2011 publications citing ADF

First author: Takahata, Yuji, Substituent effects in chain and ring pi-systems studied by core-electron binding energies calculated by density functional theory, COMPUTATIONAL AND THEORETICAL CHEMISTRY, 978, 77, (2011)
Abstract: The substituent effects of X- in 1-X-hexatrienes, which are chain pi-systems with conjugated double bonds, was compared with those in Ph-X, which are ring pi-systems, using core electron binding energy shifts (Delta CEBE) of the carbon atoms in the molecules. The Delta CEBE of C-1-C-4 in 1-X-hexatrienes are generally close to Delta CEBE of C-1-C-4 in Ph-X. The Delta CEBE of carbon atoms in the 1-X-hexatrienes are not only highly correlated to the Hammett sigma substituent constants, but their numerical values are also close to each other. The core electron binding energies (CEBE) of the six carbons in 1-X-hexatriynes, which are the chain pi-systems with conjugated triple bonds, were calculated by density functional theory (DFT) and the substituent effect was investigated. Average Delta CEBE of the five carbon atoms between C-2 and C-6 in 1-X-hexatriyne were calculated. The magnitude and sign of the average Delta CEBE provides quantitative strength and direction, electron withdrawing or donating, of a substituent X.

First author: von Eschwege, Karel G., Dithizone and Its Oxidation Products: A DFT, Spectroscopic, and X-ray Structural Study, JOURNAL OF PHYSICAL CHEMISTRY A, 115, 14637, (2011)
Abstract: Air oxidation of ortho-fluorodithizone resulted in the first X-ray resolved structure of a disulfide of dithizone, validating the last outstanding X-ray structure in the oxidation of dithizone, H(2)Dz, which proceeds via the disulfide, (HDz)(2), to the deprotonated dehydrodithizone tetrazolium salt, Dz. Density functional theory calculations established the energetically favored tautomers along the entire pathway; in gas phase and in polar as well as nonpolar solvent environments. DFT calculations using the classic pure OLYP and PW91, or the newer B3LYP hybrid functional, as well as MP2 calculations, yielded the lowest energy structures in agreement with corresponding experimental X-ray crystallographic results. Atomic charge distribution patterns confirmed the cyclization reaction pathway and crystal packing of Dz. Time dependent DFT for the first time gave satisfactory explanation for the solvatochromic properties of dithizone, pointing to different tautomers that give rise to the observed orange color in methanol and green in dichloromethane. Concentratochromism of H(2)Dz was observed in methanol. Computed orbitals and oscillators are in close agreement with UV-visible spectroscopic experimental results.

First author: Mitoraj, Mariusz Pawel, Bonding in Ammonia Borane: An Analysis Based on the Natural Orbitals for Chemical Valence and the Extended Transition State Method (ETS-NOCV), JOURNAL OF PHYSICAL CHEMISTRY A, 115, 14708, (2011)
Abstract: In the present study the natural orbitals for chemical valence (NOCVs) combined with the energy decomposition scheme (ETS) were used to characterize bonding in various clusters of ammonia borane (borazane): dimer D, trimer TR, tetramer TE, and the crystal based models: nonamer N and tetrakaidecamer TD. ETS-NOCV results have shown that shortening of the B-N bond (by similar to 01 angstrom) in ammonia borane crystal (as compared to isolated borazane molecule) is related to the enhancement of donation (by 6.5 kcal/mol) and electrostatic (by 11.3 kcal/mol) contributions. This, in turn, is caused solely by the electrostatic dipole-dipole interaction between ammonia borane units; dihydrogen bonding, BH center dot center dot center dot HN, formed between borazane units exhibits no direct impact on B-N bond contraction. On the other hand, formation of dihydrogen bonding appeared to be very important in the total stabilization of single borazane unit, namely, ETS-based data indicated that it leads to significant electronic stabilization Delta E-orb = -17.5 kcal/mol, which is only slightly less important than the electrostatic term, aEelstat = -19.4 kcal/mol. Thus, both factors contribute to relatively high melting point of the borazane crystal. Deformation density contributions (Delta rho(i)) obtained from NOCVs allowed to conclude that dihydrogen bonding is primarily based on outflow of electron density from B-H bonding orbitals to the empty sigma*(N-H) (charge transfer component). Equally important is the covalent contribution resulting from the shift of the electron density from hydrogen atoms of both NH and BH groups to the interatomic regions of NH center dot center dot center dot HB. Quantitatively, averaged electronic strength of dihydrogen bond per one BH center dot center dot center dot HN link varies from 1.95 kcal/mol (for the crystal structure model, N), 2.47 kcal/mol (for trimer TR), through 2.65 kcal/mol (for tetramer TE), up to 3.95 kcal/mol (for dimer D).

First author: Azpiroz, Jon M., Modeling ZnS and ZnO Nanostructures: Structural, Electronic, and Optical Properties,JOURNAL OF PHYSICAL CHEMISTRY C, 115, 25219, (2011)
Abstract: We report the computational modeling of ZnS and ZnO nanostructures by defining realistic nanoparticle models similar to 1.5 nm sized for each material and investigating their structural, electronic, and optical properties by means of DFT/TDDFT calculations. To provide a direct comparison of calculated data to experimentally characterized nanoparticles, 3D (ZnX)(111) nanoclusters of prismatic shape have been set up starting from the bulk wurtzite (X = O, S), with two different saturation patterns of the polar surfaces. The investigated models have been optimized by means of Car-Parrinello molecular dynamics and local geometry optimization techniques. The investigated systems exhibit a well-opened HOMO-LUMO energy gap, without any artificial intraband-gap states. TDDFT calculation of the lowest excitation energies are in excellent agreement, within 0.1-0.2 eV, with the experimental absorption onsets reported for similarly sized ZnO and ZnS nanoparticles (3.70 and 4.40 eV, respectively). We have also investigated the electronic structure of the considered nanoparticles, with reference to the valence band structure, finding calculated binding energies for the Zn d-shell to be only slightly displaced toward lower values compared to experimental values, possibly due to quantum confinement effects. This work provides the required computational framework for modeling ZnX and in general II-VI semiconductor nanomaterials, opening the way to simulation of ligand/semiconductor interactions.

First author: Jacob, Christoph R., Unambiguous optimization of effective potentials in finite basis sets, JOURNAL OF CHEMICAL PHYSICS, 135, 25219, (2011)
Abstract: The optimization of effective potentials is of interest in density-functional theory (DFT) in two closely related contexts. First, the evaluation of the functional derivative of orbital-dependent exchange-correlation functionals requires the application of optimized effective potential methods. Second, the optimization of the effective local potential that yields a given electron density is important both for the development of improved approximate functionals and for the practical application of embedding schemes based on DFT. However, in all cases this optimization turns into an ill-posed problem if a finite basis set is introduced for the Kohn-Sham orbitals. So far, this problem has not been solved satisfactorily. Here, a new approach to overcome the ill-posed nature of such finite-basis set methods is presented for the optimization of the effective local potential that yields a given electron density. This new scheme can be applied with orbital basis sets of reasonable size and makes it possible to vary the basis sets for the orbitals and for the potential independently, while providing an unambiguous potential that systematically approaches the numerical reference.

First author: Denning, Robert G., Covalency in the 4f Shell of tris-Cyclopentadienyl Ytterbium (YbCp3)-A Spectroscopic Evaluation, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 133, 20644, (2011)
Abstract: Evidence is presented of significant covalency in the ytterbium 4f shell of tris-cyclopentadienyl ytterbium (YbCp3) in its electronic ground state, that can be represented by the superposition of an ionic configuration Yb(III):4f(13)(Cp-3) and a charge-transfer configuration Yb(II):4f(14)(Cp-3)(-1). The relative weights of these configurations were determined from (i) the difference in their 4f photoionization cross sections, (ii) the accumulation of spin-density centered on the C-13 atoms of the Cp ring, as measured by a pulsed EPR (HYSCORE) experiment, (iii) the reduction in the spin-density in the 4f shell, manifest in the Yb-171 hyperfine interaction, and (iv) the principal values of the g-tensor, obtained from the EPR spectrum of a frozen glass solution at 5.4 K. Each of these methods finds that the spin density attributable to the charge transfer configuration is in the range 12-17%. The presence of configuration interaction (CI) also accounts for the highly anomalous energies, intensities, and vibronic structure in the “f-f” region of the optical spectrum, as well as the strict adherence of the magnetic susceptibility to the Curie law in the range 30-300 K.

First author: Pavanello, Michele, Modelling charge transfer reactions with the frozen density embedding formalism,JOURNAL OF CHEMICAL PHYSICS, 135, 20644, (2011)
Abstract: The frozen density embedding (FDE) subsystem formulation of density-functional theory is a useful tool for studying charge transfer reactions. In this work charge-localized, diabatic states are generated directly with FDE and used to calculate electronic couplings of hole transfer reactions in two p-stacked nucleobase dimers of B-DNA: 5′-GG-3′ and 5′-GT-3′. The calculations rely on two assumptions: the two-state model, and a small differential overlap between donor and acceptor subsystem densities. The resulting electronic couplings agree well with benchmark values for those exchange-correlation functionals that contain a high percentage of exact exchange. Instead, when semilocal GGA functionals are used the electronic couplings are grossly overestimated.

First author: Thomas, Kolle E., Synthesis and Molecular Structure of Gold Triarylcorroles, INORGANIC CHEMISTRY, 50, 12844, (2011)
Abstract: A number of third-row transition-metal corroles have remained elusive as synthetic targets until now, notably osmium, platinum, and gold corroles. Against this backdrop, we present a simple and general synthesis of beta-unsubstituted gold(III) triarylcorroles and the first X-ray crystal structure of such a complex. Comparison with analogous copper and silver corrole structures, supplemented by extensive scalar-relativistic, dispersion-corrected density functional theory calculations, suggests that “inherent saddling” may occur for of all coinage metal corroles. The degree of saddling, however, varies considerably among the three metals, decreasing conspicuously along the series Cu > Ag > Au. The structural differences reflect significant differences in metal corrole bonding, which are also reflected in the electrochemistry and electronic absorption spectra of the complexes. From Cu to Au, the electronic structure changes from noninnocent metal(II) corrole(center dot 2-) to relatively innocent metal(III) corrole(3-).

First author: Uray, Georg, Absolute configuration of axially chiral bisquinolones: DFT calculations and X-ray crystallography, COMPUTATIONAL AND THEORETICAL CHEMISTRY, 977, 103, (2011)
Abstract: The absolute configuration of axially chiral bisquinolones is established by comparison of experimental CD spectra and those simulated on the basis of TDDFT calculation. Specifically, the previous ambiguous assignment for 3,3′-dibromo-6,6′,7,7′-tetramethoxy-4,4′-biscarbostyril could be resolved as aR axial chirality for the first eluted enantiomer. The computational findings are corroborated by X-ray crystallography.

First author: Jacobs, Michael B., A Surfaced-Enhanced Raman Spectroscopy and Density Functional Theory Study of [Au(CN)(2)](-)/[Au(CN)(4)](-) Adsorbed on Gold Nanoparticles, JOURNAL OF PHYSICAL CHEMISTRY C, 115, 24115, (2011)
Abstract: Surface-enhanced Raman spectroscopy (SERS) can be used to study chemical reactions on metal surfaces. Its detection limit makes it possible to observe long-lived intermediates and conformational changes to reactants and products. However, the interaction between the surface and the adsorbate makes interpretation of SERS spectra difficult. A case in point is provided by our studies of gold nanoparticles exposed to aqueous cyanide solution. These systems are characterized by time-dependent SERS spectra, suggesting either conformational or chemical changes to gold adsorbed cyanide species. Though there has been conjecture as to the nature of the process responsible for the evolving spectra, there is no definitive answer. Herein, we report the results of first-principles studies that, when combined with the SERS data, suggest that the observed shift of the SERS signals is attributable to the transformation of dicyanoaurate ions ([Au(CN)(2)](-)) to tetracyanoaurate ions ([Au(CN)(4)](-)) adsorbed to the metal. In the former case, we argue that the C-infinity axis of the ion is oriented parallel to the surface, and in the latter, the 4-fold axis is normal to the gold (111) surface. Further, the [Au(CN)(4)](-) complex is slightly distorted from its D-4h symmetry to enhance surface bonding.

First author: Jimenez-Halla, J. Oscar C., Organomagnesium clusters: Structure, stability, and bonding in archetypal models, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 696, 4104, (2011)
Abstract: We have studied the molecular structure and the nature of the chemical bond in the monomers and tetramers of the Grignard reagent CH3MgCl as well as MgX2 (X = H, Cl, and CH3) at the BP86/TZ2P level of theory. For the tetramers, we discuss the stability of three possible molecular structures of C-2h, D-2h, and T-d symmetry. The most stable structure for (MgCl2)(4) is D-2h, the one for (MgH2)(4) is C-2h, and that of (CH3MgCl)(4) is T-d. The latter is 38 kcal/mol more stable with chlorines in bridge positions and methyl groups coordinated to a Mg vertex than vice versa. We find through a quantitative energy decomposition analysis (EDA) that the tetramerization energy is predominantly composed of electrostatic attraction Delta V-elstat (60% of all bonding terms Delta V-elstat + Delta E-oi) although the orbital interaction Delta E-oi also provides an important contribution (40%).

First author: Pietrzyk, Piotr, Heterogeneous Binding of Dioxygen: EPR and DFT Evidence for Side-On Nickel(II)-Superoxo Adduct with Unprecedented Magnetic Structure Hosted in MFI Zeolite, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 133, 19931, (2011)
Abstract: This article reports on the activation of dioxygen on nickel(I) dispersed inside the nanopores of the ZSM-5 zeolite, which can be regarded as a heterogeneous mimetic system (zeozyme) for Ni-bearing enzymes. The side-on eta 2-coordination of the resulting nickel-bound superoxo adduct was ascer16O2 species supported by computer simulations of the spectra tamed by detailed analysis of the EPR spectra of both 16O2 and 17O2 species supported by computer simulations of the spectra and relativistic DFT calculations of the EPR signatures. Molecular analysis of the g and A(17O) tensors (gxx = 2.0635, gyy = 20.884, gzz = 2.1675; vertical bar Axx vertical bar approximate to 1.0 mT, vertical bar Ayy vertical bar = 5.67 mT, vertical bar A(zz)vertical bar approximate to 1.3 mT 1.3 mT) and quantum chemical modeling revealed an unusual electronic and magnetic structure of the observed adduct (with g(zz)(g(max)) > g(yy)(g(mid)) > g(xx)(g(min)) and the largest O-17 hyperfine splitting along the g(mid) direction) in comparison to the known homogeneous and enzymatic nickel-superoxo systems. It is best described as a mixed metalloradical with two supporting oxygen donor-ligands and even triangular spin-density redistribution within the)eta 2(-){NiO2}(11) magnetophore. The semioccupied molecular orbital (SOMO) is constituted by highly covalent 6 overlap between the out-of-plane 2p(pi(g)*) MO of dioxygen and the 3d(x2-y2) MO nickel. By means of the extended transition state-natural orbitals for the chemical valence approach (ETS-NOCV), three distinct orbital channels (associated with a, pi, and delta overlap) of congruent and incongruent charge and spin density flows within the eta(2)-{NiO2}(11) unit, contributing jointly to activation of the attached dioxygen, were identified. Their individual energetic relevance was quantified, which allowed for explaining the oxygen binding mechanism with unprecedented accuracy. The nature and structure sensitivity of the g tensor was rationalized in terms of the contributions due to the magnetic field-induced couplings of the relevant molecular orbitals that control the g-tensor anisotropy. The calculated O-17 hyperfine coupling constants correspond well with the experimental parameters, supporting assignment of the adduct. To the best of our knowledge, the eta(2)-{NiO2}(11) superoxo adducts have not been observed yet for digonal mononuclear nickel(I) centers supported by oxygen donor ligands.

First author: Mandal, Sukhendu, [As7M(CO)(3)](3-) M = Cr, Mo, W: Bonding and Electronic Structure of Cluster Assemblies with Metal Carbonyls, JOURNAL OF PHYSICAL CHEMISTRY C, 115, 23704, (2011)
Abstract: Understanding the factors controlling the band gap energy of cluster-assembled materials is an important step toward nanoassemblies with tailored properties. To this end, we have investigated the band gap energies of cluster assemblies involving arsenic clusters bound to carbonyl charge-transfer complexes, M(CO)(3), M = Cr, Mo, W. The binding of a single charge-transfer complex is shown to have a small effect on the band gap energy because the arsenic lone pair orbital and metal carbonyl orbitals are closely aligned in energy, resulting in a gap similar to the original cluster. The band gap energy is also found to be insensitive to the architecture of the assembled material. In the case where two charge-transfer complexes are bound to the cluster, the bottom of the conduction band is shown to be localized on a solvent molecule bound to the metal carbonyl.

First author: Ikeda, Yuji, Theoretical Study of Gallium Nitride Crystal Growth Reaction Mechanism, JAPANESE JOURNAL OF APPLIED PHYSICS, 50, 23704, (2011)
Abstract: In this work, we investigate GaN(0001) crystal growth focusing on gas-phase and surface reactions from the viewpoint of metalorganic chemical vapor deposition (MOCVD) by ab initio calculations. We consider the adsorption of compounds of Ga and N atoms on a Ga-covered surface cluster model. For the adsorption of these compounds, it is found that Ga-Ga bonds undesirable for the steady growth appear for alkylgallium with amino group, and the compounds which have coordinate bonds with NH3 can be a solution for this problem, since they do not make Ga-Ga bonds.

First author: Zhao, Xiu-ming, Chemical Enhancement on Surface-Enhanced Resonance Raman Scattering of Au-3-1,4-Benzenedithiol-Au-3 Junction, CHINESE JOURNAL OF CHEMICAL PHYSICS, 24, 665, (2011)
Abstract: Surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS) spectra of the 1,4-benzenedithiol molecule in the junction of two Au-3 clusters have been calculated using density functional theory; (DFT) and time-dependent DFT method. In order to investigate the contribution of charge transfer (CT) enhancement, the wavelengths of incident light are chosen to be at resonance with four representative excited states, which correspond to CT in four different forms. Compared with SERS spectrum, SERBS spectra are enhanced enormously with distinct enhancement factors, which can be attributed to CT resonance in different forms.

First author: Belhocine, Y., DFT and TD-DFT Study of Structure and Properties of Semiconductive Hybrid Networks Formed by Bismuth Halides and Different Polycyclic Aromatic Ligands, E-JOURNAL OF CHEMISTRY, 8, S195, (2011)
Abstract: The structure and spectroscopic properties of polycyclic aromatic ligands of 2,3,6,7,10,11-hexakis (alkylthio) triphenylene (alkyl: methyl, ethyl, and isopropyl; corresponding to the abbreviations of the molecules: HMTT, HETT and HiPTT) were studied using density functional theory (DFT) and time dependent density functional theory (TD-DFT) methods with triple-zeta valence polarization (TZVP) basis set. It was shown that the type of functional theory used, Becke-Perdew (BP) and Leeuwen-Baerends (LB94) implemented in Amsterdam Density functional (ADF) program package, does not have essential influence on the geometry of studied compounds in both ground and excited states. However, significant differences were obtained for the band gap values with relativistic effects of the zero order regular approximation scalar corrections (ZORA) and LB94 functional seems to reproduce better the experimental optical band gap of these systems.

First author: El Moll, Hani, Lanthanide Polyoxocationic Complexes: Experimental and Theoretical Stability Studies and Lewis Acid Catalysis, CHEMISTRY-A EUROPEAN JOURNAL, 17, 14129, (2011)
Abstract: The [epsilon-(PMo8Mo4O36)-Mo-V-O-VI(OH)(4){Ln(III)(H2O)}(4)](5+) (Ln=La, Ce, Nd, Sm) polyoxocations, called epsilon Ln(4), have been synthesized at room temperature as chloride salts soluble in water, MeOH, EtOH, and DMF. Rare-earth metals can be exchanged, and P-31 NMR spectroscopic studies have allowed a comparison of the affinity of the reduced {epsilon-PMo12} core, thus showing that the La-III ions have the highest affinity and that rare earths heavier than Eu-III do not react with the epsilon-Keggin polyoxometalate. DFT calculations provide a deeper insight into the geometries of the systems studied, thereby giving more accurate information on those compounds that suffer from disorder in crystalline form. It has also been confirmed by the hypothetical La -> Gd substitution reaction energy that Ln ions beyond Eu cannot compete with La in coordinating the surface of the epsilon-Keggin molybdate. Two of these clusters (Ln=La, Ce) have been tested to evidence that such systems are representative of a new efficient Lewis acid catalyst family. This is the first time that the catalytic activity of polyoxocations has been evaluated.

First author: Chong, Delano P., Density functional theory study of the vertical ionization energies of the valence and core electrons of cyclopentadiene, pyrrole, furan, and thiophene, CANADIAN JOURNAL OF CHEMISTRY-REVUE CANADIENNE DE CHIMIE, 89, 1477, (2011)
Abstract: The procedure abbreviated as Delta PBE0(SAOP)/et-pVQZ, based on density functional theory, was developed recently for the calculation of vertical ionization energies of the valence electrons of organic and other small molecules and succeeded in giving results with an average absolute deviation of 0.21 eV from experiment for a collection of 115 reliable test cases of nonperhalo molecules. The objective of this work is to add a number of test cases to the benchmark database. We chose the set of molecules cyclo-C4H4X, with X = CH2, NH, O, and S, previously studied by many workers both experimentally and theoretically. The results show that the Delta PBE0(SAOP)/et-pVQZ procedure is not only as good as ab initio methods such as SAC-CI, OVGF, and ADC(3) in performance, but also handles inner valence ionized cations more efficiently. Although the core-electron binding energies of the titled molecules have not been as well investigated theoretically, we apply the methods we developed in recent years to calculate the binding energies of C1s, N1s, O1s, S1s, and S2p, which compare well with available experimental data.

First author: Loginov, Dmitry A., (Methoxyborole)cobalt Complexes – Synthesis, Structures and Bonding, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 89, 5422, (2011)
Abstract: Heating (?-C4H4BCy)Co(CO)2I (Cy = cyclohexyl) in benzene in the presence of AlCl3 and subsequent methanolysis affords the cationic benzene complex [(?-C4H4BOMe)Co(?-C6H6)]+ (1). Under visible-light irradiation, 1 reacts with MeCN and tBuNC to give the tris(ligand) complexes [(?-C4H4BOMe)Co(L)3]+ [L = MeCN (2), tBuNC (4)]. A similar reaction with P(OMe)3 in MeCN affords [(?-C4H4BOMe)Co(MeCN){P(OMe)3}2]+ (5). Cation 2 reacts with BPh4 in CH2Cl2 to give the zwitterionic arene complex (?-C4H4BOMe)Co(?-C6H5BPh3) (3). Reactions of 2 with TlCp and Tl(?-9-SMe2-7,8-C2B9H10) afford the sandwich compounds (?-C4H4BOMe)CoCp (6) and (?-C4H4BOMe)Co(?-9-SMe2-7,8-C2B9H10) (7). The structures of 3 and 7 were determined by X-ray diffraction. The bonding in the borole complexes [(C4H4BR)Co(C6H6)]+ and (C4H4BR)CoCp (R = H, OMe) was compared with that in the cyclobutadiene analogues [(C4R4)Co(C6H6)]+ and (C4R4)CoCp (R = H, Me) using energy decomposition analysis.

First author: Stachowicz, Anna, DFT studies of cation binding by beta-cyclodextrin, THEORETICAL CHEMISTRY ACCOUNTS, 130, 939, (2011)
Abstract: Interactions of the beta-cyclodextrin (beta-CD) ligand with Na+, Cu+, Mg2+, Zn2+, and Al3+ cations were investigated using density functional theory modeling. The objective of this study was to give insight into the mechanism of cation complexation. Two groups of conformers were found. The first group preserved the initial orientation of glucopyranose residues inside the beta-CD ligand. The mutual orientation of glucopyranose residues was strongly affected by the cation in the second group of conformers. The system interaction energy was decomposed into electrostatic (ES), Pauli and orbital contributions using the Ziegler-Rauk energy partitioning scheme. The total electrostatic energy, i.e., the sum of ES energy and polarization energy, is the dominating term in the interaction energy. In vacuum, the complexes formed with Al3+ were found to be more stable than with di- and monocations. The vacuum stability sequence was changed in aqueous solution.

First author: Cong, Sha, Quantum chemical studies of Lindqvist-type polyoxometalates containing late 3d transition metals ([(py)(MW5O18)-W-II](4-) (M = Fe, Co, Ni)): M-II-N bonding and second-order nonlinear optical properties, THEORETICAL CHEMISTRY ACCOUNTS, 130, 1043, (2011)
Abstract: The electronic and nonlinear optical (NLO) properties of Lindqvist-type tungstate containing late 3d transition metals [(py)MW5O18](4-) (M = Fe, Co, Ni) have been systematically investigated using density functional theory (DFT) method. The character of M-N bond is analyzed using natural bond orbital methods. The first hyperpolarizabilities of [(py)MW5O18](4-) anions have been investigated by Coulomb-attenuating method (CAM-B3LYP). The NLO properties of [(py)MW5O18](4-) with different spin states are also studied. The results show that the static second-order polarizability (beta (0)) of [(py)(FeW5O18)-Fe-5](4-) (Fe = quintet state) is 525.10 x 10(-30) esu, which is larger than those of [(py)(CoW5O18)-Co-4](4-) (beta (0) = 120.72 x 10(-30) esu) and [(py)(NiW5O18)-Ni-3](4-) (beta (0) = 30.45 x 10(-30) esu) anions. Time-dependent DFT results reveal that the substituted transition metals-to-pyridine charge transfer may be responsible for the NLO properties of this kind of polyoxometalates.

First author: Hu, Jian Zhi, Characterizing Surface Acidic Sites in Mesoporous-Silica-Supported Tungsten Oxide Catalysts Using Solid-State NMR and Quantum Chemistry Calculations, JOURNAL OF PHYSICAL CHEMISTRY C, 115, 23354, (2011)
Abstract: The acidic sites in dispersed tungsten oxide supported on SBA-15 mesoporous silica were investigated using a combination of pyridine titration, both fast- and slow-MAS N-15 NMR, static H-2 NMR, and quantum chemistry calculations. It is found that the bridging acidic -OH groups in surface-adsorbed tungsten dimers or multimers (i.e., W-OH-W) are the Bronsted acid sites. The unusually strong acidity of these Bronsted acid sites is confirmed by quantum chemistry calculations. In contrast, terminal W-OH sites are very stable and only weakly acidic as are terminal Si-OH sites. Furthermore, molecular interactions between pyridine molecules and the Bronsted and terminal W-OH sites for dispersed tungsten oxide species are strong. This results in restricted molecular motion for the interacting pyridine molecules even at room temperature, that is, a reorientation mainly about the molecular C-2 symmetry axis. The restricted reorientation results in efficient H-1-N-15 cross-polarization, making it possible to estimate the relative ratio of the Bronsted to the weakly acidic terminal W-OH sites in the catalyst using the slow-MAS H-1-N-15 CP PASS method.

First author: Wang, Jian-Ping, DFT studies on the electronic properties of organometallic-polyoxomolybdate anions [Cp*nMo6O19-n]((2-n)-) (n=1 or 2): Revealing bonding features of Cp*-Mo, COMPUTATIONAL AND THEORETICAL CHEMISTRY, 976, 1, (2011)
Abstract: In this paper, the electronic properties of organometallic-polyoxomolybdate anions [Cp*Mo6O18](-) (Cp*Mo-6), [Cp*2Mo6O17] (CP*Mo-2(6)), and [Cp*TiMo5O18](3-) (Cp*TiMo5) are investigated by density functional theory calculations, and several principles for structure-property relationship are obtained. The bonding energy calculations show that the cis-isomer of anion Cp*Mo-2(6) is more stable than the trans-isomer due to large orbital mixing effect. The phenomena that central oxygen atom largely moves to Mo atom bearing Cp* fragment and extra surface charges likely extend to the trans-position terminal oxygen atoms in anions Cp*Mo-6, Cp*Mo-2(6), and Cp*TiMo5 are explained by trans-influence. Compared with [Mo6O19](2-), the energy gap between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital of anion Cp*Mo-6, as well as Cp*Mo-2(6), is narrowed due to the raised HOMO which is mainly localized on Cp* fragment. Fragment analysis reveals that Cp*-Mo bond characterizes two non-classical sigma bonds and two pi bonds, while only pi bonds contribute to the bond order. The static first hyperpolarizabilities of Cp*Mo-6 and Cp*Mo-2(6) are smaller than that of [Mo6O18NPh](2-) due to weak intramolecular charge transfer. The peculiar Cp*-Mo bond would provoke the studies on novel POM-based organic-inorganic hybrid materials.

First author: Perras, Frederic A., Residual dipolar coupling between quadrupolar nuclei under magic-angle spinning and double-rotation conditions, JOURNAL OF MAGNETIC RESONANCE, 213, 82, (2011)
Abstract: Residual dipolar couplings between spin-1/2 and quadrupolar nuclei are often observed and exploited in the magic-angle spinning (MAS) NMR spectra of spin-1/2 nuclei. These orientation-dependent splittings contain information on the dipolar interaction, which can be translated into structural information. The same type of splittings may also be observed for pairs of quadrupolar nuclei, although information is often difficult to extract from the quadrupolar-broadened lineshapes. Here, the complete theory for describing the dipolar coupling between two quadrupolar nuclei in the frequency domain by Hamiltonian diagonalization is given. The theory is developed under MAS and double-rotation (DOR) conditions, and is valid for any spin quantum numbers, quadrupolar coupling constants, asymmetry parameters, and tensor orientations at both nuclei. All terms in the dipolar Hamiltonian become partially secular and contribute to the NMR spectrum. The theory is validated using experimental B-11 and Cl-35/37 NMR experiments carried out on powdered B-chlorocatecholborane, where both MAS and DOR are used to help separate effects of the quadrupolar interaction from those of the dipolar interaction. It is shown that the lineshapes are sensitive to the quadrupolar coupling constant of both nuclei and to the J coupling (including its sign). From these experiments, the dipolar coupling constant for a heteronuclear spin pair of quadrupolar nuclei may be obtained as well as the sign of the quadrupolar coupling constant of the perturbing nucleus; these are two parameters that are difficult to obtain experimentally otherwise.

First author: Panigrahi, Swati, Structure and Energy of Non-Canonical Basepairs: Comparison of Various Computational Chemistry Methods with Crystallographic Ensembles, JOURNAL OF BIOMOLECULAR STRUCTURE & DYNAMICS, 29, 541, (2011)
Abstract: Different types of non-canonical basepairs, in addition to the Watson-Crick ones, are observed quite frequently in RNA. Their importance in the three dimensional structure is not fully understood, but their various roles have been proposed by different groups. We have analyzed the energetics and geometry of 32 most frequently observed basepairs in the functional RNA crystal structures using different popular empirical, semi-empirical and ab initio quantum chemical methods and compared their optimized geometry with the crystal data. These basepairs are classified into three categories: polar, non-polar and sugar-mediated, depending on the types of atoms involved in hydrogen bonding. In case of polar basepairs, most of the methods give rise to optimized structures close to their initial geometry. The interaction energies also follow similar trends, with the polar ones having more attractive interaction energies. Some of the C-H center dot center dot center dot O/N hydrogen bond mediated non-polar basepairs are also found to be significantly stable in terms of their interaction energy values. Few polar basepairs, having amino or carboxyl groups not hydrogen bonded to anything, such as G:G H:W C, show large flexibility. Most of the non-polar basepairs, except A:G s:s T and A:G w:s C, are found to be stable; indicating C-H center dot center dot center dot O/N interaction also plays a prominent role in stabilizing the basepairs. The sugar mediated basepairs show variability in their structures, due to the involvement of flexible ribose sugar. These presumably indicate that the most of the polar basepairs along with few non-polar ones act as seed for RNA folding while few may act as some conformational switch in the RNA.

First author: Zarate, Ximena, A DFT/TDDFT Study of Porphyrazines and Phthalocyanine Oxo-Titanium Derivatives as Potential Dyes in Solar Cells, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 111, 4186, (2011)
Abstract: Density functional theory and time dependent density functional theory calculations at the level of LDA/BP86/TZ2P were performed systematically on several Ti(IV) complexes of porphyrazines and one phthalocyanine. We performed an analysis of the frontier molecular orbitals of the ground state electronic structures and also discuss in particular the good concordance of our results with the experimental data, which affords to predict the geometrical and optical properties of new complexes (3, 4, and 7). We also emphasize the characterization of the UV-vis absorption spectra and propose transitions that contribute to the Q and B bands. Some useful calculated properties in complexes 2, 3, and 7, like: high light absorption in the visible region of the spectra, transitions involved in these bands with a determined direction, charge separation, bigger highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps than complexes 4 and 5, and the energy of their LUMO orbitals (that are higher than the lowest energy level of the conduction band of the TiO2) indicate that system complexes 2, 3, and 7 could act as light-harvesting sensitizers for dye-sensitized solar cells (DSCs). These proposals were made using a model of the previously experimentally known phthalocyanine, which was used as sensitizer in DSCs devices, comparing its electronic properties with the herein proposed sensitizers.

First author: Courcot, Blandine, Modeling the Interactions Between Polyoxometalates and Their Environment, JOURNAL OF COMPUTATIONAL CHEMISTRY, 32, 3143, (2011)
Abstract: To develop a force field suitable both for polyoxometalates (POMs) and organic cations, the Merck molecular force field 94x (MMFF94x) has been selected to describe the counterions used in POMs synthesis and has been combined with our force field optimized for type-II POMs with electrostatic and Van der Waals interactions included in the potential. Nontransferability of force fields is well-known and, to overcome this limitation, a charge-scaling factor (SF) has been introduced and optimized to tune the POMs force field parameters and adapt them to MMFF94x. The mixed MMFF94x/POMFF-II force field has been optimized and tested on different clusters based on hepta-molybdate. To validate our mixed force field comparison of the results obtained after molecular mechanics (MM), geometry optimizations with density-functional (DFT) calculations have been performed on the smallest system of interest. This has enabled a study of the accuracy of different functionals, especially on the description of hydrogen bonding, to be made. Results are promising in terms of structural accuracy. MM geometry optimization can be used on small POM clusters, competing reasonably well with DFT. When quantum approaches increase considerably the computational cost because of the size of the system studied, MM can be used, with the small reservation that even if the charge SF introduced improves the performance of the force field, further optimizations of the nonbonded term and the model used for the atomic charges may be necessary in further studies.

First author: Chai, Shuo, Density Functional Theory Study on Electron and Hole Transport Properties of Organic Pentacene Derivatives with Electron-Withdrawing Substituent, JOURNAL OF COMPUTATIONAL CHEMISTRY, 32, 3218, (2011)
Abstract: Attaching electron-withdrawing substituent to organic conjugated molecules is considered as an effective method to produce n-type and ambipolar transport materials. In this work, we use density functional theory calculations to investigate the electron and hole transport properties of pentacene (PENT) derivatives after substituent and simulate the angular resolution anisotropic mobility for both electron and hole transport. Our results show that adding electron-withdrawing substituents can lower the energy level of lowest unoccupied molecular orbital (LUMO) and increase electron affinity, which are beneficial to the electron injection and ambient stability of the material. Also the LUMO electronic couplings for electron transport in these pentacene derivatives can achieve up to a hundred meV which promises good electron transport mobility, although adding electron-withdrawing groups will introduce the increase of electron transfer reorganization energy. The final results of our angular resolution anisotropic mobility simulations show that the electron mobility of these pentacene derivatives can get to several cm(2) V-1 s(-1), but it is important to control the orientation of the organic material relative to the device channel to obtain the highest electron mobility. Our investigation provide detailed information to assist in the design of n-type and ambipolar organic electronic materials with high mobility performance.

First author: Zhang, Yi-Quan, Strong anisotropy barriers of two theoretically modeled cyano-bridged magnets [(PY5Me(2))(4)M4Re(CN)(7)](5+) (M = V-II, Ni-II): DFT predictions, POLYHEDRON, 30, 3228, (2011)
Abstract: On the basis of the experimentally synthesized [(PY5Me(2))(4)Mn4Re(CN)(7)](5+), the theoretically modeled clusters of [(PY5Me(2))(4)V4Re(CN)(7)](5+) and [(PY5Me(2))(4)Ni4Re(CN)(7)](5+) both have strong magnetic anisotropy energy barriers.

First author: Tavernelli, Ivano, Nonadiabatic molecular dynamics with solvent effects: A LR-TDDFT QM/MM study of ruthenium (II) tris (bipyridine) in water, CHEMICAL PHYSICS, 391, 101, (2011)
Abstract: The previously derived trajectory-based nonadiabatic molecular dynamics scheme [E. Tapavicza, I. Tavernelli, U. Rothlisberger, Phys. Rev. Lett. 98 (2007) 023001] is extended to include the coupling of the quantum system with a classically described environment. The dynamics is performed using LR-TDDFT energies and forces computed on-the-fly together with the nonadiabatic coupling vectors needed for the propagation of the nuclear coefficients according to Tully’s fewest-switches surface hopping algorithm. The resulting LR-TDDFT-QM/ MM approach is applied to the study of the ultrafast relaxation of the photoexcited singlet metal-to-ligand-charge-transfer state ((MLCT)-M-1) of [Ru(bpy)(3)](2+) (bpy = 2,2′-bipyridine) in water. The observed intersystem crossing dynamics with the triplet MLCT is in good agreement with available experimental results.

First author: Kovyrshin, Arseny, Potential-energy surfaces of local excited states from subsystem- and selective Kohn-Sham-TDDFT, CHEMICAL PHYSICS, 391, 147, (2011)
Abstract: Calculating excited-state potential-energy surfaces for systems with a large number of close-lying excited states requires the identification of the relevant electronic transitions for several geometric structures. Time-dependent density functional theory (TDDFT) is very efficient in such calculations, but the assignment of local excited states of the active molecule can be difficult. We compare the results of the frozen-density embedding (FDE) method with those of standard Kohn-Sham density-functional theory (KS-DFT) and simpler QM/MM-type methods. The FDE results are found to be more accurate for the geometry dependence of excitation energies than classical models. We also discuss how selective iterative diagonalization schemes can be exploited to directly target specific excitations for different structures. Problems due to strongly interacting orbital transitions and possible solutions are discussed. Finally, we apply FDE and the selective KS-TDDFT to investigate the potential energy surface of a high-lying pi -> pi* excitation in a pyridine molecule approaching a silver cluster.

First author: Trueba, A., Cr3+-Doped Fluorides and Oxides: Role of Internal Fields and Limitations of the Tanabe-Sugano Approach, JOURNAL OF PHYSICAL CHEMISTRY A, 115, 13399, (2011)
Abstract: This work is aimed at clarifying the changes on optical spectra of Cr3+ impurities due to either a host lattice variation or a hydrostatic pressure, which can hardly be understood by means of the usual Tanabe-Sugano (TS) approach assuming that the Racah parameter, B, grows when covalency decreases. For achieving this goal, the optical properties of Cr3+-doped LiBaF3 and KMgF3 model systems have been explored by means of high level ab initio calculations on CrF63- units subject to the electric field, E-R(r), created by the rest of the lattice ions. These calculations, which reproduce available experimental data, indicate that the energy, E(E-2), of the E-2(t(2g)(3)) -> (4)A(2)(t(2g)(3)) emission transition is nearly independent of the host lattice. By contrast, the energy difference corresponding to (4)A(2)(t(2g)(3)) -> T-4(1) (t(2g)(2)e(g)(1)) and (4)A(2)(t(2g)(3)) -> T-4(2)(t(2g)(2)e(g)(1)) excitations, Delta(T-4(i); T-4(2)), is shown to increase on passing from the normal to the inverted perovskite host lattice despite the increase in covalency, a fact which cannot be accounted for through the usual TS model. Similarly, when the Cr3+-F- distance, R, is reduced both Delta(T-4(i); T-4(2)) and the covalency are found to increase. By analyzing the limitations of the usual model, we found surprising results that are shown to arise from the deformation of both 3d(Cr) and ligand orbitals in the antibonding e(g) orbital, which has a a character and is more extended than the pi t(2g) orbital. By contrast, because of the higher stiffness of the t(2g) orbital, the dependence of E(E-2) with R basically follows the corresponding variation of covalency in that level. Bearing in mind the similarities of the optical properties displayed by Cr3+ impurities in oxides and fluorides, the present results can be useful for understanding experimental data on Cr3+-based gemstones where the local symmetry is lower than cubic.

First author: Hu, Shao-Wen, Reaction Mechanism of Cl-2 and 1-Alkyl-3-methylimidazolium Chloride Ionic Liquids,JOURNAL OF PHYSICAL CHEMISTRY A, 115, 13452, (2011)
Abstract: Systems containing 1-alkyl-3-methylimidazolium chloride ionic liquid and chlorine gas were investigated. Using relativistic density functional theory, we calculated the formation mechanism of trichloride and hydrogen dichloride anions in an Emim(+)Cl(-) + Cl-2 system. Emim(+)Cl(3)(-) forms without energy barriers. The more stable species ClEmim(+)HCl(2)(-) forms through chlorine substitution. Substitution of a H on the imidazolium ring is much easier than substitution on the alkyl side chains. Infrared, Raman, ESI-MS, and H-1 NMR spectra were measured for EmimCl, BmimCl, and DmimCl with and without Cl-2 gas. The coexistence of Cl-3(-) and HCl2-, as well as chlorine-substituted cations, was confirmed by detection of their spectroscopic signals in the Cl-2 added ionic liquids. Cl substitution appears less serious for cations with longer side chains.

First author: Hatakeyama, Takuji, Synthesis of BN-Fused Polycyclic Aromatics via Tandem Intramolecular Electrophilic Arene Borylation, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 133, 18614, (2011)
Abstract: A tandem intramolecular electrophilic arene borylation reaction has been developed for the synthesis of BN-fused polycyclic aromatic compounds such as 4b-aza-12b-boradibenzo[g,p]chrysene (A) and 8b,11b-diaza-19b,22b-diborahexabenzo[a,c,fg,j,l,op]tetracene. These compounds adopt a twisted conformation, which results in a tight and offset face-to-face stacking array in the solid state. Time-resolved microwave conductivity measurements prove that the intrinsic hole mobility of A is comparable to that of rubrene, one of the most commonly used organic semiconductors, indicating that BN-substituted PAHs are potential candidates for organic electronic materials.

First author: Pellegrin, Yann, New Heteroleptic Bis-Phenanthroline Copper(I) Complexes with Dipyridophenazine or Imidazole Fused Phenanthroline Ligands: Spectral, Electrochemical, and Quantum Chemical Studies, INORGANIC CHEMISTRY, 50, 11309, (2011)
Abstract: Two new sterically challenged diimine ligands L-1 (2,9-dimesityl-2-(4′-bromophenyl)imidazo[4,5-f][1,10]phenanthroline) and L-2 (3,6-di-n-butyl-11-bromodipyrido[3,2-a:2′,3′-c]phenazine) have been synthesized with the aim to build original heteroleptic copper(I) complexes, following the HETPHEN concept developed by Schmittel and co-workers. The structure of L-1 is based on a phen-imidazole molecular core, derivatized by two highly bulky mesityl groups in positions 2 and 9 of the phenanthroline cavity, preventing the formation of a homoleptic species, while L-2 is a dppz derivative, bearing n-butyl chains in alpha positions of the chelating nitrogen atoms. The unambiguous formation of six novel heteroleptic copper(I) complexes based on L-1, L-2, and complementary matching ligands (2,9-R-2-1,10-phenanthroline, with R = H, methyl, n-butyl or mesityl) has been evidenced, and the resulting compounds were fully characterized. The electronic absorption spectra of all complexes fits well with DFT calculations allowing the assignment of the main transitions. The characteristics of the emissive excited state were investigated in different solvents using time-resolved single photon counting and transient absorption spectroscopy. The complexes with ligand L-2, bearing a characteristic dppz moiety, exhibit a very low energy excited-state which mainly leads to fast nonradiative relaxation, whereas the emission lifetime is higher for those containing the bulky ligand L-1. For example, a luminescence quantum yield of about 3 x 10(-4) is obtained with a decay time of about 50 ns for C2 ([Cu-I(nBu-phen)(L-1)(+)) with a weak influence of strong coordinating solvent on the luminescence properties. Overall, the spectral features are those expected for a highly constrained coordination cage. Yet, the complexes are stable in solution, partly due to the beneficial pi stacking between mesityl groups and vicinal phenanthroline aromatic rings, as evidenced by the X-ray structure of complex C3 ([Cu-I(Mes-phen)(L-2)](+)). Electrochemistry of the copper(I) complexes revealed reversible anodic behavior, corresponding to a copper(I) to copper(II) transition. The half wave potentials increase with the steric bulk at the level of the copper(I) ion, reaching a value as high as 1 V vs SCE, with the assistance of ligand induced electronic effects. L-1 and L-2 are further end-capped by a bromo functionality. A Suzuki cross-coupling reaction was directly performed on the complexes, in spite of the handicapping lability of copper(I) phenanthroline complexes.

First author: Banerjee, Abhishek, Polyoxomolybdodiphosphonates: Examples Incorporating Ethylidenepyridines,INORGANIC CHEMISTRY, 50, 11667, (2011)
Abstract: We have synthesized and structurally characterized three pridylethylidene-functionalized diphosphonate-containing polyoxomolybdates, [{(MoO3)-O-VI}(2){(Mo2O4)-O-V}{HO3PC-(O)(CH2-3-C5NH4)PO3}(2)](6-) (1), [{(Mo2O6)-O-VI}(2){(Mo2O4)-O-V}{O3PC(O)(CH2-3-C5NH4)-PO3}(2)](8-) (2), and [{(Mo2O4)-O-V(H2O)}(4){O3PC(O)(CH2-3-C5NH4)PO3}(4)](12-) (3). Poly-anions 1-3 were prepared in a one-pot reaction of the dinuclear, dicationic {(Mo2O4-)-O-V(H2O)(6)}(2+) with 1-hydroxo-2-(3-pyridyl)ethylidenediphosphonate (Risedronic acid) in aqueous solution. Polyanions 1 and 2 are mixed-valent Mo-VI/V species with open tetranuclear and hexanuclear structures, respectively, containing two diphosphonate groups. Polyanion 3 is a cyclic octanuclear structure based on four {(Mo2O4)-O-V(H2O)} units and four diphosphonates. Polyanions 1 and 2 crystallized as guanidinium salts [C(NH2)(3)](5)H[{(MoO3)-O-VI}(2){(Mo2O4)-O-V}-{HO3PC(O)(CH2-3-C5NH4)PO3} (2)]center dot 13H(2)O (1a) and [C(NH2)(3)](6)H-2[{(Mo2O6)-O-VI}(2)-{(Mo2O4)-O-V} {O3PC(O)(CH2-3-C5NH4)PO3}(2)]center dot 10H(2)O (2a), whereas polyanion 3 crystallized as a mixed sodium-guanidinium salt, Na-8[C(NH2)(3)](4)[{(Mo2O4)-O-V(H2O)}(4){O3PC(O)(CH2-3-C5NH4)PO3}(4)]cen ter dot 8H(2)O (3a). The compounds were characterized in the solid state by single-crystal X-ray diffraction, IR spectroscopy, and thermogravimetric and elemental analyses. The formation of polyanions 1 and 3 is very sensitive to the pH value of the reaction solution, with exclusive formation of 1 above pH 7.4 and 3 below pH 6.6. Detailed solution studies by multinuclear NMR spectrometry were performed to study the equilibrium between these two compounds. Polyanion 2 was insoluble in all common solvents. Detailed computational studies on the solution phases of 1 and 3 indicated the stability of these polyanions in solution, in complete agreement with the experimental findings.

First author: Jones, Travis E., Bond Bundles and the Origins of Functionality, JOURNAL OF PHYSICAL CHEMISTRY A,115, 12582, (2011)
Abstract: We briefly review the method by which the electron charge density of atomic systems is decomposed into unique volumes called bond bundles, which are characterized by well-defined and additive properties. We then show that boundaries of bond bundles topologically constrain their chemical reactivity. To illustrate this fact, we model the response of the bond bundles of ethane and ethene to electrophilic attack and from the results of these models posit that functional group properties can be inferred from the shapes of their bond bundles. By relating functionality to bond bundle shape, it is possible to see subtle changes in chemical reactivity that are otherwise difficult to explain, as is illustrated by comparing bond bundles through a series of impact sensitive polynitroaromatic molecules.

First author: Rimola, Albert, Ab Initio Design of Chelating Ligands Relevant to Alzheimer’s Disease: Influence of Metalloaromaticity, JOURNAL OF PHYSICAL CHEMISTRY A, 115, 12659, (2011)
Abstract: Evidence supporting the role of metal ions in Alzheimer’s disease (AD) has rendered metal ion chelation as a promising therapeutic treatment. The rational design of efficient chelating ligands requires, however, a good knowledge of the electronic and molecular structure of the complexes formed. In the present work, the coordinative properties of a set of chelating ligands toward Cu(II) have been analyzed by means of DFT(B3LYP) calculations. Special attention has been paid to the aromatic behavior of the metalated rings of the complex and its influence on the chelating ability of the ligand. Ligands considered have identical metal binding sites (through N/O coordination) and only differ on the kind and size of the aromatic moieties. Results indicate that there is a good correlation between the stability constants (log beta(2)) and the degree of metalloaromaticity determined through the I-NG and HOMA indices; that is, the higher the metalloaromaticity, the larger the log beta(2) value. MOs and aromaticity descriptors confirm that present complexes exhibit Mobius metalloaromaticity. Detailed analysis of the nature of the Cu(II)-ligand bonding, performed through an energy decomposition analysis, indicates that ligands with less aromatic moieties have the negative charge more localized in the metalated ring, thus increasing their sigma-donor character and the metalloaromaticity of the complexes they form.

First author: Cukrowski, Ignacy, QTAIM and ETS-NOCV Analyses of Intramolecular CH center dot center dot center dot HC Interactions in Metal Complexes, JOURNAL OF PHYSICAL CHEMISTRY A, 115, 12746, (2011)
Abstract: The topological analysis, based on the quantum theory of atoms in molecules (QTAIM) of Bader and the ETS-NOCV charge and energy decomposition method have been used to characterize coordination bonds, chelating rings, and additional intramolecular interactions in the ZnNTA and ZnNTPA complexes in solvent. The QTAIM and ETS-NOCV studies have conclusively demonstrated that the H-clashes (they are observed only in the ZnNTPA complex and classically are interpreted as steric hindrance destabilizing a complex) are characterized by (i) the electron flow channel between the H-atoms involved, as discovered by the ETS-NOCV analysis (on average, Delta E-orb = -1.35 kcal mol(-1)) and (ii) QTAIM-defined a bond path that indicates the presence of a preferred quantum-mechanical exchange channel, hence, they should be seen as H-H intramolecular bonding interactions. The main reason for the formation of a weaker ZnNTPA complex was attributed to the strain energy (from both QTAIM and ETS-NOCV techniques) and the larger Pauli repulsion contribution found from the ETS-NOCV analysis. An excellent agreement between physical properties controlling the stability of the two complexes was found from the two techniques, QTAIM and ETS-NOCV.

First author: von Hopffgarten, Moritz, Building a Bridge between Coordination Compounds and Clusters: Bonding Analysis of the Icosahedral Molecules [M(ER)(12)] (M = Cr, Mo, W; E = Zn, Cd, Hg), JOURNAL OF PHYSICAL CHEMISTRY A,115, 12758, (2011)
Abstract: The bonding situation of the icosahedral compounds [M(EH)(12)] (M = Cr, Mo, W; E = Zn, Cd, Hg), which are model systems for the isolated species [Mo(ZnCp*)(3)(ZnMe)(9)] possessing the coordination number 12 at the central atom M, have been analyzed with a variety of charge and energy decomposition methods (AIM, EDA-NOCV, WBI, MO). The results give a coherent picture of the electronic structure and the nature of the interatomic interactions. The compounds [M(EH)(12)] are transition metal complexes that possess 12 M-EH radial bond paths (AIM) that can be described as 6 three-center two-electron bonds (MO). The radial M-EH bonds come from the electron sharing interactions mainly between the singly occupied valence s and d AOs of the central atom M and the singly occupied EH valence orbitals (MO, EDA-NOCV). The orbital interactions provide similar to 42% of the total attraction, while the electrostatic attraction contributes similar to 58% to the metal-ligand bonding (EDA-NOCV). There is a weak peripheral E-E bonding in [M(EH)(12)] that explains the unusually high coordination number (MO). The peripheral bonding leads for some compounds [M(EH)(12)] to the emergence of E-E bond paths, while in others it does not (AIM). The relative strength of the radial and peripheral bonding in [Al-13](-) and [Pt@Pb-12](2-) is clearly different from the situation in [M(EH)(12)], which supports the assignments of the former species as cluster compounds or inclusion compounds (MO, WBI). The bonding situation in [WAu12] is similar to that in [M(EH)(12)].

First author: Anderson, James S. M., Quantum Theory of Atoms in Molecules: Results for the SR-ZORA Hamiltonian,JOURNAL OF PHYSICAL CHEMISTRY A, 115, 13001, (2011)
Abstract: The quantum theory of atoms in molecules (QTAIM) is generalized to include relativistic effects using the popular scalar-relativistic zeroth-order regular approximation (SR-ZORA). It is usually assumed that the definition of the atom as a volume bounded by a zero-flux surface of the electron density is closely linked to the form of the kinetic energy, so it is somewhat surprising that the atoms corresponding to the relativistic kinetic-energy operator in the SR-ZORA Hamiltonian are also bounded by zero-flux surfaces. The SR-ZORA Hamiltonian should be sufficient for qualitative descriptions of molecular electronic structure across the periodic table, which suggests that QTAIM-based analysis can be useful for molecules and solids containing heavy atoms.

First author: Fischer, A., Experimental and Theoretical Charge Density Studies at Subatomic Resolution, JOURNAL OF PHYSICAL CHEMISTRY A, 115, 13061, (2011)
Abstract: Analysis of accurate experimental and theoretical structure factors of diamond and silicon reveals that the contraction of the core shell due to covalent bond formation causes significant perturbations of the total charge density that cannot be ignored in precise charge density studies. We outline that the nature and origin of core contraction/expansion and core polarization phenomena can be analyzed by experimental studies employing an extended Hansen-Coppens multipolar model. Omission or insufficient treatment of these subatomic charge density phenomena might yield erroneous thermal displacement parameters and high residual densities in multipolar refinements. Our detailed studies therefore suggest that the refinement of contraction/expansion and population parameters of all atomic shells is essential to the precise reconstruction of electron density distributions by a multipolar model. Furthermore, our results imply that also the polarization of the inner shells needs to be adopted, especially in cases where second row or even heavier elements are involved in covalent bonding. These theoretical studies are supported by direct multipolar refinements of X-ray powder diffraction data of diamond obtained from a third-generation synchrotron-radiation source (SPring-8, BLO2B2).

First author: Feixas, Ferran, Understanding Conjugation and Hyperconjugation from Electronic Delocalization Measures,JOURNAL OF PHYSICAL CHEMISTRY A, 115, 13104, (2011)
Abstract: The concepts of conjugation and hyperconjugation play an important role to provide an explanation for several fundamental phenomena observed in organic chemistry. Because these effects cannot be directly measured experimentally, their assessment became a primary concern for chemists from the very beginning. In general, the stabilization produced by both phenomena has been studied by means of isodesmic reactions and energy based analysis such as the energy decomposition analysis. In recent years, electronic delocalization measures have been successfully applied to elucidate the nature of chemical bonding and the aromatic character of all kind of molecules. Because conjugation and hyperconjugation stabilizations are strongly linked to the concept of electron delocalization, this paper will give an account of both effects from the point of view of electronic delocalization measures calculated within the framework of the quantum theory of atoms in molecules. In particular, we focus our attention in the controversial case of the stabilization by conjugation in 1,3-butadiyne and 1,3-butadiene. Unexpectedly, theoretical calculations based on the scheme proposed by Kistiakowsky to quantify the extent of stabilization due to conjugation predicted that the conjugation of 1,3-butadiyne was zero. Subsequent energetic analyses contradicted this observation. These studies pointed out the presence of hyperconjugation stabilization in the hydrogenated product of 1,3-butadiyne and 1,3-butadiene that were used as reference systems in the Kistiakowsky’s scheme. Consequently, the extra stabilization of 1-butyne due to hyperconjugation hides the stabilization by conjugation of 1,3-butadiyne. Our results based on electron delocalization measures confirm both the presence of conjugation in 1,3-butadiene and 1,3-butadiyne and hyperconjugation stabilization in their respective hydrogenated products, 1-butene and 1-butyne.

First author: Diebold, Adrienne R., Activation of alpha-Keto Acid-Dependent Dioxygenases: Application of an {FeNO}(7)/{FeO2}(8) Methodology for Characterizing the Initial Steps of O-2 Activation, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 133, 18148, (2011)
Abstract: The alpha-keto acid-dependent dioxygenases are a major subgroup within the O-2-activating mononuclear nonheme iron enzymes. For these enzymes, the resting ferrous, the substrate plus cofactor-bound ferrous, and the Fe-IV=O states of the reaction have been well studied. The initial O-2-binding and activation steps are experimentally inaccessible and thus are not well understood. In this study, NO is used as an O-2 analogue to probe the effects of alpha-keto acid binding in 4-hydroxyphenylpyruvate dioxygenase (HPPD). A combination of EPR, UV-vis absorption, magnetic circular dichroism (MCD), and variable-temperature, variable-field (VTVH) MCD spectroscopies in conjunction with computational models is used to explore the HPPD-NO and HPPD-HPP-NO complexes. New spectroscopic features are present in the alpha-keto acid bound {FeNO}(7) site that reflect the strong donor interaction of the alpha-keto acid with the Fe. This promotes the transfer of charge from the Fe to NO. The calculations are extended to the O-2 reaction coordinate where the strong donation associated with the bound alpha-keto acid promotes formation of a new, S = 1 bridged Fe-IV-peroxy species. These studies provide insight into the effects of a strong donor ligand on O-2 binding and activation by Fe-II in the alpha-keto acid-dependent dioxygenases and are likely relevant to other subgroups of the O-2 activating nonheme ferrous enzymes.

First author: Poltev, V. I., DFT study of DNA sequence dependence at the level of dinucleoside monophosphates,COMPUTATIONAL AND THEORETICAL CHEMISTRY, 975, 69, (2011)
Abstract: In this work we search for new energy minima of desoxydinucleoside monophosphate complexes with Na-ions (dDMPs) as the minimal fragments of DNA single strand via Density Functional Theory (DFT) computations and summarize our previous findings in this field. The analysis is illustrated by graphs of distribution of sugar-phosphate and glycosyl torsions as well as of sugar puckering for energy minima of various base sequences to elucidate the contributions of intra-strand interactions to DNA structure and polymorphism. Our recent computations revealed that the characteristic features of BI, BII, and AI families of DNA duplex conformations are initially predisposed in the dDMPs and namely in their local energy minima. New calculations and the analysis of our previous results enable us to verify and to draw conclusions about important role of sugar-phosphate backbone in the formation and sequence dependence of DNA duplexes. The optimized conformations of dDMPs with purine-purine and purine-pyrimidine sequences are characterized by substantial superposition of base rings whereas those with pyrimidine-pyrimidine and pyrimidine-purine sequences have small if any superposition. This result reveals itself as a universal rule for energy minima corresponding to all four families of right-handed duplexes with Watson-Crick base pairs (RI, BII, AI and AII). The character of base-base overlap is independent of the degree of variation of each of the backbone torsions, which may vary substantially or only slightly with the nucleoside sequence within a family. Computations on dDMP structures corresponding to duplexes with Hoogsteen pairs, started from the torsion angle values of the duplex, located characteristic energy minima for dApdT and dTpdA representative of this conformation. We observe that the rule of sequence dependence of base superposition does not apply to these systems. Biological consequences of existence of the obtained minima and the implications of the revealed regularities are discussed.

First author: Santhanamoorthi, N., Long-Range Charge Transfer in Donor-Peptide Bridge-Acceptor Model Systems-A Theoretical Study, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 111, 3904, (2011)
Abstract: The quantum mechanical calculations were performed to study the effect of geometrical fluctuations of peptide on charge transfer in model oligopeptides linked between donor and acceptor molecules. The charge transfer parameters have been calculated based on the density functional theory method. Results show that the overall charge transfer in peptide mediated donor-acceptor complexes is determined by the conformations and chain length of the intermediate peptide bridge. The analysis of excess charge distribution show that the localization of an excess positive and negative charge are strongly depend on the conformations and chain length of the donor-bridge-acceptor system.

First author: Ravelli, Davide, Predicting the UV Spectrum of Polyoxometalates by TD-DFT, JOURNAL OF COMPUTATIONAL CHEMISTRY, 32, 2983, (2011)
Abstract: UV absorption spectra of the Lindqvist polyoxometalate [W6O19](2-) were predicted by relativistic time-dependent density functional theory with several combinations of density functional and basis set. Hybrid functionals with frozen-core Slater basis sets were found to provide the best agreement with experiment while keeping reasonable computational demand. The approach was extended to [W10O32](4-) and [PW12O40](3-), suggesting that it can be applied to the polyoxometalates family.

First author: Zhekova, Hristina R., Calculation of the exchange coupling constants of copper binuclear systems based on spin-flip constricted variational density functional theory, JOURNAL OF CHEMICAL PHYSICS, 135, 2983, (2011)
Abstract: We have recently developed a methodology for the calculation of exchange coupling constants J in weakly interacting polynuclear metal clusters. The method is based on unrestricted and restricted second order spin-flip constricted variational density functional theory (SF-CV(2)-DFT) and is here applied to eight binuclear copper systems. Comparison of the SF-CV(2)-DFT results with experiment and with results obtained from other DFT and wave function based methods has been made. Restricted SF-CV(2)-DFT with the BH&HLYP functional yields consistently J values in excellent agreement with experiment. The results acquired from this scheme are comparable in quality to those obtained by accurate multi-reference wave function methodologies such as difference dedicated configuration interaction and the complete active space with second-order perturbation theory.

First author: Safa, Muhieddine, The Chemistry of [PtMe2(1,2-bis(2-pyridyl)ethane)]: Remarkable Impact of an Easily Dissociated Chelate Ligand, ORGANOMETALLICS, 30, 5625, (2011)
Abstract: The title compound [PtMe2(bpe)], 1, bpe = 1,2-bis(2-pyridyl)ethane, is easily oxidized to give octahedral organoplatinum(IV) complexes, and the subsequent chemistry is profoundly influenced by the accompanying strain induced in the seven-membered Pt(bpe) chelate ring. In reactions with bromine or iodine, X-2, the platinum(IV) complexes [PtX2Me2(bpe)] are formed initially, but they decompose primarily by reductive elimination of MeX to give ultimately the platinum(II) complexes [PtX2(bpe)]. When X = I, a minor reaction occurred to give the first example of metalation of a CH2 group of the bpe ligand. On reaction of 1 with HCl, the initial product [PtHClMe2(bpe)] undergoes reductive elimination of methane to form [PtClMe(bpe)]. In contrast, methyl iodide reacts with 1 to give [PtIMe3(bpe)], and this decomposes by loss of the bpe ligand to give the cubane [(PtIMe3)(4)] and not by reductive elimination. Finally, a new class of platinum(IV) double cubane clusters was obtained on oxidation of complex 1 either with hydrogen peroxide to give [Pt-4(mu-OH)(4)(mu(3)-OH)(2)Me-10], as a mixed complex with [PtMe2(CO3)(bpe)], or with oxygen in methanol to give [Pt-4(mu-OH)(2)(mu-OMe)(2)(mu(3)-OMe)(2)Me-10

First author: Zhang Di, Density Functional Theory Studies on the Electronic Properties of Dilacunary gamma-Keggin Polyoxometalate Anions, CHEMICAL JOURNAL OF CHINESE UNIVERSITIES-CHINESE, 32, 2613, (2011)
Abstract: The geometrical structures and electronic properties of dilacunary gamma-Keggin polyanions [gamma-Xn+ (WO36)-O-10]((12-n)-) (X = Al-III, Si-IV, P-V, S-VI, Ga-III, Ge-IV, As-V, Se-VI) were investigated via density functional theory(DFT) methods. The results show that the bond lengths between central tetrahedral oxygen atom O-a and central heteroatom X, as well as tungsten atom depend on the central heteroatom X. However, the sizes of XO4 are independent with the central heteroatom. The highest occupied molecular orbital(HOMO) of [gamma-Xn+ (WO36)-O-10]((12-n)-) mainly concentrates on the bridge oxygen atoms. Except for [gamma-SeW10O36](6-), the lowest unoccupied molecular orbital(LUMO) of polyanion is from d orbitals of tungsten atoms. The energies of HOMO and LUMO of [gamma-Xn+ (WO36)-O-10]((12-n)-) depend on the central heteroatom X. The LUMO energy decreases with the increasing of the atomic numbers, and the central atoms are in the same row in periodic table.

First author: Makowska-Janusik, M., Peculiarities of the Environmental Influence on the Optical Properties of Push-Pull Nonlinear Optical Molecules: A Theoretical Study, JOURNAL OF PHYSICAL CHEMISTRY A, 115, 12251, (2011)
Abstract: Gas-phase geometry optimization of NLO-active molecules is one of the standard approaches in the first principle computational methodology, whereas the important role of the environment is usually not considered during the evaluation of structural parameters. With a wide variety of environmentally influenced models in most cases only the high quality single point calculations are prepared. Among different approaches, the most used polarizable continuum model (PCM) seems to be promising. In this study, we have compared the electronic properties of gas-phase optimized geometries of imidazole-derived push-pull compounds with those optimized using PCM solvation approach including CH2Cl2 and PMMA as media. We have focused particularly on the linear optical properties of investigated molecules, namely on the UV-vis absorption spectra. The analysis of presented results shows the applicability of the different quantum chemical (QC) methods for the UV-vis spectra calculations of linear NLO molecules. Herein we also present the need of molecule geometry optimization affected by the environment. Following the performed calculations, the electronic properties of gas-phase optimized molecules give conformable results with respect to those obtained by more time-consuming continuum optimizations. All computational data are supported by experimental investigations.

First author: Canac, Yves, Flexible Diphosphine Ligands with Overall Charges of 0,+1, and +2: Critical Role of the Electrostatics in Favoring Trans over Cis Coordination, INORGANIC CHEMISTRY, 50, 10810, (2011)
Abstract: The influence of the formal electrostatic interaction on the cis/trans coordination mode at a PdCl2 center is investigated in a family of isostructural flexible diphosphine ligands Ph2P-X-C6H4-Y-PPh2, where X and Y stand for neutral or cationic N,C-imidazolylene linkers. While the neutral and monocationic diphosphine spontaneously behave as classical cis-chelating ligands, only the dicationic diphosphine, where the electrostatic repulsion between the formal positive charges specifically takes place, is observed to behave as a trans-chelating ligand. The crucial role of electrostatics is analyzed on the basis of P-31 NMR data in solution and X-ray diffraction data in the crystal state. Comparative theoretical studies of the cis- and trans-chelated complexes, including EDA, static P-31 NMR, MESP, and AIM analyses, have been undertaken on the basis of DFT calculations in the gas phase or in the acetonitrile continuum. Whereas the cis-coordination mode is shown to be thermodynamically favored for the neutral ligand, the trans-coordination mode is found to be preferred for the dicationic homologue. The stereochemical preference is thus shown to be parallel to the expected effect of the formal electrostatic interaction. The results open perspectives for control of the cis- and trans-chelating behavior of flexible bidentate ligands by more or less reversible charge transfer at the periphery of the coordination sphere of a metallic center.

First author: Wiebelhaus, Nicholas J., Metal-Sulfur Valence Orbital Interaction Energies in Metal-Dithiolene Complexes: Determination of Charge and Overlap Interaction Energies by Comparison of Core and Valence Ionization Energy Shifts,INORGANIC CHEMISTRY, 50, 11021, (2011)
Abstract: The electronic interactions between metals and dithiolenes are important in the biological processes of many metalloenzymes as well as in diverse chemical and material applications. Of special note is the ability of the dithiolene ligand to support metal centers in multiple coordination environments and oxidation states. To better understand the nature of metal dithiolene electronic interactions, new capabilities in gas-phase core photoelectron spectroscopy for molecules with high sublimation temperatures have been developed and applied to a series of molecules of the type Cp2M(bdt) (Cp = eta(5)-cyclopentadienyl, M = Ti, V, Mo, and bdt = benzenedithiolato). Comparison of the gas-phase core and valence ionization energy shifts provides a unique quantitative energy measure of valence orbital overlap interactions between the metal and the sulfur orbitals that is separated from the effects of charge redistribution. The results explain the large amount of sulfur character in the redox-active orbitals and the ‘leveling’ of oxidation state energies in metal dithiolene systems. The experimentally determined orbital interaction energies reveal a previously unidentified overlap interaction of the predominantly sulfur HOMO of the bdt ligand with filled pi orbitals of the Cp ligands, suggesting that direct dithiolene interactions with other ligands bound to the metal could be significant for other metal dithiolene systems in chemistry and biology.

First author: Guerra, Celia Fonseca, Telomere Structure and Stability: Covalency in Hydrogen Bonds, Not Resonance Assistance, Causes Cooperativity in Guanine Quartets, CHEMISTRY-A EUROPEAN JOURNAL, 17, 12612, (2011)
Abstract: We show that the cooperative reinforcement between hydrogen bonds in guanine quartets is not caused by resonance-assisted hydrogen bonding (RAHB). This follows from extensive computational analyses of guanine quartets (G(4)) and xanthine quartets (X-4) based on dispersion-corrected density functional theory (DFT-D). Our investigations cover the situation of quartets in the gas phase, in aqueous solution as well as in telomere-like stacks. A new mechanism for cooperativity between hydrogen bonds in guanine quartets emerges from our quantitative Kohn-Sham molecular orbital (MO) and corresponding energy decomposition analyses (EDA). Our analyses reveal that the intriguing cooperativity originates from the charge separation that goes with donor-acceptor orbital interactions in the selectron system, and not from the strengthening caused by resonance in the p-electron system. The cooperativity mechanism proposed here is argued to apply, beyond the present model systems, also to other hydrogen bonds that show cooperativity effects.

First author: El-Hamdi, Majid, An Analysis of the Isomerization Energies of 1,2-/1,3-Diazacyclobutadiene, Pyrazole/Imidazole, and Pyridazine/Pyrimidine with the Turn-Upside-Down Approach, JOURNAL OF ORGANIC CHEMISTRY, 76, 8913, (2011)
Abstract: The isomerization energies of 1,2- and 1,3-diazacyclobutadiene, pyrazole and imidazole, and pyridazine and pyrimidine are 10.6, 9.4, and 20.9 kcal/mol, respectively, at the BP86/TZ2P level of theory. These energies are analyzed using a Morokuma-like energy decomposition analysis in conjunction with what we have called turn-upside-down approach. Our results indicate that, in the three cases, the higher stability of the 1,3-isomers is not due to lower Pauli repulsions but because of the more favorable sigma-orbital interactions involved in the formation of two C-N bonds in comparison with the generation of C-C and N-N bonds in the 1,2-isomers.

First author: Chen, Xian-Kai, A Promising Approach to Obtain Excellent n-Type Organic Field-Effect Transistors: Introducing Pyrazine Ring, JOURNAL OF PHYSICAL CHEMISTRY C, 115, 21416, (2011)
Abstract: The effects of the pyrazine ring on the geometrical and electronic structures, molecular stacking motifs, carrier injection, and transport properties as well as electronic band structures for some typical molecules with pyrazines (such as tetracene, pentacene, and pi-extended tetrathiafulvalene derivatives) were theoretically investigated by quantum chemical methods. The introduction of pyrazine does not affect the molecular planarity and in the meantime largely decreases the energies of the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals and hence improves their stability in air and ability of electron injection. More important, it is very helpful for prompting the molecular pi-stacking. Small electron reorganization energies and large electronic coupling originated from their dense pi-stacking give rise to their excellent electron transport properties, which makes them become a class of promising candidates for excellent n-type organic field-effect transistor (OFET) materials. So introducing pyrazine is an effective approach to obtain the excellent n-type OFET materials.

First author: Jissy, A. K., pi-Stacking interactions between G-quartets and circulenes: A computational study, JOURNAL OF CHEMICAL SCIENCES, 123, 891, (2011)
Abstract: Structures of planar and bowl-shaped circulenes as well as their stacks with G-quartet (G4) have been investigated through dispersion-corrected Density Functional Theory (DFT-D). The binding energies are substantial similar to 10 kcal/mol with d similar to 3.5 angstrom between the stacking rings. The calculations show that G4 binds much more effectively to planar circulenes as compared to bowl shaped molecules. The strength of binding between a G-quartet and a non-planar circulene molecule depends on the orientation of the circulene (concave or convex) with respect to G-quartet. An AIM analysis of the M05-2X wave-functions has also been performed to confirm the presence of weak intermolecular interactions between guanine quartets and circulenes. Apart from pi-stacking interactions, the concave bowl-shaped circulenes also interact with G4 through C-H center dot center dot center dot pi interactions. The charge transport properties between the two moieties have also been analysed through effective transport integral. The calculations provide an understanding for the basis of molecular recognition by G4 for non-planar systems.

First author: Shi Le-Lei, Valence orbitals of W(CO)(6) using electron momentum spectroscopy, CHINESE PHYSICS B, 20, 891, (2011)
Abstract: The binding energy spectra and the momentum distributions of the outer valence orbitals of W( CO) 6 have been studied by using electron momentum spectroscopy as well as non-relativistic, scalar relativistic and spin-orbital relativistic DFT-B3LYP calculations. The experimental momentum profiles of the outer valence orbitals obtained with the impact energies of 1200 eV and 2400 eV were compared with various theoretical calculation results. The relativistic calculations could provide better descriptions for the experimental momentum distributions than the non-relativistic ones. Moreover, a new ordering of orbitals 10t(1u), 3t(2g), and 7e(g), i.e., 10t(1u) < 3t(2g) < 7e(g) < 10a(1g), is established in this work.

First author: Johansen, Inge, Substituent effects on metallocorrole spectra: insights from chromium-oxo and molybdenum-oxo triarylcorroles, JOURNAL OF PORPHYRINS AND PHTHALOCYANINES, 15, 1335, (2011)
Abstract: The Soret maxima of a number of metallotriarylcorroles shift sensitively in response to varying substituents on the meso-aryl groups. The effect is most pronounced for copper corroles but is not seen for silver and gold corroles. In the copper case, the effect has been attributed to a small HOMO-LUMO gap. Chromium-oxo corroles share a small HOMO-LUMO gap with copper corroles, as well as a substantially metal-based LUMO, yet the Soret maxima of chromium-oxo triarylcorroles do not shift in response to substitution on the meso-aryl groups. Molybdenum-oxo corroles are substituent-insensitive in the same sense. TDDFT calculations, focusing on chromium-oxo and molybednum-oxo triarylcorroles, are reported here in an attempt to explain the divergent spectroscopic behavior of different metallocorrole families.

First author: Gryff-Keller, Adam, Theoretical modeling of C-13 NMR chemical shiftsuHow to use the calculation results,CONCEPTS IN MAGNETIC RESONANCE PART A, 38A, 289, (2011)
Abstract: Owing to wide accessibility of the general utility quantum chemistry programs, theoretical calculations of spectral parameters defining NMR spectra have become relatively easy for medium size molecules. This new and powerful tool allows investigators to perform much deeper interpretation of the NMR data and gain new information valuable for structural chemistry studies. It is usually realized and well understood that theoretical calculations of NMR parameters, as for any quantum mechanical calculations, have several limitations, difficult to overcome, and that the accuracy of calculation results is strongly dependent on the theoretical method applied. On the other hand, it is less commonly recognized that the effectiveness of all the combined calculational/spectroscopic approach depends meaningfully on the method of comparison of the experimental and theoretical data as well. This article is addressed primarily to experimental chemists who use in their everyday work C-13 NMR spectroscopy to solve various structural and physicochemical problems. After recalling some basic concepts concerning NMR parameters and their calculations, some suggestions concerning the rational choice of the calculational method and the experiment/theory comparison method are formulated. To support these recommendations and convince the reader of their utility, several practical examples are presented in the text. All these concepts reflect the author’s beliefs which, albeit well-grounded, by no means should be treated as indispensable truths; they are rather worth considering as hints about how to solve various practical dilemmas.

First author: Megger, Dominik A., Silver(I)-mediated Hoogsteen-type base pairs, JOURNAL OF INORGANIC BIOCHEMISTRY, 105, 1398, (2011)
Abstract: Metal-mediated Hoogsteen-type base pairs are useful for the construction of DNA duplexes containing contiguous stretches of metal ions along the helical axis. To fine-tune the stability of such base pairs and the selectivity toward different metal ions, the availability of a selection of artificial nucleobases is highly desirable. In this study, we follow a theoretical approach utilizing dispersion-corrected density functional methods to evaluate a variety of artificial nucleobases as candidates for metal-mediated Hoogsteen-type base pairs. We focus on silver(I)-mediated Hoogsteen- and reverse Hoogsteen-type base pairs formed between 1-deaza- and 1,3-dideazapurine-derived nucleobases, respectively, and cytosine. Apart from two coordinative bonds, these base pairs are stabilized by a hydrogen bond. We elucidate the impact of different substituents at the C6 position and the presence or absence of an endocyclic N3 nitrogen atom on the overall stability of a base pair and concomitantly on the strength of the hydrogen and coordinative bonds. All artificial base pairs investigated in this study are less stable than the experimentally established benchmark base pair C-Ag+-G. The base pair formed from 1,3-dideaza-6-methoxypurine is isoenergetic to the experimentally observed C-Ag+-C base pair. This makes 1,3-dideaza-6-methoxypurine a promising candidate for the use as an artificial nucleobase in DNA.

First author: Kepenekian, Mikael, Toward Reliable DFT Investigations of Mn-Porphyrins through CASPT2/DFT Comparison, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 7, 3532, (2011)
Abstract: The low-energy spectroscopies of Mn(II) and Mn(III) porphyrin (P) complexes were investigated using complete active space and subsequent perturbative treatment (CASPT2) as well as DFT-based calculations. Starting from DFT optimizations of (MnP)-P-II and (MnPCl)-P-III using crystallographic data, the CASPT2 results show that whatever the relative position of the Mn(II) ion with respect to the porphyrin cavity, the high-spin state S = 5/2 of the [MnP] unit lies much lower in energy than the intermediate S = 3/2 state. Not only are these results in agreement with experimental observations but they also differ from previous theoretical conclusions. In the Mn(III) complexes, sigma and pi charge redistributions compete to result in a S = 2 ground state. The performances of different functionals have been tested in the reproduction of the CASPT2 spin gaps. Our results confirm that the Mn (II) system is very challenging, as GGA functionals fail in the spin states ordering and in the reproduction of the gaps, unless a high percentage of exact HF exchange (55%), as in KMLYP, is incorporated. This inspection demonstrates the need for specific active space functional to investigate the low-energy spectroscopy of [MnP] units.

First author: Steinmann, Stephan N., Comprehensive Bench marking of a Density-Dependent Dispersion Correction,JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 7, 3567, (2011)
Abstract: Standard density functional approximations cannot accurately describe interactions between nonoverlapping densities. A simple remedy consists in correcting for the missing interactions a posteriori, adding an attractive energy term summed over all atom pairs. The density-dependent energy correction, dDsC, presented herein, is constructed from dispersion coefficients computed on the basis of a generalized gradient approximation to Becke and Johnson’s exchange-hole dipole moment formalism. dDsC also relies on an extended Tang and Toennies damping function accounting for charge-overlap effects. The comprehensive benchmarking on 341 diverse reaction energies divided into 18 illustrative test sets validates the robust performance and general accuracy of dDsC for describing various intra- and intermolecular interactions. With a total MAD of 1.3 kcal mol(-1), B97-dDsC slightly improves the results of M06-2X and B2PLYP-D3 (MAD = 1.4 kcal mol(-1) for both) at a lower computational cost. The density dependence of both the dispersion coefficients and the damping function makes the approach especially valuable for modeling redox reactions and charged species in general.

First author: Chai, Shuo, Understanding electron-withdrawing substituent effect on structural, electronic and charge transport properties of perylene bisimide derivatives, ORGANIC ELECTRONICS, 12, 1806, (2011)
Abstract: A series of n-type perylene bisimide (PBI) derivatives with electron-withdrawing substituents at both bay and imide nitrogen positions were investigated. The effects of these substituents on internal energy relaxation, molecular orbitals, air stability, electronic properties and charge transport behaviors were systematically discussed with density functional theory (DFT) which has been demonstrated reliable for organic semiconductor study. The investigated derivatives with electron-withdrawing substituents show favorable performances in terms of these properties. The LUMO levels are greatly stabilized by at least 0.3 eV and these derivatives show the strong absorption from 400 to 700 nm which match with the solar spectra very well. The charge transport mainly happens between molecules in the same organic molecular layer and electronic couplings between layer-to-layer molecules are very weak, thus the mobility along layer-to-layer direction is less efficient. The variation of molecular packings and intermolecular interactions produce the highly anisotropic mobilities. The derivative with two fluorine atoms at bay positions and -CH2C3F7 at imide group has broad and strong absorption in the UV-Visible region and the electron mobility could get to 0.514 cm(2) V (1) s (1) which is greatly encouraging for molecular and material design in organic solar-cell devices. These calculated results are in good agreement with the experimental data. However, not all the functionalization with halogen substituents would induce the increase of the electronic coupling and electron mobility. The derivatives with four halogen substituents at the bay positions could not show advantages in terms of electron mobility which is induced by the distorted conjugated structures. The theoretical understanding of these n-type organic semiconductors figures out the importance of tuning the molecular geometry to get high performance semiconductor materials.

First author: Fantacci, Simona, A computational approach to the electronic and optical properties of Ru(II) and Ir(III) polypyridyl complexes: Applications to DSC, OLED and NLO, COORDINATION CHEMISTRY REVIEWS, 255, 2704, (2011)
Abstract: Ruthenium(II) and Iridium(III) polypyridyl complexes have been intensively investigated due to their use in energy conversion and light-emitting devices and materials for non-linear optics. Quantum mechanical computer simulations of molecules and materials have become increasingly popular in the scientific community. Along with experimental investigations, such computational analyses can provide complementary information on the electronic and optical properties of transition metal compounds of interest for optoelectronic applications. Here, we provide a unified review of recent work carried out on computational investigations of a large series of Ruthenium(II) and Iridium(III) polypyridyl complexes, discussing the relations between their electronic structure and optical properties and their device functioning. Our results, obtained for vastly different systems, allow us to trace some general conclusions concerning the modeling of these transition metal complexes, casting the bases for the computational design and screening, even before their synthesis, of new and more efficient transition metal complexes for photonics applications.

First author: Barngrover, Brian M., Incremental Binding Energies of Gold(I) and Silver(I) Thiolate Clusters, JOURNAL OF PHYSICAL CHEMISTRY A, 115, 11818, (2011)
Abstract: Density functional theory is used to find incremental fragmentation energy, overall dissociation energy, and average monomer fragmentation energy of cyclic gold(I) thiolate clusters and anionic chain structures of gold(I) and silver(I) thiolate dusters as a measure of the relative stability of these systems. Two different functionals, BP86 and PBE, and two different basis sets, TZP and QZ4P, are employed. Anionic chains are examined with various residue groups including hydrogen, methyl, and phenyl. Hydrogen and methyl are shown to have approximately the same binding energy, which is higher than phenyl. Gold-thiolate clusters are bound more strongly than corresponding silver clusters. Lastly, binding energies are also calculated for pure Au-25(SR)(18)(-), Ag-25(SR)(18)(-), and mixed Au-13 (Ag-2(SH)(3))(6-) and Ag-13(Au-2(SH)(3))(6-) nanoparticles.

First author: Luo, Sijie, Noncollinear Spins Provide a Self-Consistent Treatment of the Low-Spin State of a Biomimetic Oxomanganese Synthetic Trimer Inspired by the Oxygen Evolving Complex of Photosystem II, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 2, 2629, (2011)
Abstract: We employ noncollinear density functional theory to show that the low-spin state of Mn-3 in a model of the oxygen-evolving complex of photosystem II avoids frustrated spin coupling by adopting a noncollinear arrangement of spins, thereby lowering the energy by 7 kcal/mol. The high-spin state also has noncollinear spins. The optimum self-consistent field solutions for this multinuclear oxomanganese complex correspond to states that cannot be described by the unrestricted Slater determinants used in Kohn-Sham collinear density functional methods. This kind of spin coupling can be important in many open-shell systems, and the conventional collinear spin interpretation of chemical bonding in such systems should be viewed with caution.

First author: Ong, S. Vincent, Origin of Oxidation and Support-Induced Structural Changes in Pd-4 Clusters Supported on TiO2, JOURNAL OF PHYSICAL CHEMISTRY C, 115, 20217, (2011)
Abstract: Theoretical first-principles studies of the effect of oxidation on the atomic and electronic structure of a Pd-4 cluster and the nature of cluster support interactions have been carried out by investigating a Pd-4 cluster deposited on a rutile TiO2(110) surface. Our studies based on a gradient-corrected density functional approach indicate that the deposited Pd-4 has a compact ground state with an energetically close pseudoplanar structure that is expected to coexist with the ground state. The compact ground state undergoes a transition to a planar structure upon the absorption of a single O atom. The addition of a second O, however, generates two different structures: (1) a pseudoplanar structure where a Pd site mediates the interaction between the two O atoms, and (2) an energetically more stable species with a planar Pd-4 structure and O in a “spillover” mode. Experimental evidence supporting this spillover O is discussed. Detailed analysis of the electronic states and charge densities reveals that the interaction between the Pd and the lattice O sites is mainly responsible for the variations in structure of the deposited species as well as the relaxation of the underlying lattice. Specifically, variations in the charge state of the lattice Ti and O sites are shown to lead to large displacements of Ti ions providing a microscopic mechanism of observed strong metal support interactions.

First author: Srebro, Monika, Optical Rotation Calculated with Time-Dependent Density Functional Theory: The OR45 Benchmark, JOURNAL OF PHYSICAL CHEMISTRY A, 115, 10930, (2011)
Abstract: Time-dependent density functional theory (TDDFT) computations are performed for 42 organic molecules and three transition metal complexes, with experimental molar optical rotations ranging from 2 to 2 x 10(4) deg cm(2) dmol(-1). The performances of the global hybrid functionals B3LYP, PBE0, and BHLYP, and of the range-separated functionals CAM-B3LYP and LC-PBE0 (the latter being fully long-range corrected), are investigated. The performance of different basis sets is studied. When compared to liquid-phase experimental data, the range-separated functionals do, on average, not perform better than B3LYP and PBE0. Median relative deviations between calculations and experiment range from 25 to 29%. A basis set recently proposed for optical rotation calculations (LPol-ds) on average does not give improved results compared to aug-cc-pVDZ in TDDFT calculations with B3LYP. Individual cases are discussed in some detail, among them norbornenone for which the LC-PBE0 functional produced an optical rotation that is close to available data from coupled-cluster calculations, but significantly smaller in magnitude than the liquid-phase experimental value. Range-separated functionals and BHLYP perform well for helicenes and helicene derivatives. Metal complexes pose a challenge to first-principles calculations of optical rotation.

First author: Bouchakri, Naima, Bonding analysis and electronic structure of transition metal-benzoquinoline complexes: A theoretical study, POLYHEDRON, 30, 2644, (2011)
Abstract: The geometric and electronic structures of a series of hypothetical compounds of the types CpM(C13H9N) and (CO)(3)M(C13H9N) (M = first row transition metal and C13H9N = 7,8-benzoquinoline) have been investigated by means of density functional theory (DFT). The benzoquinoline ligand can bind to the metal through eta(1)-eta(6) coordination modes, adopting structures of types a, b and c, in agreement with the electron count and the nature of the metal. In the investigated species, the most favored closed-shell count is 18-MVE, except for the Ti and V models which prefer the open-shell 16-MVE configuration. This study has shown the difference in the coordination ability of this heteropolycyclic ligand and coordination of the inner C-6 ring is less favored than the outer C-6 and C5N rings, in agreement with the pi-electron density localization.

First author: Martinie, Ryan J., Computational Investigations of Ligand Fluxionality in Fe-3(C8H8)(3),ORGANOMETALLICS, 30, 5196, (2011)
Abstract: The recently synthesized tris(mu-1,3,5,7-cyclooctatetraene)triiron, Fe-3(C8H8)(3), was investigated by DFT computational studies. In the gas phase, the cluster adopts C-3h symmetry and pseudo-eta(3):eta(5) hapticity to each of the cyclooctatetraene (COT) ligands, which exist in a pi-delocalized V conformation with each ligand bridging two metal atoms. A higher symmetry structure, D-3h, lies only slightly above the C-3h structure and represents a transition state between two energetically identical C-3h structures. The computed charge on the iron atoms is near 0 by both the Hirshfeld and Voronoi methods and comports with the compound having a formal oxidation state of 0. In addition, the cluster can adopt a second conformation with the three COT ligands in a pi-delocalized tub configuration with a decrease in stability of only similar to 3 kcal/mol. The ligands can also rotate about the metal-metal framework with a transition barrier of only similar to 1 kcal/mol. Dissociation of a single COT ligand requires similar to 57 kcal/mol. The low-energy ligand conformational changes, sliding, and rotation likely make significant contribution to the experimentally observed fluxionality of the ligands. A triplet structure was also examined and found to be nearly isoenergetic with the singlet. The triplet potential energy surface resembles that of the singlet in that a variety of low-energy transformations can contribute to ligand fluxionality.

First author: Jochmann, Phillip, Preparation, Structure, and Ether Cleavage of a Mixed Hapticity Allyl Compound of Calcium, ORGANOMETALLICS, 30, 5291, (2011)
Abstract: The synthesis, characterization, and decomposition pathway of the 18-crown-6 adduct of bis(allyl)calcium [Ca(eta(1)-C3H5)(eta(3)-C3H5)(18-crown-6)] (2) are reported. The solid-state structure of adduct 2 features one sigma- and one pi-bonded ally] ligand at the metal center. 2 is the first structurally characterized example of a mononuclear calcium complex bearing a purely sigma-bound allyl ligand. DFT calculations indicate that [Ca(eta(1)-C3H5)(eta(3)-C3H5) (18-crown-6)] and [Ca(eta(1)-C3H5)(2)(18-crown-6)] conformations are dose in energy. In THF solution, eta(3)-allyl ligands are observed exclusively at both ambient temperature and -95 degrees C. 2 undergoes rapid cleavage of the crown ether to give vinyl-terminated alcoholates of different chain length with a half-life of t(1/2) = 2.5

First author: Morton, Seth Michael, A discrete interaction model/quantum mechanical method to describe the interaction of metal nanoparticles and molecular absorption, JOURNAL OF CHEMICAL PHYSICS, 135, 5291, (2011)
Abstract: A frequency-dependent quantum mechanics/molecular mechanics method for the calculation of response properties of molecules adsorbed on metal nanoparticles is presented. This discrete interaction model/quantum mechanics (DIM/QM) method represents the nanoparticle atomistically, thus accounting for the local environment of the nanoparticle surface on the optical properties of the adsorbed molecule. Using the DIM/QM method, we investigate the coupling between the absorption of a silver nanoparticle and of a substituted naphthoquinone. This system is chosen since it shows strong coupling due to a molecular absorption peak that overlaps with the plasmon excitation in the metal nanoparticle. We show that there is a strong dependence not only on the distance of the molecule from the metal nanoparticle but also on its orientation relative to the nanoparticle. We find that when the transition dipole moment of an excitation is oriented towards the nanoparticle there is a significant increase in the molecular absorption as a result of coupling to the metal nanoparticle. In contrast, we find that the molecular absorption is decreased when the transition dipole moment is oriented parallel to the metal nanoparticle. The coupling between the molecule and the metal nanoparticle is found to be surprisingly long range and important on a length scale comparable to the size of the metal nanoparticle. A simple analytical model that describes the molecule and the metal nanoparticle as two interacting point objects is found to be in excellent agreement with the full DIM/QM calculations over the entire range studied. The results presented here are important for understanding plasmon-exciton hybridization, plasmon enhanced photochemistry, and single-molecule surface-enhanced Raman scattering.

First author: Per, Manolo C., Zero-variance zero-bias quantum Monte Carlo estimators for the electron density at a nucleus, JOURNAL OF CHEMICAL PHYSICS, 135, 5291, (2011)
Abstract: We derive new quantum Monte Carlo (QMC) estimators for the electronic density at the position of a point nucleus using the zero-variance and zero-bias principles. The resulting estimators are highly efficient, and are significantly simpler to implement and use than alternative methods, as they contain no adjustable parameters. In addition, they can be used in both variational and diffusion QMC calculations. Our best estimator is used to calculate the most accurate available estimates of the total electron density at the nucleus for the first-row atoms Li-Ne, the Ar atom, and the diatomic molecules B-2, N-2, and F-2.

First author: Munoz-Castro, Alvaro, Bonding and Magnetic Response Properties of Several Toroid Structures. Insights of the Role of Ni2S2 as a Building Block from Relativistic Density Functional Theory Calculations, JOURNAL OF PHYSICAL CHEMISTRY A, 115, 10789, (2011)
Abstract: Relativistic density functional calculations were carried out on several nickel toroid mercaptides of the general formula [Ni(mu-SR)(2)](n), with the aim to characterize and analyze their stability and magnetic response properties, in order to gain more insights into their stabilization and size dependent beha- vior. The Ni-ligand interaction has been studied by means projected density of states and energy decomposition analysis, which denotes its stabilizing character. The graphical representation of the response to an external magnetic field is applied for the very first time taking into account the spin orbit term. This map allows one to clearly characterize the magnetic behavior inside and in the closeness of the toroid structure showing the prescence ofparatropic ring currents inside the Ni-n, ring, and by contrast, diatropic currents confined in each Ni2S2 motif denoting an aromatic behavior (in terms of magnetic criteria). The calculated data suggests that the Ni2S2 moiety can be regarded as a stable constructing block, which can afford several toroid structures of different nudearities in agreement with that reported in the experimental literature. In addition, the effects of the relativistic treatment over the magnetic response properties on these lighter compounds are denoted by comparing nonrelativistic, scalar relativistic, and scalar plus spin orbit relativistic treatments, showing their acting, although nonpronunced, role.

First author: Gruden-Pavlovic, Maja, Treatment of the Multimode Jahn-Teller Problem in Small Aromatic Radicals,JOURNAL OF PHYSICAL CHEMISTRY A, 115, 10801, (2011)
Abstract: The family of the Jahn-Teller (JT) active hydrocarbon rings, CH (n = 5-7), was analyzed by the means of multideterminantal density functional theory (DFT) approach. The multimode problem was addressed using the intrinsic distortion path (IDP) method, in which the JT distortion is expressed as a linear combination of all totally symmetric normal modes in the low symmetry minimum energy conformation. Partitioning of the stabilization energy into the various physically meaningful terms arising from Kohn Sham DFT has been performed to get further chemical insight into the coupling of the nuclear movements and the electron distribution.

First author: Ji, Minbiao, Interdependence of Conformational and Chemical Reaction Dynamics during Ion Assembly in Polar Solvents, JOURNAL OF PHYSICAL CHEMISTRY B, 115, 11399, (2011)
Abstract: We have utilized time-resolved vibrational spectroscopy to study the interdependence of the conformational and chemical reaction dynamics of ion assembly in solution. We investigated the chemical interconversion dynamics of the LiNCS ion pair and the (LiNCS)(2) ion-pair dimer, as well as the spectral diffusion dynamics of these ionic assemblies. For the strongly coordinating Lewis base solvents benzonitrile, dimethyl carbonate, and ethyl acetate, we observe Li+ coordination by both solvent molecules and NCS- anions, while the weak Lewis base solvent nitromethane shows no evidence for solvent coordination of Li+ ions. The strong interaction between the ion-pair dimer structure and the Lewis base solvents leads to ion-pair dimer solvation dynamics that proceed more slowly than the ion-pair dimer dissociation. We have attributed the slow spectral diffusion dynamics to electrostatic reorganization of the solvent molecules coordinated to the Li+ cations present in the ion-pair dimer structure and concluded that the dissociation of ion-pair dimers depends more critically on longer length scale electrostatic reorganization. This unusual inversion of the conformational and chemical reaction rates does not occur for ion-pair dimer dissociation in nitromethane or for ion pair association in any of the solvents.

First author: Alperovich, Igor, Understanding the Electronic Structure of 4d Metal Complexes: From Molecular Spinors to L-Edge Spectra of a di-Ru Catalyst, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 133, 15786, (2011)
Abstract: L-2,L-3-edge X-ray absorption spectroscopy (XAS) has demonstrated unique capabilities for the analysis of the electronic structure of di-Ru complexes such as the blue dimer cis,cis-[(Ru2O)-O-III(H2O)(2)(bpy)(4)](4+) water oxidation catalyst. Spectra of the blue dimer and the monomeric [Ru(NH3)(6)](3+) model complex show considerably different splitting of the Ru L-2,L-3 absorption edge, which reflects changes in the relative energies of the Ru 4d orbitals caused by hybridization with a bridging ligand and spin-orbit coupling effects. To aid the interpretation of spectroscopic data, we developed a new approach, which computes L-2,L-3-edges XAS spectra as dipole transitions between molecular spinors of 4d transition metal complexes. This allows for careful inclusion of the spin-orbit coupling effects and the hybridization of the Ru 4d and ligand orbitals. The obtained theoretical Ru L-2,L-3-edge spectra are in close agreement with experiment. Critically, existing single-electron methods (FEFF, FDMNES) broadly used to simulate XAS could not reproduce the experimental Ru L-edge spectra for the [Ru(NH3)(6)](3+) model complex nor for the blue dimer, while charge transfer multiplet (CTM) calculations were not applicable due to the complexity and low symmetry of the blue dimer water oxidation catalyst. We demonstrated that L-edge spectroscopy is informative for analysis of bridging metal complexes. The developed computational approach enhances L-edge spectroscopy as a tool for analysis of the electronic structures of complexes, materials, catalysts, and reactive intermediates with 4d transition metals.

First author: Tanase, Stefania, Rationalization of the Lanthanide-Ion-Driven Magnetic Properties in a Series of 4f-5d Cyano-Bridged Chains, INORGANIC CHEMISTRY, 50, 9678, (2011)
Abstract: Magnetic properties of new d-f cyanido-bridged 1D assemblies [RE(pzam)(3)(H2O)W(CN)(8)]center dot H2O (RE(III) = Gd, 1, Tb, 2, Dy, 3; pzam = pyrazine-2-carboxamide) were studied by temperature- and field-dependent magnetization measurements. No evidence for 3D interchain magnetic ordering is found above 2 K. Multiconfiguration ab initio calculations and subsequent modeling afforded simulation of the weak zero-field splitting effect in 1 and discussion of magnetic anisotropy in the f units of compounds 2 and 3. A semiquantitative corroboration with the experimental magnetic measurements is presented, performing the simulation of magnetic susceptibility vs temperature and magnetization vs field variation. The association into molecular and supramolecular architectures is analyzed by means of energy decomposition subsequent to the DFT calculations on idealized molecular models extracted from the experimental chain structure.

First author: Silvi, Bernard, Localization and Localizability in Quantum Organic Chemistry: Localized Orbitals and Localization Functions, CURRENT ORGANIC CHEMISTRY, 15, 3555, (2011)
Abstract: The utility of the localization and localizability concepts for describing chemical situation is discussed. Two routes can be followed to get such a picture from wave functions which are in principle delocalized in nature. On the one hand are orbital localization techniques which are described in the context of their applicability to organic chemistry problems. On the other hand are methods relying on local functions which perform a partition of the molecular space into connected non overlapping regions. The Becke and Edgecombe localization function is presented in detail and its application to organic quantum chemistry reviewed.

First author: Andrews, Lester, Matrix Infrared Spectroscopy and a Theoretical Investigation of SUO and US2, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 15, 4457, (2011)
Abstract: US2 and SUO molecules have been prepared by laser ablation of the solid materials and reaction of the elements during condensation in solid argon, which give the same absorptions as earlier U atom reactions with sulfur vapor and sulfur dioxide. The antisymmetric stretching mode of US2 shifts from 438.7 cm(-1) in solid argon to 442.3 cm(-1) in solid neon, which shows that the same electronic state is trapped in both matrix environments. Density functional calculations find a bent (B-3(2)) ground state for the US2 molecule, and CASSCF/CASPT2 calculations reveal a multiconfigurational mixture of (5f phi)(1)(5f delta)(1)-type states, whereas the most stable state for UO2 is a linear structure of the (5f phi)(7s) type. The bent triplet ground state SUO molecule exhibits similar multireference character with the U-O stretching mode at 857.1 cm(-1) in solid argon. The linear SUO molecule computed at the CASPT2 level is only 2 kcal/mol above the bent structure. A detailed analysis of the bonding in US2 and SUO is provided and compared to the better known UO2 molecule.

First author: Petz, Wolfgang, The Reaction of BeCl2 with Carbodiphosphorane C(PPh3)(2); Experimental and Theoretical Studies, ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 637, 1702, (2011)
Abstract: The use of 2-Br-fluorobenzene as the solvent permitted the isolation of the addition compound [Cl2Be(C{PPh3}(2))] (5) from the reaction of the carbodiphosphorane 1 (carbon) with BeCl2 featuring a three coordinate beryllium atom. In other solvents such as THF, DCM, etc. deprotonation occurs with formation of the cations (HC{PPh3}(2))(+) or (H2C{PPh3}(2))(2+). Compound 5 was characterized by an X-ray diffraction analysis. The analysis of the bonding situation in Cl2Be <- 1 reveals that the orbital donation comes mainly from the sigma lone-pair orbital of 1, whereas the pi donation is rather weak. However, the Cl2Be <- 1 pi donation appears strong enough to make the donation of a second donor species 1 unfavorable. The calculation of 1 -> Cl2Be <- 1 shows that the latter complex is higher in energy than 1 -> Cl2Be and free 1. The carbodiphosphorane may bind, albeit weakly, a second BeCl2 species in the complex Cl2Be <- 1 -> BeCl2. The bond dissociation energies for the first and second BeCl2 fragments are D-e = 31.8 kcal.mol(-1) and 7.0 kcal.mol(-1). The dimerization of Cl2Be <- 1 is energetically slightly endoenergetic.

First author: Takagi, Nozomi, Bonding Situation in “Early-Late” Transition Metal Complexes Cl3M-M ‘(PCl3)(4) (M = Ti, Zr, Hf; M ‘ = Co, Rh, Ir) – Theoretical Study for a Ligand Fine Tuning of M-M ‘ Bonds, ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 637, 1728, (2011)
Abstract: Density functional theory calculations using the BP86 functional in combination with triple-xi quality basis sets have been carried out for the “early-late” transition metal complexes Cl3M-M ‘(PCl3)(4) (M = Ti, Zr, Hf; M ‘ = Co, Rh, Ir) and the derivatives R3M-M ‘ L-4 (R = Cl, NH2; L = PCl3, PH3, CO). The calculations demonstrate that the metal-metal bond strength in R3M-M ‘ L-4 can be strongly influenced by the nature of the ligands R and L. The intrinsic interaction energy Delta E-int and the bond dissociation energy of the M-M ‘ bonds in Cl3M-M ‘(PCl3)(4) are much smaller than in the previously investigated species (H2N)(3)M-M ‘(CO)(4). The M-M ‘ bonds become stronger in both sets of compounds when the metal atoms become heavier. The equilibrium geometries of Cl3M-M ‘(PCl3)(4) which have bipyramidal structures have C-3 symmetry. The M-Co bonds in Cl3Zr-Co(PCl3)(4) and Cl3Hf-Co(PCl3)(4) and to a lesser degree in Cl3Ti-Co(PCl3)(4) are unusually long because of direct interactions between the equatorial PCl3 groups and the group 4 atoms Zr, Hf. The analysis of the metal-metal interactions suggests that Cl3M-M ‘(PCl3)(4) has M-M ‘ single bonds.

First author: Wei, Fan, Excited States and Absorption Spectra of UF6: A RASPT2 Theoretical Study with Spin-Orbit Coupling, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 7, 3223, (2011)
Abstract: Uranium hexafluoride (UF6) is an important compound in nuclear chemistry. The theoretical investigation of its excited states is difficult due to the large number of uranium valence orbitals and ligand lone pairs. We report here a detailed relativistic quantum chemical investigation of its excited states up to about 10 eV using restricted active space second-order perturbation theory (RASPT2). Scalar and spin orbit (SO) relativistic effects are treated by a relativistic small-core pseudopotential. The RASPT2/SO results remain moderately accurate when the electrons in the active space are restricted to single and double excitations. All eight major spectral peaks corresponding to ligand-to-metal charge transfer have been reproduced within an accuracy of about 0.2 eV and are tentatively assigned. We find that BLYP-based hybrid density functional with 35% Hartree-Fock exchange well reproduce the excitation energies of UF6.

First author: Sandala, Gregory M., Calibration of DFT Functionals for the Prediction of Fe-57 Mossbauer Spectral Parameters in Iron-Nitrosyl and Iron-Sulfur Complexes: Accurate Geometries Prove Essential, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 7, 3232, (2011)
Abstract: Six popular density functionals in conjunction with the conductor-like screening (COSMO) solvation model have been used to obtain linear Mossbauer isomer shift (IS) and quadrupole splitting (QS) parameters for a test set of 20 complexes (with 24 sites) comprised of nonheme nitrosyls (Fe-NO) and non-nitrosyl (Fe-S) complexes. For the first time in an IS analysis, the Fe electron density was calculated both directly at the nucleus, rho(0)(N), which is the typical procedure, and on a small sphere surrounding the nucleus, rho(0)(S), which is the new standard algorithm implemented in the ADF software package. We find that both methods yield (near) identical slopes from each linear regression analysis but are shifted with respect to rho(0) along the x axis. Therefore, the calculation of the Fe electron density with either method gives calibration fits with equal predictive value. Calibration parameters obtained from the complete test set for OLYP, OPBE, PW91, and BP86 yield correlation coefficients (r(2)) of approximately 0.90, indicating that the calibration fit is of good quality. However, fits obtained from B3LYP and B3LYP* with both Slater-type and Gaussian-type orbitals are generally found to be of poorer quality. For several of the complexes examined in this study, we find that B3LYP and B3LYP* give geometries that possess significantly larger deviations from the experimental structures than OLYP, OPBE, PW91, or BP86. This phenomenon is particularly true for the di- and tetranuclear Fe complexes examined in this study. Previous Mossbauer calibration fit studies using these functionals have usually included mononuclear Fe complexes alone, where these discrepancies are less pronounced. An examination of spin expectation values reveals that B3LYP and B3LYP* approach the weak-coupling limit more closely than the GGA exchange-correlation functionals. The high degree of variability in our calculated S-2 values for the Fe-NO complexes highlights their challenging electronic structure. Significant improvements to the isomer shift calibrations are obtained for B3LYP and B3LYP* when geometries obtained with the OLYP functional are used. In addition, greatly improved performance of these functionals is found if the complete test set is grouped separately into Fe-NO and Fe-S complexes. Calibration fits including only Fe NO complexes are found to be excellent, while those containing the non-nitrosyl Fe-S complexes alone are found to demonstrate less accurate correlations. Similar trends are also found with OLYP, OPBE, PW91, and BP86. Correlations between experimental and calculated QSs were also investigated. Generally, universal and separate Fe-NO and Fe-S fit parameters obtained to determine QSs are found to be of good to excellent quality for every density functional examined, especially if [Fe-4(NO)(4)(mu(3)-S)(4)](-) is removed from the test set.

First author: Su, Jing, Theoretical Study of the Luminescent States and Electronic Spectra of UO2Cl2 in an Argon Matrix,JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 7, 3293, (2011)
Abstract: The electronic absorption and emission spectra of free UO2Cl2 and its Ar-coordinated complexes below 27 000 cm(-1) are investigated at the levels of ab initio complete active space second-order perturbation theory (CASPT2) and coupled-cluster singles and doubles and perturbative triples [CCSD(T)] using valence 3 zeta-polarized basis sets. The influence of the argon matrix in the I2K experiment on the electronic spectra is explored by investigating the excited states of argon complexes ArnUO2Cl2. The calculated two most stable complexes with n = 2, 3 can explain the observed two matrix sites corresponding to the experimental two-component luminescence decay. In these uranyl complexes, Ar-coordination is found to have little influence on the (3)Phi (Omega = 2(g)) character of the luminescent state and on the electronic spectral shape. The calculations yield a coherent assignment of the experimental excitation spectra that improves on previous assignments. The simulated luminescence spectral curves based on the calculated spectral parameters of UO2Cl2 from both CASPT2 and CCSD(T) agree well with experiment.

First author: Kavun, V. Ya, Intramolecular mobility and phase transitions in ammonium oxofluoroniobates (NH4)(2)NbOF5 and (NR4)(3)NbOF6, a NMR and DFT study, JOURNAL OF FLUORINE CHEMISTRY, 132, 698, (2011)
Abstract: Molecular structure, ionic mobility and phase transitions in six- and seven-coordinated ammonium oxofluoroniobates (NH4)(2)NbOF5 and (NH4)(3)NbOF6 were studied by F-19, H-1 NMR and DFT calculations. Equatorial fluorine atoms (F-cq) in [NbOF5](2-) and [NbOF6](3-) are characterized by high F-19 NMR chemical shifts while axial fluorine atoms (F-ax) have those essentially lower. The high-temperature ionic mobility in (NH4)(2)NbOF5 does not stimulate the ligand exchange F-eq <-> F-ax, whereas it is observed in (NH4)(3)NbOF6 as pseudorotation typical for seven-coordinated polyhedra. The transformation of pentagonal bipyramidal structure (BP) of [NbOF6](3-) into capped trigonal prismatic (CTP) one takes place during the phase transition (PT) at 260 K. The PT of order-disorder type in (NH4)(2)NbOF5 is accompanied by transition of anionic sublattice to a rigid state. The F-19 and H-1 NMR data corroborate the independent motions of NH4 groups and anionic polyhedra in (NH4)(2)NbOF5 while they are coordinated in (NH4)(3)NbOF6.

First author: Liu, Z., H+ ions on graphene electrode as hydrogen storage reservoirs, COMPUTATIONAL MATERIALS SCIENCE, 50, 3257, (2011)
Abstract: A new idea for hydrogen storage is proposed in which H+ ions are adsorbed chemically on graphene sheet and it is possible to overcome the fundamental problem of current methods that hydrogen is not able to reversibly adsorbed/desorbed in appropriate temperature and under moderate pressure. As the top priority to test the feasibility. H+ ions storing capacity is studied by theoretical calculations. And the bonding and structural properties of H+/graphene complexes are investigated thoroughly. Our data yield promising results. The graphene fragment C62H20, in a quasi one-dimensional arch-like tunnel geometry, can absorb up to 54 H+ ions on the same side (6.6 wt.% H-2) while maintaining its conductivity because of the sp(2)-rich structure. The feasibility of the new idea is proved from a viewpoint of hydrogen storing capacity. Additional calculation using an infinite graphene sheet model gives credibility to our conclusions. Considering the successful development of synthesis techniques in mass-producing atom-thick graphene sheets, it is really worth expecting a hydrogen-based energy economy can be realized by hydrogen-ion storage graphene electrodes.

First author: Muecke, Philipp, Electron delocalization in vinyl ruthenium substituted cyclophanes: Assessment of the through-space and the through-bond pathways, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 696, 3186, (2011)
Abstract: Pseudo-para[2.2]paracyclophane- and [2.1]orthocyclophane-bridged diruthenium complexes 2 and 3 with two interlinked electroactive styryl ruthenium moieties have been prepared and investigated. Both complexes undergo two reversible consecutive one-electron oxidation processes which are separated by 270 or 105 mV. Stepwise electrolysis of the neutral complexes to first the mixed-valent radical cations and then the dioxidized dications under IR monitoring reveal incremental shifts of the charge-sensitive Ru(CO) bands and allow for an assignment of their radical cations as moderately or very weakly coupled mixed-valent systems of class II according to Robin and Day. Ground-state delocalization in the mixed-valent forms of these complexes as based on the CO band shifts is considerably larger for the “closed” paracyclophane as for the “half-open” orthocyclophane. Experimental findings are backed by the calculated IR band patterns and spin density distributions for radical cations of slightly simplified model complexes 2Me(.+) and 3Me(.+) with the (PPr3)-Pr-i ligands replaced by PMe3. Radical cations 2(.+) and 3(.+) feature a characteristic NIR band that is neither present in their neutral or fully oxidized forms nor in the radical cation of the monoruthenium [2.2] paracyclophane complex 1 with just one vinyl ruthenium moiety. These bands are thus assigned as intervalence charge-transfer (IVCT) transitions. Our results indicate that, for the radical cations, electronic coupling “through-space” via the stacked styrene decks is significantly more efficient than the “through-bond” pathway.

First author: Djukic, Jean-Pierre, Adventitious formation of a new oxopentadienyl Mn(I) tricarbonyl complex: Structural study and bonding investigation of (eta(5)-CH2C(Fc)CHC(Fc)O)Mn(CO)(3), JOURNAL OF ORGANOMETALLIC CHEMISTRY, 696, 3268, (2011)
Abstract: A Mn(I) tricarbonyl complex of a 1,3-diferrocenyl-1-oxopentadienyl ligand was synthesised adventitiously by what seems to be an in-situ aldol-like condensation of two acetylferrocene units promoted by benzyl-Mn(CO)(5). X-ray structural analysis of this unexpected product confirms the eta(5) coordination of the 1,3-diferrocenyl-1-oxopentadienyl ligand to the Mn(CO)(3) moiety. The nature of the metal-ligand bonding relationship was studied by theoretical calculations; it outlines the charge unbalance (polarisation) at the oxopentadienyl moiety as well as the lack of ketone character of the latter Mn-bound ligand.

First author: Yan Anping, DFT Study on the Interaction between Fullerere and Cerium Porphrin, ACTA CHIMICA SINICA,69, 2075, (2011)
Abstract: The 5 different configurations of fullerene-cerium-porphyrin complexes are optimized using the Perdew-Burke-Ernzerhof (PBE) density functional theory. Judged from the geometrical criteria, C-60 and cerium porphrin can form supramolecular guest-host complexes. Binding energies also confirmed this conclusion. The most likely effect of orientation is the 5:6 C-C bond of C-60. In an effort to comprehend the underlying basis of this interaction, a decomposition of the interaction energies is also carried out using the extended transition state method. The results indicate that the contribution of the electrostatic energies to the total attractive energy is about 60%, it shows that electrostatic interaction is one of the main factors for stabilizing complexes. Lastly, the electron flow for complexes is studied, the results show that the guest-host interactions are also associated with a charge transfer from the cerium porphyrin moiety to the fullerene guest.

First author: Wang Yongxia, DFT Study on the Copolymerization Mechanism of Ethylene with Cyclopentadiene by the Titanium Complexes Bearing Two beta-Enaminoketonato Ligands, ACTA CHIMICA SINICA, 69, 2085, (2011)
Abstract: We employed DFT calculations for copolymerization mechanism of ethylene (E) with cyclopentadiene (CPD) catalyzed by [PhNC(CH3)CHC(CF3)O](2)TiCl2. Our calculations show that the CPD can incorporate into polymer chain via both 1,2 and 2,1-insertion, and it is predicted that 1,2-insertion might be a preferred pathway due to the lower barrier. And in the copolymerization process, reaction barriers of ethylene insertion into both Metal-E and Metal-CPD bonds are lower than the barriers of CPD insertion, consequently, there might be more E sequences in the growing polymer chain. The CPD insertion into Metal-E bond can occur a certain extent due to the relative low insertion barrier, while for the process of CPD insertion into Metal-CPD chain, its insertion barrier is too high to make this reaction occur. The present conclusion is in line with the experimental fact that no consecutive sequence of CPD has been observed in the polymer product.

First author: Garcia-Lastra, J. M., Communication: Strong excitonic and vibronic effects determine the optical properties of Li2O2, JOURNAL OF CHEMICAL PHYSICS, 135, 2085, (2011)
Abstract: The band structure and optical absorption spectrum of lithium peroxide (Li2O2) is calculated from first-principles using the G(0)W(0) approximation and the Bethe-Salpeter equation, respectively. A strongly localized (Frenkel type) exciton corresponding to the pi*->sigma* transition on the O-2(-2) peroxide ion gives rise to a narrow absorption peak around 1.2 eV below the calculated bandgap of 4.8 eV. In the excited state, the internal O-2(-2) bond is significantly weakened due to the population of the sigma* orbital. As a consequence, the bond is elongated by almost 0.5 angstrom leading to an extreme Stokes shift of 2.6 eV. The strong vibronic coupling entails significant broadening of the excitonic absorption peak in good agreement with diffuse reflectance data on Li2O2 which shows a rather featureless spectrum with an absorption onset around 3.0 eV. These results should be important for understanding the origin of the high potential losses and low current densities, which are presently limiting the performance of Li-air batteries.

First author: Chval, Zdenek, Modeling the RNA 2 ‘ OH Activation: Possible Roles of Metal Ion and Nucleobase as Catalysts in Self-Cleaving Ribozymes, JOURNAL OF PHYSICAL CHEMISTRY B, 115, 10943, (2011)
Abstract: The RNA 2’OH activation as taking place in the first chemical step of self-cleaving ribozymes is studied theoretically by DFT and MP2 methods using a continuum solvation model (CPCM). The reaction of proton transfer is studied in the presence of two kinds of catalysts: a fully hydrated metal ion (Mg2+) or partially hydrated nucleobase (guanine), taken separately or together leading to three different modes of activation. The metal ion is either directly bound (inner-sphere) or indirectly bound (outer-sphere) to the 2’OH group and a hydroxide ion acts as a general or specific base; the nucleobase is taken in anionic or in neutral enoltautomeric forms playing itself the role of general base. The presence of a close metal ion (outer-sphere) lowers the pK(a) value of the 2’OH group by several log units in both metal-ion and nuleobase catalysis. The direct metal coordination to the 2’OH group (inner-sphere) further stabilizes the developing negative charge on the nucleophile. The switching from the inner-sphere to the outer-sphere coordination appears to be driven by the energy cost for reorganizing the first coordination shell rather than by the electrostatic repulsion between the ligands. The metal-ion catalysis is more effective with a specific base in the dianionic mechanism. On the other hand, the nucleobase catalysis is more effective in the monoanionic mechanism and in the presence of a metal ion acting as a cofactor through nonspecific electrostatic interactions. The results establish a baseline to study the possible roles of metal and nudeobase catalysts and their environment in more realistic models for self-cleaving ribozymes.

First author: Zhekova, Hristina R., First Principle Simulation of the Temperature Dependent Magnetic Circular Dichroism of a Trinuclear Copper Complex in the Presence of Zero Field Splitting, JOURNAL OF PHYSICAL CHEMISTRY A, 115, 10323, (2011)
Abstract: We present a test of a recently developed density functional theory (DFT) based methodology for the calculation of magnetic circular dichroism (MCD) spectra in the presence of zero-field splitting (ZFS). The absorption and MCD spectra of the trinuclear copper complex mu O-3 ([Cu-3(L)(mu(3)-O)](4+)), which models the native intermediate produced in the catalytic cycle of the multicopper oxidases, have been simulated from first principle within the framework of adiabatic time dependent N density functional theory. The effects of the ZFS of the quartet (4)A(2) ground state on the theoretical MCD spectrum of mu O-3 have been analyzed. The simulated spectra are consistent with experimental ones. The theoretical assignments of the MCD spectra are based on direct simulation as well as a detailed analysis of the molecular orbitals in mu O-3. Some of the assignments differ from those given in previous studies. The ZFS effects in the presence of a strong external magnetic field (7 T) prove negligible. The change of the sign of the ZFS changes systematically the intensity of the MCD bands of the z-polarized excitations. The effect of the ZFS on the x,y-polarized excitations is not uniform.

First author: Conrad, Karen S., Spectroscopic and Computational Studies of Glutathionylcobalamin: Nature of Co-S Bonding and Comparison to Co-C Bonding in Coenzyme B-12, INORGANIC CHEMISTRY, 50, 8755, (2011)
Abstract: Glutathionylcobalamin (GSCbl) is a unique, biologically relevant cobalamin featuring an axial Co-S bond that distinguishes it from the enzymatically active forms of vitamin B-12, which possess axial Co-C bonds. GSCbl has been proposed to serve as an intermediate in cobalamin processing and, more recently, as a therapeutic for neurological disorders associated with oxidative stress. In this study, GSCbl and its dose relative cysteinylcobalamin (CysCbl) were investigated using electronic absorption, circular didiroism, magnetic circular dichroism, and resonance Raman spectroscopies. The spectroscopic data were analyzed in the framework of density functional theory (DFT) and time-dependent DFT computations to generate experimentally validated electronic structure descriptions. Although the change in the upper axial ligand from an alkyl to a thiol group represents a major perturbation in terms of the size, basicity, and polarizability of the coordinating atom, our spectroscopic and computational results reveal striking similarities in electronic structure between methylcobalamin (MeCbl) and GSCbl, especially with regard to the a donation from the alkyl/thiol ligand and the extent of mixing between the cobalt 3d and the ligand frontier orbitals. A detailed comparison of Co-C and Co-S bonding in MeCbl and GSCbl, respectively, is presented, and the implications of our results with respect to the proposed biological roles of GSCbl are discussed.

First author: Ramirez-Tagle, Rodrigo, Probing the aromaticity of the [(HtAc)(3)(mu(2)-H)(6)], [(HtTh)(3)(mu(2)-H)(6)],(+), and [(HtPa)(3)(mu(2)-H)(6)] clusters, JOURNAL OF CHEMICAL PHYSICS, 135, 8755, (2011)
Abstract: In this study we report about the aromaticity of the prototypical [(HtAc)(3)(mu(2)-H)(6)], [(HtTh)(3)(mu(2)-H)(6)](+), and [(HtPa)(3)(mu(2)-H)(6)] clusters via two magnetic criteria: nucleus-independent chemical shifts (NICS) and the magnetically induced current density. All-electron density functional theory calculations were carried out using the two-component zeroth-order regular approach and the four-component Dirac-Coulomb Hamiltonian, including scalar and spin-orbit relativistic effects. Four-component current density maps and the integration of induced ring-current susceptibilities clearly show that the clusters [(HtAc)(3)(mu(2)-H)(6)] and [(HtTh)(3)(mu(2)-H)(6)](+) are non-aromatic whereas [(HtPa)(3)(mu(2)-H)(6)] is anti-aromatic. However, for the thorium cluster we find a discrepancy between the current density plots and the classification through the NICS index. Our results also demonstrate the increasing influence of f orbitals, on bonding and magnetic properties, with increasing atomic number in these clusters. We think that the enhanced electron mobility in [(HtPa)(3)(mu(2)-H)(6)] is due the significant 5f character of its valence shell. Also the participation off orbitals in bonding is the reason why the protactinium cluster has the shortest bond lengths of the three clusters. This study provides another example showing that the magnetically induced current density approach can give more reliable results than the NICS index.

First author: Smith, Arthur R. G., Spin-Orbit Coupling in Phosphorescent Iridium(III) Complexes, CHEMPHYSCHEM, 12, 2428, (2011)
Abstract: We study the excited states of two iridium(III) complexes with potential applications in organic light-emitting diodes: factris(2-phenylpyridyl) iridium(III) [Ir(ppy)(3)] and fac-tris(1-methyl-5-phenyl-3-n-propyl-[1,2,4]triazolyl)iridium(III) [Ir(ptz)(3)]. Herein we report calculations of the excited states of these complexes from time-dependent density functional theory (TDDFT) with the zeroth-order regular approximation (ZORA). We show that results from the one-component formulation of ZORA, with spin-orbit coupling included perturbatively, accurately reproduce both the results of the two-component calculations and previously published experimental absorption spectra of the complexes. We are able to trace the effects of both scalar relativistic correction and spin-orbit coupling on the low-energy excitations and radiative lifetimes of these complexes. In particular, we show that there is an indirect relativistic stabilisation of the metal-to-ligand charge transfer (MLCT) states. This is important because it means that indirect relativistic effects increase the degree to which SOC can hybridise singlet and triplet states and hence plays an important role in determining the optical properties of these complexes. We find that these two compounds are remarkably similar in these respects, despite Ir(ppy)(3) and Ir(ptz)(3) emitting green and blue light respectively. However, we predict that these two complexes will show marked differences in their magnetic circular dichroism (MCD) spectra.

First author: Zhou, Binbin, A Highly Distorted Open-Shell Endohedral Zintl Cluster: [Mn@Pb-12](3-), INORGANIC CHEMISTRY, 50, 8028, (2011)
Abstract: Reaction of an ethylenediamine (en) solution of K4Pb9 and 212,2-crypt (4,7,13,16,21,24-hexama-1,10-diazabicydo[8.8.8]hexacosane) with a tetrahydrofuran (THF) solution of Mn-3(Mes)(6) (Mes = 2,4,6-trimethylphenyl) yielded the anionic cluster [Mn@Pb-12](3-). This species was observed in the positive and negative ion-mode electrospray mass-spectra of the crude reaction mixture. The crystalline samples obtained from such solutions allowed us to confirm the composition of the sample as [K(2,2,2-crypt)](3)[Mn@Pb-12] .1.5en (1). Because of numerous issues related to crystal sample quality and crystallographic disorder a high-quality crystal structure solution could not be obtained. Despite this, however, the data collected permit us to draw reasonable conclusions about the charge and connectivity of the [Mn@Pb-12](3) cluster anion. Crystals of 1 were further characterized by elemental analysis and electron paramagnetic resonance (EPR). Density Functional Theory (DFT) calculations on such a system reveal a highly distorted endohedral cluster anion, consistent with the structural distortions observed by single crystal X-ray diffraction. The cluster anions are considerably expanded compared to the 36-electron dosed-shell analogue [Ni@Pb-12](2-) and, moreover, exhibit significant low-symmetry distortions from the idealized icosahedral (I-h) geometry that is characteristic of related endohedral dusters. Our computations indicate that there is substantial transfer of electron density from the formally Mn(-I) center to the low-lying vacant orbitals of the [Pb-12](2-) cage.

First author: Gardner, Benedict M., The Nature of Unsupported Uranium-Ruthenium Bonds: A Combined Experimental and Theoretical Study, CHEMISTRY-A EUROPEAN JOURNAL, 17, 11266, (2011)
Abstract: Four new uranium-ruthenium complexes, [(Tren(TMS))URu(eta(5)-C5H5)( CO)(2)] (9), [(Tren(DMSB))URu(eta(5)-C5H5)(CO)(2)] (10), [(Ts-Tolyl)(THF)URu-( eta(5)-C5H5)(CO)(2)] (11), and [(Ts-Xylyl)-(THF)URu(eta(5)-C5H5)(CO)(2)] (12) [Tren(TMS) = N(CH2CH2NSiMe3)(3); Tren(DMSB) = N(CH(2)CH(2)NSiMe(2)tBu)(3)]; Ts-Tolyl = HC(SiMe2NC6H4-4-Me)(3); Ts-Xylyl = HC(SiMe2NC6H3-3,5-Me-2)(3)], were prepared by a salt-elimination strategy. Structural, spectroscopic, and computational analyses of 9-12 shows: i) the formation of unsupported uranium-ruthenium bonds with no isocarbonyl linkages in the solid state; ii) ruthenium-carbonyl backbonding in the [Ru(eta(5)-C5H5)(CO)(2)](-) ions that is tempered by polarization of charge within the ruthenium fragments towards uranium; iii) closed-shell uranium-ruthenium interactions that can be classified as predominantly ionic with little covalent character. Comparison of the calculated U-Ru bond interaction energies (BIEs) of 9-12 with the BIE of [(eta(5)-C5H5) 3URu( eta(5)-C5H5)( CO)(2)], for which an experimentally determined U-Ru bond disruption enthalpy (BDE) has been reported, suggests BDEs of approximately 150 kJ mol(-1) for 9-12.

First author: Stephen, Emma, Redox Non-Innocence of Thioether Crowns: Spectroelectrochemistry and Electronic Structure of Formal Nickel(III) Complexes of Aza-Thioether Macrocycles, CHEMISTRY-A EUROPEAN JOURNAL, 17, 10246, (2011)
Abstract: The Ni-II complexes [Ni([9]aneNS(2)-CH3)(2)](2+) ([9]aneNS(2)-CH3=N-methyl-1-aza-4,7-dithiacyclononane), [Ni(bis[9]aneNS(2)-C2H4)](2+) (bis[9]aneNS(2)-C2H4=1,2-bis-(1-aza-4,7-dithiacyclononylethane) and [Ni([9]aneS(3))(2)](2+) ([9]aneS(3)=1,4,7-trithiacyclononane) have been prepared and can be electrochemically and chemically oxidized to give the formal Ni-III products, which have been characterized by X-ray crystallography, UV/Vis and multi-frequency EPR spectroscopy. The single-crystal X-ray structure of [Ni-III([9]aneNS(2)-CH3)(2)](ClO4)(6)center dot(H5O2)(3) reveals an octahedral co-ordination at the Ni centre, while the crystal structure of [Ni-III(bis[9]aneNS(2)-C2H4)](ClO4)(6)center dot(H3O)(3)center dot 3H(2)O exhibits a more distorted coordination. In the homoleptic analogue, [Ni-III([9]aneS(3))(2)](ClO4)(3), structurally characterized at 30 K, the Ni-S distances [2.249(6), 2.251(5) and 2.437(2) angstrom] are consistent with a Jahn-Teller distorted octahedral stereochemistry. [Ni([9]aneNS(2)-CH3)(2)](PF6)(2) shows a one-electron oxidation process in MeCN (0.2M NBu4PF6, 293 K) at E-1/2 = +1.10 V versus Fc(+)/Fc assigned to a formal Ni-III/Ni-II couple. [Ni(bis[9]aneNS(2)-C2H4)](PF6)(2) exhibits a one-electron oxidation process at E-1/2 = +0.98 V and a reduction process at E-1/2 = -1.25 V assigned to Ni-II/Ni-III and Ni-II/Ni-I couples, respectively. The multi-frequency X-, L-, S-, K-band EPR spectra of the 3+ cations and their 86.2% Ni-61-enriched analogues were simulated. Treatment of the spin Hamiltonian parameters by perturbation theory reveals that the SOMO has 50.6%, 42.8% and 37.2% Ni character in [Ni([9]aneNS(2)-CH3)(2)](3+), [Ni(bis[9]aneNS(2)-C2H4)](3+) and [Ni([9]aneS(3))(2)](3+), respectively, consistent with DFT calculations, and reflecting delocalisation of charge onto the S-thioether centres. EPR spectra for [Ni-61([9]aneS(3))(2)](3+) are consistent with a dynamic Jahn-Teller distortion in this compound.

First author: Sharif, Muhammad, 1-(Arylalkenyl)pyrenes – Synthetic, Structural, Photophysical, Theoretical, and Electrochemical Investigations, EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, 17, 5261, (2011)
Abstract: As a new approach for tuning the electronic properties of pyrene derivatives, we converted 1-bromopyrene into different substituted styrenes using the Mizoroki-Heck reaction. Several 1-(arylalkenyl)pyrenes have been characterized and their electronic properties studied by absorption and emission spectroscopy. The effect of the electronic ambience on the emission spectra of these compounds is discussed. Amongst the intramolecular influences, such as electron donating or withdrawing groups, other influences in the form of solvatochromatism are considered. Electrochemical oxidation potentials determined by DPV (differential pulse voltammetry) are discussed with regard to substituent effects. The fine structure of the absorbance spectra obtained from photophysical measurements is compared with theoretical calculations performed by time dependent B3LYP DFT (TD-DFT) methods using the 6-31G* basis set. In this context, we discuss the calculated potential energy surfaces and geometric structures with regard to the substitution pattern of the pyrenes.

First author: Biswas, Achintesh Narayan, Regiospecific C(naphthyl)-H Bond Activation by Platinum(II) – Isolation, Characterization, Reactivity and TD-DFT Study of the Cycloplatinate Complexes, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 17, 3739, (2011)
Abstract: The regiospecific activation of C(naphthyl)-H bonds in a group of naphthylazo-2′-hydroxyarene ligands (H2L) has been achieved by platinum(II) compounds under different reaction conditions, and stable cycloplatinates [(PtL)-L-II(D)] have been isolated in presence of neutral Lewis bases (D). Structures of the cycloplatinate complexes of platinum(II) have been established by single-crystal X-ray crystallography. The platinum(II) centres are surrounded by a C,N,O-terdentate ligand frame (L) and Lewis base (D) in a distorted square planar fashion. These cycloplatinate species have been found to react with halogens and methyl iodide undergoing metal-centered two electron oxidation affording platinum(IV) cycloplatinates with distorted octahedral geometry. In the reactions with halogens and methyl iodide, trans oxidative addition has been found for [Pt(L)D] (D = 4-picoline), whereas cis addition has been observed for [Pt(L)D] where D is a more sterically demanding triphenylphosphane. Structures of two representative platinum(IV) cycloplatinate species have been determined by single-crystal X-ray crystallography. A time dependent (TD)-DFT study of representative cycloplatinate compounds has been performed. Optical absorption spectra of the cycloplatinate compounds in dichloromethane have been simulated using the TD-DFT method, and the experimental spectra are in very good agreement.

First author: Li, Qiaohong, Mechanism Insights into Second-Order Nonlinear Optical Responses of Anionic Metal Clusters,JOURNAL OF CLUSTER SCIENCE, 22, 365, (2011)
Abstract: We present the first-principle calculations on the electronic excitations and second-order properties in solution phase of two typical inorganic trinuclear anionic clusters, [MoCu2S4(SPh)(2)](2-) and [Mo2CuS4](1-)(edt)(2)(PPh3) (edt=1,2-ethanedithiolato) in the framework of density functional theory (DFT). The computed excitation energies are in good agreement with the outcome of the measurements. The predicted values of the molecular quadratic hyperpolarizabilities are of the comparable order of those of the typical organometallic chromophores. We demonstrate the significant contributions to the second-order responses from the charge transfers between the metal centers (MMCT) which are ascribed to the direct metal-metal bonding interactions in these two charged clusters. This meaningful ligand-independent mechanism for the second-order response largely relates to metal-metal bonding strength, and the understanding will benefit to the future design of the new-generation molecular based nonlinear optical materials and optoelectronic devices by means of the conscious tuning of metal-metal interactions and metal-core structures of inorganic polynuclear clusters.

Abstract: A novel, neural network controlled, dynamic evolutionary algorithm is proposed for the purposes of molecular geometry optimization. The approach is tested for selected model molecules and some molecular systems of importance in biochemistry. The new algorithm is shown to compare favorably with the standard, statically parametrized memetic algorithm.

First author: Boguslawski, Katharina, Can DFT Accurately Predict Spin Densities? Analysis of Discrepancies in Iron Nitrosyl Complexes, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 7, 2740, (2011)
Abstract: Iron nitrosyl complexes are a particularly challenging case for density functional theory. In particular, for the low-spin state, different exchange correlation functionals yield very different spin densities [Conradie, J.; Ghosh, A. J. Phys. Chem. B 2007, 111, 12621-12624]. Here, we investigate the origin of these differences in detail by analyzing the Kohn-Sham molecular orbitals. Furthermore, to decide which exchange correlation functionals yield the most accurate spin densities, we make comparisons to CASSCF calculations. To ensure that the spin densities are converged with respect to the size of the active space, this comparison is performed for [Fe(NO)](2+) as a model system. We find that none of the investigated exchange-correlation functionals are able to reproduce the CASSCF spin densities accurately.

First author: Jacobsen, Heiko, A Failure of DFT Is Not Necessarily a DFT Failure-Performance Dependencies on Model System Choices, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 7, 3019, (2011)
Abstract: The claim that DFT does not provide an accurate description of a weak Ru-C interaction (J. Chem. Theory Comput. 2007, 3, 665-670) is put into broader perspective. The mismatch between structures obtained from DFT (BP86) as well as DFT-D (BP86-D2) calculations of isolated molecules in the gas phase and geometries resulting from X-ray crystal structure determination is due to a dissatisfactory chemical model system. Intermolecular forces within the molecular surroundings of the crystal obtained from semiempirical lattice energy calculations emerge as likely candidates responsible for the incongruity of experimental results and computation.

First author: Ganesan, Aravindhan, Effects of alkyl side chains on properties of aliphatic amino acids probed using quantum chemical calculations, JOURNAL OF SYNCHROTRON RADIATION, 18, 733, (2011)
Abstract: Effects of alkyl side chains (R-) on the electronic structural properties of aliphatic amino acids are investigated using quantum mechanical approaches. The carbon (C 1s) binding energy spectra of the aliphatic amino acids are derived from the C 1s spectrum of glycine (the parent spectrum) by the addition of spectral peaks, depending on the alkyl side chains, appearing in the lower energy region IP < 290 eV (where IP is the ionization potential). The two glycyl parent spectral peaks of the amide 291.0 eV [C-(2)] and carboxylic 293.5 eV [C-(1)] C atoms are shifted in the aliphatic amino acids owing to perturbations depending on the size and structure of the alkyl chains. The pattern of the N 1s and O 1s spectra in glycine is retained in the spectra of the other amino acids with small shifts to lower energy, again depending on the alkyl side chain. The Hirshfeld charge analyses confirm the observations. The alkyl effects on the valence binding energy spectra of the amino acids are concentrated in the middle valence energy region of 12-16 eV, and hence this energy region of 12-16 eV is considered as the ‘fingerprint’ of the alkyl side chains. Selected valence orbitals, either inside or outside of the alkyl fingerprint region, are presented using both density distributions and orbital momentum distributions, in order to understand the chemical bonding of the amino acids. It is also observed that the HOMO-LUMO energy gaps of the aliphatic amino acids are reduced with the growth of the alkyl side chain.

First author: Mitoraj, Mariusz Pawel, Applications of the ETS-NOCV method in descriptions of chemical reactions,JOURNAL OF MOLECULAR MODELING, 17, 2337, (2011)
Abstract: The present study characterizes changes in the electronic structure of reactants during chemical reactions based on the combined charge and energy decomposition scheme, ETS-NOCV (extended transition state-natural orbitals for chemical valence). Decomposition of the activation barrier, Delta E (#), into stabilizing (orbital interaction, Delta E (orb), and electrostatic, Delta E (elstat)) and destabilizing (Pauli repulsion, Delta E (Pauli), and geometry distortion energy, Delta E (dist)) factors is discussed in detail for the following reactions: (I) hydrogen cyanide to hydrogen isocyanide, HCN -> aEuro parts per thousand CNH isomerization; (II) Diels-Alder cycloaddition of ethene to 1,3-butadiene; and two catalytic processes, i.e., (III) insertion of ethylene into the metal-alkyl bond using half-titanocene with phenyl-phenoxy ligand catalyst; and (IV) B-H bond activation catalyzed by an Ir-containing catalyst. Various reference states for fragments were applied in ETS-NOCV analysis. We found that NOCV-based deformation densities (Delta rho (i)) and the corresponding energies Delta E (orb)(i) obtained from the ETS-NOCV scheme provide a very useful picture, both qualitatively and quantitatively, of electronic density reorganization along the considered reaction pathways. Decomposition of the barrier Delta E-# into stabilizing and destabilizing contributions allowed us to conclude that the main factor responsible for the existence of positive values of Delta E (#) for all processes (I, II, III and IV) is Pauli interaction, which is the origin of steric repulsion. In addition, in the case of reactions II, III and IV, a significant degree of structural deformation of the reactants, as measured by the geometry distortion energy, plays an important role. Depending on the reaction type, stabilization of the transition state (relatively to the reactants) originating either from the orbital interaction term or from electrostatic attraction can be of vital importance. Finally, use of the ETS-NOCV method to describe catalytic reactions allows extraction of information on the role of catalysts in determination of Delta E (#).

First author: Ullmann, R. Thomas, Coupling of Protonation, Reduction, and Conformational Change in azurin from Pseudomonas aeruginosa Investigated with Free Energy Measures of Cooperativity, JOURNAL OF PHYSICAL CHEMISTRY B, 115, 10346, (2011)
Abstract: We used free energy calculations within a continuum electrostatics model to analyze the coupling of protonation, reduction, and conformational change in azurin from Pseudomonas aeruginosa (PaAz). PaAz was characterized extensively with a variety, of experimental methods. Experimentally determined pK(a) values and pH-dependent reduction potentials are used to validate our computational model. It is well-known from experiment that the reduction of the copper center is coupled to the protonation of at least two titratable residues (His-35 and His-83) and to the flip of the peptide bond between Pro-36 and Gly-37. Free energy measures of cooperativity are used for a detailed analysis of the coupling between protonation, reduction, and conformational change in PaAz. The reduction of the copper center, the protonation of His-35, and peptide flip are shown to be cooperative. Our results show that cooperativity free energies are useful in detecting and quantifying thermodynamic coupling between events in biomolecular systems. The protonation of His-35 and the peptide flip are found to be so tightly coupled that these events happen effectively concerted. This concerted change results in a marked alteration of the electrostatic surface potential of azurin that might affect the interaction of azurin with its binding partners.

First author: Tyo, Eric C., Analogous Reactivity of Pd+ and ZrO+: Comparing the Reactivity with Small Hydrocarbons,JOURNAL OF PHYSICAL CHEMISTRY C, 115, 16797, (2011)
Abstract: Although early transition metals are too reactive to serve as effective combustion catalysts, it has been proposed that combining them with nonmetallic elements may moderate the reactivity and allow them to replace more expensive catalysts. To test this hypothesis, we use ZrO+ as our replacement and compare the reactivity with Pd+, in a synergistic study employing gas-phase guided-ion-beam mass spectroscopy in conjunction with theoretical investigations. The findings reveal similar reactivity patterns for both ethane and propane with the scission of a C-C bond being the primary reaction mechanism for the interaction of both gases with ZrO+ and Pd+. Hydrogen abstraction is also observed with similar branching ratios for both ions. It is proposed that the similar reactivity is due to ZrO+ having molecular orbitals with 4d components that participate in the reaction in a similar way as the 4d orbitals of Pd+.

First author: Zhuang, Zhiping, Surface-enhanced Raman scattering of trans-1,2-bis (4-pyridyl)-ethylene on silver by theory calculations, SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY, 79, 1593, (2011)
Abstract: Surface-enhanced Raman spectra of trans-1,2-bis (4-pyridyl)-ethylene (t-BPE) on silver foil were detected at laser line of 514.5,633,785 and 1064 nm, respectively. The structure of Ag-t-BPE,Ag-4-t-BPE,Ag-6-t-BPE, Ag-10-t-BPE and Ag-20-t-BPE complexes has been calculated using a local version of the Amsterdam density functional program package. The Raman spectra and electronic polarizability of t-BPE-Ag at 514.5, 633, 785 and 1064 nm excitation lines were calculated. The Raman bands of t-BPE were assigned according to the calculation of potential energy distribution. The experimental and calculated Raman spectra of t-BPE-Ag at 514.5, 633, 785 and 1064 nm were compared. The relative Raman intensities change at different excitation lines were discussed based on the Raman enhanced mechanism and surface selection rules.

First author: La Penna, Giovanni, Measuring electron sharing between atoms in first-principle simulations, THEORETICAL CHEMISTRY ACCOUNTS, 130, 27, (2011)
Abstract: Calculations of large scale electronic structure within periodic boundary conditions, mostly based on solid state physics, allow the modeling of atomic forces and molecular dynamics for atomic assemblies of 100-1000 atoms, thus providing complementary information in material and macromolecular sciences. Nevertheless, these methods lack connections with the chemistry of simple molecules as isolated entities. In order to contribute to establish a conceptual connection between solid state physics and chemistry, the calculation of the extent of electron sharing between atoms, also known as delocalization index, is performed on simple molecules and on complexes with transition metal atoms, using density functional calculations where the Kohn-Sham molecular orbitals are represented in terms of plane waves and in periodic boundary conditions. These applications show that the useful measure of electron sharing between atomic pairs can be recovered from density functional calculations using the same set-up applied to large atomic assemblies in condensed phases, with no projections of molecular orbitals onto atomic orbitals.

First author: Erasmus, J. J. C., Oxidative addition of methyl iodide to [Rh(CH3COCHCOCH3)(CO)(P(OCH2)(3)CCH3)],INORGANICA CHIMICA ACTA, 375, 128, (2011)
Abstract: The reaction rate of the oxidative addition and the following CO insertion step of methyl iodide with [Rh(acac)(CO)(P(OCH2)(3)CCH3)] is determined. The key finding is that while [Rh(acac)(CO)(P(OCH2)(3)CCH3)] oxidatively adds methyl iodide ca 300 times faster than the Monsanto catalyst, the CO insertion step is much slower. However, the rate-determining step of the oxidative addition reaction of the phosphorus-containing acetylacetonato-rhodium(I) complex, the carbonyl insertion step, is still in the same order or faster than the rate-determining oxidative addition step of iodomethane to [Rh(CO)(2)I-2].

First author: Bayat, Mehdi, Energy decomposition analysis of the metal-oxime bond in [M{RC(NOH)C(NO)R}(2)] (M = Ni(II), Pd(II), Pt(II), R = CH3, H, F, Cl, Br, Ph, CF3), JOURNAL OF ORGANOMETALLIC CHEMISTRY, 696, 2976, (2011)
Abstract: Quantum chemical calculations using gradient-corrected DFT at the BP86/TZ2P+ level were carried out for the metal-dioxime complexes [M{RC(NOH)C(NO)R}(2)] with M = Ni, Pd, Pt, R = CH3, H, F, Cl, Br, Ph, CF3. The nature of the metal-ligand bond was investigated with an energy decomposition analysis (EDA). The complexes with electron donating substituents R = H, CH3 have the strongest metal-ligand interaction energies Delta E-int, as well as the largest bond dissociation energies. The analysis of the bonding situation revealed that the metal <- ligand sigma donation is much stronger than the metal -> ligand pi backdonation. The breakdown of the orbital interactions into the contributions of orbitals with different symmetry indicates that the donation from the in-plane lone-pair donor-orbitals of nitrogen into the d(xy) AO of the metal provides about one half of the stabilization which comes from Delta E-orb. Inspection of the EDA data indicates that the electrostatic term Delta E-elstat is more important for the trend of the metal-oxime interactions in [M{RC(NOH)C(NO)R}(2)] than the orbital term Delta E-orb.

First author: Pinter, Balazs, Conformational fluxionality in a palladium(II) complex of flexible click chelator 4-phenyl-1-(2-picolyl)-1,2,3-triazole: A dynamic NMR and DFT study, POLYHEDRON, 30, 2368, (2011)
Abstract: An experimental and theoretical DFT study was carried out on the solution behavior in [D-7]DMF for bis-chelate complex [Pd(L)(2)](BF4)(2)center dot 2CH(3)CN (L = 4-phenyl-1-(2-picolyl)-1,2,3-triazole). In structure of [Pd(L)(2)](2+), the central square-planar palladium(II) cation is trans-chelated by two L substrates, each through the pyridine and the triazole N2 nitrogen atoms, forming two six-membered metallacycles. These can adopt boat-like conformations anti-trans-[Pd(L)(2)](2+) and syn-trans-[Pd(L)(2)](2+) in which the picolyl methylene carbons are anti or syn, respectively, relative to the palladium coordination plane. In solution, the boat-to-boat inversion at both metallacycles takes place. The conformers are in a dynamic equilibrium, which was monitored by variable-temperature (VT) H-1 NMR spectroscopy in the temperature range of 223-353 K. The equilibrium lies on the side of the anti-trans-[Pd(L)(2)](2+) conformer and the corresponding reaction enthalpy and entropy is estimated to be 0.6 +/- 0.5 kcal mol(-1) and 0.8 +/- 1 cal mol(-1) K-1, respectively. From the full-line-shape analysis of resonances in the VT H-1 NMR spectra, the activation enthalpy and activation entropy was determined to be 13.0 +/- 0.4 kcal mol(-1) and 2.7 +/- 1.6 cal mol(-1) K-1, respectively. The activation entropy close to zero suggests a nondissociative mechanism for the isomerisation. DFT investigation revealed that the isomerisation proceeds through a one step mechanism with a barrier of 11.40 kcal mol(-1). The structures of the syn and anti conformers as well as that of the transition state were characterized. Energy decomposition analysis was carried out in order to explore the origins of the stability difference between the syn and anti isomers.

First author: Conradie, Marrigje M., Iodomethane oxidative addition to beta-diketonatobis(triphenylphosphite)rhodium(I) complexes: A synthetic, kinetic and computational study, POLYHEDRON, 30, 2345, (2011)
Abstract: New rhodium(I)- and rhodium(III)-beta-diketonato complexes of the type [Rh(FcCOCHCOR)(P(OPh)(3))(2)] and [Rh(FcCOCHCOR)(P(OPN3)(2)(CH3)(I)], with Fc = ferrocenyl and R = Fc, CH3 and CF3, have been synthesized. The reactivity of complexes of the type [Rh(beta-diketonato)(P(OPh)(3))(2)] increase in the order: beta-diketonato = (CF3COCHCOCF3)(-) < (CF3COCHCOPh)(-) < (CF3COCHCOCH3)(-) < (PhCOCHCOPh)(-) < (CF(3)COCHCOFc)(-) < (CH3COCHCOPh)(-) < (CH3COCHCOCH3)(-) < (CH(3)COCHCOFc)(-) < (FcCOCHCOFc)(-), giving linear relationships between the kinetic parameter In k(2) and the parameters that are related to the electron density on the rhodium centre; the sum of the group electronegativities of the beta-diketonato side groups (chi(R) + chi(R’)) and the pK(a) of the uncoordinated beta-diketone RCOCH2COR’. The large negative values of the volume and entropy of activation indicated a mechanism which occurs via a polar transition state. A density functional theory study, at the PW91/TZP level of theory, indicates that oxidative addition of iodo methane to [Rh(FcCOCHCOCF(3))(P(OCH3)(3))(2)] occurs via a two-step mechanism. This mechanism involves a nucleophilic attack by the metal on the methyl carbon to displace iodide to form a metal-carbon bond and the coordination of iodide to the five-coordinated intermediate to give a six-coordinated trans alkyl product.

First author: Marzouk, Asma, Vibrational Spectrum and Structure of CoO6: A Model Compound for Molecular Oxygen Reversible Binding on Cobalt Oxides and Salts; A Combined IR Matrix Isolation and Theoretical Study, JOURNAL OF PHYSICAL CHEMISTRY A, 115, 9014, (2011)
Abstract: The formation and structure of a novel species, a disuperoxo-cobalt dioxide complex (CoO6), has been investigated using matrix isolation in solid neon and argon, coupled to infrared spectroscopy and by quantum chemical methods. It is found that CoO6 can be formed by successive complexation of cobalt dioxide by molecular oxygen without activation energy by diffusion of ground state O-2 molecules at 9K in the dark. The IR data on one combination and seven fundamentals, isotopic effects, and quantum chemical calculations are both consistent with an asymmetrical structure with two slightly nonequivalent oxygen ligands complexing a cobalt dioxide subunit. Evidence for other, metastable states is also presented, but the data are not complete. The electronic structure and formation pathway of this unique, formally +VI oxidation state, complex has been investigated using several functionals of current DFT within the broken-symmetry unrestricted formalism. It has been shown that the M06L pure local functional well reproduce the experimental observations. The ground electronic state is predicted to be an open shell (2)A” doublet with the quartet states above by more than 9 kcal/mol and the sextet lying even higher in energy. The ground state has a strong and complex multireference character that hinders the use of more precise multireference approaches and requires caution in the methodology to be used. The geometrical, energetic, and vibrational properties have been computed.

First author: Popov, Alexey A., The State of Asymmetric Nitride Clusters in Endohedral Fullerenes as Studied by N-14 NMR Spectroscopy: Experiment and Theory, JOURNAL OF PHYSICAL CHEMISTRY C, 115, 15257, (2011)
Abstract: While the role of asymmetric nitride clusters on the cage size and symmetry in fullerene-based structures is already well-known, the role of the asymmetric arrangement of metals in nitride clusters on the nitrogen is studied in detail in this work. It is discovered that asymmetric mixed-metal nitride clusters give sufficiently narrow N-14 NMR signals to make NMR the method of choice to characterize the endohedral cluster from the inside. In the series of mixed-metal nitride clusterfullerenes LuxSc3-xN@C-80 and LuxY3-xN@C-80 (x = 0-3) the delta(N-14) values are found to be linear functions of x showing that N-14 chemical shifts are additive values with specific increment for each kind of metal atoms. Density functional theory calculations are performed to interpret the experimentally measured spectra. To reveal the main factors affecting N-14 chemical shifts in nitride clusterfullerenes, shielding tensor components are analyzed in terms of Ramsey theory both in localized and canonical molecular orbitals. N-14 chemical shifts in M3N@C-80 and related systems are shown to be determined solely by nitrogen-localized orbitals and in particular by the p(x,y,z) atomic orbitals of nitrogen. As a result, the peculiarities of the nitrogen shielding in nitride clusterfullerenes can be interpreted by the simple analysis of the nitrogen-projected density of states and its variation in different chemical environments.

First author: Vasiliu, Monica, Prediction of the Thermodynamic Properties of Key Products and Intermediates from Biomass, JOURNAL OF PHYSICAL CHEMISTRY C, 115, 15686, (2011)
Abstract: The high-level G3MP2 computational chemistry method was used to predict the thermodynamic properties of a wide range of compounds relevant to the conversion of biomass-derived oxygenated feedstocks into fuels or chemical feedstocks. The starting compounds were glucose, 5-hydroxymethyl furfural, sorbitol, levulinic acid, succinic acid, gamma-valerolactone, and glycerol. The calculated G3MP2 gas-phase heats of formation were mostly within +/- 2 kcal/mol of the available experimental values. Heats of formation of the liquid were obtained from calculations of the boiling point combined with the rule of Pictet and Trouton using modified values for Delta S-vap. The modified values for Delta S-vap arise because of the presence of intermolecular hydrogen bonding, Delta S-vap = 0.031 cal/(mol K) for carboxylic acids, 0.035 cal/(mol K) for dialcohols, and 0.040 cal/(mol K) for higher polyalcohols. The thermodynamics of a wide range of reactions were predicted. Reaction energies in the aqueous phase at 298 K were estimated from self-consistent reaction field calculations of the solvation energy using the COSMO parametrization. Most of the reactions were exothermic, and the reaction products were stabilized by aqueous solvation. Exceptions include dehydrogenation, decarbonylation, ring-opening, and dehydration reactions when only one mole of water is eliminated.

First author: Jovic, Marija, Non-innocent Character of Oxyanions in Ruthenium Metathesis Catalysts,ORGANOMETALLICS, 30, 3971, (2011)
Abstract: The synthesis, characterization, reactivity, and selectivity of six novel ruthenium metathesis catalysts containing oxyanions as ligands are described. A drop in chemoselectivity and/or reactivity in alternating ring-opening metathesis polymerization of norbornene and cyclooctene for catalysts with nitrate, acetate, and benzoate ligands (i.e., catalysts 7, 8, and 10a) compared to the parent complex bearing chloride as a ligand (513) is observed, while catalysts with trifluoroacetate, methylbenzoate, and triisopropylbenzoate ligands (i.e., catalysts 9, 10b, and 10c) exhibit the expected activities and chemoselectivities. A model accounting for the aforementioned observations is based on a chelating effect of oxyanion ligands in these complexes and is supported by NMR data, crystal structures of the new complexes, and DFT calculations. Through comparison of selectivity and reactivity in copolymerizations with NMR and X-ray structures, we have uncovered correlations that serve as predictive tools for catalyst design.

First author: Scuppa, Stefano, Anti-Kasha’s Rule Fluorescence Emission in (2-Ferrocenyl)indene Generated by a Twisted Intramolecular Charge-Transfer (TICT) Process, JOURNAL OF PHYSICAL CHEMISTRY A, 115, 8344, (2011)
Abstract: A twisted intramolecular charge-transfer (TICT) process has been identified in (2-ferrocenyl)indene. This photochemical process explains the anti-Kasha’s rule fluorescence emission observed for this system. Experimental and model investigations on (2-ferrocenyl)tetramethylindene and (2-ferrocenyl)-hexamethylindene were also performed, in order to evaluate the effect of a steric hindrance on the TICT mechanism. The energy of the lowest main excited states was computed with a TD-DFT approach, as a function of the rotation of the dihedral angle between the indene and the cyclopentadienyl planes. To the best of our knowledge, this is the first example of TICT generated by metal-to-ligand charge transfer (MLCT) in a ferrocene-containing complex and, more generally, the first case of complexes in which a metal center is directly involved.

First author: Esterhuysen, Catharine, Distinguishing Carbones from Allenes by Complexation to AuCl, CHEMISTRY-A EUROPEAN JOURNAL, 17, 9944, (2011)
Abstract: Quantum chemical calculations have been performed for the dicoordinated carbon compounds C(PPh3)(2), C(NHCMe)(2), R2C=C=CR2 (R=H, F, NMe2), C3O2, C(CN)(2)(-) and N-methyl-substituted N-heterocyclic carbene (NHCMe). The geometries of the complexes in which the dicoordinated carbon molecules bind as ligands to one and two AuCl moieties have been optimized and the strength and nature of the metal-ligand interactions in the mono- and diaurated complexes were investigated by means of energy decomposition analysis. The goal of the study is to elucidate the differences in the chemical behavior between carbones, allenes and carbenes. The results show that carbones bind one and two AuCl species in eta(1) fashion, whereas allenes bind them in eta(2) fashion. Compounds with latent divalent carbon(0) character can coordinate in more than one way, with the dominant mode indicating the degree of carbone or allene character. The calculated structures of the mono-and diaurated tetraaminoallenes (TAAs) reveal that TAAs exhibit a chameleon-like behavior: The bonding situation in the equilibrium structure is best described as allene [(R2N)(2)]C=C=C[(NR2)(2)] in which the central carbon atom is a tetravalent C-IV species, but the reactivity suggests that TAAs should be considered as divalent C-0 compounds C{C[(NR2)(2)]}(2), that is, as “hidden” carbones. Carbon suboxide binds one AuCl preferentially in the eta(1) mode, whereas the equilibrium structures of the eta(1)- and eta(2)-bonded diaurated complex are energetically nearly degenerate. The doubly negatively charged isoelectronic carbone C(CN)(2)(2-) binds one and two AuCl very strongly in characteristic eta(1) fashion. The N-heterocyclic carbene complex, [NHCMe(AuCl)], possesses a high bond dissociation energy (BDE) for the splitting off of AuCl. The diaurated NHC adduct, [NHCMe(AuCl)(2)], has two eta(1)-bonded AuCl moieties that exhibit aurophilic attraction, which yield a moderate bond strength that might be large enough for synthesizing the complex. The BDE for the second AuCl in [NHCMe(AuCl)(2)] is clearly smaller than the values for the second AuCl in doubly aurated carbone complexes.

First author: Guerra, Celia Fonseca, Remote Communication in a DNA-Based Nanoswitch, CHEMISTRY-A EUROPEAN JOURNAL, 17, 8816, (2011)
Abstract: Quantum chemical calculations have been performed for the dicoordinated carbon compounds C(PPh3)(2), C(NHCMe)(2), R2C=C=CR2 (R=H, F, NMe2), C3O2, C(CN)(2)(-) and N-methyl-substituted N-heterocyclic carbene (NHCMe). The geometries of the complexes in which the dicoordinated carbon molecules bind as ligands to one and two AuCl moieties have been optimized and the strength and nature of the metal-ligand interactions in the mono- and diaurated complexes were investigated by means of energy decomposition analysis. The goal of the study is to elucidate the differences in the chemical behavior between carbones, allenes and carbenes. The results show that carbones bind one and two AuCl species in eta(1) fashion, whereas allenes bind them in eta(2) fashion. Compounds with latent divalent carbon(0) character can coordinate in more than one way, with the dominant mode indicating the degree of carbone or allene character. The calculated structures of the mono-and diaurated tetraaminoallenes (TAAs) reveal that TAAs exhibit a chameleon-like behavior: The bonding situation in the equilibrium structure is best described as allene [(R2N)(2)]C=C=C[(NR2)(2)] in which the central carbon atom is a tetravalent C-IV species, but the reactivity suggests that TAAs should be considered as divalent C-0 compounds C{C[(NR2)(2)]}(2), that is, as “hidden” carbones. Carbon suboxide binds one AuCl preferentially in the eta(1) mode, whereas the equilibrium structures of the eta(1)- and eta(2)-bonded diaurated complex are energetically nearly degenerate. The doubly negatively charged isoelectronic carbone C(CN)(2)(2-) binds one and two AuCl very strongly in characteristic eta(1) fashion. The N-heterocyclic carbene complex, [NHCMe(AuCl)], possesses a high bond dissociation energy (BDE) for the splitting off of AuCl. The diaurated NHC adduct, [NHCMe(AuCl)(2)], has two eta(1)-bonded AuCl moieties that exhibit aurophilic attraction, which yield a moderate bond strength that might be large enough for synthesizing the complex. The BDE for the second AuCl in [NHCMe(AuCl)(2)] is clearly smaller than the values for the second AuCl in doubly aurated carbone complexes.

First author: Ziegler, Tom, The Application of Constricted Variational Density Functional Theory to Excitations Involving Electron Transitions from Occupied Lone-Pair Orbitals to Virtual pi* Orbitals, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 7, 2485, (2011)
Abstract: We have applied the constricted variational density functional method (CV(n)-DFT) to n(->)pi* transitions in which an electron is moved from an occupied lone-pair orbital n to a virtual pi* orbital. A total of 34 transitions involving 16 different compounds were considered using the local density approximation (LDA), Becke, three-parameter, Lee-Yang-Parr (B3LYP), and BHLYP functionals. The DFT-based results were compared to the “best estimates” (BE) from high-level ab initio calculations. With energy terms included to second order in the variational parameters (CV(2)-DFT), our theory is equivalent to the adiabatic version of time-dependent density functional theory (DFT). We find that calculated excitation energies for CV(2)-DFT using LDA and BHLYP differ substantially from BE with root-mean-square-deviations (rmsd) of 0.86 and 0.69 eV, respectively, whereas B3LYP affords an excellent fit with BE at rmsd = 0.18 eV. Resorting next to CV(infinity)-DFT, where energy terms to all orders in the variational parameters are included, results in all three functionals in too high excitation energies with rmsd = 1.69, 1.14, and 0.93 eV for LDA, B3LYP, and BHLYP, respectively. Adding in orbital relaxation considerably improves the results with rmsd = 0.54, 0.30, and 0.48 eV for LDA, B3LYP, and BHLYP, respectively. It is concluded that CV(infinity)-DFT with orbital relaxation is a robust method for which the accuracy is less functionally dependent than that of CV(2)-DFT or adiabatic TDDFT.

First author: Tvaroska, Igor, QM/MM Insight on Enzymatic Reactions of Glycosyltransferases, MINI-REVIEWS IN ORGANIC CHEMISTRY, 8, 263, (2011)
Abstract: Glycosyltransferases comprise a group of enzymes that catalyze the transfer of glycosyl residues from donors containing nucleoside phosphates to other molecules. The molecular details of the catalytic mechanism involving these enzymes are not well understood. Hybrid QM/MM methods have become important in providing new insights into the atomic details of enzymatic reactions. The QM/MM calculations of GnT-I and beta 4GalT-1 show that inverting glycosyltransferases utilize an S(N)2 type mechanism, with one amino acid functioning as a base catalyst. In addition, the computed transition state structures provide a rational basis for the design of transition state analog inhibitors.

First author: Martinie, Ryan J., Bond Order and Chemical Properties of BF, CO, and N-2, JOURNAL OF CHEMICAL EDUCATION, 88, 1094, (2011)
Abstract: The traditional chemical approaches, Lewis electron dot structures and molecular orbital theory, predict the relative bond orders of boron monofluoride, carbon monoxide, and dinitrogen to be BF < CO < N-2. This is quantified by quantum mechanical, theoretical studies that show the bond orders to be similar to 1.4, similar to 2.6, and similar to 3.0, respectively. These results also confirm the chemical intuition that the change in bond order is primarily due to the pi component. The differences in bond order have a dramatic effect on the ligand behavior of the three molecules, particularly the propensity of BF to function as a bridging ligand.

First author: da Costa, Leonardo Moreira, Interactions between alkaline earth cations and oxo ligands. DFT study of the affinity of the Mg2+ cation for phosphoryl ligands, JOURNAL OF MOLECULAR MODELING, 17, 2061, (2011)
Abstract: DFT (B3LYP/6-31+G(d)) calculations of Mg2+ affinities for a set of phosphoryl ligands were performed. Two types of ligands were studied: a set of trivalent [O = P(R)] and a set of pentavalent phosphoryl ligands [O = P(R)(3)] (R = H, F, Cl, Br, OH, OCH3, CH3, CN, NH2 and NO2), with R either bound directly to the phosphorus atom or to the para position of a phenyl ring. The affinity of the Mg2+ cation for the ligands was quantified by means of the enthalpy for the substitution of one water molecule in the [Mg(H2O)(6)](2+) complex for a ligand. The enthalpy of substitution was correlated with electronic and geometric parameters. Electron-donor groups increase the interaction between the cation and the ligand, while electron-acceptor groups decrease the interaction enthalpy.

First author: Malvolti, Floriane, New thiocyanato and azido adducts of the redox-active Fe(eta(5)-C5Me5)(eta(2)-dppe) center: Synthesis and study of the Fe(II) and Fe(III) complexes, INORGANICA CHIMICA ACTA, 374, 288, (2011)
Abstract: The new thiocyanato- (5) and azido- (6) complexes were synthesized and studied under their Fe(II) and Fe(III) redox states. For the first time among the various [Fe(eta(5)-C5Me5)(eta(2)-dppe)]-based cationic radicals studied so far, the magnitude and spatial orientation of the g-tensor diagonal values were experimentally determined for 5[PF6]. These data are in good agreement with those issued from a DFT modelization. The changes experienced by the electronic structure of the Fe(II) complexes subsequent to oxidation are reminiscent of these previously observed for the known arylalkynyl analogues, albeit some differences can be pointed out. Thus, the differences observed in the H-1 NMR spectra of 5[PF6] and 6[PF6] are attributed to a slower electronic spin relaxation and to the differently oriented magnetic anisotropy. The sizeable spin density evidenced by DFT on the terminal atom of the ligands of the Fe(III) complexes renders these new paramagnetic metallo-ligands quite appealing for accessing larger polynuclear molecular assemblies with magnetically interacting centers.

First author: Simo, Frantisek, The Molecular and Crystal Structures of 2-Iodokojic Acid: Experimental and Theoretical Determination, JOURNAL OF CHEMICAL CRYSTALLOGRAPHY, 41, 1093, (2011)
Abstract: The crystal structure of 2-iodokojic acid, (2-jodo-3-hydroxy-6-hydroxymethyl)-4-H-pyran-4-one) (C6H5IO4, Mr = 268.00) has been determined by single crystal X-ray diffraction analysis. The compound crystallizes in the orthorhombic crystal system with space group Pc2(1)b and unit cell parameters: a = 4.0830(2), b = 15.3510(5), c = 23.517(1) and Z = 8. The final reliability index is 0.0288 for 2,584 observed reflections. The two molecules of iodokojic acid, slightly differing in their molecular structure, are localized in independent part of unit cell. The crystal packing is stabilized by O-H center dot center dot center dot O hydrogen bonds and I center dot center dot center dot O intermolecular interactions. The molecular structure of iodokojic acid determined experimentally little differs from that obtained by the applied theoretical (Hartree-Fock and four versions of DFT) methods, the differences should not be taken as a measure of the reliability of the theoretical methods.

First author: Li, Ping, Explorations of the nature of the coupling interactions between vitamin C and methylglyoxal: a DFT study, STRUCTURAL CHEMISTRY, 22, 783, (2011)
Abstract: As the first step toward understanding the augment role of vitamin C (Vc) for the anticancer effect of methylglyoxal (MG), the nature of the coupling interactions between Vc and MG has been systematically investigated at the B3LYP/6-311++G** level of theory in combination with the atoms in molecules (AIM) theory, natural bond orbital (NBO) method, and energy decomposition analysis (EDA). The possible stable complexes have been located on their potential energy surface (PES). Most of them are characterized by one or two intermolecular H-bonds with the binding energies varying from -11.1 to -2.0 kcal/mol. AIM analyses suggest that all the intermolecular H-bonds have been predominated by the electrostatic interaction. A good linear correlation between the intermolecular H-bond distance and the electron density as well as its Laplacian at the bond critical point of the intermolecular H-bond has been observed. Depending on the selected coupling modes between Vc and MG, the origin of the blue-shifts of the stretching vibrational frequencies of different C-H bonds has been elucidated. Additionally, the inherent reason for the positive role of Vc in the anticancer process for MG has been verified through the investigation of the one-electron oxidation behaviors of the most stable complex.

First author: Tacca, Alessandra, Ternary thiophene-X-thiophene semiconductor building blocks (X = fluorene, carbazole, phenothiazine): Modulating electronic properties and electropolymerization ability by tuning the X core,ELECTROCHIMICA ACTA, 56, 6638, (2011)
Abstract: To achieve rationalization criteria for target-oriented molecular design of Th-X-Th (Th = thiophene) semiconductor building blocks, we have carried out an extensive investigation on the effects of the X core (X = fluorene, carbazole or phenothiazine) on the electronic properties and polymerization ability of Th-X-Th monomers and on the electronic and structural properties of the corresponding periodic conducting polymers -(Th-X-Th)(n)-, obtained by electropolymerization and, for comparison’s sake, by FeCl3-catalyzed polymerization and/or Suzuki coupling. The effects of molecule bending and of solubilising bulky alkyl substituents have also been considered. The systematic, exhaustive template sequence combined with a rigorous, multitechnique investigation protocol affords a unique data library and a complete set of reliable interpretative/predictive guidelines.

First author: Jacob, Christoph R., Software News and Updates PyADF – A Scripting Framework for Multiscale Quantum Chemistry, JOURNAL OF COMPUTATIONAL CHEMISTRY, 32, 2328, (2011)
Abstract: Applications of quantum chemistry have evolved from single or a few calculations to more complicated workflows, in which a series of interrelated computational tasks is performed. In particular multiscale simulations, which combine different levels of accuracy, typically require a large number of individual calculations that depend on each other. Consequently, there is a need to automate such workflows. For this purpose we have developed PYADF, a scripting framework for quantum chemistry. PYADF handles all steps necessary in a typical workflow in quantum chemistry and is easily extensible due to its object-oriented implementation in the Python programming language. We give an overview of the capabilities of PYADF and illustrate its usefulness in quantum-chemical multiscale simulations with a number of examples taken from recent applications.

First author: Cavigliasso, German, Achieving C-N bond cleavage in dinuclear metal cyanide complexes, DALTON TRANSACTIONS, 40, 7327, (2011)
Abstract: Cleavage of cyanide is more difficult to achieve compared to dinitrogen and carbon monoxide, even though these species contain triple bonds of greater strength. In this work, we have used computational methods to investigate thermodynamic and mechanistic aspects of the C-N bond cleavage process in [L3M-CN-M’L-3] systems consisting of a central cyanide unit bound in an end-on fashion to two terminal metal tris-amide complexes. In these systems, [M] is a d(3) transition metal from the 3d, 4d, 5d, or 6d series and groups 4 through 7, and [L] is either [NH2], [NMe2], [(NPrPh)-Pr-i], or [(NBuAr)-Bu-t]. A comparison of various models for the experimentally relevant [L3Mo-CN-MoL3] system has shown that while the C-N cleavage step appears to be an energetically favourable process, a large barrier exists for the dissociation of [L3Mo-CN-MoL3]((-)) into [L3Mo-C]((-)) and [N-MoL3], which possibly explains why C-N bond scission is not observed experimentally. The general structural, bonding, and thermochemical trends across the transition metal series investigated, indicate that the systems exhibiting the greatest degree of C-N activation, and most favourable energetics for C-N cleavage, also possess the most favourable electronic properties, namely, a close match between the relevant pi-like orbitals on the metal-based and cyanide fragments. The negative charge on the cyanide fragment leads to significant destabilization of the pi* level which needs to be populated through back-donation from the metal centres in order for C-N bond scission to be achieved. Therefore, metal-based systems with high-lying d(pi) orbitals are best suited to C-N cleavage. In terms of chemical periodicity, these systems can be identified as the heavier members within a group and the earlier members within a period. As a consequence, Mo complexes are not well suited to cleaving the C-N bond, whereas the Ta analogues are the most favourable systems and should, in principle, be capable of cleaving cyanide under relatively mild conditions. An important conclusion from this work is that a successful strategy for achieving cleavage of multiply-bonded, and relatively unreactive, molecular fragments, may simply lie in tuning the electronic structures and orbital interactions by judicious choice of metal sites and ligand groups.

First author: Ruiz, Juan M., tert-Butyl Cation Affinities of Maingroup-Element Hydrides: Effect of Methyl Substituents at the Protophilic Center, JOURNAL OF PHYSICAL CHEMISTRY A, 115, 8310, (2011)
Abstract: We have conducted an extensive computational exploration of how the gas-phase tert-butyl cation affinities (t-BCA) of archetypal anionic and neutral bases across the periodic H. H. system are affected by stepwise replacement of all hydrogen atoms at the protophilic center with methyl substituents. This study was conducted using zeroth-order regular approximation relativistic density functional theory (DFT) at the BP86/QZ4P//BP86/TZ2P level. The trends are interpreted in terms of the steric effects of methyl substituents at the protophilic center of the anionic (MemXHn-1-m-) and neutral bases (MemXHn-m). Besides insight, this work also provides an intrinsically consistent set of values of the 298 K tert-butyl cation affinities of all (partially) methyl-substituted or unsubstituted bases constituted by maingroup-element hydrides of groups 14-16 in anionic cases (MemXHn-1-m-) and groups 15-17 in neutral ones (MemXHn-m) along periods 2-6. The effect of long-range dispersion (van der Waals) interactions was estimated through dispersion-corrected density functional theory (DFT-D3) at the BP86-D3/QZ4P//BP86/TZ2P level.

First author: Jing, Su, Theoretical Studies on Fluorescence Spectra of Actinide Complexes, PROGRESS IN CHEMISTRY,23, 1329, (2011)
Abstract: In this mini-review, we have briefly summarized the experimental research on fluorescence spectra of actinide complexes, the electronic structures of actinyl complexes, and the basic principle for computational simulations of fluorescence spectra. Although numerous fluorescence spectroscopy data had been available experimentally, there were no theoretical investigations on vibrationally resolved fluorescence spectra of actinide complexes. Recently we have performed for the first time computational modeling of vibrationally resolved fluorescence spectra of uranyl complexes using Heller’ s time-dependent theory for electronic spectroscopy. Herein reviewed are the theoretical results from computational chemistry modeling on the coordination structures, stabilization energies and fluorescence properties of uranyl-glycine-water complexes. Our research has shown that the vibrationally resolved electronic spectra and the unusually high intensity of the illustrious uranyl hot-band can be interpreted by combining state-of-the-art computational chemistry and contemporary experimental techniques. This integrated theory and experiment approach can lead to a detailed understanding of the geometries, energetics, and luminescence properties of actinide compounds, including those with bio-ligands.

First author: Pis Diez, Reinaldo, The diatomic dication CuZn2+ in the gas phase, JOURNAL OF CHEMICAL PHYSICS,135, 1329, (2011)
Abstract: In the present combined experimental and theoretical study we report the observation of the novel gas-phase dication CuZn2+ and provide some theoretical insight into the electronic binding of this exotic metastable molecule and its formation mechanism. Using mass spectrometry we have detected four isotopomer signals of CuZn2+ at half-integer m/z values for ion flight times of about 14 mu s. CuZn2+ was unambiguously identified by its isotopic abundance. High-current energetic Ar+ ion bombardment of a brass surface was used for its production. Subsequent dication formation was found to take place in the ion extraction region of our mass spectrometer several tens of microns in front of the sputtered brass surface. The dication formation mechanism appears to be resonant electron transfer in soft gas-phase collisions between sputter-ejected singly charged CuZn+ molecular ions and incoming Ar+ projectiles. This conclusion is supported by our theoretical study that obtained an ionization energy of CuZn+ of 15.75 eV, in excellent agreement with both the experimental and calculated ionization energy of Ar (15.76 and 15.67 eV, respectively). The ground state of CuZn2+ is found to be a metastable one with a very shallow potential well at an internuclear equilibrium distance of about 2.7 angstrom, the dissociation energy being very difficult to estimate. Interestingly, spin-orbit corrections are found to be necessary to get an adequate description of the metastable state of CuZn2+, whereas relativistic corrections have no effects on neutral CuZn nor on CuZn+.

First author: Rodriguez, Juan I., Size evolution study of “molecular” and “atom-in-cluster” polarizabilities of medium-size gold clusters, JOURNAL OF CHEMICAL PHYSICS, 135, 1329, (2011)
Abstract: A study on static polarizabilities for a family of gold clusters (Au-n, n = 6, 12, 20, 34, 54) is presented. For each cluster, a density functional theory perturbation theory calculation was performed to compute the cluster polarizability and the polarizability of each atom in the cluster using Bader’s “quantum theory of atoms in molecules” formalism. The cluster polarizability tensor,. a cluster, is expressed as a sum of the atom-in-molecule tensors, alpha(<->)(cluster) = Sigma(Omega)alpha(<->)(Omega). A strong quadratic correlation (R-2 = 0.98) in the isotropic polarizability of atoms in the cluster and their distance to the cluster center of mass was observed. The cluster polarizabilities are in agreement with previous calculations.

First author: Bhave, Devayani P., Geometric and Electrostatic Study of the [4Fe-4S] Cluster of Adenosine-5 ‘-Phosphosulfate Reductase from Broken Symmetry Density Functional Calculations and Extended X-ray Absorption Fine Structure Spectroscopy, INORGANIC CHEMISTRY, 50, 6610, (2011)
Abstract: Adenosine-5′-phosphosulfate reductase (APSR) is an iron sulfur protein that catalyzes the reduction of adenosine-5′-phosphosulfate (APS) to sulfite. APSR coordinates to a [4Fe-4S] cluster via a conserved CC-X-similar to 80-CXXC motif; and the cluster is essential for catalysis. Despite extensive functional, structural, and spectroscopic studies, the exact role of the iron sulfur cluster in APS reduction remains unknown. To gain an understanding into the role of the cluster, density functional theory (DFT) analysis and extended X-ray fine structure spectroscopy (EXAFS) have been performed to reveal insights into the coordination, geometry, and electrostatics of the [4Fe-4S] cluster. X-ray absorption near-edge structure (XANES) data confirms that the cluster is in the [4Fe-4S](2+) state in both native and substrate-bound APSR while EXAFS data recorded at similar to 0.1 angstrom resolution indicates that there is no significant change in the structure of the [4Fe-4S] cluster between the native and substrate-bound forms of the protein. On the other hand, DFT calculations provide an insight into the subtle differences between the geometry of the cluster in 1 native and APS-bound forms of APSR A comparison between models with and without the tandem cysteine pair coordination of the cluster suggests a role for the unique coordination in facilitating a compact geometric structure and “fine-tuning” the electronic structure to prevent reduction of the cluster. Further, calculations using models in which residue Lys144 is mutated to Ala confirm the finding that Lys144 serves as a crucial link in the interactions involving the [4Fe-4S] cluster and APS.

First author: Ajitha, Manjaly J., Role of Stereoelectronic Features of Imine and Enamine in (S)-proline Catalyzed Mannich Reaction of Acetaldehyde: An In silico Study, JOURNAL OF COMPUTATIONAL CHEMISTRY, 32, 1962, (2011)
Abstract: A detailed mechanistic investigation of sixteen possible diastereomeric pathways for the C-C bond formation step in (S)-proline catalyzed Mannich reaction of acetaldehyde with N-acetyl protected benzaldimine in acetonitrile solvent has been carried out to understand how stereoelectronic features invoke enantioselectivity of the final product. Both kinetic and thermodynamic factors of the reaction obtained using various density functional theory methods point out that si-enantiofacial nucleophilic attack of anti-enamine on the iminium carbon of the E, s-cis N-acetyl protected imine is the stereoselective pathway. Structural features of the transition states predicted that enamine in anti conformation attacks the imine through a Burgi-Dunitz trajectory to yield the stereocenter. Computations at B3LYP-PCM/6-311++G(3df, 2p)//B3LYP-PCM/6-31G(d, p) level showed a strong linear correlation between Burgi-Dunitz angle and activation energy when anti-enamine is used as nucleophile to react with all the configurations of the imine. Further, energy decomposition analysis has been carried out at B3LYP/TZ2P+ level for all the transition states, which revealed that the most dominant factor that control the enantioselectivity of the (S)-proline catalyzed Mannich reaction is steric effect. Though the less favored transition states showed high amount of stabilizing orbital interaction, the destabilizing steric effects from both Pauli repulsion and preparation energy for the reactant molecules are very high and overshadowed the stabilizing effects. However, in the most favored transition state, a balanced outcome of electronic and steric effects was observed. Solvation effect was nearly same for all the transition states and electrostatic effects showed no correlation to the rank order of the energy of the transition states.

First author: Ivanov, Sergei A., Density Functional Analysis of Geometries and Electronic Structures of Gold-Phosphine Clusters. The Case of Au-4(PR3)(4)(2+) and Au-4(mu(2)-I)(2)(PR3)(4), JOURNAL OF PHYSICAL CHEMISTRY A, 115, 8017, (2011)
Abstract: Geometries, ligand binding energies, electronic structure, and excitation spectra are determined for Au-4(PR3)(4)(2+) and Au-4(mu(2)-I)(2)(PR3)(4) clusters (R = PH3, PMe3, and PPh3). Density functionals including SVWNS, X alpha, OPBE, LC-omega PBE, TPSS, PBE0, CAM-B3LYP, and SAOP are employed with basis sets ranging from LANL2DZ to SDD to TZVP. Metal-metal and metal-ligand bond distances are calculated and compared with experiment. The effect of changing the phosphine ligands is assessed for geometries and excitation spectra. Standard DFT and hybrid ONIOM calculations are employed for geometry optimizations with PPh3 groups. The electronic structure of the gold-phosphine clusters examined in this work is analyzed in terms of cluster (“superatom”) orbitals and d-band orbitals. Transitions out of the d band are significant in the excitation spectra. The use of different basis sets. and DFT functionals leads to noticeable variations in the relative intensities of strong transitions, although the overall spectral profile remains qualitatively unchanged. The replacement of PMe3 with PPh3 changes the nature of the electronic transitions in the cluster due to low-lying pi*-orbitals. To reproduce the experimental geometries of clusters with PPh3 ligands, computationally less expensive PH3 or PMe3 ligands are sufficient for geometry optimizations. However, to predict cluster excitation spectra, the full PPh3 ligand must be considered.

First author: Espinas, Jeff, Synthesis of Novel Tantalacalixarene Complexes: First Example of Intramolecular CH Activation of Monodepleted Aromatic Ring, ORGANOMETALLICS, 30, 3512, (2011)
Abstract: The alkylation of (dichlorotantala)-p-tert-butylcalix[4]arenes 1 and 3 by two equivalents of NpMgCl (Np = neopentyl) affords the corresponding unreported (bisneopentyltantala)-p-tert-butylcalix[4]arenes 4 and S. These complexes can undergo dealkylation by modest increase of the temperature to yield 6 and 7. The characterization and structural conformation of the complexes 6 and 7 were determined by H-1, C-13, NOESY, and COSY spectroscopic studies and single-crystal X-ray diffraction. 7 exhibits unprecedented use of an intramolecular C H activation of an aromatic ring and simultaneously releases of one equivalent of neopentane. DFT calculation supports a mechanism in which the metal passes through a transition state involving a coplanar arrangement with its three ligands (C-Ar, H-Ar., C-Np).

First author: Slepkov, Vladimir, Spontaneous Dissociation of Xenon Tetroxide: Phase and Structural Changes, JOURNAL OF PHYSICAL CHEMISTRY A, 115, 7811, (2011)
Abstract: XeO4 is a noble gas compound remarkable for its high explosiveness in the crystalline state and spontaneous explosion at melting temperature. Both phenomena are studied by analyzing potential energy surfaces corresponding to elementary dissociation acts. It is shown that a spontaneous explosion of xenon tetroxide can be explained by a phase transition associated with structural T-d -> D-2h change and be triggered by rearrangement of electron levels due to the Jahn-Teller effect.

First author: Popov, Alexey A., Dimerization of Radical-Anions: Nitride Clusterfullerenes versus Empty Fullerenes,JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 2, 1592, (2011)
Abstract: In contrast with empty fullerenes, nitride clusterfullerenes usually exhibit irreversible reduction steps at moderate electrochemical scan rates. However, these reduction steps are chemically reversible, indicating that reversible follow-up reaction takes place. To explain this phenomenon, we analyze in this work if anion-radicals of nitride clusterfullerenes are more prone to dimerization than anion-radicals of empty fullerenes. Extensive DFT computations are performed to find the most stable dianionic dimeric structures of Sc3N@C-68, Sc3N@C-80, Sc3N@C-80(CF3)(2), [5,6] and [6,6] pyrrolidine adducts of Sc3N@C-80 and Y3N@C-80, a series of Y3N@C-2n (2n = 78, 80, 84, 86, 88), as well as those of empty fullerenes C-60, C-70, and C-84. Dimerization energies of the most stable isomers are computed in the gas phase, with the use of van der Waals corrections, and in solution. It is found that dianionic dimers of nonderivatized nitride clusterfullerenes are substantially more stable than those of empty fullerenes, which can be an explanation of the electrochemical irreversibility of the former.

First author: Perras, Frederic A., A ZORA-DFT and NLMO study of the one-bond fluorine-X indirect nuclear spin-spin coupling tensors for various VSEPR geometries, CANADIAN JOURNAL OF CHEMISTRY-REVUE CANADIENNE DE CHIMIE, 89, 789, (2011)
Abstract: Zeroth-order regular approximation (ZORA) density functional theory (DFT) calculations of one-bond X-F-19 indirect nuclear spin-spin coupling (J) tensors were performed on a series of fluorine-containing compounds covering several valence shell electron pair repulsion (VSEPR) theory geometries for which J, by symmetry, is not required to be axially symmetric. The calculations show that the antisymmetric components of J are only of the same order of magnitude as the principal components of the symmetric J-coupling tensor for a few geometries, and that in cases of approximate axial symmetry along the bond, J remains nearly axially symmetric with its unique component along the bond. In general, different species having the same nominal geometry tend to have similar tensor orientations, magnitudes of anisotropy of J relative to the isotropic coupling constant, as well as the same dominant contributions from the different coupling mechanisms. Structures are also systematically modified to determine how the tensor components depend on geometrical parameters. The isotropic coupling constants are subsequently interpreted using a natural localized molecular orbital (NLMO) approach. Our results could prove to be useful for future experimental characterizations of J tensors in systems having symmetry properties that do not force J to be axially symmetric or coincident with the dipolar coupling tensor.

First author: Le Guennic, Boris, [Pt@Pb-12](2-) – A challenging system for relativistic density functional theory calculations of Pt-195 and Pb-207 NMR parameters, CANADIAN JOURNAL OF CHEMISTRY-REVUE CANADIENNE DE CHIMIE, 89, 814, (2011)
Abstract: We report computations of NMR chemical shifts and indirect spin-spin coupling constants (J couplings) for the [Pt@Pb-12](2-) “superatom”. The system is strongly influenced by relativistic effects. The Pt-Pb coupling constant is predicted to be negative, with its magnitude being in reasonable agreement with experiment. Pt and Pb chemical shifts also agree reasonably well with experiment. The Pb shielding tensor is strongly anisotropic, with a large deshielding principal component dominated by magnetic coupling between frontier orbitals of the cluster that resemble atomic g orbitals. The NMR parameters are sensitive to approximations made in the computations and require the inclusion of spin-orbit coupling in the theoretical model to achieve reliable results. Computing the NMR parameters of the compact [Pt@Pb-12](2-) system with its many electrons proves to be a challenging test case for relativistic density functional methods.

First author: Lucier, Bryan E. G., Multinuclear solid-state NMR of square-planar platinum complexes – Cisplatin and related systems, CANADIAN JOURNAL OF CHEMISTRY-REVUE CANADIENNE DE CHIMIE, 89, 919, (2011)
Abstract: Multinuclear solid-state nuclear magnetic resonance (SSNMR) experiments have been performed on cisplatin and four related square-planar compounds. The wideband uniform rate smooth truncation – Carr-Purcell-Meiboom-Gill (WURST-CPMG) pulse sequence was utilized in NMR experiments to acquire Pt-195, N-14, and Cl-35 ultra-wideline NMR spectra of high quality. Standard Hahn-echo and magic-angle spinning Pt-195 NMR experiments are also performed to refine extracted chemical shielding (CS) tensor parameters. Platinum magnetic shielding (MS) tensor orientations are calculated using both plane-wave density functional theory (DFT) and standard DFT methods. The tensor orientations are shown to be highly constrained by molecular symmetry elements, but also influenced to some degree by intermolecular interactions. N-14 WURST-CPMG experiments were performed on three compounds and electric field gradient (EFG) parameters (the quadrupolar coupling constant, C-Q, and the asymmetry parameter, eta(Q)) are reported. First principles calculations of the N-14 EFG tensor parameters and orientations and affirm their dependence on the local hydrogen bonding environment. Cl-35 WURST-CPMG experiments on cisplatin and transplatin are reported, using two different static magnetic fields to extract EFG and CS tensor parameters, and Cl-35 EFG tensor magnitudes and orientations are predicted using first principles calculations. Transverse (T-2) relaxation data for all nuclei are used to investigate heteronuclear dipolar relaxation mechanisms, as well as the nature of the local hydrogen bonding environments.

First author: Carraro, Mauro, Reactive Zr-IV and Hf-IV Butterfly Peroxides on Polyoxometalate Surfaces: Bridging the Gap between Homogeneous and Heterogeneous Catalysis, CHEMISTRY-A EUROPEAN JOURNAL, 17, 8371, (2011)
Abstract: At variance with previously known coordination compounds, the polyoxometalate (POM)-embedded Zr-IV and Hf-IV peroxides with formula: [M-2(O-2)(2)(alpha-XW11O39)(2)](12-) (M = Zr-IV, X = Si (1), Ge (2); M = Hf-IV, X = Si (3)) and [M-6(O-2)(6)(OH)(6)(gamma-SiW10O36)(3)](18-) (M = Zr-IV (4) or Hf-IV (5)) are capable of oxygen transfer to suitable acceptors including sulfides and sulfoxides in water. Combined H-1 NMR and electrochemical studies allow monitoring of the reaction under both stoichiometric and catalytic conditions. The reactivity of peroxo-POMs 1-5 is compared on the basis of substrate conversion and kinetic. The results show that the reactivity of POMs 1-3 outperforms that of the trimeric derivatives 4 and 5 by two orders of magnitude. Reversible peroxidation of 1-3 occurs by H2O2 addition to the spent catalysts, restoring oxidation rates and performance of the pristine system. The stability of 1-3 under catalytic regime has been confirmed by FT-IR, UV/Vis, and resonance Raman spectroscopy. The reaction scope has been extended to alcohols, leading to the corresponding carbonyl compounds with yields up to 99% under microwave (MW) irradiation. DFT calculations revealed that polyanions 1-3 have high-energy peroxo HOMOs, and a remarkable electron density localized on the peroxo sites as indicated by the calculated map of the electrostatic potential (MEP). This evidence suggests that the overall description of the oxygen-transfer mechanism should include possible protonation equilibria in water, favored for peroxo-POMs 1-3.

First author: Vlaisavljevich, Bess, On the Nature of Actinide- and Lanthanide-Metal Bonds in Heterobimetallic Compounds, CHEMISTRY-A EUROPEAN JOURNAL, 17, 8424, (2011)
Abstract: Eleven experimentally characterized complexes containing heterobimetallic bonds between elements of the f-block and other elements were examined by quantum chemical methods: [(eta(5)-C5H5)(2)(THF)LuRu(eta(5)-C5H5)(CO)(2)], [(eta(5)-C5Me5)(2)(I)ThRu(eta(5)-C5H5)(CO)(2)], [(eta(5)-C5H5)(2)YRe(eta(5)-C5H5)(2)], [{N(CH2CH2NSiMe3)(3)}URe(eta(5)-C5H5)(2)], [Y{Ga(NArCh)(2)}{C(PPh2NSiH3)(2)}(CH3OCH3)(2)], [{N(CH2CH2NSiMe3)(3)}U{Ga(NArCH)(2)}(THF)], [(eta(5)-C5H5)(3)UGa(eta(5)-C5Me5)], [Yb(eta(5)-C5H5){Si(SiMe3)(3)(THF)(2)}], [(eta(5)-C5H5)(3)U(SnPh3)], [(eta(5)-C5H5)(3)U(SiPh3)], and (Ph[Me]N)(3)USi(SiMe3)(3). Geometries in good agreement with experiment were obtained at the density functional level of theory. The multi-configurational complete active space self-consistent field method (CASSCF) and subsequent corrections with second order perturbation theory (CASPT2) were applied to further understand the electronic structure of the lanthanide/actinide-metal (or metal-metalloid) bonds. Fragment calculations and energy-decomposition analyses were also performed and indicate that charge transfer occurs from one supported metal fragment to the other, while the bonding itself is always dominated by ionic character.

First author: Makal, Anna, The development of Laue techniques for single-pulse diffraction of chemical complexes: time-resolved Laue diffraction on a binuclear rhodium metal-organic complex, ACTA CRYSTALLOGRAPHICA SECTION A, 67, 319, (2011)
Abstract: A modified Laue method is shown to produce excited-state structures at atomic resolution of a quality competitive with those from monochromatic experiments. The much faster data collection allows the use of only one or a few X-ray pulses per data frame, which minimizes crystal damage caused by laser exposure of the samples and optimizes the attainable time resolution. The method has been applied to crystals of the alpha-modification of Rh-2(mu-PNP)(2)(PNP)(2) (BPh4)(2) [PNP = CH3N(P(OCH3)(2))(2), Ph = phenyl]. The experimental results show a shortening of the Rh-Rh distance in the organometallic complex of 0.136 (8) angstrom on excitation and are quantitatively supported by quantum-mechanical (OM)/molecular-mechanics (MM) theoretical calculations which take into account the confining effect of the crystal environment, but not by theoretical results on the isolated complex, demonstrating the defining effect of the crystal matrix.

First author: Shankar, R., Interaction studies of cysteine with Li+, Na+, K+, Be2+, mg(2+), and Ca2+ metal cation complexes, JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, 24, 553, (2011)
Abstract: The coordination geometries, electronic features, metal ion affinities, entropies, and the energetics of Li+, Na+, K+, Be2+, Mg2+, and Ca2+ metal cations with different possible conformations of cysteine complexes were studied. The complexes were optimized using density functional theory (B3LYP) and second order Moller-Plesset Perturbation (MP2) theory methods using 6-311 + +G** basis set. The interactions of the metal cations at different nucleophilic sites of cysteine conformations were considered after a careful selection among several binding sites. All the metal cations coordinate with cysteine in a tridentate manner and also the most preferred position for the interaction. It is found that, the overall structural parameters of cysteine are not altered by metal ion substitution, but, the metal ion-binding site has undergone a noticeable change. All the complexes were characterized by an electrostatic interaction between ligand and metal ions that appears slightly more pronounced for lithium and beryllium metal complexes. The metal ion affinity (MIA) and basis set superposition error (BSSE) corrected interaction energy were also computed for all the complexes. The effect of metal cations on the infrared (IR) stretching vibrational modes of amino N-H bond, side chain thiol group S-H bond, hydroxyl O-H bond, and Carbonyl C=O bond in cysteine molecules have also been studied. The nature of the metal ion-ligand bond and the coordination properties were examined using natural bond order (NBO) at bond critical point (electron density and their Laplacian of electron density) through Atoms in Molecules (AIM) analyses.

First author: Baskaran, Sambath, Understanding the stability, electronic and molecular structure of some copper(III) complexes containing alkyl and non alkyl ligands: Insights from DFT calculations, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 696, 2627, (2011)
Abstract: DFT calculations have been performed for some Cu(III)-alkyl complexes. Complexes 1-19 were optimized to the square planar (sq) geometry and observed no imaginary frequencies. Although formally copper adopts d(8) configuration (Cu(III)) in all the complexes, the Natural Population Analysis (NPA) revealed that the copper actually in d(10) (Cu(I)) configuration, Bond order calculation suggested that the Cu(III)-Et-trans bond gets more bond order in the presence of poor pi-acidic co-ligand (probe ligand). Relatively smaller bond order was calculated for Cu(III)-Me-cis bond than Cu(III)-Et-trans bond and therefore Cu(III)-Et-trans bond is the strongest bond in all the complexes. Calculated less Chemical hardness (eta) of complexes 1-19 suggested that all these complexes are less stable in nature. Energy Decomposition Analysis (EDA) revealed that the Cu(III)-Et-trans bond is relatively more stable than the Cu(III)-Me-cis and Cu(III)-L (L = co-ligand/probe ligand) bonds. And also the Cu(III)-alkyl (Cu(III)-Me-cis and Cu(III)-Et-trans) bond in complexes 1-17 is more of ionic in nature. However, Cu(III)-Et-trans bond is relatively more ionic than Cu(III)-Me-cis bond.

First author: Stewart, Hamish, Ultraviolet Photofragmentation Spectroscopy of Alkaline Earth Dication Complexes with Pyridine and 4-Picoline (4-Methyl pyridine), JOURNAL OF PHYSICAL CHEMISTRY A, 115, 6948, (2011)
Abstract: A detailed experimental and theoretical study has been undertaken of the UV photofragmentation spectroscopy of the alkaline earth metal dications Mg2+, Ca2+, and Sr2+ complexed with pyridine and 4-methyl pyridine (4-picoline). The ion complexes have been prepared using the pick-up technique and held in an ion trap where their internal temperature has been reduced to < 150 K. Exposure of the trapped ions to tunable UV laser radiation leads to the appearance of photofragments with intensities that show significant variation as a function of wavelength. For all three metal dications, the resultant spectra show evidence of resolved features. Time-dependent density functional theory (TDDFT) has been used to identify possible electronic transitions that might be present in the [M(pyridine)(4)](2+) complexes (M = Mg, Ca, and Sr) within the wavelength range studied. These calculations show that the spectra are dominated by strong pi* <- pi and weaker pi* <- n transitions localized on the pyridine ligands. The calculations correctly identify those regions of the experimental spectra where UV transitions begin to occur in the complexes and also the wavelengths at which absorption maxima are reached; however, more subtle features of the spectra are difficult to assign with confidence.

First author: Jissy, A. K., Nucleic Acid G-quartets: Insights into Diverse Patterns and Optical Properties, JOURNAL OF PHYSICAL CHEMISTRY C, 115, 12530, (2011)
Abstract: Structures of various conformers of G-quartets (G4) with different types of hydrogen bonding patterns have been investigated through various levels of Density Functional Theory (DFT). Their structure and stability has been compared with the diad (G2), triad (G3), pentad (G5) and hexad (G6) of guanine. The calculations show that G4 has the highest stabilization through hydrogen-bond interaction which explains the tendency of guanine rich strands in the telomeric region to favor the formation of the quadruplex structure. We have also performed calculations for Li+, Na+, K+, Be2+, Mg2+ and Ca2+ complexes of G4. Calculations show that for an isolated quartet, the metal ion with the smallest ionic radius in their respective groups (IA and IIA) form more stable complexes. Other properties such as the HOMO-LUMO gap and polarizability have also been analyzed. The variation in the polarizability has been studied with respect to the movement of cations along the central cavity of the quartet. Such movement leads to a large anisotropy of polarization and hence the refractive index (eta) thereby creating optical birefringence which have potential applications in biomolecular imaging.

First author: Petz, Wolfgang, Syntheses and Crystal Structures of [Hg{C(PPh3)(2)}(2)][Hg2I6] and [Cu{C(PPh3)(2)}(2)]I and Comparative Theoretical Study of Carbene Complexes [M(NHC)(2)] with Carbone Complexes [M{C(PH3)(2)}(2)] (M = Cu+, Ag+, Au+, Zn2+, Cd2+, Hg2+), ORGANOMETALLICS, 30, 3330, (2011)
Abstract: The synthesis and X-ray structure analysis of the carbodiphosphorane (CDP) complexes [Hg{C(PPh3)(2)}(2)][Hg2I6] and [Cu{C(PPh3)(2)}(2)] I are reported. The cations [Hg{C(PPh3)(2)}(2)](2+) and [Cu{C(PPh3)(2)}(2)](+) have approximately linearly coordinated metal atoms. Quantum chemical calculations of model compounds bearing N-heterocyclic carbene (NHC) ligands, [M(NHC)(2)] and [M{C(PH3)(2)}(2)] (M = Cu+, Ag+, Au+, Zn2+, Cd2+, Hg2+), have been carried out at the BP86/TZ2P level. The metal-ligand bonds are very strong, and the bond dissociation energies exhibit a V-shaped trend for first-, second-, and third-row transition metals: Ag+ < Cu+ < Au+ and Cd2+ < Zn2+ < Hg2+, The investigation of the bonding situation in the complexes using an energy decomposition analysis shows that the metal-ligand bonding comes mainly from electrostatic attraction. Inspection of the orbital interactions shows that the M-q-(NHC)(2) and Mq-{C(PH3)(2)}(2) sigma donation provides between 65 and 75% of the total orbital interactions Delta E-orb. The contribution of the M-q-(NHC)(2) and M-q-{C(PH3)(2)}(2) pi back-donation is very weak. The nature and strength of the donor-acceptor bonds of the two-electron donor ligand NHC and the four-electron donor ligand CDP with the group 11 and group 12 metal cations are very similar.

First author: Vasiliu, Monica, Bond Energies in Models of the Schrock Metathesis Catalyst, JOURNAL OF PHYSICAL CHEMISTRY C, 115, 12106, (2011)
Abstract: Heats of formation, adiabatic and diabatic bond dissociation energies (BDEs) of the model Schrock-type metal complexes M(NH)(CRR’)(OH)(2) (M = Cr, Mo, W; CRR’ = CH2, CHF, CF2) and MO2(OH)(2) compounds, and Bronsted acidities and fluoride affinities for the M(NH)(CH2)(OH)(2) transition metal complexes are predicted using high level CCSD(T) calculations. The metallacycle intermediates formed by reaction of C2H4 with M(NH)(CH2)(OH)(2) and MO2(OH)(2) are investigated at the same level of theory. Additional corrections were added to the complete basis set limit to obtain near chemical accuracy (+/- 1 kcal/mol). A comparison between adiabatic and diabatic BDEs is made and provides an explanation of trends in the BDEs. Electronegative groups bonded on the carbenic carbon lead to less stable Schrock-type complexes as the adiabatic BDEs of M=CF2 and M=CHF bonds are much lower than the M=CH2 bonds. The Cr compounds have smaller BDEs than the W or Mo complexes and should be less stable. Different M(NH)(OH)(2)(C3H6) and MO(OH)(2)(OC2H4) metallacycle intermediates are investigated, and the lowest-energy metallacycles have a square pyramidal geometry. The results show that consideration of the singlet triplet splitting in the carbene in the initial catalyst as well as in the metal product formed by the retro [2 + 2] cycloaddition is a critical component in the design of an effective olefin metathesis catalyst in terms of the parent catalyst and the groups being transferred.

First author: Sanchez Costa, Jose, Coexistence of Intramolecular Ligand-Mediated and Through Hydrogen-Bond Magnetic Interactions in a Chain of Dicopper(II) Units, INORGANIC CHEMISTRY, 50, 5696, (2011)
Abstract: The reaction of 2,8-dimethyl-5,11-bis(pyridin-2-ylmethyl)-1,4,5,6,7,10,11,12-octahydroim idazo[4,5-h]imidazo-[4,5-c][1,6]-diazecine (dimp) with copper(II) nitrate in water produces the compound [Cu-2(dimp)(H2O)(2)(NO3)(2)](NO3)(2). The single-crystal X-ray structure shows the formation of hydrogen-bonded chains in the lattice that are formed by dicopper(II) units doubly connected by nitrate/water bridges. Within the one-dimensional chains, the Cu ions are separated by either intramolecular or intermolecular distances of 7.309(2) angstrom or 6.255(2) angstrom, respectively. The magnetic susceptibility data revealing weak antiferromagnetic exchange interactions between the copper(II) ions were interpreted by considering two possible models, namely, an isolated dinuclear and a 1-D chain picture. The latter leads to an alternation J(1) = -11.6 and J(2) = -3.0 cm(-1) along the chain. In order to clarify the relative strengths of the exchange couplings through hydrogen bonds and via the bridging dimp ligand, solution EPR studies and quantum chemical calculations were carried out. EPR studies unambiguously conclude on the existence of an exchange interaction J(a) mediated by the dinucleating dump ligand, while the through-H coupling J(b) is physically absent in solution. On the basis of dinuclear units extracted from the X-ray data, J(a) was estimated around -5.0 cm(-1) from DFT-based calculations (M06 functional), whereas J(b) is negligible. In contrast, wave function configuration interaction calculations (DDCI) support a description where both inter- and intramolecular pathways coexist with a preeminent role of H bonds with J(a) = -2.8 and J(b) = -10.4 cm(-1). Not only are these values very consistent with the extracted set of parameters (J(1), J(2) = -11.6, -3.0 cm(-1)) but the possibility to generate leading exchange coupling through weak bonds is evidenced by means of wave function-based calculations.

First author: Monakhov, Kirill Yu., Alkali-Metal-Supported Bismuth Polyhedra-Principles and Theoretical Studies,INORGANIC CHEMISTRY, 50, 5755, (2011)
Abstract: We have quantum chemically investigated the structure, stability, and bonding mechanism in higihly aggregated alkali-metal salts of bismuthanediide anions [RBi](2-) using relativistic density functional theory (DFT, at ZORA-BP86/TZ2P) in combination with a quantitative energy decomposition analysis (EDA). Our model systems are alkali-metal-supported bismuth polyhedra [(RBi)(n)M2n-4](4-) with unique interpenetrating shells of a bismuth polyhedron and an alkali-metal superpolyhedron. Furthermore, we have analyzed the trianionic inclusion complexes [M’@{(RBi)(n)M2n-4}](3-) involving an additional endohedral alkalimetal ion M’. The main objective is to assist the further development of synthetic approaches toward this class of compounds. Our analyses led to electron-counting rules relating, for example, the number of bonding orbitals (N-bond) of the cage molecules [(RBi)(n)M2n+Q](Q) to the number of bismuth atoms (n(Bi)), alkali-metal atoms (n(M)), and net charge Q as N-bond = n(Bi) + n(M) – Q(R = one-electron donor ligand; M = alkali metal; n = 4-12; Q = -4, -6, -8). Finally, on the basis of our findings, we predict the next members in the S-fold symmetrical row of alkali-metallobismaspheres with a macroicosahedral arrangement.

First author: Wade, Casey R., Synthesis, Structure, and Properties of a T-Shaped 14-Electron Stiboranyl-Gold Complex,JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 133, 8948, (2011)
Abstract: A cyclic stiboranyl-gold complex (1) supported by two 1,8-naphthalenediyl linkers has been synthesized and structurally characterized. The gold atom of this complex adopts a T-shaped geometry and is separated from the antimony center by only 2.76 angstrom. Surprisingly, the trivalent gold atom of this complex is involved in an aurophilic interaction, a phenomenon typically only observed for monovalent gold complexes. This phenomenon indicates that the stiboranyl ligand possesses strong sigma-donating properties making the trivalent gold atom of 1 electron rich. This view is supported by DFT calculations as well as Au L-3- and Sb K-edge XANES spectra which reveal that 1 may also be described as an aurate-stibonium derivative. In agreement with this view, complex 1 shows no reactivity toward the halides Cl-, Br-, and I-. It does, however, rapidly react with F- to form an unprecedented anionic aurate fluorostiborane complex ([2](-)) which has been isolated as the tetra-n-butylammonium salt. The increased coordination number of the antimony center in this anionic complex ([2](-)) does not notably affect the Au-Sb separation (2.77 angstrom) or the geometry at the gold atom which remains T-shaped.

First author: Boguslawski, Katharina, Construction of CASCI-type wave functions for very large active spaces, JOURNAL OF CHEMICAL PHYSICS, 134, 8948, (2011)
Abstract: We present a procedure to construct a configuration-interaction expansion containing arbitrary excitations from an underlying full-configuration-interaction-type wave function defined for a very large active space. Our procedure is based on the density-matrix renormalization group (DMRG) algorithm that provides the necessary information in terms of the eigenstates of the reduced density matrices to calculate the coefficient of any basis state in the many-particle Hilbert space. Since the dimension of the Hilbert space scales binomially with the size of the active space, a sophisticated Monte Carlo sampling routine is employed. This sampling algorithm can also construct such configuration-interaction-type wave functions from any other type of tensor network states. The configuration-interaction information obtained serves several purposes. It yields a qualitatively correct description of the molecule’s electronic structure, it allows us to analyze DMRG wave functions converged for the same molecular system but with different parameter sets (e. g., different numbers of active-system (block) states), and it can be considered a balanced reference for the application of a subsequent standard multi-reference configuration-interaction method.

First author: Herrmann, Carmen, Designing organic spin filters in the coherent tunneling regime, JOURNAL OF CHEMICAL PHYSICS, 134, 8948, (2011)
Abstract: Spin filters, that is, systems which preferentially transport electrons of a certain spin orientation, are an important element for spintronic schemes and in chemical and biological instances of spin-selective electronic communication. We study the relation between molecular structure and spin filtering functionality employing a theoretical analysis of both model and stable organic radicals based on substituted benzene, which are bound to gold electrodes, with a combination of density functional theory and the Landauer-Imry-Buttiker approach. We compare the spatial distribution of the spin density and of the frontier central subsystem molecular orbitals, and local contributions to the transmission. Our results suggest that the delocalization of the singly occupied molecular orbital and of the spin density onto the benzene ring connected to the electrodes, is a good, although not the sole indicator of spin filtering functionality. The stable radicals under study do not effectively act as spin filters, while the model phenoxy-based radicals are effective due to their much larger spin delocalization. These conclusions may also be of interest for electron transfer experiments in electron donor-bridge-acceptor complexes.

First author: Zeng, Tao, Two-component natural spinors from two-step spin-orbit coupled wave functions, JOURNAL OF CHEMICAL PHYSICS, 134, 8948, (2011)
Abstract: We developed an algorithm to obtain the natural orbitals (natural spinors) from the two-step spin-orbit coupled wave functions. These natural spinors are generally complex-valued, mixing two spin components, and they can have similar symmetry properties as the j-j spinors from the one-step spin-orbit coupling calculations, if the reduced density equally averages all the components of a multi-dimensional irreducible representation. Therefore, the natural spinors can serve as an approximation to the j-j spinors and any wave function analysis based on the j-j spinors can also be performed based on them. The comparison between the natural spinors and the j-j spinors of three representative atoms, Tl, At, and Lu, shows their close similarity and demonstrates the ability of the natural spinors to approximate the j-j spinors.

First author: Harris, Travis V., Comparative Assessment of the Composition and Charge State of Nitrogenase FeMo-Cofactor, INORGANIC CHEMISTRY, 50, 4811, (2011)
Abstract: A significant limitation in our understanding of the molecular mechanism of biological nitrogen fixation is the uncertain composition of the FeMo-cofactor (FeMo-co) of nitrogenase. In this study we present a systematic, density functional theory-based evaluation of spin-coupling schemes, iron oxidation states, ligand protonation states, and interstitial ligand composition using a wide range of experimental criteria. The employed functionals and basis sets were validated with molecular orbital information from X-ray absorption spectroscopic data of relevant iron-sulfur clusters. Independently from the employed level of theory, the electronic structure with the greatest number of antiferromagnetic interactions corresponds to the lowest energy state for a given charge and oxidation state distribution of the iron ions. The relative spin state energies of resting and oxidized FeMo-co already allowed exclusion of certain iron oxidation state distributions and interstitial ligand compositions. Geometry-optimized FeMo-co structures of several models further eliminated additional states and compositions, while reduction potentials indicated a strong preference for the most likely charge state of FeMo-co. Mossbauer and ENDOR parameter calculations were found to be remarkably dependent on the employed training set, density functional, and basis set. Overall, we found that a more oxidized [Mo-IV-2Fe(II)-5Fe(III)-9S(2-)-C4-] composition with a hydroxyl-protonated homocitrate ligand satisfies all of the available experimental criteria and is thus favored over the currently preferred composition of [Mo-II-4Fe(II)-3Fe(III)-9S(2-)-N3-] from the literature.

First author: Roberts, Matthew N., Charge Transfer and Intraligand Excited State Interactions in Platinum-Sensitized Dithienylethenes, INORGANIC CHEMISTRY, 50, 4956, (2011)
Abstract: The photophysical behavior for two photochromic Pt-terpyridine acetylide complexes containing pendant dithienylethenes (DTEs) bound to the metal through the alkynyl linkage is presented. Selective excitation of the Pt complex with visible light resulted in the metal-sensitized ring closing of the DTE unit. The central purpose of this study was to understand how excited state interactions govern the photophysics by correlating differences in the linkage of the two components with differences in the intramolecular energy transfer processes that occur between the Pt complex and the DTE. A series of model complexes without photochromic ligands were prepared and studied to elucidate the contributions of the triplet metal-to-ligand charge transfer and triplet intraligand states. It is demonstrated that reducing the orbital overlap of the metal-based and intraligand states by lengthening the linkage and eliminating a conjugated pathway is effective at dramatically decreasing the efficiency of intramolecular energy transfer. This is evidenced by the appearance of Pt-terpyridine based phosphorescence and a significant decrease in the observed rate of metal-sensitized ring closing of the DTE.

First author: Steinmann, Stephan N., Dispersion-Corrected Energy Decomposition Analysis for Intermolecular Interactions Based on the BLW and dDXDM Methods, JOURNAL OF PHYSICAL CHEMISTRY A, 115, 5467, (2011)
Abstract: As the simplest variant of the valence bond (VB) theory, the block-localized wave function (BLW) method defines the intermediate electron-localized state self-consistently at the DFT level and can be used to explore the nature of intermolecular interactions in terms of several physically intuitive energy components. Yet, it is unclear how the dispersion interaction affects such a kind of energy decomposition analysis (EDA) as standard density functional approximations neglect the long-range dispersion attractive interactions. Three electron densities corresponding to the initial electron-localized state, optimal electron-localized state, and final electron-delocalized state are involved in the BLW-ED approach; a density-dependent dispersion correction, such as the recently proposed dDXDM approach, can thus uniquely probe the impact of the long-range dispersion effect on EDA results computed at the DFT level. In this paper, we incorporate the dDXDM dispersion corrections into the BLW-ED approach and investigate a range of representative systems such as hydrogen-bonding systems, acid base pairs, and van der Waals complexes. Results show that both the polarization and charge-transfer energies are little affected by the inclusion of the long-range dispersion effect, which thus can be regarded as an independent energy component in EDA.

Abstract: The silylant 3-cloropropyltriethoxysilyl was anchored over silica gel in anhydrous conditions in order to react with thiourea to obtain modified silica gel with thiouronium. The aim to obtain an inorganic support that is able to hijack metals from the VIII group such as palladium. The product was characterized by S-BET and FTIR infrared spectroscopy. For the determination of the structure in the modified silica gel NMR spectra of silicon and carbon were preformed in solid state. The coordination form of the modified silica gel to the metal was studied computationally in the context of the DFT theory, using the ADF code. This was a collaborative work with “Fundacion Chile’. for the recuperation of precious metals from the mining industry.

First author: Senthilnathan, Dhurairajan, Imidozirconocene-Mediated Ring Cleavage of Epoxides – Evidence for Bifunctional Reactivity from DFT, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 56, 2842, (2011)
Abstract: The ring cleavage of epoxides mediated by bis(cyclopentadienyl)(tert-butylimido)zirconium (Cp2Zr=N-tBu)(THF) has been investigated using DFT calculations with a view to understand the mechanism of epoxide ring cleavage and the role of the imidozirconocene complex. Two types of epoxides have been chosen; some with and some without accessible beta-hydrogen atoms. Epoxides without accessible beta-hydrogen atoms undergo only insertion, whereas those with undergo both insertion and elimination. Although insertion is found to follow a zwitterionic mechanism, the elimination passes through a concerted intramolecular hydrogen transfer step. The role of the imidozirconocene complex has been elucidated by EDA and NBO analysis, which show that the vacant 1a(1) molecular orbital of the Lewis acidic metal center of Cp2Zr=N-tBu fragment initiates the reaction as a Lewis acidic center and the Lewis basic imido nitrogen atom of the Cp2Zr=N-tBu fragment completes the reaction. The coordinate to covalent bond conversion and the involvement of the 1a(1) and 2a(1) molecular orbitals of the Cp2Zr=N-tBu fragment in the reaction have been examined. The formation of a five-membered metallacycle in the insertion and the alkoxy allyl product in the elimination predicted by calculations concur with experimental observations. Topological analysis has been carried out to further elucidate the mechanism and to reveal the bifunctional reactivity of imidozirconocene in epoxide ring opening reactions.

First author: Fievez, Tim, Regioselectivity in Electrophilic Aromatic Substitution: Insights from Interaction Energy Decomposition Potentials, EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, 56, 2958, (2011)
Abstract: The SEAr reaction was scrutinized using a quantitative, fragment-based interaction energy decomposition analysis (EDA) as implemented in the ADF program. The interaction energy between monosubstituted benzene derivatives and a model electrophile at the onset of the reaction was studied and decomposed into Pauli repulsion, electrostatic interaction and orbital interaction terms for a plane parallel to the molecular plane. As such experimentally observed selectivity patterns arise in the orbital interaction, stressing again the role of both electrophile and benzene derivative in determining the regioselectivity. Using the HSAB principle and MO theory, the orientation mechanism of the SEAr is further explored.

First author: Zhekova, Hristina, Introduction of a New Theory for the Calculation of Magnetic Coupling Based on Spin-Flip Constricted Variational Density Functional Theory. Application to Trinuclear Copper Complexes which Model the Native Intermediate in Multicopper Oxidases, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 7, 1858, (2011)
Abstract: We have introduced a new method for the calculation of spin exchange between weakly interacting electron spins on different metal centers. The method is based on spin flip constricted variational density functional theory (SF-CV-DFT). The application of SF-CV-DFT to two trinuclear systems [Cu-3(L)(mu(3)-O)](4+) and [(L’)(3)]Cu-3(mu-OH)(3)](3+) revealed that SF-CV-DFT affords exchange coupling constants that are similar to the values obtained by the traditional broken-symmetry (BS) scheme for the same functional. The BHandHLYP functional affords for both systems the best fit to experiment and results from high-level theory in the case of BS-DFT as well as SF-CV(2)-DFT. All methods and functionals predict [Cu(L)(mu(3)-O)](4+) to be ferromagnetic and the [(L’)(3)Cu-3(mu-OH)(3)](3+) system to be antiferromagnetic. The SF-CV(2)-DFT method is not only able to evaluate exchange coupling constants, it can in addition calculate the full multiplet spectrum with complete use of spatial symmetry. Further, in its restricted formulation, calculations can be carried out with use of full spin symmetry without spin contamination.

First author: McGeehan, John E., Raman-assisted crystallography of biomolecules at the synchrotron: Instrumentation, methods and applications, BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS, 1814, 750, (2011)
Abstract: Raman spectroscopy is a powerful technique that, in recent years, has been successfully coupled to X-ray crystallography for the analysis of biological macromolecular systems. The complementarity between both techniques is illustrated at multiple stages, including sample preparation, data collection and structural interpretation with a mechanistic perspective. The current state of instrumentation is described, focusing on synchrotron based setups. Present and future applications of Raman microspectrophotometry are reviewed with reference to recent examples dealing with metallo-, photosensitive-, and redox-proteins. The added value of Raman microspectrophotometry to assess X-radiation damage is discussed, and its applicability to investigate crystalline DNA molecules is also emphasized. This article is part of a Special Issue entitled: Protein Structure and Function in the Crystalline State.

First author: Ruusuvuori, Kai, Density-functional study of the sign preference of the binding of 1-propanol to tungsten oxide seed particles, COMPUTATIONAL AND THEORETICAL CHEMISTRY, 966, 322, (2011)
Abstract: The binding of 1-propanol to neutral and singly charged tungsten oxide seed particles was studied using quantum chemical methods. Three different density functionals and three basis sets were employed, and the results were compared with each other as well as with results previously published by other groups. Our results implicate a positive sign preference for all studied tungsten oxide species. Molecular structures obtained for pure tungsten oxide show good agreement with previous results.

First author: Seth, Michael, Time-dependent density functional theory gradients in the Amsterdam density functional package: geometry optimizations of spin-flip excitations, THEORETICAL CHEMISTRY ACCOUNTS, 129, 331, (2011)
Abstract: An implementation of time-dependent density functional theory (TDDFT) energy gradients into the Amsterdam density functional theory program package (ADF) is described. The special challenges presented by Slater-type orbitals in quantum chemical calculation are outlined with particular emphasis on details that are important for TDDFT gradients. Equations for the gradients of spin-flip TDDFT excitation energies are derived. Example calculations utilizing the new implementation are presented. The results of standard calculations agree well with previous results. It is shown that starting from a triplet reference, spin-flip TDDFT can successfully optimize the geometry of the four lowest singlet states of CH2 and three other isovalent species. Spin-flip TDDFT is used to calculate the potential energy curve of the breaking of the C-C bond of ethane. The curve obtained is superior to that from a restricted density functional theory calculation, while at the same time the problems with spin contamination exhibited by unrestricted density functional theory calculations are avoided.

First author: Clavaguera, Carine, Theoretical study of the bent U(eta(8)-C8H8)(2)(CN)(-) complex, THEORETICAL CHEMISTRY ACCOUNTS, 129, 447, (2011)
Abstract: The ground-state electronic structure of the cyanido complex [U(eta(8)-C8H8)(2)(CN)](-) as well as the thermodynamic properties and infrared spectrum are investigated using density functional theory including scalar relativistic effects. The complex is compared with the well-known uranocene U(eta(8)-C8H8)(2). Despite the broken symmetry, the gain in electrostatic interaction and a significant uranium-CN- orbital interaction is sufficient to stabilize the bent CN- complex with respect to uranocene. The formation of the CN- complex is exothermic justifying the recently experimentally reported compound.

First author: Wei, Fan, Geometries, electronic structures, and excited states of UN2, NUO+, and UO22+: a combined CCSD(T), RAS/CASPT2 and TDDFT study, THEORETICAL CHEMISTRY ACCOUNTS, 129, 467, (2011)
Abstract: The ground- and excited-state geometries and electronic structures of the isoelectronic series of molecules UN2, NUO+, and UO (2) (2+) are investigated by using relativistic density functional theory (DFT) and ab initio wavefunction theory (WFT). Scalar relativistic and spin-orbit-coupled quantum chemical methods at the CASPT2, RASPT2, CCSD(T), DFT and TDDFT levels are applied. Relativistic effects as elucidated by Pekka Pyykko play an important role in these uranium compounds, in particular for the excited states. The three molecular species exhibit significantly different spectroscopic properties, concerning their excitation energies, bond lengths and vibrations. Density functional approaches yield qualitatively correct results for the ground states and the valence -> U.7s,6d excited states. However, the performance of TDDFT for valence -> U.5f type excitations (in particular of UN2 and NUO+) is less satisfactory, indicating the importance of the self-interaction correction for such excitations.

First author: Rutkowski, Philip X., Hydration of gas-phase ytterbium ion complexes studied by experiment and theory,THEORETICAL CHEMISTRY ACCOUNTS, 129, 575, (2011)
Abstract: Hydration of ytterbium (III) halide/hydroxide ions produced by electrospray ionization was studied in a quadrupole ion trap mass spectrometer and by density functional theory (DFT). Gas-phase YbX2 (+) and YbX(OH)(+) (X = OH, Cl, Br, or I) were found to coordinate from one to four water molecules, depending on the ion residence time in the trap. From the time dependence of the hydration steps, relative reaction rates were obtained. It was determined that the second hydration was faster than both the first and third hydrations, and the fourth hydration was the slowest; this ordering reflects a combination of insufficient degrees of freedom for cooling the hot monohydrate ion and decreasing binding energies with increasing hydration number. Hydration energetics and hydrate structures were computed using two approaches of DFT. The relativistic scalar ZORA approach was used with the PBE functional and all-electron TZ2P basis sets; the B3LYP functional was used with the Stuttgart relativistic small-core ANO/ECP basis sets. The parallel experimental and computational results illuminate fundamental aspects of hydration of f-element ion complexes. The experimental observations-kinetics and extent of hydration-are discussed in relationship to the computed structures and energetics of the hydrates. The absence of pentahydrates is in accord with the DFT results, which indicate that the lowest energy structures have the fifth water molecule in the second shell.

First author: Fliegl, Heike, Theoretical investigation of photoelectron spectra and magnetically induced current densities in ring-shaped transition-metal oxides, THEORETICAL CHEMISTRY ACCOUNTS, 129, 701, (2011)
Abstract: The molecular structures of cyclic group 6 transition-metal (M = Cr, Mo, W, Sg) oxides (M O-3 (9) (0/1-/2-) ) species have been optimized at density functional theory (DFT) levels. The photoelectron spectra (PES) of M O-3 (9) (-) (M = Cr, Mo, W) were calculated at the time-dependent DFT and approximate coupled-cluster singles doubles (CC2) levels and compared with experimental results. The CC2 calculations did not yield any reliable PES, whereas the molecular structures can be identified by comparing PES obtained at the DFT level with experiment. Magnetically induced current densities were calculated at the DFT level using the gauge-including magnetically induced current (gimic) approach. The current strengths and current pathways of the neutral M3O9 and the dianionic M3O (9) (2-) (M = Cr, Mo) oxides were investigated and analyzed with respect to a previous prediction of d-orbital aromaticity for Mo3O9 anions. Current-density calculations provide ring-current strengths that are used to assess the degree of aromaticity. Comparison of current-density calculations and calculations of nucleus-independent chemical shifts (NICS) shows that NICS calculations are not a reliable tool for determining the degree of aromaticity of the metal oxides.

First author: Gardner, Benedict M., An Unsupported Uranium-Rhenium Complex Prepared by Alkane Elimination,CHEMISTRY-A EUROPEAN JOURNAL, 17, 6909, (2011)
Abstract: The molecular structures of cyclic group 6 transition-metal (M = Cr, Mo, W, Sg) oxides (M O-3 (9) (0/1-/2-) ) species have been optimized at density functional theory (DFT) levels. The photoelectron spectra (PES) of M O-3 (9) (-) (M = Cr, Mo, W) were calculated at the time-dependent DFT and approximate coupled-cluster singles doubles (CC2) levels and compared with experimental results. The CC2 calculations did not yield any reliable PES, whereas the molecular structures can be identified by comparing PES obtained at the DFT level with experiment. Magnetically induced current densities were calculated at the DFT level using the gauge-including magnetically induced current (gimic) approach. The current strengths and current pathways of the neutral M3O9 and the dianionic M3O (9) (2-) (M = Cr, Mo) oxides were investigated and analyzed with respect to a previous prediction of d-orbital aromaticity for Mo3O9 anions. Current-density calculations provide ring-current strengths that are used to assess the degree of aromaticity. Comparison of current-density calculations and calculations of nucleus-independent chemical shifts (NICS) shows that NICS calculations are not a reliable tool for determining the degree of aromaticity of the metal oxides.

First author: Swart, Marcel, Atomic Radii in Molecules for Use in a Polarizable Force Field, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 111, 1763, (2011)
Abstract: We report here the results for an ab initio approach to obtain the parameters needed for molecular simulations using a polarizable force field. These parameters consist of the atomic charges, polarizabilities, and radii. The former two are readily obtained using methods reported previously (van Duijnen and Swart, J Phys Chem A 1998, 102, 2399; Swart et al. J Comput Chem 2001, 22, 79), whereas here we report a new approach for obtaining atomic second-order radii (SOR), which is based on second-order atomic moments in scaled Voronoi cells. These parameters are obtained from quantum-chemistry calculations on the monomers, and used without further adaptation directly for intermolecular interactions. The approach works very well as shown here for four dimers, where high-level coupled cluster with singles and doubles, and perturbative triples (CCSD(T)) and density functional theory (DFT) Swart-Sola-Bickelhaupt functional including Grimme’s dispersion correction (SSB-D) reference data are available for comparison. The energy surfaces for the three methods are very similar, which is also the case for the interaction between a water molecule with either a chloride anion or a sodium cation. These latter systems had previously been used to criticize Thole’s damped point-dipole method, but here we show that with the correct use of the method, it is perfectly able to describe the intermolecular interactions. This is most obvious for the induced dipole moment as function of the chloride-oxygen distance, where the direct (discrete) reaction field results are virtually indistinguishable from those obtained at CCSD(T)/aug-cc-pVTZ.

First author: Courcot, Blandine, Optimization of a Molecular Mechanics Force Field for Type-II Polyoxometalates Focussing on Electrostatic Interactions: A Case Study, JOURNAL OF COMPUTATIONAL CHEMISTRY, 32, 1703, (2011)
Abstract: In this study, we have focussed on type-II polyanions such as [M7O24](6-), and we have developed and validated optimized force fields that include electrostatic and van der Waals interactions. These contributions to the total steric energy are described by the nonbonded term, which encompasses all interactions between atoms that are not transmitted through the bonds. A first validation of a stochastic technique based on genetic algorithms was previously made for the optimization of force fields dedicated to type-I polyoxometalates. To describe the new nonbonded term added in the functional, a fixed-charged model was chosen. Therefore, one of the main issues was to analyze that which partial atomic charges could be reliably used to describe these interactions in such inorganic compounds. Based on several computational strategies, molecular mechanics (MM) force field parameters were optimized using different types of atomic charges. Moreover, the influence of the electrostatic and van der Waals buffering constants and 1,4-interactions scaling factors used in the force field were also tested, either being optimized as well or fixed with respect to the values of CHARMM force field. Results show that some atomic charges are not well adapted to CHARMM parameters and lead to unrealistic MM-optimized structures or a MM divergence. As a result, a new scaling factor has been optimized for Quantum Theory of Atoms in Molecules charges and charges derived from the electrostatic potential such as ChelpG. The force fields optimized can be mixed with the CHARMM force field, without changing it, to study for the first time hepta-anions interacting with organic molecules.

First author: Miao, Y. R., Dyson orbitals of N2O: Electron momentum spectroscopy and symmetry adapted cluster-configuration interaction calculations, JOURNAL OF CHEMICAL PHYSICS, 134, 1703, (2011)
Abstract: Electron momentum spectroscopy and symmetry adapted cluster-configuration interaction (SACCI) theory were combined to study electron correlation effects in nitrous oxide molecule (N2O). The SAC-CI General-R method accurately reproduced the experimental ionization spectrum. This bench-marked method was also introduced for calculating the momentum distributions of N2O Dyson orbitals. Several calculated momentum distributions with different theoretical methods were compared with the high resolution experimental results. In the outer-valence region, Hartree-Fock (HF), density functional theory (DFT), and SAC-CI theory can well describe the experimental momentum distributions. SAC-CI presented a best performance among them. In the inner-valence region, HF and DFT cannot work well due to the severe breaking of the molecular orbital picture, while SACCI still produced an excellent description of experimental momentum profiles because it can accurately take into account electron correlations. Moreover, the thermally averaged calculation showed that the geometrical changes induced by the vibration at room temperature have no noticeable effects on momentum distribution of valence orbitals of N2O.

First author: Roy, Subhendu, Theoretical Studies on the Structure and Bonding of Metallacyclocumulenes, -cyclopentynes, and -cycloallenes, ORGANOMETALLICS, 30, 2670, (2011)
Abstract: In this paper, we compare the electronic structure of the hafnacycloallene complex Cp(2)HfC(4)Rr’R-2 ” (5Hf), which was previously described by Erker et al., with those of the titanium, zirconium, and hafnium complexes Cp2M(eta(4)-RHC4HR) (3M; i.e. metallacyclopent-2,3,4-trienes, metallacyclocumulenes) and Cp2M(eta(2)-R2C4R2) (4M; i.e. 1-metallacyclopent-3-ynes) using density functional theory (BP86/LANL2DZ) calculations. Moreover, the eta(3)-phenylallenyl zirconocene complex 7Zr, which was synthesized by Wojcicki et al., is included for the comparison. These calculations and extended Huckel calculations show that the bonding in complex 5Hf is remarkably similar to that of complexes 4M and 7Zr. An analysis of the structural parameters and bonding reveals that the unique interaction of the internal carbon atoms along with the terminal carbon atoms with the bent-metallocene moiety is the reason for the unusual stability of these metallacycles. The molecular orbital analysis further suggests that complex 5Hf can react with another metal fragment to give the bimetallic complexes 9 and 10. The electronic structures of complexes 3M, 4M, 5Hf, and 7Zr have been comparatively studied to get a general understanding of the bonding in these metallacycles.

First author: Bruce, Michael I., Oxidative Dimerization of Arylalkynyl-Ruthenium Complexes, ORGANOMETALLICS, 30, 2861, (2011)
Abstract: Chemical oxidation of Ru(C CPh)(PPh3)(2)Cp with [FeCp2]PF6 affords the binuclear cationic complexes [Cp(PPh3)(2)Ru{=C=CHC6H4CPh=C=}Ru(PPh3)(2)Cp] (PF6)(2) (2) and [Cp(PPh3)(2)Ru{C C(C6H4)CPh=C=}Ru(PPh3)(2)Cp]PF6 (3) by radical coupling at sites shown to be electron-rich by DFT studies, particularly involving the acetylide C-beta and C-para atoms and, to a lesser extent, the Cp carbon atoms. Complexes 2 and 3 are related by facile deprotonation/protonation reactions. When the 4-position of the Ph group is blocked, attack by C-beta upon the Cp group occurs to give the bis (vinylidene) [Ru{=C=C(C6H4Me-4)-eta-C5H4[Ru(PPh3)(2){=C=CH(C6H4Me-4)}(PPh3)(2) Cp]}](PF6)(2) (4), which can be deprotonated to give [Ru{=C=C(C6H4Me-4)-eta-CsH4[Ru(PPh3)(2){C C(C6H4Me-4)}(PPh3)(2)Cp]}]PF6 (5). Complex 4 is rapidly oxidized during workup to form [Ru{=C=C(C6H4Me)-eta-C5H4[Ru(CO)(PPh3)(2)]}(PPh3)(2)Cp](PF6)(2) (6). Single-crystal X-ray structure determinations of the salts 2, 3, and 6 are reported.

First author: Sun, Shaorui, Density Functional Theory Study of the Oxygen Reduction Reaction on Metalloporphyrins and Metallophthalocyanines, JOURNAL OF PHYSICAL CHEMISTRY C, 115, 9511, (2011)
Abstract: In this paper, density functional theory is applied to study the electrochemical reduction of oxygen on iron phthalocyanine (FePc), iron porphyrin (FeP), cobalt phthalocyanine (CoPc), and cobalt porphyrin (CoP). According to the calculation results, for the four metal macrocyclic complexes, O-2 will not directly be cleaved without the cooperation of hydrogen. In the reduction process, on FePc or FeP, H2O2 does not form as an intermediate, and O-2 is reduced to H2O, while on CoPc or CoP, O-2 is just reduced to H2O2. The reason why the oxygen reduction ability of FePc or FeP is higher than that of CoPc or CoP, respectively, is that the energy level of the highest-occupied 3d orbital of the former is higher than that of the later. The high energy level of the metal 3d orbital leads to the strong ability of oxygen reduction.

First author: Cunden, Lisa S., Fe(CO)(4) and Related Compounds as Isolobal Fragments, INORGANIC CHEMISTRY, 50, 4428, (2011)
Abstract: The M(CO)(4) fragment can be assigned to be isolobal with both CH3+ and CH2. In order to investigate this ambiguous isolobal assignment, we report calculations on compounds of the type M(CO)(4)L-n, where M is Fe (n = 0), Mn (n = -1), and Co (n = +1) and L is an eta(2) ligand with a pi bond, generally an alkene. The L’s are varied in electron-withdrawing ability, and patterns in computed structural parameters are investigated. We report that the equatorial OC-M-CO angle is sensitive to the electron-withdrawing ability of the alkene just as the isolobal prediction suggests. Other structural parameters that vary monotonically with electron-withdrawing ability of the alkene are the “bending back” of the alkene, the metal ligand bond distances, and carbon oxygen bond distances. Changing the metal from neutral Fe to a negatively charged Mn or positively charged Co has the result of increasing and decreasing, respectively, the OC-M-CO angle. Several compounds of Ni(CO)(3)L are also investigated as a further example of the ability of the isolobal concept to yield chemically useful information.

First author: Grobbelaar, Ebeth, A kinetic investigation of the oxidative addition reactions of the dimeric Bu4N[Ir-2(mu-Dcbp)(CO)(2)(PCy3)(2)] complex with iodomethane, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 696, 1990, (2011)
Abstract: The IR and UV/visible kinetic results of the oxidative addition of iodomethane toBu(4)N[Ir-2(mu-Dcbp)(CO)(2)(PCy3)(2)] (Dcbp = 3,5-dicarboxylatepyrazolate anion) showed three time separable reactions. The first, very fast reaction corresponds to the a Ir(I)-Ir(III) alkyl species formation within 10(-3) s. The second, relative fast reaction corresponds to Ir(III)-Ir(III) alkyl formation with a rate constant of 3.25(4) x 10(-2) M-1 s(-1) while the third and slowest reaction corresponds to Ir(III)-Ir(III) acyl formation with a rate constant of 1.42 x 10(-5) s(-1). The IR data clearly show the existence of a number of equilibria with the formation of an Ir(I)-Ir(III) alkyl product which then react to form the Ir(III)-Ir(III) which then slowly react to form the Ir(III)-Ir(III) acyl product. A solvent study indicated increased oxidative addition activity in the presence of polar solvents, which is indicative of a polar transition state. The large negative entropy of activation for the Ir(III)-Ir(III) alkyl formation step (k(2)) of -178(23) JK(-1) mol(-1) is indicative of an associative process. DFT calculations successfully identified the stereochemistry of the starting complex, [Ir-2(mu-Dcbp)(CO)(2)(PCy3)(2)](-) as well as that of the Ir-alkyl and acyl isomers. A reaction pathway, using the IR data and DFT calculations, is proposed for the reaction.

First author: Djukic, Jean-Pierre, Synthesis of a 2-benzocymantrenylpyridine and further mechanistic insights, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 696, 2101, (2011)
Abstract: The synthesis of a new benzocymantrene derivative containing an appended pyridyl moiety was attempted by reacting a lithioindenylpyridine with (CO)(5)MnBr. The reaction led to the formation of small amounts of the targeted benzocymantrene, which was subsequently characterized by structural X-ray diffraction analysis. Alternative treatment of the same ligand with (eta(1)-benzyl)pentacarbonylmanganese led to the formation of a five-membered manganacycle resulting from the C-H bond activation at the five-membered ring of the indenyl group. To rationalize the origin of the poor yield in the benzocymantrene derivative a complete study of the reaction profile was carried out by means of a state-of-the-art DFT-D2 method. The theory indicated that the main difficulty in producing the targeted benzocymantrene stems from the relatively high activation energy barrier necessary to convert a (eta(1)-indenyl)Mn(CO)(5) intermediate into a (eta(3)-indenyl)Mn(CO)(4) transient species.

First author: Quintal, Susana, Synthesis and properties of new Mo(II) complexes with N-heterocyclic and ferrocenyl ligands, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 696, 2142, (2011)
Abstract: New Mo(II) complexes with 2,2′-dipyridylamine (L1), [Mo(CH3CN)(eta(3)-C3H5)(CO)(2)(L1)]OTf (C1a) and [{MoBr(eta(3)-C3H5)(CO)(2)(L1)}(2)(4,4′-bipy)](PF6)(2) (C1b), with {[bis(2-pyridyl)amino]carbonyl}ferrocene (L2), [MoBr(eta(3)-C3H5)(CO)(2)(L2)] (C2), and with the new ligand N,N-bis(ferrocenecarbonyl)-2-aminopyridine (L3), [MoBr(eta(3)-C3H5)(CO)(2)(L3)] (C3), were prepared and characterized by FTIR and H-1 and C-13 NMR spectroscopy. C1a, C1b, L3, and C2 were also structurally characterized by single crystal X-ray diffraction. The Mo(II) coordination sphere in all complexes features the facial arrangement of allyl and carbonyl ligands, with the axial isomer present in C1a and C2, and the equatorial in the binuclear C1b. In both C1a and C1b complexes, the L1 ligand is bonded to Mo(II) through the nitrogen atoms and the NH group is involved in hydrogen bonds. The X-ray single crystal structure of C2 shows that L2 is coordinated in a kappa(2)-N,N-bidentate chelating fashion. Complex C3 was characterized as [MoBr(eta(3)-C3H5)(CO)(2)(L3)] with L3 acting as a kappa(2)-N,O-bidentate ligand, based on the spectroscopic data, complemented by DFT calculations.The electrochemical behavior of the monoferrocenyl and diferrocenyl ligands L2 and L3 has been studied together with that of their Mo(II) complexes C2 and C3. As much as possible, the nature of the different redox changes has been confirmed by spectrophotometric measurements. The nature of the frontier orbitals, namely the localization of the HOMO in Mo for both in C2 and C3, was determined by DFT studies.

First author: Dijkstra, Arend G., Modeling the Vibrational Dynamics and Nonlinear Infrared Spectra of Coupled Amide I and II Modes in Peptides, JOURNAL OF PHYSICAL CHEMISTRY B, 115, 5392, (2011)
Abstract: The amide vibrational modes play an important role in energy transport and relaxation in polypeptides and proteins and provide us with spectral markers for structure and structural dynamics of these macromolecules. Here, we present a detailed model to describe the dynamic properties of the amide I and amide II modes and the resulting linear and nonlinear spectra. These two modes have large oscillator strengths, and their mutual coupling plays an important role in their relaxation. Using first-principles calculations of NMA-d(7) and a dipeptide in a fluctuating bath described by molecular dynamics simulations, we model the frequencies of the local vibrations as well as the coupling between them. Both the coherent couplings and the fluctuations induced by contact with their environment are taken into account. We apply the resulting model of interacting fluctuating oscillators to study the collective vibrations and the partially coherent transport of vibrational energy through a model a-helix. We find that the instantaneous vibrations are delocalized over a few (up to four) amide units, while the coherences in the helix survive for 0.5-1 ps, leading to coherent transport on a similar time scale.

First author: Emerich, Brian M., Protecting-Group-Free Access to a Three-Coordinate Nickel(0) Tris-isocyanide,ORGANOMETALLICS, 30, 2598, (2011)
Abstract: Details are presented regarding a convenient synthesis of the nickel trisisocyanide complex Ni(CNArDipp2)(3) (Ar-Dipp2 = 2,6-[i-Pr](2)C6H3)(2)C6H3). A previous synthesis of a Ni tris-isocyanide complex relied on a 11(I) coordination-site protection strategy to discourage the formation of a tetrakis-isocyano complex. However, protecting-group-free access to Ni(CNArr(Dipp2))3 is enabled by the encumbering m-terphenyl isocyanide CNArDipp2. Treatment of Ni(COD)2 with CNArDipp2 affords Ni(COD)(CNArDipp2)2, which is readily oxidized to NiI2(CNArDipp2)2 upon addition of I-2. Reduction of NiI2(CNArDipp2)2 with Mg metal gent:rates Ni(CNArDipp2)3 and does not require the addition of a third equivalent of CNArDipp2. Tris-isocyanide Ni(CNArDipp2)3 is active toward Lewis acid bindin)and oxidative addition reactions. Treatment of Ni(CNArDipp2)3 with TlOTf (OTf = [O3SCF3](-)) generates the salt [TINi(CNArDipp2)(3)] OTf, in which the Ni center functions as a Lewis base toward Tl. The Ni center in Ni(CNArDipp2)(3) also oxidativel adds across C-X bonds in a number of alkyl, aryl, and main-group halides and is accompanied by varying degrees of CNArDipp2 ligand loss. Formation of eta(2)-iminoacyl complexes deactivates the Ni center toward additional reactivity.

First author: Barngrover, Brian M., Electron and Hydride Addition to Gold(I) Thiolate Oligomers: Implications for Gold-Thiolate Nanoparticle Growth Mechanisms, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 2, 990, (2011)
Abstract: Electron and hydride addition to Au(I):SR oligomers is investigated using density functional theory. Cyclic and chain-like clusters are examined in this work. Dissociation to Au- ions and Au-n(SR)(n+1)(-) chains is observed after 2-4 electrons are added to these systems. The free thiolate (SR-) is rarely produced in this work; dissociation of Au- is preferred over dissociation of SR-. Electron affinities calculated in gas phase, toluene, and water suggest that the electron addition process is unlikely, although it may be possible in polar solvents. In contrast, hydride addition to Au(I):SR oligomers yields free thiols and complexes containing Au-Au bonds, which are plausible intermediates for gold nanoparticle growth. The resulting compounds can react to form larger nanoparticles or undergo further reduction by hydride to yield additional Au-Au bonds.

First author: Bhattacharyya, Arunasis, Selective Americium(III) Complexation by Dithiophosphinates: A Density Functional Theoretical Validation for Covalent Interactions Responsible for Unusual Separation Behavior from Trivalent Lanthanides,INORGANIC CHEMISTRY, 50, 3913, (2011)
Abstract: The separation of trivalent actinides and lanthanides is a challenging task for chemists because of their similar charge and chemical behavior. Soft donor ligands like Cyanex-301 were found to be selective for the trivalent actinides over the lanthanides. Formation of different extractable species for Am3+ and various lanthanides (viz. La3+, Eu3+, and Lu3+) was explained on the basis of their relative stabilities as compared to their corresponding trinitrato complexes calculated using the density functional method. Further, the metal-ligand complexation energy was segregated into electrostatic, Pauli repulsion, and orbital interaction components. Higher covalence in the M-S bond in the dithiophosphinate complexes as compared to the M-O bond in the nitrate complexes was reflected in the higher orbital and lower electrostatic interactions for the complexes with increasing number of dithiophosphinate ligands. Higher affinity of the dithiophosphinate ligands for Am3+ over Eu3+ was corroborated with higher covalence in the Am-S bond as compared to the Eu-S bond, which was reflected in shorter bond length in the case of the former and higher ligand to metal charge transfer in Am(III)-dithiophosphinate complexes. The results were found to be consistent in gas phase density functional theory (DFT) calculations using different GGA functional. More negative complexation energies in the case of Eu3+ complexes of Me2PS2- as compared to the corresponding Am3+ complexes in spite of marginally higher covalence in the Am-S bond as compared to the Eu-S bond might be due to higher ionic interaction in the Eu3+ complexes in the gas phase calculations. The higher covalence in the Am-S bond obtained from the gas phase studies of their geometries and electronic structures solely cannot explain the selectivity of the dithiophosphinate ligands for Am3+ over Eu3+. Presence of solvent may also play an important role to control the selectivity as observed from higher complexation energies for Am3+ in the presence of solvent. Thus, the theoretical results were able to explain the experimentally observed trends in the metal-ligand complexation affinity.

First author: Knapp, Caroline M., Heteroatomic Molecular Clusters Derived from Group 15 Zintl Ion Cages: Synthesis and Isolation of [M-2(HP7)(2)](2-) (M = Ag, Au), Two Novel Cluster Anions Exhibiting Metallophilic Interactions, INORGANIC CHEMISTRY, 50, 4021, (2011)
Abstract: Ethylenediamine (en) solutions of K3P7 and 2,2,2-crypt (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo [8.8.8] hexacosane) were reacted with the homoleptic group 11 complexes [M(nbe)(3)][SbF6] (M = Ag, Au; nbe = norbornene) yielding two novel cluster anions, [M-2(HP7)(2)](2-) both of which were isolated in low crystalline yields as [K(2,2,2-crypt)](2) [M-2(HP7)(2)] (M = Ag (1) and Au (2)). Optimization of the reaction conditions by incorporation of a proton source (ammonium tetraphenylborate) and the replacement of the light-sensitive nbe adducts of silver and gold with the chloride salts MCl (M = Ag Au) was found to greatly increase the yield and purity in which 1 and 2 were isolated. Compounds 1 and 2 were characterized by single crystal X-ray diffraction, electrospray ionization mass-spectrometry (ESI- MS), elemental analysis, and H-1 and P-31 NMR spectroscopy. Density functional theory (DFT) calculations on the cluster anions were also conducted.

First author: Liu, Yang, Electronic Ground States and Vibrational Frequency Shifts of Diatomic Ligands in Heme Adducts,JOURNAL OF COMPUTATIONAL CHEMISTRY, 32, 1279, (2011)
Abstract: DFT calculations were carried out to study heme complexes with diatomic ligand (CO, NO, or O-2) and trans-imidazole ligand. The optimized electronic ground states of CO, NO, and O-2 adducts are singlet, doublet, and open-shell singlet, respectively. For O-2 adduct, the open-shell singlet is slightly lower in energy than the close-shell singlet. However, important differences are found in optimized structures and vibrational frequencies. Particularly, the trans-imidazole-induced frequency up-shift of the Fe-O(O) stretching mode can be predicted only with the open-shell singlet as ground state. An analysis of normal modes confirms that the up-shifts in the bent (NO and O-2) adducts are mainly due to mixing of Fe-X(O) stretching mode with Fe-X-O bending coordinate. Our study of binding mechanism indicates that a secondary source of the upshifts is the diminished weakening of the Fe-X(O) bonds. The Fe-X(O) bond strengths are modulated by sigma competition mechanism, which weakens the Fe-X(O) bond and sigma-pi cooperation mechanism, which only exists in the bent adducts and enforce the Fe-X(O) bond.

First author: Peric, Berislav, High-Temperature Experimental and Theoretical Study of Magnetic Interactions in Diamond and Pseudo-Diamond Frameworks Built up from Hexanuclear Tantalum Clusters, CHEMISTRY-A EUROPEAN JOURNAL,17, 6263, (2011)
Abstract: Magnetic interactions in solid-state tantalum cluster compounds have been evidenced by using magnetic susceptibility measurements and corroborated by broken-symmetry DFT calculations. The three selected compounds are based on [Ta6X12(H2O)(6)](3+) (X= Cl or/and Br) units with edge-bridged Ta-6 octahedral clusters. Although two of them crystallise in the tetragonal space group I4(1)/a, all compounds exhibit a similar arrangement of paramagnetic clusters related to the diamond structural framework (Fd (3) over barm space group). Magnetic parameters were fitted by using the [5,4] Pade approximant of high-temperature series expansion of susceptibility for the Heisenberg model (S= 1/2) in the diamond framework, assuming only nearest-neighbouring interactions. Such a model appropriately describes magnetic-susceptibility measurements at temperatures T > 0.7 |J|/ k. The magnetic interaction parameter J between two [Ta6Cl12(H2O)(6)](3+) clusters is estimated to be -64.28(7) cm(-1); it has been enhanced by replacing several chlorine inner ligands with bromine ones (J= -123(3) cm(-1) for two [Ta6Br7.7(1) Cl-4.3(1) (H2O)(6)](3+) clusters) and is strongest between two bromine [Ta6Br12(H2O)(6)](3+) clusters with a value of -155(1) cm(-1). Broken-symmetry DFT calculations within spin-dimer analysis confirmed this trend. Those interactions can be explained on the basis of the overlap between singly occupied a(2u) orbitals localised on neighbouring clusters.

First author: Thomas, Simil, Nonlinear Optical Properties of Stacked Conjugated Systems, CRYSTAL GROWTH & DESIGN, 11, 1846, (2011)
Abstract: We study linear and nonlinear optical properties of two push-pull polyenes stacked in head to head (HtH) and head to tail (HtT) configurations, at different stacking angles within the Pariser-Parr-Pople model using exact diagonalization method. By varying the stacking angle between the polyenes, we find that the optical gap varies marginally, but transition dipoles show large variations. We find that the dominant first-order hyperpolarizability component beta(XXX) for HtH arrangement and beta(YYY) for HtT arrangement strongly depend on the distance of separation between molecules, while the other smaller component beta(XYY) for HtH arrangement and beta(XXY) for HtT arrangement) does not show this variation with distance. We find that the beta(XXX) for HtH configuration shows a maximum at an angle away from 0, in contrast with the oriented gas model. This angle varies with distance between the polyenes, and at large distance it falls to 0. The ratio of all components of beta of a dimer to monomer is less than two for HtH configuration for all angles. But for HtT configurations the ratio of the dominant beta component is greater than two at large angles. Our ZINDO study on two monomers (4-hydroxy-4′-nitroazobenzene) connected in a nonconjugative fashion shows a linear increase in vertical bar(beta) over right arrow (av)vertical bar without much red shift in optical gap. There is a linear increase in vertical bar(beta) over right arrow (av)vertical bar with increase in number of monomers connected nonconjugatively without resulting in a red shift in optical gap.

First author: Datta, K. K. R., Base-Selective Adsorption of Nucleosides to Pore-Engineered Nanocarbon, Carbon Nanocage, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 11, 3959, (2011)
Abstract: Selective molecular recognition is an important subject in supramolecular science as well as in practical applications such as sensing, drug delivery, and biomedical processes. In this research we have investigated adsorption behavior of nucleosides (adenosine, guanosine, and thymidine) onto various porous supports. When compared with mesoporous silica, porous carbons exhibit superior adsorptive performance. We serendipitously observed a pronounced selectivity between purine-base and pyrimidine-base nucleosides by carbon naonocage. These findings are useful for design of materials for applications in adsorption-based separations and as column stationary phases for separation of costly and important biomolecules.

First author: Jaszewski, Adrian R., Toward the Assignment of the Manganese Oxidation Pattern in the Water-Oxidizing Complex of Photosystem II: A Time-Dependent DFT Study of XANES Energies, CHEMISTRY-A EUROPEAN JOURNAL,17, 5699, (2011)
Abstract: Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations are reported on three sets of isomeric models of the {Mn-4/Ca} water-oxidizing complex of photosystem II (PS II), which share the general formula [CaMn4O4(N2C3H4)-(RCOO)(6)](q center dot)(H2O)(n) (R = H, CH3; q = -1, 0, + 1, + 2; n = 3, 4, 5, 6, 7). Comparison with the full range of available data on Mn K-edge X-ray absorption energy values determined for the photosystem allows us to validate the structures that correspond to the particular S states and to determine their Mn oxidation patterns. By using a new TDDFT procedure, it is shown that variations in the absolute K-edge energy values for a particular S state, reported by different research groups, can be quantitatively explained by different geometries adopted by the Mn cluster, which demonstrates flexibility in the position of the fourth ‘dangling’ Mn atom in relation to a cubane structure created by the Ca atom and the three other Mn atoms. Computational results show that each step of the S cycle occurs by removal of one electron directly from the Mn cluster. This Mn-centered oxidation still agrees with the small difference observed experimentally between the K-edge energy values of the S-2 and S-3 states of the photosystem, thus resolving a controversy as to whether this represents ligand-centered or metal-centered oxidation. The overall oxidation state of Mn atoms in the tetramanganese cluster during functional turnover changes from 2.75 for S-0, 3.00 for S-1, and 3.25 for S-2 up to 3.50 for the S-3 state, which is systematically 0.50 lower than the previously proposed oxidation states of the cluster. The calculations give insight into why these earlier, purely empirical, assignments of the Mn oxidation levels in PS II could be in error.

First author: Megger, Dominik A., Contiguous Metal-Mediated Base Pairs Comprising Two Ag-I Ions, CHEMISTRY-A EUROPEAN JOURNAL, 17, 6533, (2011)
Abstract: The incorporation of transition-metal ions into nucleic acids by using metal-mediated base pairs has proved to be a promising strategy for the site-specific functionalization of these biomolecules. We report herein the formation of Ag+-mediated Hoogsteen-type base pairs comprising 1,3-dideaza-2′-deoxyadenosine and thymidine. By defunctionalizing the Watson-Crick edge of adenine, the formation of regular base pairs is prohibited. The additional substitution of the N3 nitrogen atom of adenine by a methine moiety increases the basicity of the exocyclic amino group. Hence, 1,3-dideazaadenine and thymine are able to incorporate two Ag+ ions into their Hoogsteen-type base pair (as compared with one Ag+ ion in base pairs with 1-deazaadenine and thymine). We show by using a combination of experimental techniques (UV and circular dichroism (CD) spectroscopies, dynamic light scattering, and mass spectrometry) that this type of base pair is compatible with different sequence contexts and can be used contiguously in DNA double helices. The most stable duplexes were observed when using a sequence containing alternating purine and pyrimidine nucleosides. Dispersion-corrected density functional theory calculations have been performed to provide insight into the structure, formation and stabilization of the twofold metalated base pair. They revealed that the metal ions within a base pair are separated by an Ag center dot center dot Ag-center dot distance of about 2.88 angstrom. The Ag-Ag interaction contributes some 16 kcalmol(-1) to the overall stability of the doubly metal-mediated base pair, with the dominant contribution to the Ag-Ag bonding resulting from a donor-acceptor interaction between silver 4d-type and 4s orbitals. These Hoogsteen-type base pairs enable a higher functionalization of nucleic acids with metal ions than previously reported metal-mediated base pairs, thereby increasing the potential of DNA-based nanotechnology.

First author: Facelli, Julio C., Chemical shift tensors: Theory and application to molecular structural problems,PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY, 58, 176, (2011)
Abstract: The incorporation of transition-metal ions into nucleic acids by using metal-mediated base pairs has proved to be a promising strategy for the site-specific functionalization of these biomolecules. We report herein the formation of Ag+-mediated Hoogsteen-type base pairs comprising 1,3-dideaza-2′-deoxyadenosine and thymidine. By defunctionalizing the Watson-Crick edge of adenine, the formation of regular base pairs is prohibited. The additional substitution of the N3 nitrogen atom of adenine by a methine moiety increases the basicity of the exocyclic amino group. Hence, 1,3-dideazaadenine and thymine are able to incorporate two Ag+ ions into their Hoogsteen-type base pair (as compared with one Ag+ ion in base pairs with 1-deazaadenine and thymine). We show by using a combination of experimental techniques (UV and circular dichroism (CD) spectroscopies, dynamic light scattering, and mass spectrometry) that this type of base pair is compatible with different sequence contexts and can be used contiguously in DNA double helices. The most stable duplexes were observed when using a sequence containing alternating purine and pyrimidine nucleosides. Dispersion-corrected density functional theory calculations have been performed to provide insight into the structure, formation and stabilization of the twofold metalated base pair. They revealed that the metal ions within a base pair are separated by an Ag center dot center dot Ag-center dot distance of about 2.88 angstrom. The Ag-Ag interaction contributes some 16 kcalmol(-1) to the overall stability of the doubly metal-mediated base pair, with the dominant contribution to the Ag-Ag bonding resulting from a donor-acceptor interaction between silver 4d-type and 4s orbitals. These Hoogsteen-type base pairs enable a higher functionalization of nucleic acids with metal ions than previously reported metal-mediated base pairs, thereby increasing the potential of DNA-based nanotechnology.

Abstract: In the, review article, we survey the relatively of orbital magnetization in solids – often referred to as the “modern theory of orbital magnetization” and its applications. Surprisingly, while the calculation of the orbital magnetization in finite systems such as atoms and molecules is straight forward, in extended systems or solids it has long eluded calculations owing to the fact that the position operator is ill-defined in such a context. Approaches that overcome this problem were first developed in 2005 and in the first part of this review We present the main ideas reaching from a Wannier function approach to semi classical and finite temperature formalisms. In the second part, we describe practical aspects of calculating the orbital magnetization, such as taking k-space derivatives, a formalism for pseudopotentials, a single k-point derivation, a Wannier interpolation scheme, and DE T specific aspects. We then show results of recent calculations on Fe, Co, and Ni. In the last part of this review, we focus on direct applications of the orbital magnetization. In particular, we will review how properties such as the nuclear magnetic resonance shielding tensor and the electron paramagnetic resonance g-tensor can be elegantly calculated in terms of a derivative of the orbital magnetization.

First author: Goodpaster, Jason D., Embedded density functional theory for covalently bonded and strongly interacting subsystems, JOURNAL OF CHEMICAL PHYSICS, 134, 1429, (2011)
Abstract: Embedded density functional theory (e-DFT) is used to describe the electronic structure of strongly interacting molecular subsystems. We present a general implementation of the Exact Embedding (EE) method [J. Chem. Phys. 133, 084103 (2010)] to calculate the large contributions of the nonadditive kinetic potential (NAKP) in such applications. Potential energy curves are computed for the dissociation of Li+-Be, CH3-CF3, and hydrogen-bonded water clusters, and e-DFT results obtained using the EE method are compared with those obtained using approximate kinetic energy functionals. In all cases, the EE method preserves excellent agreement with reference Kohn-Sham calculations, whereas the approximate functionals lead to qualitative failures in the calculated energies and equilibrium structures. We also demonstrate an accurate pairwise approximation to the NAKP that allows for efficient parallelization of the EE method in large systems; benchmark calculations on molecular crystals reveal ideal, size-independent scaling of wall-clock time with increasing system size.

First author: Hieringer, Wolfgang, The Surface Trans Effect: Influence of Axial Ligands on the Surface Chemical Bonds of Adsorbed Metalloporphyrins, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 133, 6206, (2011)
Abstract: The chemical bond between an adsorbed, laterally coordinated metal ion and a metal surface is affected by an additional axial ligand on the metal ion. This surface analogon of the trans effect was studied in detail using monolayers of various M(II)-tetraphenylporphyrins (MTTPs, M = Fe, Co, Zn) and their nitrosyl complexes on a Ag(111) surface. X-ray photoelectron spectroscopy (XPS) shows that the oxidation state of the Fe and Co (but not Zn) ions in the MTPP monolayers is reduced because of the interaction with the substrate. This partial reduction is accompanied by the appearance of new valence states in the UV photoelectron and scanning tunneling spectra (UPS and STS), revealing the covalent character of the ion-substrate bond. Subsequent coordination of nitric oxide (NO) to the metal ions (Fe, Co) reverses these surface-induced effects, resulting in an increase of the oxidation states and the disappearance of the new valence states. Removal of the NO ligands by thermal desorption restores the original spectroscopic features, indicating that the described processes are fully reversible. The NO coordination also changes the spin state and thus the magnetic properties of the metal ions. Density-functional theory (DFT) calculations on model systems provide structural and energetic data on the adsorbed molecules and the surface chemical bond. The calculations reveal that competition effects, similar to the trans effect, play a central role and lead to a mutual interference of the two axial ligands, NO and Ag, and their bonds to the metal center. These findings have important implications for sensor technology and catalysis using supported planar metal complexes, in which the activity of the metal center is sensitively influenced by the substrate.

First author: Jaszewski, Adrian R., Structural and Electronic Models of the Water Oxidizing Complex in the S-0 State of Photosystem II: A Density Functional Study., JOURNAL OF PHYSICAL CHEMISTRY B, 115, 4484, (2011)
Abstract: Large size (228 atom, 229 atom for protonated form) molecular models of the oxygen evolving complex of photosystem II (OEC), with a complete set of ligating aminoacids, the redox-active tyrosine Y-z, and proton/water transfer channels terminating at the water oxidizing Mn/Ca cluster, are constructed based on the highest available resolution X-ray diffraction structures of the protein and our previous density functional theory (DFT) studies of isolated metal cluster model structures. Geometries optimized using the general gradient approximation (GGA) or hybrid density functionals are compared with high-resolution extended X-ray absorption fine structure (EXAFS) spectroscopic data and show that an antiferromagnetic configuration of the Mn centers in the cluster gives computed metal metal distances in excellent agreement with experiment. The excitation energies predicted by time-dependent density functional theory (TDDFT) calculations for truncated 106 atom and 78 atom structures derived from the large models show that a previously proposed III-III-III-II oxidation pattern of the Mn atoms agrees very well with the X-ray absorption near-edge structure (XANES) observed for the S-0 state of the OEC. This supports a “low’ Mn oxidation state paradigm for the OEC, when a realistic protein imposed environment for the catalytic metal cluster is used in calculations. The probable protonation sites in the cluster and roles of the proton/water transfer channels are discussed in light of the computational results.

First author: Thomas, Kolle E., Corroles Cannot Ruffle, INORGANIC CHEMISTRY, 50, 3247, (2011)
Abstract: X-ray structures of Co-III[(CF3)(3)Cor](PPh3) [(CF3)(3)Cor = meso-tris(trifluoromethyl)corrolato] and Cu[(CF3)(4)Por] [(CF3)(4)Por = meso-tetralcis(trifluoromethyl)porphyrinato] revealed planar and highly ruffled macrocycle conformations, respectively, in line with analogous observations for a handful of other meso-perfluoroalkylated porphyrins and corroles reported in the literature. To gain insights into the difference in conformational behavior, we evaluated DFT (BP86-D/TZP) ruffling potentials for a variety of corrole complexes, as well as their porphyrin analogues. The calculations led us to conclude that corrole derivatives, in essence, cannot ruffle.

First author: Christe, Karl O., Why Are [P(C6H5)(4)]N-+(3)- and [As(C6H5)(4)]N-+(3)- Ionic Salts and Sb(C6H5)(4)N-3 and Bi(C6H5)(4)N-3 Covalent Solids? A Theoretical Study Provides an Unexpected Answer, INORGANIC CHEMISTRY, 50, 3752, (2011)
Abstract: A recent crystallographic study has shown that, in the solid state, P(C6H5)(4)N-3 and As(C6H5)(4)N-3 have ionic [M(C6H5)(4)]N-+(3)–type structures, whereas Sb(C6H5)(4)N-3 exists as a pentacoordinated covalent solid. Using the results from density functional theory, lattice energy (VBT) calculations, sublimation energy estimates, and Born-Fajans-Haber cycles, it is shown that the maximum coordination numbers of the central atom M, the lattice energies of the ionic solids, and the sublimation energies of the covalent solids have no or little influence on the nature of the solids. Unexpectedly, the main factor determining whether the covalent or ionic structures are energetically favored is the first ionization potential of [M(C6H5)(4)]. The calculations show that at ambient temperature the ionic structure is favored for P(C6H5)(4)N-3 and the covalent structures are favored for Sb(C6H5)(4)N-3 and Bi(C6H5)(4)N-3, while As(C6H5)(4)N-3 presents a borderline case.

First author: Hartsock, Robert W., Characterizing the Deformational Isomers of Bimetallic Ir-2(dimen)(4)(2+) (dimen=1,8-diisocyano-p-menthane) with Vibrational Wavepacket Dynamics, JOURNAL OF PHYSICAL CHEMISTRY A, 115, 2920, (2011)
Abstract: We studied the Ir-2(dimen)(4)(2+) complex with ultrafast transient absorption spectroscopy and density functional theory and concluded that it possesses two singlet ground state isomers in room temperature solution. The molecule can adopt either a paddle wheel or a propeller conformation in solution, where the paddle wheel structure possesses a metal-metal bond of 4.4 angstrom and a dihedral angle between the quasi-C-4v planes of 0 degrees and the propeller structure has a metal metal bond of 3.6 angstrom and a dihedral angle of 17 degrees when crystallized. Each conformation has a distinct absorption in the visible attributed to a (1)(d sigma(z)* -> p sigma(z)) excitation, with the long eclipsed structure absorbing at 475 nm and the short twisted structure absorbing at 585 nm. We independently pumped at each of these visible transitions to form vibrational wavepackets on the ground and excited state potential energy surfaces, which modulated the ground state bleach and stimulated emission signals, respectively. We found that the ground state wavepacket oscillates with a frequency of 48 cm(-1) when pumping the red peak and 11 cm(-1) when pumping the blue peak. We assign these frequencies to the Ir-Ir symmetric stretch, with the variation in frequency reflecting the variation in metal metal bond strength in support of our assignment of the blue peak to the longer Ir-Ir bond length conformer and the red peak to the shorter Ir-Ir bond length conformer. When pumping the red peak, we found two modes with frequencies of 80 and 119 cm(-1) the stimulated emission and only one mode at 75 cm when pumping the blue peak. We assign the 75-80 cm(-1) frequency to the Ir-Ir stretch and the 119 cm(-1) vibration to the dihedral angle twist in the excited state. The variation in the excited state dynamics does not result from the excitation of different electronic states, but rather from excitation to different Franck-Condon regions of the same electronic excited state potential energy surface. This occurs because of the large difference in ground state molecular structure. DFT calculations support the existence of a single electronic excited state being accessed from two distinct structural isomers with conformations similar to those observed with X-ray crystallography.

First author: Guidez, Emilie B., Initial Growth Mechanisms of Gold-Phosphine Clusters, JOURNAL OF PHYSICAL CHEMISTRY C, 115, 6305, (2011)
Abstract: Gold-phosphine cluster growth was studied at the BP86/TZV level of theory, starting from the precursor AuClPR3 (R = H, Me, and Ph), up to clusters containing four gold atoms. For all three substituents, AuClPR3 is linear. For R = H and R = Me, the anionic species AuClPR3- are bent, whereas for R = Ph, it is linear because of the addition of the electron in a pi* orbital mainly localized on the benzyl rings. Chloride ion dissociation, especially from negatively charged clusters, is very common during cluster growth. Phosphine groups can also dissociate, although this becomes less favorable as the R group becomes larger. The growth products obtained strongly depend on the relative orientation of the reactants, leading to a wide variety of clusters. The inclusion of a classical dispersion term gives similar monomers and dimers to regular BP86 but may lead to different trimers. Most reactions involved in cluster growth are exothermic. Dispersion forces tend to increase the reaction energies involving a low charge and decrease the reaction energies involving a high negative charge. Trimers tend to have a triangular core and be negatively charged. Tetramers have a diamond, tetrahedral, or Y-shaped core. Diamonds and tetrahedra mostly have a positively charged or neutral core, as opposed to Y shapes, which have a negatively charged or neutral core. The optimized tetrahedral structure Au4Cl2(PH3)(4) was found to be similar to the experimental cluster [Au-4(mu-I)(2)(PPh3)(4)] and to be one of the lowest energy structures.

First author: Dzik, Wojciech I., Open-Shell Organometallic [M-II(dbcot(bislutidylamine)](2+) Complexes (M = Rh, Ir): Unexpected Base-Assisted Reduction of the Metal Instead of Amine Ligand Deprotonation, ORGANOMETALLICS, 30, 1902, (2011)
Abstract: Cationic rhodium and iridium complexes with dibenzo[a,e]cyclooctatetraene (dbcot) and bislutidylamine (bla) were synthesized from the respective [M(mu-Cl) (dbcot)(2) dimers and the bla ligand and were characterized by NMR, X-ray diffraction, and cyclic voltammetry. Both [M-I(dbcot)(bla)(+) complexes are easily oxidized by one electron to form paramagnetic dicationic analogues [M-II(dbcot)(bla)](2+) (M = Rh, Ir). In the solid state, the geometry changes from a distorted trigonal bipyrainid to square pyramidal upon oxidation of the metal from M-I to M-II, as evidenced by X-ray diffraction studies of the iridium complexes. The paramagnetic complexes undergo facile one-electron reduction in the presence of base, most likely involving oxidation of the solvent or hydroxide anions. A control experiment using the corresponding [Rh-II(dbcot)(Bn-bla)](2+) complex, wherein Bn-bla is the N-benzyl-protected bla ligand, gives similar results, which strongly suggests that deprotonation of the N-H moiety of the [M-II(dbcot)(bla)](2+) plays a minor role (if any at all) in the observed base-mediated reduction processes. Reaction of bla with [Ir(mu-Cl)(coe)](2) (coe = ciscyclooctene) results in oxidative addition of the vinylic C-H bond of coe to the metal center, as evidenced by X-ray diffraction.

First author: Chamberlin, Adam C., Iron Porphyrin Dications with Neutral Axial Ligands: DFT Calculations Delineate Similarities with Heme Protein Compound II Intermediates, JOURNAL OF PHYSICAL CHEMISTRY B, 115, 3642, (2011)
Abstract: OLYP/TZP calculations on two symmetrized model complexes [Fe(TPP)(py)(2)](2+) and [Fe(TPP)(PhNC)(2)](2+) (TPP = meso-tetraphenylporphyrin, py = pyridine, PhNC = phenylisocyanide) reveal dense manifolds of low-energy electronic states. For the latter complex, broken-symmetry calculations successfully reproduce the unique S = 0 ground state that is expected on the basis of experimental measurements on a closely related complex; the S = 0 state arises from antiferro-magnetic coupling between a low-spin d(xy)(l)(d(xz),d(yz))(4) Fe(III) center and a porphyrin “a(2u)” radical. Furthermore, the calculations indicate low-energy Fe(IV) states for both complexes. Overall, the results contribute to our deepening understanding of the factors contributing to the stability of iron(IV) centers. Thus, a dianionic donor oxo ligand is no longer deemed a requirement for the stability of heme-based Fe(IV) centers; iron(IV) intermediates of heme proteins such as chloroperoxidase, catalase, and MauG, having only monanionic ligands such as hydroxide, thiolate, and phenolate and/or (in the case of MauG) a neutral histidine as axial ligands, are now firmly established.

First author: Zurek, Eva, Alkali Metals in Ethylenediamine: A Computational Study of the Optical Absorption Spectra and NMR Parameters of [M(en)(3)(delta+) center dot M delta-] Ion Pairs, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 133, 4829, (2011)
Abstract: The optical absorption spectra of alkali metals in ethylenediamine have provided evidence for a third oxidation state, -1, of all of the alkali metals heavier than lithium. Experimentally determined NMR parameters have supported this interpretation, further indicating that whereas Na- is a genuine metal anion, the interaction of the alkali anion with the medium becomes progressively stronger for the larger metals. Herein, first-principles computations based upon density functional theory are carried out on various species which may be present in solutions composed of alkali metals and ethylenediamine. The energies of a number of hypothetical reactions computed with a continuum solvation model indicate that neither free metal anions, M-, nor solvated electrons are the most stable species. Instead, [Li(en)(3)](2) and [M(en)(3)(delta+) center dot M delta-] (M = Na, K, Rb, Cs) are predicted to have enhanced stability. The M(en)3 complexes can be viewed as superalkalis or expanded alkalis, ones in which the valence electron density is pulled out to a greater extent than in the alkali metals alone. The computed optical absorption spectra and NMR parameters of the [Li(en)(3)](2) superalkali dimer and the [M(en)(3)(delta+)- center dot M delta-] superalkali-alkali mixed dimers are in good agreement with the aforementioned experimental results, providing further evidence that these may be the dominant species in solution. The latter can also be thought of as an ion pair formed from an alkali metal anion (M-) and solvated cation (M(en)(3)(+)).

First author: Odoh, Samuel O., QM and QM/MM Studies of Uranyl Fluorides in the Gas and Aqueous Phases and in the Hydrophobic Cavities of Tetrabrachion, INORGANIC CHEMISTRY, 50, 3141, (2011)
Abstract: The structural properties and electronic structures of penta-coordinated uranyl complexes belonging to the [UO2Fn(H2O)(5-n)](2-n) series have been studied in the gas and aqueous phases using density functionals with relativistic pseudopotentials and all-electron basis sets in the gas-phase calculations in combination with COSMO in the aqueous phase. In addition, the conformational orientation and structural and electronic properties of [UO2F5](3-) in the hydrophobic cavities of the right-handed coiled-coil (RHCC) protein of tetrabrachion have been determined using the hybrid QM/MM method. Although there is good agreement between the available experimental geometrical parameters and the values obtained in the aqueous phase using pseudopotentials or all-electron basis sets, variation of the uranyl U=O bond with the number of fluoride ligands is only truly captured after the inclusion of five water molecules in the second coordination sphere around the molecules. The docking procedure used in this work shows that there are only two possible orientations of the uranyl group of [UO2F5](3-) embedded in the hydrophobic cavities of the RHCC protein. The two orientations are exclusively along the axes perpendicular to the protein axial channel with no possible orientation of the uranyl group along the axial channel because of both steric effects and interaction with the alkyl chain of the isoleucine residues pointing into the axial channel. In addition, the embedded complex is always positioned nearer to the isoleucine residues at the N-terminal ends of the hydrophobic cavities. Energy analysis, however, reveals that both conformations can only be observed in cavity 2, the largest hydrophobic cavity. The structural and electronic properties of the ligand embedded in this cavity are very similar to those of the gas-phase structure. A comparable study of [Pt(CN)(6)](2-) and the anticancer drug cisplatin, [PtCl2(NH3)(2)], in cavity 2, revealed the existence of just two orientations for the former, similar to the uranyl complex, and multiple orientations for the latter.

First author: Alemayehu, Abraham, A First TDDFT Study of Metallocorrole Electronic Spectra: Copper meso-Triarylcorroles Exhibit Hyper Spectra, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 50, 1857, (2011)
Abstract: The Soret maxima of a number of metallotriarylcorrole derivatives, notably the copper corroles, are exquisitely sensitive to substitutions on the meso phenyl groups. In contrast, the Soret maxima of silver triarylcorroles are essentially invariant with respect to phenyl-group substituents. TDDFT calculations indicate that the substituent sensitivity in the copper case results from significant phenyl-to-metal charge-transfer character in the main peaks of the Soret region. In other words, copper triarylcorroles exhibit so-called hyper spectra. By contrast, the Soret region in the silver case is largely pi-pi* in nature. DFT calculations suggest that the difference in nature of the Soret bands reflects the energy difference between the LUMOs of the copper and silver complexes, which, in both cases, may be described as an antibonding metal(d(x2-y2))-corrole(pi)-based MO. Strong support for this picture comes from electrochemistry: the reduction potentials of silver triarylcorroles are about 0.7-0.8 V more negative than for the analogous copper complexes. In the same vein, the “electrochemical HOMO-LUMO gaps” are ca. 1 eV for the silver corroles and only 0.8 eV for their copper analogues.

First author: Thomas, Kolle E., A Metallocorrole with Orthogonal Pyrrole Rings, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 50, 1865, (2011)
Abstract: In contrast to sterically hindered metalloporphyrins, which are almost always strongly nonplanar, similarly substituted metallocorroles are generally relatively planar. A crystal structure of a copper beta-octakis(trifluoromethyl)-meso-triarylcorrole, however, has revealed a corrole macrocycle with an unprecedented degree of saddling. With the exception of the bipyrrole unit, any two adjacent pyrrole rings are essentially orthogonal to each other. Furthermore, the C-2-symmetric molecular structure is chiral and NMR spectroscopy and DFT calculations suggest that the enantiomers do not interconvert readily. Once resolved, the molecule may provide us with a novel example of an inherently chiral chromophore.

First author: Smalo, Hans S., Field dependence on the molecular ionization potential and excitation energies compared to conductivity models for insulation materials at high electric fields, JOURNAL OF APPLIED PHYSICS, 109, 1865, (2011)
Abstract: The aim is to improve the understanding of high-field phenomena (such as preinception currents/conduction, streamer initiation and propagation) in insulating materials in terms of the molecular properties of the substances involved. In high electric fields, ionization is a likely process, and in all such processes, the ionization potential is an important parameter. A fundamental question is how these processes depend on the electric field, and therefore, based on the interaction between a negative point charge and a molecular cation as modeled by density functional theory, a field-dependent model for the ionization potential is developed. In addition, the first excitation energies as a function of the electric field are calculated using time-dependent density functional theory. It is demonstrated that empirical high-field conduction models for cyclohexane and n-tridecane can be explained in terms of the difference between the ionization potential and the first excitation energy. It is also suggested that the reduction of the ionization potential with electric fields, can help explain how fast-mode streamers propagate.

First author: Bakova, Radka, Relativistic effects in spectroscopy and photophysics of heavy-metal complexes illustrated by spin-orbit calculations of [Re(imidazole)(CO)(3)(phen)](+), COORDINATION CHEMISTRY REVIEWS, 255, 975, (2011)
Abstract: Spin-orbit coupling (SOC) is an essential factor in photophysics of heavy transition metal complexes. By enabling efficient population of the lowest triplet state and its strong emission, it gives rise to a very interesting photophysical behavior and underlies photonic applications such as organic light emitting diodes (OLED) or luminescent imaging agents. SOC affects excited-state characters, relaxation dynamics, radiative and nonradiative decay pathways, as well as lifetimes and reactivity. We present a new photophysical model based on mixed-spin states, illustrated by relativistic spin-orbit TDDFT and MS-CASPT2 calculations of [Re(imidazole)(CO)3(1,10-phenanthroline)](+). An excited-state scheme is constructed from spin-orbit (SO) states characterized by their energies, double-group symmetries, parentages in terms of contributing spin-free singlets and triplets, and oscillator strengths of corresponding transitions from the ground state. Some of the predictions of the relativistic SO model on the number and nature of the optically populated and intermediate excited states are qualitatively different from the spin-free model. The relativistic excited-state model accounts well for electronic absorption and emission spectra of Re-I carbonyl diimines, as well as their complex photophysical behavior. Then, we discuss the SO aspects of photophysics of heavy metal complexes from a broader perspective. Qualitative SO models as well as previous relativistic excited-state calculations are briefly reviewed together with experimental manifestations of SOC in polypyridine and cyclometallated complexes of second- and third row d(6) metals. It is shown that the relativistic SO model can provide a comprehensive and unifying photophysical picture.

First author: Terao, Hiroshi, Ethylene and Ethylene/alpha-Olefin (Co)Polymerization Behavior of Bis(phenoxy-imine)Ti Catalysts: Significant Substituent Effects on Activity and Comonomer Incorporation, ACS CATALYSIS, 1, 254, (2011)
Abstract: The ethylene and ethylene/alpha-olefin (co)polymerization behavior of bis(phenoxy-imine)Ti complexes 1-7 possessing a series of substituents ortho to the phenoxy O’s (ortho substituents 1, Pr-i; 2, cyclohexyl; 3, cyclooctyl; 4, cydododecyl; 5, Bu-t; 6, CMe2Ph; 7, Ph) With dried methylaluminoxane activation was investigated. At 50 degrees C, all complexes displayed some of the characteristics of living ethylene polymerization and produced polyethylenes (PEs) with very narrow molecular weight distributions (M-w/M-n 1.08-1.19, M-w 14 900-62 100), albeit under limited conditions. Generally, the Ti complexes with sterically bulkier ortho substituents exhibited higher activities [e.g., 6: activity 93.2 kg of PE/(mol of cat. min)]; the ortho substituents with quaternary alpha-c atoms attached to the phenoxy rings, providing higher activities than those with tertiary alpha-C atoms on the basis of the steric bulk of the entire ortho substituent To our surprise, complex 7 incorporating an ortho phenyl group displayed the highest activity and formed the highest-molecular-weight PE [activity 230 kg of PE/(mol of cat. min), M-w 456 000], demonstrating the beneficial effects of the ortho phenyl group. Conversely, as to ethylene/propylene copolymerization, an increase in the steric bulk of the ortho substituent resulted in reduced activity for complexes Sand 6 having quaternary alpha-C atoms, although the increase led to enhanced activity for complexes 1-4 having tertiary alpha-C atoms. In addition, complexes 1-4 displayed far higher propylene incorporation (25.5-26.4 mol %) than complexes Sand 6 (6.3 and 4.2 mol %). Again, complex 7 with the ortho phenyl group displayed exceptional behavior and had the highest copolymerization activity coupled with the highest propylene incorporation (38.8 mol %). It should be noted that a wide range of propylene incorporation (4.2-38.8 mol %) was achieved with complexes 1-7 under identical conditions. Moreover, for ethylene/1-hexene and ethylene/1-decene copolymerizations, complexes 4 (cyclododecyl) and 7 (phenyl) achieved high comonomer incorporation while maintaining high catalytic efficiency.

First author: Vijayakumar, M., Towards understanding the poor thermal stability of V5+ electrolyte solution in Vanadium Redox Flow Batteries, JOURNAL OF POWER SOURCES, 196, 3669, (2011)
Abstract: The V5+ electrolyte solution from Vanadium Redox Flow Batteries was studied by variable temperature O-17 and V-51 Nuclear Magnetic Resonance (NMR) spectroscopy and density functional theory (DFT) based computational modeling. It was found that the V5+ species exist as hydrated penta co-ordinated vanadate ion, i.e. [VO2(H2O)(3)](1+). This hydrated structure is not stable at elevated temperature and change into neutral H3VO4 molecule via a deprotonation process and subsequently leading to the observed V2O5 precipitation in Vs electrolyte solutions.

First author: Babashkina, Maria G., Intramolecular hydrogen bonding controls 1,3-N,S- vs. 1,5-S,S ‘-coordination in Ni-II complexes of N-thiophosphorylated thioureas RNHC(S)NHP(S)(OiPr)(2), DALTON TRANSACTIONS, 40, 3142, (2011)
Abstract: Reaction of the deprotonated N-thiophosphorylated thioureas RNHC(S)NHP(S)(OiPr)(2) (R = Ph, HLI; 2-MeC6H4-, HLII; 2,6-Me2C6H3-, HLIII; 2,4,6-Me3C6H2-, HLIV; Me-, HLV) with Ni-II leads to complexes of the formula [NiL2I-V]. The molecular structures of the thioureas HLII-V and the complexes [NiL2II-V] in the solid were elucidated by single-crystal X-ray diffraction analysis. In the complexes, the metal is found to be in a square planar trans-N2S2 ([NiL2II-IV]) environment formed by the C=S sulfur atoms and the P-N nitrogen atoms, or in a square planar trans-S2S'(2) ([NiL2V]) environment formed by the C=S and P=S sulfur atoms of two deprotonated ligands. DFT calculations confirmed that the [Ni(LII-IV-N,S)(2)] isomers are more stable (by 16-21 kcal mol(-1)) than the corresponding [Ni(LII-IV-S,S’)(2)] conformers. The main reason for higher stability of the 1,3-N,S vs. 1,5-S,S’ isomers is the formation of intramolecular N-H center dot center dot center dot S=P hydrogen bonds. In solution the complexes [Ni(LII-V-N,S)(2)] have an exclusive 1,3-N,S coordination, while the compound [Ni(L-I-N,S)(2)] exhibits two isomers in the H-1 and P-31 NMR spectra. The major species is assigned to the 1,3-N,S coordinated isomer, while the minor (similar to 25%) signals are due to the 1,5-S,S’ isomer. UV-Vis spectroscopic results are in line with this. The electrochemical measurements reveal reversible one-electron reduction and irreversible oxidations, both assigned to ligand-centred processes.

First author: Chong, Delano P., Density functional theory study of the electron spectra of formamide vapor, JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA, 184, 164, (2011)
Abstract: The ionization and excitation spectra of the valence and core electrons of formamide in the gas phase are studied with density functional theory. The calculated ionization energies of both valence and core electrons agree very well with experiment, with an average absolute deviation of only 0.1 eV from experiment for all twelve MOs, and confirm the nonplanarity of formamide. The theoretical valence-electron absorption spectrum also agrees well with experiment. However, the inner-shell excitation spectra are not as well reproduced by the present calculations and require further study.

First author: Garcia-Fernandez, P., Impurities bound to vacancies in insulators: Electronic relaxation and physical properties of the Cr3+-V-M model center in KMF3 (M = Mg, Zn), PHYSICAL REVIEW B, 83, 164, (2011)
Abstract: This work is aimed at gaining a better insight into the influence of a close vacancy, V, on the properties of impurities in insulating materials. To achieve this goal the Cr3+ – V-M model center formed in KMF3 ( M = Mg, Zn) fluoroperovskites has been explored in detail by means of ab initio calculations on clusters involving up to 87 ions. It is shown that the presence of the M2+ vacancy, V-M, induces a significant structural relaxation on the CrF63- cubic complex which cannot be fully understood assuming that ions were rigid spheres that could not be polarized. Thus, although V-M forces all the ligands to move away, the Cr3+ – F- distance corresponding to the furthest ligand, F-far, is found to be slightly higher than that for the closer equatorial ions. This unexpected fact is shown to be due to the electronic relaxation also induced by V-M on the CrF63- complex, causing a charge of 0.2e to be transferred from the closest ligand to V-M, F-next, mainly to F-far, and, to a lesser extent, to any equatorial ligand. This transfer of charge is mainly accomplished through orbitals lying in planes containing the C-4 axis. In spite of these changes due to the vacancy, the (4)A(2g) -> T-4(2g) optical transition is found to be weakly altered, a fact that concurs with available experimental data and whose origin is discussed. In contrast, electron paramagnetic resonance parameters such as gyromagnetic or superhyperfine tensors, which do depend on the electronic density around a point of the CrF63- complex, are shown to be particularly sensitive to the electronic relaxation induced by V-M. In particular, the present study explains that the dominant component of the superhyperfine tensor for the F-next ligand is clearly higher than that for F-far, in agreement with experimental data. The relevance of the present results for understanding the electronic properties of other systems involving vacancies is also discussed. Some results on the Cr3+ – Li+ center formed in KMgF3 are also discussed for comparison.

First author: Neugebauer, Johannes, Theoretical Spectroscopy of Astaxanthin in Crustacyanin Proteins: Absorption, Circular Dichroism, and Nuclear Magnetic Resonance, JOURNAL OF PHYSICAL CHEMISTRY B, 115, 3216, (2011)
Abstract: The bathochromic shift (> 0.5 eV) in the absorption spectrum of the carotenoid astaxanthin upon incorporation into crustacyanin proteins is investigated. Several previously suggested explanations are tested and assessed by direct comparison to experimental absorption and circular dichroism spectra. We investigate the effect of extended models for the protein binding pocket, which results in only small contributions to the total shift. The possible explanation in terms of protonated histidine residues interacting with the astaxanthin molecules is analyzed by calculation of nuclear magnetic resonance chemical shifts. The results indicate that such a protonation is unlikely. In addition, we show that excitonic couplings are too weak to explain the red shift in the absorption spectrum, but the resulting intensity distribution actually leads to a blue shift of the major absorption peak. These findings are corroborated by a comparison of the theoretical and experimental circular dichroism spectra. We analyze changes in the relative orientation of the two astaxanthin molecules present in beta-crustacyanin, which may lead to increased excitonic coupling and modified intensity distributions.

First author: Shamov, Grigory A., Oxidative Nucleophilic Substitution of Hydrogen in the Sapphyrin Dioxouranium(VI) Complex: A Relativistic DFT Study, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 133, 4316, (2011)
Abstract: A potentially trianionic expanded porphyrin ligand, sapphyrin does not form a 1:1 complex with the uranyl cation. However, in the presence of methanol, a complex of uranyl and meso-methoxy-substituted iso-sapphyrin is formed [Burrel et al. J. Chem. Soc., Chem. Commun. 1991, 24, 1710]. Here we performed a relativistic DFT study on the thermodynamics and the possible mechanism of the reaction. Our results have shown that (1) the reason for the failure of sapphyrin to stabilize its 1:1 uranyl complex is the highly basic character of the trianionic form of ligand that is hard to achieve in solution, (2) a driving force for the reaction lies in the better affinity of the methanol-substituted (and isomerized) ligand dianion to the uranyl cation, compared with the unsubstituted sapphyrin dianion, and (3) for the single-stage synchronous methanol addition pathways explored in this work, there is a path corresponding to noninnocent uranium behavior, via a neutral, triplet U(IV) intermediate complex. However, if the solvation effects were taken into account, this pathway would be unfavorable compared with singlet U(VI) pathways involving anionic intermediate complexes. The later pathway can be described as classical oxidative nucleophilic substitution of hydrogen in an aromatic system.

First author: Huebner, Ralph, Reversible Intramolecular Single-Electron Oxidative Addition Involving a Hemilabile Noninnocent Ligand, ORGANOMETALLICS, 30, 1414, (2011)
Abstract: Using the noninnocent ligand Q[= 4,6-di-tert-butyl-(2-methylthiophenylimino)-o-berizoquinone] with a thioether group as potential coordination function, it has been possible to substantiate a single-electron transfer induced oxidative addition;within the complex [IrCp*Q](0/+) (Cp* = C5Me5) via structural characterization (catecholato -> semiquinonato transition coupled with reversible S -> Ir coordination), via cyclic voltammetry, EPR, and DFT (semiquinone formulation with about 8% Ir participation). The intramolecular rearrangement of the 16-electron precursor [IrCp*Q] triggered by electron removal illuminates the complementary activities of the substrate binding metal and the electron-buffering ligand as was recently employed by Ringenberg et al. in dihydrogen activation (Organometallics 2010, 29, 1956).

First author: Lin, Myat T., Exploring by Pulsed EPR the Electronic Structure of Ubisemiquinone Bound at the Q(H) Site of Cytochrome bo(3) from Escherichia coli with in Vivo C-13-Labeled Methyl and Methoxy Substituents, JOURNAL OF BIOLOGICAL CHEMISTRY, 286, 10105, (2011)
Abstract: The cytochrome bo(3) ubiquinol oxidase from Escherichia coli resides in the bacterial cytoplasmic membrane and catalyzes the two-electron oxidation of ubiquinol-8 and four-electron reduction of O-2 to water. The one-electron reduced semiquinone forms transiently during the reaction, and the enzyme has been demonstrated to stabilize the semiquinone. The semiquinone is also formed in the D75E mutant, where the mutation has little influence on the catalytic activity, and in the D75H mutant, which is virtually inactive. In this work, wild-type cytochrome bo3 as well as the D75E and D75H mutant proteins were prepared with ubiquinone-8 C-13-labeled selectively at the methyl and two methoxy groups. This was accomplished by expressing the proteins in a methionine auxotroph in the presence of L-methionine with the side chain methyl group C-13-labeled. The C-13-labeled quinone isolated from cytochrome bo(3) was also used for the generation of model anion radicals in alcohol. Two-dimensional pulsed EPR and ENDOR were used for the study of the C-13 methyl and methoxy hyperfine couplings in the semiquinone generated in the three proteins indicated above and in the model system. The data were used to characterize the transferred unpaired spin densities on the methyl and methoxy substituents and the conformations of the methoxy groups. In the wild type and D75E mutant, the constraints on the configurations of the methoxy side chains are similar, but the D75H mutant appears to have altered methoxy configurations, which could be related to the perturbed electron distribution in the semiquinone and the loss of enzymatic activity.

First author: Pop, Lucian-Cristian, Relativistic calculations of aminotroponiminate complexes containing group 15 (P, As, Sb, Bi) elements, POLYHEDRON, 30, 841, (2011)
Abstract: The relativistic electronic structure calculations of N,N’-chelated pnictogenium cations containing aminotroponiminate units, (E = P(1), As(2), Sb(3), Bi(4)), have been investigated employing density functional (DF) methods, including spin-orbit relativistic corrections, via the two-component zeroth order regular approximation (ZORA) Hamiltonian. The role of replacement of the pnictogen atom when going down into the 15 group was discussed on the basis of geometrical parameters, Hirshfield charge analyses, OF reactivity indexes. The degree of electronic delocalization into the five- and seven membered rings was estimated via the electron localization function (ELF) and the nuclear independent chemical shifts (NICS) indexes.Our results show an existence of a lack of systems 2-4 to act as donor ligands for the metal complexation, compared with 1, due to the positive charge over the pnictogen atoms besides the lone-pair orbital of the pnictogen atom which lies at low energies from their corresponding reacting HOMO’s. It is also interesting to note some effects over the aromaticity when going down into the 15 group, i.e., the C-5 ring is affected by the change of the pnictogen atom, while the aromaticity on the C-7 ring is not affected, as suggested by the analysis of the ELF, NICS and geometrical parameters.

First author: Schott, Eduardo, Relativistic scalar and spin-orbit density functional calculations of the electronic structure, NICS index and ELF function of the [Re-2(CO)(8)(mu-BiPh)(2)] and [Re-2(CO)(8)(mu-BiPh2)(2)] clusters, POLYHEDRON,30, 846, (2011)
Abstract: Relativistic scalar and spin-orbit density functional calculations of the electronic structure, Nucleus-Independent Chemical Shift (NICS) index and ELF function of the [Re-2(CO)(8)(mu-BiPh)(2)] and [Re-2(CO)(8)(mu-BiPh2)(2)] clusters are reported. We show here that the [Re-2(CO)(8)(mu-BiPh)(2)] cluster has large negative NICS values in the region defined by the Re-Bi-Re-Bi four-membered ring and the ELF function shows significant electron delocalization density in the center of the metallic ring, thus indicating an aromatic cluster. In contrast the Re-Bi-Re-Bi four-membered ring in the [Re-2(CO)(8)(mu-BiPh2)(2)] cluster has negligible paratropic ring currents and the ELF function shows a low-density region within the metallic ring indicating that aromaticity is switched off. However, the phenyl ligands in both clusters show the expected aromatic character.

First author: Ferraro, Franklin, Spin-orbit effects on the optical and magnetic properties of cerium (III) hexahalides,POLYHEDRON, 30, 860, (2011)
Abstract: In this work we study the [CeX6](3-), X = Cl, Br, I octahedral complexes. The DFT geometry optimizations and the molecular properties calculations were performed using the PBE functional and TZ2P basis set through the use of the two-component ZORA Hamiltonian to include the scalar and spin-orbit relativistic effects. The optimized structures were used in the four-component SCF DSW code to calculate the molecular orbital energies and the paramagnetic resonance (g(iso) and A(hfi)) parameters. These results are in agreement with cerium chlorine-elpasolite (Cs2NaCeCl6) experimental studies. Experimentally, the ground state span the Gamma(7u) symmetry in octahedral geometry, and the excited states give rise to four “4f-4f” type transitions and three “4f-5d” type transitions. The correct descriptions of such transitions are only possible by calculations which include spin-orbit coupling effects, such as, the four-component Dirac equation or its two-component ZORA approximation. Such results confirm the need to include relativistic effects in the calculations of optical and magnetic properties in these lanthanide complexes. These results are in agreement with the spectrochemical series, in which the effect of the ligands follows the usual order: CL- > Br- > I-.

First author: Pietrzyk, Piotr, Spin Ground State and Magnetic Properties of Cobalt(II): Relativistic DFT Calculations Guided by EPR Measurements of Bis(2,4-acetylacetonate)cobalt(II)-Based Complexes, JOURNAL OF PHYSICAL CHEMISTRY A, 115, 2316, (2011)
Abstract: The spin ground state of the core ion and structure of the bis(2,4-acetylacetonate)cobalt(II) model complex and its synthetic aqua and ethanol derivatives, Co(acac)(2)L-n, (L = EtOH, H2O), were examined by means of density functional theory (DFT) calculations supported by electron paramagnetic resonance (EPR) measurements. Geometry optimizations were carried out for low-spin (doublet) and high-spin (quartet) states. For the Co(acac)(2) complex two possible conformations, a square-planar and a tetrahedral one, were taken into account. For all structures relative energies were calculated with both “pure” and hybrid functionals. The calculated data were complemented with the results of the EPR investigations carried out at liquid helium temperature, allowing for definite assignment of the high spin state for the Co(acac)(2)-(EtOH)(2) complex. However, because of the unresolved spectral features, only effective g-values could be assessed, whereas the zero field splitting parameters (ZFS) were calculated by means of the spin orbit mean field (SOMF) relativistic DFT method for which direct spin spin (SS) and spin orbit coupling (SOC) contributions were quantified.

First author: Su, Jing, Uranyl-Glycine-Water Complexes in Solution: Comprehensive Computational Modeling of Coordination Geometries, Stabilization Energies, and Luminescence Properties, INORGANIC CHEMISTRY, 50, 2082, (2011)
Abstract: Comprehensive computational modeling of coordination structures, thermodynamic stabilities, and luminescence spectra of uranyi-glycine-water complexes [UO2(Gly)(n)aq(m)](2+) (Gly = glycine, aq = H2O, n = 0-2, m = 0-5) in aqueous solution has been carried out using relativistic density functional approaches. The solvent is approximated by a dielectric continuum model and additional explicit water molecules. Detailed pictures are obtained by synergic combination of 4′ experimental and theoretical data. The optimal equatorial coordination numbers E of uranyl are determined to be five. The energies of several complex conformations z are competitively close to each other. In non-basic solution the most probable complex forms are those with two water ligands replaced by the bidentate carboxyl groups of zwitterionic glycine. The N,O-chelation in non-basic solution is neither entropically nor enthalpically favored. The symmetric and antisymmetric stretch vibrations of the nearly linear O-U-O unit determine the luminescence features. The shapes of the vibrationally resolved experimental solution spectra are reproduced theoretically with an empirically fitted overall linewidth parameter. The calculated luminescence origins correspond to thermally populated, near-degenerate groups of the lowest electronically excited states of (3)Delta(g) and (3)Phi(g), character, originating from (U-O)sigma(u)->,(U-5f)delta(w)phi(u) configurations of the linear [OUO](2+) unit The intensity distributions of the vibrational progressions are consisten: with U-0 bond-length changes around 51/2 pm. The unusually high intensity of the short wavelength foot is explained by near-degeneracy of vibrationally and electronically excited states, and by intensity enhancement through the asymmetric O-U-O stretch mode. The combination of contemporary computational chemistry and experimental techniques leads to a detailed understanding of structures, thermodynamics, and luminescence of actinide compounds, including those with bioligands.

First author: Mitoraj, Mariusz P., Multiple Boron-Boron Bonds in Neutral Molecules: An Insight from the Extended Transition State Method and the Natural Orbitals for Chemical Valence Scheme, INORGANIC CHEMISTRY, 50, 2168, (2011)
Abstract: We have analyzed the character of B=B and B B bonds in the neutral molecules of general form: LHB=BHL (2-L) and LB BL (3-L), for various ancillary ligands L attached to the boron center, based on a recently developed method that combines the extended transition state scheme with the theory of natural orbitals for chemical valence (ETS-NOCV). In the case of molecules with the B=B bond, 2-L, we have included L = PMe3, PF3, PCl3, PH3, C3H4N2=C(NHCH)(2), whereas for molecules containing the BB connection, 3-L, the following ligands were considered L = CO, PMe3, PCl3, (Me2NCH2CH2O)(2)Ge. The results led us to conclude that use of phosphorus ligands leads to strengthening of the B=B bond by 6.4 kcal/mol (for 2-PMe3), by 4.4 (for 2-PF3) and by 9.2 (for 2-PH3), when compared to a molecule developed on the experimental basis, 2-C3H4N2 (Delta E-total = -118.3 kcal/mol). The ETS scheme has shown that all contributions, that is, (i) orbital interaction Delta E-orb, (ii) Pauli repulsion Delta E-Pauli, and (iii) electrostatic stabilization Delta E-elstat are important in determining the trend in the B=B bond energies, Delta E-total. ETS-NOCV results revealed that both sigma(B=B) and pi(B=B) contributions are responsible for the changes in Delta E-orb values. All considered molecules of the type LB BL, 3-L, exhibit a stronger B B bond when compared to a double B=B connection in 2-L (vertical bar Delta E-total vertical bar lower by 11.8-42.5 kcal/mol, depending on the molecule). The main reason is a lower Pauli repulsion contribution noted for 3-CO, 3-PMe3, and 3-PCl3 molecules. In addition, in the case of 3-PMe3 and 3-PCl3, the orbital interaction term is more stabilizing; however, the effect is less pronounced compared to the drop in the Pauli repulsion term. In all of the systems with double and triple boron boron bonds, the electronic factor (Delta E-orb) dominates over the electrostatic contribution (Delta E-elstat). Finally, the strongest B B connection was found for 3-Ge [L = (Me2NCH2CH2O)(2)Ge], predominantly as a result of the strongest sigma- and pi-contributions, despite the highest destabilization originating from the sizable bulkiness of the germanium-containing ligand. The data on energetic stability of multiple boron boron bonds (relatively high values of bond dissociation energies vertical bar Delta E-total vertical bar), suggest that it should be possible to isolate experimentally the novel proposed systems with double BB bonds, 2-PMe3, 2-PP3, 2-PCl3, and 2-PH3, and those with triple B B connections, 3-PMe3, 3-Ge, and 3-PCl3.

First author: Han, Wen-Ge, DFT Calculations for Intermediate and Active States of the Diiron Center with a Tryptophan or Tyrosine Radical in Escherichia coli Ribonucleotide Reductase, INORGANIC CHEMISTRY, 50, 2302, (2011)
Abstract: Class Ia ribonucleotide reductase subunit R2 contains a diiron active site. In this paper, active-site models for the intermediate X-Trp48(center dot+) and X-Tyr122(center dot), the active Fe(III)Fe(III)-Tyr122(center dot), and the met Fe (III)Fe(II) states of Escherichia coli R2 are studied, using broken-symmetry density functional theory incorporated with the conductor-like screening solvation model. Different structural isomers and different protonation states have been explored. Calculated geometric, energetic, Mossbauer, hyperfine, and redox properties are compared with available experimental data. Feasible detailed structures of these intermediate and active states are proposed. Asp84 and Trp48 are most likely the main contributing residues to the result that the transient Fe(IV)Fe(IV) state is not observed ill wild-type class Ia E. coli R2. Asp84 is proposed to serve as a proton-transfer conduit between the diiron cluster and Tyr122 in both the tyrosine radical activation pathway and the first steps of the catalytic proton-coupled electron-transfer pathway. Proton-coupled and simple redox potential calculations show that the kinetic control of proton transfer to Tyr122(center dot) plays a critical role in preventing reduction from the active Fe(III)Fe(III)-Tyr122(center dot) state to the met state, which is potentially the reason why Tyr122(center dot) in the active state can be stable over a very long period.

First author: Asaduzzaman, Abu Md, Degradation Mechanism of Methyl Mercury Selenoamino Acid Complexes: A Computational Study, INORGANIC CHEMISTRY, 50, 2366, (2011)
Abstract: Density functional theory (DFT) calculations have been carried out on the possible degradation/demethylation mechanism of methyl mercury (CH3Hg+) complexes with free cysteine and seleonocysteine. The binding of CH3Hg+ ions with one (seleno)amino acid is thermodynamically favorable. However, the binding with another acid molecule is a highly unfavorable process. The CH3Hg-(seleno)cysteinate then degrades to bis(methylmercuric)sulphide (selenide for the Se-containing complex) which in turn forms dimethyl mercury and HgS/HgSe, the latter being precipitated out as nanoparticles. The dimethyl mercury interacts with water molecules and regenerates the CH3HgOH precursor. The calculated free energies of formation confirm the thermodynamic feasibility of every intermediate step of the degradation cycle and fully support earlier experimental results. In completing the cycle, one unit of mercury precipitates out from two unit: of sources, and thereby Se antagonizes the Hg toxicity. The degradation of CH3Hg-L-cysteinate is thermodynamically more favorable than the formation of CH3Hg-L-cysteinate. The preferred degradation of the CH3Hg-L-cysteinate suggests that another mechanism for CH3Hg to cross the blood-brain barrier should exist.

First author: Marino, Nadia, Isostructural Pd-II and Pt-II Pyrophosphato Complexes: Polymorphism and Unusual Bond Character in d(8)-d(8) Systems, INORGANIC CHEMISTRY, 50, 2507, (2011)
Abstract: Isostructural, “clamshell”-like, neutral dimeric pyrophosphato complexes of general formula {[M(bipy)](2)(mu-P2O7)) [M = Pd-II (1) or Pt-II (2)] were synthesized and studied through single-crystal X-ray diffraction, IR, P-31 NMR spectroscopy, and MALDI-TOF mass spectrometry. Compound 1 was synthesized through the reaction of palladium(II) acetate, 2,2′-bipyridine (bipy), and sodium pyrophosphate (Na4P2O7) in water. Compound 2 was prepared through two different routes. The first involved the reaction of the Pt-IV precursor Na2PtCl6, bipy, and Na2P2O7 water, followed by reduction in DMF. The second involved the reaction of the Pt-II precursor K2PtCl4, bipy, and Na4P2O7 in water. Both complexes crystallize in the monoclinic chiral space group Cc as hexahydrates, 1 center dot 6H(2)O (1a, yellow crystals) and 2 center dot 6H(2)O (2a, orange crystals), and exhibit a zigzag chain-like supramolecular packing arrangement with short and long intra/intermolecular metal-metal distances [3.0366(3)/4.5401(3) angstrom in 1a; 3.0522(3)/4.5609(3) angstrom in 2a]. A second crystalline phase of the Pt species was also isolated, with formula 2 center dot 3.5H(2)O (2b, deep green crystals), characterized by a dimer-of-dimers (pseudo-tetramer) structural submotif. Green crystals of 2b could be irreversibly converted to the orange form 2a by exposure to air or water, without retention of crystallinity, while a partial, reversible crystal-to-crystal transformation occurred when 2a was dried in vacuo. P-31 NMR spectra recorded for both 1 and 2 at various pHs revealed the occurrence of a fluxional protonated/deprotonated system in solution, which was interpreted as being composed, in the protonated form, of [HO=PO3](+) (P-alpha) and O=PO3 (P-beta) pyrophosphate subunits. Compounds 1 and 2 exhibited two successive one-electron oxidations, mostly irreversible in nature; however, a dependence upon pH was observed for 1, with oxidation only occurring in strongly basic conditions. Density functional theory and atoms in molecules analyses showed that a d(8)-d(8) interaction was present in 1 and 2.

First author: Grimme, Stefan, Cation-Cation “Attraction”: When London Dispersion Attraction Wins over Coulomb Repulsion, INORGANIC CHEMISTRY, 50, 2619, (2011)
Abstract: London forces are omnipresent in nature and relevant to molecular engineering. Proper tuning of their energetic contribution may stabilize molecular aggregates, which would be otherwise highly unstable by virtue of other overwhelming repulsive terms. The literature contains a number of such noncovalently bonded molecular aggregates, of which the “binding mode” has never been thoroughly settled. Among those are the emblematic cationic complexes of tetrakis(isonitrile)rhodium(I) studied by a number of researchers. The propensity of these complexes to spontaneously produce oligomers has been an “open case” for years. For the (inner [(PhNC)(4)Rh](2)(2+), one of the archetypes of such oligomers, density functional theory methods (DFT-D3) and wave function based spin-component-scaled second-order Moller-Plesset perturbation theory (SCS-MP2) quantum chemical calculations indicate that when the eight isonitrile ligands arrange spatially in an optimal pi-stacked fashion, the energy due to dispersion not only overcomes Coulombic repulsion but also the entropy penalty of complex formation. This central role of long-range electron correlation explains such cation cation attractive interactions. Furthermore, the present findings relativize the role of the metal metal “d(8)-d(8)” interactions, which are present on a relatively small scale compared to the effects of the ligands; d(8)-d(8) interactions represent about 10-15% of the total dispersion contribution to the binding energy.

First author: Ilie, Adriana, Metallophilic Bonding and Agostic Interactions in Gold(I) and Silver(I) Complexes Bearing a Thiotetrazole Unit, INORGANIC CHEMISTRY, 50, 2675, (2011)
Abstract: Gold(I) and silver(I) complexes of 1-methyl-5-thio-tetrazole (1) have been prepared and the coordination chemistry of this ligand toward metal-phosphine frameworks has been explored. As indicated by IR and Raman data, ligand 1 is deprotonated and the resulted anion acts as a bidentate (S,N)-tetrazole-5-thiolato unit in the new gold(I) complexes, [Au(SCN4Me)(PPh3)] (2), [{Au(SCN4Me)}(2)(mu-dppm)] (3), and [{Au(SCN4Me)}(2)(mu-dppe)] (4), while it is coordinated only through the sulfur atom as its neutral tetrazole-5-thione form in the silver(I) derivative, [Ag(HSCN4Me)(PPh3)](2)(OTf)(2) (5). Further characterization of the new compounds was performed using multinuclear (H-1, C-13, P-31, F-19) NMR spectroscopy, mass spectrometry, and DSC measurements. Single-crystal X-ray diffraction studies revealed basically linear P-M-S arrangements in complexes 3-5. The bidentate (S,N) coordination pattern results in a T-shaped (S,N)PAu core in 3 and 4, whereas, in 5, a similar coordination geometry is achieved in the dimer association based on S-bridging ligand 1. Herein, weak (C)H center dot center dot center dot Au and (C)H center dot center dot center dot Ag agostic interactions were observed. An intramolecular Au center dot center dot center dot Au contact occurs in 3, while in 4 intermolecular aurophilic bonds lead to formation of a chain polymer. An intermolecular Ag center dot center dot center dot Ag contact is also present in the dimer unit of 5. Low-temperature P-31 NMR data for 5 evidenced the presence of monomer and dimer units in solution. Theoretical calculations on model of the complexes 2 and 4 are consistent with the geometries found by X-ray diffraction studies.

First author: Sutton, Andrew D., Regeneration of Ammonia Borane Spent Fuel by Direct Reaction with Hydrazine and Liquid Ammonia, SCIENCE, 331, 1426, (2011)
Abstract: Ammonia borane (H3N-BH3, AB) is a lightweight material containing a high density of hydrogen (H-2) that can be readily liberated for use in fuel cell-powered applications. However, in the absence of a straightforward, efficient method for regenerating AB from dehydrogenated polymeric spent fuel, its full potential as a viable H-2 storage material will not be realized. We demonstrate that the spent fuel type derived from the removal of greater than two equivalents of H-2 per molecule of AB (i.e., polyborazylene, PB) can be converted back to AB nearly quantitatively by 24-hour treatment with hydrazine (N2H4) in liquid ammonia (NH3) at 40 degrees C in a sealed pressure vessel.

First author: Wang, Xuefeng, Matrix Infrared Spectroscopic and Computational Investigations of the Lanthanide-Methylene Complexes CH(2)LnF(2) with Single Ln-C Bonds, JOURNAL OF PHYSICAL CHEMISTRY A, 115, 1913, (2011)
Abstract: Laser-ablated lanthanide metal atoms were condensed with CH2F2 in excess argon at 6 K or neon at 4 K New infrared absorption bands are assigned to the oxidative addition product methylene lanthanide difluorides on the basis of deuterium substitution and vibrational frequency calculations with density functional theory (DFT). Two dominant absorptions in the 500 cm, region are identified as lanthanide fluoride stretching modes for this very strong infrared absorption. The predominantly lanthanide carbon stretching modes follow a similar trend of increasing with metal size and have characteristic 30 cm(-1) deuterium and 14 cm(-1) C-13 isotopic shifts. The electronic structure calculations show that these CH(2)LnF(2) complexes are not analogous to the simple transition and actinide metal methylidenes with metal carbon double bonds that have been investigated previously, because the lanthanide metals (in the +2 or +3 oxidation state) do not appear to form a pi-type bond with the CH2 group. The DFT and ab initio correlated molecular orbital theory calculations predict that these complexes exist as multiradicals, with a Ln-C sigma bond and a single electron on C-2p weakly coupled with f(x) (x = 1 (Ce), 2 (Pr), 3 (Nd), etc.) electrons in the adjacent Ln-4f orbitals. The Ln-C sigma bond is composed of about 15% Ln-5d,6s and 85% C-sp(2) hybrid orbital. The Ln orbital has predominantly 6s and 5d character with more d-character for early lanthanides and increasing amounts of s-character across the row. The Ln F bonds are almost purely ionic. Accordingly, the argon neon matrix shifts are large (13-16 cm(-1)) for the ionic Ln F bond stretching modes and small (similar to 1 cm(-1)) for the more covalent Ln C bond stretching modes.

First author: Huang, Jin-Dou, Simulation of Hole Mobility in alpha-Oligofuran Crystals, JOURNAL OF PHYSICAL CHEMISTRY B, 115, 2140, (2011)
Abstract: We investigated oligofuran (nF) (n = 3, 4, 6) heterocyclic oligomers as p-type organic semiconductor materials, based on quantum chemistry calculations combined with the Marcus Hush electron transfer theory. It was found that 6F single crystal, with a structure similar to that of 6T, possesses high hole-transfer mobility, which is nearly 17 times larger than that of 6T single crystal. In addtion, the ionization potential (IP) value of 6F is about 5.60 eV, that is, slightly smaller than the IP value of 6T (5.74 eV). The relatively small IP values ensure effective hole injection from the source electrode. Considering that 6T and functional oligothiophenes are active p-type semiconducting materials widely used in organic electronic devices, nFs and nF-based molecules have the potential to be developed as potential high efficiency p-type organic semiconducting materials.

First author: Goedecke, Catharina, When Does Carbonylation of Carbenes Yield Ketenes? A Theoretical Study with Implications for Synthesis, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 133, 3557, (2011)
Abstract: Quantum-chemical calculations using DFT and ab initio methods have been carried out for 32 carbenes RR`C which comprise different classes of compounds and the associated ketenes RR`C=C=O. The calculated singlet-triplet gaps Delta ES-T of the carbenes exhibit a very high correlation with the bond dissociation energies (BDEs) of the ketenes. An energy decomposition analysis of the RR`C-CO bond using the triplet states of the carbene and CO as interacting fragments supports the assignment of Delta ES-T as the dominant factor for the BDE but also shows that the specific interactions of the carbene may sometimes compensate for the S/T gap. The trend of the interaction energy Delta E-int values is mainly determined by the Pauli repulsion between the carbene and CO. The stability of amino-substituted ketenes strongly depends on the destabilizing conjugation between the nitrogen lone-pair orbital and the ketene double bonds. There is a ketene structure of the unsaturated N-heterocyclic carbene parent compound NHC1 with CO as a local energy minimum on the potential-energy surface. However, the compound NHC1-CO is thermodynamically unstable toward dissociation. The saturated homologue NHC2-CO has only a very small bond dissociation energy of D-e = 3.2 kcal/mol. The [3]ferrocenophanetype compound FeNHC-CO has a BDE of D-e = 16.0 kcal/mol.

First author: Stuurman, Nomampondomise F., Characterization of [Rh(PhCOCHCOCH2CH2CH3)(CO)(2)] by X-ray crystallography, a computational and a statistical study, POLYHEDRON, 30, 660, (2011)
Abstract: [Rh(PhCOCHCOCH2CH2CH3)(CO)(2)] is characterised by crystallographic and density functional theory computational methods. The experimental structure is compared to the calculated structure, as well as to the structurally similar compound [Rh(PhCOCHCOCH2CH3)(CO)(2)] using root-mean-square calculations and a half-normal probability plot analyses.

First author: Trueba, A., Spectrochemical Series and the Dependence of Racah and 10Dq Parameters on the Metal-Ligand Distance: Microscopic Origin, JOURNAL OF PHYSICAL CHEMISTRY A, 115, 1423, (2011)
Abstract: The origin of the spectrochemical series and the different dependence of crystal-field splitting (10Dq) and Racah parameters on the metal-ligand distance, R, is explored through ab initio calculations on Cr3+-doped K2NaScF6, Cs2NaYCl6, Cs2NaYBr6, and Cs2NaYI6 lattices. For this purpose both periodic and cluster calculations have been performed. An analysis of ab initio results proves that 10Dq values mostly come from the small admixture of deep ills ligand orbitals present in the antibonding e(g)(similar to x(2)-y(2),3z(2)-r(2)) level and not from the dominant covalency with valence n(L)p ligand orbitals, which is actually responsible for the reduction of Racah parameters. This study thus reveals the microscopic origin of the stronger dependence upon R of 10Dq when compared to that observed for Racah parameters, thus explaining why electronic transitions which are 10Dq-independent give rise to sharp optical bands. As a salient feature, while the covalency with n(L)p levels increases significantly on passing from CrF63- to CrI63-, the n(L)s admixture in e(g) is found to be practically unmodified This fact helps to understand the progressive decrease of 10Dq through the series of CrF63-, CrCl63-, CrBr63-, and CrI63- complexes embedded in the corresponding host lattices when compared at the corresponding equilibrium distance at zero pressure. The growing importance of the n(L)s admixture is well-depicted using deformation density diagrams on passing from the ground state (4)A(2)(t(2g)(3)) to the T-4(2)(t(2g)(2)e(g)) excited state depicted at several R values.

First author: Li, Fang-Fang, Reactivity of Metallic Nitride Endohedral Metallofullerene Anions: Electrochemical Synthesis of a Lu3N@I-h-C-80 Derivative, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 133, 2760, (2011)
Abstract: Electrochemically generated Lu3N@I-h-C-80 dianions react with the electrophile, PhCHBr2, to produce a methano derivative of Lu3N@I-h-C-80(CHC6H5) (1) with high regioselectivity. The compound was characterized by MALDI-TOF, NMR, and UV-vis-NIR absorption spectroscopy. Electrochemical characterization of this Lu3N@I-h-C-80(CHC6H5) derivative showed the typical irreversible reductive behavior of the pristine Lu3N@I-h-C-80, similar to those observed for Bingel adducts of Lu3N@Ih-C80. Using the same conditions, the reaction between Sc3N@I-h-C-80 dianions and PhCHBr2 was conducted for comparison. Unexpectedly, no nucleophilic reaction was observed, indicating that Sc3N@I-h-C-80 dianions are not reactive toward the electrophile. Theoretical studies for both dianionic Lu3N@T-h-C-80 and Sc3N@I-h-C-80 showed that the HOMO is more highly localized on the fullerene cage for [Lu3N@I-h-C-80](2-) and more localized on the inside cluster for [Sc3N@I-h-C-80](2-), providing an explanation for the drastically different reactivities observed.

First author: Pro, Tiziana, From Atomistic to Device Level Investigation of Hybrid Redox Molecular/Silicon Field-Effect Memory Devices, IEEE TRANSACTIONS ON NANOTECHNOLOGY, 10, 275, (2011)
Abstract: In this paper, an extensive investigation of hybrid molecular/Si field-effect memories is presented, where redox ferrocene (Fc) molecules play the role of the memory charge storage nodes. Engineering of the organic linkers between Fc and Si is achieved by grafting Fc with different linker lengths. The study shows a clear correlation between results from atomistic computational density functional theory, electrochemical measurements (cyclic voltammetry) and electrical data obtained by a detailed study on capacitors and pseudo-MOS devices. Physical-chemical analyses (atomic force microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy), corroborate the quality of molecular layers on devices.

First author: Senthilnathan, Dhurairajan, Antitumor activity of bent metallocenes: electronic structure analysis using DFT computations, JOURNAL OF MOLECULAR MODELING, 17, 465, (2011)
Abstract: The antitumor activities of bent metallocenes [Cp-M-Cp](2+) (M = Ti, V, Nb, Mo) and complexes of them with guanine, adenine, thymine and cytosine nucleotides have been probed using electronic structure calculations. DFT/BP86 calculations have revealed that the bent metallocene-nucleotide interaction strongly depends on the stability of the hydrolyzed form of the bent metallocene dichloride [Cp2M](2+) species, and in turn the stability of the [Cp2M](2+) species strongly depends on the electronic structure of [Cp2M](2+). Detailed electronic structure and Walsh energy analyses have been carried out for the hydrolyzed forms of four [Cp-M-Cp](2+) (M = Ti, V, Nb, Mo) species to find out why the bent structure is unusually stable. Energy changes that occur during the bending process in frontier molecular orbitals as well as the p(pi)-d(pi) overlap have been invoked to account for the anticipated antitumor activities of these species. The bonding situation and the interactions in bent metallocene-nucleotide adducts were elucidated by fragment analysis. Of the four nucleotides complexed with the four bent metallocenes, adenine and guanine show better binding abilities than the other two nucleotides. Metallocenes of second-row transition metals exhibit better binding with pyrimidine-base nucleotides. In particular, the Lewis acidic bent metallocenes interact strongly with nucleotides. The antitumor activity is directly related to the binding strength of the bent metallocene with nucleotide adducts, and the computed interaction energy values correlate very well with the experimentally observed antitumor activities.

First author: Greer, Brandon J., Characterising Lone-Pair Activity of Lead(II) by Pb-207 Solid-State NMR Spectroscopy: Coordination Polymers of [N(CN)(2)](-) and [Au(CN)(2)](-) with Terpyridine Ancillary Ligands, CHEMISTRY-A EUROPEAN JOURNAL, 17, 3609, (2011)
Abstract: A series of lead(II) coordination polymers containing [N(CN)(2)](-) (DCA) or [Au(CN)(2)](-) bridging ligands and substituted terpyridine (terpy) ancillary ligands ([Pb(DCA)(2)] (1), [Pb-(terpy)(DCA)(2)] (2), [Pb-(terpy){Au(CN)(2)}(2)] (3), [Pb(4′-chloro-terpy){Au(CN)(2)}(2)] (4) and [Pb(4’bromo- terpy)(mu-OH2)(0.5){Au(CN)(2)}(2)] (5)) was spectroscopically examined by solid-state Pb-207 MAS NMR spectroscopy in order to characterise the structural and electronic changes associated with lead(II) lone-pair activity. Two new compounds, 2 and [Pb(4′-hydroxy-terpy){Au(CN)(2)}(2)] (6), were prepared and structurally characterised. The series displays contrasting coordination environments, bridging ligands with differing basicities and structural and electronic effects that occur with various substitutions on the terpyridine ligand (for the [Au(CN)(2)](-) polymers). Pb-207 NMR spectra show an increase in both isotropic chemical shift and span (Omega) with increasing ligand basicity (from delta(iso) = -3090 ppm and Omega = 389 ppm for 1 (the least basic) to delta(iso) = – 1553 ppm and Omega= 2238 ppm for 3 (the most basic)). The trends observed in Pb-207 NMR data correlate with the coordination sphere anisotropy through comparison and quantification of the Pb N bond lengths about the lead centre. Density functional theory calculations confirm that the more basic ligands result in greater p-orbital character and show a strong correlation to the Pb-207 NMR chemical shift parameters. Preliminary trends suggest that Pb-207 NMR chemical shift anisotropy relates to the measured birefringence, given the established correlations with structure and lone-pair activity.

First author: Beuerle, Florian, Optical and Vibrational Properties of Toroidal Carbon Nanotubes, CHEMISTRY-A EUROPEAN JOURNAL, 17, 3868, (2011)
Abstract: Toroidal carbon nanotubes (TCNTs), which have been evaluated for their potential applications in terahertz communication systems, provide a challenge of some magnitude from a purely scientific perspective. A design approach to TCNTs, as well as a classification scheme, is presented based on the definition of the six hollow sections that comprise the TCNT, slicing each of them to produce a (possibly creased) planar entity, and projecting that entity onto a graphene lattice. As a consequence of this folding approach, it is necessary to introduce five-and seven-membered rings as defect sites to allow the fusing together of the six segments into final symmetric TCNTs. This analysis permits the definition of a number of TCNT geometry families containing from 108 carbons up to much larger entities. Based on density functional theory (DFT) calculations, the energies of these structural candidates have been investigated and compared with [60]fullerene. The structures with the larger tube diameters are computed to be more stable than C-60, whereas the smaller diameter ones are less stable, but may still be within synthetic reach. Computational studies reveal that, on account of the stiffness of the structures, the vibrational frequencies of characteristic low-frequency modes decrease more slowly with increasing ring diameter than do the lowest optical excitation energies. It was found that this particular trend is true for the “breathing mode” vibrations when the diameter of the tubes is small, but not for more flexible toroidal nanotubes with larger diameters.

First author: Gryff-Keller, Adam, NMR and DFT calculation study on structures of 2-[2-nitro-4-(trifluoromethyl)benzoyl]-cyclohexane-1,3-dione (NTBC) and its two metabolites isolated from urine of patients suffering from tyrosinemia type I,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, 24, 249, (2011)
Abstract: 2-[2-Nitro-4-(trifluoromethyl)benzoyl]cyclohexane-1,3-dione (NTBC) is an active component of nitisinone, a medicine against tyrosinemia type I. Using H-1, C-13 and F-19 NMR spectroscopy it has been found that in the urine of patients treated with nitisinone two compounds possessing CF3 group are always present. They have been isolated by using TLC technique and identified as 4-hydroxy-2-[2-nitro-4-(trifluoromethyl)benzoyl]cyclohexane-1,3-dione and 5-hydroxy-2-[2-nitro-4-(trifluoromethyl)benzoyl]cyclohexane-1,3-dione, the latter being previously unknown. The constitution, tautomerism and stereochemistry of these compounds have been thoroughly investigated using H-1 and C-13 NMR spectroscopy supported by theoretical calculations. Molecular structures have been optimized using density functional theory (OFT) with PBE1PBE functional and 6-31G* basis set. In NMR parameter calculations, the larger 6-311++G(2d,p) basis set has been used. At both calculation stages, the polarizable continuum model of the solvent has been employed.

First author: Jung, Jaehoon, Gold Behaves as Hydrogen in the Intermolecular Self-Interaction of Metal Aurides MAu4 (M=Ti, Zr, and Hf), CHEMISTRY-AN ASIAN JOURNAL, 6, 868, (2011)
Abstract: We performed density functional calculations to examine the intermolecular self-interaction of metal tetraauride MAu4 (M=Ti, Zr, and Hf) clusters. We found that the metal auride clusters have strong dimeric interactions (2.8-3.1 eV) and are similar to the metal hydride analogues with respect to structure and bonding nature. Similarly to (MH4)(2), the (mu-Au)(3) C-s structures with three three-center two-electron (3c-2e) bonds were found to be the most stable. Natural orbital analysis showed that greater than 96% of the Au 6s orbital contributes to the 3c-2e bonds, and this predominant s orbital is responsible for the similarity between metal aurides and metal hydrides (>99% H 1s). The favorable orbital interaction between occupied Au 6s and unoccupied metal d orbitals leads to a stronger dimeric interaction for MAu4-MAu4 than the interaction for MH4-MH4. There is a strong relationship between the dimeric interaction energy and the chemical hardness of its monomer for (MAu4)(2) and (MH4)(2).

First author: Cozzolino, Anthony F., Parametrization of a Force Field for Te-N Secondary Bonding Interactions and Its Application in the Design of Supramolecular Structures Based on Heterocyclic Building Blocks, CRYSTAL GROWTH & DESIGN, 11, 668, (2011)
Abstract: 1,2,5-Telluradiazole rings have a remarkably strong tendency toward association through Te-N secondary bonding interactions in the solid state. The reproducibility of the bond lengths and angles in the known crystal structures allowed the parametrization of an anharmonic force field to accommodate both the inter- and intramolecular Te-N bonds. The new parameters were tested against published crystal structures and were able to accurately reproduce the experimentally observed geometries. The incorporation of these parameters into a molecular mechanics force field enables the modeling of large and complex structures with significantly less computational effort than Hartree-Fock (HF) or density functional theory (DFT) methods. Simple modifications to the parameter set allowed the modeling of the structures of acyclic tellurium diamides. A series of 4,7-disubstituted benzo-2,1,3-telluradiazoles were modeled to probe the steric barrier of dimerization; only the groups with large spherical bulks such as t-butyl, trimethylsilyl, and adamantyl were able to destabilize the dimers. Modeling based on bifunctional building blocks suggests strategies for the construction of novel two- and three-dimensional supramolecular architectures.

First author: Sancy, Mamie, Optimizing the Electrocatalytic Activity of Surface Confined Co Macrocyclics for the Electrooxidation of Thiocyanate at pH 4, ELECTROANALYSIS, 23, 711, (2011)
Abstract: We have studied the trends in catalytic activity of several Co macrocyclics confined on the surface graphite electrodes for the oxidation of thiocyanate. A plot of log i (at constant E) versus the formal potential of the catalyst gives a volcano correlation, indicating that the Co(II/I) redox potential needs to be tuned, in order to achieve maximum reactivity. Graphite electrodes modified with Co phthalocyanine at pH 4 exhibit linear amperometric response for thiocyanate concentration in the range 10(-7) and 10(-3) M. Theoretical calculations show that electrocatalytic activity (as log i at constant E) plotted versus the energy of the LUMO of the Co complex also gives a volcano correlation.

First author: Pantazis, Dimitrios A., All-Electron Scalar Relativistic Basis Sets for the Actinides, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 7, 677, (2011)
Abstract: Increasing interest in the computational modeling of actinide compounds creates the need for alternative choices when in comes to fine tuning the computational methodology in order to best fit the problem at hand. All-electron scalar relativistic density functional theory can be a useful approach for a variety of actinide systems and would benefit from atomic basis sets geared to that level of theory. In this paper we present segmented all-electron relativistically contracted (SARC) basis sets for the complete actinide series Ac-89-Lr-103, optimized for use with the popular Douglas-Kroll-Hess to the second order and zeroth-order regular approximation scalar relativistic Hamiltonians. The quality of the SARC basis sets is assessed in terms of their intrinsic incompleteness and contraction errors, with respect to total energies, orbital properties, and ionization energies. Calculations on diatomic Ac and Lr molecules confirm that the valence-space construction results in negligible basis set superposition errors. The performance of the basis sets is further evaluated for molecular geometries, vibrational frequencies, and bond dissociation energies in an illustrative study of uranium fluorides UFn (n = 1-6).

First author: Bakken, Vebjorn, Chemisorption on cobalt surfaces: The effect of subsurface rhenium atoms from quantum chemical cluster model calculations, SURFACE SCIENCE, 605, 513, (2011)
Abstract: We have calculated chemisorption energies for different sorbates on cluster models for a number of sites on pure and subsurface rhenium-doped cobalt surfaces. Bonding energies follow the trend water<co<propyl<methyl<hydrogen<hydroxyl, and=”” are=”” in=”” good=”” agreement=”” with=”” experimental=”” results=”” where=”” available.=”” the=”” indicate=”” that=”” for=”” single-bond=”” radicals=”” (hydrogen,=”” alkyl,=”” hydroxyl),=”” rhenium=”” inclusion=”” stabilizes=”” chemisorbed=”” species.=”” further,=”” stabilization=”” leads=”” to=”” a=”” greater=”” number=”” of=”” sites=”” being=”” energetically=”” close=”” most=”” stable=”” ones,=”” possibly=”” enhancing=”” surface=”” mobility=”” hydrogen=”” is=”” less=”” stabilized=”” by=”” substitution=”” compared=”” propyl,=”” indicating=”” possible=”” mechanism=”” yield=”” long-chained=”” hydrocarbons=”” afforded=”” rhenium-doped=”” catalysts.=”” carbon=”” monoxide,=”” conclusive=”” as=”” does=”” not=”” influence=”” chemisorption=”” energies=”” so=”” strongly.<=”” p=””>

First author: Louwen, Jaap N., Computational assessment of the environmental fate, bioaccumulation, and toxicity potential of brominated benzylpolystyrene, TOXICOLOGY MECHANISMS AND METHODS, 21, 183, (2011)
Abstract: Brominated benzylpolystyrene (BrBPS) is a fire safety polymer, which imparts flame retardancy in a variety of styrenic polymers and resins. In this study, the individual components of BrBPS were evaluated using a novel screening process to inform various endpoints relevant for assessing risks to the environment and human health. For this purpose, representative components were created using the B3LYP density functional method to generate the energetically optimal bromine substitution patterns of the parent molecules toluene, ethylbenzene, and cumene. Representative low energy conformations of the components were identified by using repetitive short bursts of Molecular Dynamics, followed by Molecular Mechanics minimization. The resulting structures were energy minimized at the quantum mechanical Becke-Perdew GGA density functional level. Thereafter, octanol:water partition coefficients, maximum molecular lengths, average maximum diameters, and cross-sectional diameters were calculated to inform parameters on environmental fate, bioaccumulation, and mammalian and ecological toxicity. The relevance of these data for informing risk assessment is discussed.

First author: Ruiz, Juan M., Steric Effects on Alkyl Cation Affinities of Maingroup-Element Hydrides, JOURNAL OF COMPUTATIONAL CHEMISTRY, 32, 681, (2011)
Abstract: We have carried out an extensive exploration of gas-phase alkyl cation affinities (ACA) of archetypal anionic and neutral bases across the periodic system using zeroth order regular approximation-relativistic density functional theory at BP86/QZ4P//BP86/TZ2P. ACA values were computed for the methyl, ethyl, i-propyl and t-butyl cations and compared with the corresponding proton affinities (PA). One purpose. of this work is to provide an intrinsically consistent set of values of the 298 K ACA of all anionic (XHn-1-) and neutral bases (XHn) constituted by maingroup-element hydrides of groups 14-17 and the noble gases (group 18) along the periods 1-6. Another purpose is to determine and rationalize the trend in affinity for a cation as the latter varies from proton to t-butyl cation. This undertaking is supported by quantitative bond energy decomposition analyses. Correlations are established between PA and ACA values.

First author: Armangue, Lluis, Nuclear Shieldings with the SSB-D Functional, JOURNAL OF PHYSICAL CHEMISTRY A,115, 1250, (2011)
Abstract: The recently reported SSB-D functional [J. Chem. Phys. 2009, 131, 094103] is used to check the performance for obtaining nuclear magnetic resonance (NMR) shielding constants. Four different databases were studied, which contain a diversity of molecules and nuclear shielding constants. The SSB-D functional is compared with its “parent” functionals (PBE, OPBE), the KT2 functional that was designed specially for NMR applications and the coupled cluster CCSD(T) method. The best performance for the experimentally most-used elements (H-1, C-13) is obtained for the SSB-D and KT2 functionals.

First author: Bandyopadhyay, Indrajit, Structure and Stability of (TiO2)(n), (SiO2)(n), and Mixed TimSin-mO2n [n=2-5, m=1 to (n-1)] Clusters, JOURNAL OF PHYSICAL CHEMISTRY A, 115, 868, (2011)
Abstract: Structures, energetics, and vibrational spectra are investigated for small pure (TiO2)(n), (SiO2)(n), and mixed TimSin-mO2n [n = 2-5, m = 1 to (n – 1)] oxide clusters by density functional theory (DFT). The BP86/ATZP level of theory is employed to obtain constitutional isomers of the oxide clusters. In accordance with previous studies, our calculations show three-dimensional compact structures are preferred for pure (TiO2)(n) with Oxo-stabilized higher hexavalent states, and linear chain structures are favored for pure (SiO2)(n) with tetravalent states. However, the herein theoretically first reported mixed TimSin-mO2n oxide clusters prefer either three-dimensional compact or linear chain structures depending upon the stoichiometry of the compound. Vibrational analysis of the important modes of some highly stable structures is provided. Coupled-cluster single and double excitation (with triples) [CCSD(T)] computed energy gaps for the TiO2 dimers compare well with results from previous study. Excitation energies are computed by use of time-dependent (TD) DFT and equation-of-motion coupled-cluster calculations with singles and doubles (EOM-CCSD) for the most stable isomers.

First author: Takagi, Nozomi, Bonding Analysis of Metal-Metal Multiple Bonds in R3M-M ‘ R-3 (M, M ‘ = Cr, Mo, W; R = Cl, NMe2), INORGANIC CHEMISTRY, 50, 819, (2011)
Abstract: The bonding situation of homonuclear and heteronuclear metal-metal multiple bonds in R3M-M’R-3 (M, M’ = Cr, Mo, W; R = Cl, NMe2) is investigated by density functional theory (DFT) calculations, with the help of energy decomposition analysis (EDA). The M-M’ bond strength increases as M and M’ become heavier. The strongest bond is predicted for the 5d-5d tungsten complexes (NMe2)(3)W-W(NMe2)(3) (D-e = 103.6 kcal/mol) and Cl3W-WCl3 (D-e = 99.8 kcal/mol). Although the heteronuclear molecules with polar M-M’ bonds are not known experimentally, the predicted bond dissociation energies of up to 94.1 kcal/mol for (NMe2)(3)Mo-W(NMe2)(3) indicate that they are stable enough to be isolated in the condensed phase. The results of the EDA show that the stronger R3M-M’R-3 bonds for heavier metal atoms can be ascribed to the larger electrostatic interaction caused by effective attraction between the expanding valence orbitals in one metal atom and the more positively charged nucleus in the other metal atom. The orbital interaction reveal that the covalency of the homonuclear and heteronuclear R3M-M’R-3 bonds is due to genuine triple bonds with one sigma- and one degenerate pi-symmetric component. The metal-metal bonds may be classified as triple bonds where pi-bonding is much stronger than sigma-bonding; however, the largest attraction comes from the quasiclassical contribution to the metal-metal bonding. The heterodimetallic species show only moderate polarity and their properties and stabilities are intermediate between the corresponding homodimetallic species, a fact which should allow for the experimental isolation of heterodinuclear species. CASPT2 calculations of Cl3M-MCl3 (M = Cr, Mo, W) support the assignment of the molecules as triply bonded systems.

First author: Soldatova, Alexandra V., Near-Infrared-Emitting Phthalocyanines. A Combined Experimental and Density Functional Theory Study of the Structural, Optical, and Photophysical Properties of Pd(II) and Pt(II) alpha-Butoxyphthalocyanines, INORGANIC CHEMISTRY, 50, 1135, (2011)
Abstract: The structural, optical, and photophysical properties of 1,4,8,11,15,18,22,25-octabutoxyphthalocyaninato-palladium-(II), PdPc(OBu)(8), and the newly synthesized platinum analogue PtPc(OBu)(8) are investigated combining X-ray crystallography, static and transient absorption spectroscopy, and relativistic zeroth-order regular approximation (ZORA) Density Functional Theory (DFT)/Time Dependent DFT (TDDFT) calculations where spin-orbit coupling (SOC) effects are explicitly considered. The results are compared to those previously reported for NiPc(OBu)(8) (J. Phys. Chem. A 2005, 109, 2078) in an effort to highlight the effect of the central metal on the structural and photophysical properties of the group 10 transition metal octabutoxyphthalocyanines. Different from the nickel analogue, PdPc(OBu)(8) and PtPc(OBu)(8) show a modest and irregular saddling distortion of the macrocycle, but share with the first member of the group similar UV-vis spectra, with the deep red and intense Q-band absorption experiencing a blue shift down the group, as observed in virtually all tetrapyrrolic complexes of this triad. The blue shift of the Q-band along the MPc(OBu)(8) (M = Ni, Pd, Pt) series is interpreted on the basis of the metal-induced electronic structure changes. Besides the intense deep red absorption, the title complexes exhibit a distinct near-infrared (NIR) absorption due to a transition to the double-group 1E (pi,pi(star)) state, which is dominated by the lowest single-group E-3 (pi,pi(star)) state. Unlike NiPc(OBu)(8), which is nonluminescent, PdPc(OBu)(8) and PtPc(OBu)(8) show both deep red fluorescence emission and NIR phosphorescence emission. Transient absorption experiments and relativistic spin orbit TDDFT calculations consistently indicate that fluorescence and phosphorescence emissions occur from the S-1(pi,pi(star)) and T-1(pi,pi star) states, respectively, the latter being directly populated from the former, and the triplet state decays directly to the S-0 surface (the triplet lifetime in deaerated benzene solution was 3.04 mu s for Pd and 0.55 mu s for Pt). Owing to their triplet properties, PdPc(OBu)(8) and PtPc(OBu)(8) have potential for use in photodynamic therapy (PDT) and are potential candidates for NIR light emitting diodes or NIR emitting probes.

First author: Huang, Wenliang, Transmetalation Reactions of a Scandium Complex Supported by a Ferrocene Diamide Ligand, INORGANIC CHEMISTRY, 50, 978, (2011)
Abstract: Efforts to transfer to aluminum the heterocyclic ligand of a ring-opened imidazole scandium complex, which was previously reported, are presented. A ring-opened imidazole aluminum compound was formed at 50 degrees C and characterized as a trialuminum complex. At high temperature (85 degrees C), the formation of an unusual scandium/aluminum methylidene was observed. The reaction products were characterized by standard spectroscopic techniques and X-ray crystallography. Density functional theory calculations were used to understand the electronic structure of the scandium/aluminum methylidene complex.

First author: Mahadevi, A. Subha, A Theoretical Study on Interaction of Cyclopentadienyl Ligand with Alkali and Alkaline Earth Metals, JOURNAL OF PHYSICAL CHEMISTRY B, 115, 703, (2011)
Abstract: Ab initio and density functional theory calculations are performed on half-sandwich (M-Cp) and sandwich (Cp-M-Cp) complexes of alkali and alkaline earth metals (M = Li, Na, K, Mg, and Ca) with cyclopentadienyl ligand (Cp). A comparison of dissociation energies demonstrates the ease of dissociation of the complex as ions in solvent phase and preference for dissociation as radicals in gas phase. Atoms in molecules analysis is used to characterize this cation-pi interaction based on electron density values obtained at the cage critical point. The contribution of various components to the complex energy is estimated using reduced variational space analysis confirming maximum contribution from the coulomb exchange followed by contributions from polarization and charge transfer components of cyclopentadienyl ligand.

First author: Martin-Diaconescu, Vlad, Electronic structure of S-nitrosothiols from sulfur K-edge X-ray absorption spectroscopy, CANADIAN JOURNAL OF CHEMISTRY-REVUE CANADIENNE DE CHIMIE, 89, 93, (2011)
Abstract: Sulfur K-edge X-ray absorption spectroscopy (S K-edge XAS) was applied to investigate the electronic structure of primary and tertiary S-nitrosothiols. Our experimental data, supported by density functional calculations, indicate that changes at C-alpha affect the S-nitroso group through both inductive and direct orbital effects. Furthermore, our data are consistent with a weakening of the S-N bond in tertiary S-nitrosothiols as compared to their primary S-nitroso analogues. These results support existing computational models and suggest that the reactivity of S-nitrosothiols is not dominated by the electronics of the S-N bond.

First author: Kaminski, Radoslaw, The Role of the C-H center dot center dot center dot pi Interactions in the Cyclisation Reactions Leading to New Aryl- Bridged Tetraazamacrocyclic Complexes of Copper and Nickel, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 89, 479, (2011)
Abstract: A series of neutral macrocyclic transition metal complexes of Cu-II and Ni-II, with bridging polyether linkers joining them to aromatic fragments, has been synthesised and their crystal and molecular structures have been established by single-crystal X-ray diffraction. These molecules adopt an “equatorial” conformation of the bridge due to formation of C-H center dot center dot center dot pi interactions. Because of these interactions only cyclic products are formed in the S(N)2 reaction. DFT calculations also confirm experimental results.

First author: Liu, Chun-Guang, Bonding Interactions between Nitrous Oxide (N2O) and Mono-Ruthenium Substituted Keggin-Type Polyoxometalates: Electronic Structures of Ruthenium/N2O Adducts, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 89, 489, (2011)
Abstract: Density functional theory (DFT) calculations were performed for three ruthenium/nitrous oxide(N2O) adducts, (RuCl2)-Cl-II(eta(1)-N2O)(P-N)(PPh3) {P-N = [o-(dimethylamino) phenyl] diphenylphosphane} (1), Ru-II(eta(1)-N2O)(TMP)(THF) (TMP = dianion of tetramesitylporphyrin, THF = tetrahydrofuran) (2), and [PW11O39{Ru-II/(eta(1)-N2O/H2O)}](n-) (3). The bonding interactions between the N2O molecule and the metal-ruthenium fragment were determined from the energy-decomposition analysis (EDA) and their electronic structures. The results show that the bonding in the ruthenium(II)/N2O adducts 1-3 can be interpreted in terms of weak donor-acceptor interactions between the N2O molecule and the ruthenium(II) center. The geometrical optimization of the polyoxometalate (POM) adduct 3 indicates a bent Ru-NNO linkage, which effectively enhances donor-acceptor interactions with the quasi pi-symmetry orbital. The mono-ruthenium(II) substituted Keggin-type POM adduct 3 is a potential reagent for the activation of the N2O molecule because of the strong Ru-NNO bond and the significant RuNN-O pi*-antibonding orbital character relative to adducts 1 and 2, according to our DFT calculations.

First author: Hogben, H. J., Spinach – A software library for simulation of spin dynamics in large spin systems, JOURNAL OF MAGNETIC RESONANCE, 208, 179, (2011)
Abstract: We introduce a software library incorporating our recent research into efficient simulation algorithms for large spin systems. Liouville space simulations (including symmetry, relaxation and chemical kinetics) of most liquid-state NMR experiments on 40+ spin systems can now be performed without effort on a desktop workstation. Much progress has also been made with improving the efficiency of ESR, solid state NMR and Spin Chemistry simulations.Spinach is available for download at http://spindynamics.org.

First author: Liu Kun, Probing the distorted wave effects in (e, 2e) reaction for the outer valence orbitals of ferrocene,ACTA PHYSICA SINICA, 60, 179, (2011)
Abstract: The binding energy spectrum and electron momentum spectra of outer valence orbitals of ferrocene have been obtained by using our high efficiency electron momentum spectrometer at two different impact energies of 600 eV and 1500 eV. The theoretical momentum profiles of outer valence orbitals of ferrocene for the eclipsed and staggered conformations have been calculated by non-relativistic and scalar relativistic density functional methods. It was found that the outer valence orbitals in the eclipsed conformation are in one-to-one correspondence with the ones in the staggered conformation, and there is little difference between theoretical momentum profiles of them. In addition, it was found that relativistic effects have little influence on the momentum distributions of outer valence orbital of ferrocene. Strong distorted wave effect in the low momentum region related to the outer valence orbitals were observed, Which is due to that those orbitals are mainly composed of Fe 3d atomic orbital.

First author: Lukose, Binit, The Structure of Layered Covalent-Organic Frameworks, CHEMISTRY-A EUROPEAN JOURNAL, 17, 2388, (2011)
Abstract: Covalent-Organic Frameworks (COFs) are a new family of 2D and 3D highly porous and crystalline materials built of light elements, such as boron, oxygen and carbon. For all 2D COFs, an AA stacking arrangement has been reported on the basis of experimental powder XRD patterns, with the exception of COF-1 (AB stacking). In this work, we show that the stacking of 2D COFs is different as originally suggested: COF-1, COF-5, COF-6 and COF-8 are considerably more stable if their stacking arrangement is either serrated or inclined, and layers are shifted with respect to each other by similar to 1.4 angstrom compared with perfect AA stacking. These structures are in agreement with to date experimental data, including the XRD patterns, and lead to a larger surface area and stronger polarisation of the pore surface.

First author: Fan, Jing, A Theoretical Study on the Exciton Circular Dichroism of Propeller-like Metal Complexes of Bipyridine and Tripodal Tris(2-pyridylmethyl)amine Derivatives, CHIRALITY, 23, 155, (2011)
Abstract: Time-dependent density functional theory (TD-DFT) has been employed to simulate the circular dichroism (CD) spectra of bipyridyl ruthenium(II) complexes as well as zinc(II) and copper(II) complexes containing tris(2-pyridylmethyl) amine (TPA) derivatives. A qualitative model is used to account for the mechanism by which the bis- and tris-bipyridine complexes (or analogous systems) exhibit exciton CD. The model is further used to predict the sign of the exciton CD bands. The predictions are in agreement with experiment and DFT calculations. A comprehensive analysis is presented of the subtle differences in the CD spectra of this series of related complexes. Chirality 23:155-166, 2011.

First author: Ganesan, Aravindhan, Intramolecular Interactions of L-Phenylalanine: Valence Ionization Spectra and Orbital Momentum Distributions of its Fragment Molecules, JOURNAL OF COMPUTATIONAL CHEMISTRY, 32, 525, (2011)
Abstract: Intramolecular interactions between fragments of L-phenylalanine, i.e., phenyl and alaninyl, have been investigated using dual space analysis (DSA) quantum mechanically. Valence space photoelectron spectra (PES), orbital energy topology and correlation diagram, as well as orbital momentum distributions (MDs) of L-phenylalanine, benzene and L-alanine are studied using density functional theory methods. While fully resolved experimental PES of L-phenylalanine is not yet available, our simulated PES reproduces major features of the experimental measurement. For benzene, the simulated orbital MDs for 1e(1g) and 1a(2u) orbitals also agree well with those measured using electron momentum spectra. Our theoretical models are then applied to reveal intramolecular interactions of the species on an orbital base, using DSA. Valence orbitals of L-phenylalanine can be essentially deduced into contributions from its fragments such as phenyl and alaninyl as well as their interactions. The fragment orbitals inherit properties of their parent species in energy and shape (ie., MDs). Phenylalanine orbitals show strong bonding in the energy range of 14-20 eV, rather than outside of this region. This study presents a competent orbital based fragments-in-molecules picture in the valence space, which supports the fragment molecular orbital picture and building block principle in valence space. The optimized structures of the molecules are represented using the recently developed interactive 3D-PDF technique.

First author: Courcot, Blandine, Optimization of a Molecular Mechanics Force Field for Polyoxometalates Based on a Genetic Algorithm, JOURNAL OF COMPUTATIONAL CHEMISTRY, 32, 240, (2011)
Abstract: A stochastic technique based on genetic algorithms was implemented to develop new force fields by optimizing molecular mechanics (MM) parameters. These force fields have been optimized for inorganic compounds such as polyoxometalates (POMs) and especially for type-I polymolybdate and polytungstate clusters. Focussing on the methodology of the development of the force fields, they were tested for the prediction of structural parameters, comparing the MM optimized structures with the geometry obtained after an optimization based on density functional theory. Results show that the genetic algorithm converges toward an optimum combination of parameters which successfully reproduces POMs structures with a high degree of accuracy.

First author: Gartia, Manas Ranjan, Metal-Molecule Schottky Junction Effects in Surface Enhanced Raman Scattering,JOURNAL OF PHYSICAL CHEMISTRY A, 115, 318, (2011)
Abstract: We propose a complementary interpretation of the mechanism responsible for the strong enhancement observed in surface enhanced raman scattering (SERS). The effect of a strong static local electric field due to the Schottky barrier at the metal-molecule junction on SERS is systematically investigated. The study provides a viable explanation to the low repeatability of SERS experiments as well as the Raman peak shifts as observed in SERS and raw Raman spectra. It was found that a strong electrostatic built-in field at the metal-molecule junction along specific orientations can result in 2-4 more orders of enhancement in SERS.

First author: Sun, Zhixiang, Quantitative Atomic Force Microscopy with Carbon Monoxide Terminated Tips, PHYSICAL REVIEW LETTERS, 106, 318, (2011)
Abstract: Noncontact atomic force microscopy (AFM) has recently progressed tremendously in achieving atomic resolution imaging through the use of small oscillation amplitudes and well-defined modification of the tip apex. In particular, it has been shown that picking up simple inorganic molecules (such as CO) by the AFM tip leads to a well-defined tip apex and to enhanced image resolution. Here, we use the same approach to study the three-dimensional intermolecular interaction potential between two molecules and focus on the implications of using molecule-modified AFM tips for microscopy and force spectroscopy experiments. The flexibility of the CO at the tip apex complicates the measurement of the intermolecular interaction energy between two CO molecules. Our work establishes the physical limits of measuring intermolecular interactions with scanning probes.

First author: O’Dell, Luke A., Interaction Tensors and Local Dynamics in Common Structural Motifs of Nitrogen: A Solid-State N-14 NMR and DFT Study, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 133, 527, (2011)
Abstract: N-14 solid-state NMR powder patterns have been obtained at high field (21.1 T) using broadband, frequency-swept pulses and a piecewise acquisition method. This approach allowed the electric field gradient (EFG) tensor parameters to be obtained from model organic and inorganic systems featuring spherically asymmetric nitrogen environments (C-Q values of up to ca. 4 MHz). The advantages and limitations of this experimental approach are discussed, and the observation of N-14 T-2 relaxation anisotropy in certain systems is also reported, which can shed light on dynamic processes, allowing motional geometries and jump rates to be probed. In particular, we show that observable effects of dynamics on N-14 spectra can be mediated by modulation of either the EFG tensor or heteronuclear dipolar couplings. It is demonstrated that the QCPMG protocol can be used to selectively enhance certain types of nitrogen environments on the basis of differences in T-2. We also present the results of extensive density functional theory calculations on these systems, which show remarkably good correlation with the experimental results and allow the prediction of tensor orientations, assignment of parameters to crystallographic sites, and a rationalization of the origin of the EFG tensors in terms of contributions from individual molecular orbitals. This work demonstrates that ultra-wideline N-14 solid-state NMR can, under favorable circumstances, be a straightforward, useful, and informative probe of molecular structure and dynamics.

First author: Smith, A. R. G., Relativistic effects in a phosphorescent Ir(III) complex, PHYSICAL REVIEW B, 83, 527, (2011)
Abstract: We compare high field magnetic circular dichroism, absorption, and photoluminescence spectra for Ir(ptz)(3) with time-dependent density functional theory. By gradually turning on the relativistic effects we identify several distinct relativistic effects in the spectra of this complex. We show that relativistic effects must be included to accurately predict the low-temperature spectra. This leads to new insights into the low-lying excitations responsible for the observed phosphorescence, and suggests new avenues to improve the performance of organic light emitting diodes.

First author: Baranoff, Etienne, Cyclometalated Iridium(III) Complexes Based on Phenyl-Imidazole Ligand, INORGANIC CHEMISTRY, 50, 451, (2011)
Abstract: Phenyl-imidazole-based ligands with various substitution patterns have been used as the main ligand for heteroleptic bis-cyclometalated Iridium complexes. Two series of complexes have been prepared and their photophysical and electrochemical properties were studied. The phosphorescence emission maxima range from about 490 to 590 nm, that is, from greenish-blue to orange. The first series is of the form Ir(L)(2)(acac) (L: a phenyl-imidazole based ligand; acac: acetylacetonate). In the first complex, la, L is 1,4,5-trimethyl-2-phenyl-1H-imidazole. Then, methyl groups are replaced with phenyl groups and chlorines are grafted on the cyclometalated phenyl ring. The second series is of the form Ir(4,5-dimethyl-1,2-diphenyl-1H-imidazole)(2)(L-a) (L-a: ancillary ligand being acetylacetonate, acac, N,N-dimethylamir o-picolinate, NPic, picolinate, Pic, or 2-(diphenylphosphino)acetic acid, P). These series show that modifying the substitution pattern on the ligands can alter the photophysical and electrochemical properties of the complexes. Overall, we show that compared to complexes containing phenyl-pyridine ligands, highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) are more delocalized over the entire main ligand in complexes containing phenyl-imidazole. Contrary to expectations, when chlorine atoms are used as strong acceptor substituents on the orthometalated phenyl, a red shift of the emission is observed. This behavior has been rationalized using theoretical calculations on the excited state of the chloro-substituted complex 3a compared to the model 1a.

First author: Engerer, Laura K., Geometric Effects in Olefinic Cation-pi Interactions with Alkali Metals: A Computational Study, JOURNAL OF ORGANIC CHEMISTRY, 76, 42, (2011)
Abstract: Although cation a interactions commonly involve aromatic or heteroaromatic rings as the source of pi-electrons, isolated and nonconjugated olefins are equally effective donors of pi-electron density. Previous comparisons of these pi-electron sources have indicated that the net energy of the binding interactions is not a simple additive function of the number of pi-bonds involved. For instance, the enthalpy of binding (Delta H degrees) of Li+, Na+, or K+ cations to two ethylene molecules or to one benzene molecule is approximately the same, despite the 4:6 ratio of pi-electrons involved. This present density functional theory study indicates that geometric factors can partially account for the proportionally greater interaction energies of olefins, but whether they are symmetrically placed around the cation or grouped on one hemisphere has little effect on the binding energy. Instead, flexible ligands that permit olefinic pi-electrons to be oriented more favorably toward the metal than those in rigid aromatic rings can be correlated with greater bonding. For Li+ complexes, this appears to be an appreciable factor, although it is less significant with Na+ and K+ complexes. For all three cations, stronger polarization interactions with olefins compared to arenes contribute to the strength of cation a interactions involving olefinic pi-bonds.

First author: Biswas, Achintesh Narayan, C(naphthyl)-H bond activation by rhodium: isolation, characterization and TD-DFT study of the cyclometallates, RSC ADVANCES, 1, 1279, (2011)
Abstract: The C1(naphthyl)-H, C2(naphthyl)-H, C3(naphthyl)-H and C8(naphthyl)-H bonds of the naphthyl group present in a group of naphthylazo-29-hydroxyarenes (H2L) have been activated by [Rh(PPh3)(3)Cl] in a toluene medium. Here the cyclometallation is accompanied by metal centered oxidation [Rh(I)-> Rh(III)]. All the resulting cyclometallates [Rh(PPh3)(2)(L)Cl] (2-5) have been isolated in a pure form. The characterization of the cyclometallates [Rh(PPh3()2)(L) Cl] have been done on the basis of spectral (IR, UV-vis, and FAB mass) data. The structures of the representative cyclometallates 2a, 3a, 4a, 4b and 5b have been determined by X-ray diffraction. In all the cyclometallates, rhodium(III) is coordinated to naphthylazo-2′-hydroxyarenes via terdentate C(naphthyl), N(diazene), O(phenolato/naphtholato) donor centers & one chloride ion in a plane along with two axial trans PPh3 molecules. Intermolecular association in the solid state is observed due to C-H center dot center dot center dot pi and pi center dot center dot center dot pi interactions. Compounds show an oxidative response within 0.93 to 1.11 V (vs. SCE) and a reductive response at similar to -1.0 V (vs. SCE). Both the responses are based on the coordinated diazene function and are irreversible in nature, indicating limited stability of the oxidized and reduced species. The electronic structures of selected cyclometallates have been calculated using a TD-DFT model and the simulated spectra are consistent with the observed spectra of those cyclometallates.

First author: Wang, Congzhi, The first nonmetal-centered binuclear sandwich-like complexes based on the tetraatomic species E-4(2-) (E = N, P, As, Sb, Bi) and boron atoms, NEW JOURNAL OF CHEMISTRY, 35, 2527, (2011)
Abstract: The first nonmetal-centered binuclear sandwich-like complexes, B-2(eta(4)-E-4)(2) (E = CMe, N, P, As, Sb, Bi; Me = CH3), have been investigated by density functional theory (DFT) to explore whether the nonmetal element can be at the center to form stable sandwich-like complexes. The stable conformer for each species is the D-4d staggered one, in which there exists strong interaction between the two boron atoms. Natural bonding orbital (NBO) analysis indicates that the boron-boron bonds are all sigma single bonds, which are predicted to be derived mostly from the s and p(z) orbitals of the boron atoms. The boron-boron bond dissociation energies are higher than that of the Zn-Zn bond in the synthesized complex Cp*ZnZnCp* (Cp* = C5Me5; Me = CH3) suggesting that these nonmetal-centered sandwich-like complexes may be synthesized in future experiments. According to the energy decomposition analysis (EDA), the boron-boron bond is much weaker than the boron-ligand bond and the ability of the E-4(2-) ligands to stabilize the boron-boron bonds is in the order of N-4(2-) > P-4(2-) > As-4(2-) > Sb-4(2-) > Bi-4(2-). Nucleus-independent chemical shift (NICS) values reveal that E-4(2-) (E = CMe, N, P, As, Sb) rings of B-2(eta(4)-E-4)(2) exhibit characteristics of pi aromaticity at 1.0 angstrom above the ring center, whereas Bi-4(2-) rings of B-2(eta(4)-Bi-4)(2) possess antiaromaticity. In addition, the differences in the bonding nature between the nonmetal-centered and metal-centered binuclear sandwich-like complexes were also investigated. In these nonmetal-centered complexes B-2(eta(4)-E-4)(2), the interactions between the boron atoms and the E(4)(2-)ligands are more than half covalent, while in the metal-centered binuclear sandwich-like complexes, the metal-ligand interactions are mainly ionic.

Abstract: Our calculations have shown that a series of the studied monosubstituted phenol derivatives containing substituents with different electronic effects on the ortho-, meta- and para-positions, show a direct relationship between the H-abstraction of the hydroxyl groups and the low values of nucleus-independent chemical shift (Delta NICS) activity, and these in turn are related to antioxidant activity, hence are in the lowest values of the enthalpy of dissociation, and this is demonstrated by the values of small Delta NICS. All calculations of bond dissociation enthalpy (BDE) and the criterion of aromaticity (Delta NICS) were calculated using density functional theory (DFT) methods.

First author: Teresa Garland, Maria, Electronic structure and metal-metal communication in (CpM)(2)(as-indacene) and (CpM)(2)(s-indacene) (M = Mn, Fe, Co, Ni) complexes: a DFT investigation, NEW JOURNAL OF CHEMISTRY, 35, 2136, (2011)
Abstract: DFT calculations with full geometry optimization have been performed on the series (CpM)(2)(as-indacene) and (CpM)(2)(s-indacene) (M = Mn, Fe, Co, Ni), as well as on the cations of the Fe, Co and Ni complexes. The compounds where M = Fe and Ni (as-indacene series) and M = Mn, Fe and Co (s-indacene series) were found to possess closed-shell ground states. In the mixed-valent cations as well as in the other open-shell species, the degree of metal-metal communication and the participation of the ligand into the spin density were evaluated. In general, the larger the total electron number, the larger the metal-metal communication and ligand participation to the frontier orbitals.

First author: Fontaine, Bruno, Octahedral niobium cluster-based solid state halides and oxyhalides: effects of the cluster condensation via an oxygen ligand on electronic and magnetic properties, NEW JOURNAL OF CHEMISTRY, 35, 2245, (2011)
Abstract: The influences of an oxygen ligand on the structural, magnetic and electronic properties of octahedral niobium cluster-based oxides and oxychlorides are reported. The Nb-6 metal cluster is edge-bridged by twelve inner ligands and additionally bonded to six apical ligands to form (Nb6L12L6a)-L-i units (L = Cl, O) wherein oxygen and chlorine are perfectly ordered. Oxygen favours the interconnection of clusters via double Oi-a/Oa-i bridges in a similar way to the double Si-a/Sa-i bridges found in Chevrel phases based on face capped (Mo6L8L6a)-L-i units. Periodic density functional theory (DFT) calculations confirm that increasing the number of inner oxygen ligands at the expense of chlorine atoms favours the 14 metal-electron (ME) count per octahedral cluster unit. It is also shown that weak interactions occur between neighbouring clusters. Indeed, magnetic measurements performed on A(x)Nb(6)Cl(12)O(2) (A = Rb, x = 0.816(8); A = Cs, x = 1) series containing 15-ME species evidence antiferromagnetic interactions at low temperatures. Broken-symmetry DFT calculations of exchange parameters within spin dimer analysis confirm the experimental results.

First author: Liao, Meng-Sheng, FeP(Im)-AB bonding energies evaluated with a large number of density functionals (P = porphine, Im = imidazole, AB = CO, NO, and O-2), MOLECULAR PHYSICS, 109, 2035, (2011)
Abstract: Sixty-four density functionals, ranging from GGA, meta-GGA, hybrid GGA to hybrid meta-GGA, were tested to evaluate the FeP(Im)-AB bonding energies (E-bond) in the heme model complexes FeP(Im)(AB) (P porphine, Im imidazole, AB CO, NO, and O-2). The results indicate that an accurate prediction of E-bond for the various ligands to heme is difficult with the DFT methods; usually, a functional successful for one system does not perform equally well for other system(s). Relatively satisfactory results for the various FeP(Im)-AB bonding energies are obtained with the meta-GGA functionals BLAP3 and Bm tau 1; they yield E-bond values of ca. 1.1, 1.2, and 0.4 eV for AB CO, NO, and O-2, respectively, which are in reasonable agreement with experimental data (0.78-0.85 eV for CO, 0.99 eV for NO, and 0.44 – 0.53 eV for O-2). The other functionals show more or less deficiency for one or two of the systems. The performances of the various functionals in describing the spin-state energetics of the five-coordinate FeP(Im) complex were also examined.

First author: Liu, Chun-Guang, Quantum chemical studies on Re-Re quadruple-bonded Keggin-type polyoxometalate ([Re-2(III)(PW11O39)(2)](8-)): Bonding feature and electron spectrum, MOLECULAR PHYSICS, 109, 1851, (2011)
Abstract: Density functional theory (DFT) was employed to calculate the bonding feature, electron spectrum, and redox properties of a dumbbell-shaped polyoxometalate (POM) cluster, [Re-2(III)(PW11O39)(2)](8-). Our DFT calculations confirm that the quadruple bond interaction between two Re-III centers consists of sigma, 2 pi, and delta orbital overlaps, and the strength of the bonding interactions is in the order sigma-bond > pi-bond > delta-bond. Time-dependent (TD) DFT calculations suggest that this cluster possesses one strong and four weak absorption bands between 0.7 and 2.5 eV. Excited state calculations show that the Re-Re bond length increases when one electron of the Re-Re bonding delta orbital is shifted to the Re-Re delta* antibonding orbital. Molecular orbital predictions and spin unrestricted calculations indicate that the two Re atoms form the reduced center. The Re-Re bond length increases in one-and two-electron reduction processes because the Re-Re delta* antibonding orbital becomes occupied. However, these changes in the Re-Re bond length in excitation and reduction processes are not substantial because of the weak delta bond. The substitution effect of the central tetrahedron heteroatom of the POM ligand affects the Re-Re bond length, with the Re-Re distance decreasing with the substitution of X from Al to S, Al (2.345 angstrom) > Si (2.310 angstrom) > P (2.282 angstrom) > S (2.257 angstrom).

First author: Liu, Chun-Guang, TDDFT study on the second-order nonlinear optical properties of a series of mono- and di-nuclear [60] fullerene complexes, COMPUTATIONAL AND THEORETICAL CHEMISTRY, 963, 98, (2011)
Abstract: Time-dependent density functional theory (TDDFT) was employed to study second-order nonlinear optical (NLO) properties of transition metal fullerene complexes with a face to face model. The results show that the ruthenium species possesses the larger second-order NLO response than that of the iron species. Chemical modifications of the fullerene by carbon-carbon bond scission can tune charge transfer character in these complexes, and increase the static first hyperpolarizability. The electronic structure analysis and TDDFT calculations show that the open-cage complex in the ruthenium species possesses low-lying and strong charge transfer transitions, and thus give the largest second-order NLO response.

First author: Majerz, Irena, Geometric Aspects of Aromaticity: Interrelations between Intramolecular Hydrogen Bonds, Steric Effects and pi-Electron De localisation in Nitroanilines, EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, 963, 280, (2011)
Abstract: The influence of intramolecular hydrogen bonds and steric hindrance on distortion from planarity of the benzene ring and its aromaticity is shown for a series of substituted 2,4,6-trinitroanilines. The crystal structure geometry and the geometry optimized at the B3LYP/6-311++G** level are compared with analogues without intramolecular hydrogen bonds. The HOMA index and the parameter Delta P describing the distortion from planarity of the benzene ring were used to characterize the aromacity of the investigated molecules. NBO and AIM analysis were also applied.

First author: Song, Ping, Theoretical investigation of second-order nonlinear optical response – Hexamolybdate as a superior donor over metal carbonyl complexes in the D-pi-A model, CANADIAN JOURNAL OF CHEMISTRY-REVUE CANADIENNE DE CHIMIE, 89, 61, (2011)
Abstract: Density functional theory (DFT) calculations were carried out to investigate the nonlinear optical (NLO) response for the donor-conjugated bridge-accepter (D-pi-A) model of p-nitroaniline (PNA)-hexamolybdate derivatives and PNA-metal-carbonyl complexes. The bond length alternation (BLA) values decrease with lengthening of the pi-conjugated bridge, especially for PNA-hexamolybdate derivatives, which dramatically enhances the NLO response. In addition, the introduction of Mo equivalent to N in PNA-hexamolybdate derivatives is expected to provide a better electron transition channel, consequently generating lower BLA values and an outstanding NLO response compared with PNA-metal-carbonyl complexes. It is shown that the hexamolybdate acts as an electron donor when incorporating metal-carbonyl complexes into one molecule. All these behaviors reflect the superiority of hexamolybdate as a donor moiety in the D-pi-A model for the design of potential NLO materials.

First author: van Dam, Hubertus J. J., Designing a Scalable Fault Tolerance Model for High Performance Computational Chemistry: A Case Study with Coupled Cluster Perturbative Triples, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 7, 66, (2011)
Abstract: In the past couple of decades, the massive computational power provided by the most modern supercomputers has resulted in simulation of higher-order computational chemistry methods, previously considered intractable. As the system sizes continue to increase, the computational chemistry domain continues to escalate this trend using parallel computing with programming models such as Message Passing Interface (MPI) and Partitioned Global Address Space (PGAS) programming models such as Global Arrays. The ever increasing scale of these supercomputers comes at a cost of reduced Mean Time Between Failures (MTBF), currently on the order of days and projected to be on the order of hours for upcoming extreme scale systems. While traditional disk-based check pointing methods are ubiquitous for storing intermediate solutions, they suffer from high overhead of writing and recovering from checkpoints. In practice, checkpointing itself often brings the system down. Clearly, methods beyond checkpointing are imperative to handling the aggravating issue of reducing MTBF. In this paper, we address this challenge by designing and implementing an efficient fault tolerant version of the Coupled Cluster (CC) method with NWChem, using in-memory data redundancy. We present the challenges associated with our design, including an efficient data storage model, maintenance of at least one consistent data copy, and the recovery process. Our performance evaluation without faults shows that the current design exhibits a small overhead. In the presence of a simulated fault, the proposed design incurs negligible overhead in comparison to the state of the art implementation without faults.

First author: Scherer, Wolfgang, The Nature of beta-Agostic Bonding in Late-Transition-Metal Alkyl Complexes,ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 50, 2845, (2011)
Abstract: In the past couple of decades, the massive computational power provided by the most modern supercomputers has resulted in simulation of higher-order computational chemistry methods, previously considered intractable. As the system sizes continue to increase, the computational chemistry domain continues to escalate this trend using parallel computing with programming models such as Message Passing Interface (MPI) and Partitioned Global Address Space (PGAS) programming models such as Global Arrays. The ever increasing scale of these supercomputers comes at a cost of reduced Mean Time Between Failures (MTBF), currently on the order of days and projected to be on the order of hours for upcoming extreme scale systems. While traditional disk-based check pointing methods are ubiquitous for storing intermediate solutions, they suffer from high overhead of writing and recovering from checkpoints. In practice, checkpointing itself often brings the system down. Clearly, methods beyond checkpointing are imperative to handling the aggravating issue of reducing MTBF. In this paper, we address this challenge by designing and implementing an efficient fault tolerant version of the Coupled Cluster (CC) method with NWChem, using in-memory data redundancy. We present the challenges associated with our design, including an efficient data storage model, maintenance of at least one consistent data copy, and the recovery process. Our performance evaluation without faults shows that the current design exhibits a small overhead. In the presence of a simulated fault, the proposed design incurs negligible overhead in comparison to the state of the art implementation without faults.

First author: Bonet, Amadeu, Transition-Metal-Free Diboration Reaction by Activation of Diboron Compounds with Simple Lewis Bases, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 50, 7158, (2011)
Abstract: In the past couple of decades, the massive computational power provided by the most modern supercomputers has resulted in simulation of higher-order computational chemistry methods, previously considered intractable. As the system sizes continue to increase, the computational chemistry domain continues to escalate this trend using parallel computing with programming models such as Message Passing Interface (MPI) and Partitioned Global Address Space (PGAS) programming models such as Global Arrays. The ever increasing scale of these supercomputers comes at a cost of reduced Mean Time Between Failures (MTBF), currently on the order of days and projected to be on the order of hours for upcoming extreme scale systems. While traditional disk-based check pointing methods are ubiquitous for storing intermediate solutions, they suffer from high overhead of writing and recovering from checkpoints. In practice, checkpointing itself often brings the system down. Clearly, methods beyond checkpointing are imperative to handling the aggravating issue of reducing MTBF. In this paper, we address this challenge by designing and implementing an efficient fault tolerant version of the Coupled Cluster (CC) method with NWChem, using in-memory data redundancy. We present the challenges associated with our design, including an efficient data storage model, maintenance of at least one consistent data copy, and the recovery process. Our performance evaluation without faults shows that the current design exhibits a small overhead. In the presence of a simulated fault, the proposed design incurs negligible overhead in comparison to the state of the art implementation without faults.

First author: Castro, Pascal M., SPOs as new ligands in Rh(III) catalyzed enantioselective transfer hydrogenation,CATALYSIS SCIENCE & TECHNOLOGY, 1, 401, (2011)
Abstract: The self-assembly of Secondary Phosphine Oxides (SPOs) into anionic bidentate chelates was used to construct unique systems for metal catalyzed transfer hydrogenation of ketones in isopropanol. Chelating bidentate or tridentate ligands were formed by assembly of secondary phosphine oxides through hydrogen bonding in the presence of rhodium trichloride as demonstrated by means of NMR spectroscopy and X-ray diffraction. When a chiral version of an SPO was used in asymmetric transfer hydrogenation of isopropanol and acetophenone, an enantiomeric excess of 89% was achieved. The presence of at least two ligands in the catalytically active species was confirmed by a positive non-linear effect. DFT calculations were applied to characterize several intermediates for the isopropanol dehydrogenation to produce a rhodium hydride complex and acetone. A transition state for the hydrogen-transfer was fully characterized, which revealed that the process occurs via a concerted outer-sphere mechanism.

First author: Benedict, Jason B., Time-resolved Laue diffraction of excited species at atomic resolution: 100 ps single-pulse diffraction of the excited state of the organometallic complex Rh-2(mu-PNP)(2)(PNP)(2)center dot BPh4, CHEMICAL COMMUNICATIONS, 47, 1704, (2011)
Abstract: The polychromatic Laue technique has been applied in 100 ps delay synchrotron pump-probe experiments of the triplet excited state of a Rh(I) dinuclear complex. The observed contraction of the Rh-Rh distance of 0.154 (13) angstrom is less than predicted by a series of theoretical calculations, a difference attributed to the constraining effect of the crystal lattice.

First author: Pan, Qing-Jiang, Theoretical predictions of cofacial bis(actinyl) complexes of a stretched Schiff-base calixpyrrole ligand, CHEMICAL COMMUNICATIONS, 47, 5720, (2011)
Abstract: Actinyl and actinyl-transition metal complexation by a polypyrrolic macrocycle with anthracenyl linkers between the N-4-donor compartments was evaluated using relativistic density functional theory which predicts that a highly unusual cofacial bis-actinyl structure complex is stable.

First author: Solomon, Sophia A., A donor-functionalized, silyl-substituted pentadienyllithium: structural insight from experiment and theory, CHEMICAL COMMUNICATIONS, 47, 6162, (2011)
Abstract: A donor-functionalized, silyl-substituted pentadienyllithium has been synthesized and characterized by crystallography and NMR spectroscopy. The pentadienyl negative charge was found to be partially localized, which DFT revealed to be due to the polarizing power of the lithium cation.

First author: Poater, Jordi, Selectivity in DNA replication. Interplay of steric shape, hydrogen bonds, pi-stacking and solvent effects, CHEMICAL COMMUNICATIONS, 47, 7326, (2011)
Abstract: Our dispersion-corrected DFT computations reveal key factors behind the intrinsic affinity of a DNA template-primer complex to select the correct nucleotide.

First author: Seubert, Kristof, Chimeric GNA/DNA metal-mediated base pairs, CHEMICAL COMMUNICATIONS, 47, 11041, (2011)
Abstract: DNA double helices comprising chimeric GNA/DNA metal-mediated base pairs have been synthesized and characterized (GNA = glycol nucleic acid). The possibility to combine different nucleic acid backbones within one metal-mediated base pair expands the applicability of metal-functionalized nucleic acids.

First author: Tu, Xiaoyan, Geometrically Specific Imino Complexes of the [Re-6(mu(3)-Se)(8)](2+) Core-Containing Clusters, CHEMISTRY-A EUROPEAN JOURNAL, 17, 580, (2011)
Abstract: The reactions of nitrile complexes of the [Re-6(mu(3)-Se)(8)](2+) core-containing clusters, [Re-6(mu(3)-Se)(8)(PEt3)(n)-(CH3CN)(6-n)](2+) [n=5 (1); n=4, cis- (2) and trans- (3); n=0 (4)], with organic azides C6H5CH(CH3)N-3 and C6H5CH2N3 produced the corresponding cationic imino complexes of the general formula [Re-6(mu(3)-Se)(8)-(PEt3)(n)(L)(6-n)](2+) [L=PhN=CHCH3: n=5 (5); n=4, cis- (6) and trans- (7); n=0 (8) and L=HN=CHPh: n=5 (9); n=4, cis- (10) and trans- (11)]. These novel complexes were characterized by NMR spectroscopy (H-1 and P-31) and single-crystal X-ray diffraction. A mechanism involving the migration of one of the groups on the azido alpha-C atom to the alpha-N atom of the azido complex, concerted with the photo-expulsion of N-2, was invoked to rationalize the formation of the imino complexes. Density functional theory (DFT) calculations indicated that due to the coordination with and activation by the cluster core, the energy of the electronic transition responsible for the photo-decomposition of a cluster-bound azide is much reduced with respect to its pure organic counterpart. The observed geometric specificity was rationalized by using the calculated and optimized preferred ground-state conformation of the cluster-azido intermediates.

First author: Fernandez, Israel, Aromaticity in Group 14 Homologues of the Cyclopropenylium Cation, CHEMISTRY-A EUROPEAN JOURNAL, 17, 2215, (2011)
Abstract: The nature of the bonding and the aromaticity of the heavy Group 14 homologues of cyclopropenylium cations E3H3+ and E2H2E’H+ (E, E’=C-Pb) have been investigated systematically at the BP86/TZ2P DFT level by using several methods. Aromatic stabilization energies (ASE) were evaluated from the values obtained from energy decomposition analysis (EDA) of charged acyclic reference molecules. The EDA-ASE results compare well with the extra cyclic resonance energy (ECRE) values given by the block localized wavefunction (BLW) method. Although all compounds investigated are Huckel 4n+2 pi electron species, their ASEs indicate that the inclusion of Group 14 elements heavier than carbon reduces the aromaticity; the parent C3H3+ ion and Si2H2CH+ are the most aromatic, and Pb3H3+ is the least so. The higher energies for the cyclopropenium analogues reported in 1995 employed an isodesmic scheme, and are reinterpreted by using the BLW method. The decrease ill the strength of both the pi cyclic conjugation and the aromaticity in the order C >> Si > Ge > Sn > Pb agrees reasonably well with the trends given by the refined nucleus-independent chemical shift NICS(0)(pi zz) index.

First author: Wu, Jing, Isohexide Derivatives from Renewable Resources as Chiral Building Blocks, CHEMSUSCHEM, 4, 599, (2011)
Abstract: The nature of the bonding and the aromaticity of the heavy Group 14 homologues of cyclopropenylium cations E3H3+ and E2H2E’H+ (E, E’=C-Pb) have been investigated systematically at the BP86/TZ2P DFT level by using several methods. Aromatic stabilization energies (ASE) were evaluated from the values obtained from energy decomposition analysis (EDA) of charged acyclic reference molecules. The EDA-ASE results compare well with the extra cyclic resonance energy (ECRE) values given by the block localized wavefunction (BLW) method. Although all compounds investigated are Huckel 4n+2 pi electron species, their ASEs indicate that the inclusion of Group 14 elements heavier than carbon reduces the aromaticity; the parent C3H3+ ion and Si2H2CH+ are the most aromatic, and Pb3H3+ is the least so. The higher energies for the cyclopropenium analogues reported in 1995 employed an isodesmic scheme, and are reinterpreted by using the BLW method. The decrease ill the strength of both the pi cyclic conjugation and the aromaticity in the order C >> Si > Ge > Sn > Pb agrees reasonably well with the trends given by the refined nucleus-independent chemical shift NICS(0)(pi zz) index.

First author: Babashkina, Maria G., Solvent-induced 1,3-N,S- vs. 1,5-S,S ‘-coordination in the Ni-II complex [Ni{p-Me2NC6H4NHC(S)NP(S)(OiPr)(2)}(2)], CRYSTENGCOMM, 13, 5321, (2011)
Abstract: Reaction of the deprotonated N-thiophosphorylated thiourea p-Me2NC6H4NHC(S)NHP(S)(OiPr)(2) (HL) with NiCl2 leads to violet [Ni(L-1,3-N,S)(2)] or dark violet [Ni(L-1,5-S,S’)(2)]center dot(CH3)(2)C=O crystals that were isolated by recrystallization from a mixture of CH2Cl2 or acetone, respectively, and n-hexane.

First author: Dakovic, Marijana, Coordination-driven self-assembly of thiocyanate complexes of Co(II), Ni(II) and Cu(II) with picolinamide: a structural and DFT study, CRYSTENGCOMM, 13, 5863, (2011)
Abstract: The new heteroleptic complexes, [M(NCS)(2)(pia)(2)] M Co(II) (1), Ni(II) (2), and [Cu(SCN)(2)(pia)(2)] (3), pia = pyridine-2-carboxamide, were synthesized and characterized. Their single crystal X-ray diffraction structures showed octahedral units, with the two thiocyanate ligands occupying cis-positions and binding through the nitrogen atom in Co(II) and Ni(II). In the Cu(II) complex, they were trans and S-bound. The crystal structures display a 2-d structure with NH center dot center dot center dot S hydrogen bonds for the Co(II) and Ni(II), forming tetrameric units, and are isomorphous with the Zn(II) complex, [Zn(NCS) 2(pia) 2], and a 2-d structure with NH center dot center dot center dot N for the Cu(II). DFT calculations were performed on the new complexes and the analogous polymorphs of [Zn(NCS)(2)(pia)(2)], including a second one containing dimeric motifs. The calculated vibrational modes of the thiocyanate ligands corroborate the experimental ones and reflect the coordination mode of the ligand. A comparison between the two Zn(II) polymorphs showed that the NH center dot center dot center dot S bond in the tetramer is stronger (-7.50 kcal mol(-1) per metal) than the NH center dot center dot center dot O bond in the dimer (-4.01 kcal mol(-1) per metal), indicating a preference for the formation of tetrameric units. The NH center dot center dot center dot N hydrogen bonds calculated in the Cu(II) crystal are stronger (-9.15 kcal mol(-1) per metal) than the NH center dot center dot center dot S ones in Ni(II) and Zn(II).

First author: Kirker, Ian, Does covalency really increase across the 5f series? A comparison of molecular orbital, natural population, spin and electron density analyses of AnCp(3) (An = Th-Cm; Cp = eta(5)-C5H5), DALTON TRANSACTIONS,40, 124, (2011)
Abstract: The title compounds are studied with scalar relativistic, gradient-corrected (PBE) and hybrid (PBE0) density functional theory. The metal-Cp centroid distances shorten from ThCp3 to NpCp3, but lengthen again from PuCp3 to CmCp3. Examination of the valence molecular orbital structures reveals that the highest-lying Cp pi(2,3)-based orbitals transform as 1e + 2e + 1a(1) + 1a(2). Above these levels come the predominantly metal-based 5f orbitals, which stabilise across the actinide series such that in CmCp3 the 5f manifold is at more negative energy than the Cp pi(2,3)-based levels. Mulliken population analysis shows metal d orbital participation in the e symmetry Cp pi(2,3)-based orbitals. Metal 5f character is found in the 1a(1) and 1a(2) levels, and this contribution increases significantly from ThCp3 to AmCp3. This is in agreement with the metal spin densities, which are enhanced above their formal value in NpCp3, PuCp3 and especially AmCp3 with both PBE and PBE0. However, atoms-in-molecules analysis of the electron densities indicates that the An-Cp bonding is very ionic, increasingly so as the actinide becomes heavier. It is concluded that the large metal orbital contributions to the Cp pi(2,3)-based levels, and enhanced metal spin densities toward the middle of the actinide series arise from a coincidental energy match of metal and ligand orbitals, and do not reflect genuinely increased covalency (in the sense of appreciable overlap between metal and ligand levels and a build up of electron density in the region between the actinide and carbon nuclei).

First author: Knapp, Caroline M., A versatile salt-metathesis route to heteroatomic clusters derived from phosphorus and arsenic Zintl anions, DALTON TRANSACTIONS, 40, 735, (2011)
Abstract: Salt metathesis reactions between ethylenediamine (en) solutions of the K3E7 (E = P, As) Zintl phases and post-transition metal halides (InCl3, TlCl, SnI2 and PbI2) have yielded a family of novel heteroatomic cluster anions, [In(E-7)(2)](3-), [TlE7](2-) and [E’E-15](3-) (E’ = Sn, Pb; E = P, As). Several of these new species have been characterized by single-crystal X-ray diffraction as salts of sequestered potassium cations in [K(2,2,2-crypt)](3)[In(P-7)(2)]center dot 3.5py (1), [K(2,2,2-crypt)](2)[TlP7]center dot py (3), [K(18-crown-6)](2)[TlAs7] (4b), [K(2,2,2-crypt)] 3[E’P15]center dot en (E’ = Sn (5), Pb (6)) and [K(2,2,2-crypt)](3)[SnAs15]center dot 2en (7). The presence of all of the cluster anions in solution was confirmed by electrospray mass-spectrometry and by H-1 and P-31{H-1} NMR spectroscopy when pertinent.

First author: Liu, Chun-Guang, Quantum chemical characterization of the generation of high-valent oxoruthenium species of Keggin type polyoxometalates: electronic structure and bonding features, DALTON TRANSACTIONS, 40, 2967, (2011)
Abstract: High-valent transition-metal-substituted Keggin-type polyoxometalates (POMs) are active and robust oxidation catalyst. The important oxidized intermediates of these POM complexes are very difficult to be characterized by using the experimental method, and thus no detail information is available on such species. In the present paper, density functional theory (DFT) calculations have been carried out to characterize the electronic structures of a series of mono-ruthenium-substituted Keggin-type POMs. We find that the aquaruthenium(II/III/IV) species possess d(xy)(2)d(xz)(2)d(yz)(2), d(xy)(2)d(xz)(2)d(yz)(1), and d(xy)(2)d(xz)(1)d(yz)(1) electronic configuration, respectively, and hydroxyl/oxoruthenium(IV/V/VI) species possess d(xy)(2)d(xz)(1)pi*(1)(yz), d(xy)(2)pi*(1)(xz)pi*(1)(yz), d(xy)(1)pi*(1)(xz)pi*(1)(yz), and d(xy)(1)pi*(1)(xz)pi*(0)(yz) electronic configuration, respectively. Mulliken spin population shows that spin density is localized on the ruthenium center in aquaruthenium(II/III/IV) POM complexes, and the RuOa unit in hydroxyl/oxoruthenium(IV/V/VI) POM complexes. The O-a atom has substantial radical character in oxoruthenium(IV/V) species, and the radical character of the Oa atom are significantly weakened in the oxoruthenium(VI) species. The relevant energy of the important Ru-O-a pi*-antibonding unoccupied orbitals with high RuOa compositions of oxoruthenium(IV/V/VI) POM complexes decrease in the order: oxoruthenium(IV) > oxoruthenium(V) > oxoruthenium(VI). The pH-independent multiple reduction energies for Ru(III/II), Ru(V/IV), and Ru(VI/V) couples are calculated, which is in agreement with the experimental data.

First author: Antonova, Nadya S., Theoretical characterization of a Ru N-Heterocyclic Carbene derivative of a polyoxometalate. Enhanced pi-interaction in oxide supported TM-organic linkages, DALTON TRANSACTIONS, 40, 2975, (2011)
Abstract: The electronic structure of the N-heterocyclic carbene (NHC) functionalized polyoxometalate [K(PW9O34)(2)(cis-WO2)(cis-RuLMe2)](12-) (1) is studied computationally; and its Ru-NHC bonding situation is compared with other monometallic Ru-NHC complexes, as well as other representative carbene complexes. The DFT analysis further supports the low spin configuration, S = 1/2, as the ground state, as the unoccupied d ruthenium orbitals are high in energy and mixed with the d-type orbitals of W. We gauge the TM-carbene bonding nature by means of atoms in molecules (AIM) quantum theory and a modified version of energy decomposition analysis (EDA) based on orbital deletion. According to the calculations, the NCH ligand in POM derivative 1 is more tightly bonded than in its analogous neutral monometallic Ru-NHC complexes. This is manifested in a higher electron density rho(r) at the bond critical point (bcp) between Ru and the carbene carbon atoms. The energetic contribution of sigma-donation is similar for all Ru-NHC complexes, and significantly higher than for Fischer-type carbene complex, in agreement with the description of the N-heterocyclic carbene ligand as a strong sigma-donor. Among the studied Ru-NHC complexes, the POM derivative 1 shows the largest pi-back-donation ability, explaining the observed short Ru-C-carbene bond distance and the calculated high interaction energy. The POM framework acting as ligand makes the ruthenium d electrons more loose via orbital mixing and promotes the back-donation to the ligand.

First author: van Zeist, Willem-Jan, Steric nature of the bite angle. A closer and a broader look, DALTON TRANSACTIONS, 40, 3028, (2011)
Abstract: The bite angle (ligand-metal-ligand angle) is known to greatly influence the activity of catalytically active transition-metal complexes towards bond activation. Here, we have computationally explored how and why the bite angle has such effects in a wide range of prototypical C-X bonds and palladium complexes, using relativistic density functional theory at ZORA-BLYP/TZ2P. Our model reactions cover the substrates H3C-X (with X = H, CH3, Cl) and, among others, the model catalysts, Pd[PH2(CH2)(n)PH2] (with n = 2-6) and Pd[PR2(CH2)nPR(2)] (n = 2-4 and R = Me, Ph, t-Bu, Cl), Pd(PH3) X-(X = Cl, Br, I), as well as palladium complexes of chelating and non-chelating N-heterocyclic carbenes. The purpose is to elaborate on an earlier finding that bite-angle effects have a predominantly (although not exclusively) steric nature: a smaller bite angle makes more room for coordinating a substrate by bending away the ligands. Indeed, the present results further consolidate this steric picture by revealing its occurrence in this broader range of model reactions and by identifying and quantifying the exact working mechanism through activation strain analyses.

First author: Schau-Magnussen, Magnus, Synthesis and X-ray crystal structure of a novel organometallic (mu(3)-oxido)(mu(3)-imido) trinuclear iridium complex, DALTON TRANSACTIONS, 40, 4212, (2011)
Abstract: Reaction of the organometallic aqua ion [Cp*Ir(H2O)(3)](2+) with tert-butyl(trimethylsilyl) amine in acetone yielded a novel trinuclear (mu(3)-oxido)(mu(3)-imido)pentamethylcyclopentadienyliridium(III) complex, [(Cp*Ir)(3)(O)((NBu)-Bu-t)](2+). Single crystal structure analyses show the complex can be isolated both in the double salt ((BuNH3)-Bu-t)[(Cp*Ir)(3)(O)((NBu)-Bu-t)](CF3SO3)(3) (1) and in the simple triflate [(Cp*Ir)(3)(O)((NBu)-Bu-t)](CF3SO3)(2) (2). The double salt is stabilized by hydrogen bonding between the tert-butylammonium ion and the three triflate anions. It is the first time that a trinuclear (mu(3)-oxido)(mu(3)-imido) transition metal complex has been structurally characterized.

First author: Wu, Yong, Forward molecular design for highly efficient OLED emitters: A theoretical analysis of photophysical properties of platinum(II) complexes with N-heterocyclic carbene ligands, DALTON TRANSACTIONS, 40, 4480, (2011)
Abstract: The electronic structures and photophysical properties of eight Pt-complexes with different N-heterocyclic carbene ligands and potential to serve as light emitting diode materials were investigated by density functional theory and time-dependent density functional theory, employing the BP86 functional for geometry optimisations, SAOP potential for excited state calculations and all-electron TZ2P basis set throughout. Non-radiative and radiative decay rate constants were determined for each system through analyses of the geometric relaxations, d-orbital splitting and spin-orbit couplings at the optimised S-0 and T-1 geometries. Three Pt-systems bound to two N-heterocyclic carbenes were shown to be nonemissive, while a fourth was shown to be emissive from the T-1 excited state. Similar T-1-initated emission was observed for three other Pt-systems investigated, each bound to four N-heterocyclic carbenes, while a fourth similarly tetra-ligated system showed T-2-initation of emission. The results highlight the coupling of ligand-identity to photophysical properties and more importantly, the potential for rational optimisation and tuning of emission wavelengths and phosphorescent efficiencies. Encouragingly, two of the tetra-N-heterocyclic carbene ligated systems show strong potential to serve as highly-efficient blue and green light emitting materials, respectively.

First author: Conradie, Marrigje M., Methyl iodide oxidative addition to [Rh(acac)(CO)(PPh3)]: an experimental and theoretical study of the stereochemistry of the products and the reaction mechanism, DALTON TRANSACTIONS, 40, 8226, (2011)
Abstract: Density functional theory was used to investigate the oxidative addition and subsequent carbonyl insertion and deinsertion steps of the reaction of methyl iodide to a rhodium(I) acetylacetonato complex of the formula [Rh(acac)(CO)(PPh3)] (Hacac = acetylacetone). This process has been studied experimentally for many rhodium beta-diketonato complexes, but, to the best of our knowledge, this is the first systematic computational study of the complete reaction sequence. Experimental H-1 techniques complement the theoretical results on the stereochemistry of the reaction intermediates and products. H-1 NMR also revealed the existence of a second rhodium(III)-acyl product, which has not been previously observed in this reaction. The calculated Gibbs free energy of activation of the oxidative addition reaction is 71 kJ mol(-1), which is in agreement with the experimental value of 82(1) kJ mol(-1). The DFT-calculated oxidative addition corresponds to an associative S(N)2 nucleophilic attack by the rhodium metal centre on the methyl iodide, which is in agreement with calculated and experimental (in brackets) activation parameters of the reaction, 27 (38.8) kJ mol(-1) for Delta H-not equal and -147 (-146) J K-1 mol(-1) for Delta S-not equal.

First author: Johansson, Mikael P., Subtle effects control the polymerisation mechanism in alpha-diimine iron catalysts,DALTON TRANSACTIONS, 40, 8419, (2011)
Abstract: alpha-diimine iron complexes have been suggested to catalyse polymerisation via two distinct pathways, depending on the spin state of the iron complex. Here, we study a typical complex of this family, (R ”)[N,N]FeCl2, with [N,N] = Cy-N CR ”-CR ”= N-Cy (Cy = cyclohexyl, R ” = PhF (para-fluorophenyl), PhOMe (para-methoxyphenyl), PhNMe2 (para-dimethylaminophenyl). With R ” = PhF, PhOMe, polymerisation proceeds as a catalytic chain transfer (CCT) mechanism, with R ” = PhNMe2, the polymerisation follows an atom transfer radical polymerisation (ATRP) pathway. Contrary to previous suggestions, we show that the spin-states of the complexes involved are not affected by the R ” group. Instead, the different behaviour arises from a subtle interplay between the electron-withdrawing or donating character of the reasonably distant phenyl substituent and the iron centre, and small but crucial differences in the reorganisation energies affected during the reactions.

First author: Deibel, Naina, Isomeric separation in donor-acceptor systems of Pd(II) and Pt(II) and a combined structural, electrochemical and spectroelectrochemical study, DALTON TRANSACTIONS, 40, 9925, (2011)
Abstract: Compounds of the form [(pap)M(Q(2-))] (pap = phenylazopyridine; Q = 3,5-di-tert-butyl-benzoquinone, M = Pd, 1a and 1b, M = Pt, 2a and 2b; Q = 4-tert-butyl-benzoquinone, M = Pd, 3a and 3b; M = Pt, 4a and 4b) were synthesized in a one-pot reaction. The geometrical isomers, which are possible because of the built in asymmetry of these ligands, have been separated by using different temperatures and variable solubility. Structural characterization of 1b shows that the metal centers are in a square planar environment, the pap ligand is in the unreduced neutral state and the quinones are in the doubly reduced, Q(2-) catecholate form. Cyclic voltammetric measurements on the complexes display two one-electron oxidations and two one-electron reductions. EPR and vis-NIR spectra of the one-electron oxidized forms of the complexes indicate that the first oxidation takes place on the Q(2-) ligands to produce a metal bound semiquinone (Q(center dot-)) radical. Reduction takes place on the pap ligand, generating metal bound pap(center dot-) as seen from the N-14 (I = 1) coupling in their EPR spectrum. All the complexes in their [(pap)M(Q(2-))] neutral forms show strong absorptions in the NIR region which are largely LLCT (ligand to ligand charge transfer) in origin. These NIR bands can be tuned over a wide energy range by varying the metal center as well as the Q ligand. In addition, the intensity of NIR bands can be switched on and off by a simple electron transfer at relatively low potentials. DFT studies were used to corroborate these findings.

First author: Whalley, Alexandra L., Synthesis, structure and redox properties of bis(cyclopentadienyl)dithiolene complexes of molybdenum and tungsten, DALTON TRANSACTIONS, 40, 10457, (2011)
Abstract: The compounds [Cp2M(S2C2(H)R)] (M = Mo or W; R = phenyl, pyridin-2-yl, pyridin-3-yl, pyridin-4-yl or quinoxalin-2-yl) and [Cp2Mo(S2C2(Me)(pyridin-2-yl)] have been prepared by a facile and general route for the synthesis of dithiolene complexes, viz. the reaction of [Cp2MCl2] (M = Mo or W) with the dithiolene pro-ligand generated by reacting the corresponding 4-(R)-1,3-dithiol-2-one with CsOH. These Mo compounds were reported previously (Hsu et al., Inorg. Chem. 1996, 35, 4743); however, the preparative method employed herein is more versatile and generates the compounds in good yield and all of the W compounds are new. Electrochemical investigations have shown that each compound undergoes a diffusion controlled one-electron oxidation (OXI) and a one-electron reduction (REDI) process; each redox change occurs at a more positive potential for a Mo compound than for its W counterpart. The mono-cations generated by chemical or electrochemical oxidation are stable and the structures of both components of the [Cp2Mo(S2C2(H)R)](+)/[Cp2Mo(S2C2(H)R)] (R = Ph or pyridin-3-yl) redox couples have been determined by X-ray crystallography. For each redox related pair, the changes in the Mo-S, S-C and C-C bond lengths of the {MoSCCS} moiety are generally consistent with OXI involving the loss of an electron from a pi-orbital that is Mo-S and C-S antibonding and C-C bonding in character. These results have been interpreted successfully within the framework provided by DFT calculations accomplished for [Cp2M(S2C2(H)Ph)](n) (M = Mo or W; n = +1, 0 or -1). The HOMO of the neutral compounds is derived mainly from the dithiolene pi(3) orbital (65%); therefore, OXI is essentially a dithiolene-based process. The similarity of the potentials for OXI (ca. 30 mV) for analogous Mo and W compounds is consistent with this interpretation and the EPR spectra of each of the Mo cations show that the unpaired electron is coupled to the dithiolene proton but relatively weakly to Mo-95,Mo-97. The DFT calculations indicate that the unpaired electron is more localised on the metal in the mono-anions than in the mono-cations. In agreement with this, the EPR spectrum of each of the Mo-containing mono-anions manifests a larger Mo-95,Mo-97 coupling (A(iso)) than observed for the corresponding mono-cation and REDI for a W compound is significantly (ca. 300 mV) more negative than that of its Mo counterpart. [Cp2W(S2C2(H)(quinoxalin-2-yl))] is anomalous; REDI occurs at a potential ca. 230 mV more positive than expected from that of its Mo counterpart and the EPR spectrum of the mono-anion is typical of an organic radical. DFT calculations indicate that these properties arise because the electron is added to a quinoxalin-2-yl pi-orbital.

First author: Aitken, Georgina, Reductive coupling of carbon monoxide by U(III) complexes-a computational study,DALTON TRANSACTIONS, 40, 11080, (2011)
Abstract: The role of U((eta-C8H6{(SiPr3)-Pr-i-1,4}(2))(eta-C5Me5) and U((eta-C8H6{(SiPr3)-Pr-i-1,4}(2))(eta-C5Me4H) in the reductive di-tri- and tetramerization of CO has been modelled using density functional methods and U(C8H8)(C5H5) as the metal fragment. The orbital structure of U(C8H8)(C5H5) is described. CO binding to form a monocarbonyl U(C8H8)(C5H5)(CO) is found, by a variety of methods, to place spin density on the CO ligand via back-bonding from the U5f orbitals. A possible pathway for formation of the yne diolate complex [U(C8H8)(C5H5)](2)C2O2 is proposed which involves dimerization of U(C8H8)(C5H5)CO via coordination of the CO O atoms to the opposing U atoms followed by C-C bond formation to form a zig-zag intermediate, stable at low temperatures. The intermediate then unfolds to form the yne diolate. The structures of [U(C8H8)(C5H5)]C2O2, the deltate complex [U(C8H8)(C5H5)]C3O3 and the squarate complex [U(C8H8)(C5H5)]C4O4 are optimized and provide good models for the experimental compounds. The reaction of further CO with a zig-zag intermediate to form deltate and squarate complexes was explored using Th(C8H8)(C5H5) as a model and low energy pathways are proposed.

First author: Han, Wen-Ge, Mossbauer properties of the diferric cluster and the differential iron(II)-binding affinity of the iron sites in protein R2 of class Ia Escherichia coli ribonucleotide reductase: a DFT/electrostatics study, DALTON TRANSACTIONS, 40, 11164, (2011)
Abstract: The R2 subunit of class-Ia ribonucleotide reductase (RNR) from Escherichia coli (E. coli) contains a diiron active site. Starting from the apo-protein and Fe(II) in solution at low Fe(II)/apoR2 ratios, mononuclear Fe(II) binding is observed indicating possible different Fe(II) binding affinities for the two alternative sites. Further, based on their Mossbauer spectroscopy and two-iron-isotope reaction experiments, Bollinger et al. (J. Am. Chem. Soc., 1997, 119, 5976-5977) proposed that the site Fe1, which bonds to Asp84, should be associated with the higher observed Fe-57 Mossbauer quadrupole splitting (2.41 mm s(-1)) and lower isomer shift (0.45 mm s(-1)) in the Fe(III)Fe(III) state, site Fe2, which is further from Tyr122, should have a greater affinity for Fe(II) binding than site Fe1, and Fe(IV) in the intermediate X state should reside at site Fe2. In this paper, using density functional theory (DFT) incorporated with the conductor-like screening (COSMO) solvation model and with the finite-difference Poisson-Boltzmann self-consistent reaction field (PB-SCRF) methodologies, we have demonstrated that the observed large quadrupole splitting for the diferric state R2 does come from site Fe1(III) and it is mainly caused by the binding position of the carboxylate group of the Asp84 sidechain. Further, a series of active site clusters with mononuclear Fe(II) binding at either site Fe1 or Fe2 have been studied, which show that with a single dielectric medium outside the active site quantum region, there is no energetic preference for Fe(II) binding at one site over another. However, when including the explicit extended protein environment in the PB-SCRF model, the reaction field favors the Fe(II) binding at site Fe2 rather than at site Fe1 by similar to 9 kcal mol(-1). Therefore our calculations support the proposal of the previous Mossbauer spectroscopy and two-iron-isotope reaction experiments by Bollinger et al.

First author: Birjkumar, Krishna Hassomal, Computational investigation of the speciation of uranyl gluconate complexes in aqueous solution, DALTON TRANSACTIONS, 40, 11248, (2011)
Abstract: The geometries, relative energies and spectroscopic properties of a range of D-gluconate complexes of uranyl(VI) are studied computationally using density functional theory. The effect of pH is accommodated by varying the number of water and hydroxide ligands accompanying gluconate in the equatorial plane of the uranyl unit. For 1 : 1 complexes, the calculated uranyl (V) over tilde (asym) stretching frequency decreases as pH increases, in agreement with previous experimental data. Three different gluconate chelating modes are studied. Their relative energies are found to be pH dependent, although the energetic differences between them are not sufficient to exclude the possibility of multiple speciation. C-13 NMR chemical shifts are calculated for the coordinated gluconate in the high pH mimics, and show good agreement with experimental data, supporting the experimental conclusion that the six-membered chelate ring is favoured at high pH. Attempts to improve the description of the aqueous environment via the addition of second solvation shell water molecules resulted in significantly worse agreement with experiment for (V) over tilde (asym). The effect of increasing the gluconate concentration is modelled by calculating 1 : 2 and 1 : 3 uranyl : D-gluconate complexes.

First author: Terrett, R., On the unprecedented level of dinitrogen activation in the calix[4]arene complex of Nb(III),DALTON TRANSACTIONS, 40, 11267, (2011)
Abstract: The calix[4]arene niobium(III) complex ([L]Nb-N=N-Nb[L] where [L] = p-tert-butylcalix[4]arene), reported to bind N-2 in a mu(2)-linear dimeric capacity and to activate the N-2 triple bond to 1.39 angstrom, corresponding to the longest N-2 bond known in the end-on coordination mode, was subjected to a computational investigation involving both density functional and wavefunction based methods to establish the basis for the unprecedented level of activation. Replacement of the calix[4]arene ligand with hydroxide or methoxide ligands reveals that the organic backbone structure of the calix[4]arene ligand exerts negligible electronic influence over the metal centre, serving only to geometrically constrain the coordinating phenoxide groups. A fragment bonding analysis shows that metal-to-dinitrogen pi* backbonding is the principal Nb N interaction, providing a strong electronic basis for analogy with other well-characterised three-and four-coordinate complexes which bind N-2 end-on. While the calculated structure of the metallacalix[4]arene unit is reproduced with high accuracy, as is also the Nb-Nb separation, the calculated equilibrium geometry of the complex under a variety of conditions consistently indicates against a 1.39 angstrom activation of the N-2 bond. Instead, the calculated N-N distances fall within the range 1.26-1.30 angstrom, a result concordant with closely related three-and four-coordinate mu(2)-N-2 complexes as well as predictions derived from trends in N-N stretching frequency for a number of crystallographically characterized linear N-2 activators. A number of potential causes for this bond length discrepancy are explored.

First author: Schulten, Christian, Deoxygenation of Isocyanates via Transient Electrophilic Terminal Phosphinidene Complexes: Are Strained P-Heterocycles Involved?, HETEROATOM CHEMISTRY, 22, 275, (2011)
Abstract: Synthesis of 1,3,2,4 sigma(3)lambda(3-)dioxadiphosphetane complexes 3a,b and 4a,b was achieved via thermal decomposition of 2 H-azaphosphirene complexes of chromium (1a) and tungsten (1b) in the presence of tert-butyl isocyanate; as reactive intermediates 3-imino-oxaphosphirane complexes 8a,b are proposed, which decompose to give phosphinidene oxide complexes 9a,b. The intermediacy of the latter is inferred from a cross-dimerization experiment (decomposition of a 1:1 mixture of 2H-azaphosphirene complexes la,b with tert-butyl isocyanate), which furnished the mixed metal dinuclear cis and trans complexes 5a/b and 6a/b. (31)P NMR spectroscopy revealed the formation of [bis(trimethylsilyl)methyl]cyanophosphane complexes 11a,b as by-products. Thermal reaction of complex lb with the less bulky ethyl isocyanate furnished the novel 1,3,4 sigma(3)lambda(3)-diazaphospholidin-5-imin-2-one complex 7 together with complexes 3b and 4b. For the latter case, 3-imino-oxaphosphirane (12) and azaphosphiridin-3-one (13) complexes are proposed as reactive intermediates. All final products were characterized by multinuclear NMR spectroscopy, IR, MS, and single-crystal X-ray crystallography in the cases of complexes 3b and 4a,b. DFT calculations strongly support the transient formation and decomposition of 3-imino-oxaphosphirane complex 12 to form 9b and isonitrile. Azaphosphiridin-3-one complex 13 was characterized computationally as the methyl model. In accordance with the calculations, final products 1,3,2,4 sigma(3)lambda(3)-dioxadiphosphetane complexes 3a,b and 4a,b form by dimerization of transient terminal phosphinidene oxide complexes 9a,b.

First author: de Macedo, Luiz Guilherme M., Fully Relativistic 4-Components DFT Investigation on Bonding and Dissociation Energy of HgO, JOURNAL OF COMPUTATIONAL AND THEORETICAL NANOSCIENCE, 8, 38, (2011)
Abstract: The dissociation energy of HgO obtained through all electron 4-component DFT calculations shows good agreement with experimental data, opposing some high level calculations from literature. It suggests that the reaction Hg + BrO -> HgO + Br is feasible to take place under atmospheric conditions.

First author: Conradie, Marrigje M., Capturing the spin state diversity of iron(III)-aryl porphyrins OLYP is better than TPSSh, JOURNAL OF INORGANIC BIOCHEMISTRY, 105, 84, (2011)
Abstract: DFT calculations with a variety of exchange-correlation functionals including PW91 OLYP TPSSh B3LYP and B3LYP* have been carried out on the low-energy spin states of chloroiron(III) porphyrin and four aryliron(111) porphyrins viz Fe-III(P)Ph (S=1/2) Fe-III(P)C6F6 (S=5/2) Fe-III(P)(3 4 5 C6F3H2) (S=1/2) Fe-III(P)(2 4 6-C6F3H2) (S=5/2) where the expected spin states have been indicated within parentheses Qualitatively OLYP reproduces all the expected ground spin states B3LYP appears to have some difficulty yielding the observed sextet ground states B3LYP* TPSSh and PW91 all fall to reproduce the sextet ground states the latter two by rather large margins of energy As far as this study is concerned the overall performance of the functionals appears to be OLYP/OPBE>B3LYP>B3LYP*>> TPSSh>PW91/BLYP/BP86/TPSS

First author: Paragi, Gabor, Neutral and positively charged new purine tetramer structures: a computational study of xanthine and uric acid derivatives, NEW JOURNAL OF CHEMISTRY, 35, 119, (2011)
Abstract: New tetramer structures, based on 9-methylxanthine (Xa), 9-methylxanthine protonated at N7 (XaH(+)) and 9-methyluric acid (Ua), were investigated by high-level density functional calculations. We have found that homo-and heterotetrads (XaH+)(4), (XaH(+)-Xa)(2), (XaH(+)-Ua)(2) carrying positive charges can be formed by low barrier hydrogen bonds. Systems with zero charge [(Xa)(4), (Xa-Ua)(2), (Ua)(4)] were also constructed, investigated and compared to the guanine tetrad [(G)(4)]. It was shown that the new tetramers can bind cations and anions without the necessity of stacking interactions. Application of the calculated systems in higher-ordered structures (e.g. quadruplexes) is promising with or without intercalating ions.

First author: Szolomajer, Janos, 3-Substituted xanthines as promising candidates for quadruplex formation: computational, synthetic and analytical studies, NEW JOURNAL OF CHEMISTRY, 35, 476, (2011)
Abstract: Our computational studies suggest that 3-substituted xanthines are good candidates for tetrad and quadruplex structures. 3-Methylxanthine (3MX) has been synthesized from 7-benzylxanthine, and the existence of tetrameric and octameric aggregates of 3MX with NH4+, Na+ and K+ ions in the gas phase (MS) and in DMSO-d(6) solution (NMR) has been observed. The “internal” H-bonds (N1H center dot center dot center dot O6) are stronger than the “external” ones (N7H center dot center dot center dot O2) in these clusters (NMR).

First author: Li, Ping, Theoretical studies on the coupling interactions in H2SO4 center dot center dot center dot HOO center dot center dot center dot center dot(H2O)(n) (n=0-2) clusters: toward understanding the role of water molecules in the uptake of HOO center dot radical by sulfuric acid aerosols, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 941, (2011)
Abstract: A detailed knowledge of coupling interactions among sulfuric acid (H2SO4), the hydroperoxyl radical (HOO center dot), and water molecules (H2O) is crucial for the better understanding of the uptake of HOO center dot radicals by sulfuric acid aerosols at different atmospheric humidities. In the present study, the equilibrium structures, binding energies, equilibrium distributions, and the nature of the coupling interactions in H2SO4 center dot center dot center dot HOO center dot center dot center dot center dot(H2O)(n) (n = 0 2) clusters have been systematically investigated at the B3LYP/6-311+ + G(3df,3pd) level of theory in combination with the atoms in molecules (AIM) theory, natural bond orbital (NBO) method, energy decomposition analyses, and ab initio molecular dynamics. Two binary, five ternary, and twelve tetramer clusters possessing multiple intermolecular H-bonds have been located on their potential energy surfaces. Two different modes for water molecules have been observed to influence the coupling interactions between H2SO4 and HOO center dot through the formations of intermolecular H-bonds with or without breaking the original intermolecular H-bonds in the binary H2SO4 center dot center dot center dot HOO center dot cluster. It was found that the introduction of one or two water molecules can efficiently enhance the interactions between H2SO4 and HOO center dot, implying the positive role of water molecules in the uptake of the HOO center dot radical by sulfuric acid aerosols. Additionally, the coupling interaction modes of the most stable clusters under study have been verified by the ab initio molecular dynamics.

First author: Kocherzhenko, Aleksey A., Single molecule charge transport: from a quantum mechanical to a classical description, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 2096, (2011)
Abstract: This paper explores charge transport at the single molecule level. The conductive properties of both small organic molecules and conjugated polymers (molecular wires) are considered. In particular, the reasons for the transition from fully coherent to incoherent charge transport and the approaches that can be taken to describe this transition are addressed in some detail. The effects of molecular orbital symmetry, quantum interference, static disorder and molecular vibrations on charge transport are discussed. All of these effects must be taken into account (and may be used in a functional way) in the design of molecular electronic devices. An overview of the theoretical models employed when studying charge transport in small organic molecules and molecular wires is presented.

First author: Juarez, Rosalba, Radon hydrides: structure and bonding, PHYSICAL CHEMISTRY CHEMICAL PHYSICS,13, 2222, (2011)
Abstract: Quantum chemical calculations, using gradient-correct density functional at the BP86 level in conjunction with TZ2P basis sets, have been carried out for the radon hydrides HRnY (with Y = F, Cl, Br, I, CCH, CN, and NC). The bonding in HRnY is studied using different bond ruptures, establishing the role of those stabilizing (and destabilizing) factors that prevent these species to be dissociated. Although all HRnY systems studied here are bound equilibrium structures, they are metastable species with respect to the HRnY -> Rn + HY decomposition channel. However, the HRnY -> H + Rn + Y reaction is endothermic. So, these results indicate the possibility to identify the radon hydrides in noble-gas matrices.

First author: Poor Kalhor, Mahboubeh, From CO2 to dimethyl carbonate with dialkyldimethoxystannanes: the key role of monomeric species, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 2401, (2011)
Abstract: The formation of dimethyl carbonate (DMC) from CO2 and methanol with the dimer [n-Bu2Sn(OCH3)(2)](2) was investigated by experimental kinetics in support of DFT calculations. Under the reaction conditions (357-423 K, 10-20 MPa), identical initial rates are observed with three different reacting mixtures, CO2/toluene, supercritical CO2, and CO2/methanol, and are consistent with the formation of monomeric di-n-butyltin(IV) species. An intramolecular mechanism is, therefore, proposed with an Arrhenius activation energy amounting to 104 +/- 10 kJ mol(-1) for DMC synthesis. DFT calculations on the [(CH3)(2)Sn(OCH3)(2)](2)/CO2 system show that the exothermic insertion of CO2 into the Sn-OCH3 bond occurs by a concerted Lewis acid-base interaction involving the tin center and the oxygen atom of the methoxy ligand. The Gibbs energy diagrams highlight that, under the reaction conditions, the dimer-monomer equilibrium is significantly shifted towards monomeric species, in agreement with the experimental kinetics. Importantly, the two Sn-OCH3 bonds are prompt to insert CO2. These results provide new insight into the reaction mechanism and catalyst design to enhance the turnover numbers.

First author: Osuna, Silvia, The reactivity of endohedral fullerenes. What can be learnt from computational studies?,PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 3585, (2011)
Abstract: The last two decades have witnessed major advances in the synthesis and characterization of endohedral fullerenes. These species have interesting physicochemical properties with many potential interesting applications in the fields of magnetism, superconductivity, nonlinear optical properties, radioimmunotherapy, and magnetic resonance imaging contrast agents, among others. In addition to the synthesis and characterization, the chemical functionalization of these species has been a main focus of research for at least four reasons: first, to help characterize endohedral fullerenes that could not be well described structurally otherwise; second, to generate materials with fine-tuned properties leading to enhanced functionality in one of their multiple potential applications; third, to produce water-soluble endohedral fullerenes needed for their use in medicinal sciences; and fourth, to generate electron donor-acceptor conjugates that can be used in solar energy conversion/storage. The functionalization of these species has been achieved through different types of reactions, the most common being the Diels-Alder reactions, 1,3-dipolar cycloadditions, Bingel-Hirsch reactions, and free-radical reactions. It has been found that the performance of these reactions in endohedral fullerenes may be quite different from that of the empty fullerenes. Indeed, encapsulated species have a large influence on the thermodynamics, kinetics, and regiochemistry of these reactions. A detailed understanding of the changes in chemical reactivity due to incarceration of atoms or clusters of atoms is essential to assist the synthesis of new functionalized endohedral fullerenes with specific properties. This Perspective seeks to highlight the key role played by computational chemistry in the analysis of the chemical reactivity of these systems. It is shown that the information obtained through calculations is highly valuable in the process of designing new materials based on endohedral fullerenes.

First author: Leyva, Veronica, A comparative analysis of the UV/Vis absorption spectra of nitrobenzaldehydes, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 4269, (2011)
Abstract: In a joint experimental and theoretical study, the UV/Vis absorption spectra of the three isomers (ortho, meta, para) of nitrobenzaldehyde (NBA) were analyzed. Absorption spectra are reported for NBA vapors, cyclohexane and acetonitrile solutions. All spectra are poor in vibronic structure and hardly affected in shape by the surroundings (vapor or solution). Moderate solvatochromic shifts of B similar to-0.2 eV are measured. For all isomers vertical transition energies, oscillator strengths, and excited state dipole moments were computed using the MS-CASPT2/CASSCF and CC2 methods. Based on these calculations the experimental transitions were assigned. The spectra of all isomers are characterized by weak (epsilon(max) approximate to 100 M-1 cm(-1)) transitions around 350 nm (3.6 eV), arising from n pi* absorptions starting from the lone pairs of the nitro and aldehyde moieties. The next band of intermediate intensity peaking around 300 nm (4.2 eV, epsilon(max) approximate to 1000 M-1 cm(-1)) is dominated by pi pi* excitations within the arene function. Finally, strong absorptions (epsilon(max) approximate to 10 000 M-1 cm(-1)) were observed around 250 nm (5.0 eV) which we ascribe to pi pi* excitations involving the nitro and

First author: Bagno, Alessandro, Relativistic DFT calculations of the NMR properties and reactivity of transition metal methane sigma-complexes: insights on C-H bond activation, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 4285, (2011)
Abstract: Relativistic ZORA DFT methods have been employed to predict the NMR properties of methane and methyl hydride complexes of rhodium and iridium. Two of these compounds, the rhodium methane and the iridium methyl hydride complexes, have been recently characterized by NMR spectroscopy. Calculations reveal that relativistic effects are largely responsible of the high shielding observed for the proton and carbon resonances of the methane moiety. The key steps for the reaction mechanism of C-H cleavage catalyzed by both compounds have been investigated at the relativistic level. Although the structure of the intermediates and TSs for the Rh and Ir complexes is rather similar, subtle differences in the energetics are responsible of the different catalytic activity of the two complexes.

First author: Foroutan-Nejad, Cina, The critical re-evaluation of the aromatic/antiaromatic nature of Ti-3(CO)(3): a missed opportunity?, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 4576, (2011)
Abstract: The nature of bonding and aromaticity of Ti-3(CO)(3), a mill-shaped metal-carbonyl complex, is studied carefully. A unique bonding mechanism between metal and carbonyl groups is found in this species. Ti-3(CO)(3) is an example of a metal-carbonyl complex with prominent metal to carbonyl donation. Moreover, it is proven that not only is Ti-3(CO)(3) not an antiaromatic complex but also it is the first synthesized example of d-block, sigma+pi aromatic species. A quick survey among the first row of transition metals in the periodic table shows that other local minima with similar structures and aromaticity are present and Ti-3(CO)(3) is the first synthesized species of an unknown family.

First author: Li, Ping, Theoretical studies on the electron capture properties of the H2SO4 center dot center dot center dot HOO center dot complex and its implications as an alternative source of HOOH, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 5931, (2011)
Abstract: To better understand the potential role of sulfuric acid aerosols in the atmosphere, the electron capture properties of the H2SO4 center dot center dot center dot HOO center dot complex have been systematically investigated by employing the MP2 and B3LYP methods in combination with the atoms in molecules (AIM) theory, energy decomposition analysis (EDA), and ab initio molecular dynamics. It was found that the electron capture process is a favorable reaction thermodynamically and kinetically. The excess electron can be captured by the HOO center dot fragment initially, and then the proton of the H2SO4 fragment associated with the intermolecular H-bonds is transferred to the HOO center dot fragment without any activation barriers, resulting in the formation of the HOOH species directly. Therefore, the electron capture process of the H2SO4 center dot center dot center dot HOO center dot complex provides an alternative source of HOOH in the atmosphere. The nature of the coupling interactions in the electron capture products are clarified, and the most stable anionic complex is also determined. Additionally, the influences of the adjacent water molecules on the electron capture properties are investigated, as well as the distinct IR features of the most stable electron capture product.

First author: Tecmer, Pawel, Electronic spectroscopy of UO22+, NUO+ and NUN: an evaluation of time-dependent density functional theory for actinides, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 6249, (2011)
Abstract: The performance of the time-dependent density functional theory (TDDFT) approach has been evaluated for the electronic spectrum of the UO22+, NUO+ and NUN molecules. Different exchange-correlation functionals (LDA, PBE, BLYP, B3LYP, PBE0, M06, M06-L, M06-2X, CAM-B3LYP) and the SAOP model potential have been investigated, as has the relative importance of the adiabatic local density approximation (ALDA) to the exchange-correlation kernel. The vertical excitation energies have been compared with reference data obtained using accurate wave-function theory (WFT) methods.

First author: Mo, Yirong, Energy decomposition analysis based on a block-localized wavefunction and multistate density functional theory, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 6760, (2011)
Abstract: An interaction energy decomposition analysis method based on the block-localized wavefunction (BLW-ED) approach is described. The first main feature of the BLW-ED method is that it combines concepts of valence bond and molecular orbital theories such that the intermediate and physically intuitive electron-localized states are variationally optimized by self-consistent field calculations. Furthermore, the block-localization scheme can be used both in wave function theory and in density functional theory, providing a useful tool to gain insights on intermolecular interactions that would otherwise be difficult to obtain using the delocalized Kohn-Sham DFT. These features allow broad applications of the BLW method to energy decomposition (BLW-ED) analysis for intermolecular interactions. In this perspective, we outline theoretical aspects of the BLW-ED method, and illustrate its applications in hydrogen-bonding and pi-cation intermolecular interactions as well as metal-carbonyl complexes. Future prospects on the development of a multistate density functional theory (MSDFT) are presented, making use of block-localized electronic states as the basis configurations.

First author: Ospadov, Egor, Ground-state properties of LiH by reptation quantum Monte Carlo methods, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 8031, (2011)
Abstract: We apply reptation quantum Monte Carlo to calculate one-and two-electron properties for ground-state LiH, including all tensor components for static polarizabilities and hyperpolarizabilities to fourth-order in the field. The importance sampling is performed with a large (QZ4P) STO basis set single determinant, directly obtained from commercial software, without incurring the overhead of optimizing many-parameter Jastrow-type functions of the inter-electronic and internuclear distances. We present formulas for the electrical response properties free from the finite-field approximation, which can be problematic for the purposes of stochastic estimation. The alpha, gamma, A and C polarizability values are reasonably consistent with recent determinations reported in the literature, where they exist. A sum rule is obeyed for components of the B tensor, but B-zz,B-zz as well as beta(zzz) differ from what was reported in the literature.

First author: Nicu, Valentin Paul, Signatures of counter-ion association and hydrogen bonding in vibrational circular dichroism spectra, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 8811, (2011)
Abstract: We study the effect of counter-ion complexation on the example of Cl- ions interacting with the [Co(en)(3)](3+) complex. The H-bonding of the N-H groups of the ethylenediamine (en) ligands with the Cl- ions may lead to giant enhancement of the VCD intensity for the N-H stretches, but may also lead to VCD sign changes in the finger print region of N-H wagging, twisting and scissoring motions. Such sign changes should not be mistaken for signatures of the presence of the other enantiomer. We elucidate the mechanism for the sign changes and give a recommendation on how to deal with this problem. We also show that the experimental spectrum is only in good accord with the calculations if complexation of 5 Cl- ions (two axial, three equatorial) is assumed, but not with two (axial) or three (equatorial) Cl- ions, thus showing the potential of VCD to be used as an experimental probe for complexation.

First author: Wawrzyniak, P. K., Acetyl group orientation modulates the electronic ground-state asymmetry of the special pair in purple bacterial reaction centers, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 10270, (2011)
Abstract: Recent experimental data point to an asymmetric ground-state electronic distribution in the special pair (P) of purple bacterial reaction centers, which acts as the primary electron donor in photosynthesis. We have performed a density functional theory investigation on an extended model including the bacteriochlorophyll dimer and a few relevant surrounding residues to explore the origin of this asymmetry. We find strong evidence that the ground-state electron density in P is intrinsically asymmetric due to protein-induced distortions of the porphyrin rings, with excess electron charge on the P-M bacteriochlorophyll cofactor. Moreover, the electron charge asymmetry is strongly modulated by the specific orientation of the C3(1) acetyl group, which is hydrogen bonded to His168. The electronic excitation has a significant charge transfer character inducing a displacement of electron charge from P-L to P-M, in agreement with experimental data in the excited state. These results are relevant for the understanding of the unidirectional electron transfer path in photosynthesis.

First author: Swart, Marcel, A multi-scale approach to spin crossover in Fe(II) compounds, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 10449, (2011)
Abstract: We report here for the first time a multi-scale study on the concept of spin-crossover compounds, which integrates improved density functionals, a polarizable force field and hybrid QM/MM calculations. This multi-scale setup is applied to the temperature dependence of spin states of a Fe(II) compound with trispyrazolylborate ligands that exhibits spin-crossover. Our study shows a transition temperature of around 290 K, which is in perfect agreement with experimental results. Moreover, based on our data we provide the origin of why spin transition occurs in this iron-compound: it results directly from spin-state changes in the iron-compound that lead to more favourable electrostatic interactions for the high-spin state.

First author: Koenig, Carolin, First-principles calculation of electronic spectra of light-harvesting complex II, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 10475, (2011)
Abstract: We report on a fully quantum chemical investigation of important structural and environmental effects on the site energies of chlorophyll pigments in green-plant light-harvesting complex II (LHC II). Among the tested factors are technical and structural aspects as well as effects of neighboring residues and exciton couplings in the chlorophyll network. By employing a subsystem time-dependent density functional theory (TDDFT) approach based on the frozen density embedding (FDE) method we are able to determine site energies and electronic couplings separately in a systematic way. This approach allows us to treat much larger systems in a quantum chemical way than would be feasible with a conventional density functional theory. Based on this method, we have simulated a series of mutagenesis experiments to investigate the effect of a lack of one pigment in the chlorophyll network on the excitation properties of the other pigments. From these calculations, we can conclude that conformational changes within the chlorophyll molecules, direct interactions with neighboring residues, and interactions with other chlorophyll pigments can lead to non-negligible changes in excitation energies. All of these factors are important when site energies shall be calculated with high accuracy. Moreover, the redistribution of the oscillator strengths due to exciton coupling has a large impact on the calculated absorption spectra. This indicates that modeling mutagenesis experiments requires us to consider the entire set of chlorophyll molecules in the wild type and in the mutant, rather than just considering the missing chlorophyll pigment. An analysis of the mixing of particular excitations and the coupling elements in the FDEc calculation indicates that some pigments in the chlorophyll network act as bridges which mediate the interaction between other pigments. These bridges are also supported by the calculations on the “mutants” lacking the bridging pigment.

First author: Li, Ching-Hsiu, Halogenated 6,13-bis(triisopropylsilylethynyl)-5,7,12,14-tetraazapentacene: applications for ambipolar air-stable organic field-effect transistors, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 11148, (2011)
Abstract: Density functional theory calculations were performed to explore the influence of halogenation on the reorganization energies (lambda), adiabatic ionization potentials (IPs), adiabatic electron affinities (EAs), and air stabilities of a series of pentacene (PENT) and tetraceno[2,3-b]thiophene (TbTH) derivatives. According to calculated IP and EA values, all well-known PENT and TbTH derivatives in this paper are air-stable p-channel but not air-stable n-channel organic field-effect transistors (OFETs) due to insufficient EAs, consistent with experimental observations. The calculated results show that attaching two or more halogen atoms onto air-unstable 6,13-bis(triisopropylsilylethynyl)-5,7,12,14-tetraazapentacene (TIPS-N4PENT) is sufficient for promoting ambipolar air-stable properties. The electronic coupling and band structure calculations indicate that halogenated TIPS-N4PENT derivatives have potential applications in high-performance ambipolar air-stable OFETs. They also provide rational guidelines for the design of ambipolar air-stable organic semiconductors (OSCs).

First author: Perez-Peralta, Nancy, Stabilizing carbon-lithium stars, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 12975, (2011)
Abstract: We have explored in silico the potential energy surfaces of the C5Linn-6 (n = 5, 6, and 7) clusters using the Gradient Embedded Genetic Algorithm (GEGA) and other computational strategies. The most stable forms of C5Li5- and C5Li6 are two carbon chains linked by two lithium atoms in a persistent seven membered ring capped by two Li atoms. The other Li atoms are arrayed on the edge of the seven membered ring. In contrast, the global minimum structure for C5Li7+ is a bicapped star of D-5h symmetry. The molecular orbital analysis and computed magnetic field data suggest that electron delocalization, as well as the saturation of the apical positions of the five-membered carbon ring with lithium atoms in C5Li7+ plays a key role in the stabilization of the carbon-lithium star. In fact, the planar star sub-structure for the carbon ring are unstable without the apical caps. This is also what has been found for the Si analogues. The split of the B-z(ind) in its sigma-and pi-contribution indicates that C5Li7+ is a p-aromatic and sigma-nonaromatic system.

First author: Pan, Qing-Jiang, Structures, spectroscopic properties and redox potentials of quaterpyridyl Ru(II) photosensitizer and its derivatives for solar energy cell: a density functional study, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 14481, (2011)
Abstract: Scalar relativistic density functional theory (DFT) has been used to explore the spectroscopic and redox properties of Ruthenium-type photovoltaic sensitizers, trans-[Ru(L-R)(NCS)(2)] (L-R = 4,4”’-di-R-4′,4 ”-bis(carboxylic acid)-2,2′ : 6′,2 ” : 6 ”,2”’-quaterpyridine, R = H(1), Me (2), Bu-t (3) and COOH (4); L-R = 4,4”’-di-R-4′,4 ”-bis(carboxylic acid)-cycloquaterpyridine, R = COOH (5)). The geometries of the molecular ground, univalent cationic and triplet excited states of 1-5 were optimized. In complexes 1-4, the quaterpyridine ligand retains its planarity in the molecular, cationic and excited states, although the C=N-Ru angle representing the SCN -> Ru coordination approaches 180 degrees in the univalent cationic and triplet excited states. The theoretically designed complex 5 displays a curved cycloquaterpyridine ligand with significantly distorted SCN -> Ru coordination. The electron spin density distributions reveal that one electron is removed from the Ru/NCS moieties upon oxidation and the triplet excited state is due to the Ru/NCS -> polypyridine charge transfer (MLCT/L’LCT). The experimental absorption spectra were well reproduced by the time-dependent DFT calculations. In the visible region, two MLCT/L’LCT absorption bands were calculated to be at 652 and 506 nm for 3, agreeing with experimental values of 637 and 515 nm, respectively. The replacement of the R- group with -COOH stabilizes the lower-energy unoccupied orbitals of pi* character in the quaterpyridine ligand in 4. This results in a large red shift for these two MLCT/L’LCT bands. In contrast, the lower-energy MLCT/L’LCT peak of 5 nearly disappears due to the introduction of cycloquaterpyridine ligand. The higher energy bands in 5 however become broader and more intense. As far as absorption in the visible region is concerned, the theoretically designed 5 may be a very promising sensitizer for DSSC. In addition, the redox potentials of 1-5 were calculated and discussed, in conjunction with photosensitizers such as cis-[Ru(L-1)(2)(X)(2)] (L-1 = 4,4′-bis(carboxylic acid)-2,2′-bipyridine; X = NCS-(6), Cl-(7) and CN-(8)), cis-[Ru(L-1′)(2)(NCS)(2)] (L-1′ = 4,7-bis(carboxylic acid)-1,10-phenanthroline, 9), [NH4][Ru(L-2)(NCS)(3)] (L-2 = 4,4′,4 ”-tris(carboxylic acid)-2,2′ : 6′,2 ”-terpyridine, 10) and [Ru(L-2)(NCS)(3)]-(11).

First author: Nicu, Valentin Paul, On the origin dependence of the angle made by the electric and magnetic vibrational transition dipole moment vectors, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 16126, (2011)
Abstract: The concept of robustness of rotational strengths of vibrational modes in a VCD spectrum has been introduced as an aid in assignment of the absolute configuration with the help of the VCD spectrum. The criteria for robustness have been based on the distribution around 90 degrees of the angles xi(i) between electric and magnetic transition dipoles of all the modes i of a molecule. The angles xi(i) (not, of course, the rotational strengths) are, however, dependent on the choice of origin. The derived criteria are for the center of mass chosen as the origin of the coordinate system. We stress in this note that application of the derived criteria assumes that excessive translation of the coordinate origin is not applied. Although the xi(i) angles are not very sensitive to the position of the origin, very small displacements (a few angstrom) are not a problem, excessive translation of the origin does have considerable effect on the xi(i) angles. In this note we quantify this effect and demonstrate how the distribution of xi(i) angles is affected. Although it is possible to recalibrate the robustness criteria for the angles for a specific (large) displacement, we recommend that such displacement simply be avoided. It is to be noted that some modeling software does yield output with excessively displaced coordinate origin; this should be checked and corrected.

First author: Kim, Soowhan, Chloride supporting electrolytes for all-vanadium redox flow batteries, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 18186, (2011)
Abstract: This paper examines vanadium chloride solutions as electrolytes for an all-vanadium redox flow battery. The chloride solutions were capable of dissolving more than 2.3 M vanadium at varied valence states and remained stable at 0-50 degrees C. The improved stability appeared due to the formation of a vanadium dinuclear [V2O3 center dot 4H(2)O](4+) or a dinuclear-chloro complex [V2O3Cl center dot 3H(2)O](3+) in the solutions over a wide temperature range. The all-vanadium redox flow batteries with the chloride electrolytes demonstrated excellent reversibility and fairly high efficiencies. Only negligible, if any, gas evolution was observed. The improved energy capacity and good performance, along with the ease in heat management, would lead to substantial reduction in capital cost and life-cycle cost, making the vanadium chloride redox flow battery a promising candidate for stationary applications.

First author: Cuny, Jerome, Mo-95 nuclear magnetic resonance parameters of molybdenum hexacarbonyl from density functional theory: appraisal of computational and geometrical parameters, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 19471, (2011)
Abstract: Solid-state Mo-95 nuclear magnetic resonance (NMR) properties of molybdenum hexacarbonyl have been computed using density functional theory (DFT) based methods. Both quadrupolar coupling and chemical shift parameters were evaluated and compared with parameters of high precision determined using single-crystal Mo-95 NMR experiments. Within a molecular approach, the effects of major computational parameters, i.e. basis set, exchange-correlation functional, treatment of relativity, have been evaluated. Except for the isotropic parameter of both chemical shift and chemical shielding, computed NMR parameters are more sensitive to geometrical variations than computational details. Relativistic effects do not play a crucial part in the calculations of such parameters for the 4d transition metal, in particular isotropic chemical shift. Periodic DFT calculations were tackled to measure the influence of neighbouring molecules on the crystal structure. These effects have to be taken into account to compute accurate solid-state Mo-95 NMR parameters even for such an inorganic molecular compound.

First author: Vila-Nadal, Laia, Connecting theory with experiment to understand the initial nucleation steps of heteropolyoxometalate clusters, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 20136, (2011)
Abstract: A complimentary combination of Density Functional Theory (DFT) methodology and Electrospray Ionization-Mass Spectrometry (ESI-MS) has been utilized to increase our limited understanding of the first nucleation steps in the formation of the [XM12O40](n-) Keggin polyoxometalates (POMs) (where addenda metal atom M = W or Mo, and the heteroatom X = P or As). We postulate that the first key steps of nucleation into discrete, high nuclearity heteropolyanions proceed via the formation of isodinuclear species (e. g. [M2O7](2-)), which undergo successive steps of protonation and water condensation to form a heterotrinuclear fragment, which acts as a template for the constituent parts required for subsequent aggregation and formation of the plenary Keggin heteropolyanion. The stability of calculated structures of the numerous postulated intermediates has been analysed and discussed in detail, and these results complemented using experimental mass spectrometry, using an assembly (reaction solution analysis) and disassembly (fragmentation of single crystals) approach. Overall, no significant differences between the Keggin POMs were found when changing the addenda metal atom (W or Mo) or the heteroatom (P or As); although small differences among the lowest-energy structures were detected.

First author: Jung, Sunghan, Noncovalent endo-binding of fullerenes to diprotonated bisporphyrins, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 20248, (2011)
Abstract: Noncovalent binding of fullerenes to bisporphyrins was studied in the gas phase by energy-dependent collision-induced dissociation (CID) with Xe under single-collision conditions. The electrospray ionization mass spectra of calix[4] arene-linked bisporphyrins show that bisporphyrins take up to 3-4 protons, depending on the type of meso-substituents. Of the protonated bisporphyrins, the diprotonated species form stable 1:1 complexes with fullerenes (C-60 and C-70). CID cracking patterns of the diprotonated bisporphyrins indicate that each monomeric porphyrin moiety is singly protonated. CID yield-energy curves obtained from the 1:1 diprotonated bisporphyrin-fullerene complexes suggest that a fullerene occupies the endo-binding site intercalated between the two singly protonated porphyrin moieties. In the cases of 1:2 diprotonated bisporphyrin-fullerene complexes, CID results show that one fullerene binds inside (endo-binding) and the other outside (exo-binding). The exo-binding mode is energetically almost identical to the binding of fullerenes to singly protonated porphyrin monomers. The endo-binding energy is at least twice the exo-binding energy. To gain insights into the binding mode, we optimized structures of diprotonated bisporphyrins and their 1:1 endo-complexes with fullerenes, and calculated the endo-binding energy for C-60, C-70 (end-on), and C-70 (side-on). The endo-binding of fullerenes to diprotonated bisporphyrins nearly doubles the pi-pi interactions while reducing the electrostatic repulsion between the two singly protonated porphyrin moieties. The side-on binding of C-70 is favored over the end-on binding because the former exerts less steric strain to the lower rim of calixarene.

First author: Poater, Jordi, All-metal aromatic clusters M-4(2-) (M = B, Al, and Ga). Are pi-electrons distortive or not?,PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 20673, (2011)
Abstract: The pi-electrons in benzene, the quintessential aromatic molecule, were previously shown to be distortive, i.e., they prefer localized double bonds alternating with single bonds. It is the sigma-electrons that force the double bonds to delocalize, leading to a regular, D-6h geometry. Herein, we computationally investigate the double-bond localizing or delocalizing propensities of sigma- and pi-electrons in the archetypal all-metal aromatic cluster Al-4(2-) and its second- and fourth-period analogs B-4(2-) and Ga-4(2-), using Kohn-Sham molecular orbital (MO) theory at BP86/TZ2P in combination with quantitative bond energy decomposition analyses (EDA). We compare the three all-metal aromatic clusters with the structurally related organic species C4H42+, C4H4, and C4H42-. Our analyses reveal that the pi-electrons in the group-13 M-4(2-) molecules have a weak preference for localizing the double bonds. Instead, the sigma-electrons enforce the regular D-4h equilibrium geometry with delocalized double bonds.

First author: Majerz, Irena, Mechanism of proton transfer in the strong OHN intermolecular hydrogen bond, RSC ADVANCES, 1, 219, (2011)
Abstract: The structure of the complex of 3,5-dinitrobenzoaic acid with 3,5-dimethylpyridine was studied by neutron diffraction at 330, 300, 270, 240, 210, 180, 150, 120, 90, 60, and 30 K. The O center dot center dot center dot H bond length gradually changes from 1.403(10) angstrom at 300 K to 1.424(4) angstrom at 30 K. The proton shifts in the hydrogen bridge towards the acceptor nitrogen atom. Temperature-dependent changes in the strong OHN hydrogen bond are used to discuss the proton transfer mechanism.

First author: Teixeira-Dias, Bruno, Binding of 6-mer single-stranded homo-nucleotides to poly(3,4-ethylenedioxythiophene): specific hydrogen bonds with guanine, SOFT MATTER, 7, 9922, (2011)
Abstract: Complexes formed by 6-mer of single-stranded homo-nucleotides and poly(3,4-ethylenedioxythiophene), a pi-conjugated polymer, have been investigated from both experimental and theoretical points of view. UV-Vis absorption and circular dichroism spectra indicate that adenine and cytosine homo-nucleotides form stable and compact adducts with the conducting polymer, which are stabilized by non-specific electrostatic interactions. In contrast, complexes involving the guanine homonucleotide are clearly dominated by specific hydrogen bonds. A hierarchical modeling approach has been used to gain some information of the complex formed by the homo-nucleotide of guanine and the polymer at both the molecular and electronic levels. Atomistic molecular dynamics simulations reveal that upon complexation, the B-DNA conformation of the homo-nucleotide unfolds into a completely disordered arrangement, which allows the simultaneous formation of N-H center dot center dot center dot O and N-H center dot center dot center dot S hydrogen bonds, N-H center dot center dot center dot pi, pi-pi stacking and electrostatic interactions with the extended polymer molecule. In spite of such variety of interactions, specific hydrogen bonds have been found to be the most abundant and decisive in this complex. This study has been complemented by ab initio and density functional theory calculations to examine the specific interactions between 1-methylguanine and 3,4-ethylene-dioxythiophene (G:EDOT). The energy decomposition analyses performed show that the stability of the different structures is governed by the attractive electrostatic interaction and reveal the reason why the N-H center dot center dot center dot O hydrogen bond is the strongest specific interaction between these two molecules.

First author: Conradie, Jeanet, Structure of Coordination Complexes: The Synergy between NMR Spectroscopy and Computational Chemistry, SOUTH AFRICAN JOURNAL OF CHEMISTRY-SUID-AFRIKAANSE TYDSKRIF VIR CHEMIE,64, 190, (2011)
Abstract: Illustrative examples of how NMR spectroscopy and computational chemistry data can be used in synergy to gain information on structure, coordination mode, bonding, symmetry and isomeric distribution of transition metal complexes, is presented. Isomer distribution and the most stable structures in a series of Ti(beta-diketonato)(2)Cl-2 and Ti(beta-diketonato)(2)(biphen) complexes as determined by density functional theory (DFT) methods and the application of the Boltzmann equation, are in agreement with crystal structures and variable temperature NMR results. Secondly, the DFT determined coordination mode of the 4-amino-3,5-bis(pyridine-2-yl)-1,2,4-triazole, (bpt-NH2) which has the appropriate chemical geometry to behave as anionic or neutral bidentate chelating group to form a 5- or 6-membered complex, is shown to be in agreement with H-1 NMR shifts for [Rh(bpy)(2)(bpt-NH)](2+), [Rh(phen)(2)(bpt-NH)](2+), [Rh(bpt-NH)(cod)] and [Ir(bpt-NH)(cod)] (cod = 1,5-cyclooctadiene, phen = 1,10-phenanthroline, bpy = 2,2′-bipyridine). The oxidative addition of CH3I to [Rh(beta-diketonato)(CO)(PPh3)] complexes consist of three reaction steps and involves isomers of two different Rh-III-alkyl and two different Rh-III-acyl species. For this reaction experimental 1H NMR techniques complement the stereochemistry of reaction intermediates and products as calculated by density functional theory. NMR properties, in agreement with computational results, proved to be useful to access the nature of the kappa(3) to kappa(2) distortion in coinage metal-ethylene complexes supported by tris(pyrazolyl)borates. The last example showed that NMR, X-ray crystal and computational results showed C-2 symmetry for a series of metal(II) complexes coordinated to a 16-membered pentaaza macrocycle.

First author: von Eschwege, Karel G., Redox Potentials of Ligands and Complexes – a DFT Approach, SOUTH AFRICAN JOURNAL OF CHEMISTRY-SUID-AFRIKAANSE TYDSKRIF VIR CHEMIE, 64, 203, (2011)
Abstract: A review of the limited literature concerned with theoretical ways to predict experimentally measured redox potentials of ligands and complexes is presented. Electrochemical and related DFT studies involving series of para-substituted nitrobenzenes and beta-diketone bidentate ligands are discussed. New studies involving ferrocenes and bimetallic complexes (containing both rhodium and iron) are additionally reported. Correlations of redox potentials with calculated descriptors; electron affinity (EA), group electronegativity (chi(R)), electrophilicity index (omega), LUMO energy (E-LUMO) and HOMO energy (E-HOMO) – obtained from calculated electronic energies of neutral, anionic and cationic molecules, are compared. Observed E-0′, E-pa or E-pc gave excellent correlations in the linear relationships between E-pc and E-LUMO (R-2 > 0.99), and E-pa and E-HOMO (R-2 > 0.92). Close correlation with the HOMO-1 energy was also found with the ferrocene-based second oxidation in the Rh complex.

First author: Alabugin, Igor V., Hyperconjugation, WILEY INTERDISCIPLINARY REVIEWS-COMPUTATIONAL MOLECULAR SCIENCE, 1, 109, (2011)
Abstract: This review outlines the ubiquitous nature of hyperconjugative interactions and their role in the structure and reactivity of organic molecules. After defining the common hyperconjugative patterns, we discuss the main factors controlling the magnitude of hyperconjugative effects, including orbital symmetry, energy gap, electronegativity, and polarizibility. The danger of underestimating the magnitude of hyperconjugative interactions are illustrated by a number of spectroscopic, conformational, and structural effects. Through the use of advanced computational techniques, the true role of hyperconjugative effects, as it pertains to their influence on stereoelectronics, conformational equilibria, and reactivities relative to other electronic effects, continue to be uncovered.