, JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, 53, , (2020)
Abstract: We theoretically investigate the isotopic substitution reactions in gaseous samples at ultracold temperature (T MUCH LESS-THAN 1 K) during atom-molecule collisions where one of the constituent atoms of the molecule is replaced by its isotope. We focus on molecular species that can be created experimentally in this range. We show that the molecular products are translationally cold, which could allow their trapping and thus their detection in order to shed new light on ultracold molecular collisions. We also demonstrate that in a few cases, the molecular products may occupy only the lowest rotational states. We discuss the possibility of controlling the kinetic energy release of such chemical reactions by an external electric field.

First author: Chai, SY, A grand product design model for crystallization solvent design, COMPUTERS & CHEMICAL ENGINEERING, 135, , (2020)
Abstract: Solvents play an important role in crystallization processes. The screening/design of solvents for crystallization (crystallization solvents) is still of great concern in research and development. At present, most of the design/screening methods of crystallization solvents are still based on the trial-and-error approach. Even though some computer-aided design methods have been proposed, the process model as well as economic/environmental/health issues have not been fully established for a wide application range. In this paper, the Grand Product Design (GPD) model is applied for the screening/design of crystallization solvents. The GPD-model includes process sub-model, property sub-model, quality sub-model, cost sub-model, pricing sub-model, economic sub-model and environmental sub-model as well as other factors such as company strategy, government policies and regulations. The general equations of the GPD-model for crystallization solvent screening/design are presented in this paper. Solution strategies are given for three cases: solvent design for a fixed process, process design for a fixed solvent and simultaneous design of solvent and process. Taking 2-Mercapotobenzothiazole (MBT) as an example, the solvent design for a fixed (existing) process design is carried out by using the problem specific GPD-model, in which the GPD-model is formulated as Mixed-Integer Non-Linear Programming (MINLP) model with objective function, process sub-model, property sub-model, quality sub-model, pricing sub-model, cost sub-model, economic sub-model and environmental sub-model. The established MINLP model is then solved by the decomposition-based approach. Experiments are carried out to verify the candidate solvents, which is found to perform better in terms of product purity and recovery than the best-known solvents in use.

First author: Kharitonov, VB, Mononuclear (C5R5)Ir-complexes with pi-linked biaryls: Stability and fluorescence quenching, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 911, , (2020)
Abstract: The arene iridium complexes [(eta(5)-C5R5)M(eta(6)-PhX)](SbF6)(2) (1a: R = H, X = CH=CHPh; 1b: R = Me, X = CH=CHPh; 2: R = Me, X = C=CPh; 3: R = Me, X = 4-Me-1H-isochromen-1-one) were synthesized by the reactions of the halides [CpIrI2]n or [Cp*IrCl2](2) with trans-stilbene, tolan and 3-phenyl-4-methyl-1H-isochromen-1-one in the presence of AgSbF6. They have proved to be stable towards the arene replacement with nucleophiles (such as acetonitrile, water and KI). The structures of 1b(SbF6)(2) and 3(SbF6)(2) were determined by X-ray diffraction. The experimental and DFT calculation data showed that the coordination of trans-stilbene and 3-phenyl-4-methyl-1H-isochromen-1-one with the Cp*Ir-moiety leads to the fluorescence quenching due to the intramolecular charge transfer from the ligand to iridium.

First author: Ali, E, Improved theoretical calculations for electron-impact ionization of DNA analogue molecules, JOURNAL OF CHEMICAL PHYSICS, 152, , (2020)
Abstract: Ionizing interactions between charged particles and molecules of biological relevance have attracted considerable interest in the last decade due to its importance in medical radiation therapy. We have previously calculated triply differential cross sections for five biomolecules in collaboration with experimental groups. We used the molecular 3-body distorted wave approximation for these calculations. For ionization of biomolecules, experimentalists are unable to determine the orientation of the molecule at the time of ionization, which means that the calculated cross sections need to be averaged over all molecular orientations. At the time the calculations were performed, it was not numerically feasible for us to perform proper averaging over orientations, so we introduced the orientation averaged molecular orbital approximation to make the calculations possible. We now have the computational capability to properly perform this average, so, here, we present new results with a proper average over orientations and compare with the previous calculations and experiment. Since the original calculations, results from two different distorted-wave models have also been published and the new results will also be compared with those calculations. Overall, the new results are in better agreement with the experiment.

First author: Shaik, S, Two-state Reactivity: Personal Recounting of Its Conception and Future Prospects, ISRAEL JOURNAL OF CHEMISTRY, 152, , (2020)
Abstract: This essay tells the story of the conception of the Two-State Reactivity (TSR) notion. Since scientific career is part of life’s flow, the story blends sub-stories of scientific colleagues and events. This is also a story of a beguiling paradigm, which has started from a puzzling reactivity of the diatomic oxidant FeO+, has continued to larger oxidants, like the active species of Cytochrome P450 and of nonheme enzymes, and its extension to reductive processes. Finally, the essay discusses prospects of experimental probing of the reactive spin-state, and of the transition state constitution for these reactions by means of tunneling-augmented kinetic isotope effects.

First author: Kelley, MP, delta and phi back-donation in An(IV) metallacycles, NATURE COMMUNICATIONS, 11, , (2020)
Abstract: In all known examples of metal-ligand (M-L) delta and bonds, the metal orbitals are aligned to the ligand orbitals in a “head-to-head” or “side-to-head” fashion. Here, we report two fundamentally new types of M-L delta and phi interactions; “head-to-side” delta and “side-to-side” phi back-bonding, found in complexes of metallacyclopropenes and metallacyclocumulenes of actinides (Pa-Pu) that makes them distinct from their corresponding Group 4 analogues. In addition to the known Th and U complexes, our calculations include complexes of Pa, Np, and Pu. In contrast with conventional An-C bond decreasing, due to the actinide contraction, the An-C distance increases from Pa to Pu. We demonstrate that the direct L-An sigma and pi donations combined with the An-L delta or phi back-donations are crucial in explaining this non-classical trend of the An-L bond lengths in both series, underscoring the significance of these delta/phi back-donation interactions, and their importance for complexes of Pa and U in particular. p id= Par Metal-ligand delta and phi interactions, though considered weak, may be necessary for fully describing the electronic and geometric structures of certain compounds. Here, in actinide metallacycles, the authors discover two new types of M-L delta and phi back-bonds that contribute substantially to their unusual chemical behavior.

First author: Majid, A, DFTB Investigations on Transition Metals Doped TiO2 Quantum Dots, JOURNAL OF ELECTRONIC MATERIALS, 11, , (2020)
Abstract: The structural, optical and electronic properties of different-sized pure as well as transition metals doped TiO2 quantum dots were investigated using density functional tight binding (DFTB) methods. The self-consistent charge density functional tight binding theory (SCC-DFTB) was used to model the TiO2 quantum dots (QDs) of increasing size up to 3.03 nm. The size dependence of density of states, position of molecular orbitals, and gap between highest orbital molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) of the QDs were studied. It appeared that, when the size of QDs approaches 3.03 nm, the energy gap narrowed down due to quantum confinement effects. The QD Ti27O54 was doped with 3d transition metals to further explore the possibility of tailoring the properties. The dopants introduced 3d impurity gap states which opens the opportunity to modify the band gap or positions of principal bands. The position of a shifted Fermi level was monitored to explore the changes in conductivity and n- or p-type behaviors of the doped QDs. It was observed that TiO2 QDs doped with V and Cr showed the n-type behavior while those doped with Sc, Mn and Fe showed p-type behavior. The findings are helpful to enhance the photocurrent efficiency of dye-sensitized solar cells and use the materials in electronic and optoelectronic properties.

First author: Conradie, J, Redox behaviour of [Ru(beta-diketonato)(3)] compounds, ELECTROCHIMICA ACTA, 337, , (2020)
Abstract: The reduction potentials of the Ru-III/II and the Ru-III/IV redox couples of fourteen [Ru(beta-diketonato)(3)] compounds are related both to electronic descriptors that describe the electron donating or withdrawing properties of the R and R’ groups on the beta-diketonato ligand (RCOCHCOR’)(-), as well as to their density functional theory (DFT) calculated energies. Most of these linear relationships have a R-2 value of above 0.90. The relationship between the experimental reduction potential of both the Ru-III/II and the Ru-IV/III redox couples and their calculated HOMO and LUMO energy values respectively, the latter directly obtainable from the DFT computed output files, can conveniently be used to theoretically predict the redox potentials of related customized [Ru(beta-diketonato)(3)] compounds, prior to synthesis of such compounds.

First author: Sarkar, S, Experimental evidence of N-H center dot center dot center dot N hydrogen bonding in the heterodimers of pyrrole with nitrogen bases, JOURNAL OF MOLECULAR STRUCTURE, 1204, , (2020)
Abstract: ( )The hydrogen bonded heterodimers of pyrrole (C4H5N) with nitrogen bases, ammonia (NH3), pyridine (C5H5N) and quinoline (C9H7N) have been studied in Ar and N-2 matrices at low temperatures. The heterodimers were characterized using infrared spectroscopy. To account for the possible structures of the heterodimers, quantum chemical calculation at MP2/aug-cc-pVDZ level of theory was performed which indicated five, four and three minima for the 1:1 C4H5N-NH3, C4H5N-C5H5N and C4H5N-C9H7N heterodimers, respectively. The global minimum heterodimer in each of the systems studied are stabilized by a robust N-H center dot center dot center dot N bonding between the weak proton donor C4H5N, and the strong proton acceptors viz. NH3, C5H5N and C9H7N. The experimental evidence for the formation of the heterodimers was observed in the N-H stretching and bending, C-H bending modes of C4H5N and N-H bending modes of NH3. Since, NH3 is a small molecule, the possibility of forming a vivid range of higher clusters with C4H5N was explored by computational and experimental methods. NBO and ED analyses were performed to understand the nature of the interactions prevailing in the heterodimers.

First author: Cabrera-Trujillo, JJ, Understanding the role of frustrated Lewis pairs as ligands in transition metal-catalyzed reactions, DALTON TRANSACTIONS, 49, 3129, (2020)
Abstract: The role of frustrated Lewis pairs (FLPs) as ligands in gold(I) catalyzed-reactions has been computationally investigated by using state-of-the-art density functional theory calculations. To this end, the nature of (P,B)-FLP-transition metal interactions in different gold(I)-complexes has been first explored in detail with the help of the energy decomposition analysis method, which allowed us to accurately quantify the so far poorly understood AuB interactions present in these species. The impact of such interactions on the catalytic activity of gold(I)-complexes has been then evaluated by performing the Au(I)-catalyzed hydroarylation reaction of phenylacetylene with mesitylene. With the help of the activation strain model of reactivity, the factors governing the higher activity of Au(I)-complexes having a FLP as a ligand as compared to that of the parent PPh3 system have also been quantitatively identified.

First author: Windorff, CJ, Probing a variation of the inverse-trans-influence in americium and lanthanide tribromide tris(tricyclohexylphosphine oxide) complexes, CHEMICAL SCIENCE, 11, 2770, (2020)
Abstract: The synthesis, characterization, and theoretical analysis of meridional americium tribromide tris(tricyclohexylphosphine oxide), mer-AmBr3(OPcy(3))(3), has been achieved and is compared with its early lanthanide (La to Nd) analogs. The data show that homo trans ligands display significantly shorter bonds than the cis or hetero trans ligands. This is particularly pronounced in the americium compound. DFT along with multiconfigurational CASSCF calculations show that the contraction of the bonds relates qualitatively with overall covalency, i.e. americium shows the most covalent interactions compared to lanthanides. However, the involvement of the 5p and 6p shells in bonding follows a different order, namely cerium > neodymium similar to americium. This study provides further insight into the mechanisms by which ITI operates in low-valent f-block complexes.

First author: Kumar, V, Double Chalcogen Bonds: Crystal Engineering Stratagems via Diffraction and Multinuclear Solid-State Magnetic Resonance Spectroscopy, CHEMISTRY-A EUROPEAN JOURNAL, 26, 3275, (2020)
Abstract: Group 16 chalcogens potentially provide Lewis-acidic sigma-holes, which are able to form attractive supramolecular interactions with electron rich partners through chalcogen bonds. Here, a multifaceted experimental and computational study of a large series of novel chalcogen-bonded cocrystals, prepared using the principles of crystal engineering, is presented. Single-crystal X-ray diffraction studies reveal that dicyanoselenadiazole and dicyanotelluradiazole derivatives work as promising supramolecular synthons with the ability to form double chalcogen bonds with a wide range of electron donors including halides and oxygen- and nitrogen-containing heterocycles. Extensive Se-77 and Te-125 solid-state nuclear magnetic resonance spectroscopic investigations of cocrystals establish correlations between the NMR parameters of selenium and tellurium and the local chalcogen bonding geometry. The relationships between the electronic environment of the chalcogen bond and the Se-77 and Te-125 chemical shift tensors were elucidated through a natural localized molecular orbital density functional theory analysis. This systematic study of chalcogen-bond-based crystal engineering lays the foundations for the preparation of the various multicomponent systems and establishes solid-state NMR protocols to detect these interactions in powdered materials.

First author: Cavo, S, Accurate optical spectra of solids from pure time-dependent density functional theory, PHYSICAL REVIEW B, 101, 3275, (2020)
Abstract: We present accurate optical spectra of semiconductors and insulators within a pure Kohn-Sham time-dependent density functional approach. In particular, we show that the onset of the absorption is well reproduced when comparing to experiment. No empirical information nor a theory beyond Kohn-Sham density functional theory, such as GW, is invoked to correct the Kohn-Sham gap. Our approach relies on the link between the exchange-correlation kernel of time-dependent density functional theory and the derivative discontinuity of ground-state density functional theory. We show explicitly how to relate these two quantities. We illustrate the accuracy and simplicity of our approach by applying it to various semiconductors (Si, GaP, GaAs) and wide-gap insulators (C, LiF, Ar).

First author: Senanayake, RD, Electronic relaxation dynamics in [Au-25(SR)(18)](-1) (R = CH3, C2H5, C3H7, MPA, PET) thiolate-protected nanoclusters, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 5272, (2020)
Abstract: We investigate the excited electron dynamics in [Au-25(SR)(18)](-1) (R = CH3, C2H5, C3H7, MPA, PET) [MPA = mercaptopropanoic acid, PET = phenylethylthiol] nanoparticles to understand how different ligands affect the excited state dynamics in this system. The population dynamics of the core and higher excited states lying in the energy range 0.00-2.20 eV are studied using a surface hopping method with decoherence correction in a real-time DFT approach. All of the ligated clusters follow a similar trend in decay for the core states (S-1-S-6). The observed time constants are on the picosecond time scale (2-19 ps), which agrees with the experimental time scale, and this study confirms that the time constants observed experimentally could originate from core-to-core transitions and not from core-to-semiring transitions. In the presence of higher excited states, R = H, CH3, C2H5, C3H7, and PET demonstrate similar relaxations trends whereas R = MPA shows slightly different relaxation of the core states due to a smaller gap between the LUMO+1 and LUMO+2 gap in its electronic structure. The S-1 (HOMO -> LUMO) state gives the slowest decay in all ligated clusters, while S-7 has a relatively long decay. Furthermore, separate electron and hole relaxations were performed on the [Au-25(SCH3)(18)](-1) nanocluster to understand how independent electron and hole relaxations contribute to the overall relaxation dynamics.

First author: Syatunek, D, Concerted [4+2] and Stepwise (2+2) Cycloadditions of Tetrafluoroethylene with Butadiene: DFT and DLPNO-UCCSD(T) Explorations, JOURNAL OF ORGANIC CHEMISTRY, 85, 3858, (2020)
Abstract: Tetrafluoroethylene and butadiene form the 2 + 2 cycloadduct under kinetic control, but the Diels-Alder cycloadduct is formed under thermodynamic control. Borden and Getty showed that the preference for 2 + 2 cycloaddition is due to the necessity for syn-pyramidalization of the two CF2 groups in the 4 + 2 transition state. We have explored the full potential energy surface for the concerted and stepwise reactions of tetrafluoroethylene and butadiene with density functional theory, DFT (B3LYP and M06-2X), DLPNO-UCCSD(T), and CASSCF-NEVPT2 methods and with the distortion/interaction-activation strain model to explain the energetics of different pathways. The 2 + 2 cycloadduct is formed by an anti-transition state followed by two rotations and a final bond formation transition state. Energetics are compared to the reaction of maleic anhydride and ethylene.

First author: Koenis, MAJ, Analysis of Vibrational Circular Dichroism Spectra of Peptides: A Generalized Coupled Oscillator Approach of a Small Peptide Model Using VCDtools, JOURNAL OF PHYSICAL CHEMISTRY B, 124, 1665, (2020)
Abstract: Vibrational circular dichroism (VCD) is one of the major spectroscopic tools to study peptides. Nevertheless, a full understanding of what determines the signs and intensities of VCD bands of these compounds in the amide I and amide II spectral regions is still far from complete. In the present work, we study the origin of these VCD signals using the general coupled oscillator (GCO) analysis, a novel approach that has I recently been developed. We apply this approach to the ForVa1NHMe model peptide in both alpha-helix and beta-sheet configurations. We show that the intense VCD signals observed in the amide I and amide II spectral regions essentially have the same underlying mechanism, namely, the through-space coupling of electric dipoles. The crucial role played by intramolecular hydrogen bonds in determining VCD intensities is also illustrated. Moreover, we find that the contributions to the rotational strengths, considered to be insignificant in standard VCD models, may have sizable magnitudes and can thus not always be neglected. In addition, the VCD robustness of the amide I and II modes has been investigated by monitoring the variation of the rotational strength and its contributing terms during linear transit scans and by performing calculations with different computational parameters. From these studies-and in particular, the decomposition of the rotational strength made possible by the GCO analysis-it becomes clear that one should be cautious when employing measures of robustness as proposed previously.

First author: Chen, Y, Probing Conformational Evolution and Associated Dynamics of Mg(N(SO2CF3)(2))(2)center dot Dimethoxyethane Adduct Using Solid-State F-19 and H-1 NMR, JOURNAL OF PHYSICAL CHEMISTRY C, 124, 4999, (2020)
Abstract: Bis(trifluoromethanesulfonimide) or TFSI is widely used as a counter anion in electrolyte design due to its structural flexibility and chemical stability. We studied the conformational variations and associated dynamics of TFSI in adduct of Mg(TFSI)(2) with dimethoxyethane (DME), a solvate crystalline material using solid-state H-1 and F-19 NMR. TFSI molecular motion in this solvate structure falls within the timescale of the F-19 NMR experiment, yielding spectroscopic signatures for unique TFSI conformers under the coordination environment of Mg2+ cation. Within the temperature range of -5 to 82 degrees C, we observe nine distinct TFSI sites in both crystalline and disordered regions using F-19 NMR, reflecting complexity of structural and dynamics of TFS1 anions within solvate structure. The four distinguishable sites in the disordered region for the two CF3 groups of the same TFSI molecule are identified using chemical shift analysis. The exchange rate constants from site to site are calculated through variable temperature F-19 NMR and twodimensional (2D) exchange spectroscopy (EXSY) experiments, along with respective activation enthalpies using Eyring’s formulation. The flip rate of CF3 around the S-C bond is estimated as similar to 15 s(-1) at 8 degrees C with Delta H-not equal similar to 22 kJ/mol, but the rotation of the entire TFSI is 4.8 s(-1) at 8 degrees C with a significantly greater Delta H-not equal = 98 +/- 10 kJ/mol. Furthermore, the slow conversion of trans to cis conformers at a lower temperature (T <= 1 degrees C) in the crystalline region is monitored, with a conversion rate of similar to 2 x 10(-5) s(-1) at -5 degrees C. Density functional theory (DFT)-based calculations were performed to support further the assignment of experimental chemical shifts, and the activation energy E-a = 21.1 kJ/mol obtained for the cis to trans transition is consistent with experimental values. The combined set of F-19 and H-1 under both one-dimensional (1D) and 2D NMR methods demonstrated here can be further used for examining electrode-electrolyte interfaces to probe the motions of various constituents that can enable detailed studies of interfacial processes and dynamics. Ultimately, such studies will aid in the design and discovery of interfacial constructs in which directed defect chemistry, chemical moiety distribution, and nanostructure are employed to drive efficient charge transport.

First author: Persaud, RR, Prediction of Structures and Atomization Energies of Coinage Metals, (M)(n), n < 20: Extrapolation of Normalized Clustering Energies to Predict the Cohesive Energy, JOURNAL OF PHYSICAL CHEMISTRY A, 124, 1775, (2020)
Abstract: The geometries of the group 11 coinage metals (n = 2-20) were optimized to determine the lowest energy isomers for each cluster size, singlets for even numbers and doublets for odd numbers. For copper and silver, 2-D (planar) geometries were favored up to n = 6. For gold, 2D (planar) geometries were favored up to n = 13. Normalized clustering energies were plotted as a function of cluster size (n(-1/3), for n = 4-20) with various DFT functionals and the CCSD(T)-F12b method and were extrapolated to predict the bulk cohesive energy. In the case of copper and silver, there is excellent agreement between the cohesive energies predicted at the CCSD(T)-F12b level of theory and the experimental values. For gold, the CCSD(T)-F12b values needed to be corrected for spin-orbit relativistic effects to obtain good agreement with experiment. Electronic properties including the HOMO-LUMO gaps for the even clusters and the spin densities for the odd clusters were calculated. The lowest gap is predicted to occur for n = 16 where the HOMO and LUMO are very similar in shape.

First author: Muller, FMA, Conformational preference of nitroformazans: A computational study, JOURNAL OF MOLECULAR STRUCTURE, 1203, 1775, (2020)
Abstract: A conformation analysis of all possible isomers of 22 differently substituted 1,5-bis(phenyl)-3-nitroformazans is presented. Results clearly showed that, except for 1,5-bis(m-OPh-phenyl)-3-nitroformazan, the closed ring trans-syn, s-cis isomer (DD) is preferred. This result agrees with available experimental structures of differently substituted 1,5-bis(phenyl)-3-nitroformazans that all exhibit the closed ring trans-syn, s-cis conformation. The preference for the closed ring trans-syn, s-cis conformation was further explored by natural bond orbital and quantum theory of atoms in molecules analysis. It was hereby shown that the donor-acceptor interaction and electron density of the bond path related to the intramolecular N-H center dot center dot center dot N hydrogen bond in the closed ring trans-syn, s-cis isomer (DD) is stronger and larger respectively than in other isomeric forms such as the open trans-syn, s-trans (UD and DU) and linear trans-anti, s-trans (UU) configurations.

First author: Truscott, JC, Synthesis, structure and DFT study of novel Ga(III) complexes containing a tetradentate ligand, JOURNAL OF MOLECULAR STRUCTURE, 1203, 1775, (2020)
Abstract: The synthesis, structure and density functional theory (DFT) calculations of two novel Ga(III) complexes, the first containing a tetradentate Schiff base ligand (L1) and the second containing a tetradentate carboxamide ligand (L2), are presented. The complexes are isolated as octahedral complexes with two water molecules attached to the axial positions. Both experimental and DFT calculations show that when [Ga(L1)(H2O)(2)]center dot NO3 is dissolved in dimethyl sulfoxide (DMSO), spontaneous substitution of axial water groups by DMSO occur to form [Ga(L1)(DMSO)(2)]center dot NO3.

First author: Bettens, T, Ambident Nucleophilic Substitution: Understanding Non-HSAB Behavior through Activation Strain and Conceptual DFT Analyses, CHEMISTRY-A EUROPEAN JOURNAL, 26, 3884, (2020)
Abstract: The ability to understand and predict ambident reactivity is key to the rational design of organic syntheses. An approach to understand trends in ambident reactivity is the hard and soft acids and bases (HSAB) principle. The recent controversy over the general validity of this principle prompted us to investigate the competing gas-phase S(N)2 reaction channels of archetypal ambident nucleophiles CN-, OCN-, and SCN- with CH3Cl (S(N)2@C) and SiH3Cl (S(N)2@Si), using DFT calculations. Our combined analyses highlight the inability of the HSAB principle to correctly predict the reactivity trends of these simple, model reactions. Instead, we have successfully traced reactivity trends to the canonical orbital-interaction mechanism and the resulting nucleophile-substrate interaction energy. The HOMO-LUMO orbital interactions set the trend in both S(N)2@C and S(N)2@Si reactions. We provide simple rules for predicting the ambident reactivity of nucleophiles based on our Kohn-Sham molecular orbital analysis.

First author: Sadhu, B, Periodic trends and complexation chemistry of tetravalent actinide ions with a potential actinide decorporation agent 5-LIO(Me-3,2-HOPO): A relativistic density functional theory exploration, JOURNAL OF COMPUTATIONAL CHEMISTRY, 26, 3884, (2020)
Abstract: A relativistic density functional theory (DFT) study is reported which aims to understand the complexation chemistry of An(4+) ions (An = Th, U, Np, and Pu) with a potential decorporation agent, 5-LIO(Me-3,2-HOPO). The calculations show that the periodic change of the metal binding free energy has an excellent correlation with the ionic radii and such change of ionic radii also leads to the structural modulation of actinide-ligand complexes. The calculated structural and binding parameters agree well with the available experimental data. Atomic charges derived from quantum theory of atoms in molecules (QTAIM) and natural bond order (NBO) analysis shows the major role of ligand-to-metal charge transfer in the stability of the complexes. Energy decomposition analysis, QTAIM, and electron localization function (ELF) predict that the actinide-ligand bond is dominantly ionic, but the contribution of orbital interaction is considerable and increases from Th4+ to Pu4+. A decomposition of orbital contributions applying the extended transition state-natural orbital chemical valence method points out the significant pi-donation from the oxygen donor centers to the electron-poor actinide ion. Molecular orbital analysis suggests an increasing trend of orbital mixing in the context of 5f orbital participation across the tetravalent An series (Th-Pu). However, the corresponding overlap integral is found to be smaller than in the case of 6d orbital participation. An analysis of the results from the aforementioned electronic structure methods indicates that such orbital participation possibly arises due to the energy matching of ligand and metal orbitals and carries the signature of near-degeneracy driven covalency.

First author: Adeyiga, O, Activating Water and Hydrogen by Ligand-Modified Uranium and Neptunium Complexes: A Density Functional Theory Study, INORGANIC CHEMISTRY, 59, 3102, (2020)
Abstract: Organometallic uranium complexes that can activate small molecules are well-known. In contrast, there are no known organometallic trans-uranium species capable of small-molecule transformations. Using density functional theory, we previously showed that changing actinide-ligand bonds from U-O groups to Np-N- (amide/imido) bonds makes redox small-molecule activation more energetically favorable for Np species. Here, we determine how general this ligand-modulation strategy is for affecting small-molecule activation in Np species. We focus on two reactions, one involving redox transformation of the actinide(s) and the other involving no change in the oxidation state of the actinide(s). Specifically, we considered the hydrogen evolution reaction (HER) from H2O by actinide tris-aryloxide species. We also considered H-2 capture and hydride transfer by actinide siloxide and silylamide complexes. For the HER, the barriers for Np(III) systems are much higher than those of U(III). The overall reaction energies are also much worse. An-O -> An-N substitutions marginally improve the barriers by 1-4 kcal/mol and more substantially improve the reaction energies by 9-15 kcal/mol. For H-2 capture and hydride transfer, the reaction energies for the U and Np species are similar. For both actinides, like-for-like An-O -> An-N substitutions lead to improved reaction energies. Interestingly, in a recent report, it seemingly appears that U-O (siloxide) -> U-N (silylamide) leads to complete shutdown of reactivity for H-2 capture and hydride transfer. This observation is reproduced and explained with calculations. The ligand environments of the siloxide and silylamide that were compared are vastly different. The steric environment of the siloxide is conducive for reactivity while the particular silylamide is not. We conclude that small-molecule activation with organometallic neptunium species is achievable with a guided choice of ligands. Additional emphasis should be placed on ligands that can allow for improved transition state barriers.

First author: Chen, YM, Theoretical Insights into Modification of Nitrogen-Donor Ligands to Improve Performance on Am(III)/Eu(III) Separation, INORGANIC CHEMISTRY, 59, 3221, (2020)
Abstract: Nitrogen-donor ligands have been considered to be promising agents for separating trivalent actinides (An(III)) from lanthanides (Ln(III)). Thereinto, how to decorate these ligands for better extraction performance is urgent to design “perfect” separating extractants. In this work, we systematically explored a series of heterocyclic N-donor ligands (L-1 = dipyridazino[4,3-c:3′,4′-h]acridine, L-2 = dipyridazino[3,4-a:4′,3′-j]phenazine, L-3 = 2,6-di(cinnolin-3-yl)pyridine)), as well as their substituted derivatives, and compared their extraction and complexation ability toward An(III) and Ln(III) ions by using quasi-relativistic density functional theory (DFT). We found that the pyridazine N atoms probably play a notable role in electron donation to metal cations by molecular orbital (MO) and bond order analyses. Besides, the calculated results clearly verified that these N-donor ligands possess higher coordination affinity toward Am(III) over Eu(III). The rigid ligands (L-1 and L-2) exhibit higher selective abilities for the Am(III)/Eu(III) separation compared with that of the flexible ligand (L-3). For each ligand, the 1:2 (metal/ligand) extraction reaction is predicted to be most probable in the separation process. The introduction of an alkyl group on the lateral chain or an electron-donating group on the main chain gives rise to a better extraction performance of the ligands, and the CyMe4 or MeO substituted ligands show higher extraction and separation ability. Simultaneous introduction of CyMe4 and MeO groups can enhance the extraction ability of the ligand to metal ions, but the separating ability depends on the differences of the extraction capacity of An(III) and Ln(III). This work can help to gain a more in-depth understanding the selectivity differences of similar N-donor ligands and provide more theoretical insights into the design of novel extractants for An(III)/Ln(III) separation.

First author: Rahman, MH, Infrared Spectroelectrochemistry of Iron-Nitrosyl Triarylcorroles. Implications for Ligand Noninnocence, INORGANIC CHEMISTRY, 59, 3232, (2020)
Abstract: Recent DFT calculations have suggested that iron nitrosyl triarylcorrole complexes have substantial {FeNO}(7)-corrole(center dot 2-) character. With this formulation, reduction of Fe(C)(NO) complexes, where C = triarylcorrole, should be centered on the corrole macrocycle rather than on the {FeNO}(7) moiety. To verify this proposition, visible and infrared spectroelectrochemical studies of Fe(C)(NO) were carried out and the results were interpreted using DFT (B3LYP/STO-TZP) calculations. The first reduction of Fe(C)(NO) led to significant changes in the Soret and Q-band regions of the visible spectrum as well as to a significant downshift in the nu(NO) and changes in the corrole vibrational frequencies. DFT calculations, which showed that the electron was mostly added to the corrole ligand (85%), were also able to predict the observed shifts in the v No and corrole bands upon reduction. These results underscore the importance of monitoring both the corrole and nitrosyl vibrations in ascertaining the site of reduction. By contrast, the visible spectroelectrochemistry of the second reduction revealed only minor changes in the Soret band upon reduction, consistent with the reduction of the FeNO moiety.

First author: Dohm, S, Semiautomated Transition State Localization for Organometallic Complexes with Semiempirical Quantum Chemical Methods, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 16, 2002, (2020)
Abstract: We present an efficient computational protocol for robust transition state localization that can be routinely applied to complex (organometallic) reactions. The capabilities of the combination of extended tight-binding semiempirical methods (GFNn-xTB) with a state-of-the-art transition state localization algorithm (mGSM) is demonstrated on a modified version of the MOBH35 benchmark set, consisting of 29 organometallic reactions and transition states. Furthermore, for three examples we demonstrate how error-prone the conventional (manual) approach based on chemical intuition can be and how errors are avoided by a semiautomated generation of reaction profiles. The performance of the GFNn-xTB methods is carefully assessed and compared with that of the widely used PM6-D3H4 and PM7 semiempirical methods. The GFNn-xTB methods show much higher success rates of 89.7% (GFN1-xTB) and 86.2% (GFN2-xTB) compared with 72.4% for PM6-D3H4 and 69.0% for PM7. The barrier heights and reaction energies are computed with much better accuracy at reduced computational cost for the GFNn-xTB methods compared with the PMx methods, allowing a semiquantitative assessment of possible reaction pathways already at a semiempirical level. The mean error of GFN2-xTB for the barrier heights (8.2 kcal mol(-1)) is close to what low-cost density functional approximations provide and substantially smaller than the corresponding error of the competitor methods.

First author: Bacha, RUS, Graphdiyne-actinyl complexes as potential catalytic materials: A DFT perspective from their structural, bonding, electronic and redox properties, ARABIAN JOURNAL OF CHEMISTRY, 13, 4564, (2020)
Abstract: Versatile graphdiyne (GDY) substrate has been modified by numerous transition metals and resulting composites showed excellent photo/electro-catalytic performance. However, GDY materials modified by actinides that are stockpiled waste product due to large-scale use in nuclear industry, are particularly scarce and remains great challenge. To deeply understand the structural properties, GDY complexating actinyl (An(m)O(2))(n+) (An = U, Np, Pu; m = VI, V) species with its atomistic pore was investigated by relativistic density functional theory (DFT). The GDY pore was found suitable to hold actinyl species, by forming organometallic An-C dative bonds. This chemical coupling interaction was further confirmed by quantum theory of atoms-in-molecule and electronic structure calculations. The GDY-uranyl(V), for instance, shows a pi(U-C) bonding HOMO, which is anticipated to improve electron transfer between ligand and metal. Orbital structures and compositions of complexes suggest their implication towards catalysis, which were further corroborated by calculations on redox potentials of GDY-actinyl complexes. Hence, our results show the potential applications of GDY complexating actinyl species towards novel catalytic surfaces.

First author: Kang, S, The key role of acceptor moieties on the structural and the electronic properties of thermally activated delayed fluorescence emitters in excited states: A computational study, ORGANIC ELECTRONICS, 78, 4564, (2020)
Abstract: The insight into understanding the effect of acceptor moieties with phenoxazine (PXD) donor and bridging phenyl (Ph) spacer on structural and electronic properties of excited state was theoretically investigated through density functional theory simulations. Di-phenyltriazine (DPhTRZ), di-phenyl pyrimidine (DPhPyM), and dipyridyl pyrimidine (DPyPyM) were chosen as acceptor moieties for thermally activated delayed fluorescence (TADF) emitters. It was found that planar structure between phenyl spacer and DPhTRZ/DPyPyM was dominantly determined by intramolecular H-bonds at inner side of acceptor moiety. Depending on the acceptor moieties, the adiabatic excitation energy in singlet and triplet state is shifted to higher energies in order: DPyPyM (blue) > DPhPyM (greenish-blue) > DPhTRZ (green). In the perspective of spin conversion, the exact spin flip barrier, defined as total energy barrier for triplet-to-singlet transition, is in order of DPhTRZ < DPyPyM < DPhPyM. The calculated spin-orbit coupling matrix element with DPyPyM is relatively larger than that with DPhTRZ and DPhPyM. The calculated reverse intersystem crossing rate for triplet conversion is the largest with DPhTRZ and the smallest with DPhPyM. The comprehensive analyses conclusively suggest that DPyPyM acceptor moiety can be utilized for blue TADF emitters with superb structural rigidity, large spin conversion rate and low spin flip barrier.

First author: Majid, A, Assessment of 2H-SiC based intercalation compound for use as anode in lithium ion batteries, CERAMICS INTERNATIONAL, 46, 5297, (2020)
Abstract: The improvement in electrode materials to upgrade lithium ion battery (LIB) is at heart of research related to energy devices. Herein, we report on the prospects of using 2H-SiC as an anode material in LIB on the basis of first principles based theoretical predictions. The energy profiling of high symmetry structural sites pointed out that the site T-c related to tetrahedral configuration with carbon is favorable intercalation site in the host. The reaction of Li with stoichiometric as well as non-stoichiometric 2H-SiC are found endothermic which points to their unsuitability for lithiation process in LIBs. However, Li intercalation into the host in presence of Si monovacancy appeared an exothermic process which motivated us to study this system in detail. The Li atom after intercalation into the host is found ionized thereby donating its 2s electron to carbon atoms. The average value of the lithium insertion voltage and theoretical capacity are calculated as 1.87 V and 85 mA h/g respectively for the host simulated in the form of supercell LixSi15C16. The diffusion barrier faced by lithium atom while moving along crystalline a-axis is minimum (among all the paths considered here) when it follows a path that links hexagonal rings while passing carbon atoms. On the other hand, in case of motion along c-axis, similar results are found for minimum energy path that is along Tc site. The low diffusion barrier will facilitate the lithium ion to move quickly that points to fast charging capability of the battery.

First author: 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, 120, 5297, (2020)
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 dyesensitized 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 p-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* -> Dye(+) + e(-)) is stronger and more spon than the adsorption reaction (Dye(+) + TiO2 [+e(-)] -> 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: Vlahovic, F, Density functional approximations for consistent spin and oxidation states of oxoiron complexes, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 120, 5297, (2020)
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: Ponce, S, First-principles calculations of charge carrier mobility and conductivity in bulk semiconductors and two-dimensional materials, REPORTS ON PROGRESS IN PHYSICS, 83, 5297, (2020)
Abstract: One of the fundamental properties of semiconductors is their ability to support highly tunable electric currents in the presence of electric fields or carrier concentration gradients. These properties are described by transport coefficients such as electron and hole mobilities. Over the last decades, our understanding of carrier mobilities has largely been shaped by experimental investigations and empirical models. Recently, advances in electronic structure methods for real materials have made it possible to study these properties with predictive accuracy and without resorting to empirical parameters. These new developments are unlocking exciting new opportunities, from exploring carrier transport in quantum matter to in silico designing new semiconductors with tailored transport properties. In this article, we review the most recent developments in the area of ab initio calculations of carrier mobilities of semiconductors. Our aim is threefold: to make this rapidly-growing research area accessible to a broad community of condensed-matter theorists and materials scientists; to identify key challenges that need to be addressed in order to increase the predictive power of these methods; and to identify new opportunities for increasing the impact of these computational methods on the science and technology of advanced materials. The review is organized in three parts. In the first part, we offer a brief historical overview of approaches to the calculation of carrier mobilities, and we establish the conceptual framework underlying modern ab initio approaches. We summarize the Boltzmann theory of carrier transport and we discuss its scope of applicability, merits, and limitations in the broader context of many-body Green’s function approaches. We discuss recent implementations of the Boltzmann formalism within the context of density functional theory and many-body perturbation theory calculations, placing an emphasis on the key computational challenges and suggested solutions. In the second part of the article, we review applications of these methods to materials of current interest, from three-dimensional semiconductors to layered and two-dimensional materials. In particular, we discuss in detail recent investigations of classic materials such as silicon, diamond, gallium arsenide, gallium nitride, gallium oxide, and lead halide perovskites as well as low-dimensional semiconductors such as graphene, silicene, phosphorene, molybdenum disulfide, and indium selenide. We also review recent efforts toward high-throughput calculations of carrier transport. In the last part, we identify important classes of materials for which an ab initio study of carrier mobilities is warranted. We discuss the extension of the methodology to study topological quantum matter and materials for spintronics and we comment on the possibility of incorporating Berry-phase effects and many-body correlations beyond the standard Boltzmann formalism.

First author: Lima, GBV, Novel trivalent europium beta-diketonate complexes with N-(pyridine-2-yl)amides and N-(pyrimidine-2-yl)amides as ancillary ligands: Photophysical properties and theoretical structural modeling, JOURNAL OF LUMINESCENCE, 219, 5297, (2020)
Abstract: Eighteen new Eu3+ complexes and their Gd3+ analogues with 1,3-diketonate as main ligands and N-(pyridine-2-yl)amides or N-(pyrimidine-2-yl)amides as ancillary ligands were synthesized. The replacement of water molecules by those amides in the Eu3+ complexes increase the intrinsic quantum yields of luminescence, making them comparable or even more efficient than Eu3+ complexes with standard ancillary ligands such as 2,2′-bipyridine. The luminescence spectra of Gd3+ complexes in comparison with the Eu3+ ones show that efficient ligand-tometal intramolecular energy transfer processes take place. In most cases the experimental Judd-Ofelt intensity parameters (Omega(2) and Omega(4)) for the Eu3+ complexes show variations as a function of the temperature (77 and 300K) that overall apparently does not follow clearly any trend. For this reason, geometric variations (on the azimuthal angle phi and ancillary ligands distances) were carried out in the coordination polyhedron for simulating thermally induced structural changes. It has been observed that, in this way, the Omega(2) and Omega(4) can be satisfactorily reproduced by in silica experiments. It was concluded that, at low-temperature, the ancillary ligands become closer to the Eu3+ ion and the angular variations affect more Omega(2) than Omega(4), in agreement to the theoretical calculations. The use of N-(pyridine-2-yl)amides or N-(pyrimidine-2-yl)amides as ancillary ligands in Eu3+ 1,3-diketonates looks to be a good strategy for obtaining highly luminescent complexes.

First author: Eng, J, Competition between the heavy atom effect and vibronic coupling in donor-bridge-acceptor organometallics, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 4659, (2020)
Abstract: The excited state properties and intersystem crossing dynamics of a series of donor-bridge-acceptor carbene metal-amides based upon the coinage metals Cu, Ag, Au, are investigated using quantum dynamics simulations and supported by photophysical characterisation. The simulated intersystem rates are consistent with experimental observations making it possible to provide a detailed interpretation of the excited state dynamics which ultimately control their functional properties. It is demonstrated that for all complexes there is a competition between the direct intersystem crossing occurring between the (CT)-C-1 and (CT)-C-3 states and indirect pathways which couple to an intermediate locally excited pi pi* triplet state ((LE)-L-3) on either the donor or acceptor ligands. The energy of the (LE)-L-3 states decreases as the size of the metal decreases meaning that the indirect pathway plays an increasingly important role for the lighter metals. Importantly whenever the direct pathway is efficient, the presence of indirect pathways is detrimental to the overall rate of ISC as they provide a slower alternative pathway. Our results provide a detailed insight into the mechanism of intersystem crossing in these complexes and will greatly facilitate the design of new higher performing molecules.

First author: Marazzi, M, Trans-to-cis photoisomerization of cyclocurcumin in different environments rationalized by computational photochemistry, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 4749, (2020)
Abstract: Cyclocurcumin is a turmeric component that has attracted much less attention compared to the well-known curcumin. In spite of the less deep characterization of its properties, cyclocurcumin has shown promising anticancer effects when used in combination with curcumin. Especially, due to its peculiar molecular structure, cyclocurcumin can be regarded as an almost ideal photoswitch, whose capabilities can also be exploited for relevant biological applications. Here, by means of state-of-the-art computational methods for electronic excited-state calculations (TD-DFT, MS-CASPT2, and XMS-CASPT2), we analyze in detail the absorption and photoisomerization pathways leading from the more stable trans isomer to the cis one. The different molecular surroundings, taken into account by means of the electrostatic solvent effect and compared with available experimental data, have been found to be critical in describing the fate of irradiated cyclocurcumin: when in non-polar environments, an excited state barrier prevents photoisomerization and favours fluorescence, whereas in polar solvents, an almost barrierless path results in a striking decrease of fluorescence, opening the way toward a crossing region with the ground state and thus funneling the photoproduction of the cis isomer.

First author: Plasser, F, TheoDORE: A toolbox for a detailed and automated analysis of electronic excited state computations, JOURNAL OF CHEMICAL PHYSICS, 152, 4749, (2020)
Abstract: The advent of ever more powerful excited-state electronic structure methods has led to a tremendous increase in the predictive power of computation, but it has also rendered the analysis of these computations much more challenging and time-consuming. TheoDORE tackles this problem through providing tools for post-processing excited-state computations, which automate repetitive tasks and provide rigorous and reproducible descriptors. Interfaces are available for ten different quantum chemistry codes and a range of excited-state methods implemented therein. This article provides an overview of three popular functionalities within TheoDORE, a fragment-based analysis for assigning state character, the computation of exciton sizes for measuring charge transfer, and the natural transition orbitals used not only for visualization but also for quantifying multiconfigurational character. Using the examples of an organic push-pull chromophore and a transition metal complex, it is shown how these tools can be used for a rigorous and automated assignment of excited-state character. In the case of a conjugated polymer, we venture beyond the limits of the traditional molecular orbital picture to uncover spatial correlation effects using electron-hole correlation plots and conditional densities. Published under license by AIP Publishing.

First author: Grover, P, Adsorption of Actinide (U-Pu) Complexes on the Silicene and Germanene Surface: A Theoretical Study, JOURNAL OF PHYSICAL CHEMISTRY A, 124, 1522, (2020)
Abstract: Adsorption of actinide (Ac = U, Np, Pu) complexes with environmentally relevant ligands on silicene and germanene surfaces has been investigated using density functional theory to determine the geometrical, energetic, and electronic properties. Three types of ligands for each central metal atom are considered: OH-, NO3-, and CO32- with common oxo ligands in all cases. Among these, carbonate complexes show the strongest adsorption followed by hydroxide and nitrate. Two types of model, cluster and periodic models, have been considered to include the short- and long-range effects. The cluster and periodic models are complementary, although the former has not yet been widely used for studies of 2D materials. Two cluster sizes have been investigated to check size dependency. Calculations were performed in the gas phase and water solvent. On the basis of the adsorption energy, for the CO32- and OH- ligands, the bond position between two Si atoms in the silicene sheet is the most strongly adsorbed site in the cluster model for silicene whereas in the periodic model these complexes exhibit strong binding on the Si atom of the silicene surface. The Ac complexes with the NO3- ligand show strong affinity at the hollow space at the center of a hexagonal ring of silicene in both models. The H site is most favorable for the binding of complexes on the germanene cluster whereas these sites vary in the periodic model. Electronic structure calculations have been performed that show a bandgap range from 0.130 to 0.300 eV for the adsorption of actinide complexes on silicene that can be traced to charge transfer. Density of states calculations show that the contribution of the nitrate complexes is small near the Fermi level, but it is larger for the carbonate complexes in the silicene case. Strong interactions between Ac complexes and silicene are due to the formation of strong Si-O bonds upon adsorption which results in reduction of the actinide atom. Such bonding is lacking in germanene.

First author: Chang, CK, Improved Prediction of Phase Behaviors of Ionic Liquid Solutions with the Consideration of Directional Hydrogen Bonding Interactions, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 59, 3550, (2020)
Abstract: The consideration of directional hydrogen bonding in the COSMO-SAC model based on the minima in the molecular electrostatic potential has been shown to significantly improve the description of solvation properties of a wide variety of associating fluids containing nonionic species. In this work, we report the use of this method for the prediction of thermodynamic properties and phase equilibria of ionic liquid solutions, including infinite dilution activity coefficients (IDAC), osmotic coefficients (phi), liquid- liquid equilibria (LLE), and vapor-liquid equilibria (VLE). When compared to the previous version of the COSMO-SAC model without the consideration of directional hydrogen bonding, the new method, which has a tendency giving more polar sigma-profiles, improves the prediction of osmotic coefficients and VLE by 10% (26% AARD, 1372 data points) and 5% (32% AARD, 1645 data points), respectively. Comparable results are observed from the two methods in LLE [0.2 and 0.1 root mean square (rms) error for ionic liquid-rich and solvent-rich regions, respectively, with 2876 data points] and IDAC (0.71 rms error with 3555 data points) predictions.

First author: Danes, S, Bonding Situation in Stannocene and Plumbocene N-Heterocyclic Carbene Complexes, ORGANOMETALLICS, 39, 516, (2020)
Abstract: A detailed experimental and computational study of a series of stannocene and plumbocene N-heterocyclic carbene complexes is presented. This unique class of group 14 Lewis acid-base adducts was obtained from reactions of the corresponding metallocenes and N-heterocyclic carbenes (NHC) and was structurally characterized by single-crystal X-ray diffraction. The obtained structures show a perpendicular pose of the NHC with respect to the metallocene, hence precluding the maximum interaction between the moieties. The nature of the Sn-C-NHC and Pb-C-NHC bonds has been investigated by applying natural bond orbital (NBO) analysis and energy decomposition analysis (EDA-NOCV). For the sake of comparison, known stannocene and plumbocene Lewis base complexes have been included in the series. The attractive chemical bonding interactions are around 50% electrostatic, 30% covalent, and 20% dispersion. Indeed, dispersion interactions play a determining role the larger the substituents become. The covalent interactions derive from the donation of the carbene ligand into the empty p orbital of the metallocene.

First author: Benti, NE, The effect of CO2 contamination in rechargeable non-aqueous sodium-air batteries, JOURNAL OF CHEMICAL PHYSICS, 152, 516, (2020)
Abstract: Metal-air batteries have higher theoretical specific energies than existing rechargeable batteries including Li-ion batteries. Among metal-air batteries, the Na-O-2 battery has gained much attention due to its low discharge/charge overpotentials (100 mV) at relatively high current densities (0.2 mA/cm2), high electrical energy efficiency (90%), high theoretical energy density, and low cost. However, there is no information reported regarding the effect of CO2 contamination in non-aqueous Na-air batteries. Density functional theory has, here, been applied to study the effect of low concentrations of CO2 contamination on NaO2 and Na2O2 growth/depletion reaction pathways and overpotentials. This was done on step surfaces of discharge products in non-aqueous Na-air batteries. Adsorption energies of CO2 at various nucleation sites for both step surfaces were determined, and results revealed that CO2 preferentially binds at the step valley sites of (001) NaO2 and (1100) Na2O2 surfaces with binding energies of -0.65 eV and -2.67 eV, respectively. CO2 blocks the step nucleation site and influences the reaction pathways and overpotentials due to carbonate formation. The discharge electrochemical overpotential increases remarkably from 0.14 V to 0.30 V and from 0.69 V to 1.26 V for NaO2 and Na2O2 surfaces, respectively. CO2 contamination is thus drastically impeding the growth/depletion mechanism pathways and increases the overpotentials of the surface reaction mechanism, hampering the performance of the battery. Avoiding CO2 contamination from intake of gas and electrolyte decomposition is thus critical in development of Na-air batteries.

First author: Moustafa, ME, Photoswitchable organoplatinum complexes with an azobenzene derivative of di-2-pyridylamine, NEW JOURNAL OF CHEMISTRY, 44, 2882, (2020)
Abstract: A new di-2-pyridylamine ligand with an appended azobenzene group (2-C5H4N)(2)N-4-C6H4-N & xe001;N-Ph, dpaa, is reported. This ligand readily forms the platinum(ii) complexes [PtMe2(dpaa)], 1, and [PtCl2(dpaa)], 2. Complex 1 is electron-rich and it undergoes oxidative addition with I-2, MeI or PhCH2Br to give the corresponding organoplatinum(iv) complexes [PtI2Me2(dpaa)], [PtIMe3(dpaa)] or [PtBrMe2(CH2Ph)(dpaa)]. Both the ligand dpaa and its platinum complexes undergo photoswitching by trans-cis isomerization about the N & xe001;N linkage.

First author: Bergmann, TG, Towards theoretical spectroscopy with error bars: systematic quantification of the structural sensitivity of calculated spectra, CHEMICAL SCIENCE, 11, 1862, (2020)
Abstract: Molecular spectra calculated with quantum-chemical methods are subject to a number of uncertainties (e.g., errors introduced by the computational methodology) that hamper the direct comparison of experiment and computation. Judging these uncertainties is crucial for drawing reliable conclusions from the interplay of experimental and theoretical spectroscopy, but largely relies on subjective judgment. Here, we explore the application of methods from uncertainty quantification to theoretical spectroscopy, with the ultimate goal of providing systematic error bars for calculated spectra. As a first target, we consider distortions of the underlying molecular structure as one important source of uncertainty. We show that by performing a principal component analysis, the most influential collective distortions can be identified, which allows for the construction of surrogate models that are amenable to a statistical analysis of the propagation of uncertainties in the molecular structure to uncertainties in the calculated spectrum. This is applied to the calculation of X-ray emission spectra of iron carbonyl complexes, of the electronic excitation spectrum of a coumarin dye, and of the infrared spectrum of alanine. We show that with our approach it becomes possible to obtain error bars for calculated spectra that account for uncertainties in the molecular structure. This is an important first step towards systematically quantifying other relevant sources of uncertainty in theoretical spectroscopy.

First author: Dutta, S, Cooperative Donor-Acceptor Interactions in Stabilizing Carbene-Borane and Carbene-Alane Compounds: A Theoretical Insight, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 2020, 638, (2020)
Abstract: Density functional theory calculations have been performed to elucidate the electronic structure and bonding scenario in various carbene-borane (L-BX & x2083;) and carbene-alane (L-AlX & x2083;) compounds (X = -H, -Me, -Cl, -Ph, -C6F5). We have performed extended transition state (ETS) analysis to reveal the nature of the donor-acceptor bonds (C (c)(arb)-E; E = B, Al) and also for the assessment of the intrinsic donor-acceptor strength in this class of compounds. Our computations suggest that the C (c)(arb)-Al bonds in all the L-AlX & x2083; adducts have substantially higher electrostatic nature than covalent character. Conversely, the nature of the C (c)(arb)-B bonds in L-BX & x2083; have a strong dependence on the electronic nature of both carbene and borane. Moreover, unlike alanes in L-AlX & x2083;, the intrinsic Lewis acid strength of the boranes in L-BX & x2083; has a strong dependence on the electronic nature of the carbenes. We have also explored the correlation of the interaction energies (Delta E-int) with various bonding parameters i.e., geometrical and Natural bond orbital (NBO) parameters of L-EH & x2083;. Furthermore, natural orbital for chemical valence (NOCV) calculations are performed to have a qualitative understanding of the relative sigma-donating and pi-accepting abilities of the carbenes in L-EH & x2083;. Additionally, we have investigated the abilities of carbenes to activate the B-H bonds in BH3 and pinacolborane. ETS analysis shows a strong dependence of the B-H activation barriers on the distortion energies of both carbene and borane fragments.

First author: Dasgupta, S, Using Atomic Confining Potentials for Geometry Optimization and Vibrational Frequency Calculations in Quantum-Chemical Models of Enzyme Active Sites, JOURNAL OF PHYSICAL CHEMISTRY B, 124, 1137, (2020)
Abstract: Quantum-chemical studies of enzymatic reaction mechanisms sometimes use truncated active-site models as simplified alternatives to mixed quantum mechanics molecular mechanics (QM/MM) procedures. Eliminating the MM degrees of freedom reduces the complexity of the sampling problem, but the trade-off is the need to introduce geometric constraints in order to prevent structural collapse of the model system during geometry optimizations that do not contain a full protein backbone. These constraints may impair the efficiency of the optimization, and care must be taken to avoid artifacts such as imaginary vibrational frequencies. We introduce a simple alternative in which terminal atoms of the model system are placed in soft harmonic confining potentials rather than being rigidly constrained. This modification is simple to implement and straightforward to use in vibrational frequency calculations, unlike iterative constraint-satisfaction algorithms, and allows the optimization to proceed without constraint even though the practical result is to fix the anchor atoms in space. The new approach is more efficient for optimizing minima and transition states, as compared to the use of fixed-atom constraints, and also more robust against unwanted imaginary frequencies. We illustrate the method by application to several enzymatic reaction pathways where entropy makes a significant contribution to the relevant reaction barriers. The use of confining potentials correctly describes reaction paths and facilitates calculation of both vibrational zero-point and finite-temperature entropic corrections to barrier heights.

First author: Jones, LO, Embedding Methods for Quantum Chemistry: Applications from Materials to Life Sciences, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 142, 3281, (2020)
Abstract: Quantum mechanical embedding methods hold the promise to transform not just the way calculations are performed, but to significantly reduce computational costs and improve scaling for macro-molecular systems containing hundreds if not thousands of atoms. The field of embedding has grown increasingly broad with many approaches of different intersecting flavors. In this perspective, we lay out the methods into two streams: QM:MM and QM:QM, showcasing the advantages and disadvantages of both. We provide a review of the literature, the underpinning theories including our contributions, and we highlight current applications with select examples spanning both materials and life sciences. We conclude with prospects and future outlook on embedding, and our view on the use of universal test case scenarios for cross-comparisons of the many available (and future) embedding theories.

First author: Ricciarelli, D, Spin-Forbidden Reactivity of Transition Metal Oxo Species: Exploring the Potential Energy Surfaces, CHEMISTRY-A EUROPEAN JOURNAL, 26, 3080, (2020)
Abstract: Spin-forbidden reactions are frequently encountered when transition metal oxo species are involved, particularly in oxygen transfer reactivity. The computational study of such reactions is challenging, because reactants and products are located on different spin potential energy surfaces (PESs). One possible approach to describe these reactions is the so-called minimum energy crossing point (MECP) between the diabatic reactants and products PESs. Alternatively, inclusion of spin-orbit coupling (SOC) effects allows to locate a saddle point on a single adiabatic PES (TS SOC). The TS SOC approach is rarely applied because of its high computational cost. Recently evidence for a TS SOC impact on significantly lowering the activation barrier in dioxygen addition to a carbene-gold(I)-hydride complex reaction (Chem. Sci. 2016, 7, 7034-7039) or even on predicting a qualitatively different reaction mechanism in mercury methylation by cobalt corrinoid (Angew. Chem. Int. Ed. 2016, 55, 11503-11506) has been put forward. Using MECP and TS SOC approaches a systematic analysis is provided here of three prototypical transition metal oxo spin-forbidden processes to investigate their implications on reactivity. Cycloaddition of ethylene to chromyl chloride (CrO2Cl2+C2H4), iron oxide cation insertion into the hydrogen molecule (FeO++H-2) and H-abstraction from toluene by a Mn-V-oxo-porphyrin cation (MnOP(H2O)(+)+C6H5CH3) are case studies. For all these processes the MECP and TS SOC results are compared, which show that the spin-forbidden reactivity of transition metal oxo species can be safely described by a MECP approach, at least for the first-row transition metals investigated here, where the spin-orbit coupling is relatively weak. However, for the Mn-oxo reactivity, the MECP and TS SOC have been found to be crucial for a correct description of the reaction mechanism. In particular, the TS SOC approach allows to straightforwardly explore detailed features of the adiabatic potential energy surface which in principle could affect the overall reaction rate in cases where the involved diabatic PESs are tricky.

First author: Dash, C, Organic Azide and Auxiliary-Ligand-Free Complexes of Coinage Metals Supported by N-Heterocyclic Carbenes, INORGANIC CHEMISTRY, 59, 2188, (2020)
Abstract: Organic azide complexes of copper(I) and silver(I), [(SIPr)CuN(1-Ad)NN][SbF6] [(SIPr)CuN(2-Ad)-NN][SbF6], [(SIPr)CuN(Cy)NN][SbF6], and [(SIPr)AgN(1-Ad)NN][SbF6] have been synthesized by using Ag[SbF6] and the corresponding organic azides with (SIPr)CuBr and (SIPr)AgCl (SIPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene). The copper and silver organic azide complexes were characterized by various spectroscopic techniques and X-ray crystallography. Group trends of isoleptic Cu(I), Ag(I), and Au(I) organic azide complexes are presented on the basis of experimental data and a detailed computational study. The nu(asym) (N-3) values of the metal-bound 1-AdNNN in [(SIPr)-MN(1-Ad)NN](+) follow the order Ag < Cu < Au. DFT calculations show that gold(I) forms the strongest bond with 1-AdNNN in this series, while silver has the weakest interaction. Furthermore, auxiliary ligand free coinage metal N-heterocyclic carbene complexes, [(SIPr)M][SbF6], have been synthesized via metathesis reactions of (SIPr)MCl (M = Cu, Ag, Au) with Ag[SbF6]. X-ray crystal structures of dinuclear [(SIPr)Ag](2) [SbF6](2) and [(SIPr)Au](2)[SbF6](2) are also reported. They show close metallophilic contacts. [(SIPr)Au](2)[SbF6](2) reacts with OEt2, SMe2, and (CNBu)-Bu-t to afford [(SIPr)Au(OEt2)][SbF6], [(SIPr)Au(SMe2)][SbF6], and [(SIPr)An((CNBu)-Bu-t)]-[SbF6] adducts, respectively.

First author: Baghdasaryan, A, Thiolato Protected Copper Sulfide Cluster with the Tentative Composition Cu74S15(2-PET)(45), INORGANIC CHEMISTRY, 59, 2200, (2020)
Abstract: Ligand protected copper nanoclusters with precise compositions have attracted considerable attention due to their unique photoluminescent properties. However, the acquisition of structural information, knowledge of the factors affecting the stability, and high quantum yields are prerequisites for assessing their applications in biomedicine as fluorescent contrast agents, biosensors, and probes for cells. Despite all the effort, only finite examples of single crystal structures of CuNCs are reported. Herein, we report the phosphine-free synthesis and structure determination of 2-PET protected CuNCs. The structure analysis established by single crystal X-ray diffraction reveals the formation of binary Cu74S15(2-PET)(45) sulfide cluster. A similar phenomenon has been observed for several other chalcogenide-bridged copper clusters. The synthesized cluster possesses a rod-like structure, protected with 45 thiol ligands on the surface. Fifteen independent bridged-sulfur atoms couple to the copper atoms inside the core. Calculations for both a neutral and negatively charged cluster showed no major differences in their geometrical structures. Further analysis of frontier MO levels of the closed-shell anion predicts the HOMO-LUMO transition to be intramolecular L7 -> L1 charge transfer, where “L7” and “L1” abbreviations refer to the corresponding sulfur layer in the structure. For the neutral cluster, the calculated spin density is delocalized over the two moieties. On the basis of TDDFT+TB calculations, the onset of the measured absorption spectrum could be satisfactorily reproduced.

First author: Realista, S, Structural and electronic properties in asymmetric binuclear Zn(II) amphiphilic compounds, JOURNAL OF COORDINATION CHEMISTRY, 73, 634, (2020)
Abstract: A new type of asymmetric binuclear Zn(II) complex was synthesized from a suitable mononuclear precursor. One Zn(II) was coordinated to a salphen ligand (salphen = N,N ‘-disalicylidene-1,2-phenylenediamine) and the other to a modified salphen bearing OC12H25 chain in the 4,4’ positions, the two being joined by phenylene rings. The molecular structure, determined by DFT calculations (ADF/BP86(COSMO:THF)/TZ2P), showed the non-planarity of each of the two complexes, the dihedral angle at the junction being similar to 36 degrees. The absorption spectra of 2 and its precursor 1 in DMSO showed a strong band in the visible at 427 and 408 nm, respectively, assigned based on TDDFT calculations mainly to intra- and interligand pi ->pi* transitions. Complex 2 displayed emission at 531 nm in DMSO and 534 nm in other solvents. The long alkyl chain of its substituents promoted self-assembly of these amphiphilic molecules. No gels were formed in DMSO, but several bands (420, 418 and 480 nm) and shoulders appeared in other solvents, and gels were detected when increasing concentration. The formation of aggregates was studied by scanning electron microscopy and atomic force microscopy, and the images found in the three solvents reflected different supramolecular arrangements. These studies revealed that the binuclear compound formed stable gels above 8.88 mM for tetrahydrofuran and 13.3 mM for toluene and chloroform.

First author: Lachmanova, SN, Electrochemical characterization of the artificial metalloenzyme papain-[(eta(6)-arene)Ru(1,10-phenanthroline)Cl](+), JOURNAL OF ELECTROANALYTICAL CHEMISTRY, 859, 634, (2020)
Abstract: Electrochemical properties were studied for [(eta(6)-arene)Ru(1,10-phenanthroline)Cl]Cl (arene = C6H5(CH2)(2)NHCOCH2Cl) organometallic complex 1, protein Papain PAP and its conjugate with organometallic complex 1 PAP. The latter can serve as an artificial metalloenzyme with catalytic activity in transfer hydrogenation. This work demonstrates that AC voltammetry and electrochemical impedance spectroscopy can be used as fast tools to screen the catalytic ability of 1-PAP electrochemically by studies of the catalytic hydrogen evolution reaction (HER). Proteins are known to catalyze this process, but we have shown that additional HER signal associated with the catalytic activity of 1 is observed for its conjugate with Papain 1-PAP.

First author: Kong, XH, Coordination behavior of uranyl with PDAM derivatives in solution: Combined study with ESI-MS and DFT, JOURNAL OF MOLECULAR LIQUIDS, 300, 634, (2020)
Abstract: Although the extraction behaviors of the tetradentate 1,10-phenanthroline-2,9-dicarboxamide (PDAM, L) derivative ligands toward actinide and lanthanide ions have been reported, the coordination structures and species determination of the complexes are still involved and are also of great significance. To reveal the coordination structure of U(VI) ion and three PDAM derivative ligands with different alkyl chain, electrospray ionization mass spectrometry (ESI-MS) combined with density functional theory (OFT) calculations were carried out. The [UO2L(NO3)](+) complexes are the dominant species for the three PDAM derivative ligands based on the ESI-MS spectra. Collision-induced dissociation (CID) results further show that the U(VI) ions strongly bind with the phenanthroline fragment, while the amine groups and the alkyl moieties are apt to lost. Furthermore, DFT calculations further confirm that three PDAM derivative ligands can be well combined with uranyl, and [UO2L(NO3)](+) species are more stable than [UO2L(OH)center dot H2O](+) one. The length of the alkyl chain has little effect on the coordination structure of uranyl complexes, but affects their thermodynamic behaviors due to the steric hindrance effect. Therefore, the studies on the coordination chemistry of uranyl with three PDAM derivative ligands at the molecular level provide basic information for efficient actinides separation in spent fuel reprocessing.

First author: Szczepanska, M, Electronic excited states and luminescence properties of palladium(II)corrin complex, JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, 389, 634, (2020)
Abstract: The DFT and TD-DFT calculations were performed for palladium(II)1,2,2,7,12,12-heptamethylo-15-cyanocorrin complex aPd(II)HM-CN-corr](+)). Experimentally [Pd(II)HM-CN-corr](+) exhibits a weak fluorescence and strong phosphorescence. For the [Pd(II)HM-CN-corr](+) complex the electronic spectrum was calculated using the BP86 and B3LYP functionals. The results shows that BP86 gives electronic transition energies in good agreement with the experiment, while B3LYP overestimates the calculated transition energies, which can be related to the order and energy of molecular orbitals. Therefore, the BP86 functional was used in further calculations. The presence of the solvent was taken into account by the use of the COSMO model. The spin-orbit (SO) states were calculated along the PEC determined by N-Pd-N bending angle active coordinate in the S-1 using the ZORA method. The rate constants of fluorescence, phosphorescence and intersystem crossing processes were determined. Based on calculations the photophysical processes occurring in [Pd(II)HM-CN-corr](+) can be explained. After light absorption there is excitation to the S-1 or S-2 states and then the internal conversion to S-1 state from S-2. Comparison of the calculated rate constants of fluorescence (3.3.10(7)S(-1)) and ISC to the close lying T-2 state (8.5.10(10)s(-1)) in the S-1 minimum shows that the ISC is more probable. This is an explanation why fluorescence in [Pd(II)HM-CN-corr](+) is weak. The vibrationally resolved fluorescence and phosphorescence band shapes were determined using the Franck-Condon approximation. The obtained band profiles agree qualitatively with the experimental ones. The most important molecular vibrations contributing to vibrational bands were determined. The calculated rate constants values and the obtained picture of photophysical processes agree qualitatively with the experimental data.

First author: Gildeh, SFG, Experimental and theoretical probing of the physicochemical properties of ionic liquids composed of [Bn-DBU](+) cation and various anions, JOURNAL OF MOLECULAR STRUCTURE, 1202, 634, (2020)
Abstract: The experimental approaches coupled with computational methods are powerful tools to understand the physicochemical properties of ionic liquids. The 1,8-diazobicyclo[5.4.0]undec-7-ene-8-benzylium ([BnDBU](+)) cation is a N-substituted DBU cation that was joined with various anions for production of [BnDBU][Y1-8], (Y1- 8 = CH3CO2-, PhSO2-, PhSO3-, HCO3-, HSO4-, CF3CO2-, BF4-, and SCN-) ionic liquids (ILs). In this study, at first, several aprotic ionic liquids composed of [Bn-DBU](+) cation and various anions were synthesized and characterized experimentally by the combined of (HNMR)-H-1 and FTIR spectroscopies, and thermogravimetric analysis (TGA). Then, density functional theory (DFT) at M06-2X/6-311++G(d,p) level of theory was used for calculation of the molecular electrostatic potential (MESP), interaction energies, structural parameters, vibrational frequencies, topological properties, charge transfer (CT) values and non-covalent interaction index.

First author: Tanaka, S, DNP NMR spectroscopy of cross-linked organic polymers: rational guidelines towards optimal sample preparation, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 3184, (2020)
Abstract: Cross-linked polystyrenes (PS) are an important class of polymers, whose properties are strongly dependent on incorporated functionalities, for which detailed understanding of their structure remains a challenge. Here, we develop a rational guideline for dynamic nuclear polarization (DNP) sample formulation for cross-linked PS to interrogate their structure. We show that the DNP enhancement on a series of cross-linked PS bearing alkylammonium groups as prototypical organic polymers correlates with the polymer swelling properties in both apolar and polar formulations (TEKPol/1,1,2,2-tetrachloroethane and AMUPol/dimethyl sulfoxide). This work provides guidelines to easily optimize DNP formulation using a simple swelling test and enables natural abundance N-15 NMR to be recorded on a series of PS-supported quaternary alkylammonium salts, allowing a detailed structural analysis.

First author: Khan, MI, A DFT study on a borophene/boron nitride interface for its application as an electrode, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 3304, (2020)
Abstract: In order to search for a new anode material for lithium-ion batteries (LIBs), a borophene/boron nitride (B/BN) interface was investigated in detail using density functional theory. Borophene is an excellent two-dimensional (2D) anode material that offers high charging capacity and a low energy barrier, but it suffers from stability issues when it is used in its free-standing form. The findings of this work indicate that the thermal and mechanical stabilities of the borophene epilayer are notably increased by preparing its interface with a boron nitride substrate. The electronic properties of the lithiated and delithiated interface exhibited metallic behavior, whereas the mechanical stiffness of the interface increased three times when compared with that of the pristine borophene. The thermal stability was calculated by molecular dynamics and indicated a six times increase in its value for the interface. The interface exhibited a specific charging capacity of 1698 mA h g(-1), which is higher than that of bare borophene and several other 2D materials. Furthermore, nudged elastic band (NEB) calculations indicated a low energy barrier to diffusion of Li in the interface. These advantages of the B/BN interface make it an excellent choice as an anode material for LIBs.

First author: Campeggio, J, Multiscale modeling of reaction rates: application to archetypal S(N)2 nucleophilic substitutions, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 3455, (2020)
Abstract: We propose an approach to the evaluation of kinetic rates of elementary chemical reactions within Kramers’ theory based on the definition of the reaction coordinate as a linear combination of natural, pseudo Z-matrix, internal coordinates of the system. The element of novelty is the possibility to evaluate the friction along the reaction coordinate, within a hydrodynamic framework developed recently [J. Campeggio et al., J. Comput. Chem. 2019, 40, 679-705]. This, in turn, allows to keep into account barrier recrossing, i.e. the transmission coefficient that is employed in correcting transition state theory evaluations. To test the capabilities and the flaws of the approach we use as case studies two archetypal S(N)2 reactions. First, we consider to the standard substitution of chloride ion to bromomethane. The rate constant at 295.15 K is evaluated to k/c(circle minus) = 2.7 x 10(-6) s(-1) (with c(circle minus) = 1 M), which compares well to the experimental value of 3.3 x 10(-6) s(-1) [R. H. Bathgate and E. A. Melwyn-Hughes, J. Chem. Soc 1959, 2642-2648]. Then, the method is applied to the SN2 reaction of methylthiolate to dimethyl disulfide in water. In biology, such an interconversion of thiols and disulfides is an important metabolic topic still not entirely rationalized. The predicted rate constant is k/c(circle minus) = 7.7 x 10(3) s(-1). No experimental data is available for such a reaction, but it is in accord with the fact that the alkyl thiolates to dialkyl disulfides substitutions in water have been found to be fast reactions.

First author: Zhang, Y, BDF: A relativistic electronic structure program package, JOURNAL OF CHEMICAL PHYSICS, 152, 3455, (2020)
Abstract: The BDF (Beijing Density Functional) program package is in the first place a platform for theoretical and methodological developments, standing out particularly in relativistic quantum chemical methods for chemistry and physics of atoms, molecules, and periodic solids containing heavy elements. These include the whole spectrum of relativistic Hamiltonians and their combinations with density functional theory for the electronic structure of ground states as well as time-dependent and static density functional linear response theories for electronically excited states and electric/magnetic properties. However, not to be confused by its name, BDF nowadays comprises also of standard and novel wave function-based correlation methods for the ground and excited states of strongly correlated systems of electrons [e.g., multireference configuration interaction, static-dynamic-static configuration interaction, static-dynamic-static second-order perturbation theory, n-electron valence second-order perturbation theory, iterative configuration interaction (iCI), iCI with selection plus PT2, and equation-of-motion coupled-cluster]. Additional features of BDF include a maximum occupation method for finding excited states of Hartree-Fock/Kohn-Sham (HF/KS) equations, a very efficient localization of HF/KS and complete active space self-consistent field orbitals, and a unique solver for exterior and interior roots of large matrix eigenvalue problems.

First author: Choudhary, S, Sequential multicomponent site-selective synthesis of 4-iodo and 5-iodopyrrole-3-carboxaldehydes from a common set of starting materials by tuning the conditions, ORGANIC & BIOMOLECULAR CHEMISTRY, 18, 1155, (2020)
Abstract: A simple and straightforward method for the synthesis of 4-iodo and 5-iodopyrrole-3-carboxaldehydes is developed from a common set of starting materials by tuning the reaction conditions. This sequential multicomponent protocol involves I-2-mediated regioselective C4-iodination and aromatization of intermediate dihydropyrrole, generated through proline-catalyzed direct Mannich reaction-cyclization sequence between succinaldehyde and imines, to access 4-iodopyrroles. While aerobic oxidative aromatization of dihydropyrrole to pyrrole followed by NIS-mediated regioselective iodination furnished 5-iodopyrroles in a two-pot fashion. A series of site-selective C4/C5-iodopyrroles have been synthesized in good to high yields (up to 78%) and DFT calculations of these compounds were also performed.

First author: Fu, MX, Bonding Analysis of the Shortest Bond between Two Atoms Heavier than Hydrogen and Helium: O-2(2+), JOURNAL OF PHYSICAL CHEMISTRY A, 124, 1087, (2020)
Abstract: Quantum chemical calculations using ab initio methods at the CCSD(T) level with large basis sets and DFT calculations using the BP86 functional have been carried out for O-2(2+) and N An energy decomposition analysis of the chemical bonds suggests that the shorter bond in O-2(2+) compared with isoelectronic N-2 is due to the weaker Pauli repulsion in the dication, which overcompensates the weakening of attractive interactions that are operative in N-2. At the equilibrium distance of N-2, the orbital (covalent) bonding in O-2(2+) is weaker than in N-2, and the attractive Coulomb interactions in the neutral diatomic system become repulsive in the dication, but the weakening of the Pauli repulsion caused by the shrinking of the orbitals in O-2(2+) compensates for these forces and leads to a shortening of the bond. The results also show that the bond dissociation energy is not a reliable indicator for the strength of bond, which is more faithfully given by the (local) force constant.

First author: Narsaria, AK, Distortion-Controlled Redshift of Organic Dye Molecules, CHEMISTRY-A EUROPEAN JOURNAL, 26, 2080, (2020)
Abstract: It is shown, quantum chemically, how structural distortion of an aromatic dye molecule can be leveraged to rationally tune its optoelectronic properties. By using a quantitative Kohn-Sham molecular orbital (KS-MO) approach, in combination with time-dependent DFT (TD-DFT), the influence of various structural and electronic tuning parameters on the HOMO-LUMO gap of a benzenoid model dye have been investigated. These parameters include 1) out-of-plane bending of the aromatic core, 2) bending of the bridge with respect to the core, 3) the nature of the bridge itself, and 4) a-a stacking. The study reveals the coupling of multiple structural distortions as a function of bridge length and number of bridges in benzene to be chiefly responsible for a decreased HOMO-LUMO gap, and consequently, red-shifting of the absorption wavelength associated with the lowest singlet excitation (lambda approximate to 560 nm) in the model cyclophane systems. These physical insights together with a rational approach for tuning the oscillator strength were leveraged for the proof-of-concept design of an intense near-infrared (NIR) absorbing cyclophane dye at lambda = 785 nm. This design may contribute to a new class of distortion-controlled NIR absorbing organic dye molecules.

First author: Berkefeld, A, C-P vs C-H Bond Cleavage of Triphenylphosphine at Platinum(0): Mechanism of Formation, Reactivity, Redox Chemistry, and NMR Chemical Shift Calculations of a mu-Phosphanido Diplatinum(II) Platform, ORGANOMETALLICS, 39, 443, (2020)
Abstract: Transition-metal phosphanides M-PR2 are key intermediates in catalytic C-P bond functionalization. M-PR2 formation from tertiary phosphines through P-C bond cleavage widens the scope beyond P-H functionalized substrates, but mechanistic understanding of this reaction still is fragmentary. Starting from a defined coordination complex has allowed monitoring the reaction of a Pt-PPh3 moiety and Pt(0) by NMR spectroscopy. Initial Pt(0) transfer is rate-limiting and leads to products from PPh3-borne ortho-C-H and C-P bond cleavage along kinetically distinct pathways. Albeit kinetically favored, the reversibility of C-H bond cleavage eventually leads to thermodynamically preferred C-P bond scission. This pathway affords a robust [Pt(mu-PPh2)Pt] core structure whose redox chemistry and reactivity toward external ligands are reported. Organometallic products have been substantiated by a combination of magnetic resonance and absorption spectroscopies, X-ray diffraction, and DFT computations.

First author: Tang, Q, Reverse Turn Foldamers: An Expanded beta-Turn Motif Reinforced by Double Hydrogen Bonds, ORGANIC LETTERS, 22, 1003, (2020)
Abstract: Hybrid tetrapeptides sharing a backbone with a central alpha/beta-dipeptide segment flanked by aromatic gamma-amino acid residues fold into the same hairpin conformation with an expanded beta-turn. This hairpin/beta-turn motif is general for accommodating different alpha- and beta-amino acid residues. Replacing glycine with other alpha-amino acid residues has an insignificant influence on or slightly decreases the stabilities of the folded conformations; substituting beta-alanine with other beta-amino acid residues enhances the stabilities of the folded structures.

First author: Domanski, MA, The high covalence of metal-ligand bonds as stability limiting factor: the case of Rh(IX)O-4(+) and Rh(IX)NO3, JOURNAL OF MOLECULAR MODELING, 26, 1003, (2020)
Abstract: Rhodium, a 4d transition metal and a lighter analogue of iridium, is known to exhibit its highest VIth oxidation state in RhF6 molecule. In this report, the stability and decomposition pathways of two species containing rhodium at a potentially formal +IX oxidation state, [RhO4](+) and RhNO3, have been investigated theoretically within the framework of the relativistic two-component Hamiltonian calculations. Possible rearrangement into isomers featuring lower formal oxidation numbers has been explored. We found that both species studied are metastable with respect to elimination of O-2 or NO. However, the local minima containing Rh(IX) are protected by sufficient energy barriers on the decomposition pathway, and they could in principle be prepared. The analysis of a broader set of compounds containing group 8 and 9 metals in high formal oxidation states that correspond to the group number showed that, in contrast to a standard trend, the limits of formally attainable oxidation state correlate with high level of covalent bonding character in the complexes studied.

First author: Mobley, TA, Relativistic DFT Calculations of (1)J(WH) and (1)J(WC) Provide Detailed Structural Insight of Cyclopentadienyl Binding in Cp2WH2, JOURNAL OF PHYSICAL CHEMISTRY A, 124, 966, (2020)
Abstract: Experimental measurements of the one-bond scalar coupling of Cp2WH2 in tetrahydrofuran ((1)J(WH) = 73.4 Hz and (1)J(WC) = 4.8 Hz) are compared to density functional theory calculations of the same based upon geometries minimized utilizing a variety of approximate functionals typically utilized to calculate organometallic geometries. One difference between the various functionals is the Cp-W distance, and d(CpW) is linearly correlated to the calculated values for both (1)J(WH) and (1)J(WC). Differences in the structures of the Cp2WH2 reported in the literature are compared to the calculated geometries, utilizing calculated values of (1)J(WH) to provide insight into the differences. The distance between the tungsten and attached hydride as well as the angle of the cyclopentadienyl plane with respect to the tungsten cyclopentadienyl centroid vector also have a strong effect on (1)J(WH). A natural bond orbital (NBO) analysis of the orbital origins of (1)J(WH) indicates that the W-H sigma-bonding orbital is the primary contributor to the coupling constant.

First author: Gieseking, RLM, Analytical Approaches To Identify Plasmon-like Excited States in Bare and Ligand-Protected Metal Nanoclusters, JOURNAL OF PHYSICAL CHEMISTRY C, 124, 3260, (2020)
Abstract: Noble metal nanoclusters containing dozens to hundreds of metal atoms are of great interest because of their unique optical properties. Classical electrodynamics fails to describe the optical properties of clusters smaller than a few nanometers, so quantum-mechanical models are needed to describe these clusters. However, it is challenging to identify which features of the computed excited states indicate plasmon-like character, particularly in a way that is generalizable to the ligand-protected clusters that are commonly studied in experiments. We present an analytical method to identify plasmon-like excited states using three quantifiable indicators that must be considered in combination: (1) large superatomic character, (2) large collectivity among single-particle excitations, and (3) large additivity of contributions of these single-particle excitations to the transition dipole moment. Visualizing these three indicators on a single plot enables rapid classification of hundreds of excited states into plasmon-like, collective, single-particle, or interband categories or as intermediate between these categories. This method is used to identify excited states with plasmon-like character in both bare and ligand-protected Ag clusters at the TDDFT level. Using these three nearly orthogonal indicators in combination provides more information than any one criterion can provide.

First author: Petelski, AN, Hydrogen-Bonded Rosettes of Aminotriazines for Selective-Ion Recognition, JOURNAL OF PHYSICAL CHEMISTRY C, 124, 3352, (2020)
Abstract: Ion recognition is still an emerging topic in supramolecular chemistry and has aroused great attention in the last few years. In this work, we have examined the assemblies of selected hexameric rosettes of melamine and ammeline and their capacities to host halide and alkali ions in the gas phase and in water. Using relativistic dispersion-corrected density functional theory (DFT-D), we first studied the stability and the effect of introducing monovalent anions (Cl-, Br-, and I-) and cations (Na+, K+, and Rb+) in the center of the rosette’s cavity. Finally, we explored the interactions in two stacked rosettes with an interlayer ion. Our computations reveal that amine-substituted triazines are promising candidates for anion and cation recognition either in self-assembled monolayers or pillar array structures. The anion recognition process is governed by both the electrostatic and charge-transfer (donor-acceptor) interactions, while the cation recognition is governed by electrostatic and polarization. In addition, melamine and ammeline could constitute a potent mixture for dual-ion recognition strategies.

First author: Alkorta, I, An experimental and computational NMR study of organometallic nine-membered rings: Trinuclear silver(I) complexes of pyrazolate ligands, MAGNETIC RESONANCE IN CHEMISTRY, 58, 319, (2020)
Abstract: This work reports the calculation of the nuclear magnetic resonance (NMR) chemical shifts of eight trinuclear Ag(I) complexes of pyrazolate ligands using the relativistic program ZORA. The data from the literature concern exclusively H-1, C-13, and F-19 nuclei. For this reason, one of the complexes that is derived from 3,5-bis-trifluoromethyl-1H-pyrazole has been studied anew, and the N-15 and Ag-109 chemical shifts determined for the first time in solution. Solid-state NMR data of this compound have been obtained for some nuclei (H-1, C-13, and F-19) but not for others (N-14, N-15, and Ag-109).

First author: Gostynski, R, X-ray diffraction and QTAIM calculations of the non-covalent intermolecular fluorine-fluorine interactions in tris(trifluoroacetylacetonato)-manganese(III), JOURNAL OF MOLECULAR STRUCTURE, 1201, 319, (2020)
Abstract: An X-ray study was conducted on tris(trifluoroacetylacetonato)-manganese(III). The two different molecules in the unit cell exhibit a distorted octahedral geometry and moderate compression Jahn-Teller distortion respectively. A number of F center dot center dot center dot H and F center dot center dot center dot F intermolecular interactions were observed in the packing of the crystals in the solid state. The crystal packing effects could lead to the observed compressed Jahn-Teller distortion, instead of the expected elongation Jahn-Teller distortion. A Quantum Theory of Atoms in Molecules (QTAIM) study on selected molecular pairs identified intermolecular bond paths (BP) between fluorine atoms with bond critical points (BCP) which have positive electron density (rho) and Laplacian of electron density (del(2)rho) values, which are indicative of weak F center dot center dot center dot F non-covalent bonding interactions.

First author: Sergeieva, T, Ligand-Mediated Regioselective Rhodium-Catalyzed Benzotriazole-Allene Coupling: Mechanistic Exploration and Quantum Chemical Analysis, CHEMISTRY-A EUROPEAN JOURNAL, 26, 2342, (2020)
Abstract: The ligand-controlled rhodium-catalyzed regioselective coupling of 1,2,3-benzotriazoles and allenes was investigated by DFT calculations. Because allylation can occur at either the N1 or N2 position of the 1,2,3-benzotriazole, the complete Gibbs free energy profiles for both pathways were computed. A kinetic preference emerged for the experimentally observed N1 allylation with the JoSPOphos ligand, whereas N2 allylation was favored with DPEphos. Analysis of the regiodetermining oxidative addition step by using the activation strain model in conjunction with a matching energy decomposition analysis has revealed that the unprecedented N2 reaction regioselectivity is dictated by the strength of the electrostatic interactions between the 1,2,3-benzotriazole and the rhodium catalyst. The nature of the electrostatic interaction was rationalized by analysis of the electrostatic potential maps and Hirshfeld charges: a stabilizing electrostatic interaction was found between the key atoms involved in the oxidative addition for the N2 pathway, analogous interactions are weaker in the N1 case.

First author: Gupta, M, Metal-Organic Frameworks of Cu(II) Constructed from Functionalized Ligands for High Capacity H-2 and CO2 Gas Adsorption and Catalytic Studies, INORGANIC CHEMISTRY, 59, 1810, (2020)
Abstract: Two Cu(II)-based metal-organic frameworks (MOFs) having paddle-wheel secondary building units (SBUs), namely, 1(Me) and 1(ip)(r) were synthesized solvothermally using two new bent di-isophthalate ligands incorporating different substituents. The MOFs showed high porosity (BET surface area, 2191 m(2)/g for 1(Me) and 1402 m(2)/g for For 1(Me), very high CO2 adsorption (98.5 wt % at 195 K, 42.9 wt % at 273 K, 23.3 wt % at 298 K) at 1 bar was found, while for 1(ipr) it was significantly less (14.3 wt % at 298 K and 1 bar, 54.4 wt % at 298 K at 50 bar). 1(Me) exhibited H-2 uptake of 3.2 wt % at 77 K and 1 bar of pressure, which compares well with other benchmark MOFs. For 1(Me), the H-2 uptake was found to be 2.54 wt % under similar experimental conditions. The significant adsorption of H-2 and CO2 for 1(Me) could be due to the presence of micropores as well as unsaturated metal sites in these MOFs besides the presence of substituents that interact with the gas molecules. The experimental adsorption behavior of the MOFs could be justified by theoretical calculations. Additionally, catalytic conversions of CO2 and CS2 into useful chemicals like cyclic carbonates, cyclic trithiocarbonates, and cyclic dithiocarbonates could be achieved.

First author: Ciancaleoni, G, Disentanglement of orthogonal hydrogen and halogen bonds via natural orbital for chemical valence: A charge displacement analysis, JOURNAL OF COMPUTATIONAL CHEMISTRY, 41, 1185, (2020)
Abstract: As known, the electron density of covalently bound halogen atoms is anisotropically distributed, making them potentially able to establish many weak interactions, acting at the same time as halogen bond donors and hydrogen bond acceptors. Indeed, there are many examples in which the halogen and hydrogen bond coexist in the same structure and, if a correct bond analysis is required, their separation is mandatory. Here, the advantages and limitations of coupling the charge displacement analysis with natural orbital for chemical valence method (NOCV-CD) to separately analyze orthogonal weak interactions are shown, for both symmetric and asymmetric adducts. The methodology gives optimal results with intermolecular adducts but, in the presence of an organometallic complex, also intramolecular interactions can be correctly analyzed. Beyond the methodological aspects, it is shown that correctly separate and quantify the interactions can give interesting chemical insights about the systems.

First author: Conradie, J, Tris(beta-ketoiminato)ruthenium(III) – Structural and electronic data of the neutral, oxidized and reduced forms, DATA IN BRIEF, 28, 1185, (2020)
Abstract: In this data article, density functional theory (DFT) calculated data for the optimized geometries and electronic structure data of the neutral, oxidized and reduced forms of the fac and mer isomers of tris(amino-pent-3-en-2-onato-N,O)ruthenium(III) as representative example of tris(beta-ketoiminato)ruthenium(III) complexes is provided. Energy-level diagrams of the neutral, oxidized and reduced molecules, show the effect on the molecular energy levels and the electron occupation of the frontier orbitals, when the neutral complex is oxidized or reduced. The DFT calculated data also confirms the spin state of the molecules and show that the fac and mer isomers of tris(amino-pent-3-en-2-onato-N,O)ruthenium(III) are equi-energetic.

First author: Cao, MJ, Theoretical Study on Electronic Structural Properties of Catalytically Reactive Metalloporphyrin Intermediates, CATALYSTS, 10, 1185, (2020)
Abstract: Metalloporphyrins have attracted great attention in the potential application of biomimetic catalysis. Especially, they were widely investigated as green catalysts in the chemical oxidation of various hydrocarbons through the catalytic activation of molecular oxygen. The structural properties of active central metal ions were reported to play a decisive role in catalytic activity. However, those delicate structural changes are difficult to be experimentally captured or elucidated in detail. Herein, we explored the electronic structural properties of metalloporphyrins (metal porphyrin (PMII, (PMCl)-Cl-III)) and their corresponding catalytically active intermediates (metal(III)-peroxo(PMIII-O-2), metal(III)-hydroperoxo(PMIII-OH), and metal(IV)-oxo(PMIV =O), (M=Fe, Mn, and Co)) through the density functional theory method. The ground states of these intermediates were determined based on the assessment of relative energy and the corresponding geometric structures of ground states also further confirmed the stability of energy. Furthermore, our analyses of Mulliken charges and frontier molecular orbitals revealed the potential catalytic behavior of reactive metalloporphyrin intermediates.

First author: Alkorta, I, Regium Bonds between Silver(I) Pyrazolates Dinuclear Complexes and Lewis Bases (N-2, OH2, NCH, SH2, NH3, PH3, CO and CNH), CRYSTALS, 10, 1185, (2020)
Abstract: A theoretical study and Cambridge Structural Database (CSD) search of dinuclear Ag(I) pyrazolates interactions with Lewis bases were carried out and the effect of the substituents and ligands on the structure and on the aromaticity were analyzed. A relationship between the intramolecular Ag-Ag distance and stability was found in the unsubstituted system, which indicates a destabilization at longer distances compensated by ligands upon complexation. It was also observed that the asymmetrical interaction with phosphines as ligands increases the Ag-Ag distance. This increase is dramatically higher when two simultaneous PH3 ligands are taken into account. The calculated Ag-109 chemical shielding shows variation up to 1200 ppm due to the complexation. Calculations showed that six-membered rings possessed non-aromatic character while pyrazole rings do not change their aromatic character significantly upon complexation.

First author: Lefeuvre, B, Redox-Modulations of Photophysical and Single-molecule Magnet Properties in Ytterbium Complexes Involving Extended-TTF Triads, MOLECULES, 25, 1185, (2020)
Abstract: The reaction between the 2,2′-benzene-1,4-diylbis(6-hydroxy-4,7-di-tert-butyl-1,3-benzodithiol-2-ylium-5-olate triad (H(2)SQ) and the metallo-precursor [Yb(hfac)(3)].2H(2)O led to the formation of a dinuclear coordination complex of formula [Yb-2(hfac)(6)(H(2)SQ)].0.5CH(2)Cl(2) (H(2)SQ-Yb). After chemical oxidation of H(2)SQ in 2,2′-cyclohexa-2,5-diene-1,4-diylidenebis(4,7-di-tert-butyl-1,3-benzodithiole-5,6-dione (Q), the latter triad reacted with the [Yb(hfac)(3)].2H(2)O precursor to give the dinuclear complex of formula [Yb-2(hfac)(6)(Q)] (Q-Yb). Both dinuclear compounds have been characterized by X-ray diffraction, DFT optimized structure and electronic absorption spectra. They behaved as field-induced Single-Molecule Magnets (SMMs) nevertheless the chemical oxidation of the semiquinone to quinone moieties accelerated by a factor of five the relaxation time of the magnetization of Q-Yb compared to the one for H(2)SQ-Yb. The H(2)SQ triad efficiently sensitized the Yb-III luminescence while the chemical oxidation of H(2)SQ into Q induced strong modification of the absorption properties and thus a quenching of the Yb-III luminescence for Q-Yb. In other words, both magnetic modulation and luminescence quenching are reached by the oxidation of the protonated semiquinone into quinone.

First author: Zierkiewicz, W, Competition between Intra and Intermolecular Triel Bonds. Complexes between Naphthalene Derivatives and Neutral or Anionic Lewis Bases, MOLECULES, 25, 1185, (2020)
Abstract: A TrF2 group (Tr = B, Al, Ga, In, Tl) is placed on one of the alpha positions of naphthalene, and its ability to engage in a triel bond (TrB) with a weak (NCH) and strong (NC-) nucleophile is assessed by ab initio calculations. As a competitor, an NH2 group is placed on the neighboring C-alpha, from which point it forms an intramolecular TrB with the TrF2 group. The latter internal TrB reduces the intensity of the pi-hole on the Tr atom, decreasing its ability to engage in a second external TrB. The intermolecular TrB is weakened by a factor of about two for the smaller Tr atoms but is less severe for the larger Tl. The external TrB can be quite strong nonetheless; it varies from a minimum of 8 kcal/mol for the weak NCH base, up to as much as 70 kcal/mol for CN-. Likewise, the appearance of an external TrB to a strong base like CN- lessens the ability of the Tr to engage in an internal TrB, to the point where such an intramolecular TrB becomes questionable.

First author: Chen, YM, Complexation of trivalent lanthanides and actinides with diethylenetriaminepentaacetic acid: Theoretical unraveling of bond covalency, JOURNAL OF MOLECULAR LIQUIDS, 299, 1185, (2020)
Abstract: Separation of trivalent actinides (An(III)) and lanthanides (Ln(III)) is a pivotal step with respect to the treatment of nuclear waste based on the partitioning and transmutation (P&T) strategy, which is also extraordinarily challenging due to their similar coordination chemistry. The diethylenetriaminepentaacetate (DTPA) ligand has been demonstrated to possess selective separation ability toward An(III) over Ln(III) in aqueous media. Nevertheless, the extracted complexes of An(III)/Ln(III) with DTPA, and the origin of selectivity for An(III) are still not well deciphered. In this work, from theoretical perspective and at the molecular level, the geometrical structures, bonding nature as well as thermodynamic behaviors of possible complexes of An(III) (An = Am, Cm, Cf) and Ln(III) (Ln = Nd, Eu) with DTPA in the aqueous phase have been systematically studied using scalar relativistic density functional theory (DFT). All bonding analyses indicate that the metal-ligand bonds possess weak but non-negligible covalent interactions, and An(III)-DTPA species demonstrate more covalency compared to Ln(III) analogues. In addition, the covalency of the metal-ligand bonding of An(III)-DTPA increases across the actinide series from Am to Cf, which stems from the increased orbital degeneracy of the 5f orbitals of actinides and the 2p orbitals of the ligands. According to thermodynamic analysis, the anhydrous species [Cf(HDTPA)](-) is the most likely species for Cf(III) in acidic solution, whereas [M(HDTPA)(H2O)](-) are more favorable for Am(III) and Cm (III), probably due to the different bonding nature of the transplutonium series. This work affords new theoretical insights into the coordination chemistry of An(III)/Ln(III)-DTPA complexes, and paves the way to further design efficient DTPA-based ligands for An(III)/Ln(III) separation. Moreover, the DTPA ligand may also be applied for in-group separation of trivalent actinides, which is quite meaningful for the extraction of Cf(III).

First author: Forster, A, A Quadratic Pair Atomic Resolution of the Identity Based SOS-AO-MP2 Algorithm Using Slater Type Orbitals, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 16, 875, (2020)
Abstract: We report a production level implementation of pair atomic resolution of the identity (PARI) based second-order Moller-Plesset perturbation theory (MP2) in the Slater type orbital (STO) based Amsterdam Density Functional (ADF) code. As demonstrated by systematic benchmarks, dimerization and isomerization energies obtained with our code using STO basis sets of triple-zeta-quality show mean absolute deviations from Gaussian type orbital, canonical, basis set limit extrapolated, global density fitting (DF)-MP2 results of less than 1 kcal/mol. Furthermore, we introduce a quadratic scaling atomic orbital based spin-opposite-scaled (SOS)-MP2 approach with a very small prefactor. Due to a worst-case scaling of O(N-3), our implementation is very fast already for small systems and shows an exceptionally early crossover to canonical SOS-PARI-MP2. We report computational wall time results for linear as well as for realistic three-dimensional molecules and show that triple-zeta quality calculations on molecules of several hundreds of atoms are only a matter of a few hours on a single compute node, the bottleneck of the computations being the SCF rather than the post-SCF energy correction.

First author: Majerz, I, Substituent effect on inter-ring interaction in paracyclophanes, MOLECULAR DIVERSITY, 24, 11, (2020)
Abstract: The theoretical calculations, namely multipole-derived charge analysis, quantum theory of atom in molecules, and non-bonding interaction (NCI), were performed for [2.2]paracyclophanes, [2.2]paracyclophane-7,9-dienes, and [3.3]paracyclophanes optimized at B3LYP/6-311++G** level, including dispersion correction. The substituent effect of the electron donor N(Me)(2) and electron acceptor NO2 group and the influence of the length of bridges joining the aromatic ring on aromatic ring interaction energy (AIE) and strain energy were discussed. The local and electrostatic character of the substituent effect in paracyclophanes was shown. The presence of the weak orbital through-space C center dot center dot center dot C interaction between the [3.3]paracyclophane ring and weak CH center dot center dot center dot O hydrogen bonds between the substituents in the different rings was shown.

First author: Hoffmann, JM, pi-Hole Interactions with Various Nitro Compounds Relevant for Medicine: DFT Calculations and Surveys of the Cambridge Structural Database (CSD) and the Protein Data Bank (PDB), SYNTHESIS-STUTTGART, 52, 521, (2020)
Abstract: Model DFT computations and a thorough evaluation of the Cambridge structural database (CSD) and the protein data bank (PDB) were conducted to assess the occurrence and significance of intermolecular pi-hole interactions with various nitro compounds relevant to medicine. DFT calculations indicate interaction energies between -3.9 to -6.5 kcal.mol(-1), which is in the order of typical hydrogen- and halogen-bonding interactions. Ample structural evidence for the occurrence of nitro pi-hole interactions was found within the CSD and the PDB.

First author: Hughes, HJ, The orientation of a membrane probe from structural analysis by enhanced Raman scattering, BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES, 1862, 521, (2020)
Abstract: Small fluorescent molecules are widely used as probes of biomembranes. Different probes optically indicate membrane properties such as the lipid phase, thickness, viscosity, and electrical potential. The detailed molecular mechanisms behind probe signals are not well understood, in part due to the lack of tools to determine probe position and orientation in the membrane. Optical measurements on aligned biomembranes and lipid bilayers provide some degree of orientational information based on anisotropy in absorption, fluorescence, or nonlinear optical properties. These methods typically find the polar tilt angle between the membrane normal and the long axis of the molecule. Here we show that solution-phase surface enhanced Raman scattering (SERS) spectra of lipid membranes on gold nanorods can be used to determine molecular orientation of molecules within the membrane. The voltage sensitive dye 4-(2-(6-(dibutylamino)-2-naphthalenypetheny1)-1-(3-sulfopropyl)-hydroxide, known as di-4-ANEPPS, is studied. Through the analysis of several peaks in the SERS spectrum, the polar angle from the membrane normal is found to be 66 degrees, and the roll angle around the long axis of the molecule to be 305 degrees from the original orientation. This structural analysis method could help elucidate the meaning of fluorescent membrane probe signals, and how they are affected by different lipid compositions.

First author: Zhang, HZ, Highly efficient blue-emitting of bis-cyclometalated tetravalent platinum (IV) complexes: A theoretical study, INORGANICA CHIMICA ACTA, 501, 521, (2020)
Abstract: Pt(IV) complexes bespeak the prospect as phosphorescent materials because of their excellent properties, whereas the reports of excavating potential properties for Pt (IV) complexes in phosphorescence are limited. To address this issue, a DFT/TDDFT calculation has been applied on two series of biscyclometalated Pt(IV) complexes ([Pt(ppy)(2)XCl], where X = -CH3(1-Me); -CF3(1a-CF3); -CN(1a-CN), -(CH3)(3) (1b-tBu); -CH2NH2(1b-AMe); -C6H5(2-Ph); -C6F5(2a-C-6 F-5) and -2,4,6-(CH3)(3) C6H5 (2b-Mes)) to shed light on the effects of systematic single monodentate ancillary ligand modifications on structure and photophysical properties. The calculated results confirm that all complexes displayed blue emission in dichloromethane solution with varying emission efficiencies that were found to be influenced by the electronic nature of the ancillary ligand. The stronger the electron-releasing ability and the smaller degree of extended conjugation in the monodentate ancillary ligand can give rise to intensive the radiative decay. Regardless of whether pi conjugation exists or not, increasing electron-withdrawing character in ancillary ligand of parent complexes 1-Me ([Pt(ppy)(2)CH3Cl]) or 2-Ph ([Pt(ppy)(2)C6H5Cl]) can be unbeneficial for the nonradiative decay process. In addition, the results demonstrate that complexes 1a-CN ([Pt(ppy)(2)CNCl]) exhibits a better blue phosphorescent material with a higher quantum yield.

First author: Dasgupta, N, ReaxFF molecular dynamics simulations on the structure and dynamics of electrolyte water systems at ambient temperature, COMPUTATIONAL MATERIALS SCIENCE, 172, 521, (2020)
Abstract: ReaxFF molecular dynamics simulations have been performed to study the effect of cations Li+, Na+ and K+ and anion Cl- on the structural and dynamical properties of water, using the force field recently developed by Fedkin and co-workers. The structural relationship of ion and water has been analyzed from the radial distribution function and angular distribution. Comparisons of ReaxFF angle variation of ions and water within the first solvation shell were made and found to be in good agreement with literature. The disruption of hydrogen bond network of water by ions is elucidated by ion-water residence times, water-water hydrogen bond dynamics and reorientational dynamics. ReaxFF diffusion coefficient and residence times of electrolyte water system were compared with ab initio and non-reactive potentials to analyze the difference in dynamics. We gained insight into the ion interaction with water and how it can accelerate or decelerate water dynamics. ReaxFF outlines the formation and dissolution of metal hydroxides and metal chlorides over the course of simulation to explain the diffusion dynamics of water in salt solutions, allowing us to elucidate the impact of concentration on the self-diffusivity of water and ions in solutions, and to reveal that this effect always decreases the mobility and is not at all ion-specific. The obtained results have opened new opportunities to extend the ReaxFF methodology towards systems involving electrolytes.

First author: Mavrommati, SA, Initial-state preparation effects in time-resolved electron paramagnetic resonance experiments, JOURNAL OF CHEMICAL PHYSICS, 152, 521, (2020)
Abstract: We explain a recent experimental observation that the time-resolved electron paramagnetic resonance spectra of an organic molecule for optical excitation within a highly absorbing region of the molecule has similar intensities to the spectra for optical excitation in a nonabsorbing region [D. L. Meyer et al., J. Phys. Chem. Lett. 8, 1677 (2017)]. We demonstrate that this phenomenon is due to an initial-state preparation effect of photoexcitation that leads to similar initial populations of triplet states for both optical excitation regions. Due to the low intersystem crossing rates, the initial triplet populations are not perturbed on the time scale of the experiment, so they determine the relative intensities of the paramagnetic resonance spectra. The effect is surprising given the weak spin-orbit interactions of organic molecules. Such initial-state preparation effects are likely to occur in systems where the intersystem crossing time scales are long compared to the time scale of the experiment. Published under license by AIP Publishing.

First author: Geerlings, P, Conceptual density functional theory: status, prospects, issues, THEORETICAL CHEMISTRY ACCOUNTS, 139, 521, (2020)
Abstract: This paper results from a round table discussion at the CCTC2018 Conference in Changsha City, Hunan, China, in December 2018. It presents a report on the status, prospects, and issues of conceptual density functional theory (CDFT). After a short exposition on the history of CDFT, its fundamentals, philosophy, and successes are highlighted. Then ten issues for reflection on the future of conceptual DFT are formulated and discussed, ending with one or more summarizing statements on the present status of various concepts/principles/practices and proposed directions for future research. The issues include the further analysis of the energy functional, E[N,v], extended to include effects of temperature, solvent, and mechanical forces, basic requirements for physically acceptable response functions as reactivity descriptors, the use of the grand canonical ensemble, the relevance of CDFT for chemical kinetics and thermodynamics, the domain of validity of CDFT-based principles, the combination of CDFT with reaction path calculations, information-theoretic descriptors, and the treatment of excited states and time dependence. The final issue advocates the transition of CDFT from an interpretative to a predictive mode; we believe this is of utmost importance for promoting CDFT as a viable alternative to wave function-based methods for the practicing chemist, a separate issue treated in the final section.

First author: Pietrasiak, E, Understanding Te-125 NMR chemical shifts in disymmetric organo-telluride compounds from natural chemical shift analysis, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 2319, (2020)
Abstract: Organotellurium compounds of general formula X-Te-R display a broad range of chemical shifts that are very sensitive to the X and R substituents. In order to link the Te-125 chemical shift of a series of perfluoroalkyl aryl tellurides to their electronic structure, the chemical shielding tensors of the Te-125 nuclei were calculated by density functional theory (DFT) and further analyzed by a decomposition into contributions of natural localized molecular orbitals (NLMOs). The analysis indicated that the variation in Te-125 chemical shifts in molecules 1-13 is mainly due to the magnetic coupling of the tellurium p-character lone pair with antibonding orbitals perpendicular to it {sigma*(Te-X) and sigma*(Te-C(Ar))} upon action of an external magnetic field. The strength of the coupling is affected by electronic properties of the X-substituents, polarization of the antibonding orbitals and presence of secondary interactions perturbing the energy of these orbitals. The lower in energy and the more polarized towards tellurium the antibonding orbitals are, the stronger is the coupling and the more deshielded the tellurium nucleus.

First author: Lehtola, S, Fully numerical calculations on atoms with fractional occupations and range-separated exchange functionals, PHYSICAL REVIEW A, 101, 2319, (2020)
Abstract: recently developed finite-element approach for fully numerical atomic structure calculations [S. Lehtola, Int. J. Quantum Chem. 119, e25945 (2019)] is extended to the description of atoms with spherically symmetric densities via fractionally occupied orbitals. Specialized versions of Hartree-Fock as well as local density and generalized gradient approximation density functionals are developed, allowing extremely rapid calculations at the basis-set limit on the ground and low-lying excited states, even for heavy atoms. The implementation of range separation based on the Yukawa or complementary error function (erfc) kernels is also described, allowing complete basis-set benchmarks of modern range-separated hybrid functionals with either integer or fractional occupation numbers. Finally, the computation of atomic effective potentials at the local density or generalized gradient approximation levels for the superposition of atomic potentials (SAP) approach [S. Lehtola, J. Chem. Theory Comput. 15, 1593 (2019)] that has been shown to be a simple and efficient way to initialize electronic structure calculations is described. The present numerical approach is shown to afford beyond micro-Hartree accuracy with a small number of numerical basis functions, and to reproduce the literature results for the ground states of atoms and their cations for 1 <= Z <= 86. Our results indicate that the literature values deviate by up to 10 mu E-h from the complete basis-set limit. The numerical scheme for the erfc kernel is shown to work by comparison to results from large Gaussian basis-set calculations from the literature. Spin-restricted ground states are reported for Hartree-Fock and Hartree-Fock-Slater calculations with fractional occupations for 1 <= Z <= 118.

First author: Castro, AC, Computational NMR Spectra of o-Benzyne and Stable Guests and Their Hemicarceplexes, CHEMISTRY-A EUROPEAN JOURNAL, 26, 2626, (2020)
Abstract: The incarceration of o-benzyne and 27 other guest molecules within hemicarcerand 1, as reported experimentally by Warmuth, and Cram and co-workers, has been studied by density functional theory (DFT). The H-1 NMR chemical shifts, rotational mobility, and conformational preference of the guests within the supramolecular cage were determined, which showed intriguing correlations of the chemical shifts with structural parameters of the host-guest system. Furthermore, based on the computed chemical shifts reassignments of some NMR signals are proposed. This affects, in particular, the putative characterization of the volatile benzyne molecule inside a hemicarcerand, for which our CCSD(T) and KT2 results indicate that the experimentally observed signals are most likely not resulting from an isolated o-benzyne within the supramolecular host. Instead, it is shown that the guest reacted with an aromatic ring of the host, and this adduct is responsible for the experimentally observed signals.

First author: Pratik, SM, Boosting Photoelectric Conductivity in Porphyrin-Based MOFs Incorporating C-60, JOURNAL OF PHYSICAL CHEMISTRY C, 124, 1878, (2020)
Abstract: Electronic structure calculations show that guest C-60 in the porphyrin-containing metal organic frameworks Zn-2(TCPB)(DA-ZnP) (DA-MOF; H4TCPB = 1,2,4,5-tetrakis (4-carboxyphenyl)benzene, DA-ZnP = [ 5, 15-bis [(4-pyridyl)ethynyl]-10,20-diphenylporphinato]zinc(II)) and Zn-2(TCPB)(F-ZnP) (F-MOF; F-ZnP = [5,15-di(4-pyridyl)-10,20-bis (p entafluorophenyl)porphinato] zinc (II) ) engenders high photoelectrical conductivity due to efficient donor-acceptor charge-transfer (CT) interactions. Structural modifications at the meso position of the porphyrin influence the preferred positions of C-60 within the frameworks, giving rise to host-guest interactions with different anisotropic structural, electronic, and optoelectronic properties. A preferred slipped-parallel pi-stacked interaction of C-60 that is predicted for NH2-substituted DA-MOF and F-MOF fosters strong CT transitions and lowers band gaps by similar to 1.0 eV compared to the pristine DA-MOF and F-MOF. Hopping rates computed using Marcus theory are found to be anisotropic and accelerated by multiple orders of magnitude across pi-stacked interfaces created by C-60 incorporation, a consequence of strong electronic coupling between initial and final diabatic states. Calculations indicate that photoinduced electron transfer, as well as direct CT from porphyrin to C-60 upon irradiation, triggers a charge separation process that leads to the formation of what should be long-lived electron-trapped states at the heterojunctions. Design principles revealed here for the control of photophysical and electron-transfer processes will be useful for constructing new MOF-derived visible- and infrared-based optoelectronics.

First author: Oschinski, H, Structures and Thermodynamics of MgO/SiO Interfaces, JOURNAL OF PHYSICAL CHEMISTRY C, 124, 1923, (2020)
Abstract: Silicon monoxide is a complex material which tends to form atomic and nanoscale amorphous structures. The question is in which ways can the stability of SiO on suitable carriers or interfaces be enhanced. This was investigated by statistical thermodynamics based on density functional theory calculations on SiO layers on and in-between MgO(100) model surfaces. Furthermore, the stability of ordered close-packed SiO layers and their relaxation into amorphous structures were studied. Some selected SiO structures between thin MgO sheets were investigated and their interface energies are discussed. The results for the interface tensions can be understood by a strong lateral repulsion between atoms in ordered close-packed SiO layers on MgO(100). The SiO layer can thereby induce stress on the MgO sheets.

First author: Dong, QB, Accelerated C2H2/CO2 Separation by a Se-Functionalized Porous Coordination Polymer with Low Binding Energy, ACS APPLIED MATERIALS & INTERFACES, 12, 3764, (2020)
Abstract: High-quality pure acetylene (C2H2) is a kind of crucial starting material for various value-added products. However, selective capture of C2H2 from the main impurity of CO, via porous absorbents is a great challenge, as they possess extremely similar kinetic diameters and boiling points, as well as the explosive and reactive properties of C2H2. Herein, we report a porous coordination polymer (PCP), (NTU-55), which assembled from the coordination between a Cu dimer and a newly designed ligand with a nonmetal selenium (Se) site. Static single-component adsorption and dynamic breakthrough experiments reveal that desolvated NTU-55 can completely adsorb C2H2 from the C2H2/CO2 mixture (1/4, v/v) at 298 K, along with higher C2H2 capacity and much lower binding energy. The origin of this separation, as comprehensively revealed by density functional theory (DFT) calculations, is derived from the interaction discriminatory of C2H2 and CO, toward accessible Se and Cu adsorption sites. To the best of our knowledge, this is the first time to find the positive effect of nonmetal Se sites for selective C2H2 capture.

First author: Vorobyev, V, Synthesis of the Ruthenium Nitrosyl Complex with Coordinated Ammonia and Pyridine at Room Temperature, ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 646, 58, (2020)
Abstract: The reaction of nitrate ruthenium complex, fac-[RuNO(NH3)(2)(NO3)(3)], with pyridine resulted in cis-[RuNO(NH3)(2)Py-2(NO3)](NO3)(2)center dot H2O with 84 % yield of the product at room temperature. Addition of any solvent leads to the reaction failure; the excess of pyridine fulfilled the role of a solvent. The DFT simulation of the dissociative mechanism reveals that the nitrate loss from cis-position to NO occurs more easily than for trans-coordinated nitrate. This conclusion is in agreement with the X-ray determined structure of the product. In the solid state, the nitrosyl groups of two neighboring complexes are closely positioned to each other. The small available volume around the nitrosyl group, ca. 0.5 angstrom(3), leads to the enhanced stability of the photoinduced metastable state. The Ru-ON isomer converts back to the ground N-coordinated state with 0.001 s(-1) rate constant at 257 K. This O-coordinated isomer of the studied complex is one of the ten known most stable Ru-ON isomers ranked by the “decay” temperature.

First author: Barbon, A, Comprehensive investigation of the triplet state electronic structure of free-base 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin by a combined advanced EPR and theoretical approach, JOURNAL OF CHEMICAL PHYSICS, 152, 58, (2020)
Abstract: The nature of the photoexcited triplet state of free-base 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (H2TPPS4-) has been investigated by advanced Electron Paramagnetic Resonance (EPR) techniques combined with quantum chemical calculations. The zero-field splitting (ZFS) parameters, D and E, the orientation of the transition dipole moment in the ZFS tensor frame, and the proton hyperfine couplings have been determined by magnetophotoselection-EPR and pulse electron-nuclear double resonance spectroscopy. Both time-resolved and pulse experiments exploit the electron spin polarization of the photoexcited triplet state. Comparison of the magnetic observables with computational results, including CASSCF calculations of the ZFS interaction tensor, provides an accurate picture of the triplet-state electronic structure. The theoretical investigation has been integrated with a systematic analysis on the parent free-base porphyrin molecule to assess the effect of the sulfonatophenyl substituents on the magnetic tensors. Additionally, the magnetophotoselection effects are discussed in terms of tautomerization in the excited singlet state of H2TPPS4-.

First author: Munoz-Castro, A, Triple 1D equivalent to 1D superatomic bonding. Au-22(dppo)(6) as a pi(4)- and Delta(2)-triply bonded cluster based on Au-11 assembled units, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 1422, (2020)
Abstract: delta-Bonds have been intimately related to metal-metal bonds of d-elements since the archetypal d(4)-d(4) [Re2Cl8](2-) ion with a sigma(2)pi(4)delta(2) bond. Currently, the notion of multiple superatom arrangements as initial steps toward molecular materials within the building-up approach is dominated by P-shell characteristics, as given in the well-described Au-25(SR)(18) ligand protected cluster. In this work we rationalize the Au-22(dppo)(6) cluster as a triple-bonded 22-valence electron (ve) supermolecule, featuring a bonding scheme based on 1D + 1D shell combinations, which largely contrasts with the 14-ve Au-38(SR)(24) with mainly 1P + 1P patterns mimicking a F-2 molecule. The resulting pi(4)Delta(2)-bonding pattern shows an unprecedented superatomic counterpart of a d-shell based bond inherently related to transition-metal dimers, adding useful key aspects to the understanding of species based on cluster-assembly.

First author: Cailler, LP, Comparative Study of the Electronic Structures of mu-Oxo, mu-Nitrido, and mu-Carbido Diiron Octapropylporphyrazine Complexes and Their Catalytic Activity in Cyclopropanation of Olefins, INORGANIC CHEMISTRY, 59, 1104, (2020)
Abstract: The electronic structure of three single-atom bridged diiron octapropylporphyrazine complexes (FePzPr(8))(2)X having Fe(III)-O-Fe(III), Fe(III)-N-Fe(IV) and Fe(IV)-C-Fe(IV) structural units was investigated by Mossbauer spectroscopy and density functional theory (DFT) calculations. In this series, the isomer shift values decrease, whereas the values of quadrupole splitting become progressively greater indicating the increase of covalency of Fe-X bond in the mu-oxo, mu-nitrido, mu-carbido row. The Mossbauer data point to low-spin systems for the three complexes, and calculated data with B3LYP-D3 show a singlet state for mu-oxo and mu-carbido and a doublet state for mu-nitrido complexes. An excellent agreement was obtained between B3LYP-D3 optimized geometries and X-ray structural data. Among (FePzPr(8))(2)X complexes, mu-oxo diiron species showed a higher reactivity in the cyclopropanation of styrene by ethyl diazoacetate to afford a 95% product yield with 0.1 mol % catalyst loading. A detailed DFT study allowed to get insight into electronic structure of binuclear carbene species and to confirm their involvement into carbene transfer reactions.

First author: Pirillo, J, Trans Influence across a Metal-Metal Bond of a Paddle-Wheel Unit on Interaction with Gases in a Metal-Organic Framework, INORGANIC CHEMISTRY, 59, 1193, (2020)
Abstract: Metal-organic frameworks (MOFs) are known as promising adsorbent materials that can recognize gases specifically. In the frameworks, gases favor interacting with specific binding sites such as open metal sites (OMSs), which can consist of various metals and show characteristic adsorption properties. A recently reported framework possessing OMSs of rhodium paddle-wheel (Rh-PW) showed distinct adsorption properties between NO and CO. We investigated theoretically the reasons for stronger NO binding to the Rh-PW and different adsorption amounts between NO and CO using Rh-PW cluster models, as well as the frequently reported Cu-PW for comparison. We also analyzed the cases of CO2 and N-2, which are often used to probe functions of MOFs. We observed an increase in binding energy of NO at the second adduction of NO. On the basis of energy decomposition analysis, we found that Rh-NO bond formation inducing a trans influence is important for the stronger binding than with CO. Furthermore, we proposed a reason for twice the adsorption amount of NO than CO. The results are consistent with experimental observations, giving us insight into design functions of MOFs by selecting metal species.

First author: Leygue, N, Tripyridinophane Platform Containing Three Acetate Pendant Arms: An Attractive Structural Entry for the Development of Neutral Eu(III) and Tb(III) Complexes in Aqueous Solution, INORGANIC CHEMISTRY, 59, 1496, (2020)
Abstract: We report a detailed characterization of Eu3+ and Tb3+ complexes derived from a tripyridinophane macro cycle bearing three acetate side arms (H(3)tpptac). Tpptac(3-) displays an overall basicity (Sigma log K-i(H)) of 24.5, provides the formation of mononuclear ML species, and shows a good binding affinity for Ln(3+) (log K-LnL = 17.5-18.7). These complexes are also thermodynamically stable at physiological pH (pEu = 18.6, pTb = 18.0). It should be noted that the pGd value of Gd-tpptac (18.4) is only slightly lower than that of commercially available MRI contrast agents such as Gd-dota (pGd = 19.2). Moreover, a very good selectivity for these ions over the endogenous cations (log K-CuL = 14.4, log K-ZnL = 12.9, and log K-CaL = 9.3) is observed. The X-ray structure of the terbium complex shows the metal coordinated by the nine N6O3 donor set of the ligand and one inner-sphere water molecule. DFT calculations result in two Eu-tpptac structures with similar bond energies (Delta E = 0.145 eV): one structure in which the water is coordinated to the metal ion and one structure in which the water molecule is farther away from the ion, bound to the ligand with an OH-pi bond. By detailed luminescence experiments, we demonstrate that the europium complex in aqueous solution presents a hydration equilibrium between nine-coordinate, dehydrated [Eu-tpptac](0) and ten-coordinate, monohydrated [Eu-tpptac(H2O)](0) species. A similar trend is observed for the terbium complex. Despite the presence of this hydration equilibrium, the H(3)tpptac ligand sensitizes Eu3+ and Tb3+ luminescence efficiently in buffered water at physiological pH. Particularly, the terbium complex displays a long excited-state lifetime of 2.24 ms and an overall quantum yield of 33% with a brightness of 3600 M-1 cm(-1). Such features of Ln(3+) complexes of H(3)tpptac indicate that this platform appears to be particularly appealing for the further development of luminescent lanthanide labels.

First author: Tsoureas, N, Uranium(iv) cyclobutadienyl sandwich compounds: synthesis, structure and chemical bonding, CHEMICAL COMMUNICATIONS, 56, 944, (2020)
Abstract: The 1:1 reactions of uranium(iv) tetrakis(borohydride) with the sodium and potassium salts of the cyclobutadienyl anion [C-4(SiMe3)(4)](2-) (Cb ””) produce the half-sandwich complexes [Na(12-crown-4)(2)][U(eta(4)-Cb ””)(BH4)(3)] and [U(eta(4)-Cb ””)(mu-BH4)(3){K(THF)(2)}](2). In the 1:2 reaction of U(BH4)(4) with Na2Cb ””, formation of [U(eta(4)-Cb ””)(eta(3)-C4H(SiMe3)(3)-kappa-(CH2SiMe2)(BH4))](-) reveals that a Cb ”” ligand undergoes an intramolecular deprotonation, resulting in an allyl/tuck-in bonding mode. A computational study reveals that the uranium-Cb ”” bonding has an appreciable covalent component with contributions from the uranium 5f and 6d orbitals.

First author: Tanriver, G, Keteniminium Salts: Reactivity and Propensity toward Electrocyclization Reactions, JOURNAL OF ORGANIC CHEMISTRY, 85, 449, (2020)
Abstract: A predictive computational study was conducted in order to assess the efficiency of electrocyclization reactions of keteniminium salts, in an effort to form a variety of heterocyclic systems, namely, 3-amino(benzo)thiophenes, 3-amino(benzo)furans, 3-aminopyrroles, as well as 3-amino-indoles. A density functional theory (DFT) approach was utilized and the effect of heteroatoms (NMe, O, S) was thoroughly investigated by means of population analysis, QTAIM, NICS, ACID, and local reactivity descriptors (Parr and Fukui functions). The electrocyclization of enamines leading to 3-aminopyrroles was shown to be both kinetically and thermodynamically most favorable. Moreover, the pericyclic nature of the electrocyclizations was confirmed using FMO, QTAIM, NICS, and ACID methods. Additionally, substituent effects were investigated in order to give further insight on the reactivity of heteroatom containing keteniminium systems toward electrocyclization reactions. Finally, computational predictions were experimentally confirmed for a selection of keteniminium systems.

First author: Reese, HR, Peptide science: A “rule model” for new generations of peptidomimetics, ACTA BIOMATERIALIA, 102, 35, (2020)
Abstract: Peptides have been heavily investigated for their biocompatible and bioactive properties. Though a wide array of functionalities can be introduced by varying the amino acid sequence or by structural constraints, properties such as proteolytic stability, catalytic activity, and phase behavior in solution are difficult or impossible to impart upon naturally occurring alpha-L-peptides. To this end, sequence-controlled peptidomimetics exhibit new folds, morphologies, and chemical modifications that create new structures and functions. The study of these new classes of polymers, especially alpha-peptoids, has been highly influenced by the analysis, computational, and design techniques developed for peptides. This review examines techniques to determine primary, secondary, and tertiary structure of peptides, and how they have been adapted to investigate peptoid structure. Computational models developed for peptides have been modified to predict the morphologies of peptoids and have increased in accuracy in recent years. The combination of in vitro and in silico techniques have led to secondary and tertiary structure design principles that mirror those for peptides. We then examine several important developments in peptoid applications inspired by peptides such as pharmaceuticals, catalysis, and protein-binding. A brief survey of alternative backbone structures and research investigating these peptidomimetics shows how the advancement of peptide and peptoid science has influenced the growth of numerous fields of study. As peptide, peptoid, and other peptidomimetic studies continue to advance, we will expect to see higher throughput structural analyses, greater computational accuracy and functionality, and wider application space that can improve human health, solve environmental challenges, and meet industrial needs.

First author: Wang, J, Electronic Transport Inhibiting of Carbon Nanotubes by 5f Elements, ADVANCED THEORY AND SIMULATIONS, 3, 35, (2020)
Abstract: Based on the combination of the non-equilibrium Green’s function and density functional theory, a theoretical method for studying the transport behavior of high angular momentum 5f electrons is developed and the transport properties of the structure for actinide atoms embedded in carbon nanotubes (An@CNTs, An = Ac, Th, Pa and U) is reported. Results show that An@CNTs have lower transmission coefficients than that of CNTs. Furthermore, electrical bias to the U@(4, 4)/(5, 5) CNTs induces an additional transition spectral peak, which demonstrates that the U@(4, 4)/(5, 5) CNTs has a lower resistance. Therefore, 5f electrons of actinide atoms inhibit the electronic transport of CNTs. These findings may provide fresh insight into the transport properties of systems having higher angular momentum electrons.

First author: Chen, R, Interpreting the chemical mechanism in SERS using a Raman bond model, JOURNAL OF CHEMICAL PHYSICS, 152, 35, (2020)
Abstract: We present a first-principles model that partitions Raman intensities to atomic and bond contributions. This framework allows us to interpret the chemical mechanism in surface-enhanced Raman scattering (SERS) as interatom charge flow modulations, which we define as Raman bonds. Hirshfeld partitioning and charge density localization are applied to express polarizability derivatives as charge flow modulations. Model systems consisting of pyridines, thiols, and carbenes interacting with metal clusters are studied using time-dependent density functional theory. We demonstrate that the mode-specific enhancements can be explained as Raman bonds conjugated across the molecule-metal interface. We also illustrate that the changes in Raman intensities induced by electric fields or chemical substitutions can generally be interpreted as changes of charge flows. The model is shown to work consistently for different types of molecule-metal bonds. Furthermore, our work shows that increasing the Raman bond conjugation across the interface leads to stronger chemical enhancements. The Raman bond model developed in this work provides a quantitative and intuitive interpretation of the chemical mechanism in SERS.

First author: De, S, Molecular mechanism of Be2+-ion binding to HLA-DP2: tetrahedral coordination, conformational changes and multi-ion binding, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 799, (2020)
Abstract: The chemistry of beryllium is rather unusual, however, less explored as compared to other main group elements. This is mainly attributed to the high toxicity of beryllium, leading to chronic granulomatous pneumonitis, called chronic beryllium disease (CBD). It has been reported that Be2+-ion binding to the human leukocyte antigen protein (HLA-DP2) and peptide (M2) results in favorable interaction with the T-cell receptor protein (TCR), which initiates immune-mediated toxicity. We have carried out molecular dynamics (MD) simulations combined with quantum mechanical/molecular mechanical (QM/MM) studies to explore the binding nature of Be2+ with a HLA-DP2 protein and M2 peptide. The interaction between the negatively charged M2 peptide and the negatively charged binding cleft of HLA-DP2 is unfavorable. However, this interaction is stabilized by one Be2+ and two Na+-ions bridged by negatively charged carboxyl groups of glutamate residues (beta 26E and beta 69E) of the beta-chain of HLA-DP2 and one glutamate (p7E) and one aspartate residue (p4D) of the M2 peptide. This multi-ion cavity consists of tetrahedrally coordinated static Be2+ and Na+-ions, as well as one dynamically exchangeable Na+-ion. The smaller size and higher charge of the Be2+-ion as compared to the Na+-ion reduce the distance between the M2 peptide and the beta-chain of HLA-DP2, which results in conformational change suitable for TCR binding. However, the replacement of the Be2+ by the Na+-ion could not generate a suitable binding site for TCR.

First author: Ramanathan, N, Prototypical cyclohexane dimers: spectroscopic evidence for sigma stacking at low temperatures, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 905, (2020)
Abstract: Owing to the fact that sigma stacking is as important as pi stacking in determining the structural motifs of aliphatic saturated cyclic hydrocarbons, in this work we have provided the first unambiguous spectroscopic evidence for the existence of sigma stacking interactions in cyclohexane dimers at low temperatures. Molecular beam experiments performed using effusive nozzle and supersonic jet sources on cyclohexane in an N-2 matrix generated cyclohexane dimers stabilized through sigma stacking and the dimers were characterized by infrared spectroscopy. The ab initio computations carried out on cyclohexane dimers identified eclipsed (face-to-face), parallel displaced and T-shaped structures, which are predominantly stabilized by sigma stacking interactions. While natural bond orbital analysis substantiated a significant amount of sigma -> sigma* interactions involved in the stabilization, the Atoms in Molecules analysis indicated that the stacking is induced by a plausible ‘dihydrogen bonding’ interaction. Energy decomposition analysis disclosed that a large measure of dispersion interactions effectively contributes for the overall stability of cyclohexane dimers.

First author: Prasad, S, Hop-Skip-Jump: Monovalent Metals on the Surface of the Phenalenyl Radical, ORGANOMETALLICS, 39, 34, (2020)
Abstract: The phenalenyl radical (P) and its relatively stable cation and anion are of interest for applications in areas spanning magnetic materials and ligand development for reaction catalysis. We report on a broad investigation of the bonding, thermochemistry, and kinetics of PM complexes where M is a group 1 or 11 metal atom. The PM species that are considered in this work afford a simplified picture of the behavior of metal adatoms on hydrogen terminated graphene fragments, and, more crucially, we expand a still nascent understanding of the organometallic chemistry of P. The exceptional fluxionality of group 1 metals on the phenalenyl surface is predicted, the associated energy barriers are quantified, and the major role of relativistic effects in restricting the fluxionality of Au on the surface is demonstrated. Although relativistic effects swell the barriers to isomerization, we find that orbital size and energies, even in the absence of relativistic effects, dictate different path preferences for the motion of Au on the surface of the radical compared to Cu and Ag.

First author: Maria, L, CO2 conversion to phenyl isocyanates by uranium(vi) bis(imido) complexes, CHEMICAL COMMUNICATIONS, 56, 431, (2020)
Abstract: Uranium(vi) trans-bis(imido) complexes [U(kappa(4)-{((2ArO)-Ar-tBu)(2)Me-2-cyclam})(NPh)(NPh (R))] react with CO2 to eliminate phenyl isocyanates and afford uranium(vi) trans-[O=U=NR](2+) complexes, including [U(kappa(4)-{((2ArO)-Ar-tBu)(2)Me-2-cyclam})(NPh)(O)] that was crystallographically characterized. DFT studies indicate that the reaction proceeds by endergonic formation of a cycloaddition intermediate; the secondary reaction to form a dioxo uranyl complex is both thermodynamically and kinetically hindered.

First author: Vermeeren, P, Understanding chemical reactivity using the activation strain model, NATURE PROTOCOLS, 15, 649, (2020)
Abstract: This analysis of chemical reaction mechanisms is based on the activation strain model of reactivity. The PyFrag 2019 program is used to perform activation strain and energy decomposition analysis on each point along the energy profile.

First author: Wen, J, Electronic States of 2,3-Diamino-1,4-naphthoquinone and Its N-Alkylated Derivatives, JOURNAL OF PHYSICAL CHEMISTRY C, 124, 60, (2020)
Abstract: Diaminoquinones with a captodatively stabilized biradicaloid structure are candidates for singlet fission, but few such compounds are known. We report the solution spectroscopy and photophysics of 1,2,2,3-tetramethy1-2,3-dihydro-1H-naphtho[2,3-d]-imidazole-4,9-dione (1): its steady-state and transient UV-visible absorption, linear dichroism in stretched poly(vinyl alcohol), and magnetic circular dichroism. We also describe the absorption spectra of the stable radical ions 1(center dot+) and 1(center dot-) and of two parent structures, 2,3-diamino-1,4-naphthoquinone (2) and 2,3-bis(methylamino)-1,4-naphthoquinone (3). The spectra are interpreted and electronic transitions are assigned by comparison with the results of density functional theory and MS-CASPT2 calculations.

First author: Kukulka, M, Substituent Effect on Conformational Preferences in Ground and Excited States of Selected Schiff Bases: An Insight from Theoretical Calculations, JOURNAL OF PHYSICAL CHEMISTRY A, 124, 63, (2020)
Abstract: 2-Hydroxy aromatic Schiff bases that exhibit ESIPT (excited state intramolecular proton transfer) or TICT (twisted intramolecular charge transfer) photodeactivation pathways emerge as promising candidates for fluorescent sensors. In this computational work the influence of various substituents, differing in the electronic properties, on conformational preferences in the ground and S-1 excited state for a series of 2-hydroxy-1-naphthylmethylene-hydrazine-based ligands is systematically studied using (TD)DFT calculations. In order to shed light on physical factors which might determine the obtained conformational preferences, extensive bonding analyses are performed. The results highlight the crucial role of a substituent’s ability to form not only well-established intramolecular hydrogen bonds (e.g., O-H center dot center dot center dot N) but also unintuitive nonclassic weak interactions (e.g., C-H center dot center dot center dot O, C-H center dot center dot center dot N, and C-H center dot center dot center dot H-C) in the modulation of the equilibrium between naphthol-imine and keto-amine forms, and planar or twisted conformations, and, thus, in determination of photophysical properties of the considered bases.

First author: Ponzi, A, Photoionization of C-60: Effects of Correlation on Cross Sections and Angular Distributions of Valence Subshells, JOURNAL OF PHYSICAL CHEMISTRY A, 124, 108, (2020)
Abstract: Calculations of the photoionization cross section and asymmetry parameter, beta, are performed at the density functional theory (DFT) and time-dependent density functional theory (TDDFT) levels for all 32 valence levels of C-60. Accurate numerical results are obtained for the isolated molecule in icosahedral symmetry. A detailed analysis based on the comparison between the DFT and TDDFT results allows the identification of four types of resonances: the well-known confinement resonances of mainly geometrical origin, shape resonances native to the ionization channel, induced shape resonances, and autoionization resonances brought about by interchannel coupling, as well as their different prominence in cross section or asymmetry parameter. Generally, cross sections are enhanced at the TDDFT level, which includes contribution from the bound-state excitations from closed channels, neglected at the DFT level, and the effect persists even well above the highest ionization threshold. This effect is best seen in the total cross section, although not as dramatic as found from simpler models, probably due to the stiffer electronic structure inherent in the full molecular description. The effects of interchannel coupling on individual native resonances are rather less predictable, leading to both enhancement and decreases and often altering the details of the structure significantly. A comparison with the previous accurate total cross-sectional calculations, as well as with the available experimental data, is very good for cross sections but slightly inferior for beta’s. The results reported can serve as a reference to compare the effects of different environments on C-60, as well as chemical substitution, notably endohedral fullerenes.

First author: Ramanantoanina, H, Electronic Structure and Photoluminescence Properties of EU(eta(9)-C9H9)(2), JOURNAL OF PHYSICAL CHEMISTRY A, 124, 152, (2020)
Abstract: The electronic structure of Eu2+ compounds results from a complex combination of strongly correlated electrons and relativistic effects as well as weak ligand-field interaction. There is tremendous interest in calculating the electronic structure as nowadays the Eu2+ ion is becoming more and more crucial, for instance, in lighting technologies. Recently, interest in semiempirical methods to qualitatively evaluate the electronic structure and to model the optical spectra has gained popularity, although the theoretical methods strongly rely upon empirical inputs, hindering their prediction capabilities. Besides, ab initio multireference models are computationally heavy and demand very elaborative theoretical background. Herein, application of the ligand-field density functional theory (LFDFT) method that is recently available in the Amsterdam Modeling Suite is shown: (i) to elucidate the electronic structure properties on the basis of the multiplet energy levels of Eu configurations 4f(7) and 4f(6)5d(1) and (ii) to model the optical spectra quite accurately if compared to the conventional time-dependent density functional theory tool. We present a theoretical study of the molecular Eu(eta(9)-C9H9)(2) complex and its underlying photoluminescence properties with respect to the Eu 4f-5d electron transitions. We model the excitation and emission spectra with good agreement with the experiments, opening up the possibility of modeling lanthanides in complex environment like nanomaterials by means of LFDFT at much-reduced computational resources and cost.

First author: Oudsen, JPH, Electronic characterization of redox (non)-innocent Fe2S2 reference systems: a multi K-edge X-ray spectroscopic study, RSC ADVANCES, 10, 729, (2020)
Abstract: Di-iron dithiolate hydrogenase model complexes are promising systems for electrocatalytic production of dihydrogen and have therefore been spectroscopically and theoretically investigated in this study. The direct effect of ligand substitution on the redox activity of the complex is examined. In order to understand and eventually optimize such systems, we characterised both metal and ligand in detail, using element specific X-ray absorption Fe- and S-K edge XAS. The (electronic) structure of three different [Fe2S2] hydrogenase systems in their non-reduced state was investigated. The effect of one- and two-electron reduction on the (electronic) structure was subsequently investigated. The S K-edge XAS spectra proved to be sensitive to delocalization of the electron density into the aromatic ring. The earlier postulated charge and spin localization in these complexes could now be measured directly using XANES. Moreover, the electron density (from S K-edge XANES) could be directly correlated to the Fe-CO bond length (from Fe K-edge EXAFS), which are in turn both related to the reported catalytic activity of these complexes. The delocalization of the electron density into the conjugated pi-system of the aromatic moieties lowers the basicity of the diiron core and since protonation occurs at the diiron (as a rate determining step), lowering the basicity decreases the extent of protonation and consequently the catalytic activity.

First author: Bonde, NA, Importance of Axial Symmetry in Elucidating Lanthanide-Transition Metal Interactions, INORGANIC CHEMISTRY, 59, 235, (2020)
Abstract: In this paper, we experimentally study and model the electron donating character of an axial diamagnetic Pd2+ ion in four metalloligated lanthanide complexes of formula [PPh4] [Ln-{Pd(SAc)(4)}(2)] (SAC(-) = thioacetate, Ln = Tb, Dy, Ho, and Er). A global model encompassing inelastic neutron scattering, torque magnetometry, and dc magnetometry allows to precisely determine the energy level structure of the complexes. Solid state nuclear magnetic resonance reveals a less donating character of Pd2+ compared to the previously reported isostructural Pt2+ based complexes. Consequently, all complexes invariably show a lower crystal field strength compared to their Pt2+-analogues. The dynamic properties show an enhanced single molecule magnet behavior due to the suppression of quantum tunneling, in agreement with our model.

First author: Heiss, P, Combined Experimental and Theoretical Study on Hampered Phosphine Dissociation in Heteroleptic Ni/Zn Complexes, INORGANIC CHEMISTRY, 59, 514, (2020)
Abstract: Heterometallic Ni/Zn complexes can serve as molecular models for the semihydrogenation of acetylene catalyzed by heterogeneous Ni/Zn phases. Pursuing this target, we present the synthesis of the series [Ni(ZnCp*)(n)(ZnMe)(n)(PEt3)(4-n) (n = 1-3; 1, 2, 3) which is obtained via E/Zn exchange from [Ni(ECp*)(n)(PEt3)(4-n)](n = 1-3, E = Al, Ga; P1, P2, P3). The isolation of the intermediate compound [Ni(GaCp*)(ZnCp*) isolation of the intermediate compound [Ni(GaCp*)(ZnCp*)-ZnMe)(PEt3)(2)] (2a) supports the assumption of a stepwise Ga/Zn exchange in the formation of 3. The dissociation behavior of PEt3 in 2 and 3 was investigated experimentally using variable temperature VT) UV-vis spectroscopy indicating suppressed phosphine dissociation in both cases. For comparison, the absorption spectra of the saturated and unsaturated compounds were calculated using time dependent DFT calculations (TDDFT). Energy decomposition analysis with the natural orbital for chemical valence extension (EDA NOCV) calculations shows a bond strengthening of the Ni-P bond by successive substitution of the phosphines with (ZnR)(2) units. The influence of different phosphines (PMe3, PEt3, PPh3, P(OEt)(3)) on Ni-P bond length and on Zn-Zn interactions in [Ni(ZnR)(2n)(PR’)(4-n)] (R = Cp*, Me; R’ = Me, Et, Ph, OEt) was also studied by DFT calculations. A correlation of increasing sterical demand of the phosphine ligand and a shortening of the Zn-Zn distances is observed.

First author: Aramburu, JA, Ground State and Optical Excitations in Compounds with Tetragonal CuF64- Units: Insight into KAlCuF6 and CuFAsF6, INORGANIC CHEMISTRY, 59, 539, (2020)
Abstract: It has been argued that AAlCuF(6) (A = K, Cs) and CuFAsF6 are the only known crystals that exhibit compressed CuF64- units due to the Jahn-Teller effect. However, no grounds for this singular behavior have yet been reported. By means of first-principles calculations on such compounds and the isomorphous compounds involving Zn2+ ions instead of Cu2+, we prove that neither the ground state nor the equilibrium geometry of CuF64- complexes in KAlCuF6 and CuFAsF6 is the result of a Jahn-Teller effect. In contrast, it is shown that the internal electric field, E-R(r), created by the rest of the lattice ions upon the localized electrons in the complex, plays an important role in understanding this matter as well as the d-d transitions of these two compounds. The energy of an optical transition is shown to involve two contributions: the intrinsic contribution derived for the isolated CuF64- unit at equilibrium and the extrinsic contribution coming from the E-R(r) field. Aside from reproduction of the experimental d-d transitions observed for KAlCuF6, it is found that in CuFAsF6 the b(1g) (x(2) – y(2)) -> a(1g) (3z(2) – r(2)) transition is not the lowest one due to the stronger effects from the internal field. Interestingly, the intrinsic contribution corresponding to that transition can simply be written as beta(R-eq – R-ax) where R-eq and R-ax are the equatorial and axial Cu2+-F- distances and beta = 2.7 eV/angstrom is the same for all systems involving tetragonal CuF64- units and an average metal-ligand distance close to 2.03 angstrom. This shows the existence of a common point shared by the Jahn-Teller system KZnF3:Cu2+ and other non-Jahn-Teller systems such as KAlCuF6, CuFAsF6, K2ZnE4:Cu2+, and Ba2ZnF6:Cu2+. Although most Jahn-Teller systems display an elongated geometry, there are however many Cu’ compounds with a compressed geometry but hidden by an additional orthorhombic instability. The lack of that instability in KAlCuF6 and CuFAsF6 is also discussed.

First author: Kaiukov, R, Cs3Cu4In2Cl13 Nanocrystals: A Perovskite-Related Structure with Inorganic Clusters at A Sites, INORGANIC CHEMISTRY, 59, 548, (2020)
Abstract: An effort to synthesize the Cu(I) variant of a lead-free double perovskite isostructural with Cs2AgInCl6 resulted in the formation of Cs3Cu4In2Cl13 nanocrystals with an unusual structure, as revealed by single-nanocrystal three-dimensional electron diffraction. These nanocrystals adopt a A(2)BX(6) structure (K2PtCl6 type, termed vacancy ordered perovskite) with tetrahedrally coordinated Cu(I) ions. In the structure, 25% of the A sites are occupied by [Cu4Cl](3+) clusters (75% by Cs+), and the B sites are occupied by In3+. Such a Cs3Cu4In2Cl13 compound prepared at the nanoscale is not known in the bulk and is an example of a multinary metal halide with inorganic cluster cations residing in A sites. The stability of the compound was supported by density functional theory calculations that also revealed that its bandgap is direct but parity forbidden. The existence of the Cs3Cu4In2Cl13 structure demonstrates that small inorganic cluster cations can occupy A sites in multinary metal halides.

First author: Hussain, M, TD-DFT insights into the sensing potential of the luminescent covalent organic framework for indoor pollutant formaldehyde, SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY, 224, 548, (2020)
Abstract: This paper investigates the sensitivity of the luminescent thieno[2,3-b]thiophene-based covalent organic framework (TT-COF) towards the formaldehyde using the density functional theory and time-dependent method. The hydrogen bonding dynamics is explored by comparison of geometries, electronic transition energies, binding energies, UV-vis, and infrared spectra. Frontier molecular orbitals examination, natural population analysis, and plotted electron density difference map describe the quenching process explicitly via electron density distribution. The MOMAP program illuminates the quenching owing to TT-COF-HCHO complex radiative rate constant. Furthermore, the S1-T1 energy gap describes the facilitation of the luminescence quenching through the intersystem crossing. Above all results elaborate the TT-COF’s potential to detect the formaldehyde.

First author: Pino-Rios, R, B12N12 cluster as a collector of noble gases: A quantum chemical study, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 115, 548, (2020)
Abstract: Systematic analysis of the noble gas (Ng = He – Rn) trapping capacity of the B12N12 cluster were performed at the PBE0-D3/def2-TZVP level by means of thermochemical data, topological analysis of the electron density (QTAIM), non-covalent interactions index (NCI), and energy decomposition analysis (EDA). The results indicate that the Ng(n)B(12)N(12) (n = 1, 12) cluster can be obtained below room temperature. Additionally, it was found that this cluster can trap up to 12 noble gas atoms without losing stability, Finally, the effect of an applied electric field has been analysed, showing that the interaction energy can be improved through this strategy.

First author: Kravtsova, AN, Synchrotron-Based X-Ray Absorption Spectroscopy for the Study of Geological Materials, JOURNAL OF SURFACE INVESTIGATION, 14, 135, (2020)
Abstract: X-ray absorption spectroscopy (XAS) is a new highly effective nondestructive technique for diagnostics of the local atomic and electronic structure of materials, including those that do not have long-range order in their atomic arrangement. In particular, X-ray absorption near edge structure (XANES) spectroscopy makes it possible to identify materials, to assess the oxidation states of atoms, and to find the parameters of the full 3D local structure around absorbing atoms with a high degree of accuracy, up to 1 pm for bond lengths and several degrees for bond angles. This review describes the current state and capabilities of XAS spectroscopy and, in particular, XANES in studying terrestrial and extraterrestrial natural materials. Modern synchrotron centers allow the acquisition of XAS spectra of materials with high energy and time resolutions, with microfocusing and nanofocusing, and spectral measurements under real conditions (for example, directly under high pressures and temperatures). These broad possibilities make X-ray absorption spectroscopy a unique highly effective technique for the diagnostics of geological materials.

First author: Backler, F, Switching On/Off the Intramolecular Hydrogen Bonding of 2-Methoxyphenol Conformers: An NMR Study, AUSTRALIAN JOURNAL OF CHEMISTRY, 73, 222, (2020)
Abstract: Intramolecular hydrogen bonding of 2-methoxyphenol (2-MP, guaiacol) is studied using NMR spectroscopy combined with quantum mechanical density functional theory (DFT) calculations. The hydrogen bonding of OHO and HOH is switched on in the conformers of anti-syn (AS, 99.64% dominance) and anti-gauche (AG), respectively, with respect to the anti-anti (AA) conformer (without either such hydrogen bonding interactions). It confirms that the 13 C and 1 H NMR chemical shift of AS dominates the measured NMR spectra, as the AS conformer reproduces the measurements in CDCl3 solvent (RMSD of 1.86 ppm for 13 CNMRand of 0.27 ppm for 1 H NMR). The chemical shift of hydroxylH(1) at 5.66 pm is identified as the fingerprint of theOH(1)OCH3 hydrogen bonding in AS, as it exhibits a significant deshielding fromH(1) ofAA(4.24 ppm) andH(1) ofAG (4.38 ppm) without suchOH(1)OCH3 hydrogen bonding. TheAGconformer (C1 point group symmetry) possesses a less strong hydrogen bonding of HOHCH2O, with the methoxyl group out of the aromatic phenol plane. The substituent effect of AG due to the resonance interaction of methoxyl being out of plane in a concentrated solution shifts the ortho-and para-aromatic carbons, C(3)/C(5), of the AG to,125.05/125.44 ppm from the corresponding carbons in AS at 108.81/121.60 ppm. The hydrogen bonding exhibits inwards reduction of IR frequency regions of AS and AG from AA. Finally, energy decomposition analysis (EDA) indicates that there is a steric energy of 45.01 kcal mol1 between the AS and AG when different intramolecular hydrogen bonding is switched on.

First author: Spiegelman, F, Density-functional tight-binding: basic concepts and applications to molecules and clusters, ADVANCES IN PHYSICS-X, 5, 222, (2020)
Abstract: The scope of this article is to present an overview of the Density Functional based Tight Binding (DFTB) method and its applications. The paper introduces the basics of DFTB and its standard formulation up to second order. It also addresses methodological developments such as third order expansion, inclusion of non-covalent interactions, schemes to solve the self-interaction error, implementation of long-range short-range separation, treatment of excited states via the time-dependent DFTB scheme, inclusion of DFTB in hybrid high-level/low level schemes (DFT/DFTB or DFTB/MM), fragment decomposition of large systems, large scale potential energy landscape exploration with molecular dynamics in ground or excited states, non-adiabatic dynamics. A number of applications are reviewed, focusing on -(i)- the variety of systems that have been studied such as small molecules, large molecules and biomolecules, bare or functionalized clusters, supported or embedded systems, and -(ii)- properties and processes, such as vibrational spectroscopy, collisions, fragmentation, thermodynamics or non-adiabatic dynamics. Finally outlines and perspectives are given.

First author: Toader, AM, The Structural Details of Aspirin Molecules and Crystals, CURRENT MEDICINAL CHEMISTRY, 27, 99, (2020)
Abstract: We revisit, in the key of structural chemistry, one of the most known and important drugs: the aspirin. Although apparently simple, the factors detennining the molecular structure and supramolecular association in crystals are not trivial. We addressed the problem from experimental and theoretical sides, considering issues from X-ray measurements and results of first-principle reconstruction of molecule and lattices by ab initio calculations. Some puzzling problems can give headaches to specialists and intrigue the general public. Thus, the reported polymorphism of aspirin is disputed, a so-called form II being alleged as a result of misinterpretation. At the same time, were presented evidences that the structure of common form I can he disrupted by domains where the regular packing is changed to the pattern of form IL The problems appear even at the level of independent molecule: the most stable conformation computed by various techniques of electronic structure differs from those encountered in crystals. Because the energy difference between the related conformational isomers (computed as most stable vs. the experimental structure) is small, about 1 kcal/moll, comprised in the error bars of used methods, the unrest Mg question is whether the modelling is imprecise, or the supramolecular factors are Imitating the conformational preferences. By a detective following of the issue, the intermolecular effects were made responsible for the conformation of the molecule in crystal. The presented problems were gathered from literature results, debates, glued with modelling and analysis redone by ourselves. in order to secure the unitary view of the considered prototypic topic.

First author: Lu, L, Pnictogen, chalcogen, and halogen bonds in catalytic systems: theoretical study and detailed comparison, JOURNAL OF MOLECULAR MODELING, 26, 99, (2020)
Abstract: Although halogen bond (XB), a typical sigma-hole noncovalent interaction, has been widely exploited in organocatalysis within the last two decades, only very recently has its sister sigma-hole interactions, such as chalcogen bond (ChB) and pnictogen bond (PnB), begun to be explored for potential applications in catalysis. Herein, a detailed comparison investigation of PnB, ChB, and XB interactions in catalytic systems was performed from a theoretical point of view. Owing to the excellent properties of the pentafluorophenyl moiety (C6F5) in catalysis, the complexes of (C6F5)(3)Pn, (C6F5)(2)Ch, and C6F5X with chloride ion were firstly studied. Then, we successively substituted C6F5 by phenyl groups, to examine the influence of substituents on the characteristics of such interactions. In addition, several halogen-bonded complexes between the donor 1,3,5-trifluoro-2,4,6-triiodobenzene (C6F3I3) and heavier Pn and Ch species as acceptors were also investigated. Our calculations showed that the interactions become gradually stronger upon going from row 3 to 5 and from main group VII to V, which correlates well with the experimental observations. As the strength of the interactions enhances, the contribution of electrostatics to the attraction increases, while the orbital term contribution becomes smaller. Particularly, the significant differences between the three types of sigma-hole interactions found in catalysis and anion transport were clarified.

First author: Amati, M, The Electron Affinity as the Highest Occupied Anion Orbital Energy with a Sufficiently Accurate Approximation of the Exact Kohn-Sham Potential, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 16, 443, (2020)
Abstract: Negative ions are not accurately represented in density functional approximations (DFAs) such as (semi)local density functionals (LDA or GGA or meta-GGA). This is caused by the much too high orbital energies (not negative enough) with these DFAs compared to the exact Kohn-Sham values. Negative ions very often have positive DFA HOMO energies, hence they are unstable. These problems do not occur with the exact Kohn-Sham potential, the anion HOMO energy then being equal to minus the electron affinity. It is therefore desirable to develop sufficiently accurate approximations to the exact Kohn-Sham potential. There are further beneficial effects on the orbital shapes and the density of using a good approximation to the exact KS potential. Notably the unoccupied orbitals are not unduly diffuse, as they are in the Hartree-Fock model, with hybrid functionals, and even with (semi)local density functional approximations (LDFAs). We show that the recently developed B-GLLB-VWN approximation [Gritsenko et al. J. Chem. Phys. 2016, 144, 204114] to the exact KS potential affords stable negative ions with HOMO orbital energy close to minus the electron affinity.

First author: Thomas, KE, Gold dipyrrin-bisphenolates: a combined experimental and DFT study of metal-ligand interactions, RSC ADVANCES, 10, 533, (2020)
Abstract: Given that noninnocent and metalloradical-type electronic structures are ubiquitous among dipyrrin-bisphenolate (DPP) complexes, we synthesized the gold(iii) derivatives as potentially innocent paradigms against which the properties of other metallo-DPP derivatives can be evaluated. Electronic absorption spectra, electrochemical studies, a single-crystal X-ray structure, and DFT calculations all suggest that the ground states of the new complexes indeed correspond to an innocent Au-III-DPP3-, paralleling a similar description noted for Au corroles. Interestingly, while DFT calculations indicate purely ligand-centered oxidations, reduction of AuDPP is predicted to occur across both the metal and the ligand.

First author: Pal, R, Ligand stabilized transient “MNC” and its influence on MNC -> MCN isomerization process: a computational study (M = Cu, Ag, and Au), THEORETICAL CHEMISTRY ACCOUNTS, 139, 533, (2020)
Abstract: A theoretical investigation of the binding ability of different ligands [L = CO, H2O, H2S, N-2, NH3, 1,3-dimethylimidazole (DMI), C2H2 and C2H4] with metal isocyanide and cyanide (MNC and MCN; M = Cu, Ag, Au) compounds has been carried out using quantum chemical computations. In order to analyze the thermochemical stability of these complexes, we have calculated the changes in the related dissociation energies and free energies by considering different possible dissociation pathways (four two-body and one three-body) such as (a) LMCN(/NC) = L + MCN(/NC); (b) LMCN = LM + CN; (c) LMCN = L + M + CN; (d) LMCN = LM+ + CN-; and (e) LMCN = L- + MCN+. The possible dissociation processes are endothermic in nature at room temperature suggesting non-spontaneity at 298 K. Our inspection suggests that MNC have higher binding ability than the MCN compounds in all of the L-bonding cases and both of them follow similar trends as Au > Cu > Ag. The natural bond orbital analysis, topological analysis of the electron density from atoms in molecules technique, and energy decomposition analysis have been carried out to characterize the nature of interaction between L and MCN which shows that the L-M bonds acquire some degree of covalent character. Furthermore, in order to check the validity of the conceptual DFT-based electronic structure principles like maximum hardness and minimum electrophilicity principles, the change in the relevant global reactivity descriptors like chemical hardness (eta), chemical potential (mu), and electrophilicity index (omega) is also studied along the isomerization path, LMNC -> LMCN.

First author: Miao, SS, DFT study of non-covalent interaction mechanisms of solvents with GO surfaces and the solvent-mediated GO interaction, APPLIED SURFACE SCIENCE, 499, 533, (2020)
Abstract: Understanding the non-covalent interaction between solvent and graphene oxide (GO) is of significance to the application of GOs. Herein, the adsorption interactions of several typical solvents with GO surfaces were studied by density functional theory, in which non(less)-polar, protic polar, and aprotic polar solvents were included. The interaction energies, geometrical characteristics, and bonding natures have been characterized. The atomsin-molecule theory and the natural orbitals for chemical valence analysis reveal that miscellaneous non-covalent interaction mechanisms appear between solvent molecules and GO surfaces, covering a change from vdW (pi-pi) interaction for non(less)-polar solvents to moderate and strong hydrogen bonding interactions for polar solvents. There exists an approximately linear correlation between the interaction energies and the interfacial electron density topological parameters. The orbital interaction mechanisms and charge transfer performances have also been disclosed. We further attempt to establish a correlation between the GO-GO interaction free energies in solvents and the solvent-GO interactions, which illustrates that increasing the solvent-GO interaction can weaken the aggregative degree of GOs in the solvent media. Our simulation results not only are valuable to the solventphase processing of GOs, but also provide new binding mechanisms on GO surfaces, which lays a foundation on the functional modification of GO nanomaterials.

First author: Lamine, W, Relaxation of Kohn-Sham orbitals of organometallic complexes during the approach of a nucleophilic reactant (or an electron approach): the case of [sal(ph)en](2) Zn complexes, THEORETICAL CHEMISTRY ACCOUNTS, 139, 533, (2020)
Abstract: In a recent paper, the Lewis acidic character of a series of Zn-Sal(ph)en complexes was reviewed, using conceptual density functional theory descriptors to assess the acidic character. It was shown that the nature of the bridging diamine link in the Schiff base ligand controls this character that is mainly responsible for the coordination of the Zn2+, hence for the geometry of these complexes. However, the usual dual descriptor did exhibit significant weaknesses to retrieve the electrophilic part on the metal cation of the Zn-sal(ph)en complexes. Indeed, it is necessary to include the densities of the electronic excited states through the so-called state-specific dual descriptor. This procedure will allow us to recover successfully the appropriate reactivity of the studied complexes holding diamine bridges differing by flexible to semi-rigid and to rigid ranges. Nevertheless, the selection of the excited state allowing a meaningful description of the Lewis acidic is not a priori obtained from a direct identification of the Kohn-Sham (KS) orbitals involved in the excitation. The present work reports an analysis of the relaxation of the KS orbitals when a fraction of charge is added to a virtual orbital, and when an excitation is considered, while a fractional charge is transferred from an occupied orbital toward a virtual orbital.

First author: Tabrizi, L, Theoretical and experimental study of gold(III), palladium(II), and platinum (II) complexes with 3-((4-nitrophenyl)thio)phenylcyanamide and 2,2 ‘-bipyridine ligands: Cytotoxic activity and interaction with 9-methylguanine, INORGANICA CHIMICA ACTA, 499, 533, (2020)
Abstract: The new gold(III), palladium(II), and platinum(II) complexes with 3-((4-nitrophenyl)thio)phenylcyanamide (HL) and 2,2′-bipyridine (bpy) ligands of formula [M(bpy)LCl] (M = Pd(II),1, Pt(II), 2) or [Au(bpy)LCl]Cl, 3, have been synthesized and fully characterized. The cytotoxicity of free ligands and complexes 1-3 were evaluated against HT-29 (colorectal adenocarcinoma), MCF-7 (breast), and HeLa (human squamous cervical adenocarcinoma) cancer cell lines along with MRC-5 non-tumorigenic cells (human lung fibroblasts) and their activity has been compared to the familiar platinum-based anticancer agent cisplatin. The free ligands bpy and HL were ineffective against the cancer cell lines. However, the complexes 1-3 showed a significant in vitro antitumor activity with IC50 values in the low micromolar. The complexes 1-3 were revealed to produce cellular reactive oxygen species (ROS). The most potent ROS producer, complex 3, also elicited the highest cytotoxicity. The interaction of 9-methylguanine (9-MeG-N7) with complexes 1-3 was studied by H-1 NMR and mass spectroscopy. Furthermore, DFT calculations have been performed on complexes 1-3 and also [M(bpy)(L)(9-MeG-N7)](NO3) (M = Pd(II), 4, Pt(II), 5) or [Au(bpy)(L)(9-MeG-N7)](NO3)(2), 6, using the BP86-D and B3LYP* functionals to provide a complete rationalization of their structures and to describe their electronic structures. The energy decomposition analysis (EDA) gave a clear understanding of the bonding for all complexes 1-6 showing that the interactions are mostly governed by electrostatic ones. Strong interactions occurred between the chlorine anion and the metallic fragment, but weakened between 9-methylguanine and the metallic fragment, in agreement with the electron transfers and the interaction energies.

First author: Villagomez, CJ, A first-principles DFT dispersion-corrected C-60/Au(111) Raman study, COMPUTATIONAL MATERIALS SCIENCE, 171, 533, (2020)
Abstract: We present an extensive density functional theory (DFT) study on the interaction of C-60 molecules with Au(111), involving both periodic metal surfaces and clusters. The aim of this work is 2-fold: First, to quantify the adsorption energies per molecule (E-ads) of the C-60/Au(111) system from periodic calculations using a dispersion-corrected functional (DFT-D3). Secondly, to determine the effect of the metal substrate on the adsorbed C-60 molecule via calculated non-resonant Raman vibrational frequencies. Using a commensurate (2 root 3×2 root 3) R30 degrees phase – as proposed by experimental work as a stable C-60/Au(111) monolayer – our DFT-D3 periodic calculations show a slight C-60 molecule preference to adsorb on its hexagonal facet, with a calculated adsorption energy value of 2.40 eV. Our DFT-D3 calculations further reveal an energetic gain when the C-60 molecule is adsorbed on an HCP surface (2.40 eV) site compared to an FCC one (2.31 eV). Using a variety of finite-size, slab-type Au clusters (e.g.Au-24, Au-32 and Au-50), our DFT-D3 calculated Raman intensity profile shows a strong interaction between the C-60 fullerene molecule and the gold substrate. This influences new vibrational modes over a wide range of frequencies, compared to those active modes for the isolated C-60 gas-phase single molecule, and an overall shift of frequencies and symmetries. The DFT-D3 calculated Raman spectra of the C-60 molecule supported on Au clusters are in good agreement when confronted to those recently obtained experimentally under ultra-high vacuum (UHV) conditions using tip-enhanced Raman spectroscopy (TERS).

First author: Pietrzyk, P, Redox states of nickel in zeolites and molecular account into binding of N-2 to nickel(I) centers – IR, EPR and DFT study, MICROPOROUS AND MESOPOROUS MATERIALS, 291, 533, (2020)
Abstract: Redox chemistry of nickel centers in high-silica ZSM-5 and BEA zeolites was investigated by a combined use of temperature-programmed reduction (TPR), electron paramagnetic resonance (EPR), and infrared (FTIR) spectroscopic techniques supported by quantum chemistry methods. The isolated nickel and nickel-oxo centers were identified and quantified by means of EPR using CO and NO probes and by IR using CO as a probe molecule. The nickel-oxo species gave rise to the nickel(I) centers upon reduction in CO. Their interaction with N-2 under low temperature led to the formation of nickel(I)-dinitrogen adducts. Attribution of the IR bands and identification of the structures of dinitrogen adducts were based on the coadsorption experiments of N-14(2) and N-15(2) isotopes and complementary density functional theory (DFT) calculations. Because of the presence of a mixed ligand ((N2N2)-N-14-N-15) adduct, a structural dichotomy of possible formation of the geminal Ni(I)-(N-2)(2) and two coupled vicinal mono-adducts N-2-Ni(I)center dot center dot center dot Ni(I)-N-2 was resolved. The isolated Ni(I)-N-2 and geminal Ni(I)-(N-2)(2) adducts were identified with confidence. A mechanism of N-2 bonding was accounted for by natural orbitals for chemical valence (NOCV) population analysis. Charge flow molecular channels due to the a donation and pi back-donation effects were established in a quantitative way. This allowed for unraveling the molecular background of the observed bathochromic shift of the stretching vibrations of all dinitrogen adducts.