2006 publications citing ADF

First author: Vargas, A., Towards the engineering of enantioselective properties of supported platinum catalysts,MOLECULAR SIMULATION, 32, 1241, (2006)
Abstract: Understanding the sub-molecular structure of conformationally complex adsorbed molecules is still a difficult task for experimentalists interested in the structure of modified surfaces, therefore first principles calculations can be a fundamental tool for the investigation of structural details otherwise impossible to identify. Density functional theory (DFT) calculations of the adsorption of cinchonidine (CD) and O-phenyl-cinchonidine (OPhCD) have been performed, using large metal clusters to simulate the metal surface and a zero order regular approximation (ZORA) Hamiltonian to account for relativistic effects due to the heavy nuclei involved. The local geometry of chiral surface sites formed by CD was investigated in detail and discussed in relation to the reaction of enantioselective hydrogenation of activated ketones on cinchona modified platinum. Also, the relevant conformations of OPhCD were investigated and the resulting structure of the chiral sites is discussed and compared to those obtained for the parent alkaloid CD. The adsorption behavior on platinum of a series of substituted anisoles was also investigated, in order to evince the effect that phenyl substitution might have on the relative proportion of surface conformers in substituted OPhCD ethers, that have been shown to possess interesting enantioswitching properties when used as surface modifiers in the enantioselective hydrogenation of activated ketones on cinchona alkaloid modified platinum. A correlation between conformational distribution of the modifiers and the selectivity of the catalyst is proposed.

First author: Nafady, Ayman, Electrochemical oxidation of CoCp(CO)(2): Radical-substrate reaction of a 17 e(-)/18 e(-) pair and production of a unique dimer radical, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 16587, (2006)
Abstract: Anodic oxidation of the important half-sandwich compound CoCp(CO)(2), 1, has been studied under gentle electrolyte conditions, e.g., chlorinated hydrocarbons with weakly coordinating anion (WCA) supporting electrolyte anions. The 17-electron cation 1(+) produced at E-1/2(1) = 0.37 V vs FeCp20/+ undergoes a surprising reaction with neutral 1 to form the dimer radical cation [Co2Cp2(CO)(4)](+), 2(+), which has a metal-metal bond unsupported by bridging ligands. The dimer radical is oxidized at a slightly more positive potential (E-1/2 = 0.47 V) to the corresponding dication 2(2+). Observation of the oxidation of 2(+) is without precedent in confirming a radical-substrate (R-S) dimerization process by direct voltammetric detection of the R-S intermediate, K-eq = 3 x 10(4) M-1 for [2(+)]/[1][1(+)]. The R-S mechanism and the reaction products have been characterized by voltammetry, electrolysis, fiber-optic IR spectroscopy, and ESR measurements. DFT calculations indicate that removal of an electron from 1 results in rehybridization in 1(+), thereby opening the metal center for interaction with the neutral compound 1, which has a relatively basic metal center. The LUMO of the dimer dication 2(2+) is metal-metal antibonding, and its half-occupancy in 2(+) results in lengthening of the Co-Co bond from 2.64 angstrom to 3.14 angstrom. Inclusion of solvent in the (COSMO) calculations shows that solvation effects are necessary to account for the fact that E-1/2(2) > E-1/2(1). These results show the importance of medium effects in probing the fundamental redox chemistry of half-sandwich metal complexes.

First author: Kozmon, Stanislav, Catalytic mechanism of glycosyltransferases: Hybrid quantum mechanical/molecular mechanical study of the inverting N-acetylglucosaminyltransferase I, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 16921, (2006)
Abstract: The Golgi glycosyltransferase, N-acetylglucosaminyltransferase I (GnT-I), catalyzes the transfer of a GlcNAc residue from the donor UDP-GlcNAc to the C2-hydroxyl group of a mannose residue in the trimannosyl core of the Man(5)GlcNAc(2)-Asn-X oligosaccharide. The catalytic mechanism of GnT-I was investigated using a hybrid quantum mechanical/molecular mechanical (QM/MM) method with a QM part containing 88 atoms treated with density functional theory (DFT) at the BP/TZP level. The remaining parts of a GnT-I complex, altogether 5633 atoms, were modeled using the AMBER molecular force field. A theoretical model of a Michaelis complex was built using the X-ray structure of GnT-I in complex with the donor having geometrical features consistent with kinetic studies. The QM(DFT)/MM model identified a concerted S(N)2-type of transition state with D291 as the catalytic base for the reaction in the enzyme active site. The TS model features nearly simultaneous nucleophilic addition and dissociation steps accompanied by the transfer of the nucleophile proton H(b)2 to the catalytic base D291. The structure of the TS model is characterized by the O(b)2-C1 and C1-O1 bond distances of 1.912 and 2.542 A, respectively. The activation energy for the proposed reaction mechanism was estimated to be similar to 19 kcal mol(-1). The calculated alpha-deuterium kinetic isotope effect of 1.060 is consistent with the proposed reaction mechanism. Theoretical results also identified interactions between the H(b)6 and beta-phosphate oxygen of the UDP and a low-barrier hydrogen bond between the nucleophile and the catalytic base D291. It is proposed that these interactions contribute to a stabilization of TS. This modeling study provided detailed insight into the mechanism of the GlcNAc transfer catalyzed by GnT-I, which is the first step in the conversion of high mannose oligosaccharides to complex and hybrid N-glycan structures.

First author: Neupane, Kosh P., The influence of amine/amide versus bisamide coordination in nickel superoxide dismutase, INORGANIC CHEMISTRY, 45, 10552, (2006)
Abstract: Nickel superoxide dismutase (NiSOD) is a mononuclear nickel-containing metalloenzyme that catalyzes the disproportionation of superoxide by cycling between Ni-II and Ni-III oxidation states. In the reduced Ni-II oxidation state, the metal center is ligated by two cysteinate sulfurs, one amide nitrogen, and one amine nitrogen (from the N-terminus), while in the oxidized Ni-III state, an imidazole nitrogen coordinates to the metal center. Herein, we expand on a previous report in which we described a functional metallopeptide-based NiSOD model compound [Ni-II(SODM1)] (SODM1 = H2N-HCDLPCGVYDPA-COOH) by exploring how acylation of the N-terminus (producing [Ni-II(SODM1-Ac)]) influences the properties of the metallopeptide. Titration results, GPC data, and mass-spectrometry data demonstrate that Ni-II coordinates to SODM1-Ac in a 1:1 ratio, while variable pH studies show that Ni-II coordination is strong at a pH of 7.5 and above but not observed below a pH of 6.2. This is higher than [Ni-II(SODM1)] by similar to 1.0 pH unit consistent with bisamide ligation. Ni K-edge XAS demonstrates that the Ni-II center is coordinated in a square-planar NiN2S2 coordination environment with Ni-N distances of 1.846(4) angstrom and Ni-S distances of 2.174(3) angstrom. Comparison of the electronic absorption and CD spectrum of [Ni-II(SODM1)] versus [Ni-II(SODM1-Ac)] in conjunction with time-dependent DFT calculations suggests a decrease in Ni covalency in the acylated versus unacylated metallopeptide. This decrease in covalency was also supported by DFT calculations and Ni L-edge XAS. [Ni-II(SODM1-Ac)] has a quasireversible Ni-II/Ni-III redox couple of 0.49(1) V vs Ag/AgCl, which represents a-0.2 V shift compared with [Ni-II(SODM1)], while the peak separation suggests a change in the coordination environment upon oxidation (i.e., axial imidazole ligation). Using the xanthine/xanthine oxidase assay, we determine that [Ni-II(SODM1-Ac)] is less active than [Ni-II(SODM1)] by over 2 orders of magnitude (IC50 = 3(1) x 10(-5) vs 2(1) x 10(-7) M). Possible reasons for the decrease in activity are discussed.

First author: Hancock, Robert D., Density functional theory-based prediction of some aqueous-phase chemistry of superheavy element 111. Roentgenium(I) is the ‘softest’ metal ion, INORGANIC CHEMISTRY, 45, 10780, (2006)
Abstract: A previous approach (Hancock, R. D.; Bartolotti, L. J. Inorg. Chem. 2005, 44, 7175) using DFT calculations to predict log K-1 (formation constant) values for complexes of NH3 in aqueous solution was used to examine the solution chemistry of Rg(I) (element 111), which is a congener of Cu(I), Ag(I), and Au(I) in Group 1B. Rg(I) has as its most stable presently known isotope a t(1/2) of 3.6 s, so that its solution chemistry is not easily accessible. LFER (Linear free energy relationships) were established between Delta E(g) calculated by DFT for the formation of monoammine complexes from the aquo ions in the gas phase, and Delta G(aq) for the formation of the corresponding complexes in aqueous solution. For M2+, M3+, and M4+ ions, the gas-phase reaction was [M(H2O)(6)](n+)(g) + NH3(g) = [M(H2O)(5)NH3](n+)(g) + H2O(g) (1), while for M+ ions, the reaction was [M(H2O)(2)](+)(g) + NH3(g) = [M(H2O)NH3](+)(g) + H2O(g) (2). A value for Delta G(aq) and for Delta E for the formation of M = Cu2+ in reaction 1, not obtained previously, was calculated by DFT and shown to correlate well with the LFER obtained previously for other M2+ ions, supporting the LFER approach used here. The simpler use of Delta E values instead of Delta G(aq) values calculated by DFT for formation of monoamine complexes in the gas phase leads to LFER as good as the Delta G-based correlations. Values of Delta E were calculated by DFT to construct LFER with M+ = H+, and the Group 1B metal ions Cu+, Ag+, Au+, and Rg(+), and with L = NH3, H2S, and PH3 in reaction 3: [M(H2O)(2)](+)(g) + L(g) = [M(H2O)L](+)(g) + H2O(g) (3). Correlations involving Delta E calculated by DMol3 for H+, Cu+, Ag+, and Au+ could reliably be used to construct LFER and estimate unknown log K-1 values for Rg(I) complexes of NH3, PH3, and H2S calculated using the ADF (amsterdam density Functional) code. Log K-1 values for Rg(I) complexes are predicted that suggest the Rg(I) ion to be a very strong Lewis acid that is extremely ‘soft’ in the Pearson hard and soft acids and bases sense.

First author: Usher, Alistair J., Mixed-metal cluster chemistry. 29. Core expansion and ligand-driven metal exchange at group 6 – Iridium clusters, INORGANIC CHEMISTRY, 45, 10859, (2006)
Abstract: Reactions of the tetrahedral clusters MoIr3(mu-CO)(3)(CO)(8)(eta-L) (L = C5HMe4, C5Me5) with the carbonylmetalate anions [Mo(CO)3(eta-L)](-) afford the trigonal bipyramidal clusters Mo2Ir3(mu(3)-H)(mu-CO)(2)(CO)(9)(mu-L)(2) (L = C5HMe4 (3c), 74%; L = C5Me5 (3d), 55%) in which the group 6 metal atoms occupy the apexes; reaction of the cyclopentadienylmolybdenum-containing analogues or their cyclopentadienyltungsten-containing homologues failed to afford analogous products. Reactions of MIr3(mu-CO)(3)(CO)(8)(eta-C5H5) (M = Mo, W) with [M(CO)(3)(eta-L)](-) (L = C5HMe4, C5Me5) afford the core-expanded heteroapex clusters M2Ir3(mu(3)-H)(mu-CO)(2)(CO)(9)(eta-C5H5)(eta-L) (M = Mo, L = C5HMe4 (5c), 9%, L = C5Me5 (5d), 4%; M = W, L = C5Me5 (6d), 5%) in low yield, together with the homoapex clusters M2Ir3(mu(3)-H)(mu-CO)(2)(CO)(9)(eta-L)(2) (M = Mo, L = C5HMe4 (3c), 81%, L = C5Me5 (3d), 60%; M = W, L = C5Me5 (4d), 5%) in much higher yield for the Mo-containing examples. The identities of clusters 3c, d, 4d, and 5c, d have been confirmed by single-crystal X-ray diffraction studies, with the same disposition of ligands about the trigonal bipyramidal cluster cores being observed in each case, a ligand arrangement that has been examined by complementary density functional theory studies. While cluster 5d is accessible as above, no reaction is observed from MoIr3(mu-CO)(3)(CO)(8)(eta-C5Me5) and [M(CO)(3)(eta-C5H5)](-). Treating MoIr3(mu-CO)(3)(CO)(8)(eta-C5H5) with 1 equiv of [M(CO)(3)(eta-C5Me5)](-) affords 5d as the major product, a further 1 equiv affording some MoIr3(mu-CO)(3)(CO)(8)(eta-C5Me5) and a third 1 equiv giving a good yield of 3d. This is consistent with reaction proceeding by apex fragment addition, followed by apex fragment elimination, and finally a further apex fragment addition, the homometallic incoming apexes being distinguished from the departing vertices by their highly methylated cyclopentadienyl ligands. Spectroscopic data suggest that the electron density at these disparate-metal-containing cluster cores is tunable by progressive ( conceptual) cyclopentadienyl alkylation.

First author: Rigamonti, Luca, Copper(II) complexes of salen analogues with two differently substituted (push-pull) salicylaldehyde moieties. A study on the modulation of electronic asymmetry and nonlinear optical properties, INORGANIC CHEMISTRY, 45, 10976, (2006)
Abstract: This paper presents some copper(II) complexes of salen analogues in which the two salicylaldehyde moieties carry different (electron donor, D, and acceptor, A) substituents in position 5, producing a push-pull charge asymmetry. The X-ray structures of some compounds show the presence of pairs of stacked molecules with head-to-tail intermolecular associations. The geometries of all complexes have been optimized through density functional theory (DFT) studies, which have shown that a major influence on the coordination bond lengths is given by the presence of the electron acceptor NO2 group. Such an influence operates mainly on the Cu-phenolato bonds: elongation of the Cu-O distance of the 5-nitrosalicylaldehyde moiety, with a concomitant decrease of the other Cu-O distance; the Cu-N bonds are less affected. The D groups have only a minor influence. The nonlinear optical responses, mu(g)beta(vec), of some molecules have been determined by EFISH measurements, and the beta(vec) values have been obtained using the DFT-calculated mu(g) values because solubility problems hampered the experimental measurements of mu(g) of some derivatives; the former, however, have been found to be in agreement with the experimental values that could be obtained. Deconvolution of the absorption bands in the near-UV region has allowed recognition of the charge-transfer (CT) transition, assigned to a ligand-to-metal CT (LMCT) by time-dependent DFT computations; we have then used the solvatochromism of this transition to obtain beta(0) and beta(CT) values using the two-state model. These values were compared with those obtained by computational studies, which have also allowed evaluation of the influence of the substituents on the directions of mu(g) and beta(tot).

First author: Harding, Chris J., Sensitivity of photoelectron circular dichroism to structure and electron dynamics in the photoionization of carvone and related chiral monocyclic terpenone enantiomers, JOURNAL OF CHEMICAL PHYSICS,125, 10976, (2006)
Abstract: The photoelectron circular dichroism that arises in the angular distribution of photoelectrons emitted from the carbonyl group in randomly oriented pure enantiomers of carvone, and a number of carvone derivatives, is investigated by continuum multiple scattering calculations. Core ionization of carbonyl C 1s orbitals is examined for six different isopropenyl tail conformations of carvone. These show clear differences of behavior both between axial and equatorial conformations, and between the three rotational conformers of each. The pronounced dependence of the dichroism on orientation of a tail grouping, itself remote from the localized initial C 1s site, indicates the presence of long range final state photoelectron scattering effects. Analogous data for the outermost valence orbital, partially localized on the carbonyl group, are also presented. The apparently enhanced sensitivity of the dichroism exhibited in this work is discussed in terms of the particular dependence on photoelectron interference effects that is probed by the dichroism measurement and is contrasted with the usual beta parameter and cross section determinations.

First author: Yan, Li-Kai, A DFT study on the electronic and redox properties of [PW11O39(ReN)](n-)(n=3, 4, 5) and [PW11O39(OsN)](2-), EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 125, 5126, (2006)
Abstract: DFT calculations were carried out to investigate the electronic and redox properties of nitrido-functionalized polyoxometalate species, [PW11O39(ReN)(n-) (n = 3, 4, 5) and [PW11O39(OsN)](2-). The rhenium- and osmium-nitrido effectively modify the electronic properties. The LUMOs in fully oxidized [PW11O39(ReN)](3-) and [PW11O39(OsN)](2-) are mainly concentrated on the Re and Os centers. The high-valent transition metals Re and Os modify the components and energies of the LUMO. The LUMO energies Of [PW11O39(ReN)](3-) and [PW11O39(OsN)](2-) are lower than that of related Keggin [PW12O40](3-). In addition, Re centers will prefer to accept the electrons in the first and second reduced process of fully oxidized [PW11O39(ReN)](3-).

First author: Aikens, Christine M., TDDFT studies of absorption and SERS spectra of pyridine interacting with Au-20,JOURNAL OF PHYSICAL CHEMISTRY A, 110, 13317, (2006)
Abstract: dWe present time dependent density functional theory (TDDFT) calculations for a tetrahedral Au-20 complex interacting with pyridine for the purpose of modeling absorption and surface enhanced Raman scattering, with emphasis on chemical and electrodynamic enhancement effects. These calculations are done using the ADF code with the BP86 functional, the zeroth-order regular approximation and with the resonant electronic response modeled using a short time approximation expression for the perturbed density matrix, with a damping factor that is empirically chosen. The absorption spectrum of bare Au-20 shows strong intraband (sp-sp) and interband (sp-d) coupling with a low-energy peak at 2.89 eV that is mostly intraband and other peaks at 3.94 and 4.70 eV that have mixed intra- and interband character. SERS spectra are calculated for pyridine/Au-20 for both vertex (V) and surface (S) configurations at their respective lowest energy absorption maxima (near 2.89 eV), and we find that the V configuration has higher intensities that correspond to SERS enhancements of 10(3)-10(4), whereas S has an enhancement of 10(2)-10(3). These enhancement values are significantly lower than the analogous results for pyridine/Ag-20 primarily because of reduced oscillator strength associated with the intraband transition in Au-20. Decomposition of the pyridine/ Au-20 enhancement factor into chemical and electromagnetic contributions (through an analysis of the static SERS intensities) shows enhanced chemical enhancements compared to Ag-20 but reduced electromagnetic enhancements.

First author: Atanasov, Mihail, DFT studies on the magnetic exchange across the cyanide bridge, JOURNAL OF PHYSICAL CHEMISTRY A, 110, 13332, (2006)
Abstract: Exchange coupling across the cyanide bridge in a series of novel cyanometalate complexes with Cu-II-NC-M-III (M = Cr and low-spin Mn, Fe) fragments has been studied using the broken-symmetry DFT approach and an empirical model, which allows us to relate the exchange coupling constant with sigma-, pi-, and pi*-type spin densities of the CN- bridging ligand. Ferromagnetic exchange is found to be dominated by pi-delocalization via the CN- pi pathway, whereas spin polarization with participation of sigma orbitals ( in examples, where the d(z)(2) orbital of MIII is empty) and pi* orbitals of CN- yields negative spin occupations in these orbitals, and reduces the Cu-II-M-III exchange coupling constant. When the dz2 orbital of MIII is singly occupied, an additional positive spin density appears in the sigma(CN) orbital and leads to an increase of the ferromagnetic Cu-NC-M exchange constant. For low-spin [M-III(CN)(6)](3-) complexes, the d(z)(2) orbital occupancy results in high-spin metastable excited states, and this offers interesting aspects for applications in the area of molecular photomagnetism. The DFT values of the exchange coupling parameters resulting from different occupations of the t(2g) orbitals of low-spin (t(2g)(5)) Fe-III are used to discuss the effect of spin-orbit coupling on the isotropic and anisotropic exchange coupling in linear Cu-NC-Fe pairs.

First author: Krapp, Andreas, Orbital overlap and chemical bonding, CHEMISTRY-A EUROPEAN JOURNAL, 12, 9196, (2006)
Abstract: The chemical bonds in the diatomic molecules Li-2-F-2 and Na-2-Cl-2 at different bond lengths have been analyzed by the energy decomposition analysis (EDA) method using DFT calculations at the BP86/TZ2P level. The interatomic interactions are discussed in terms of quasiclassical electrostatic interactions Delta E-elstat, Pauli repulsion Delta E-Pauli and attractive orbital interactions Delta E-Pauli. The energy terms are compared with the orbital overlaps at different interatomic distances. The quasiclassical electrostatic interactions between two electrons occupying 1s, 2s, 2p(sigma), and 2p(pi) orbitals have been calculated and the results are analyzed and discussed. It is shown that the equilibrium distances of the covalent bonds are not determined by the maximum overlap of the sigma valence orbitals, which nearly always has its largest value at clearly shorter distances than the equilibrium bond length. The crucial interaction that prevents shorter bonds is not the loss of attractive interactions, but a sharp increase in the Pauli repulsion between electrons in valence orbitals. The attractive interactions of Delta E-orb and the repulsive interactions of Delta E-orb are both determined by the orbital overlap. The net effect of the two terms depends on the occupation of the valence orbitals, but the onset of attractive orbital interactions occurs at longer distances than Pauli repulsion, because overlap of occupied orbitals with vacant orbitals starts earlier than overlap between occupied orbitals. The contribution of Delta E-elslat in most nonpolar covalent bonds is strongly attractive. This comes from the deviation of quasiclassical electron-electron repulsion and nuclear-electron attraction from Coulomb’s law for point charges. The actual strength of Delta E-elstat depends on the size and shape of the occupied valence orbitals. The attractive electrostatic contributions in the diatomic molecules Li-2-F-2 come from the s and p(sigma) electrons, while the p(pi) electrons do not compensate for nuclear-nuclear repulsion. It is the interplay of the three terms Delta E-orb, Delta E-Pauli, and Delta E-elstat that determines the bond energies and equilibrium distances of covalently bonded molecules. Molecules like N-2 and O-2, which are usually considered as covalently bonded, would not be bonded without the quasiclassical attraction Delta E-elstat.

First author: Martineau, C., Multinuclear high-resolution NMR study of compounds from the ternary system NaF-CaF2-AlF3: From determination to modeling of NMR parameters, INORGANIC CHEMISTRY, 45, 10215, (2006)
Abstract: Al-27 and Na-23 NMR satellite transition spectroscopy and 3Q magic-angle-spinning spectra are recorded for three compounds from the ternary NaF-CaF2-AlF3 system. The quadrupolar frequency nu(Q), asymmetry parameter eta(Q), and isotropic chemical shift delta(iso) are extracted from the spectrum reconstructions for five aluminum and four sodium sites. The quadrupolar parameters are calculated using the LAPW-based ab initio code WIEN2k. It is necessary to perform a structure optimization of all compounds to ensure a fine agreement between experimental and calculated parameters. By a comparison of experimental and calculated values, an attribution of all of the 27Al and 23Na NMR lines to the crystallographic sites is achieved. High-speed F-19 NMR MAS spectra are recorded and reconstructed for the same compounds, leading to the determination of 18 isotropic chemical shifts. The superposition model developed by Bureau et al. is used, allowing a bijective assignment of the F-19 NMR lines to the crystallographic sites.

First author: Shi Shao-Qing, DFT studies on the second-order nonlinear optical properties of [M(6)Om(C25N4H18)n](2-)(M=W, Mo; n=1, 2; m=17, 18), CHEMICAL JOURNAL OF CHINESE UNIVERSITIES-CHINESE, 27, 2398, (2006)
Abstract: The geometries of Lindqvist polyoxometalates bonded with terpyridine ligands (systems 1-4) were optimized by using DFF. The optimized main bond lengths are found to be in good agreement with experimental values. On the basis of the stable structures, the second-order nonlinear optical properties were calculated by using DFT/LB94 under the zero field condition. The beta(vec) values of systems 1 and 2 are 154.4 x 10(-30) and 124.8 x 10(-30) esu, respectively. These results indicate that systems 1 and 2 have larger nonlinear optical properties. The beta(vec) value for systems containing Mo atom is larger than that of systems containing W atom. With increasing of the number of the segment, the beta(vec) value increases remarkably. The beta(vec) of the system 1 is larger than that of system 2. The beta(vec) of system 3 is larger than system 4. Moreover, the beta(3) and beta(4) are larger than beta(1) and beta(2), respectively. But, there is not the obvious multiple relationships between the beta(vec) value and the number of the segment.

First author: Steudel, Ralf, Homolytic dissociation of the vulcanization accelerator tetramethylthiuram disulfide (TMTD) and structures and stabilities of the related radicals Me2NCSn center dot (n=1-4), JOURNAL OF ORGANIC CHEMISTRY,71, 9302, (2006)
Abstract: The homolytic dissociation of the important vulcanization accelerator tetramethylthiuram disulfide (TMTD) has been studied by ab initio calculations according to the G3X(MP2) and G3X(MP2)-RAD theories. Homolytic cleavage of the SS bond requires a low enthalpy of 150.0 kJ mol(-1), whereas 268.0 kJ mol(-1) is needed for the dissociation of one of the C-S single bonds. To cleave one of the SS bonds of the corresponding trisulfide (TMTT) requires 191.1 kJ mol(-1). Me2NCS2 center dot is a particularly stable sulfur radical as reflected in the low S-H bond dissociation enthalpy of the corresponding acid Me2NC(=S)SH (301.7 kJ mol(-1)). Me2NCS2 center dot (B-2(2)) is a sigma radical characterized by the unpaired spin density shared equally between the two sulfur atoms and by a 4-center (NCS2) delocalized pi system. The ESR g-tensors of the radicals Me2NCSn center dot (n = 1-3) have been calculated. Both TMTD and the mentioned radicals form stable chelate complexes with a Li+ cation, which here serves as a model for the zinc ions used in accelerated rubber vulcanization. Although the binding energy of the complex [Li(TMTD)](+) is larger than that of the isomeric species [Li(S2CNMe2)(2)](+) (12), the dissociation enthalpy of TMTD as a ligand is smaller (125.5 kJ mol(-1)) than that of free TMTD. In other words, the homolytic dissociation of the SS bonds of TMTD is facilitated by the presence of Li+ ions. The sulfurization of TMTD in the presence of Li+ to give the paramagnetic complex [Li(S3CNMe2)(2)](+) is strongly exothermic. These results suggest that TMTD reacts with naked zinc ions as well as with the surface atoms of solid zinc oxide particles in an analogous manner producing highly reactive complexes, which probably initiate the crosslinking process during vulcanization reactions of natural or synthetic rubber accelerated by TMTD/ZnO.

First author: Bagno, Alessandro, Fries rearrangement of aryl formates: A mechanistic study by means of H-1, H-2, and B-11 NMR spectroscopy and DFT calculations, JOURNAL OF ORGANIC CHEMISTRY, 71, 9331, (2006)
Abstract: H-1, H-2, and B-11 NMR spectroscopy has been used to study the mechanism of the Fries rearrangement of aryl formates promoted by boron trichloride by monitoring both the substrate and the Lewis acid. DFT calculations were employed to investigate the energetics of several reaction paths and to calculate NMR chemical shifts of key intermediates and products. After the formation of a 1:1 substrate-Lewis acid adduct, the rearrangement proceeds in two steps, beginning with the cleavage of the ester bond and the release of formyl chloride in situ, which, in turn, acts as a formylating agent, introducing an aldehydic functionality into the aromatic ring. The high regioselectivity (only the ortho product is obtained) is also accounted for by the proposed intermolecular, Lewis acid-assisted mechanism.

First author: Liao, Yi, Theoretical study on the optoelectronic properties of electron-withdrawing substituted diethynylfluorenyl gold(I) complexes, JOURNAL OF PHYSICAL CHEMISTRY A, 110, 13036, (2006)
Abstract: We report on a quantum-chemical study of the electronic and optical properties of gold( I) complex AuTFT ( 1) and its electron-withdrawing substitutents, AuTFOT ( 2) and AuTFCNT ( 3) [ where TFT) diethynylfluorenyl, TFOT = diethynylfluorenone and TFCNT = diethynyl-( 9-( dicyanomethylene) fluorene)]. Our theoretical calculations indicate that for all systems the reorganization energies of electron and hole are in the same order of magnitude and similar to those of the well-known electrontransport material Alq(3). The substitution of -CO and -C( CN)(2) for -CH in AuTFT significantly decreases the bond length alternation and increases the electron affinity, which would effectively lower the energy barrier for electron injection from cathode and thus qualify AuTFOT ( 2) and AuTFCNT ( 3) as candidates for the electron transport layer ( ETL) in light-emitting diodes ( LEDs). The lowest lying excited-states of gold( I) diethynylfluorenyl derivatives have been studied by the singles configuration interaction ( CIS) method and time-dependent density functional method ( TDDFT). It is found that the electron-withdrawing substitutions evidently decrease the energy gap, leading to a remarkable red shift in transition energy and transformation in the direction of charge transfer. Our research is important in the development of new functional materials for the design of LEDs with enhanced performance.

First author: Liao, Meng-Sheng, DFT/TDDFT study of Lanthanide(III) mono- and bisporphyrin complexes, JOURNAL OF PHYSICAL CHEMISTRY A, 110, 13089, (2006)
Abstract: The electronic structure, molecular structure, and electronic spectra of lanthanide(III) mono- and bisporphyrin complexes are investigated using a DFT/TDDFT method. These complexes include YbP( acac), YbP2, [ YbP2](+), YbHP2, and [ YbP2](-) ( where P) porphine and acac) acetylacetonate). To shed some light on the origin of the out-of-plane displacement of Yb in YbP( acac), unligated model systems, namely, planar D-4h and distorted C-4v YbP, were calculated. For comparison, the calculations were also extended to include the (CeP2)-P-IV and [ (CeP2)-P-IV](+) systems. Even without an axial ligand, the lanthanide atom lies considerably above the porphyrin plane; the distortion of the YbP molecular structure from a planar D-4h to the nonplanar C-4v symmetry leads to a considerable energy lowering. The axial ligand makes the metal out-of-plane displacement even larger, and it also changes the redox properties of the lanthanide monoporphyrin. The ground-state configurations of YbP2 and YbHP2 were determined by considering several possible low-lying states. YbP2 is confirmed to be a single-hole radical. The special redox properties of the bisporphyrin complexes can well be accounted for by the calculated ionization potentials and electron affinities. The TDDFT results provide a clear description of the UV-vis and near-IR absorption spectra of the various lanthanide porphyrins.

First author: Jensen, Morten B., Oxygen influence on the dissociative chemisorption of methane on nickel: A quantum chemical cluster model study, CHEMICAL PHYSICS LETTERS, 432, 94, (2006)
Abstract: A quantum chemical investigation of methane activation on reduced and partially oxidized Ni(100) surfaces has been performed. For all surfaces, methane activation has been assumed to proceed by dissociative adsorption at an on-top site. The activation energy of methane adsorption on a reduced Ni-25 cluster was calculated at 108 kJ/mol, while for various Ni25O clusters (modelling partially oxidized surfaces) the activation energies were significantly higher.

First author: Suzuki, Yasuhiko, Titanium and zirconium complexes with non-salicylaldimine-type imine-phenoxy chelate ligands: Syntheses, structures, and ethylene-polymerization behavior, CHEMISTRY-AN ASIAN JOURNAL, 1, 878, (2006)
Abstract: New Ti and Zr complexes that bear imine-phenoxy chelate ligands, [12,4-di-tBu-6-(RCH=N)C6H40}MCl2] (1: M=Ti, R=Ph; 2: M=Ti, R=C6F5; 3: M=Zr, R=Ph; 4: M=Zr, R=C6F5), were synthesized and investigated as precatalysts for ethylene polymerization. H-1 NMR spectroscopy suggests that these complexes exist as mixtures of structural isomers. X-ray crystallographic analysis of the adduct 1 center dot HCl reveals that it exists as a zwitterionic complex in which H and Cl are situated in close proximity to one of the imine nitrogen atoms and the central metal, respectively. The Xray molecular structure also indicates that one imine phenoxy group with the syn C=N configuration functions as a bidentate ligand, whereas the other, of the anti C=N form, acts as a monodentate phenoxy ligand. Although Zr complexes 3 and 4 with methylaluminoxane (MAO) or [Ph3C](+)[B(C6F5)(4)]/AliBu(3)displayed moderate activity, the Ti congeners 1 and 2, in association with an appropriate activator, catalyzed ethylene polymerization with high efficiency. Upon activation with MAO at 25 degrees C, 2 displayed a very high activity of 19900 (kg PE) (mol Ti)(-1)h(-1), which is comparable to that for [Cp2TiCl2] and [Cp2ZrCl2], although increasing the polymerization temperature did result in a marked decrease in activity. Complex 2 contains a C6F5 group on the imine nitrogen atom and mediated nonliving-type polymerization, unlike the corresponding salicylaldimine-type complex. Conversely, with [Ph3C](-)/[B(C6F5)(4)](-)/AliBu(3) activation, 1 exhibited enhanced activity as the temperature was increased (25-75 degrees C) and maintained very high activity for 60 min at 75 degrees C (18740 (kg PE) (mol Ti)(-1)h(-1)). H-1 NMR spectroscopic studies of the reaction suggest that this thermally robust catalyst system generates an amine-phenoxy complex as the catalytically active species. The combinations 1/[Ph3C](+)[B(C6F5)(4)](-)/AliBu(3) and 2/MAO also worked as high-activity catalysts for the copolymerization of ethylene and propylene.

First author: Lundqvist, Maria J., DFT study of bare and dye-sensitized TiO2 clusters and nanocrystals, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 106, 3214, (2006)
Abstract: Structural and electronic properties of bare and dye-sensitized TiO2 clusters and nanoparticles with sizes of <= 2 nm have been studied by density functional theory (DFT) calculations. Starting from truncated bulk lattice structures, the degree of structural reorganization, including the formation of Ti=O surface species, of bare TiO2 anatase nanocrystals, is found to be sensitive to the quality of the computational method. The electronic structures of optimized 1-2 nm nanoparticles show well-developed band structures with essentially no electronic bandgap defect states. Significant bandgap broadening due to quantum size effects is observed as the size of the nanocrystals is reduced from 2 nm to 1 nm in diameter, but further bandgap widening is limited by increasingly severe competing surface defect sites as the particles become smaller than similar to 1 nm in diameter. The applicability of the TiO2 nanocrystals in modeling the electronic structure and electronic coupling at dye-sensitized TiO2 nanocrystal interfaces has been investigated by attachment of pyridine to one of the nanoparticle models via phosphonic or carboxylic acid anchor groups.

First author: Conradie, Jeanet, When being straight bends rules: A rationale for the linear FeNO unit in the low-spin square-pyramidal {FeNO}(7) tetracyanonitrosylferrate(2-) anion, JOURNAL OF INORGANIC BIOCHEMISTRY, 100, 2069, (2006)
Abstract: All low-spin S = 1/2 heme-NO complexes feature FeNO angles of about 140 degrees. In contrast, the square-pyramidal [Fe(CN)(4)(NO)](2-) complex features an exactly linear {FeNO}(7) unit. We have sought here to determine a possible, simple molecular orbital (MO) rationale for these structural variations. A DFT-based (DFT = density functional theory) MO analysis shows that the linearity of the latter stems from the greater pyramidalization of the Fe center, relative to nitrosylheme, which results in significant differences in d orbital hybridization. Thus, the singly occupied molecular orbital (SOMO) of [Fe(CN)(4)(NO)](2-), while primarily Fe d(alpha 2)-based, also has a significant amount of 4p(alpha) character. which makes it less stereochemically active, accounting for the linearity of the FeNO unit.

First author: Sun, Yuming, A DFT study on the electronic character of P700(+), JOURNAL OF THEORETICAL & COMPUTATIONAL CHEMISTRY, 5, 733, (2006)
Abstract: This density functional study is devoted to the long debated electronic nature of P700(+). We found that P700(+) is intrinsically a dimer of chlorophyll molecules. The unpaired electron spin distributes equally over two chlorophyll molecule halves in the bare P700(+), while the dressed P700(+) shows the spin density asymmetry mainly coming from the H-bond donated to 13(1)-keto-O of one half. The experimental contradictions on the electronic nature of P700(+) are also discussed.

First author: Pittalis, S., Optimized effective potential method in current-spin-density-functional theory, PHYSICAL REVIEW A, 74, 733, (2006)
Abstract: Current-spin-density-functional theory (CSDFT) provides a framework to describe interacting many-electron systems in a magnetic field which couples to both spin and orbital degrees of freedom. Unlike in the usual (spin-)density-functional theory, approximations to the exchange-correlation energy based on the model of the uniform electron gas face problems in practical applications. In this work, explicitly orbital-dependent functionals are used and a generalization of the optimized effective potential method to the CSDFT framework is presented. A simplifying approximation to the resulting integral equations for the exchange-correlation potentials is suggested. A detailed analysis of these equations is carried out for the case of open-shell atoms and numerical results are given using the exact-exchange energy functional. For zero external magnetic field, a small systematic lowering of the total energy for current-carrying states is observed due to the inclusion of the current in the Kohn-Sham scheme. For states without current, CSDFT results coincide with those of spin-density-functional theory.

First author: Berger, J. A., Performance of the Vignale-Kohn functional in the linear response of metals, PHYSICAL REVIEW B, 74, 733, (2006)
Abstract: Recently the linear response of metallic solids has been formulated within the time-dependent current-density-functional approach [Romaniello and de Boeij, Phys. Rev. B 71, 155108 (2005)]. The implementation, which originally used only the adiabatic local density approximation for the exchange-correlation kernel is extended in order to include also the Vignale-Kohn current functional. Within this approximation the exchange-correlation kernel is frequency dependent, thus relaxation effects due to electron-electron scattering can now be taken into account and some deficiencies of the adiabatic local density approximation (ALDA), as the absence of the low-frequency Drude-like tail in absorption spectra, can be cured. We strictly follow the previous formulation of the linear response of semiconductors by using the Vignale-Kohn functional [Berger, de Boeij, and van Leeuwen, Phys. Rev. B 71, 155104 (2005)]. The self-consistent equations for the interband and intraband contributions to the induced density and current density, which are completely decoupled within the ALDA and in the long-wavelength limit, now remain coupled. We present our results calculated for the optical properties of the noble metals Cu, Ag, and Au and we compare them with measurements found in literature. In the case of Au we treat the dominant scalar relativistic effects using the zeroth-order regular approximation in the ground-state density-functional-theory calculations, as well as in the time-dependent response calculations.

First author: Ben Yahia, M., A relativistic DFT study of cyclopentadienyl actinide complexes with no transition-metal analogues, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 777, 61, (2006)
Abstract: The geometry and electronic structure of several tris and tetrakis-cyclopentadienyl thorium and uranium complexes have been investigated using Density Functional theory (DFT) calculations in the framework of the relativistic zeroth-order regular approximation (ZORA) implemented in the ADF (Amsterdam density functional) program. In all cases, the important interaction between the metal 5f orbitals and the Cp-3 moiety is brought to light. However, coordination with a fourth ligand like H- or Cl- leading to Cp(3)AnL species involves mainly the metal 6d orbitals, whereas in the case of L = Cp-, the 5f uranium orbitals act also efficiently. The actinide 5f orbitals are more efficient in uranium than in thorium for metal to ligand bonding. Cyclopentadienyl to uranium donation is enhanced when the metal ion charge increases. Finally, our calculations indicate that the Cp3UH structure could be thermodynamically stable, although it has not yet been synthesized.

First author: Mitoraj, Mariusz, 1,3 geminal interactions as the possible trend setting factors for C-H and C-C bond energies in alkanes. Support from a density functional theory based bond energy decomposition study, JOURNAL OF ORGANIC CHEMISTRY, 71, 9208, (2006)
Abstract: [GRAPHICS]A bond energy decomposition analysis has been carried out to rationalize the well-established experimental fact that C-C and C-H bond energies decrease with increasing substitution on the carbon. It is shown that this trend is set by steric 1,3 repulsive interactions (geminal repulsion) that increase in the order 1,3 hydrogen-hydrogen < 1,3 hydrogen-carbon < 1,3 carbon-carbon. On the other hand, the radical stabilization energy has little influence on the observed trend for the C-H bond energy in H-CR1R2R3 or the C-C bond energy in H3C-CR1R2R3. Thus, it varies in H-CR1R2R3 from -7.2 kcal/mol (H-CH3) to -6.5 kcal/mol (H-C(CH3)(3)) and in H3C-CR1R2R3 from -19.0 kcal/mol (H3C-CH3) to -16.9 kcal/mol (H3C-C(CH3)(3)). It was further found that the average intrinsic C-H bond energy in H-CR1R2R3 of 129.2 kcal/mol is smaller than the average intrinsic C-C bond energy in H3C-CR1R2R3 of 143.4 kcal/mol. However, after the inclusion of steric effects, the overall C-H bond becomes stronger than the C-C bond. The role of steric 1,3 repulsive interactions as the trend setting factor has most recently been suggested by Gronert (J. Org. Chem. 2006, 71, 1209) based on an empirical fit of alkane atomization energies.

First author: Jin, Xi, Reactions of gadolinium atoms and dimers with CO: Formation of gadolinium carbonyls and photoconversion to CO activated molecules, JOURNAL OF PHYSICAL CHEMISTRY A, 110, 12585, (2006)
Abstract: Reactions of gadolinium atoms and dimers with carbon monoxide molecules in solid argon have been studied using matrix isolation infrared absorption spectroscopy. Mononuclear Gd(CO)(x) (x = 1-3) and dinuclear Gd-2(CO)(x) (x = 1, 2) gadolinium carbonyls formed spontaneously on annealing. The Gd(CO) x complexes are CO terminal-bonded carbonyls, whereas the Gd2CO and Gd-2(CO)(2) carbonyl complexes were characterized to have asymmetrically bridging and side-on-bonded CO, which are drastically activated with remarkably low C-O stretching frequencies. The cyclic Gd-2(mu-C)(mu-O) and Gd-3(mu-C)(mu-O) molecules in which the C-O triple bond is completely cleaved were also formed on annealing. The Gd-2(CO)(2) complex rearranged to the more stable c-Gd-2(mu-O)(mu-CCO) isomer, which also has a four-membered ring structure with one CO being completely activated.

First author: Yang, Guochun, Theoretical study on the electronic spectrum and the origin of remarkably large third-order nonlinear optical properties of organoimide derivatives of hexamolybdates, JOURNAL OF PHYSICAL CHEMISTRY B,110, 23092, (2006)
Abstract: Electronic spectrum of organoimide derivatives of hexamolybdates have first been calculated within the time-dependent density-functional theory in conjunction with Van Leeuwen-Baerends (LB94) exchange correlation potential, statistical average of orbital potentials (SAOP), and gradient-regulated connection potential (GRAC), respectively. The GRAC yields much better agreement with experiments for the excitation energies comparing with both LB94 and SAOP. The analysis of transition nature indicates that there is a significant difference between the diagonal and the orthogonal substituted derivatives. The static and dynamic third-order polarizabilities are calculated using time-dependent density-functional theory combined with the sum-over-states method. The results show that these derivatives possess remarkable large molecular third-order polarizabilities, especially for system 8 with -17882.6 x 10(-36) esu. This value is about 250 times that for the C-60 molecule. Adding the organoimide segment to the [Mo6O19](2-) can substantially increase the gamma value. This variation can be traced to the different electronic transition characteristics between the derivatives of [Mo6O19](2-) and [Mo6O19](2-). For our studied systems, increasing the conjugation length and diagonal substituted are efficient ways to enhance the third-order polarizability. Thus, the organoimide derivatives of hexamolybdates may comprise a new promising class of nonlinear optical materials from the standpoint of large gamma values, small dispersion behavior, and high transparency.

First author: Jacob, Christoph R., Calculation of nuclear magnetic resonance shieldings using frozen-density embedding,JOURNAL OF CHEMICAL PHYSICS, 125, 23092, (2006)
Abstract: We have extended the frozen-density embedding (FDE) scheme within density-functional theory [T. A. Wesolowski and A. Warshel, J. Phys. Chem. 97, 8050 (1993)] to include external magnetic fields and applied this extension to the nonrelativistic calculation of nuclear magnetic resonance (NMR) shieldings. This leads to a formulation in which the electron density and the induced current are calculated separately for the individual subsystems. If the current dependence of the exchange-correlation functional and of the nonadditive kinetic-energy functional are neglected, the induced currents in the subsystems are not coupled and each of them can be determined without knowledge of the induced current in the other subsystem. This allows the calculation of the NMR shielding as a sum of contributions of the individual subsystems. As a test application, we have calculated the solvent shifts of the nitrogen shielding of acetonitrile for different solvents using small geometry-optimized clusters consisting of acetonitrile and one solvent molecule. By comparing to the solvent shifts obtained from supermolecular calculations we assess the accuracy of the solvent shifts obtained from FDE calculations. We find a good agreement between supermolecular and FDE calculations for different solvents. In most cases it is possible to neglect the contribution of the induced current in the solvent subsystem to the NMR shielding, but it has to be considered for aromatic solvents. We demonstrate that FDE can describe the effect of induced currents in the environment accurately.

First author: Zhao, Yan, A new local density functional for main-group thermochemistry, transition metal bonding, thermochemical kinetics, and noncovalent interactions, JOURNAL OF CHEMICAL PHYSICS, 125, 23092, (2006)
Abstract: We present a new local density functional, called M06-L, for main-group and transition element thermochemistry, thermochemical kinetics, and noncovalent interactions. The functional is designed to capture the main dependence of the exchange-correlation energy on local spin density, spin density gradient, and spin kinetic energy density, and it is parametrized to satisfy the uniform-electron-gas limit and to have good performance for both main-group chemistry and transition metal chemistry. The M06-L functional and 14 other functionals have been comparatively assessed against 22 energetic databases. Among the tested functionals, which include the popular B3LYP, BLYP, and BP86 functionals as well as our previous M05 functional, the M06-L functional gives the best overall performance for a combination of main-group thermochemistry, thermochemical kinetics, and organometallic, inorganometallic, biological, and noncovalent interactions. It also does very well for predicting geometries and vibrational frequencies. Because of the computational advantages of local functionals, the present functional should be very useful for many applications in chemistry, especially for simulations on moderate-sized and large systems and when long time scales must be addressed.

First author: Bagno, Alessandro, Computational modeling of polyoxotungstates by relativistic DFT calculations of W-183 NMR chemical shifts, CHEMISTRY-A EUROPEAN JOURNAL, 12, 8460, (2006)
Abstract: The W-183 nuclear shielding in a variety of tungsten polyoxometalates (POM) (Lindqvist, Anderson, decatungstates, Keggin) of different shapes and charges has been modeled by DFT calculations that take into account relativistic effects, by means of the zeroorder regular approximation (ZORA), and solvent effects, by the conductor-like screening model (COSMO) continuum method. The charge/surface area ratio (q1A) is proposed as an indicator of the charge density to which the solvation energies of all POMs are correlated in a satisfactory way. Among the various theoretical levels tested (ZORA scalar or spin-orbit, frozen-core or all-electron basis set, geometry optimization in the gas phase or in the continuum solvent, etc.), the best results are obtained when both geometry optimization in solvent and spin-orbit shielding are included (mean absolute error of delta = 35 ppm). The quality of the computed chemical shifts depends systematically on the charge density as expressed by q/A; thus, POMs with low q/A ratios display the best agreement with experimental data. The performance of the method is such that computed values can aid the assignment of the W-183 NMR spectra of polyoxotungstates, as shown by the case of alpha-[PW11TiO40](5-), whose six signals are ranked computationally so as to almost reproduce the experimental ordering even though the signals are spaced by as little as 5 ppm.

First author: Balazs, Gabor, Terminally coordinated AsS and PS ligands, CHEMISTRY-A EUROPEAN JOURNAL, 12, 8603, (2006)
Abstract: The terminal AsS and PS complexes [(N3N)W(ES)] (N3N = N(CH2CH2NSiMe3)(3); E=P (3), As (4)) were synthesised by reaction of [(N,N)W As] and [(N3N)W P], respectively, with cyclohexene sulfide. Both complexes present very short W-E and E-S bond lengths. The bonding was investigated by density functional theory (DFT) calculations using the fragment calculation method and natural bond orbital (NBO) analysis. According to the fragment analysis, in which the complexes were separated in an ES and a (N3N)W fragment, the bonding in complexes 3, 4 and [(N3N)W(SbS)] (5) is realised over a set of two sigma (1 sigma and 2 sigma) and two degenerate pi molecular orbitals (MOs) (1 pi and 2 pi). The 1 sigma MO is a bonding MO extended over the N-ax-W-E-S core, whereas the 2 sigma MO is localised mainly on the E-S fragment. The 1 pi set is a E-S localised bonding molecular orbital, whereas the 2 pi set is in phase with respect to W-E but in antiphase with respect to E-S. Both methods indicate bond orders around two for both the E-S and the W-E bonds. The polarity of the complexes was examined by Hirshfeld charge analysis. This shows that complexes 3 and 4 are only slightly polarised, whereas 5 is moderately polarised toward the sulphur. As suggested by the computational results, the pi system in complexes 3-5 is best described by two three-centre four-electron bonds.

First author: Nazeeruddin, Md. K., Efficient green-blue-light-emitting cationic iridium complex for light-emitting electrochemical cells, INORGANIC CHEMISTRY, 45, 9245, (2006)
Abstract: A highly luminescent novel cationic iridium complex [iridium bis(2-phenylpyridine)(4,4 ‘-(dimethylamino)-2,2 ‘-bipyridine)]PF6 was synthesized and characterized using NMR, UV-visible absorption, and emission spectroscopy and electrochemical methods. This complex displays intense photoluminescence maxima in the green-blue region of the visible spectrum and exhibits unprecedented phosphorescence quantum yields, 80 +/- 10% with an excitedstate lifetime of 2.2 mu s in a dichloromethane solution at 298 K. Single-layer light-emitting electrochemical cells with the charged complex as conducting and electroluminescent material sandwiched between indium-tin oxide and Ag electrodes were fabricated, which emit green-blue light with an onset voltage as low as 2.5 V. Density functional theory calculations were performed to provide insight into the electronic structure of the [iridium bis(2-phenylpyridine)(4,4 ‘-(dimethylamino)-2,2 ‘-bipyridine)]PF6 complex, comparing these results with those obtained for [iridium bis(2phenylpyridine)(4,4 ‘-tert-butyl-2,2 ‘-bipyridine)]PF6.

First author: Yang, Jenny Y., Hangman salen platforms containing two xanthene scaffolds, JOURNAL OF ORGANIC CHEMISTRY, 71, 8706, (2006)
Abstract: A synthetic strategy for the construction of chiral salen ligands bearing two rigid xanthene spacers functionalized with carboxylic acid and ester groups is presented. Suzuki cross-coupling methodology is used to furnish the appropriately functionalized xanthene spacers to a salicyladehyde, which is subsequently condensed with (1R, 2R)-(-)-1,2-diaminocyclohexane to produce salen ligands featuring an expandable molecular cleft capable of multiple hydrogen-bonding interactions in addition to metallosalen oxidation chemistry. The ability of these “Hangman” platforms to support multielectron chemistry mediated by proton-coupled electron transfer (PCET) is established by their proclivity to promote the catalytic disproportionation of hydrogen peroxide to oxygen and water via a high-valent metal oxo. Within this functionalized Hangman framework, the stereochemistry of the cyclohexyl backbone of the salen platform is revealed in the epoxidation of 1,2-dihydronaphthalene by the metal oxo.

First author: Lim, Mi Hee, Direct nitric oxide detection in aqueous solution by copper(II) fluorescein complexes, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 14364, (2006)
Abstract: A series of FL(n) (n = 1-5) ligands, where FL(n) is a fluorescein modified with a functionalized 8-aminoquinoline group as a copper-binding moiety, were synthesized, and the chemical and photophysical properties of the free ligands and their copper complexes were investigated. UV-visible spectroscopy revealed a 1: 1 binding stoichiometry for the Cu(II) complexes of FL(1), FL(3), and FL(5) in pH 7.0 buffered aqueous solutions. The reactions of FL(2) or FL(4) with CuCl(2), however, appear to produce a mixture of 1: 1 and 1: 2 complexes, as suggested by Job’s plots. These binding modes were modeled by the synthesis and X-ray crystal structure determination of Cu(II) complexes of 2-[(quinolin-8-ylamino) methyl] phenol (modL), employed as a surrogate of the FL(n) ligand family. Two kinds of crystals, [Cu(modL)(2)](BF(4))(2) and [Cu(2)(modL’)(2)-(CH(3)OH)](BF(4))(2) (modL’ = 2-[(quinolin-8-ylamino) methyl] phenolate), were obtained. The structures suggest that one oxygen and two nitrogen atoms of the FL(n) ligands most likely bind to Cu(II). Introduction of nitric oxide (NO) to pH 7.0 buffered aqueous solutions of Cu(FL(n)) (1 AM CuCl2 and 1 AM FL n) at 37 C induces an increase in fluorescence. The fluorescence response of Cu(FL(n)) to NO is direct and specific, which is a significant improvement over commercially available small molecule-based probes that are capable of detecting NO only indirectly. The NO-triggered fluorescence increase of Cu(FL5) occurs by reduction of Cu(II) to Cu(I) with concomitant dissociation of the N-nitrosated fluorophore ligand from copper. Spectroscopic and product analyses of the reaction of the FL5 copper complex with NO indicated that the N-nitrosated fluorescein ligand (FL(5)-NO) is the species responsible for fluorescence turn-on. Density functional theory (DFT) calculations of FL(5) versus FL(5)-NO reveal how N-nitrosation of the fluorophore ligand brings about the fluorescence increase. The copper-based probes described in the present work form the basis for real-time detection of nitric oxide production in living cells.

First author: Mercs, Laszlo, Piano-stool iron(II) complexes as probes for the bonding of N-heterocyclic carbenes: Indications for pi-acceptor ability, ORGANOMETALLICS, 25, 5648, (2006)
Abstract: A series of new piano-stool iron(II) complexes comprising mono- and bidentate chelating N-heterocyclic carbene ligands [Fe(cp)(CO)(NHC)(L)]X have been prepared and analyzed by spectroscopic, electrochemical, crystallographic, and theoretical methods. Selectively substituting the L site with a series of ligands going from carbene to pyridine to CO suggests that CO is the strongest pi acceptor, while the behavior of pyridine and carbene is nearly identical. This suggests that in these complexes comprising an electron-rich iron(cp)( carbene) fragment, N-heterocyclic carbenes are not pure sigma donors but also moderate pi acceptors. Theoretical calculations support this bonding model and indicate charge saturation at the metal as key for pi back-bonding to N-heterocyclic carbenes. On the basis of voltammetric measurements, the Lever electrochemical parameter of these carbenes has been determined: E-L = + 0.29. Systematic substitution of the wingtip groups of the carbene revealed only subtle changes in the electronic properties of the iron center, thus providing a suitable methodology for ligand-induced fine-tuning of the coordinated metal.

First author: Kogut, Elzbieta, Neutral high-potential nickel triad bisdithiolenes: Structure and solid-state NMR properties of Pt[S2C2(CF3)(2)](2), INORGANIC CHEMISTRY, 45, 8850, (2006)
Abstract: X-ray crystallography and solid-state NMR techniques were used to determine the structure and Pt-195 NMR chemical shift ( CS) tensor of Pt[ S2C2( CF3)(2)](2). This is the first reported crystal structure of a highly oxidizing ( CN- or CF3-substituted) neutral bis( dithiolene) complex of a Ni triad metal in its pure form. The Pt-195 NMR CS tensor is highly anisotropic and asymmetric; the latter property is attributed to the noninnocent nature of the ligand. The tensor components and orientation are determined with density functional theory calculations.

First author: Fang, Hua, Density functional study of closed-shell attractions of X(AuL)(2)(q) (X = N, O, P, S, As, Se) systems, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 773, 15, (2006)
Abstract: In order to find out whether standard density functional (DF) approaches can correctly reproduce closed-shell aurophilic interactions, we have examined a series of compounds of type X(AuL)(2)(q) (X = N, O, P, S, As, Se), q = 0 or 1-, using scalar-relativistic theory. Geometric structures, NBO populations and HOMO-LUMO gaps were investigated. Experimental structure parameters of the title compounds were reproduced by X alpha. Several new X-atom complexes are predicted. The electronegativity of central atom X correlates with the Au-X-Au angle, the HOMO-LUMO gap and the electronic structure.

First author: Hofmann, Matthias, What is the best theoretical method to study molybdenum dithiolene complexes?,JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 773, 59, (2006)
Abstract: The reaction sequence of sulfoxide reduction by molybdenum complexes containing two enedithiolate and one oxide ligand is used to evaluate different density functional methods. Relative energies are computed for several stationary points: a pentacoordinate reduced complex, its adducts with water and with the sulfoxide substrate, the transition state for oxygen atom transfer to the metal center, a van der Waals complex of the reduced sulfide with the molybdenum oxo complex and the isolated oxo complex itself. Root mean square deviations from CCSD results or values extrapolated (depending on the size of the ligands used) serve to assess the quality of various popular and promising modern DFT methods available in Gaussian03 (in combination with the SDD basis set augmented by additional polarization functions) and ADF2005 (TZP basis set). B3LYP, B1B95, B97-1 and B98 form the group of best functionals provided by Gaussian according to our criteria. PBE1PBE, B1LYP, MPW1PW91 and B97-2 have increasingly larger deviations but describe the considered reaction sequence qualitatively correct. The reaction profiles produced by HCTH147, BP86, HCTH407, BLYP, G96LYP and especially by OLYP, HCTH93, BHandH and VSXC have severe flaws. These functionals are not recommended for the treatment of oxygen atom transfer reactions involving transition metals. DFT functionals used with ADF derived energies for the BP/TZP density. The relative energies show larger RMS, which can be slightly reduced by inclusion of ZORA scalar relativistic effects and in the case of hybrid functionals further by ZORA spin-orbit relativistic effects. Geometries obtained with BP/TZP produce RMS deviations comparable to the best methods identified when relative energies are derived from single point energies computed by one of these methods.

First author: Wang, Xue-Bin, Free tetra- and hexa-coordinated platinum-cyanide dianions, Pt(CN)(4)(2-) and Pt(CN)(6)(2-) : A combined photodetachment photoelectron spectroscopic and theoretical study, CHEMICAL PHYSICS, 329, 230, (2006)
Abstract: Two doubly charged transition metal complexes, Pt(CN)(4)(2-) and Pt(CN)(6)(2-) commonly found in the condensed phases, are produced as isolated species from solutions to the gas phase using electrospray ionization. Their stability and electronic structures are investigated by photodetachment photoelectron spectroscopy and density functional theory (DFT) calculations. The adiabatic electron detachment energies for the dianions to monoanions are measured to be 1.69 and 3.85 eV for Pt(CN)(4)(2-) and Pt(CN)(6)(2-) respectively. The magnitude of the repulsive Coulomb barrier is estimated to be similar to 2.5 eV for Pt(CN)(4)(2-), and similar to 1.7 eV for Pt(CN)(6)(2-). Well-resolved and distinct peaks are observed in the spectra, yielding rich electronic structure information for these complexes. DFT calculations including scalar relativistic and spin-orbit effects are carried out to determine the geometries and to interpret the observed spectral features. The calculations show that the frontier occupied molecular orbitals are largely metal-based for Pt(CN)(4)(2-) and ligand-based for Pt(CN)(6)(2-), in contrast to the standard ligand field theory description.

First author: Karawajczyk, Anna, Mechanism of bleomycin suicide: A Car-Parrinello molecular dynamics investigation,JOURNAL OF PHYSICAL CHEMISTRY B, 110, 21245, (2006)
Abstract: Using first-principles molecular dynamics simulations (Car-Parrinello method) we investigated the possible reaction pathways for decay of the active bleomycin- Fe(III)-OOH complex, so-called bleomycin suicide. The theoretical model of activated bleomycin contains the whole metal bonding domain of the bleomycin ligand. Simulations performed both in a vacuum and in water show that a facile decaying process involves a homolytic O-O bond cleavage with an almost simultaneous hydrogen atom abstraction. The formation of an intra- or intermolecular hydrogen bond appears to be crucial for the decay of the activated bleomycin. We did not observe any evidence of heterolytic cleavage of the O-O bond of the Fe( III)-OOH species.

First author: Shaw, Jennifer L., Redox non-innocence of thioether macrocycles: Elucidation of the electronic structures of mononuclear complexes of gold(II) and silver(II), JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 13827, (2006)
Abstract: The mononuclear +2 oxidation state metal complexes [Au([9]aneS(3))(2)](2+) and [Ag([18]aneS(6))](2+) have been synthesized and characterized crystallographically. The crystal structure of the Au(II) species [Au([9] aneS(3))(2)](BF4)(2) shows a Jahn-Teller tetragonally distorted geometry with Au-S(1) = 2.839(5), Au-S(2) = 2.462(5), and Au-S(3) = 2.452(5) angstrom. The related Ag(II) complex [Ag([18] aneS(6))](ClO4)(2) has been structurally characterized at both 150 and 30 K and is the first structurally characterized complex of Ag(II) with homoleptic thioether S-coordination. The single-crystal X-ray structure of [Ag([18]aneS(6))](ClO4)(2) confirms octahedral homoleptic S-6-thioether coordination. At 150 K, the structure contains two independent Ag(II)-S distances of 2.569(7) and 2.720(6) angstrom. At 30 K, the structure retains two independent Ag(II)-S distances of 2.615(6) and 2.620(6) angstrom, with the complex cation retaining 3-fold symmetry. The electronic structures of [Au([9]aneS(3))(2)](2+) and [Ag([18]aneS(6))](2+) have been probed in depth using multifrequency EPR spectroscopy coupled with DFT calculations. For [Au([9] aneS(3))(2)](2+), the spectra are complex due to large quadrupole coupling to Au-197. Simulation of the multifrequency spectra gives the principal g values, hyperfine (A) and quadrupole (P) couplings, and furthermore reveals non-co-incidence of the principal axes of the P tensor with respect to the A and g matrices. These results are rationalized in terms of the electronic and geometric structure and reveal that the SOMO has ca. 30% Au 5d(xy) character, consistent with DFT calculations (27% Au character). For [Ag([18]aneS(6))](2+), detailed EPR spectroscopic analysis confirms that the SOMO has ca. 26% Ag 4d(xy) character and DFT calculations are consistent with this result (22% Ag character).

First author: Costa, Paulo Jorge, Photochemistry of methyltrioxorhenium revisited: A DFT/TD-DFT and CASSCF/MS-CASPT2 theoretical study, ORGANOMETALLICS, 25, 5235, (2006)
Abstract: The electronic structure of (CH3)ReO3 was reanalyzed by means of DFT calculations (ADF and Gaussian03 programs). TD-DFT calculations were carried out, using the DFT-optimized structure and several functionals, to assign the electronic excitations and interpret the dissociative behavior under irradiation. The agreement between calculated and experimental wavelengths was very good and could not be improved when using highly correlated methods (CASSCF/MS-CASPT2). The lowest energy transition at 260 nm was assigned to a LMCT from p O to Re d (pi* Re-O), correcting the earlier empirical assignment. The second transition, experimentally observed at 240 nm, is assigned to a charge transfer from C and O to Re in TD-DFT, but the weight of the C participation drops significantly in the CASSCF/MS-CASPT2 approach. (C2H5)ReO3 exhibits a similar behavior. On the other hand, for (C6H5)ReO3 and {C6H3(CH3)(3)}ReO3 the strong low-energy absorption results from a LMCT from the phenyl pi* to d Re (pi* Re-O), reproducing the experimental trends.

First author: McMaster, J., Density functional theoretical studies of the Re-Xe bonds in Re(Cp)(CO) (PF3)Xe and Re(Cp)(CO)(2)Xe, ORGANOMETALLICS, 25, 5242, (2006)
Abstract: Density functional calculations have been used to probe the electronic structures of Re(Cp)(CO)(2)Xe and Re(Cp)(CO)(PF3)Xe. The calculated CO stretching frequencies compare favorably with those determined experimentally. Our calculations of delta(Xe) and (3)J(Xe-F) for Re(Cp)(CO)(PF3)Xe represent the first for a well-characterized transition metal-noble gas compound and demonstrate that DFT using the BP86 and SAOP functionals reproduces these parameters to within 1% and 8% of their experimentally determined values. The calculated Re-Xe bond dissociation energies for Re(Cp)(CO)(2)Xe (12.3 kcal mol(-1)) and Re(Cp)(CO)(PF3)Xe (11.9 kcal mol(-1)) are also in excellent agreement with the lower limits for these energies estimated from the activation parameters for the reaction of the complexes with CO in supercritical Xe. A topological analysis of the electron density in Re( Cp)( CO) 2Xe and Re(Cp)(CO)(PF3) Xe reveals positive del(2)rho(r) at the critical points (del rho(r(c)) = 0.1310 and 0.1396 e angstrom(5) for Re(Cp)(CO)(2)Xe and Re(Cp)(CO)(PF3)Xe, respectively, indicating that the Re-Xe interaction is essentially closed-shell in both complexes. Fragment and overlap density of states analyses show that the orbital interactions in these compounds is dominated by overlap involving the Xe p orbitals and the orbitals of the Cp, CO, and/or PF3 ligands; the Re d orbitals appear to contribute little to the orbital interactions between the Re(Cp)(CO)(2) and Re(Cp)(CO)(PF3), and Xe fragments.

First author: Patkowski, Konrad, Third-order interactions in symmetry-adapted perturbation theory, JOURNAL OF CHEMICAL PHYSICS, 125, 5242, (2006)
Abstract: We present an extension of many-body symmetry-adapted perturbation theory (SAPT) by including all third-order polarization and exchange contributions obtained with the neglect of intramonomer correlation effects. The third-order polarization energy, which naturally decomposes into the induction, dispersion, and mixed, induction-dispersion components, is significantly quenched at short range by electron exchange effects. We propose a decomposition of the total third-order exchange energy into the exchange-induction, exchange-dispersion, and exchange-induction-dispersion contributions which provide the quenching for the corresponding individual polarization contributions. All components of the third-order energy have been expressed in terms of molecular integrals and orbital energies. The obtained formulas, valid for both dimer- and monomer-centered basis sets, have been implemented within the general closed-shell many-electron SAPT program. Test calculations for several small dimers have been performed and their results are presented. For dispersion-bound dimers, the inclusion of the third-order effects eliminates the need for a hybrid SAPT approach, involving supermolecular Hartree-Fock calculations. For dimers consisting of strongly polar monomers, the hybrid approach remains more accurate. It is shown that, due to the extent of the quenching, the third-order polarization effects should be included only together with their exchange counterparts. Furthermore, the latter have to be calculated exactly, rather than estimated by scaling the second-order values.

First author: Sceats, Emma L., Noncovalent interactions between organometallic metallocene complexes and single-walled carbon nanotubes, JOURNAL OF CHEMICAL PHYSICS, 125, 5242, (2006)
Abstract: First principles density functional pseudopotential calculations have been used to investigate the nature of interactions between single-walled carbon nanotubes (SWNTs) and intercalated transition metal metallocene complexes, M(eta-C5H5)(2) (MCp2). Three composites, MCp2-graphene (d(t)=infinity), MCp2@(17,0) (d(t)=1.33 nm), and MCp2@(12,0) (d(t)=0.94 nm) (where M=Fe,Co), have been studied to probe the influence of the nanotube diameter (d(t)) on the nature and magnitude of the interactions. Theoretical results presented here demonstrate that these MCp2@SWNT composites are stabilized by weak pi-stacking and CH center dot pi interactions, and in the case of the CoCp2@SWNT composites there is an additional electrostatic contribution as a result of charge transfer from CoCp2 to the nanotube. The extent of charge transfer (MCp2 -> SWNT) can be rationalized in terms of the electronic structures of the two fragments, or more specifically, the relative positions of the metallocene highest occupied molecular orbital and the conduction band of the nanotube in the electronic structure of the composite.

First author: Couzijn, Erik P. A., Electronic structure and stability of pentaorganosilicates, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 13634, (2006)
Abstract: The exceptional stability of recently reported pentaorganosilicates is investigated by bond energy analyses. Experimental coupling constants are used to probe their electronic structure, entailing bonds with mixed ionic-covalent character. Our analyses reconfirm that the axial bonds are more prone to heterolytic cleavage than are the equatorial bonds. Aryl substituents provide substantial electronic stabilization by charge delocalization, but cause steric crowding due to ortho-hydrogen repulsion. In contrast, silicates with two ax, eq biaryl groups are not congested. The remaining substituent is confined to an equatorial site, where it is insensitive to elimination. These concepts adequately explain the experimentally observed stability trends and are valuable for designing other stable pentaorganosilicates.

First author: Flisak, Zygmunt, “Dormant” secondary metal-alkyl complexes are not omnipresent, PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 103, 15338, (2006)
Abstract: This theoretical study was inspired by the perpetual debate over the so-called “dormancy” of the active sites in propylene polymerization, i.e., a drop in their activity after a regioerror (2,1-insertion), which was reported to occur in many (although not all) catalytic systems. To explore the range of possible situations, we have selected two homogeneous systems of fundamentally different structure: an octahedral system Of C-2 symmetry with a tetradentate -O-N-N-O- ligand and a bridged indenyl catalyst. This choice was not accidental; it is in these two systems where the experimentalists cannot reach a consensus about dormancy. Our density-functional theory calculations explain why in certain catalytic systems both primary and secondary alkyl complexes can be equally reactive toward propylene polymerization, despite the intuitive concept of dormancy. To understand such a behavior, it was imperative to build an extensive model, including the counteranion and solvent effects. The discussion is also supplemented by our latest calculations on the classical second-generation Ziegler-Natta system.

First author: Martinho, Paulo N., New polynuclear Mo-Fe complexes with ferrocenylamidobenzimidazole ligands,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 103, 4096, (2006)
Abstract: The reaction between [Mo(eta(3)-C3H5)(CO)(2)(NCMe)(2)Br] (1) and the ferrocenylamidobenzimidazole ligands FcCO(NH(2)benzim) (L1) and (FcCO)(2)(NHbenzim) (L2) led to a binuclear (2) and a trinuclear (3) Mo-Fe complex, respectively. The single-crystal X-ray structure of [Mo(eta(3)-C3H5)(CO)(2)(L2)Br] [L2 = {[(eta(5)-C5H5)Fe(eta(5)-C5H4CO)](2)(2-NH-benzimidazol-yl)}] shows that L2 is coordinated to the endo Mo(eta(3)-C3H5)(CO)(2) group in a kappa(2)-N,O-bidentate chelating fashion whereas the Mo-II centre displays a pseudooctahedral environment with Br occupying an equatorial position. Complex 2 was formulated as [MO(eta(3)-C3H5)(CO)(2)(L1)Br] on the basis of a combination of spectroscopic data, elemental analysis, conductivity and DFT calculations. L1 acts as a kappa(2)-N,N-bidentate ligand. In both L1 and L2, the HOMOs are mainly localised on iron while the C=O bond(s) contribute to the LUMO(s) and the next highest energy orbitals are Fe-allyl antibonding orbitals. When the ligands bind to Mo(eta(3)-C3H5)(CO)(2)Br, the greatest difference is that Mo becomes the strongest contributor to the HOMO. Electrochemical studies show that, in complex 2, no electronic interaction exists between the two ferrocenyl ligands and that the first electron has been removed from the Mo-II-centred HOMO.

First author: Guan, Wei, How do the different defect structures and element substitutions affect the nonlinear optical properties of lacunary Keggin polyoxometalates? A DFT study, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY,103, 4179, (2006)
Abstract: Systematic DFT calculations have been carried out on the lacunary alpha-Keggin polyoxometalate derivatives [PW11O39](7-), [XW9O34](n-) (X = Al-III, Si-IV, Ge-IV, P-V, As-V, and Sb-V), [XW9M2O39](n-), and [XW9M3O40](n-) (X = P-V and Si-IV, M = Mo-VI, V-V, Nb-V, and Ta-V) to investigate the geometric structure and element substitution effects on the molecular nonlinear optical response. Analysis of the computed static second-order polarizability (beta(0)) predicts that the molecular nonlinear optical activity of lacunary Keggin polyoxometalate derivatives can be modified by replacing the central heteroatom and the addenda metal atom. Substitution of the central Al atom or the addenda V atom causes significant enhancement in the molecular nonlinearity. Moreover, the beta(0) values are substantially dependent on the defect structures. This class of inorganic complexes possesses remarkably large molecular optical nonlinearity, especially for the partial substitution complex [SiW9Nb2O39](10-) (IIIc), which has a computed beta(0) value of 2071.0 a.u. Thus, lacunary Keggin polyoxometalates could become excellent candidates in the field of second-order NLO.

First author: Han, Wen-Ge, Density functional theory study of Fe(IV) d-d optical transitions in active-site models of class I ribonucleotide reductase intermediate X with vertical self-consistent reaction field method, INORGANIC CHEMISTRY, 45, 8533, (2006)
Abstract: The Fe(IV) d-d transition energies for four active-site structural models of class I ribonucleotide reductase (RNR) intermediate X have been calculated using broken-symmetry density functional theory incorporated with the Slater transition state vertical self-consistent reaction field methodology. Our model I ( Figure 1), which contains two mu-oxo bridges, one terminal water, and one bidentate carboxylate group, yields the best Fe( IV) d-d transition energies compared with experiment. Our previous study (J. Am. Chem. Soc. 2005, 127, 15778-15790) also shows that most of the other calculated properties of model I in both native and mutant Y122F forms, including geometries, spin states, pK(a)’s, Fe-57, H-1, and O-17 hyperfine tensors, and Fe-57 Mossbauer isomer shifts and quadrupole splittings, are also the best in agreement with the available experimental data. This model is likely to represent the active-site structure of the intermediate state X of RNR.

First author: Yin, Biaolin, Synthesis, structure, and photophysical properties of luminescent platinum(II) complexes containing cyclometalated 4-styryl-functionalized 2-phenylpyridine ligands, INORGANIC CHEMISTRY, 45, 8584, (2006)
Abstract: A series of new luminescent cyclometalated platinum(II) complexes functionalized with various substituted styryl groups on the cyclometallating ligand [Pt(C boolean AND N-ppy-4-styryl-R)(O boolean AND O-(O)CCR’CHCR’C(O))] (ppy-4-styryl-R = E-4(4-(R)styryl-2-phenylpyridine) (3, R’ = Me (acac); 4, R’ = Bu-t (dpm); R = H, OMe, NEt2, NO2) have been prepared. All complexes undergo an E-Z photoisomerization process in CH2Cl2 solution under sunlight, as monitored by H-1 NMR. The solid-state structures of 3-OMe, 3-NEt2, 3-NO2, and 4-OMe have been determined by X-ray diffraction studies and compare well with optimized geometries obtained by density functional theory (DFT) calculations. The orbital pictures of 3-H, 3-OMe, and 3-NO2 are very similar, the highest occupied molecular orbital (HOMO) being highly Pt(5d) metal-based. For 3-NMe2, an additional contribution from the amino-styryl fragment leads to a decreased metal parentage of the HOMO, suggesting a predominantly ILCT character transition. Complexes 3-H, 3-OMe, and 3-NO2 show a low-energy band (350-400 nm) assigned to predominantly charge-transfer transitions. The amino derivative 3-NEt2 displays a very strong absorption band at 432 nm, tentatively assigned to a mixture of ILCT (Et2N -> CH=CH*) and metal-to-ligand charge-transfer (MLCT) (d pi(Pt) -> pi*) transitions. Complexes 3 are weakly luminescent in CH2Cl2 solution at room temperature; the low intensity may be due to a competitive quenching through the E-Z photoisomerization process. All complexes exhibit similar structured emission bands under these conditions (lambda(max)(em) around 520 nm), independent of the nature of the styryl-R group. In a frozen EPA glass (77 K), the spectrum of the representative complex 3-H exhibits two sets of vibronically structured bands (460-560, 570-800 nm; lambda(max) = 596 nm), due to the presence of two emitting species, the E and Z isomers, which have significantly different triplet excited-state energies. The other three complexes show similar behavior to 3-H at 77 K, but the lower-energy emission bands are progressively red-shifted in the order H < OMe < NO2 < NEt2 (e.g., for 3-NEt2, lambda(max)(em) = 658 nm; tau = 26 mu s). The very large red-shift compared to related unsubstituted complexes (e.g., to [Pt(C boolean AND N-ppy)(O boolean AND O-acac)]) is the result of the extension of the pi-conjugated system and the electronic effects of substituent R.

First author: de Jong, G. Theodoor, Oxidative addition to main group versus transition metals: Insights from the Activation Strain model, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 691, 4341, (2006)
Abstract: We have studied the oxidative addition of the methane C-H and chloromethane C-Cl bonds to a number of main group (Be, Mg and Ca) and transition metals (Pd, Zn and Cd), using relativistic density functional theory (DFT) at ZORA-BLYP/TZ2P. The purpose is to better understand what causes the characteristic differences in reactivity between main group and transition metals towards oxidative addition. Thus, we have analyzed our model reactions using the Activation Strain model in which the activation energy Delta E-not equal is decomposed into the activation strain Delta E-strain(not equal) of and the stabilizing TS interaction Delta E-int(not equal) between the reactants in the activated complex: Delta E-not equal = AE(strain)(not equal) + Delta E-int(not equal). Activation of the C-H bond goes with higher barriers than activation of the C-Cl bond because the higher bond strength of the former translates into a higher activation strain Delta E-strain(not equal). The barriers for bond activation increase along Pd < Be, Ca < Mg < Zn, Cd. This can be straightforwardly understood through the TS-interaction Delta E-int(not equal) that is, in terms of the bonding capabilities of the metals. Pd yields the lowest barriers because it achieves the most stabilizing Delta E-int(not equal). This is the result of the small HOMO-LUMO gap between its occupied 4d and unfilled 5s AOs, which makes Pd both a good electron donor and acceptor. Zn and Cd yield the highest barriers because the large HOMO-LUMO gap between the occupied valence ns and unfilled valence np AOs makes them both poor donors and poor acceptors of electronic charge.

First author: Jacobsen, Heiko, pi-Acidity and pi-basicity of N-heterocyclic carbene ligands. A computational assessment,JOURNAL OF ORGANOMETALLIC CHEMISTRY, 691, 4350, (2006)
Abstract: In this contribution we report on a systematic analysis of the bond between transition metals and N-heterocyclic carbene (NHC) ligands. We compare the sigma and pi-contributions in a series of complexes in which the formal d-electron count ranges from d(0) to d(10). Our results confirm the currently accepted idea that NHC are not pure a-donors. In the series of complexes examined here pi-contribution is 10% at least. Moreover, remarkable metal-to-ligand backdonation occurs also for d(0) complexes, and many systems present a substantial ligand-to-metal n donation.

First author: Dazinger, Georg, Formation of pyridine from acetylenes and nitriles catalyzed by RuCpCl, CoCp, and RhCp derivatives – A computational mechanistic study, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 691, 4434, (2006)
Abstract: The mechanism of the catalytic formation of pyridines from the coupling of two alkynes and the nitriles N CR (R = H, Me, Cl, COOMe) with the fragments CpRuCl, CpCo, and CpRh has been investigated by means of DFT/B3LYP calculations. According to the proposed mechanism, the key reaction step is the oxidative coupling of two alkyne ligands to give metallacyclopentatriene (Ru, Rh) and metallacyclopentadiene (Co) intermediates. In the case of ruthenium, this process is thermodynamically clearly favored over the oxidative coupling between one alkyne and one nitrile ligand to afford an azametallacycle. This alternative pathway however cannot be dismissed in the case of Co and Rh. The rate determining step of the overall catalytic cycle is the addition of a nitrile molecule to the metallacyclopentatriene and metallacyclopentadiene intermediates, respectively, which has to take place in a side-on fashion. Competitive alkyne addition leads to benzene formation. Thus, also the chemo selectivity of this reaction is determined at this stage of the catalytic cycle. In the case of the RuCpCl fragment, the addition of nitriles R-C N and acetylenes RC CH has been studied in more detail. For R = H, Cl, and COOMe the side-on addition of nitriles is kinetically more favored than alkyne addition and, in accordance with experimental results, pyridine formation takes place. In the case of R = Me nitrile addition could not be achieved and the addition of alkynes to give benzene derivatives seems to be kinetically more favored. Once the nitrile is coordinated facile C-C bond coupling takes place to afford an unusual five- and four-membered bicyclic ring system. This intermediate eventually rearranges to a very unsymmetrical azametallaheptatriene complex which in turn provides CpRuCl(kappa(1)-pyridine) via a reductive elimination step. Completion of the catalytic cycle is achieved by an exergonic displacement of the respective pyridine product by two acetylene molecules regenerating the bisacetylene complex.

First author: Zhu, Hongjuan, A theoretical study of the original Shilov reaction involving methane activation by platinum tetrachloride (PtCl42-) in an acidic aqueous solution, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 691, 4486, (2006)
Abstract: Density functional theory (DFT) has been employed to investigate the rate-determining step for the Shilov reaction in which ptCl(4)(-2) 4 can catalyze H-D exchange of alkanes in acidic aqueous solution. C-H activation and methane uptake are the two possible candidates. Associative and dissociative pathways are both considered in the methane uptake step. It was not possible to determine whether methane uptake followed an associative or dissociative mechanism due to uncertainties in the calculated contributions to the free energy of activation, from entropy and solvation. The active species in the Shilov reaction are PtCl42-, PtCl3H2O- and PtCl2(H2O)(2). We have shown that PtCl2(H2O)(2) is the most active catalyst for H/D exchange. Rate expressions for the Shilov reaction have been derived for different reaction conditions.

First author: Guillaumont, Dominique, Actinide(III) and lanthanide(III) complexes with nitrogen ligands: Counterions and ligand substituent effects on the metal-ligand bond, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 771, 105, (2006)
Abstract: Relativistic density functional theory calculations are reported for actinide(III) (An = U, Am, Cm) and lanthanide(HI) (Ln = La, Nd) complexes with tridentate aromatic nitrogen ligands. Calculations have been performed on 2,2 ‘:6 ‘,2 ”-terpyridine (Terpy) complexes with various species in the first coordination sphere of the metal ion besides one Terpy ligand (H2O, Cl- and NO3-) and on bis(1,2-4-triazin-3 -yl)pyridine (Btp) complexes with various susbtituents attached to the triazine rings (CH3, OCH3 and CN). Metal-ligand bonds in trivalent lanthanum, neodynium, americium and curium complexes are predominantly ionic, and significant variations are found in metal-nitrogen bond lengths when the total charge of the complexes is changed by the number of counterions or when the charges on the coordinating nitrogen atoms are altered by substituents. Uranium-ligand bonds are more covalent and smaller variations are found in uranium-nitrogen bond distances. The most remarkable effect on uranium-ligand bonds is obtained by attaching CN groups to the Btp, uranium(5f)-to-Btp(pi*) back-bonding is enhanced and uranium-nitrogen bonds are shortened.

First author: Santhanamoorthi, N., Charge transfer in polypeptides: Effect of secondary structures on charge-transfer integral and site energies, JOURNAL OF PHYSICAL CHEMISTRY A, 110, 11551, (2006)
Abstract: We have theoretically studied the charge transfer in glycine polypeptide using quantum mechanical models based on a tight-binding Hamiltonian approach. The charge-transfer integrals and site energies involved in the transport of positive charge through the peptide bond in glycine polypeptide have been calculated. The charge-transfer integrals and site energies have been calculated directly from the matrix elements of the Kohn-Sham Hamiltonian defined in terms of the molecular orbitals of the individual fragments of the glycine polypeptide. In addition to this, we have calculated the rate of charge transfer between a neighboring amino acid subgroup through the Marcus rate equation. These calculations have been performed for the different secondary structures of the glycine model peptide such as linear, alpha-helix, 3(10)-helix, and antiparallel beta-sheet by varying the dihedral angles omega, alpha and psi along the C-alpha-carbon of amino acid subgroup. Present theoretical results confirm that the charge transfer through the peptide bond is strongly affected by the conformations of the oligopeptide.

First author: Cotton, F. Albert, Photoelectron spectroscopy and DFT calculations of easily ionized quadruply bonded Mo-2(4+) compounds and their bicyclic guanidinate precursors, JOURNAL OF PHYSICAL CHEMISTRY B, 110, 19793, (2006)
Abstract: A series of five bicyclic guanidinate compounds containing various combinations of five- and six- membered rings and substituted alkyl groups have been shown by photoelectron spectroscopy to be easily ionized, with the one having two six- membered rings and four ethyl groups being the most easily ionized. The corresponding anions are capable of forming paddlewheel compounds having quadruply bonded Mo-2(4+) units which are also easy to ionize. The most easily ionized compound is the ethyl-substituted Mo-2(TEhpp)(4) complex which has a broad first ionization band centered around 4.27 +/- 0.03 eV and an ionization onset at the very low energy of 3.93 +/- 0.03 eV. Even the compound with ligands containing two five-membered rings, which favors a long Mo – Mo separation because of the large ligand bite, has an ionization energy (4.78 eV) that is less than those of well-known organometallic reducing agents such as (eta(5)-C9Me7)(2)Co and (eta(5)-C5Me5)(2)Cr.

First author: Schinzel, Sandra, Structural and electronic analysis of lanthanide complexes: Reactivity may not necessarily be independent of the identity of the lanthanide atom – A DFT study, JOURNAL OF PHYSICAL CHEMISTRY A, 110, 11324, (2006)
Abstract: Density functional theory calculations were used to study a given complex for the whole series of lanthanide cations: [Ln(C3H5) Cp(OMe)] (1) [Ln = La (Z = 57)- Lu (Z = 71)], the radioactive lanthanide promethium (Z = 61) excepted. Contrary to the common assumptions, the calculations suggested a significant, albeit indirect, contribution of f electrons to bonding. Relativistic effects were considered in the calculations of the bonding energies, as well as in geometry optimizations in both spin- restricted and unrestricted formalisms. The unrestricted orbitals were finally used for the analysis of the charges and the composition of the frontier orbitals. It was confirmed that the ionic character was more pronounced for complexes of the late lanthanides.

First author: Prakash, Shipra, Photo-CIDNP MAS NMR in intact cells of Rhodobacter sphaeroides R26: Molecular and atomic resolution at nanomolar concentration, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 12794, (2006)
Abstract: Photochemically induced dynamic nuclear polarization (photo-CIDNP) is observed in photosynthetic reaction centers of the carotenoid-less strain R26 of the purple bacterium Rhodobacter sphaeroides by C-13 solid-state NMR at three different magnetic fields (4.7, 9.4, and 17.6 T). The signals of the donor appear enhanced absorptive (positive) and of the acceptor emissive (negative). This spectral feature is in contrast to photo-CIDNP data of reactions centers of Rhodobacter sphaeroides wildtype reported previously (Prakash, S.; Alia; Gast, P.; de Groot, H. J. M.; Jeschke, G.; Matysik, J. J. Am. Chem. Soc. 2005, 127, 14290-14298) in which all signals appear emissive. The difference is due to an additional mechanism occurring in RCs of R26 in the long-living triplet state of the donor, allowing for spectral editing by different enhancement mechanisms. The overall shape of the spectra remains independent of the magnetic field. The strongest enhancement is observed at 4.7 T, enabling the observation of photo-CIDNP enhanced NMR signals from reaction center cofactors in entire bacterial cells allowing for detection of subtle changes in the electronic structure at nanomolar concentration of the donor cofactor. Therefore, we establish in this paper photo-CIDNP MAS NMR as a method to study the electronic structure of photosynthetic cofactors at the molecular and atomic resolution as well as at cellular concentrations.

First author: Roy, Lindsay E., Electronic transitions in [Re6S8X6](4-) (X = Cl, Br, I): Results from time-dependent density functional theory and solid-state calculations, INORGANIC CHEMISTRY, 45, 8273, (2006)
Abstract: Relativistic time-dependent density functional theory (TDDFT) calculations were performed on the excited states of the [Re6S8X6](4-) (X = Cl, Br, I) series. For all members of the series, the lowest excited states in the spectra do not correspond to a ligand-to-metal (or ligand-to-cluster) excitation but rather a cluster-cluster transition from the HOMO e(g) to antibonding t(1u) orbitals with only a modest admixture of Re-X sigma* character. These results lead to a re-evaluation of the role of the axial ligand in these compounds. The calculated excitation energies reproduce the experimental absorption and emission spectra. This work also confirms previous TDDFT calculations on the emission energies. Results for discrete cluster ions are compared with those obtained from calculations in the solid state in Cs-4[Re6S8X6]center dot CsX (X = Cl, Br) and Cs-4[Re6S8I6]center dot 2Csl. Significant differences are seen in the relatively higher energies of the antibonding t1u orbital in the solid-state case, and an inversion in the orbital character of the two allowed absorptions is calculated. The e(g)(HOMO)-to-a(2g) (LUMO) orbital energy differences corresponding to the emission transition are quite comparable for the solid state and discrete cluster calculations, and both overestimate the observed emission energy by the same margin.

First author: Pyykkoe, Pekka, Comparative theoretical study of N-heterocyclic carbenes and other ligands bound to Au-I,CHEMISTRY-AN ASIAN JOURNAL, 1, 623, (2006)
Abstract: The bonding strength of N-heterocyclic carbene (NHC) ligands to a neutral AuCl test moiety are compared to that of several phosphanes and other ligands. Of the ligands studied, the NHCs clearly form the strongest bonds to AuCl. A simplified triangular CN2 model is also introduced for the NHCs.

First author: Guerra, Celia Fonseca, Orbital interactions and charge redistribution in weak hydrogen bonds: Watson-Crick GC mimic involving C-H proton donor and F proton acceptor groups, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 106, 2428, (2006)
Abstract: The discovery by Kool and coworkers that 2,4-difluorotoluene (F) mimics thymine (T) in DNA replication has led to controversy regarding the question of whether this mimic has the capability of forming hydrogen bonds with adenine (A). Recently, we have provided evidence for an important role of both hydrogen bonding and steric effects in the replication of DNA. In the present work, we extend our study to mimics (G(FC’N), and C-N’NF) of the bases guanine (G) and cytosine (C). We address not only the question of the strengths of the hydrogen bonds in G(FC’N)’C-N’NF as compared with those in GC but we focus in particular on the nature of these interactions. Thus, we have analyzed G(FC’N’)C(N’NF) and GC at the BP86/TZ2P level of density functional theory (DFT). In line with previous experience, this approach is shown to achieve close agreement with the available data from ab initio computations and experiment: the complexation energy of G(FC’N’)C(N’NF) (-4.1 kcal/mol) is confirmed to be much weaker indeed than that of GC (-26.1 kcal/mol). Interestingly, the weak hydrogen bonds in G(FC’N’)C(N’NF) still poses a significant orbital interaction component that resembles the situation for the more strongly bound GC, as follows from (1) an analysis of the orbital electronic structure of G(FC’N’)C(N’NF) and GC, (2) a quantitative decomposition of the G(FC’N’)-C-N’NF and G-C bond energies, as well as (3) a quantitative decomposition of the charge redistribution associated with the G(FC’N’)-C-N’NF and G-C interactions based on the Voronoi deformation density (VDD) method. The VDD method allows us to decompose the charge redistribution Delta Q per atom into a component associated with the Pauli repulsive orbital interactions and a component associated with the bonding orbital interactions: Delta Q = Delta Q(Pauli) + Delta Q(oi). Implications of our findings for the mechanism of DNA replication are discussed.

First author: Swart, Marcel, Optimization of strong and weak coordinates, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 106, 2536, (2006)
Abstract: We present a new scheme for the geometry optimization of equilibrium and transition state structures that can be used for both strong and weak coordinates. We use a screening function that depends on atom-pair distances to differentiate strong coordinates from weak coordinates. This differentiation significantly accelerates the optimization of these coordinates, and thus of the overall geometry. An adapted version of the delocalized coordinates setup is used to generate automatically a set of internal coordinates that is shown to perform well for the geometry optimization of systems with weak and strong coordinates. For the Baker test set of 30 molecules, we need only 173 geometry cycles with PW91/TZ2P calculations, which compares well with the best previous attempts reported in literature. For the localization of transition state structures, we generate the initial Hessian matrix, using appropriate force constants from a database. In this way, one avoids the explicit computation of the Hessian matrix.

First author: Swart, Marcel, Proton affinities of maingroup-element hydrides and noble gases: Trends across the periodic table, structural effects, and DFT validation, JOURNAL OF COMPUTATIONAL CHEMISTRY, 27, 1486, (2006)
Abstract: We have carried out an extensive exploration of the gas-phase basicity of archetypal neutral bases across the periodic system using the generalized gradient approximation (GGA) of the density functional theory (DFT) at BP86/QZ4P//BP86/TZ2P. First, we validate DFT as a reliable tool for computing proton affinities and related thermochemical quantities: BP86/QZ4P//BP86/TZ2P is shown to yield a mean absolute deviation of 2.0 kcal/mol for the proton affinity at 298 K with respect to experiment, and 1.2 kcal/mol with high-level ab initio benchmark data. The main purpose of this work is to provide the proton affinities (and corresponding entropies) at 298 K of the neutral bases constituted by all maingroup-element hydrides of groups 15-17 and the noble gases, that is, group 18, and periods 1-6. We have also studied the effect of step-wise methylation of the protophilic center of the second- and third-period bases.

First author: Liao, Meng-Sheng, Assessment of the performance of density-functional methods for calculations on iron porphyrins and related compounds, JOURNAL OF COMPUTATIONAL CHEMISTRY, 27, 1577, (2006)
Abstract: The behaviors of a large number of GGA, meta-GGA, and hybrid-GGA density functionals in describing the spin-state energetics of iron porphyrins and related compounds have been investigated. There is a large variation in performance between the various functionals for the calculations of the high-spin state relative energies. Most GGA and meta-GGA functionals are biased toward lower-spin states and so fail to give the correct ground state for the high-spin systems, for which the meta-GGA functionals show more or less improvement over the GGA ones. The GGA functionals that use the OPTX correction for exchange show remarkably high performance for calculating the high-spin state energetics, but their results for the intermediate-spin states are somewhat questionable. A heavily parameterized GGA functional, HCTH/407, provides results which are in qualitative agreement with the experimental findings for the iron porphyrins [FeP, FeP(Cl), FeP(THF)(2)], but its relative energies for the high-spin states are probably somewhat too low. The high-spin state relative energies are then even more underestimated by the corresponding meta-GGA functional tau-HCTH. For the hybrid-GGA functionals, the Hartree-Fock (HF)-type (or exact) exchange contribution strongly stabilizes the high-spin states, and so the performance of such functionals is largely dependent upon the amount of the HF exchange admixture in them. The B3LYP, B97, 97-1, and tau-HCTH-hyb functionals are able to provide a satisfactory description of the energetics of all the systems considered.

First author: Calhorda, Maria Jose, Synthesis and ligand properties towards gold and silver of the ferrocenylamidobenzimidazole ligand, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 691, 4181, (2006)
Abstract: The treatment of FcCOCl (Fc = (C5H5)Fe(C5H4)) With amino benzimidazole in 1: 1 or 2:1 ratio gives the ferrocenyl-amido derivatives FcCO(benzimNH(2)) or (FcCO)(2)(NHbenzim), respectively. The reactivity of FcCO(benzimNH(2)) with silver or gold complexes has been studied. The reaction with the basic gold compounds [Au(acac)(PPh3)] or [O(AuPPh3)(3)]ClO4 occurs with deprotonation of the NH2 group and coordination of one or three gold(phosphine) fragments. The treatment of this ligand with silver compounds, such as Ag(OTf) or [Ag(OTf)(PPh3)], gives the complexes of stoichiometry [Ag(OTf)L] or [Ag(OTf)(PPh3)]. The ligand FcCO(benzimNH(2)) and the complex [Ag(OTf){FcCO(benzimNH(2))}(PPh3)] have been characterized by X-ray diffraction studies. DFT calculations were performed on models of this dimeric silver complex and showed that dimerization is energetically favourable, because Ag(I) achieves a four coordination environment, despite some bonds being relatively weak.

First author: Bombarda, Elisa, Influence of the membrane potential on the protonation of bacteriorhodopsin: Insights from electrostatic calculations into the regulation of proton pumping, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY,128, 12129, (2006)
Abstract: Proton binding and release are elementary steps for the transfer of protons within proteins, which is a process that is crucial in biochemical catalysis and biological energy transduction. Local electric fields in proteins affect the proton binding energy compared to aqueous solution. In membrane proteins, also the membrane potential affects the local electrostatics and can thus be crucial for protein function. In this paper, we introduce a procedure to calculate the protonation probability of titratable sites of a membrane protein in the presence of a membrane potential. In the framework of continuum electrostatics, we use a modified Poisson-Boltzmann equation to include the influence of the membrane potential. Our method considers that in a transmembrane protein each titratable site is accessible for protons from only one side of the membrane depending on the hydrogen bond pattern of the protein. We show that the protonation of sites receiving their protons from different sides of the membrane is differently influenced by the membrane potential. In addition, the effect of the membrane potential is combined with the effect of the pH gradient resulting from proton pumping. Our method is applied to bacteriorhodopsin, a light-activated proton pump. We find that the proton pumping of this protein might be regulated by Asp115, a conserved residue for which no function has been identified yet. According to our calculations, the interaction of Asp115 with Asp85 leads to the protonation of the latter if the pH gradient or the membrane potential becomes too large. Since Asp85 is the primary proton acceptor in the photocycle, bacteriorhodopsin molecules in which Asp85 is protonated cannot pump protons. Furthermore, we estimate how the membrane potential affects the energetics of the individual proton-transfer reactions of the photocycle. Most reactions, except the initial proton transfer from the Schiff base to Asp85, are influenced. Our calculations give new insights into the mechanism with which bacteriorhodopsin senses the membrane potential and the pH gradient and how the proton pumping is regulated by these parameters.

First author: Senechal-David, Katell, Synthesis, structural studies, theoretical calculations, and linear and nonlinear optical properties of terpyridyl lanthanide complexes: New evidence for the contribution of f electrons to the NLO activity,JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 12243, (2006)
Abstract: The synthesis and structural, photophysical, and second-order nonlinear optical (NLO) properties of a novel lanthanide terpyridyl-like complex family LLn(NO(3))(3) (Ln = La, Gd, Dy, Yb, and Y) are reported. The isostructural character of this series in solution and in the solid state has been established on the basis of X-ray diffraction analysis in the cases of yttrium and gadolinium complexes, theoretical optimization of geometry (DFT), and NMR spectroscopy. The absorption, emission, and solvatochromic properties of the free terpyridyl-like ligand L were thourougly investigated, and the twist intramolecular charge transfer (TICT) character of the lowest energy transition was confirmed by theoretical calculation (TDDFT and CIS). The similar ionochromic effect of the different lanthanide ions was evidenced by the similar UV-visible spectra of the complete family of complexes. On the other hand, the quadratic hyperpolarizability coefficient beta, measured by the harmonic light scattering (HLS) technique, is clearly dependent on the nature of the metal, and a careful examination of the particular case of yttrium unambiguously confirms the contribution of metal f electrons to the NLO activity.

First author: Ghosh, Sutapa, Electronic structures and absorption spectra of linkage isomers of trithiocyanato (4,4 ‘,4 ”-tricarboxy-2,2 ‘: 6,2 ”-terpyridine) ruthenium(II) complexes: A DFT study, INORGANIC CHEMISTRY, 45, 7600, (2006)
Abstract: Black dye (BD), isomer 1 ([Ru-II(H-3-tctpy)(NCS)(3)](-1), where H-3-tctpy = 4,4′,4”-tricarboxy-2,2′:6,2”-terpyridine) is known to be an excellent sensitizer for dye-sensitized solar cells and exhibits a very good near-IR photo response, compared to other ruthenium dyes. Because isothiocyanate is a linear ambidentate ligand, BD has three other linkage isomers, [Ru(H-3-tctpy)(NCS)(2)(SCN)](-1), isomer 2 and 2′, and [Ru(H-3-tctpy)(SCN)(3)](-1), isomer 3. In this study, we have calculated the geometry of BD and its isomers by DFT. Further, we have analyzed the bonding in these isomers using NBO methods. TDDFT calculations combined with scalar relativistic zero-order regular approximations (SR-ZORA) have been carried out to simulate the absorption spectra. Calculations have been performed for the isomers both in vacuo and in solvent (ethanol). The inclusion of the solvent is found to be important to obtain spectra in good agreement with the experiment. The first absorption bands are dominated by the metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT).

First author: Guan, Wei, Prediction of second-order optical nonlinearity of trisorganotin-substituted beta-Keggin polyoxotungstate, INORGANIC CHEMISTRY, 45, 7864, (2006)
Abstract: The dipole polarizabilities, second-order polarizabilities, and origin of second-order nonlinear optical (NLO) properties of trisorganotin-substituted, ss-Keggin polyoxotungstate [XW9O37(SnR)(3)]((11-n)-) (X = P, Si, Ge, R = Ph; X = Si, R = PhNO2, PhCtCPh) have been investigated by using time-dependent density functional response theory. This class of organic – inorganic hybrid complexes possesses a remarkably large molecular second-order NLO response, especially for [SiW9O37(SnPhCtCPh)(3)](7-) (system 5) with the static second-order polarizability (ss vec) computed to be 1569.66 x 10(-30) esu. Thus, these complexes have the possibility to be excellent second-order nonlinear optical materials. Analysis of the major contributions to the, vec value suggests that the charge transfer from the hetero-polyanion to the organic segment along the z-axis plays the key role in the NLO response of [XW9O37( SnR)(3)]((11-n)-). The computed ss vec values increase as a heavy central heteroatom changes in the order Ge > Si > P. Furthermore, nitro substitution on the aryl segment and the lengthening of organostannic pi-conjugation are more important in enhancing the optical nonlinearity, especially for the latter factor. The present investigation provides important insight into the origin of the NLO properties of trisorganotin-substituted heteropolyoxotungstate.

First author: Vargas, Alfredo, Density-functional theory investigation of the geometric, energetic, and optical properties of the cobalt(II)tris(2,2 ‘-bipyridine) complex in the high-spin and the Jahn-Teller active low-spin states, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 2, 1342, (2006)
Abstract: State-of-the-art generalized gradient approximation (GGA) (PBE, OPBE, RPBE, OLYP, and HCTH), meta-GGA (VSXC and TPSS), and hybrid (B3LYP, B3LYP*, O3LYP, and PBE0) functionals are compared for the determination of the structure and the energetics of the D-3 [Co(bpy)(3)](2+) complex in the (4)A(2) and E-4 trigonal components of the high-spin T-4(1g)(t(2g)(5) e(g)(2)) state and in the low-spin E-2 state of octahedral E-2(g)(t(2g)(6) e(g)(1)) parentage. Their comparison extends also to the investigation of the Jahn-Teller instability of the E-2 state through the characterization of the extrema of C-2 symmetry of this spin state’s potential energy surface. The results obtained for [Co(bpy)(3)](2+) in either spin manifold are very consistent among the functionals used and are in good agreement with available experimental data. The functionals, however, perform very differently with respect to the spin-state energetics because the calculated values of the high-spin/low-spin energy difference Delta E-HL(el) vary between -3212 and 3919 cm(-1). Semilocal functionals tend to give too large Delta E-HL(el) values and thus fail to correctly predict the high-spin state as the ground state of the isolated complex, while hybrid functionals tend to overestimate the stability of the high-spin state with respect to the low-spin state. Reliable results are, however, obtained with the OLYP, HCTH, B3LYP*, and O3LYP functionals which perform best for the description of the isolated complex. The optical properties of [Co(bpy)(3)](2+) in the two spin states are also analyzed on the basis of electronic excitation calculations performed within time-dependent density functional response theory. The calculated absorption and circular dichroism spectra agree well with experimental results.

First author: Guerra, Celia Fonseca, Nanoswitches based on DNA base pairs: Why adenin-thymine is less suitable than guanine-cytosine, CHEMPHYSCHEM, 7, 1971, (2006)
Abstract: Substituted Watson-Crick guanine-cytosine (GC) base pairs were recently shown to yield robust three-state nanoswitches. Here, we address the question: Can such supramolecular switches also be based on Watson-Crick adenine-thymine (AT) base pairs? We have theoretically analyzed AT pairs in which purine-C8 and/or pyrimidine-C6 positions carry a substituent X=NH-, NH2, NH3+ (N series), O-, OH or OH2+ (O series), using the generalized gradient approximation (GGA) of density functional theory at the BP86/TZ2P level. Thus, we explore the trend in geometrical shape and hydrogen bond strengths in AT pairs along a series of step-wise protonations of the substituents. Introducing a charge on the substituents leads to substantial and characteristic changes in the individual hydrogen bond lengths when compared to the neutral AT pair. However, the trends along the series of negative, neutral, and positive substituents are less systematic and less pronounced than for GC. In certain instances, internal proton transfer from thymine to adenine occurs. Our results suggest that AT is a less suitable candidate than GC in the quest for chemically controlled nanoswitches.

First author: Breza, Martin, DFT studies of copper complexes with biphenyldiimino dithioether II. Mechanical strain,POLYHEDRON, 25, 2559, (2006)
Abstract: The geometries of tetrahedral and square-planar Cu(bite)(q) complexes, q = +1 or +2, as well as of the macrocyclic bite ligand, bite = tetrabenz[a,e,g,k]-15,18-dithia-9,24-diaza-cyclohexadeca-9,23-diene, have been optimized using the DFT method. The reorganization and strain energy values of Cu(bite)(+/2+) Complexes are comparable with analogous DFT/MM data for tetracoordinate copper complexes with monodentate imidazole and thiolate ligands that are used as model systems for blue copper proteins.

First author: Rodriguez-Fortea, Antonio, Ab initio and DFT study of the exchange coupling in the highly reduced polyoxoanion [PMo12O40(VO)(2)](5-), CHEMICAL PHYSICS LETTERS, 428, 88, (2006)
Abstract: Density functional theory and post Hartree-Fock computations are carried out to revisit the electronic structure and the exchange coupling in the bicapped 8-electron reduced [PMo12O40(VO)(2)](5-) polyoxoanion. Our results confirm the 6/2 electronic distribution at Mo/V centers calculated some years ago at BP86 level. The six electrons on Mo pair up in molecular orbitals delocalized over all twelve Mo-centers. The coupling between the two unpaired electrons localized at the two V-centers is predicted to be negligible as expected from simple, qualitative models. The results validate the performance of DFT methods in reduced polyoxoanions when the delocalized d electrons are paired in the lowest-energy multiplet states.

First author: Rayon, Victor M., Structure and bonding in first-row transition-metal dicarbides: Are they related to the stability of met-cars?, CHEMISTRY-A EUROPEAN JOURNAL, 12, 6963, (2006)
Abstract: First-row transition-metal di-carbides MC2 (M=Sc-Zn) have been investigated by using quantum-mechanical techniques. The competition between cyclic and linear isomers in these systems has been studied and the bonding scheme for these compounds is discussed through topological analysis of electron density. All of the systems have been found to prefer a C-2v-symmetric arrangement, although for ZnC2 the energy difference between this and the linear isomer is rather small. In most cases the C-2v-symmetric structure corresponds to a T-shaped structure, with the exceptions of TiC2, CoC2, and NiC2 which have been shown to be true rings. A detailed analysis of the variation of the energy of the system with geometry has been carried out. An analysis of the bonding, taking into account the main interactions between the valence orbitals of both fragments, the M atom and the C-2 molecule, has allowed the main features of these compounds to be interpreted. A clear correlation between the dissociation energies of the first-row transition-metal dicarbides and the bonding energies of the corresponding met-cars was observed.

First author: Volkov, Anatoliy, On the calculation of the electrostatic potential, electric field and electric field gradient from the aspherical pseudoatom model, ACTA CRYSTALLOGRAPHICA SECTION A, 62, 400, (2006)
Abstract: Accurate, yet simple and efficient, formulae are presented for calculation of the electrostatic potential (ESP), electric field (EF) and electric field gradient (EFG) from the aspherical Hansen-Coppens pseudoatom model of electron density [Hansen & Coppens (1978). Acta Cryst. A34, 909-921]. They are based on the expansion of |r’-r|(-1) in spherical harmonics and the incomplete gamma function for a Slater-type function of the form R-l(r)=r(n) exp(-alpha r). The formulae are valid for 0 <= r <=infinity and are easily extended to higher values of l. Special treatment of integrals is needed only for functions with n=l and n=l+1 at r=0. The method is tested using theoretical pseudoatom parameters of the formamide molecule obtained via reciprocal-space fitting of PBE/6-31G** densities and experimental X-ray data of Fe(CO)(5). The ESP, EF and EFG values at the nuclear positions in formamide are in very good agreement with those directly evaluated from density-functional PBE calculations with 6-31G**, aug-cc-pVDZ and aug-cc-pVTZ basis sets. The small observed discrepancies are attributed to the different behavior of Gaussian- and Slater-type functions near the nuclei and to imperfections of the reciprocal-space fit. An EF map is displayed which allows useful visualization of the lattice EF effects in the crystal structure of formamide. Analysis of experimental 100 K X-ray data of Fe(CO)(5) yields the value of the nuclear quadrupole moment Q(Fe-57(m))=0.12×10(-28) m(2) after taking into account Sternheimer shielding/antishielding effects of the core. This value is in excellent agreement with that reported by Su & Coppens [Acta Cryst. (1996), A52, 748-756] but slightly smaller than the generally accepted value of 0.16 +/- 5%x10(-28) m(2) obtained from combined theoretical/spectroscopic studies [Dufek, Blaha & Schwarz (1995). Phys. Rev. Lett.25, 3545-3548].

First author: Noodleman, Louis, Structure, redox, pK(a), spin. A golden tetrad for understanding metalloenzyme energetics and reaction pathways, JOURNAL OF BIOLOGICAL INORGANIC CHEMISTRY, 11, 674, (2006)
Abstract: After a review of the current status of density functional theory (DFT) for spin-polarized and spin-coupled systems, we focus on the resting states and intermediates of redox-active metalloenzymes and electron transfer proteins, showing how comparisons of DFT-calculated spectroscopic parameters with experiment and evaluation of related energies and geometries provide important information. The topics we examine include (1) models for the active-site structure of methane monooxygenase intermediate Q and ribonucleotide reductase intermediate X; (2) the coupling of electron transfer to proton transfer in manganese superoxide dismutase, with implications for reaction kinetics; (3) redox, pK(a), and electronic structure issues in the Rieske iron-sulfur protein, including their connection to coupled electron/proton transfer, and an analysis of how partial electron delocalization strongly alters the electron paramagnetic resonance spectrum; (4) the connection between protein-induced structural distortion and the electronic structure of oxidized highpotential 4Fe4S proteins with implications for cluster reactivity; (5) an analysis of cluster assembly and central-atom insertion into the FeMo cofactor center of nitrogenase based on DFT structural and redox potential calculations.

First author: Atanasov, Mihail, DFT models for copper(II) bispidine complexes: Structures, stabilities, isomerism, spin distribution, and spectroscopy, JOURNAL OF COMPUTATIONAL CHEMISTRY, 27, 1263, (2006)
Abstract: Various DFT and ab initio methods, including B3LYP, HF, SORCI, and LF-density functional theory (DFT), are used to compute the structures, relative stabilities, spin density distributions, and spectroscopic properties (electronic and EPR) of the two possible isomers of the copper(II) complexes with derivatives of a rigid tetradentate bispidine ligand with two pyridine and two tertiary amine donors, and a chloride ion. The description of the bonding (covalency of the copper-ligand interactions) and the distribution of the unpaired electron strongly depend on the DFT functional used, specifically on the nonlocal DF correlation and the HF exchange. Various methods may be used to optimize the DFT method. Unfortunately, it appears that there is no general method for the accurate computation of copper(II) complexes, and the choice of method depends on the type of ligands and the structural type of the chromophore. Also, it appears that the choice of method strongly depends on the problem to be solved. LF-DFT and spectroscopically oriented CI methods (SORCI), provided a large enough reference space is chosen, yield accurate spectroscopic parameters; EDA may lead to a good understanding of relative stabilities; accurate spin density distributions are obtained by modification of the nuclear charge on copper; solvation models are needed for the accurate prediction of isomer distributions.

First author: Han, Wen-Ge, DFT calculations of (57)Fe Mossbauer isomer shifts and quadrupole splittings for iron complexes in polar dielectric media: Applications to methane monooxygenase and ribonucleotide reductase, JOURNAL OF COMPUTATIONAL CHEMISTRY, 27, 1292, (2006)
Abstract: To predict the isomer shifts of Fe complexes in different oxidation and spin states more accurately, we have performed linear regression between the measured isomer shifts (delta(exp)) and DFT (PW91 potential with all-electron triple-zeta plus polarization basis sets) calculated electron densities at Fe nuclei [rho(0)] for the Fe(2+,2.5+) and Fe(2.5+,3+,3.5+,1+) complexes separately. The geometries and electronic structures of all complexes in the training sets are optimized within the conductor like screening (COSMO) solvation model. Based on the linear correlation equation delta(exp) = alpha[rho(0) – 11884.0] + C, the best fitting for 17 Fe(2+,2.5+) complexes (totally 31 Fe sites) yields alpha = -0.405 +/- 0.042 and C = 0.735 +/- 0.047 mm s(-1). The correlation coefficient is r = -0.876 with a standard deviation of SD 0.075 mm s(-1). In contrast, the linear fitting for 19 Fe(2.5+,3+,3.5+,4+) complexes (totally 30 Fe sites) yields alpha = -0.393 +/- 0.030 and C = 0.435 +/- 0.014 mm s(-1), with the correlation coefficient r = -0.929 and a standard deviation SD = 0.077 mm s(-1). We provide a physical rationale for separating the Fe(2+,2.5+) fit from the Fe(2-5+,3+,3 5+,4+) fit, which also is clearly justified on a statistical empirical basis. Quadrupole splittings have also been calculated for these systems. The correlation between the calculated (Delta E(Q(exp))) and experimental (Delta E(Q(exp))) quadrupole splittings based on vertical bar Delta E(Q(exp))vertical bar = A vertical bar Delta E(Q(cal))vertical bar + B yields slope A, which is almost the ideal value 1.0 (A = 1.002 – 0.030) and intercept B almost zero (B = 0.033 +/- 0.068 mm s(-1)). Further calculations on the reduced diferrous and oxidized diferric active sites of class-I ribonucleotide reductase (RNR) and the hydroxylase component of methane monooxygenase (MMOH), and on a mixed-valent [(tpb)Fe(3+)(mu-O)(mu-CH(3)CO(2))Fe(4+)(Me(3)[9]aneN(3))](2+) (S = 3/2) complex and its corresponding diferric state have been performed. Calculated results are in very good agreement with the experimental data.

First author: Szilagyi, Robert K., On the accuracy of density functional theory for iron – Sulfur clusters, JOURNAL OF COMPUTATIONAL CHEMISTRY, 27, 1385, (2006)
Abstract: A simple, yet powerful wave function manipulation method was introduced utilizing a generalized ionic fragment approach that allows for systematic mapping of the wave function space for multispin systems with anti-ferromagnetic coupling. The use of this method was demonstrated for developing ground state electronic wave function for [2Fe-2S] and [Mo-3Fe-4S] clusters. Using well-defined ionic wave functions for ferrous and ferric irons, sulfide, and thiolate fragments, the accuracy of various density functionals and basis sets including effective core potentials were evaluated on a [4Fe-4S] cluster by comparing the calculated geometric and electronic structures with crystallographic data and experimental atomic spin densities from X-ray absorption spectroscopy, respectively. We found that the most reasonable agreement for both geometry and atomic spin densities is obtained by a hybrid functional with 5% HF exchange and 95% density functional exchange supplemented with Perdew’s 1986 correlation functional. The basis set seems to saturate only at the triple-zeta level with polarization and diffuse functions. Reasonably preoptimized structures can be obtained by employing computationally less expensive effective core potentials, such as the Stuttgart-Dresden potential with a triple-zeta valence basis set. The extension of the described calibration methodology to other biologically important and more complex iron-sulfur clusters, such as hydrogenase H-cluster and nitrogenase FeMo-co will follow.

First author: Kuta, Jadwiga, Performance of DFT in modeling electronic and structural properties of cobalamins,JOURNAL OF COMPUTATIONAL CHEMISTRY, 27, 1429, (2006)
Abstract: Computational modeling of the enzymatic activity of B-12-dependent enzymes requires a detailed understanding of the factors that influence the strength of the Co-C bond and the limits associated with a particular level of theory. To address this issue, a systematic analysis of the electronic and structural properties of coenzyme B-12 models has been performed to establish the performance of three different functionals including B3LYP, BP86, and revPBE. In particular the cobalt-carbon bond dissociation energies, axial bond lengths, and selected stretching frequencies have been analyzed in detail. Current analysis shows that widely used B3LYP functional significantly underestimates the strength of the Co-C bond while the nonhybrid BP86 functional produces very consistent results in comparison to experimental data. To explain such different performance of these functionals molecular orbital analysis associated with axial bonds has been performed to show differences in axial bonding provided by hybrid and nonhybrid functionals.

First author: Garcia-Lastra, J. M., Optical properties of Cr3+-doped oxides: Different behavior of two centers in alexandrite, PHYSICAL REVIEW B, 74, 1429, (2006)
Abstract: This work is aimed at explaining the different color exhibited by the two Cr3+ centers in the alexandrite gemstone as well as ruby and emerald. Although the average Cr3+-O2- distance in ruby, emerald, and the C-s center in alexandrite is known to be practically the same, it is shown that the different values of the ligand field parameter 10Dq of the four Cr3+ centers mainly come from the electrostatic potential of the rest of lattice ions, V-R(r), seen by the CrO69- complex where active electrons are localized. This V-R(r) potential, which strongly depends on the point symmetry group around the impurity, leads to an additional contribution to 10Dq not considered in the traditional ligand field theory. While for the C-s center (10Dq=2.19 eV) and ruby (10Dq=2.24 eV), V-R(r) has a similar shape along any Cr3+-O2- direction this is no longer true for the C-i center in alexandrite where the highest 10Dq value (equal to 2.53 eV) is measured.

First author: Atanasov, Mihail, A DFT based ligand field study of the EPR spectra of Co(II) and Cu(II) porphyrins,CHEMICAL PHYSICS LETTERS, 427, 449, (2006)
Abstract: Using a DFT based Ligand Field treatment (LFDFT) of the electronic structure of Co(II) and Cu(II) porphyrins (CoP and CuP) we analyse the origin of their EPR spectra. From a comparison between theoretical result on Co model clusters (CoP and CoP-ZnP dimer) we conclude that the g-tensor values are very sensitive to the axial coordination which stabilizes a 2 A I ground state in good agreement with experimental data. In contrast, DFT overestimates Cu-ligand covalency, leading to large discrepancy with experiments, and hence the orbital contribution to the computed g-values is too small. Using a numerical adjustment of nuclear charge for Cu, a good agreement between the computed and the experimental g-tensor values is observed. The influence of the DFT functional on the calculated g-tensor is also discussed.

First author: Pittalis, S., On the degeneracy of atomic states within exact-exchange (spin-) density functional theory,JOURNAL OF CHEMICAL PHYSICS, 125, 449, (2006)
Abstract: The problem of degenerate ground states of open-shell atoms is investigated in spin-restricted and spin-unrestricted density functional theories using the exact-exchange energy functional. For the spin-unrestricted case, spurious energy splittings of the order of 2-3 kcal/mol are found for atoms of the second and third periods which are larger than the splittings obtained from recently proposed approximate exchange functionals depending explicitly on the current density. In remarkable contrast, for spin-restricted calculations the degeneracy of different atomic ground states is recovered to within less than 0.6 kcal/mol.

First author: van Stralen, Joost N. P., Oxidative addition versus dehydrogenation of methane, silane, and heavier AH(4) congeners reacting with palladium, ORGANOMETALLICS, 25, 4260, (2006)
Abstract: We have computationally studied the oxidative addition of AH(4) to Pd (with A = C, Si, Ge, Sn, and Pb) using relativistic density functional theory (DFT) at ZORA-BLYP/TZ2P. Our purpose is threefold: (i) exploring the occurrence and competition between direct oxidative insertion (OxIn) into the A-H bond and an alternative S(N)2-type mechanism that is known to occur for oxidative addition of carbon-halogen bonds; (ii) exploring the trends in activation and reaction enthalpies as the atom A in AH4 descends in group 14 from carbon to lead; (iii) analyzing and understanding the emerging trends in terms of properties of the reactants using the activation strain model. We find that oxidative insertion of Pd proceeds via a reactant complex and a central barrier only for the C-H bond. For the heavier A-H bonds, the process is barrierless and significantly more exothermic. The higher barrier and smaller exothermicity in the case of Pd + CH4 has two main reasons: (i) the higher strain associated with the stronger C-H bond and (ii) the weaker Pd-CH4 interaction due to less attractive electrostatic interaction with the compact and less polar charge distribution of methane. Backside nucleophilic attack proceeds in none of the cases toward an S(N)2-type mechanism for oxidative addition. Instead, the process evolves into a novel mechanism for R-elimination of molecular hydrogen.

First author: Archer, Andrew M., Arene coordination in bis(imino)pyridine iron complexes: Identification of catalyst deactivation pathways in iron-catalyzed hydrogenation and hydrosilation, ORGANOMETALLICS, 25, 4269, (2006)
Abstract: The phenyl-substituted bis(imino) pyridine iron bis(dinitrogen) complex ((PrPhPDI)-Pr-i)Fe(N-2)(2) ((PrPhPDI)-Pr-i = 2,6-(2,6-Pr-i(2)-C6H3N=CPh)(2)C5H3N) was prepared by sodium amalgam reduction of the corresponding ferrous dichloride precursor under 4 atm of dinitrogen. Comparison of the infrared stretching frequencies of the bis(dinitrogen), mono(dinitrogen), and related dicarbonyl derivatives to those of the corresponding bis(imino) pyridine iron compounds bearing the methyl-substituted ligand, ((PrPDI)-Pr-i)Fe(L)(n) ((PrPDI)-Pr-i = 2,6-(2,6-Pr-i(2)-C6H3N=CMe)(2)C5H3N; L = CO, n = 2; L = N-2, n = 1, 2), established a more electrophilic iron center for the phenyl-substituted cases. Comparing the productivity of ((PrPhPDI)-Pr-i) Fe(N-2)(2) to ((PrPDI)-Pr-i)Fe(N-2)(2) in the catalytic hydrogenation and hydrosilation of 1-hexene demonstrated higher turnover frequencies for ((PrPhPDI)-Pr-i)Fe(N-2)(2). For more hindered substrates such as cyclohexene and (+)-(R)limonene, the opposite trend was observed, where the methyl-substituted precursor, ((PrPDI)-Pr-i) Fe(N-2)(2), produced more rapid conversion. The difference in catalytic performance resulted from competitive, irreversible formation of A6-aryl and -phenyl compounds with the phenyl-substituted complex. Addition of coordinating solvents such as cyclohexene or THF resulted in exclusive formation of the A6-phenyl derivative. When alkoxide substituents are introduced in the bis(imino) pyridine ligand backbone, the formation of eta(6)-aryl compounds was exclusive, as alkali metal reduction of ((PrROPDI)-Pr-i)FeBr2 ((PrROPDI)-Pr-i) 2,6-(2,6-Pr-i(2)-C6H3N=C(OR))(2)C5H3N, R = Me, Et) yielded only the catalytically inactive eta(6)-aryl species.

First author: van Bochove, Marc A., Nucleophilic substitution at phosphorus (S(N)2@P): Disappearance and reappearance of reaction barriers, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 10738, (2006)
Abstract: Pentacoordinate phosphorus species play a key role in organic and biological processes. Yet, their nature is still not fully understood, in particular, whether they are stable, intermediate transition complexes (TC) or labile transition states (TS). Through systematic, theoretical analyses of elementary S(N)2@C, S(N)2@Si, and S(N)2@P reactions, we show how increasing the coordination number of the central atom as well as the substituents’ steric demand shifts the S(N)2@P mechanism stepwise from a single-well potential (with a stable central TC) that is common for substitution at third-period atoms, via a triple-well potential (featuring a pre-and post-TS before and after the central TC), back to the double-well potential (in which pre-and postbarrier merge into one central TS) that is well-known for substitution reactions at carbon. Our results highlight the steric nature of the S(N)2 barrier, but they also show how electronic effects modulate the barrier height.

First author: Cavigliasso, German, On the paucity of molecular actinide complexes with unsupported metal-metal bonds: A comparative investigation of the electronic structure and metal-metal bonding in U(2)X(6) (X = Cl, F, OH, NH(2), CH(3)) complexes and d-block analogues, INORGANIC CHEMISTRY, 45, 6828, (2006)
Abstract: Density functional calculations have been performed on M(2)X(6) complexes (where M = U, W, and Mo and X = Cl, F, OH, NH(2), and CH(3)) to investigate general aspects of their electronic structures and explore the similarities and differences in metal-metal bonding between f-block and d-block elements. A detailed analysis of the metal-metal interactions has been conducted using molecular orbital theory and energy decomposition methods. Multiple (sigma and pi) bonding is predicted for all species investigated, with predominant f-f and d-d metal orbital character, respectively, for U and W or Mo complexes. The energy decomposition analysis involves contributions from orbital interactions (mixing of occupied and unoccupied orbitals), electrostatic effects (Coulombic attraction and repulsion), and Pauli repulsion (associated with four-electron two-orbital interactions). The general results suggest that the overall metal-metal interaction is stronger in the Mo and W species, relative to the U analogues, as a consequence of a significantly less destabilizing contribution from the combined Pauli and electrostatic (“pre-relaxation”) effects. Although the orbital-mixing (“post-relaxation”) contribution to the total bonding energy is predicted to have a larger magnitude in the U complexes, this is not sufficiently strong to compensate for the comparatively greater destabilization that originates from the Pauli-plus-electrostatic effects. Of the pre-relaxation terms, the Pauli repulsion is comparable in analogous U and d-block compounds, contrary to the electrostatic term, which is (much) less favorable in the U systems than in the W and Mo systems. This generally weak electrostatic stabilization accounts for the large pre-relaxation destabilization in the U complexes and, ultimately, for the relative weakness of the U-U bonds. The origin of the small electrostatic term in the U compounds is traced primarily to MX(3) fragment overlap effects.

First author: Christian, Gemma J., Optimizing small molecule activation and cleavage in three-coordinate M[N(R)Ar](3) complexes, INORGANIC CHEMISTRY, 45, 6851, (2006)
Abstract: The sterically hindered, three-coordinate metal systems M[N(R) Ar](3) (R = Bu-t, Pr-i; Ar = 3,5-C6H3Me2) are known to bind and activate a number of fundamental diatomic molecules via a [Ar(R)N](3)M-L-L-M[N(R)Ar](3) dimer intermediate. To predict which metals are most suitable for activating and cleaving small molecules such as N-2, NO, CO, and CN-, the M-L bond energies in the L-M(NH2)(3) (L = O, N, C) model complexes were calculated for a wide range of metals, oxidation states, and d(n) (n = 2-6) configurations. The strongest M-O, M-N, and M-C bonds occurred for the d(2), d(3), and d(4) metals, respectively, and for these dn configurations, the M-C and M-O bonds were calculated to be stronger than the M-N bonds. For isoelectronic metals, the bond strengths were found to increase both down a group and to the left of a period. Both the calculated N – N bond lengths and activation barriers for N-2 bond cleavage in the (H2N)(3)M-N-N-M(NH2)(3) intermediate dimers were shown to follow the trends in the M-N bond energies. The three-coordinate complexes of Ta-II, W-III, and Nb-II are predicted to deliver more favorable N-2 cleavage reactions than the experimentally known Mo-III system and the (ReTaIII)-Ta-III dimer, [Ar(R)N](3)-Re-CO-Ta[N(R)Ar](3), is thermodynamically best suited for cleaving CO.

First author: Bessac, Fabienne, Chemical bonding in phosphane and amine complexes of main group elements and transition metals, INORGANIC CHEMISTRY, 45, 6956, (2006)
Abstract: The geometries and bond dissociation energies of the main group complexes X3B-NX3, X3B-PX3, X3Al-NX3, and X3Al-PX3 (X = H, Me, Cl) and the transition metal complexes (CO)(5)M-NX3 and (CO)(5)M-PX3 (M = Cr, Mo, W) have been calculated using gradient-corrected density functional theory at the BP86/TZ2P level. The nature of the donor-acceptor bonds was investigated with an energy decomposition analysis. It is found that the bond dissociation energy is not a good measure for the intrinsic strength of Lewis acidity and basicity because the preparation energies of the fragments may significantly change the trend of the bond strength. The interaction energies between the frozen fragments of the borane complexes are in most cases larger than the interaction energies of the alane complexes. The bond dissociation energy of the alane complexes is sometimes higher than that of the borane analogues because the energy for distorting the planar equilibrium geometry of BX3 to the pyramidal from in the complexes is higher than for AlX3. Inspection of the three energy terms, Delta E-Pauli, Delta E-orb, and Delta E-elstat, shows that all three of them must be considered to understand the trends of the Lewis acid and base strength. The orbital term of the donor-acceptor bonds with the Lewis bases NCl3 and PCl3 have a higher d character than the bonds of EH3 and EMe3, but NCl3 and PCl3 are weaker Lewis bases because the lone-pair orbital at the donor atoms N and P has a high percent s character. The calculated Delta E-int values suggest that the trends of the intrinsic Lewis bases’ strengths in the main-group complexes with BX3 and AlX3 are NMe3 > NH3 > NCl3 and PMe3 > PH3 > PCl3. The transition metal complexes exhibit a somewhat different order with NH3 > NMe3 > NCl3 and PMe3 > PH3 > PCl3. The slightly weaker bonding of NMe3 than that of NH3 comes from stronger Pauli repulsion. The bond length does not always correlate with the bond dissociation energy, nor does it always correlate with the intrinsic interaction energy.

First author: Guthmuller, J., Linear and nonlinear optical response of aromatic amino acids: A time-dependent density functional investigation, JOURNAL OF PHYSICAL CHEMISTRY A, 110, 9967, (2006)
Abstract: The linear and nonlinear optical responses of the three aromatic amino acids tryptophan, tyrosine, and phenylalanine have been investigated by time-dependent density functional theory. The effect of the peptidic chain on the polarizabilities and the first hyperpolarizabilities is addressed by substituting different groups to the chromophores indole, phenol, and benzene. The optimized structures are in very good agreement with the experimental results. Furthermore, the calculated polarizabilities are found to match well with the empirical results, showing the evolution obtained as the chain is lengthened. A systematic and constant increase of the polarizability is found, for the three chromophores, for the various chain lengths. The first hyperpolarizability is also noticeably modified by the chains, but the evolution of this quantity is found to be more dependent on the system considered. Finally, it is suggested that each of the three aromatic amino acids has a significant contribution to the nonlinear response of proteins.

First author: Brinkmann, Andreas, Sensitivity enhancement and heteronuclear distance measurements in biological O-17 solid-state NMR, JOURNAL OF PHYSICAL CHEMISTRY B, 110, 16089, (2006)
Abstract: In this contribution we present a comprehensive approach to study hydrogen bonding in biological and biomimetic systems through O-17 and O-17-H-1 solid-state NMR combined with density functional theory calculations of O-17 and H-1 NMR parameters. We explore the signal enhancement of O-17 in L-tyrosine center dot HCl using repetitive double-frequency swept radio frequency pulses in solid-state NMR. The technique is compatible with high magnetic fields and fast magic-angle spinning of the sample. A maximum enhancement by a factor of 4.3 is obtained in the signal-to-noise ratio of the selectively excited O-17 central transition in a powdered sample of O-17(eta)-L-tyrosine, HCl at an external field of 14.1 T and a spinning frequency of 25 kHz. As little as 128 transients lead to meaningful O-17 spectra of the same sample at an external field of 18.8 T and a spinning frequency of 50 kHz. Furthermore we employed supercycled symmetry-based pulse sequences on the protons to achieve heteronuclear longitudinal two-spin-order (IzSz) recoupling to determine O-17-1H distances. These sequences recouple the heteronuclear dipolar O-17-H-1 couplings, where dipolar truncation is absent, while decoupling the homonuclear proton dipolar interactions. They can be applied at fast magic-angle-spinning frequencies up and beyond 50 kHz and are very robust with respect to O-17 quadrupolar couplings and both O-17 and H-1 chemical shift anisotropies, which makes them suitable for the use at high external magnetic fields. The method is demonstrated by determining the O-17(eta)-H-1 distance in L-tyrosine, HCl at a spinning frequency of 50 kHz and an external field of 18.8 T.

First author: Hocking, Rosalie K., Fe L-edge XAS studies of K-4[Fe(CN)(6)] and K-3[Fe(CN)(6)]: A direct probe of back-bonding, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 10442, (2006)
Abstract: Distinct spectral features at the Fe L-edge of the two compounds K-3[Fe(CN)(6)] and K-4[Fe(CN)(6)] have been identified and characterized as arising from contributions of the ligand pi* orbitals due to metal-to-ligand back-bonding. In addition, the L-edge energy shifts and total intensities allow changes in the ligand field and effective nuclear charge to be determined. It is found that the ligand field term dominates the edge energy shift. The results of the experimental analysis were compared to BP86 DFT calculations. The overall agreement between the calculations and experiment is good; however, a larger difference in the amount of pi back-donation between Fe(II) and Fe(III) is found experimentally. The analysis of L-edge spectral shape, energy shift, and total intensity demonstrates that Fe L-edge X-ray absorption spectroscopy provides a direct probe of metal-to-ligand back-bonding.

First author: Rosenthal, Joel, Spectroscopic determination of proton position in the proton-coupled electron transfer pathways of donor-acceptor supramolecule assemblies, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 10474, (2006)
Abstract: A homologous set of porphyrin derivatives possessing an isocyclic five-membered ring appended with an amidinium functionality has been used to examine proton-coupled electron transfer (PCET) through well-characterized amidine-carboxylic acid interfaces. Conjugation between the porphyrin chromophore and the amidinium interface can be altered by selective reduction of the isocyclic ring of an amidinium-purpurin to produce an amidinium-chlorin. The highly conjugated amidinium-purpurin displays large spectral shifts in the visible region upon alteration of the amidinium/amidine protonation state; no such change is observed for the chlorin homologue. Analysis of the UV-vis absorption and emission profiles of the amidinium-purpurin upon deprotonation allows for the measurement of the porphyrinic-amidinium acidity constant for the ground state (pK(a) = 9.55 +/- 0.1 in CH3CN) and excited state (pK(a)* = 10.40 +/- 0.1 in CH3CN). The absorption spectrum of the purpurin also provides a convenient handle for determining the protonation state of assembled interfaces. In this way, the purpurin macrocycle provides a general tool for PCET studies because it can be used to determine the location of a proton within PCET interfaces formed from carboxylic acid electron acceptors including dinitrobenzenes (DNBs) and naphthalenediimide (NI), which have been used extensively in previous PCET studies. An amidine-carboxylic acid interface is observed for electron-rich acceptors, whereas the ionized amidinium- carboxylate interface is observed for electron-poor acceptors. The PCET kinetics for purpurin/chlorin associated to NI are consistent with an amidine-carboxylic acid interface, which is also verified spectrally.

First author: Saeys, Mark, Adsorption of cyclohexadiene, cyclohexene and cyclohexane on Pt(111), SURFACE SCIENCE,600, 3121, (2006)
Abstract: The adsorption of 1,3-cyclohexadiene, 1,4-cyclohexadiene, cyclohexene and cyclohexane on Pt(111) was studied using ab initio density functional theory. For 1,3-cyclohexadiene three adsorption modes were distinguished: bridge 1,2-di-sigma/3,4-pi, hollow 1,4-di-sigma/2,3-pi and bridge 1,4-di-sigma/2,3-pi with adsorption energies of -155, -147 and -75 kJ/mol, respectively. Three stable adsorption modes were also identified for 1,4-cyclohexadiene: bridge quadra-sigma, hollow di-sigma/pi and bridge di-sigma with adsorption energies of -146 kJ/mol, -142 kJ/mol and -88 kJ/mol, respectively. Cyclohexene was found to adsorb in six modes: 4 di-sigma and 2 pi-adsorption modes. The preferred configuration was found to be boat di-sigma with an adsorption energy of -81 kJ/mol. The three other di-sigma adsorption modes have comparable adsorption energies, ranging from -64 to -69 kJ/mol. Molecular strain and C-Pt bonding energies are used to elucidate stability trends. Cyclohexane is found to adsorb only at the hollow site whereby the axial hydrogen atoms are positioned over surface Pt-atoms with an adsorption energy of -37 kJ/mol. The calculations correctly predict the weakening of the axial C-H bonds and provide a possible explanation for the large shift in the vibrational frequencies.

First author: Yazyev, Oleg V., O-17 nuclear quadrupole coupling constants of water bound to a metal ion: A gadolinium(III) case study, JOURNAL OF CHEMICAL PHYSICS, 125, 3121, (2006)
Abstract: Rotational correlation times of metal ion aqua complexes can be determined from O-17 NMR relaxation rates if the quadrupole coupling constant of the bound water oxygen-17 nucleus is known. The rotational correlation time is an important parameter for the efficiency of Gd3+ complexes as magnetic resonance imaging contrast agents. Using a combination of density functional theory with classical and Car-Parrinello molecular dynamics simulations we performed a computational study of the O-17 quadrupole coupling constants in model aqua ions and the [Gd(DOTA)(H2O)](-) complex used in clinical diagnostics. For the inner sphere water molecule in the [Gd(DOTA)(H2O)](-) complex the determined quadrupole coupling parameter chi root 1+eta(2)/3 of 8.7 MHz is very similar to that of the liquid water (9.0 MHz). Very close values were also predicted for the the homoleptic aqua ions of Gd3+ and Ca2+. We conclude that the O-17 quadrupole coupling parameters of water molecules coordinated to closed shell and lanthanide metal ions are similar to water molecules in the liquid state.

First author: van der Wijst, Tushar, Performance of various density functionals for the hydrogen bonds in DNA base pairs,CHEMICAL PHYSICS LETTERS, 426, 415, (2006)
Abstract: We have investigated the performance of seven popular density functionals (B3LYP, BLYP, BP86, mPW, OPBE, PBE, PW91) for describing the geometry and stability of the hydrogen bonds in DNA base pairs. For the gas-phase situation, the hydrogen-bond lengths and strengths in the DNA pairs have been compared to the best ab initio results available in the literature (MP2). For a comparison with the crystallographic experiments, the first crystal-environment shell was taken into account in our DNA model systems. BP86 and PW91 excellently recover both the ab initio and experimental values. B3LYP consistently underestimates hydrogen-bond strengths and overestimates hydrogen-bond distances.

First author: Shamov, Grigory A., Relativistic density functional theory study of dioxoactinide(VI) and -(V) complexation with alaskaphyrin and related Schiff-base macrocyclic ligands, JOURNAL OF PHYSICAL CHEMISTRY A, 110, 9486, (2006)
Abstract: Formation of complexes of alaskaphyrin 1, bi-pyen 2 and bi-tpmd 3 ligands with actinyl ions AnO(2)(n+), An = U, Np, Pu and n = 1, 2, was studied using density functional theory (DFT) within the scalar relativistic four-component approximation. The alaskaphyrin complexes of the uranyl are predicted to have a bent conformation, in contrast to the experimentally available X-ray data. This deviation is likely due to crystal packing effects. Apart from these conformational differences, calculated geometry parameters and vibrational frequencies are in agreement with the available experimental data. The character of bonding in the complexes is investigated using bond order analysis and extended transition states (ETS) energy decomposition. Metal-to-ligand bonds can be described as primarily ionic although substantial charge transfer is observed as well. Based on ETS analysis, it is shown that steric and/or fit/misfit requirements of actinyl cations to the ligand cavities, among the studied complexes, are the most favorable for the bi-pyen ligand 2, because its flexibility allows for optimal metal-to-donor-atom distances. Planarity of the equatorial coordination sphere of the actinide atom is found to be less important than the ability of a ligand to provide optimal uranium-to-nitrogen bond lengths. Experimental differences in demetalation rates between similar alaskaphyrin, bi-pyen and bi-tpmd uranyl complexes are explained as a result of easier protonation of the Schiff-base nitrogen of the latter. Reduction potentials calculated for the uranium complexes show a good agreement with the experiment, both in relative and in absolute terms.

First author: Prins, Paulette, Efficient charge transport along phenylene-vinylene molecular wires, JOURNAL OF PHYSICAL CHEMISTRY B, 110, 14659, (2006)
Abstract: We have studied the motion of charge carriers along isolated phenylene-vinylene (PV) chains using a combination of experimental and theoretical methods. The conductive properties of positive charges along PV chains in dilute solution were studied by using the pulse-radiolysis time-resolved microwave conductivity (TRMC) technique. This technique enables the measurement of high-frequency (tens of GHz) charge carrier mobilities along isolated PV chains without the use of electrodes. The charge carrier mobility along PV chains with finite and infinite length was studied theoretically by charge transport simulations with parameters from density functional theory (DFT) calculations. The high-frequency charge carrier mobility is found to depend strongly on the conjugation length of the PV chains and is found to increase both with increasing length of the PV chain and with increasing conjugation fraction. The experimental results are in good agreement with the calculated results. On the basis of this combined experimental and theoretical study an intrachain charge carrier mobility of a few tens of cm(2)/Vs is expected for an infinitely long PV chain without conjugation breaks.

First author: Tisato, Francesco, The preparation of substitution-inert Tc-99 metal-fragments: Promising candidates for the design of new Tc-99m radiopharmaceuticals, COORDINATION CHEMISTRY REVIEWS, 250, 2034, (2006)
Abstract: Tc-99 mixed-ligand complexes displaying characteristic substitution-inert metal-fragments are emerging as alternative platforms in the design of potential Tc-99m radiopharmaceuticals. Starting from the already well-known [Tc(CO)(3)](+) moiety, this review describes recent efforts in the coordination chemistry of technetium aiming at the exploitation of the metal-fragment strategy. Examples include Tc-III ‘4 + F and Tc-III ‘SSS’ systems, along with a description of the Tc-v(N)(PNP) system and the transfer of this technology to other cores (M=NPh and M=O).

First author: Costa, Paulo J., A DFT and MP2 study of luminescence of gold(I) complexes, INORGANICA CHIMICA ACTA, 359, 3617, (2006)
Abstract: Four Au(I) mixed thiolate and phosphine complexes were studied using DFT, TD-DFT, and MP2/CIS approaches. Two are mononuclear species, [(R3P)Au(p-SC6H4CH3)] differing by the phosphine (PMe3, 1, or PH3, 1h), to check the use of PH3 in the model. The others were binuclear complexes with bidentate phosphines, bridging two gold atoms, modelled by [Au-2(P-SC6H4CH3)(2)- {H2P(CH2)(n)PH2}] (n = 1, 2, 2h and 3h, respectively), to assess the role of the carbon chain in the optical properties. Both DFT and MP2 led to comparable descriptions of the geometry and the electronic structure in the mononuclear complexes, although gold has a stronger participation (and phosphorus a weaker one) in the MP2 virtual orbitals. TD-DFT and CIS give a good reproduction of the electronic absorption, the low-energy excitations being assigned as LMCT [S(p), aryl ring -> Au(p)], but CIS leads to a better emission wavelength. The two models, 2h and 3h, used to study the binuclear complexes were found to have similar geometries with comparable Au (…) Au distances, according to DFT calculations. The agreement between calculated and experimental (related complexes) electronic transitions was relatively good, the red shift experimentally observed in 2h relative to 3h being also reproduced by TD-DFT. The low energy transitions were assigned to LMCT [S(p), aryl ring Au(p)] with mixture of LMMCT, from S(p) to Au-Au dp sigma.

First author: Infante, I, A QM/MM study on the aqueous solvation of the tetrahydroxouranylate [UO2(OH)(4)](2-) complex ion, JOURNAL OF COMPUTATIONAL CHEMISTRY, 27, 1156, (2006)
Abstract: We report a QM augmented QM/MM study on the coordination of the tetrahydroxouranylate ion in aqueous solution. QM/MM geometry optimizations followed by full QM single-point calculations on the optimized structures show that a hexa-coordinated structure is more stable than the hepta-coordinated structure by 43 kJ/mol. Charge transfer of the tetrahydroxouranylate to the solvating water molecules is relatively modest, and can be modeled by including a solvation layer consisting of 12 explicit water molecules.

First author: Prins, P., Charge transport along phenylenevinylene molecular wires, MOLECULAR SIMULATION, 32, 695, (2006)
Abstract: A model to calculate the mobility of charges along molecular wires is presented. The model is based on the tight-binding approximation and combines a quantum mechanical description of the charge with a classical description of the structural degrees of freedom. It is demonstrated that the average mobility of charge carriers along molecular wires can be obtained by time-propagation of states, which are initially localised. The model is used to calculate the mobility of charges along poly-phenylenevinylene (PPV) chains with varying number of alkoxy side chains. Effects of the torsional motion of the phenyl rings on the mobility are taken into account. The results show that derivatives of PPVs can act equally well as electron and hole conductors. Experimental mobility data on di-alkoxy substituted PPV can be reproduced with the present model provided the effects of structural defects along the polymer chains are taken into account. According to the calculations, intra-chain hole and electron mobilities of the order of 100 cm(2)/Vs can be obtained for defect-free PPV chains.

First author: Guan, Jingang, Time-dependent density functional study of the electronic potential energy curves and excitation spectrum of the oxygen molecule, JOURNAL OF CHEMICAL PHYSICS, 125, 695, (2006)
Abstract: Orbital energies, ionization potentials, molecular constants, potential energy curves, and the excitation spectrum of O-2 are calculated using time-dependent density functional theory (TDDFT) with Tamm-Dancoff approximation (TDA). The calculated negative highest occupied molecular orbital energy (-epsilon(HOMO)) is compared with the energy difference ionization potential for five exchange correlation functionals consisting of the local density approximation (LDAxc), gradient corrected Becke exchange plus Perdew correlation (B-88X+P-86C), gradient regulated asymptotic correction (GRAC), statistical average of orbital potentials (SAOP), and van Leeuwen and Baerends asymptotically correct potential (LB94). The potential energy curves calculated using TDDFT with the TDA at internuclear distances from 1.0 to 1.8 A are divided into three groups according to the electron configurations. The 1 pi(4)(u)1 pi(2)(g) electron configuration gives rise to the X (3)Sigma(-)(g), a (1)Delta(g), and b (1)Sigma(+)(g) states; the 1 pi(3)(u)1 pi(3)(g) electron configuration gives rise to the c (1)Sigma(-)(u), C (3)Delta(u), and A (3)Sigma(+)(u) states; and the B (3)Sigma(-)(u), A (1)Delta(u), and f (1)Sigma(+)(u) states are determined by the mixing of two or more electron configurations. The excitation spectrum of the oxygen molecule, calculated with the aforementioned exchange correlation functionals, shows that the results are quite sensitive to the choice of functional. The LDAxc and the B-88X+P-86C functionals produce similar spectroscopic patterns with a single strongly absorbing band positioned at 19.82 and 19.72 eV, respectively, while the asymptotically corrected exchange correlation functionals of the SAOP and the LB94 varieties yield similar excitation spectra where the computed strongly absorbing band is located at 16.09 and 16.42 eV, respectively. However, all of the exchange correlation functionals yield only one strongly absorbing band (oscillator strength greater than 0.1) in the energy interval of 0-20 eV, which is assigned to a X (3)Sigma(-)(g) to (3)Sigma(-)(u) transition. Furthermore, the oxygen molecule has a rich spectrum in the energy range of 14-20 eV and no spin allowed absorption bands are predicted to be observed in the range of 0-6 eV.

First author: Tarmyshov, Konstantin B., Ion binding to cucurbit[6] uril: Structure and dynamics, JOURNAL OF PHYSICAL CHEMISTRY B, 110, 14463, (2006)
Abstract: Molecular dynamics simulations are used to study the microscopic structure and dynamics of cations bound to cucurbit[6]uril ( CB[ 6]) in water and in aqueous solutions of sodium, potassium, and calcium chloride. The molarities are 0.183 M for the salts and 0.0184 M for CB[ 6]. The cations bind only to CB[ 6] carbonyl oxygens. They are never found inside the CB[ 6] cavity. Complexes with Na+ and K+ mostly involve one cation, whereas with Ca2(+) single- and double- cation complexes are formed in similar proportions. The binding dynamics strongly depends on the type of cation. A smaller size or higher charge increases the residence time of a cation at a given carbonyl oxygen. When bound to CB[ 6], sodium and potassium cations jump mainly between nearest or second- nearest neighbors. Calcium shows no hopping dynamics. It is coordinated predominantly by one CB[ 6] oxygen. A few water molecules ( zero to four) can occupy the CB[ 6] cavity, which is limited by the CB[ 6] oxygen faces. Their residence time is hardly influenced by sodium and potassium ions. In the case of calcium the residence time of the inner water increases notably. A simple structural model for the cation activity as “lids” over the CB[ 6] portal cannot, however, be identified. The slowing of the water exchange by the ions is a consequence of the generally slower dynamics in their presence and of their stable solvation shells.

First author: Marashdeh, Ali, A density functional theory study of Ti-doped NaAlH4 clusters, CHEMICAL PHYSICS LETTERS, 426, 180, (2006)
Abstract: Density functional theory calculations have been performed on Ti-doped NaAlH4 clusters. First the electronic structure and stability of undoped clusters of different size and shape were studied, and then one of these clusters was chosen as a model system for a nano-sized NaAlH4 particle. A Ti atom added to the surface of this model preferably substituted a lattice Na near the surface, when using the NaAlH4 cluster with Ti adsorbed as the reference system and keeping the substituted atoms within the model. This may be a first step towards a model explaining the role of Ti during dehydrogenation and hydrogenation.

First author: Hnyk, Drahomir, Molecular structures of arachno-decaborane derivatives 6,9-X2B8H10 (X = CH2, NH, Se) including a gas-phase electron-diffraction study of 6,9-C2B8H14, INORGANIC CHEMISTRY, 45, 6014, (2006)
Abstract: The molecular structures of the three heterodecaboranes arachno-6,9-C2B8H14, arachno-6,9-N2B8H12, and arachno-6,9-Se2B8H10 have been determined by ab initio MO theory. In addition, the structure of arachno-6,9-C2B8H14 was experimentally determined using gas-phase electron diffraction (GED). The accuracy of all four of these structures has been confirmed by the good agreement of the B-11 chemical shifts calculated at the GIAO-MP2 level with the experimental values. A comparison of the GIAO-HF and GIAO-MP2 methods shows that for these heteroborane clusters, electron correlation effects on the computed delta(B-11) values are quite substantial and that it is necessary to go beyond the HF level in the NMR computation.

First author: Neugebauer, Johannes, Exploring the ability of frozen-density embedding to model induced circular dichroism, JOURNAL OF PHYSICAL CHEMISTRY A, 110, 8786, (2006)
Abstract: In this study, we present calculations of the circular dichroism (CD) spectra of complexes between achiral and chiral molecules. Nonzero rotational strengths for transitions of the nonchiral molecule are induced by interactions between the two molecules, which cause electronic and/or structural perturbations of the achiral molecule. We investigate if the chiral molecule (environment) can be represented only in terms of its frozen electron density, which is used to generate an effective embedding potential. The accuracy of these calculations is assessed in comparison to full supermolecular calculations. We can show that electronic effects arising from specific interactions between the two subsystems can reliably be modeled by the frozen-density representation of the chiral molecule. This is demonstrated for complexes of 2-benzoylbenzoic acid with (-)-(R)-amphetamine and for a nonchiral, artificial amino acid receptor system consisting of ferrocenecarboxylic acid bound to a crown ether, for which a complex with L-leucine is studied. Especially in the latter case, where multiple binding sites and interactions between receptor and target molecule exist, the frozen-density results compare very well with the full supermolecular calculation. We also study systems in which a cyclodextrin cavity serves as a chiral host system for a small, achiral molecule. Problems arise in that case because of the importance of excitonic couplings with excitations in the host system. The frozen-density embedding cannot describe such couplings but can only capture the direct effect of the host electron density on the electronic structure of the guest. If couplings play a role, frozen-density embedding can at best only partially describe the induced circular dichroism. To illustrate this problem, we finally construct a case in which excitonic coupling effects are much stronger than direct interactions of the subsystem densities. The frozen density embedding is then completely unsuitable.

First author: Liptak, Mathew D., Spectroscopic and computational studies of Co1+ cobalamin: Spectral and electronic properties of the “superreduced” B-12 cofactor, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 9144, (2006)
Abstract: The 4-coordinate, low-spin cob(I) alamin (Co(1+)Cbl) species, which can be obtained by heterolytic cleavage of the Co-C bond in methylcobalamin or the two-electron reduction of vitamin B-12, is one of the most powerful nucleophiles known to date. The supernucleophilicity of Co(1+)Cbl has been harnessed by a number of cobalamin-dependent enzymes, such as the B-12-dependent methionine synthase, and by enzymes involved in the biosynthesis of B-12, including the human adenosyltransferase. The nontoxic nature of the Co(1+)Cbl supernucleophile also makes it an attractive target for the in situ bioremediation of halogenated waste. To gain insight into the geometric, electronic, and vibrational properties of this highly reactive species, electronic absorption, circular dichroism (CD), magnetic CD, and resonance Raman (rR) spectroscopies have been employed in conjunction with density functional theory (DFT), time-dependent DFT, and combined quantum mechanics/molecular mechanics computations. Collectively, our results indicate that the supernucleophilicity of Co(1+)Cbl can be attributed to the large destabilization of the Co 3d(z2)-based HOMO and its favorable orientation with respect to the corrin macrocycle, which minimizes steric repulsion during nucleophilic attack. An intense feature in the CD spectrum and a prominent peak in the rR spectra of Co(1+)Cbl have been identified that may serve as excellent probes of the nucleophilic character, and thus the reactivity, of Co(1+)Cbl in altered environments, including enzyme active sites. The implications of our results with respect to the enzymatic formation and reactivity of Co(1+)Cbl are discussed, and spectroscopic trends along the series from Co(3+)Cbls to Co(2+)Cbl and Co(1+)Cbl are explored.

First author: Bagno, Alessandro, Toward the complete prediction of the H-1 and C-13 NMR spectra of complex organic molecules by DFT methods: Application to natural substances, CHEMISTRY-A EUROPEAN JOURNAL, 12, 5514, (2006)
Abstract: The NMR parameters (H-1 and C-13 chemical shifts and coupling constants) for a series of naturally occurring molecules have been calculated mostly with DFT methods, and their spectra compared with available experimental ones. The comparison includes strychnine as a test case, as well as some examples of recently isolated natural products (corianlactone, daphnipaxinin, boletunone B) featuring unusual and/or crowded structures and, in the case of boletunone B, being the subject of a recent revision. Whenever experimental spectra were obtained in polar solvents, the calculation of NMR parameters was also carried out with the Integral Equation-Formalism Polarizable Continuum Model (IEF-PCM) continuum method. The computed results generally show a good agreement with experiment, as judged not only by statistical parameters but also by visual comparison of line spectra. The origin of the remaining discrepancies is attributed to the incomplete modeling of conformational and specific solvent effects.

First author: Bolvin, Helene, An alternative approach to the g-matrix: Theory and applications, CHEMPHYSCHEM, 7, 1575, (2006)
Abstract: Starting from the formula proposed by Gerloch and McMeeking in 1975, the electronic g-matrix is expressed as a sum of two matrices called Lambda and Sigma describing the orbital and spin contributions respectively. This approach is applied on benchmark diatomic and triatomic molecules, and on TiF3 and Cu(NH3)(4)(2+) using either CASPT2 or CCSD(T) methods to calculate the spin-free states and SO-RASSI to calculate spin-orbit coupling. Results compare very well to experimental data and to previous theoretical cal work; and, for each molecule, the anisotropy of the g-matrix is modeled by the mean of a few parameters.

First author: Tomasi, Simone, Group transfer polymerizations of acrylates catalyzed by mononuclear early d-block and f-block metallocenes: A DFT study, ORGANOMETALLICS, 25, 3619, (2006)
Abstract: We present a DFT study of the monometallic group transfer polymerization (GTP) of methyl acrylate (MA) catalyzed by Sm-based and Zr-based metallocenes. The processes examined are the generation of the catalytically active species, the subsequent C-C coupling reaction, and the ring opening of a metallacyclic stable intermediate, resting state of the polymerization process, obtained from the C-C coupling. The mechanism for a neutral zirconocene, a cationic zirconocene, and a neutral samarocene are compared. The isoelectronic neutral samarocene and cationic zirconocene systems share many features, which explains their similar behavior in both the C-C coupling (no energy barrier on the potential energy surface) and the MA-assisted opening of the metallacycle. An analysis of the factors driving polymer stereoregularity in the processes catalyzed by the neutral samarocene and the cationic zirconocene has led to identifying a relationship between stereoregularity and the relative disposition of the acrylate and enolate ligands, as well as the direction of the incoming MA molecule in the opening of the metallacycle resting state. On the basis of these discoveries a kinetic model has been developed, which has proved successful in qualitatively predicting stereoregularity.

First author: Cloke, F. Geoffrey N., Reactions of (BuC)-Bu-t P with cyclooctatetraene-supported titanium imido complexes,ORGANOMETALLICS, 25, 3688, (2006)
Abstract: Reaction of the pseudo two-coordinate titanium imido complexes [Ti((NBu)-Bu-t)(COT)] (1; COT) eta(8)-C8H8) and [Ti((NBu)-Bu-t)(COT”)] (2; COT”) eta(8)-1,4-C8H6(SiMe3)(2)) with 2 equiv of (t)BuCt P generated the new complexes [Ti {N(Bu-t) PC(Bu-t) PC(Bu-t)}(COT)] (4) and [Ti {N(Bu-t) PC(Bu-t) PC(Bu-t)}(COT”)] (5), respectively. Complex 4 was crystallographically characterized, and a density functional theory (DFT) study combined with photoelectron (PE) spectroscopy revealed this apparently 20-valence-electron species to contain a HOMO which is almost entirely ligand-based. In contrast, the organic compound N(Ar)(P2C2Bu2)-Bu-t (6), which incorporates a 1,2,4-azadiphosphole ring, was the only isolated product from the reaction of the arylimido species [Ti(NAr)(COT)] (3; Ar) 2,6-(Pr2C6H3)-Pr-i) with an excess of (BuC)-Bu-t P. DFT studies indicated that the mechanisms for the formation of compounds 4 – 6 are similar. Initially, one molecule of (BuC)-Bu-t P undergoes a [2 + 2] cycloaddition with [Ti(NR)(COT)] to form [Ti{N(R)PC(Bu-t)}(COT)], which contains a Ti-C bond. Subsequently, a second molecule of (BuC)-Bu-t P reacts with [Ti{N(R)PC(Bu-t)}(COT)] to form [Ti{N(R)PC(Bu-t)PC(Bu-t)}(COT)]. When R = 2,6-(Pr2C6H3)-Pr-i or a substituent which is less sterically bulky, the formation of a heterocyclic ring such as N(Ar)(P2C2Bu2)-Bu-t (6) is favored. However, when R = Bu-t, it is sterically unfavorable to form such a ring and thus compound 4 is stable.

First author: Maurer, Jorg, Divinylphenylene-bridged diruthenium complexes bearing Ru(CO)Cl((PPr3)-Pr-i)(2) entities,ORGANOMETALLICS, 25, 3701, (2006)
Abstract: The divinylphenylene-bridged diruthenium complexes (E, E)-[{((PPr3)-Pr-i)(2)(CO)ClRu}(2)(mu-HC = CHC6H4CH = CH-1,3)] (m-2) and (E, E)-[{((PPr3)-Pr-i)(2)(CO)ClRu}(2)(mu-HC = CHC6H4CH = CH-1,4)](p-2) have been prepared and compared to their PPh3-containing analogues m-1 and p-1. The higher electron density at the metal atoms increases the contribution of the metal end groups to the bridge-dominated occupied frontier orbitals and stabilizes the various oxidized forms with respect to those of m-1 and p-1. This has been confirmed and quantified electrochemically, because the two reversible oxidation waves were observed at considerably lower potentials than for the PPh3 complexes. Owing to their greater stability, the one- and two-electronoxidized forms m-2(n+) and p-2(n+) of both complexes could be generated and spectroscopically characterized inside an optically transparent thin layer electrolysis cell. UV/vis/near-IR and ESR spectroelectrochemistry indicates that the oxidation processes are centered at the organic bridging ligand. sigma-Bonded divinylphenylenes thus constitute an unusual class of “noninnocent” ligands for organometallic compounds. Electronic transitions observed for the mono- and dioxidized forms closely resemble those of donor-substituted phenylenevinylene compounds, including oligo(phenylenevinylenes) (OPVs) and poly( phenylenevinylene) (PPV) in the respective oxidation states. Strong ESR signals and nearly isotropic g tensors are observed for the monocations in fluid and frozen solutions. The metal contribution to the redox orbitals is illustrated by a shift of the CO stretching bands to notably higher energies upon stepwise oxidation. The shifts strongly exceed those observed for the PPh3 containing, six- coordinated species (E, E)-[{PPh3)(2)(CO)Cl(L)Ru}(2)(mu-HC = CHC6H4CH = CH)](n+) (L = substituted pyridine). IR spectroelectrochemistry reveals the presence of two electronically different transition-metal moieties in m-(2+), while they resemble each other more closely in p-2(+). Differences in electronic coupling are illustrated by the charge distribution parameters calculated from the spectra. Bulk electrolysis experiments confirm the results from the in situ spectroelectrochemistry and the overall stoichiometry of the redox processes. Quantum-chemical calculations were performed in order to provide insight into the nature and composition of the frontier orbitals. The electronic transitions observed for the neutral forms were assigned by TD DFT. IR frequencies calculated for m-2 and p-2 in their various oxidation states retrace the experimental observations. They fail, however, in the case of m-2(+), where a symmetrical structure is calculated, as opposed to the distinctly asymmetric electron distribution observed by IR spectroscopy. Geometry-optimized structures were calculated for all accessible oxidation states. The structural changes following stepwise oxidation agree well with the experimental findings: e.g., a successive low-energy shift of the C = C stretching vibration of the bridge. The radical cation m-2(+) displays a broad composite electronic absorption band at low energy that extends into the mid-IR region.

First author: Bickelhaupt, F. Matthias, Covalency in highly polar bonds. Structure and bonding of methylalkalimetal oligomers (CH3M)(n) (M = Li-Rb; n=1, 4), JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 2, 965, (2006)
Abstract: We have carried out a theoretical investigation of the methylalkalimetal monomers CH3M and tetramers (CH3M)(4) with M = Li, Na, K, and Rb and, for comparison, the methyl halides CH3X with X = F, Cl, Br, and I, using density functional theory (DFT) at BP86/TZ2P. Our purpose is to determine how the structure and thermochemistry (e.g., C-M bond lengths and strengths, oligomerization energies) of organoalkalimetal compounds depend on the metal atom and to understand the emerging trends in terms of quantitative Kohn-Sham molecular orbital (KS-MO) theory. The C-M bond becomes longer and weaker, both in the monomers and tetramers, if one descends the periodic table from Li to Rb. Quantitative bonding analysis shows that this trend is not only determined by decreasing electrostatic attraction but also, even to a larger extent, by the weakening in orbital interactions. The latter become less stabilizing along Li-Rb because the bond overlap between the singly occupied molecular orbitals (SOMOs) of CH3 center dot and M center dot radicals decreases as the metal ns atomic orbital (AO) becomes larger and more diffuse. Thus, the C-M bond behaves as a typical electron-pair bond between the methyl radical and alkalimetal atom, and, in that respect, it is covalent. It is also shown that such an electron-pair bond can still be highly polar, in agreement with the large dipole moment. Interestingly, the C-M bond becomes less polar in the methylalkalimetal tetramers because metal-metal interactions stabilize the alkalimetal orbitals and, in that way, make the alkalimetal effectively less electropositive.

First author: Zbiri, Mohamed, Effect of the f-orbital delocalization on the ligand-field splitting energies in lanthanide-containing elpasolites, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 2, 1106, (2006)
Abstract: The ligand-field induced splitting energies of f-levels in lanthanide-containing elpasolites are derived using the first-principles universal orbital-free embedding formalism [Wesolowski and Warshel, J. Phys. Chem. 1993, 97, 8050]. In our previous work concerning chloroelpasolite lattice (Cs(2)NaLnCl(6)), embedded orbitals and their energies were obtained using an additional assumption concerning the localization of embedded orbitals on preselected atoms leading to rather good ligand-field parameters. In this work, the validity of the localization assumption is examined by lifting it. In variational calculations, each component of the total electron density (this of the cation and that of the ligands) spreads over the whole system. It is found that the corresponding electron densities remain localized around the cation and the ligands, respectively. The calculated splitting energies of f-orbitals in chloroelpasolites are not affected noticeably in the whole lanthanide series. The same computational procedure is used also for other elpasolite lattices (Cs(2)NaLnX(6), where X = F, Br, and I) -materials which have not been fabricated or for which the ligand-field splitting parameters are not available.

First author: Angyan, Janos G., Spherical harmonic expansion of short-range screened Coulomb interactions, JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 39, 8613, (2006)
Abstract: Spherical harmonic expansions of the screened Coulomb interaction kernel involving the complementary error function are required in various problems in atomic, molecular and solid state physics, like for the evaluation of Ewald-type lattice sums or for range-separated hybrid density functionals. A general analytical expression is derived for the kernel, which is non-separable in the radial variables. With the help of series expansions a separable approximate form is proposed, which is in close analogy with the conventional multipole expansion of the Coulomb kernel in spherical harmonics. The convergence behaviour of these expansions is studied and illustrated by the electrostatic potential of an elementary charge distribution formed by products of Slatertype atomic orbitals.

First author: Guerrero, Antonio, Zinc(II) eta(1)- and eta(2)-toluene complexes: Structure and bonding in Zn(C(6)F(5))(2)center dot(toluene) and Zn(C(6)F(4)-2-C(6)F(5))(2)center dot(toluene), ORGANOMETALLICS, 25, 3311, (2006)
Abstract: The first structural characterization of toluene complexes of zinc is reported. The ( perfluoroaryl) zinc compounds Zn(C(6)F(5))(2)center dot(toluene) and Zn(C(6)F(4)-2-C(6)F(5))(2)center dot(toluene) show toluene in eta(2) and eta(1) coordination modes, respectively. On the other hand, charge distribution calculations, Mulliken overlap population analysis, and bonding energy data suggest that the interactions between the Zn and the toluene ring are rather similar in both cases.

First author: Hauser, Andreas, Low-temperature lifetimes of metastable high-spin states in spin-crossover and in low-spin iron(II) compounds: The rule and exceptions to the rule, COORDINATION CHEMISTRY REVIEWS, 250, 1642, (2006)
Abstract: The high-spin -> low-spin relaxation in spin-crossover compounds can be described as non-adiabatic multi-phonon process in the strong coupling limit, in which the low-temperature tunnelling rate increases exponentially with the zero-point energy difference between the two states. Based on the hypothesis that the experimental bond length difference between the high-spin and the low-spin state of similar to 0.2 angstrom is also valid for low-spin iron(H) complexes, extrapolation of the single configurational coordinate model allows an estimate of the zero-point energy difference for low-spin complexes from kinetic data. DFT calculations on low-spin [Fe(bpy)(3)](2+) support the structural assumption. However, for low-spin [Fe(terpy)2]21 the relaxation rate constant shows an anomalous behaviour in so far as it is more in line with spin-crossover systems. This is attributed to very anisotropic bond length changes associated with the spin state change, and the subsequent breakdown of the single mode model.

First author: Guan, W, Density functional study of protonation sites of alpha-Keggin isopolyanions, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 106, 1860, (2006)
Abstract: Density functional theory (DFF) calculations were carried out to characterize the optimal site of the protons and the precise protonation state in the polyoxometalate (POM) anions [V13O40](15-) and [H12V13O40](3-). Six kinds of possible protonated stable isomers with the whole Keggin anion units are discussed. The calculations reveal that the preferred protonation site corresponds to bridging oxygens that belong to the same trimetallic group (isomers B and C. Both isomers B and C are comparatively stable in the gas phase, but only isomer B could exist stably in aqueous solution because of being stabilized by the electrostatic interaction. The solvent effects and protonation are also discussed. Int J Quantum Chem 106: 1860-1864,2006.

First author: Pinkert, JC, Modeling proline ligation in the heme-dependent CO sensor, CooA, using small-molecule analogs, JOURNAL OF BIOLOGICAL INORGANIC CHEMISTRY, 11, 642, (2006)
Abstract: CooA, the only protein known to employ proline as a heme ligand, is a CO-activated transcription factor found in the bacterium Rhodospirillum rubrum. Proline is a heme ligand in both the Fe(III) and Fe(II) states; the sixth ligand is cysteinate in Fe(III) CooA and histidine in Fe(II) CooA. When CO binds to Fe(II) CooA, it selectively replaces the proline ligand, activating the protein. The proposed roles of proline are to stabilize the heme pocket during the redox-mediated ligand switch and to form a weak metal-ligand bond that is preferentially cleaved to bind CO. To explore this latter proposal, binding affinity, structural, and density functional theory computational studies were performed using pyrrolidine and 2-methylpyrrolidine as analogs of proline, and imidazole as an analog of histidine. Measurement of the binding properties of these amino acid analogs in two different protein environments, CooA variant Delta P3R4 and myoglobin, revealed that CooA is tailored to accept the bulky proline ligand. Furthermore, the high pK(a) of proline facilitates selective replacement by CO. Model metalloporphyrin X-ray and computational structures suggest that the key factor leading to lengthening of the Fe-ligand bond and decreased binding affinity is steric hindrance at the C-2 position of the pyrrolidine ring. These data afford a more complete understanding of how CooA utilizes the weak proline ligand to direct CO to the distal position, thus ensuring selective retention of the histidine ligand.

First author: Bickelhaupt, F. Matthias, Structure and bonding of methyl alkali metal molecules, JOURNAL OF MOLECULAR MODELING, 12, 563, (2006)
Abstract: We have carried out a theoretical investigation of the methyl alkali metals CH3 M with M=Li, Na, K and Rb using density functional theory (DFT) at the BP86/TZ2P level. Our purpose is to determine how the structure and thermochemistry (e.g., C-M bond lengths and strengths) of these organoalkali metal compounds depend on the metal atom, and to understand the emerging trends in terms of quantitative Kohn-Sham molecular orbital (KS-MO) theory. The C-M bond becomes longer and weaker if one goes from Li to the more electropositive Rb. Also, the polarity of the C-M bond increases along this series but it preserves a strong intrinsic preference to homolytic over ionic dissociation in the gas phase. We show that a description of the bonding mechanism in terms of a polar C-M electron-pair bond between the methyl radical and alkali metal atom is just as natural as an ionic description (i.e., in terms of CH3-+M+) and that it provides a straightforward way of understanding all observed trends.

First author: Molchanov, S., Main factors governing chemical shifts of carbon and nitrogen in cyano group. An experimental and theoretical study, POLISH JOURNAL OF CHEMISTRY, 80, 1031, (2006)
Abstract: The feasibility of a description of magnetic shielding of carbon and nitrogen nuclei of cyano group in various cyano compounds as a net result of the interplay of different structural factors is discussed. Analysis of experimental data and DFT GIAO calculations of shielding constants have shown that the main factors governing the carbon chemical shifts are the heavy-atom and inductive effects, although the resonance and steric properties of a substituent are also of some importance. On the other hand, the shielding of the cyano nitrogen is connected mainly with the redistribution of pi-electrons within the cyano group, which is the result of mesomeric interaction, and, to a lesser extent, with the inductive properties of the substituent. The steric and heavy-atom effects of the substituent seem to be irrelevant for the shielding of cyano nitrogen.

First author: Theodoor de Jong, G., Oxidative addition of hydrogen halides and dihalogens to Pd. Trends in reactivity and relativistic effects, JOURNAL OF PHYSICAL CHEMISTRY A, 110, 7943, (2006)
Abstract: We have theoretically studied the oxidative addition of HX and X-2 to palladium for X = F, Cl, Br, I and At, using both nonrelativistic and ZORA-relativistic density functional theory at BLYP/QZ4P. The purpose is 3-fold: (i) to obtain a set of consistent potential energy surfaces (PESs) to infer accurate trends in reactivity for simple, archetypal oxidative addition reactions; (ii) to assess how relativistic effects modify these trends along X) F, Cl, Br, I and At; and (iii) to rationalize the trends in reactivity in terms of the reactants’ molecular-orbital ( MO) electronic structure and the H-X and X-X bond strengths. For the latter, we provide full Dirac-Coulomb CCSD(T) benchmarks. All oxidative additions to Pd are exothermic and have a negative overall barrier, except that of HF which is approximately thermoneutral and has a positive overall barrier. The activation barriers of the HX oxidative additions decrease systematically as X descends in group 17 of the periodic table; those of X-2 first increase, from F to Cl, but then also decrease further down group 17. On the other hand, HX and X-2 show clearly opposite trends regarding the heat of reaction: that of HX becomes more exothermic and that of X-2 less exothermic as X descends in group 17. Relativistic effects can be as large as 15-20 kcal/mol but they do not change the qualitative trends. Interestingly, the influence of relativistic effects on activation barriers and heats of reaction decreases for the heavier halogens due to counteracting relativistic effects in palladium and the halogens.

First author: Al Natsheh, Anas, Sulfuric acid and sulfuric acid hydrates in the gas phase: A DFT investigation (vol 108A, pg 8914, 2004), JOURNAL OF PHYSICAL CHEMISTRY A, 110, 7982, (2006)
Abstract: We have theoretically studied the oxidative addition of HX and X-2 to palladium for X = F, Cl, Br, I and At, using both nonrelativistic and ZORA-relativistic density functional theory at BLYP/QZ4P. The purpose is 3-fold: (i) to obtain a set of consistent potential energy surfaces (PESs) to infer accurate trends in reactivity for simple, archetypal oxidative addition reactions; (ii) to assess how relativistic effects modify these trends along X) F, Cl, Br, I and At; and (iii) to rationalize the trends in reactivity in terms of the reactants’ molecular-orbital ( MO) electronic structure and the H-X and X-X bond strengths. For the latter, we provide full Dirac-Coulomb CCSD(T) benchmarks. All oxidative additions to Pd are exothermic and have a negative overall barrier, except that of HF which is approximately thermoneutral and has a positive overall barrier. The activation barriers of the HX oxidative additions decrease systematically as X descends in group 17 of the periodic table; those of X-2 first increase, from F to Cl, but then also decrease further down group 17. On the other hand, HX and X-2 show clearly opposite trends regarding the heat of reaction: that of HX becomes more exothermic and that of X-2 less exothermic as X descends in group 17. Relativistic effects can be as large as 15-20 kcal/mol but they do not change the qualitative trends. Interestingly, the influence of relativistic effects on activation barriers and heats of reaction decreases for the heavier halogens due to counteracting relativistic effects in palladium and the halogens.

First author: Conradie, Jeanet, Iron(III)-nitro porphyrins: Theoretical exploration of a unique class of reactive molecules,INORGANIC CHEMISTRY, 45, 4902, (2006)
Abstract: DFT(PW91/TZP) calculations, including full geometry optimizations, have been carried on [Fe-II(P)(NO2)](-), Fe-III(P)( NO2), [Fe-II(P)(NO2)(py)]-, Fe-III(P)(NO2)(py), [Fe-III(P)(NO2)(2)](-), and Fe-III(P)(NO2)(NO), where P is the unsubstituted porphine dianion, as well as on certain picket fence porphyrin (TPivPP) analogues. The bonding in [Fe-II(P)(NO2)](-) and Fe-III(P)(NO2), as well as in their pyridine adducts, reveals a sigma-donor interaction of the nitrite HOMO and the Fe d(z)(2) orbital, where the Fe-N-nitro axis is defined as the z direction and the nitrite plane is identified as xz. Both molecules also feature a pi-acceptor interaction of the nitrite LUMO and the Fe d(yz) orbital, whereas the SOMO of the Fe((III))-nitro complexes may be identified as d(xz). The Fe((III))-nitro porphyrins studied all exhibit extremely high adiabatic electron affinities, ranging from about 2.5 eV for Fe-III(P)(NO2) and Fe-III(P)(NO2)(py) to about 3.4 eV for their TPivPP analogues. Transition-state optimizations for oxygen-atom transfer from Fe-III(P)(NO2) and Fe-III(P)(NO2)(py) to dimethyl sulfide yielded activation energies of 0.45 and 0.77 eV, respectively, which is qualitatively consistent with the observed far greater stability of Fe-III(TPivPP)(NO2)(py) relative to Fe-III(TPivPP)(NO2). Addition of NO to yield {FeNO}(6) nitro – nitrosyl adducts such as Fe(P)(NO2)(NO) provides another mechanism whereby Fe(III)-nitro porphyrins can relieve their extreme electron affinities. In Fe(P)(NO2)(NO), the bonding involves substantial Fe-NO pi-bonding, but the nitrite acts essentially as a simple sigma-donor, which accounts for the relatively long Fe-N-nitro distance in this molecule.

First author: Wasbotten, Ingar, Theoretical evidence favoring true iron(V)-oxo corrole and corrolazine intermediates,INORGANIC CHEMISTRY, 45, 4910, (2006)
Abstract: Although many formally Fe( V) intermediates are known in the form of peroxidase compound I intermediates and their synthetic models, “true” d(3) (FeO)-O-V intermediates have remained elusive and hence a Holy Grail of sorts for many bioinorganic chemists. Very recently, Newcomb and co-workers provided transient absorption spectroscopic evidence suggestive of (FeO)-O-V corrole intermediates. Here, we report DFT calculations predicting nearly isoenergetic (FeO)-O-V and (FeO)-O-IV corrolato(2-.) states for Fe(corrolato)( O) intermediates. In the course of a theoretical search for systems in which a true (FeO)-O-V state might be favored by a clear and substantial margin of energy, we have identified corrolazine as a promising supporting ligand; thus, we find that with corrolazine, the FeVO states are favored by at least 0.5 eV over (FeO)-O-IV corrolazinato(2-.) states.

First author: Wasbotten, Ingar, Biliverdine-based metalloradicals: Sterically enhanced noninnocence, INORGANIC CHEMISTRY, 45, 4914, (2006)
Abstract: This is a first density functional theory survey of transition-metal biliverdines (Blv), where we have chosen to focus on key Mn, Fe, Co, and Cu complexes. According to the calculations, the complexes are invariably noninnocent, featuring Blv(.2-) ligand radicals. In this, biliverdine complexes resemble metallocorroles, but the parallels are only approximate. Briefly, metallobiliverdines exhibit a much greater tendency to adopt noninnocent electronic structures than analogous metallocorroles. The O center dot center dot center dot O nonbonded contacts in biliverdines apparently preclude the formation of short metal – N bonds that, in turn, could stabilize high-valent metal ions. Thus, while most copper corroles ( Cor) exhibit diamagnetic Cu-III ground states, copper biliverdines are clearly Cu(II)Blv(.2-) species. In the same spirit, while chloroiron corroles are best described as Fe-III(S = 3/2) Cor(.2-), the analogous biliverdine derivative seems best described as Fe-III(S) 5/2) Blv(.2-), i.e., featuring a high-spin Fe-III center with long (> 2.0 angstrom) Fe – N bond distances. Overall, the results highlight the important role that steric effects may play in modulating the electronic structures and the potentially noninnocent nature of transition-metal complexes.

First author: Ooi, Bee-Lean, Preparation, properties, and reactivities of unprecedented oxo-sulfido Nb(IV) aqua ions and crystal structure of (Me2NH2)(6)[Nb-5(mu(3)-S)(2)(mu(3)-O)(2)(mu(2)-O)(2)(NCS)(14)]center dot 3.5H(2)O, INORGANIC CHEMISTRY, 45, 5008, (2006)
Abstract: By treatment of Zn-reduced ethanolic solutions of NbCl5 with HCl in the presence of sulfide followed by cation-exchange chromatography, two oxo-sulfido niobium aqua ions, the red [Nb-4(mu(4)-S)(mu(2)-O)(5)(H2O)(10)](4+) and the yellow-brown [Nb-5(mu(3)-S)(2)(mu(3)-O)(2)(mu(2)-O)(2)(H2O)(14)](8+), were isolated. Both readily form their respective thiocyanate complexes, for which the structure for the former has been previously reported. Brown crystals of (Me2NH2)(6)[Nb5S2O4(NCS)(14)] center dot 3.5H(2)O (1) were isolated in the case of the latter, and the structure was determined by X-ray crystallography (space group: a = 15.4018(5) angstrom, b = 21.1932( 8) angstrom, c = 22.0487( 8) angstrom, alpha = gamma = 90 degrees, beta = 103.4590(10)degrees, and R-1 = 0.0659). An unprecedented pentanuclear Nb5S2O48+ core is revealed in which short Nb – Nb distances (2.7995( 8) – 2.9111(8) angstrom) are consistent with metal – metal bonding. A stopped-flow kinetic study of the 1: 1 equilibration of NCS- with [Nb-4(mu(4)-S)(mu(2)-O)(5)(H2O)(10)](4+) has been carried out. Equilibration rate constants are independent of [H+] in the range investigated (0.5 – 2.0 M) and at 25 degrees C; k(f) = 9.5 M-1 s(-1), k(aq) = 2.6 x 10(-2) s(-1), and K = 365 M-1. Conditions with first NCS- and then [Nb-4(mu(4)-S)(mu(2)-O)(5)(H2O)(10)](4+) in excess revealed a statistical factor of 4, suggesting the presence of four kinetically equivalent Nb atoms. Attempts to study the 1: 1 substitution of NCS- with [ Nb-5(mu(3)-S)(2)(mu(3)-O)(2)(mu(2)-O)(2)(H2O)(14)](8+) showed signs of saturation kinetics. Quantum chemical calculations using the density functional theory (DFT) approach were performed on both the Nb4O5S4+ and Nb5O4S28+ naked clusters. The highest occupied and lowest unoccupied molecular orbitals have dominant Nb(4d) character. The HOMO for Nb4O5S4+ is a nondegenerate fully filled MO, whereas for Nb5O4S28+, it is a nondegenerate partially filled MO with one unpaired electron. EPR spectroscopy on [Nb-5(mu(3)-S)(2)(mu(3)-O)(2)(mu(2)-O)(2)(H2O)(14)](8+) shows that the molecule has total anisotropy (C-2v), with all three tensors, g(x) = 2.399, g(y) = 1.975, and g(z) = 1.531, resolved. No hyperfine interaction expected from the nuclear moment of I = 9/2 for Nb-93 was observed.

First author: Di Valentin, Cristiana, EPR properties of Au atoms adsorbed on various-sites of the MgO(100) surface from relativistic DFT calculations, SURFACE SCIENCE, 600, 2434, (2006)
Abstract: Using all electron fully relativistic DFT calculations we, have computed the EPR properties of Au atoms bound to various sites of the MgO surface. Changes in g-tensor and hyperfine coupling constants provide a way to identify the gold adsorption site and to map the surface morphology by comparison of measured and calculated EPR spectra. We found a strong reduction of the isotropic hyperfine coupling constant, a(iso)(Au), for adsorbed gold compared to the free atom; this reduction, which is about 45% for terrace sites, is more pronounced when Au interacts with low-coordinated sites like steps, edges and corners where it is about 60%. The reduction of a(iso)(Au) is accompanied by a corresponding increase of the superhyperfine interaction with the surface oxygen sites, as measured by a(iso)(O-17). Large anisotropies in the g-tensor are computed for all sites.

First author: Saito, Junji, Polymerization of higher alpha-olefins with a bis(phenoxyimine)Ti complex/i-Bu3Al/Ph3CB(C6F5)(4): Formation of stereo- and regioirregular high molecular weight polymers with high efficiency, MACROMOLECULES,39, 4023, (2006)
Abstract: The unique catalytic behavior of a bis(phenoxyimine) Ti complex combined with i-Bu3Al/Ph3CB(C6F5) (4) ( whose active species is a phenoxyamine Ti complex) is discussed here for use in the polymerization of higher alpha-olefins (i.e., 1-hexene, 1-octene, 1-decene, and 4-methyl-1-pentene). The catalyst system works as a single-site catalyst and exhibits high activities toward the higher alpha-olefins that were used in this study. The activities are comparable to or exceed those seen with a common metallocene catalyst, rac-[C2H4-(1-indenyl)(2)]ZrCl2. The polymerization rate has a zeroth-order dependence on the concentration of the monomer. To our surprise, the system exhibited higher activities toward higher alpha-olefins that incorporate more sterically encumbered substituents in close proximity to the olefinic moieties ( activity order: 4-methyl-1-pentene > 1-decene > 1-octene > 1-hexene). The resultant polymers have very high molecular weights (M-w 846 000- 1 450 000), representing some of the highest reported for poly( higher alpha-olefin)s. Microstructural analyses using C-13 NMR spectroscopy revealed that these high molecular weight polymers possess atactic structures with significant regioirregular units (ca. 50 mol %). Therefore, the catalyst system produced stereo- and regioirregular high molecular weight poly( higher alpha-olefin)s (“ultra-random polymers”) with high efficiency.

First author: Neugebauer, J, Assessment of a simple correction for the long-range charge-transfer problem in time-dependent density-functional theory, JOURNAL OF CHEMICAL PHYSICS, 124, 4023, (2006)
Abstract: The failure of the time-dependent density-functional theory to describe long-range charge-transfer (CT) excitations correctly is a serious problem for calculations of electronic transitions in large systems, especially if they are composed of several weakly interacting units. The problem is particularly severe for molecules in solution, either modeled by periodic boundary calculations with large box sizes or by cluster calculations employing extended solvent shells. In the present study we describe the implementation and assessment of a simple physically motivated correction to the exchange-correlation kernel suggested in a previous study [O. Gritsenko and E. J. Baerends J. Chem. Phys. 121, 655 (2004)]. It introduces the required divergence in the kernel when the transition density goes to zero due to a large spatial distance between the “electron” (in the virtual orbital) and the “hole” (in the occupied orbital). A major benefit arises for solvated molecules, for which many CT excitations occur from solvent to solute or vice versa. In these cases, the correction of the exchange-correlation kernel can be used to automatically “clean up” the spectrum and significantly reduce the computational effort to determine low-lying transitions of the solute. This correction uses a phenomenological parameter, which is needed to identify a CT excitation in terms of the orbital density overlap of the occupied and virtual orbitals involved. Another quantity needed in this approach is the magnitude of the correction in the asymptotic limit. Although this can, in principle, be calculated rigorously for a given CT transition, we assess a simple approximation to it that can automatically be applied to a number of low-energy CT excitations without additional computational effort. We show that the method is robust and correctly shifts long-range CT excitations, while other excitations remain unaffected. We discuss problems arising from a strong delocalization of orbitals, which leads to a breakdown of the correction criterion.

First author: Erhardt, Stefan, A challenge to chemical intuition: Donor-acceptor interactions in H3B-L and H2B+-L (L = CO; EC5H5, E =N-Bi), CHEMISTRY-A EUROPEAN JOURNAL, 12, 4620, (2006)
Abstract: The equilibrium geometries and bond energies of the complexes H3B-L and H2B+-L (L=CO; EC5H5: E=N, P, As, Sb, Bi) have been calculated at the BP86/TZ2P level of theory. The nature of the donor-acceptor bonds was investigated by energy decomposition analysis (EDA). The bond strengths of H3B-L have the order CO > N > P > As > Sb > Bi. The calculated values are between D-e = 37.1 kcal mol(-1) for H3B-CO and D-e = 6.9 kcal mol(-1) for H3B-BiC5H5. The bond dissociation energies of the cations H2B+-CO and HZB+-EC5H5 are larger than for H3B-L, particularly for complexes of the heterobenzene ligands. The calculated values are between D-e = 51.9 kcal mol(-1) for H2B+-CO and D-e = 122.1 kcal mol(-1) for H2B+ -NC5H5. The trend of the BDE of H2B+-CO and H2B+-EC5H5 is N > P > As > Sb > Bi > CO. A surprising result is found for H2B+-CO, which has a significantly stronger and yet substantially longer bond than H2B-CO. The reason for the longer but stronger bond in H2B+-CO compared with that in H3B-CO comes mainly from the change in electrostatic attraction and it bonding at shorter distances, which increases more in the neutral system than in the cation, and to a lesser extent from the deformation energy of the fragments. The H2B+ <- NC5H5 pi(perpendicular to) donation plays an important role for the stronger interactions at shorter distances compared with those in H3B-NC5H5. The attractive interaction in H2B+-CO further increases at bond lengths that are shorter than the equilibrium value, but this is compensated by the energy which is necessary to deform BH2+ from its linear equilibrium geometry to the bent form in the complex. The EDA shows that the contributions of the orbital interactions to the donor-acceptor bonds are always larger than the classical electrostatic contributions, but the latter term plays an important role for the trend in bond strength. The largest contributions to the orbital interactions come from the 0 orbitals. The EDA calculations suggest that heterobenzene ligands may become moderately strong pi donors in complexes with strong Lewis acids, while CO is only a weak a donor. The much stronger interaction energies in HZB+-EC5H5 compared with those in H3B-EC5H5 are caused by the significantly larger contribution of the pi(perpendicular to) orbitals in HZB+-EC5H5 and by the increase of the binding interactions of the sigma+pi(parallel to) orbitals.

First author: Zhang, Yi-Quan, Relationship between the nearest-neighbor exchange coupling constants and the number of exchange interactions in the cyano-bridged MnMo6(CN)(18) cluster: Density functional theory calculations, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 12, 2292, (2006)
Abstract: A theoretical density functional study of the relationship between the nearest-neighbor MnMo constants and the number of exchange interactions in the cyano-bridged K[(Me(3)tacn)(6)MnMo6(CN)(18)](ClO4)(3) cluster is presented. Two approaches (the first approach consisted of evaluating the exchange coupling constant J(ij) between two paramagnetic metal centers i and j in the hexanuclear molecule by calculating the energy differences between the highest and broken-symmetry spin states of a model molecule in which metal atoms except for i and j are substituted by diamagnetic Y-III cations, and the second is to calculate the different spin-state energies of hexanuclear complexes and use the Heisenberg Hamiltonian to obtain the exchange coupling constants between different metal centers) show that the antiferromagnetic coupling interactions between nearest neighbors weaken with the increase of the number of exchange interactions. The various theta angles have an influence on the interactions between the nearest-neighbor MoMn but do not change the trend between J(12) and the number of exchange interactions. Moreover, Kahn’s qualitative theory succeeded in being applied to interpret the trend.

First author: Gong, Z, A computational study on electron transfer mechanism between alkaline earth metal atoms and cyclooctatetraene to form cation-pi bonded complexes, CHEMICAL PHYSICS LETTERS, 423, 339, (2006)
Abstract: The calculations with ‘three-state model’ on the complexation between alkaline earth metal atoms and 1,3,5,7-cyclooctatetraene (COT) show that the metal atoms transfer their electrons to COT via concerted adiabatic two-electron transfer mechanism, to form cation-pi complexes. The MP2/6-311++G** calculated interaction strength and distance are in scale with chemical bonding. Decomposition on the binding energy showed that electrostatic is the main component. Thus, it could be concluded that the interaction between the alkaline earth metal atoms and COT is a chemical bond, namely cation-pi bond, which is ionic in nature.

First author: De Angelis, Filippo, Ab initio molecular dynamics simulations of organometallic reactivity, COORDINATION CHEMISTRY REVIEWS, 250, 1497, (2006)
Abstract: The energetics and reaction mechanism of prototypical organometallic reactions have been investigated by combining static and dynamic density functional calculations, based on the Car-Parrinello method. Such an approach allows us to dynamically sample the potential energy surface of the reactive system at finite temperature, providing useful insights into the reaction mechanism and evidencing the presence of reaction intermediates. Applications of this methodology are presented, ranging from the migratory insertions of carbon monoxide and alkyl-isocyanides into different metal-carbon bonds, to the SiH oxidative addition to Pt(PH3)(2) and the acetylene to vinylidene isomerization in the coordination sphere of a transition metal center.

First author: Georgieva, Elka R., High-field/high-frequency EPR study on stable free radicals formed in sucrose by gamma-irradiation, FREE RADICAL RESEARCH, 40, 553, (2006)
Abstract: The EPR spectrum of sucrose irradiated by high-energy radiation is complex due to the presence of more than one radical species. In order to decompose the spectrum and elucidate the radical magnetic parameters a high-field (HF(-)EPR) study on stable free radicals in gamma-irradiated polycrystalline sucrose (table sugar) was performed at three different high frequencies-94, 190 and 285 GHz as well as at the conventional X-band. We suggest a presence of three stable radicals R1, R2 and R3 as the main radical species. Due to the increase of g-factor resolution at high fields the g-tensors of these radicals could be extracted by accurate simulations. The moderate g-anisotropy suggests that all three radicals are carbon-centred. Results from an earlier ENDOR study on X-irradiated sucrose single crystals (Vanhaelewyn et al., Appl Radiat Isot, 52, 1221 (2000)) were used for analyzing of the spectra in more details. It was confirmed that the strongest hyperfine interaction has a relatively small anisotropy, which indicates either the absence of alpha-protons or a strongly distorted geometry of the radicals.

First author: Zhang, YQ, Theoretical study of the magnetic exchange coupling behavior substituting Cr(III) with Mo(III) in cyano-bridged transition metal complexes, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 106, 1551, (2006)
Abstract: Molecular magnetism in a series of cyano-bridged first and second transition metal complexes has been investigated using density functional theory (DFT) combined with the broken-symmetry (BS) approach. Several exchange-correlation (XC) functionals in the ADF package were used to investigate complexes I [-(Me(3)tacn)(2)(cyclam)NiMo2(CN)(6)](2+), II [-(Me(3)tacn)(2)(cyclam)Ni-Cr-2(CN)(6)](2+), III [-(Me(3)tacn)(6)MnMo6(CN)(18)](2+), and IV [(Me(3)tacn)(6)MnCr6(CN)(18)](2+) (Me(3)tacn = N,N’,N”‘-trimethyl-1,4,7-triazacyclononane). For models A (the molded structure of complex 1) and B (the modeled structure of complex II), all the XCs given qualitatively reasonable results and predict ferromagnetic coupling character between M (M = Mo-III for A or Cr-III for B) and Ni-II in coincidence with the experimental results (see Tables I and II). The calculated using Operdew, OPBE, O3LYP, and B3LYP functionals and experimental I values show that substituting Cr-III with Mo-III will enhance the ferromagnetic exchange coupling interactions. But VWN, PW91, PBE, VSXC, and tau-HCTH functionals have no way to differentiate the relative strength of the intramolecular magnetic exchange coupling interactions of A and B correctly. For models C (the modeled structure of complex 111) and D (the modeled structure of complex IV), all the XCs in ADF and B3LYP in Gaussian 03 with several basis sets show that substituting Cr-III with Mo-III will enhance the anti ferromagnetic exchange coupling interactions. From the above calculations, the substitution of Cr-III by Mo-III will enhance the magnetic coupling interactions, whether the magnetic coupling interactions are ferro- or antiferromagnetic. Moreover, Kahn’s model was applied to investigate the above facts.

First author: Van Lenthe, JH, Starting SCF calculations by superposition of atomic densities, JOURNAL OF COMPUTATIONAL CHEMISTRY, 27, 926, (2006)
Abstract: We describe the procedure to start an SCF calculation of the general type from a sum of atomic electron densities, as implemented in GAMESS-UK. Although the procedure is well known for closed-shell calculations and was already suggested when the Direct SCF procedure was proposed, the general procedure is less obvious. For instance, there is no need to converge the corresponding closed-shell Hartree-Fock calculation when dealing with an open-shell species. We describe the various choices and illustrate them with test calculations, showing that the procedure is easier, and on average better, than starting from a converged minimal basis calculation and much better than using a bare nucleus Hamiltonian.

First author: Gomez-Jeria, Juan S., On the use of the whole eigenvalue spectrum to obtain single molecule band structures and solid band gaps for molecular electronics studies., JOURNAL OF THE CHILEAN CHEMICAL SOCIETY,51, 905, (2006)
Abstract: A Density Functional microscopic model of C-60, consisting of seven molecular orbitals (3 occupied and 4 empty), was employed to get the best values for the half-width and the scanning distance of the mathematical function used to obtain the theoretical DOS spectrum. It is found that the convolution of the whole eigenvalue spectrum with a Gaussian function should be made with values of 0.1 eV for both, the broadening parameter and the scanning distance. The theoretical calculation of the VB-CB band gap for the solid from results belonging to isolated C-60. is in a relatively good agreement with most experimental results. We were able to simulate the “experimental” band gap starting from the theoretical DOS spectrum and using some experimental data. Regarding the HOMO-LUMO gap, the isolated molecule results are in very good agreement with experimental results for solid C-60. Finally it is suggested that experimentalists select their results based on in a priori knowledge of theoretical results because they intend to calculate some properties needing them.

First author: Bucknum, Michael J., On the structure of i-carbon, JOURNAL OF THEORETICAL & COMPUTATIONAL CHEMISTRY, 5, 175, (2006)
Abstract: In the carbon science literature, there have been various reports over the past few decades of potentially novel crystalline forms of carbon emerging as nanometer scale fragments recovered from the explosive remnants of heated, shock compressed graphite and other precursors of C. Two nanometric and crystalline forms of C that are particularly prominent in these studies are known as n-diamond and i-carbon forms. In our previous work, we have shown that the commonly observed diffraction pattern of n-diamond nanocrystals, recorded by several research groups around the world, is consistent with the calculated diffraction pattern of a novel form of carbon that we propose to call glitter. Glitter is a tetragonal allotrope of carbon with a calculated density of similar to 3.08 g/cm(3), and the density functional theory (DFT) optimized lattice paxameters given as a = 0.2560 nm and c = 0.5925 nm. In addition to the diffraction evidence for n-diamond having the glitter structure, the DFT calculated band structure of glitter shows it to be metallic, like the observed electrical characteristics of n-diamond. In this communication, we report on a comparison of the diffraction pattern observed for nanocrystalline i-carbon by the investigative team of Yamada et al. in 1994, with the calculated diffraction pattern of glitter based upon the optimized lattice parameters. The close fit of the latter dataset to that observed for i-carbon, as reported herein, suggests that indeed i-carbon may be of the same structure as n-diamond, and that they both may have the tetragonal glitter structure.

First author: Zhao, LL, Surface-enhanced Raman scattering of pyrazine at the junction between two Ag-20 nanoclusters,NANO LETTERS, 6, 1229, (2006)
Abstract: In this work we present a detailed time-dependent density functional theory (TDDFT) investigation of the absorption and Raman spectra of a pyrazine molecule located at the junction between two Ag-20 clusters. Surface-enhanced Raman scattering enhancements of the order of 106 have been found for the junction system, which are similar to enhancements of 105 found for individual silver nanoparticles. Surprisingly, the chemical enhancement is found to account for as much as 105, suggesting that this mechanism might be more important than previously believed, in particular for nanoparticle aggregates. Moreover, TDDFT calculations suggest that unlike larger nanoparticles, the junction between small Ag20 tetrahedral clusters does not provide an electromagnetic “hot spot”.

First author: George, SD, Metal and ligand K-edge XAS of titanium-TEMPO complexes: Determination of oxidation states and insights into Ti-O bond homolysis, INORGANIC CHEMISTRY, 45, 4468, (2006)
Abstract: Ti-TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl) provides a means for generating Ti(III) complexes by homolysis of the Ti-O bond. It has been determined that bis-Cp-Ti-TEMPO complexes readily undergo homolytic cleavage while the mono-Cp-Ti-TEMPO complexes do not. Here Ti K- and Cl K-edge XAS are applied to directly determine the oxidation state of TiCl3TEMPO, TiCpCl2TEMPO, and TiCp2ClTEMPO, with reference to Ti(III) and Ti(IV) complexes of known oxidation state. The Ti K- edge data show that Ti(III) complexes exhibit a pre-edge feature similar to 1 eV lower than any of the Ti(IV) complexes; while the Cl K- edges show that Ti(III) complexes have a Cl K- pre-edge feature to similar to 1 eV higher energy than any of the Ti(IV) complexes. Taken together, the Ti and Cl K- edge data indicate that the Ti-TEMPO complexes are best described as Ti(IV)-TEMPO anions (rather than Ti(III)-nitroxyl radicals). In addition, the Cl K- edges indicate that replacement of Cl by Cp weakens the bonding with the remaining ligands, with the Cl 3p covalency decreasing from 25% to 21% to 17% on going from TiCl3TEMPO to TiCpCl2TEMPO to TiCp2ClTEMPO. DFT calculations also show that the electronic structures of the Ti -TEMPO complexes are modulated by the replacement of chloride by Cp. The effect of the Cp on the ancillary ligation is one factor that contributes to facile Ti-O bond homolysis in TiCp2ClTEMPO. However, the results indicate the primary contribution to the energetics of Ti-O bond homolysis in TiCp2ClTEMPO is stabilization of the three-coordinate product by Cp.

First author: Chen, WZ, Spectral and structural characterization of amidate-bridged platinum-thallium complexes with strong metal-metal bonds, INORGANIC CHEMISTRY, 45, 4526, (2006)
Abstract: The reactions of [Pt(NH3)(2)((NHCOBu)-Bu-t)(2)] and TlX3 (X = NO3-, Cl-, CF3CO2-) yielded dinuclear [{Pt(ONO2)(NH3)(2-)((NHCOBu)-Bu-t)}Tl(ONO2)(2)(MeOH)] (2) and trinuclear complexes [{PtX(RNH2)(2)((NHCOBu)-Bu-t)(2)}(2)Tl](+) [X = NO3- (3), Cl- (5), CF3CO2- (6)], which were spectroscopically and structurally characterized. Strong Pt-Tl interaction in the complexes in solutions was indicated by both Pt-195 and Tl-205 NMR spectra, which exhibit very large one-bond spin-spin coupling constants between the heteronuclei ((1)J(PtTl)), 146.8 and 88.84 kHz for 2 and 3, respectively. Both the X-ray photoelectron spectra and the Pt-195 chemical shifts reveal that the complexes have Pt centers whose oxidation states are close to that of Pt-III. Characterization of these complexes by X-ray diffraction analysis confirms that the Pt and Tl atoms are held together by very short Pt-Tl bonds and are supported by the bridging amidate ligands. The Pt-Tl bonds are shorter than 2.6 angstrom, indicating a strong metal-metal attraction between these two metals. Compound 2 was found to activate the C-H bond of acetone to yield a platinum(IV) acetonate complex. This reactivity corresponds to the property of Pt-III complexes. Density functional theory calculations were able to reproduce the large magnitude of the metal-metal spin-spin coupling constants. The couplings are sensitive to the computational model because of a delicate balance of metal 6s contributions in the frontier orbitals. The computational analysis reveals the role of the axial ligands in the magnitude of the coupling constants.

First author: Hong Jia-Sui, Geometric structures and magnetic analysis of manganese clusters Mn-5 and Mn-6, ACTA CHIMICA SINICA, 64, 1063, (2006)
Abstract: Equilibrium geometries and electronic properties of transition metal clusters (Mn-5, Mn-6) have been investigated by means of the relativistic density functional approach. Present results show that these clusters exhibit rich structural varieties on the potential energy surfaces, while the spin polarization at each site and the corresponding magnetic moments are highly sensitive to structures. For Mn-5 cluster, the most stable structure is trigonal bipyramid with spin magnetism of 3 mu(B), and Mn-6 cluster has the most stable structure of ferromagnetic octahedron with spin magnetic moment of 16 mu(B). The more stable isomers of Mn-5 and Mn-6 correspond to different orientations of the atomic spins resulting from the interatomic exchange coupling.

First author: Bonalumi, Norberto, Theoretical and spectroscopic study of the effect of ring substitution on the adsorption of anisole on platinum, JOURNAL OF PHYSICAL CHEMISTRY B, 110, 9956, (2006)
Abstract: The adsorption of anisole, 3,5-dimethylanisole, and 3,5-bis-(trifluoromethyl)-anisole on Pt(111) was studied theoretically and compared to the adsorption of benzene using relativistically corrected density functional theory. A cluster of 31 platinum atoms was used to simulate the surface. The three anisoles were found to be less strongly adsorbed than the parent molecule benzene, 3,5-bis-( trifluoromethyl)-anisole showing weakest adsorption, with an adsorption energy of only one-third that of benzene. The theoretical study was complemented by in situ ATR-IR spectroscopy of the adsorption of the anisole derivatives on a polycrystalline Pt film. The spectroscopic study indicated that the adsorption strength of the anisoles follows the same order as predicted by the calculations. In addition, catalytic hydrogenation tests showed that the propensity to aromatic ring hydrogenation can also be correlated to the mode and strength of adsorption of the anisoles. The degree of saturation followed the same order as the adsorption strength found by the calculations and indicated by spectroscopy. Although 3,5-dimethyl substitution on anisole resulted in only a partial loss of adsorption energy and reactivity toward ring hydrogenation as compared to anisole, the substitution by CF3 groups led to a large loss of adsorption energy and complete loss of reactivity toward aromatic ring saturation. Along with the study of the substituent effect on the adsorption of aromatic molecules, the correlation between adsorption and propensity to saturation of aromatic substrates could be corroborated.

First author: Belkhiri, Lotfi, Investigation of the dithiolene ligand conformation in analogous U(IV)/U(V) complexes: X-ray diffraction and density functional theory analysis of the U center dot center dot center dot(C=C) interaction,ORGANOMETALLICS, 25, 2782, (2006)
Abstract: Elucidation of the crystal structure of the dianionic complex [Na(18-crown-6)(thf)(2)](2)[U(COT)(dddt)(2)] (COT = eta(8)-C8H8, dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate), complementing that of [Na(18-crown-6)( thf)][U(COT)(dddt)(2)], allowed the first structural comparison of analogous uranium( IV) and -( V) compounds with anionic sulfur ligands. The distinct conformations of the dithiolene ligands, exo-exo and exo-endo in the uranium (IV) and -(V) complexes, respectively, are the observable manifestation of the differences in the metal-ligand bonding according to the oxidation state of the metal. The relationship between electronic structure, bonding, and conformational changes in these dianionic uranium(IV) and anionic uranium(V) species and the hypothetical neutral uranium(VI) counterpart has been investigated in the framework of relativistic density functional theory. The calculations reveal the occurrence in the uranium(V) anionic species of a significant intramolecular interaction involving the 5f metal orbitals and the C=C double bond of the endo dithiolene ligand, which stabilizes its peculiar exo-endo conformation. Such an interaction does not exist in the uranium(IV) complex.

First author: Maheut, G, Chiroptical and computational studies of a bridled chiroporphyrin and of its nickel(II), copper(II), and zinc(II) complexes, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 6347, (2006)
Abstract: Circular dichroism (CD) spectra and density functional theory (DFT) calculations are reported for a series of conformationally bistable chiroporphyrins with 8-methylene bridles MBCP-8, which can display either an alpha alpha alpha alpha or an alpha beta alpha beta orientation of their meso substituents. From DFT geometry optimizations, the most stable form of ZnBCP-8 is found to be the alpha alpha alpha alpha conformer. By passing to NiBCP-8, there is a strong stabilization of the alpha beta alpha beta conformation with respect to the alpha alpha alpha alpha conformation, consistent with the X-ray structures of alpha alpha alpha alpha-ZnBCP-8 and alpha beta alpha beta- NiBCP-8. A correlation between the sign of the CD signal in the Soret region and the conformation of the BCP-8 compounds is reported: the alpha alpha alpha alpha conformers H2BCP-8 and ZnBCP-8 show a positive CD signal, whereas the alpha beta alpha beta conformers NiBCP-8 and CuBCP-8 exhibit a negative signal. The possible contributions to the rotational strengths of alpha beta alpha beta-NiBCP-8 and alpha alpha alpha-ZnBCP8, calculated on the basis of their crystal structures, have been analyzed. The CD signals are found to result from a combination of both the inherent chirality of the porphyrin and of extrinsic contributions due to the chiral bridles. These results may have a broad significance for understanding the chiroptical properties of chiral porphyrins and hemoproteins and for monitoring stimuli-responsive, conformationally bistable chiroporphyrin compounds.

First author: Buhl, M, Effect of hydration on coordination properties of uranyl(VI) complexes. A first-principles molecular dynamics study, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 6357, (2006)
Abstract: Results from Car-Parrinello molecular dynamics simulations are reported for [UO2(OH2) 5](2+), UO2(NO3)(2)(OH2)(2), and UO2(NO3)(2)(eta(2)-tmma) (tmma = tetramethylmalonamide) in the gas phase and in aqueous solution. The distances between uranyl and neutral ligands such as water and tmma are decreased by up to 0.2 angstrom upon hydration, whereas those between uranyl and the nitrate ion are increased by up to 0.08 angstrom. According to pointwise thermodynamic integration involving constrained molecular dynamics simulations, solvation facilitates the transition of the chelating nitrate ligand to a eta(1)-bonding mode: the free energy of UO2(eta(2)-NO3)(eta(1)-NO3)(OH2)(2) relative to the bis-chelating minimum drops from 3.9 kcal/mol in vacuo to 1.4 kcal/mol in water. Optimizations in a polarizable continuum (specifically, the conductor-like screening model in conjunction with the zero-order regular approximation and triple. Slater basis sets) can qualitatively reproduce the geometrical changes from explicit hydration.

First author: Sojka, Z, EPR and DFT study of NO interaction with Ni/SiO2 catalyst: Insight into mechanistic steps of disproportionation process promoted by tripodal surface nickel complex, CATALYSIS TODAY, 114, 154, (2006)
Abstract: The adsorption of NO onto Ni/SiO2 catalyst has been investigated at 77 and 296 K at various pressures by EPR spectroscopy. The principal steps of NO disproportionation involve coordination of NO molecule with concomitant formation of paramagnetic mono {Ni-3c(II)-NO.}(9)/SiO2 and diamagnetic dinitrosyl species {Ni-2c-(NO)(2)}(10)/SiO2, reduction of nickel through inner-sphere ligand-to-metal electron transfer leading to {Ni-3c(I)-NO+}(9)/SiO2, formation of {Ni-3c-NO2}(9)/SiO2 Complex via metal-oxo intermediate, and spillover of the NO2 ligand onto silica. The key reaction intermediates have been isolated and identified. Their assignment and molecular structure have been ascertained by DFT calculations.

First author: Wang, SG, The challenge of the so-called electron configurations of the transition metals, CHEMISTRY-A EUROPEAN JOURNAL, 12, 4101, (2006)
Abstract: Quite different meanings are attached by chemists to the words element, atom, orbital, order of orbitals or configurations. This causes conceptual inconsistencies, in particular with respect to the transition-metal elements and their atoms or ions. The different meanings will here be distinguished carefully. They are analyzed on the basis of empirical atomic spectral data and quasi-relativistic density functional calculations. The latter are quite reliable for different average configuration energies of transition-metal atoms. The so-called “configurations of the chemical elements”, traditionally displayed in periodic tables, are the dominant configurations of the lowest spin-orbit levels of the free atoms. They are chemically rather irrelevant. In many electron systems the ns and np AOs are significantly below the more hydrogen-like nd ones. Even (n+1)s is below nd for all light neutral atoms from C onwards, but only up to the first elements of the respective long rows! The most common orbital order in transition-metal atoms is 3p << 3d < 4s etc. The chemically relevant configuration in group g is always d(8) instead of d(g-2) s(2). Conceptually clear reasoning eliminates apparent textbook inconsistencies between simple quantum-chemical models and the empirical facts. The empirically and theoretically well-founded Rydberg (n-delta(l)) rule is to be preferred instead of the historical Madelung (n+l) rule with its large number of exceptions.

First author: Childress, MV, Thallophilic interactions in aryloxide compounds: the {Tl-2(mu(2)-OAr)(4)} structural motif in (TlOAr)(4) and Tl2Cu(OAr)(4) compounds, INORGANIC CHEMISTRY, 45, 3864, (2006)
Abstract: Two thallium aryloxide compounds TIOC6F5 (TIOArF) and bis-3,5-TIOC6H3(CF3)(2) (TIOAr’) have been recrystallized from THF and crystallographically characterized in different isomeric forms. The latter compound forms a solvated tetrameric cubane, {TlOAr’}(4)(THF)-T-., 1. The TIOArF compound crystallized with a similar stoichiometry, {TlOArF} 4, 2 THF, 2, but contains a {TI2(mu(2)-OArF)(4)} unit that includes a thallophilic interaction at a distance of 3.5943(15) angstrom. Solution (TI)-T-205 and (TI)-T-203 NMR studies of 1 and 2 support the retention of a cubane structure for 1 in solution and suggest a similar structure for 2 with coupled thallium centers down to -90 degrees C. Fluorescence spectroscopy data for both compounds 1 and 2 in THF are consistent with LMCT. DFT calculations of 1, 2, and three models of the {TI2(mu(2)-OArF)(4)} unit show a bonding overlap of the bridged thallium atoms in 2 and are also used to describe the bonding in 1. The structures of two heterobimetallic compounds, TI2Cu(OArF)(4), 4, and TI2Cu(OAr’)(4), 5, with the {TI2(mu(2)-OArF)(4)} structural motif and thallophilic contacts of 3.86( 6) and 3.564(1) angstrom, respectively, are described. The crystal structures of the unsolvated of TlOArF, 2b, solvated heterobimetallic derivative TI2Cu(OAr’)(4)center dot 2THF, 5b, and the monomeric (18-crown-6) TIOArF, 3, and (TI)-T-205 NMR spectra of TIOC6H5, 6, are also reported for comparison purposes.

First author: Chen, YG, Synthesis, crystal structure and quantum study of organoammonium polyoxomolybdate with one-dimension chain containing face-shared molybdenum-oxygen octahedra, INORGANICA CHIMICA ACTA, 359, 2550, (2006)
Abstract: Organoammoinium polyoxomolybdate [(enH)(2)(H2Mo6O20)](infinity). was formed in autogeneous pressure at 160 degrees C for 120 h. The colorless crystals of polyoxomolybdate were characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction. The crystals are in monoclinic system with a space group P2(1)/n and a = 8.0844(16), b = 14.413(3), c = 8.9153(18) angstrom, beta = 98.12(3)degrees, V = 1013.8(4) angstrom(3), Z = 4. The final R = 0.0375, wR = 0.0706 for 2370 reflections [I > sigma(I-0)]. The crystals are constructed by one-dimension infinite inorganic chains with Mo6O20 unit as building block and protonated ethylenediamine cations located in between the inorganic chains. There are many hydrogen bonds between the chains and between the chains and the cations. IR spectrum of the title compound exhibited the vibration absorption of Mo=O, Mo-O-Mo bonds and protonated ethylenediamine cations, and suggests the presence of N-H-O and O-H-O hydrogen bonds. Quantum calculation gives the distribution of charges and the composition of frontier molecular orbits. From the calculation results, it can be inferred that protonation must have occurred on the terminal oxygen atom (O3) due to its smallest charge value and the terminal oxygen atom (O3) forms hydrogen bonds with the O12 atoms of the adjacent chain (2.936 angstrom); and that Mol atom will first receive the reduced electron. The electron transition taking place between HOMO and LUMO belongs basically to O -> Mo charge transfer transition.

First author: Jensen, L, Resonance Raman scattering of rhodamine 6G as calculated using time-dependent density functional theory, JOURNAL OF PHYSICAL CHEMISTRY A, 110, 5973, (2006)
Abstract: In this work, we present the first calculation of the resonance Raman scattering (RRS) spectrum of rhodamine 6G (R6G) which is a prototype molecule in surface-enhanced Raman scattering (SERS). The calculation is done using a recently developed time-dependent density functional theory (TDDFT) method, which uses a short-time approximation to evaluate the Raman scattering cross section. The normal Raman spectrum calculated with this method is in good agreement with experimental results. The calculated RRS spectrum shows qualitative agreement with SERS results at a wavelength that corresponds to excitation of the S-1 state, but there are significant differences with the measured RRS spectrum at wavelengths that correspond to excitation of the vibronic sideband of S-1. Although the agreement with the experiments is not perfect, the results provide insight into the RRS spectrum of R6G at wavelengths close to the absorption maximum where experiments are hindered due to strong fluorescence. The calculated resonance enhancements are found to be on the order of 10(5). This indicates that a surface enhancement factor of about 10(10) would be required in SERS in order to achieve single-molecule detection of R6G.

First author: Gusarov, Sergey, Self-consistent combination of the three-dimensional RISM theory of molecular solvation with analytical gradients and the Amsterdam density functional package, JOURNAL OF PHYSICAL CHEMISTRY A, 110, 6083, (2006)
Abstract: The three-dimensional reference interaction site model with the closure relation by Kovalenko and Hirata (3D-RISM-KH) in combination with the density functional theory (DFT) method has been implemented in the Amsterdam density functional (ADF) software package. The analytical first derivatives of the free energy with respect to displacements of the solute nuclear coordinates have also been developed. This enables study of chemical reactions, including reaction coordinates and transition state search, with the molecular solvation described from the first principles. The method yields all of the features available by using other solvation approaches, for instance infrared spectra of solvated molecules. To evaluate the accuracy of the present method, test calculations have been carried out for a number of small molecules, including four glycine conformers, a set of small organic compounds, and carbon nanotubes of various lengths in aqueous solution. Our predictions for the solvation free energy agree well with other approaches as well as experiment. This new development makes it possible to calculate at modest computational cost the electronic properties and molecular solvation structure of a solute molecule in a given molecular liquid or mixture from the first principles.

First author: Amat, P, The chromophore of asFP595: A theoretical study, JOURNAL OF PHYSICAL CHEMISTRY B, 110, 9348, (2006)
Abstract: We investigate the electronic and structural properties of the chromophore of the asCP/asFP595, a newly discovered protein of the ( green) fluorescent protein family. The use of theoretical methods with different degrees of accuracy and efficiency (DFT, TDDFT, CASSCF and perturbative corrections) allows us to compare the properties of a large number of hypothetic molecular models for the chromophore. The models are sorted on the basis of the relative stability and through a comparison with the experimental values of the excitation energy. Our study indicates that the most probable structure of the photoactive moiety in the protein and in water is the one resulting from the GFP-like rather than the “alternative” cyclization scheme.

First author: Brayshaw, Simon K., High hydride count rhodium octahedra, [Rh-6(PR3)(6)H-12][BAr4F](2): Synthesis, structures, and reversible hydrogen uptake under mild conditions, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY,128, 6247, (2006)
Abstract: A new class of transition metal cluster is described, [Rh-6(PR3)(6)H-12][ BAr4F](2) (R = Pr-i (1a), Cy (2a); BAr4F) [B{C6H3(CF3)(2)}(4)](-)). These clusters are unique in that they have structures exactly like those of early transition metal clusters with edge-bridging pi-donor ligands rather than the structures expected for late transition metal clusters with pi-acceptor ligands. The solid-state structures of 1a and 2a have been determined, and the 12 hydride ligands bridge each Rh-Rh edge of a regular octahedron. Pulsed gradient spin-echo NMR experiments show that the clusters remain intact in solution, having calculated hydrodynamic radii of 9.5(3) angstrom for 1a and 10.7(2) angstrom for 2a, and the formulation of 1a and 2a was unambiguously confirmed by ESI mass spectrometry. Both 1a and 2a take up two molecules of H-2 to afford the cluster species [Rh-6((PPr3)-Pr-i)(6)H-16][BAr4F](2) (1b) and [Rh-6(PCy3)(6)H-16][BAr4F](2) (2b), respectively, as characterized by NMR spectroscopy, ESI-MS, and, for 2b, X-ray crystallography using the [1-H-CB11Me11](-) salt. The hydride ligands were not located by X-ray crystallography, but H-1 NMR spectroscopy showed a 15: 1 ratio of hydride ligands, suggesting an interstitial hydride ligand. Addition of H-2 is reversible: placing 1b and 2b under vacuum regenerates 1a and 2a. DFT calculations on [Rh-6(PH3)(6)H-x](2+) (x = 12, 16) support the structural assignments and also show a molecular orbital structure that has 20 orbitals involved with cluster bonding. Cluster formation has been monitored by P-31 {H-1} and H-1 NMR spectroscopy, and mechanisms involving heterolytic H-2 cleavage and elimination of [(HPPr3)-Pr-i](+) or the formation of trimetallic intermediates are discussed.

First author: Adams, Richard D., Unsaturated cyclopentadienyl-molybdenum and tungsten carbonyl cluster complexes containing Pd- and Pt(PBu3t) groups, ORGANOMETALLICS, 25, 2673, (2006)
Abstract: A series of new bimetallic cluster compounds, Cp2M2(CO)(4)[M'(PBu3t)](2) [M = Mo, M’ = Pt (9); M Mo, M’ = Pd (10); M = W, M’ = Pt (11); M = W, M’ = Pd (12)], have been synthesized from reactions of [CpM(CO)(3)](2) (M = Mo, W) with an excess of M'(PBu3t)(2) (M’ = Pt, Pd) at various temperatures. Each compound was fully characterized by IR, H-1 and P-31 NMR, and single-crystal X-ray diffraction analyses. The metal atoms in the structure of 9 are arranged in a butterfly configuration, while the metal atoms of 10-12 adopt a tetrahedral geometry. Compounds 9 and 12 contain two edge-bridging and two triply bridging carbonyl ligands, 10 contains four triply bridging carbonyl ligands. and 11 contains two terminal and two edge-bridging carbonyl ligands. Each of the products is electron-deficient and the M-M bonds, M = Mo and W, are short, Mo-Mo = 2.6535(4) angstrom in 9 and 2.6362(4) angstrom in 10, W-W = 2.6168(9) angstrom in 11 and 2.6320(7) angstrom in 12, which is indicative of some localized multibond character between these metal atoms within the cluster framework. The nature of the bonding within the clusters was explored with DFT calculations (ADF 2004.01, PW91) for the title compounds in C-2 symmetry as well as for a hypothetical, two-electron-reduced [Cp2Mo2Pd2(CO)(4)(PBu3t)(2)](2-) species.

First author: Giordano, L, Vibrational and electron paramagnetic resonance properties of free and MgO supported AuCO complexes, JOURNAL OF CHEMICAL PHYSICS, 124, 2673, (2006)
Abstract: The bonding, spin density related properties, and vibrational frequency of CO bound to single Au atom in the gas-phase or supported on MgO surfaces have been investigated with a variety of computational methods and models: periodic plane waves calculations have been compared with molecular approaches based on atomic orbital basis sets; pseudopotential methods with all electron fully relativistic calculations; various density functional theory (DFT) exchange-correlation functionals with the unrestricted coupled-cluster singles and doubles with perturbative connected triples [CCSD(T)]. AuCO is a bent molecule but the potential for bending is very soft, and small changes in the bond angle result in large changes in the CO gas-phase vibrational frequency. At the equilibrium geometry the DFT calculated vibrational shift of CO with respect to the free molecule is about -150 cm(-1), whereas smaller values -60/-70 cm(-1) are predicted by the more accurate CCSD(T) method. These relatively large differences are due to the weak and nonclassic bonding in this complex. Upon adsorption on MgO, the CO vibrational shift becomes much larger, about -290 cm(-1), due to charge transfer from the basic surface oxide anion to AuCO. This large redshift is predicted by all methods, and is fully consistent with that measured for MgO/AuCO complexes. The strong influence of the support on the AuCO bonding is equally well described by all different approaches.

First author: Guthmuller, J, Water solvent effect on the first hyperpolarizability of p-nitrophenol and p-nitrophenylphosphate: A time-dependent density functional study, JOURNAL OF CHEMICAL PHYSICS, 124, 2673, (2006)
Abstract: The first hyperpolarizabilities of p-nitrophenol and p-nitrophenylphosphate have been investigated in vacuum and in neutral aqueous solution by means of time-dependent density functional theory. The calculated excited states and hyperpolarizabilities obtained for these systems and for the molecules of phenol, nitrobenzene, and p-nitroaniline in vacuum match well with the experimental trends. The water solvent has been described by the conductorlike screening model and has been completed by water molecules interacting by hydrogen bonds with the solute. The results show a significant effect of the solvent on the first hyperpolarizability. In particular, the hyperpolarizability of p-nitrophenylphosphate (6.78×10(-30) esu) in vacuum is only 1.2 times larger than p-nitrophenol (5.63×10(-30) esu), whereas it is almost twice higher in aqueous environment, 12.6×10(-30) and 6.5×10(-30) esu, respectively. This difference in the nonlinear response in neutral water makes the p-nitrophenylphosphate substrate a suitable probe for measuring the activity of alkaline phosphatase enzymes.

First author: Rigaut, S, C-7 and C-9 carbon-rich bridges in diruthenium systems: Synthesis, spectroscopic, and theoretical investigations of different oxidation states, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 5859, (2006)
Abstract: Two methodologies of C-C bond formation to achieve organometallic complexes with 7 or 9 conjugated carbon atoms are described. A C-7 annelated trans-[CI(dppe)(2)Ru=C=C=C-CH=C(CH2)-C=CRu(dppe)(2)CI][X] (X = PF6, OTf) complex is obtained from the diyne trans-[Cl(dppe)(2)Ru-(C=C)(2)-R] (R H, SiMe3) in the presence of [FeCp2][PF6] or HOTf, and C7 or C9 complexes trans-[Cl(dppe)(2)Ru-(C=C)(n)-C(CH3)=C(R-1)-C(R-2)=C=C=Ru(dppe)(2)CI][X] (n = 1, 2; R, = Me, Ph, R-2 = H, Me; X = BF4, OTf) are formed in the presence of a polyyne trans-[CI(dppe)(2)Ru-(C equivalent to C)(n)-R] (n = 2, 3; R = H, SiMe3) with a ruthenium allenylidene trans-[CI(dPPe)(2)Ru=C=C=C(CH2R,)R-2][X]. These reactions proceed under mild conditions and involve cumulenic intermediates [M+]=(C=)(n)CHR (n = 3, 5), including a hexapentaenylidene. A combination of chemical, electrochemical, spectroscopic (UV-vis, IR, NIR, EPR), and theoretical (DFT) techniques is used to show the influence of the nature and conformation of the bridge on the properties of the complexes and to give a picture of the electron delocalization in the reduced and oxidized states. These studies demonstrate that the C7 bridging ligand spanning the metal centers by almost 12 A is implicated in both redox processes and serves as a molecular wire to convey the unpaired electron with no tendency for spin localization on one of the halves of the molecules. The reactivity of the C-7 complexes toward protonation and deprotonation led to original bis(acetyl ides), vinylidene-allenylidene, or carbynevinylidene species such as trans-[CI(dppe)(2)Ru=-C-CH=C(CH3)-CH=C(CH3)-HC=C=Ru(dppe)(2)Cl][BF4](3).

First author: Schottel, BL, Anion-pi interactions as controlling elements in self-assembly reactions of Ag(I) complexes with pi-acidic aromatic rings, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 5895, (2006)
Abstract: Reactions of 3,6-bis(2′-pyridyl)-1,2,4,5-tetrazine (bptz) and 3,6-bis(2′-pyridyl)-1,2-pyridazine (bppn) with the AgX salts (X = [PF6](-), [AsF6](-), [SbF6](-), and [BF4](-)) afford complexes of different structural motifs depending on the pi-acidity of the ligand central ring and the outer-sphere anion. The bptz reactions lead to the polymeric {[Ag(bptz)][PF6]}(infinity) (1) and the dinuclear compounds [Ag-2(bptz)(2)(CH3CN)(2)][PF6](2) (2) and [Ag-2(bptz)(2)(CH3CN)(2)][ASF(6)](2) (3), as well as the propeller-type species [Ag-2(bptz)(3)][AsF6](2) (4) and [Ag-2(bptz)(3)][SbF6](2) (5a and 5b). Reactions of bppn with AgX produce the grid-type structures [Ag-4(bppn)(4)][X](4) (6-9), regardless of the anion present. In 6-9 pi-pi stacking interactions are maximized, whereas multiple and shorter (therefore stronger) anion-pi interactions between the anions and the tetrazine rings are established in 1-5b. These differences reflect the more electron-rich character of the bppn pyridazine ring as compared to the bptz tetrazine ring. The evidence gleaned from the solid-state structures was corroborated by density functional theory calculations. In the electrostatic potential maps of the free ligands, a higher positive charge is present in the bptz as compared to the bppn central ring. Furthermore, the electrostatic potential maps of 3, 4, and 5b indicate an electron density transfer from the anions to the pi-acidic rings. Conversely, upon addition of the [AsF6]- ions to the cation of 7, there is negligible change in the electron density of the central pyridazine ring, which supports the presence of weaker anion-pi interactions in the bppn as compared to the bptz complexes. From the systems studied herein, it is concluded that anion-pi interactions play an important role in the outcome of self-assembly reactions.

First author: Costas, M, Copper(II) hexaaza macrocyclic binuclear complexes obtained from the reaction of their copper(I) derivates and molecular dioxygen, INORGANIC CHEMISTRY, 45, 3569, (2006)
Abstract: Density functional theory (DFT) calculations have been carried out for a series of Cu-I complexes bearing N-hexadentate macrocyclic dinucleating ligands and for their corresponding peroxo species (1c-8c) generated by their interaction with molecular O-2. For complexes 1c-7c, it has been found that the side-on peroxodicopper(II) is the favored structure with regard to the bis(mu-oxo)dicopper(III). For those complexes, the singlet state has also been shown to be more stable than the triplet state. In the case of 8c, the most favored structure is the trans-1,2-peroxodicopper(II) because of the para substitution and the steric encumbrance produced by the methylation of the N atoms. Cu-II complexes 4e, 5e, and 8e have been obtained by O-2 oxidation of their corresponding Cu-I complexes and structurally and magnetically characterized. X-ray single-crystal structures for those complexes have been solved, and they show three completely different types Of CU2II structures: (a) For 4e, the Cull centers are bridged by a phenolate group and an external hydroxide ligand. The phenolate group is generated from the evolution of 4c via intramolecular arene hydroxylation. (b) For 5e, the two Cull centers are bridged by two hydroxide ligands. (c) For the 8e case, the Cull centers are ligated to terminally bound hydroxide ligands, rare because of its tendency to bridge. The evolution of complexes 1c-8c toward their oxidized species has also been rationalized by DFT calculations based mainly on their structure and electrophilicity. The structural diversity of the oxidized species is also responsible for a variety of magnetic behavior: (a) strong antiferromagnetic (AF) coupling with J = -482.0 cm(-1) (g = 2.30; p = 0.032; R = 5.6 x 10(-3)) for 4e; (b) AF coupling with J = -286.3 cm(-1) (g = 2.07; p = 0.064; R = 2.6 x 10(-3)) for 5e; (c) an uncoupled CU2II complex for 8e.

First author: Poot, Menno, Temperature dependence of three-terminal molecular junctions with sulfur end-functionalized tercyclohexylidenes, NANO LETTERS, 6, 1031, (2006)
Abstract: We have studied the gate and temperature dependence of molecular junctions containing sulfur end-functionalized tercyclohexylidenes. At low temperatures we find temperature-independent transport; at temperatures above 150 K the current increases exponentially with increasing temperature. Over the entire temperature range (10 – 300 K), and for different gate voltages, a simple toy model of transport through a single level describes the experimental results. In the model, the temperature dependence arises from the Fermi distribution in the leads and in a three-parameter fit we extract the level position and the tunnel rates at the left and right contact. We find that these parameters increase as the bias voltage increases.

First author: Drummond, Michael L., Density functional investigation of the adsorption of a methane monolayer on an MgO(100) surface, PHYSICAL REVIEW B, 73, 1031, (2006)
Abstract: The adsorption of a monolayer of methane upon the (100) surface of MgO was studied using a first-principles-based density functional approach employing a plane-wave basis set and periodic boundary conditions. Adsorption at both magnesium and oxygen sites was investigated, as were methane orientations where one, two, or three hydrogen atoms point toward the surface plane. In addition, the effect of one methane molecule on its neighbors was investigated by considering arrangements where translational symmetry across the surface was accompanied by appropriate rotations of the methane molecule. The minimum-energy configuration has the methane molecules located directly above a surface magnesium atom, the principal axis of the C-2v molecule is normal to the surface plane, and pairs of hydrogen atoms are oriented along the lattice lines that include adjacent (surface) oxygen atoms. Furthermore, neighboring methane molecules are rotated by 90 degrees to reduce the H-H steric interactions. This arrangement has direct ramifications for the stability of other proposed, similar arrangements.

First author: Garcia-Fernandez, P., Off-center instability in SrCl2 : Fe+: Role of unoccupied 4p orbitals, PHYSICAL REVIEW B, 73, 1031, (2006)
Abstract: Recent electron nuclear double resonance experiments on the Fe(II) center in SrCl2:Fe+ have unambiguously demonstrated that an isolated Fe+ impurity (without any close defect) undergoes a big off-center motion along < 001 > type directions. As Fe+ in SrCl2 exhibits a high spin value S=3/2, its ground state in a perfect cubal symmetry would be (4)A(2) (e(g)(4)t(2g)(3)) with no orbital degeneracy, a situation which is thus different than that for d(9) and d(4) ions in fluorite-type lattices. Density functional theory (DFT) calculations carried out on clusters involving up to 51 atoms confirm that the instability of Fe+ is spontaneous. It is found that Fe+ performs a big excursion of 1.3 A from the center of the FeCl87- cube to a position close to the center of a {001} face. Despite this huge distortion, the associated well depth is found to be only 0.28 eV, so indicating the subtle origin of the instability. At a variance with what happens for Jahn-Teller distortions, off-center displacements cannot be understood by looking only to the half-filled t(2g) antibonding orbitals, which are related from the beginning to the modifications of involved wave functions as described by the pseudo-Jahn-Teller theory. The polarization of the electronic cloud through admixtures of 3d(Fe+) orbitals with deep fully occupied 3p(Cl-) as well as unoccupied 4p(Fe+) orbitals is found to play a key role, while the electrostatic field of the rest of the lattice acts against the distortion. Results obtained for different electronic configurations support these conclusions. Wave-function-based complete active space second-order perturbation theory calculations have also been carried out. At a variance with the DFT results, such calculations are unable to reproduce the subtle off-center instability.

First author: Belanzoni, P, The silicon carbonyls revisited: On the existence of a planar Si(CO)(4), THEORETICAL CHEMISTRY ACCOUNTS, 115, 448, (2006)
Abstract: Recently, some works have focused attention on the reactivity of silicon atom with closed-shell molecules. Silicon may form a few relatively stable compounds with CO, i.e. Si(CO), Si(CO)(2), Si[C2O2], while the existence of polycarbonyl (n > 2) silicon complexes has been rejected by current literature. In this paper, the reaction of silicon with carbonyl has been reinvestigated by density functional calculations. It has been found that the tetracoordinated planar Si(CO)(4) complex is thermodynamically stable. In Si(CO), silicon carbonyl, and Si(CO)(2), silicon dicarbonyl, the CO are datively bonded to Si; Si(CO)(4), silicon tetracarbonyl, may be viewed as a resonance between the extreme configurations (CO)(2)Si + 2CO and 2CO + Si(CO)(2); while Si[C2O2], c-silicodiketone, is similar to the compounds formed by silicon and ethylene. A detailed orbital analysis has shown that the Si bonding with two CO is consistent with the use of sp(2)-hybridized orbitals on silicon, while the Si bonding with four CO is consistent with the use of sp(2) d-hybridized orbitals on silicon, giving rise to a planar structure about Si.

First author: David, J, Electronic structure and molecular properties of the octacyanorhenate [Re(CN)(8)](3-) and [Re(CN)(8)](2-) complexes, CHEMICAL PHYSICS LETTERS, 422, 89, (2006)
Abstract: We report scalar and four component relativistic density functional calculations on octacyanorhenate [Re(CN)(8)](2-) and [Re(CN)(8)](3-) complexes. The relativistic calculations predict that the molecular g-tensor of the paramagnetic [Re(CN)(8)](2-) complex is isotropic. The calculated optical electronic transitions for both complexes with a polarizable continuum model using a time dependent density functional (TDDFT)/B3LYP formalism suggest that the [Re(CN)(8)](3-) complex may distort towards dodecahedral geometry in solution. The electronic excitations of LMCT type of [Re(CN)(8)](2-) are displaced at very high wavelengths with significant oscillator strength values which is characteristic of Re compounds having luminescent behaviour. Thus, our calculations predict that [Re(CN)(8)](2-) could be luminescent.

First author: Zhu, G, Oxidative addition of dihydrogen to (eta(6)-arene)Mo(PMe3)(3) complexes: Origin of the naphthalene and anthracene effects, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 5452, (2006)
Abstract: In contrast to the benzene and naphthalene compounds (eta(6)-PhH)Mo(PMe3)(3) and (eta(6)-NpH)Mo(PMe3)(3), the anthracene complex (eta(6)-AnH)Mo(PMe3)(3) reacts with H-2 to undergo a haptotropic shift and give the eta(4)-anthracene compound (eta(4)-AnH)Mo(PMe3)(3)H-2. Density functional theory calculations indicate that the increased facility of naphthalene and anthracene to adopt eta(4)-coordination modes compared to that of benzene is a consequence of the fact that the Mo-(eta(4)-ArH) bonding interaction increases in the sequence benzene < naphthalene < anthracene, while the MO-(eta(6)-ArH) bonding interaction follows the sequence benzene > naphthalene approximate to anthracene.

First author: Buhl, M, Computational studies of structures and properties of metallaboranes. 2. Transition-metal dicarbollide complexes, ORGANOMETALLICS, 25, 2173, (2006)
Abstract: A density functional study at the BP86 level is presented for metal bis(dicarbollides), [3-M-(1,2-C2B9H11)(2)](n) (M/n = Fe,Ru/2-, Co,Rh/1-, Ni,Pd/0), as well as selected mixed- and half-sandwich complexes [3-M(L)-(1,2-C2B9H11)] {M(L) = Fe(C6H3Me3) Ru(C6H6), Ru(CO)(3), Rh(C5Me5)}. Available experimental B-11 NMR chemical shifts of these complexes with closo structure of the metallacarborane moiety are reproduced reasonably well at the GIAO-B3LYP/II’ level, with mean absolute deviations of ca. 3 ppm (over a chemical-shift range of ca. 50 ppm). The potential usefulness of this computational protocol for assignments and structural refinements of transition-metal-containing heteroboranes is illustrated in an application to 14-vertex closo clusters [1,14-{(arene)Ru}(2)(x,y-C2B10H12), where the C-substitution pattern in the carborane moiety is identified.

First author: Yazyev, OV, Origin of fine structure in Si 2p photoelectron spectra at silicon surfaces and interfaces,PHYSICAL REVIEW LETTERS, 96, 2173, (2006)
Abstract: Using a first-principles approach, we investigate the origin of the fine structure in Si 2p photoelectron spectra at the Si(100)-(2×1) surface and at the Si(100)-SiO(2) interface. Calculated and measured shifts show very good agreement for both systems. By using maximally localized Wannier functions, we clearly identify the shifts resulting from the electronegativity of second-neighbor atoms. The other shifts are then found to be proportional to the average bond-length variation around the Si atom. Hence, in combination with accurate modeling, photoelectron spectroscopy can provide a direct measure of the strain field at the atomic scale.

First author: Zhang, YQ, Theoretical study of the relationship between the nearest-neighbor exchange coupling interactions and the number of peripheral complexes in the cyano-bridged CrMn6(CN)(6) and CrMn2(CN)(2) clusters,JOURNAL OF PHYSICAL CHEMISTRY A, 110, 5096, (2006)
Abstract: A theoretical density functional study of the relationship between the nearest-neighbor constants and the number of peripheral complexes in the cyano-bridged [Cr[CNMn(salen)(H2O)](6)](3+) and [(5-Brsalen)(2)(H2O)(2)-Mn2Cr(CN)(6)] clusters is presented. Two approaches show that the antiferromagnetic coupling interactions between nearest neighbors decrease with the increase of the number of peripheral complexes, although the second approach provides better results using several exchange-correlation functionals. The first approach consisted of evaluating the exchange coupling constant J(ij) between two paramagnetic metal centers i and j in the hexanuclear molecule by calculating the energy differences between the highest and broken-symmetry spin states of a model molecule in which metal atoms except for i and j are substituted by diamagnetic Zn(II) cations, while the second consisted of calculating the different spin-state energies of hexanuclear complexes and using the Heisenberg Hamiltonian to obtain the exchange coupling constants between different metal centers. Moreover, Kahn’s qualitative theory succeeded in being applied to interpret the trend.

First author: Rosa, A, Synergism of porphyrin-core saddling and twisting of meso-aryl substituents, JOURNAL OF PHYSICAL CHEMISTRY A, 110, 5180, (2006)
Abstract: The structural chemistry of meso-aryl-substituted porhyrins has uncovered a bewildering variety of macrocycle distortions. Saddling angles range up to 40 degrees, while the plane of the phenyl groups at the meso positions may be anywhere between perpendicular to the porphyrin plane (theta = 90 degrees) and tilted to quite acute angles (theta = 30 degrees or even less). These two distortions appear to be correlated. This has naturally been explained by steric hindrance: when the phenyls rotate toward the porphyrin plane, for instance, coerced by packing forces, the pyrrole rings can alleviate the steric hindrance by tilting away to a saddled conformation. We demonstrate, however, that the two motions are intrinsically coupled by electronic factors and are correlated even in the absence of external forces. A saddling motion makes it sterically possible for the phenyl rings to rotate toward the porphyrin plane, which will always happen because of increasingly favorable pi-conjugation interaction with smaller angles theta. The considerable energy lowering due to pi conjugation counteracts the energy cost of the saddling, making the concerted saddling/rotation motion very soft. Unsubstituted meso-aryl porphyrins just do not distort, but an additional driving force may tip the balance in favor of the combined distortion motion. Internal forces having this effect are repulsion of the four hydrogens that occupy the central hole of the ring in porphyrin diacids but also steric repulsion in peripherally crowded porphyrins. These findings lead to a clarification and systematization of the observed structural variety, which indeed shows a remarkable correlation between saddling and phenyl ring tilting.

First author: Stich, TA, Spectroscopic studies of the corrinoid/iron-sulfur protein from Moorella thermoacetica, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 5010, (2006)
Abstract: Methyl transfer reactions are important in a number of biochemical pathways. An important class of methyltransferases uses the cobalt cofactor cobalamin, which receives a methyl group from an appropriate methyl donor protein to form an intermediate organometallic methyl-Co bond that subsequently is cleaved by a methyl acceptor. Control of the axial ligation state of cobalamin influences both the mode (i.e., homolytic vs heterolytic) and the rate of Co-C bond cleavage. Here we have studied the axial ligation of a corrinoid iron-sulfur protein (CFeSP) that plays a key role in energy generation and cell carbon synthesis by anaerobic microbes, such as methanogenic archaea and acetogenic bacteria. This protein accepts a methyl group from methyltetrahydrofolate forming Me-Co3+CFeSP that then donates a methyl cation (Me) from MeCo3+CFeSP to a nickel site on acetyl-CoA synthase. To unambiguously establish the binding scheme of the corrinoid cofactor in the CFeSP, we have combined resonance Raman, magnetic circular dichroism, and EPR spectroscopic methods with computational chemistry. Our results clearly demonstrate that the Me-Co3+ and Co2+ states of the CFeSP have an axial water ligand like the free MeCbi(+) and Co2+ Cbi(+) cofactors; however, the Co-OH2 bond length is lengthened by about 0.2 angstrom for the protein-bound cofactor. Elongation of the Co-OH2 bond of the CFeSP-bound cofactor is proposed to make the cobalt center more “Co1+-like”, a requirement to facilitate heterolytic Co-C bond cleavage.

First author: Fratiloiu, S, Two-dimensional charge delocalization in X-shaped phenylenevinylene oligomers, CHEMISTRY OF MATERIALS, 18, 2118, (2006)
Abstract: A combined experimental and theoretical study of the optoelectronic properties of charged two-dimensional X-shaped phenylenevinylene oligomers (X-mers) is presented. Cations and anions of X-mers were produced by irradiation of solutions with high-energy electron pulses. The optical absorption spectra were measured using time-resolved visible/near-infrared spectroscopy in the range of 500-1600 nm (0.8-2.5 eV). The optical absorption spectra were also calculated using the singly excited configuration interaction method with an intermediate neglect of differential overlap reference wave function (INDO/s-CIS) together with a density functional theory (DFF) optimized geometry. The INDO/s-CIS calculations reproduce the main absorption features of charged X-mers near 1.6-1.7 eV. The charge distributions calculated with DFT show that the excess positive charge is mostly localized on the phenylene units containing methoxy substituents. In contrast, the excess negative charge is delocalized over the entire oligomer. Charge-transport calculations indicate that high charge carrier mobilities can be achieved for transport along stacks of X-mers at small mutual twist angles.

First author: Fernandez, I, Direct estimate of the strength of conjugation and hyperconjugation by the energy decomposition analysis method, CHEMISTRY-A EUROPEAN JOURNAL, 12, 3617, (2006)
Abstract: The intrinsic strength of pi interactions in conjugated and hyperconjugated molecules has been calculated using density functional theory by energy decomposition analysis (EDA) of the interaction energy between the conjugating fragments. The results of the EDA of the trans-polyenes H2C=CH-(HC=CH)(n)-CH=CH2 (n = 1-3) show that the strength of pi conjugation for each C=C moiety is higher than in trans-1,3-butadiene. The absolute values for the conjugation between Si= Si 71 bonds are around two-thirds of the conjugation between C=C bonds but the relative contributions of Delta E-pi to Delta E-orb in the all-silicon systems are higher than in the carbon compounds. The pi conjugation between C=C and C=O or C=NH bonds in H2C=CH-C(H)=O and H2C=CH-C(H)=NH is comparable to the strength of the conjugation between C=C bonds. The pi conjugation in H2C=CH-C(R)=O decreases when R=Me, OH, and NH2 while it increases when R=halogen.

First author: Seth, M, Calculation of excitation energies of open-shell molecules with spatially degenerate ground states. II. Transformed reference via intermediate configuration Kohn-Sham time dependent density functional theory oscillator strengths and magnetic circular dichroism C terms, JOURNAL OF CHEMICAL PHYSICS, 124, 3617, (2006)
Abstract: An extension of the transformed reference via an intermediate configuration Kohn-Sham time dependent density functional theory (TRICKS-TDDFT) method for calculating the transition energies of molecules with spatially degenerate ground states is proposed that enables oscillator strengths to also be evaluated. The oscillator strengths are calculated starting from a description of the degenerate ground state and the excited states of interest in terms of linear combinations of Slater determinants based upon the F-vectors obtained in the TRICKS-TDDFT calculation. This approach for calculating oscillator strengths can also be applied to several other properties that involve excited states. An example of such a property, the C term of magnetic circular dichroism (MCD), is presented. The new method is illustrated through example calculations of the absorbance and MCD spectra of several octahedral and C-4v d(5) transition metal complexes. The calculated transition energies and oscillator strengths are somewhat too low and too high, respectively, but these errors are within the range that would normally be expected for TDDFT calculations of this type. The calculations help to resolve some previously unexplained problems with the MCD spectra of the C-4v complexes.

First author: Bojin, MD, Nonclassical carbocations as C-H hydrogen bond donors, JOURNAL OF PHYSICAL CHEMISTRY A, 110, 4810, (2006)
Abstract: Computed [B3LYP/6-31+G(d,p) and MP2/6-31+G(d,p)] structures and binding energies for complexes of nonclassical cations (carbonium ions) with ammonia, in the gas phase and several solvents, are described. Overall, nonclassical cations are found to be competent C-H hydrogen bond donors. The potential relevance of the C-(HN)-N-… interactions holding the carbocation(.)amine complexes together for enzyme-catalyzed terpenoid synthesis is discussed.

First author: Stevens, F, Density functional investigation of high-spin XY (X = Cr, Mo, W and Y = C, N, O) molecules,JOURNAL OF PHYSICAL CHEMISTRY A, 110, 4846, (2006)
Abstract: The performance of a density functional theory approach in calculating the equilibrium bond length, dipole moment, and harmonic vibrational frequency in a series of group 6 (Cr, Mo, W) transition metal-containing diatomic molecules is evaluated. Using flexible basis sets comprised of Slater type functions, a wide range of exchange-correlation functionals is investigated. Comparing with known experimental values and published results from high-level theoretical calculations, the most suitable functional form is selected. The importance of relativistic effects is checked, and predictions are made for several unknown dipole moments. The best agreement with experimental parameters is obtained when using a general gradient approximation, while special and hybrid functional forms give less accurate results.

First author: Groenewold, GS, Vibrational spectroscopy of mass-selected [UO2(ligand)(n)](2+) complexes in the gas phase: Comparison with theory, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 4802, (2006)
Abstract: The gas-phase infrared spectra of discrete uranyl ([UO2](2+)) complexes ligated with acetone and/ or acetonitrile were used to evaluate systematic trends of ligation on the position of the O=U=O stretch and to enable rigorous comparison with the results of computational studies. Ionic uranyl complexes isolated in a Fourier transform ion cyclotron resonance mass spectrometer were fragmented via infrared multiphoton dissociation using a free electron laser scanned over the mid-IR wavelengths. The asymmetric O=U=O stretching frequency was measured at 1017 cm(-1) for [UO2(CH3COCH3)(2)](2+) and was systematically red shifted to 1000 and 988 cm-1 by the addition of a third and fourth acetone ligand, respectively, which was consistent with increased donation of electron density to the uranium center in complexes with higher coordination number. The values generated computationally using LDA, B3LYP, and ZORA-PW91 were in good agreement with experimental measurements. In contrast to the uranyl frequency shifts, the carbonyl frequencies of the acetone ligands were progressively blue shifted as the number of ligands increased from two to four and approached that of free acetone. This observation was consistent with the formation of weaker noncovalent bonds between uranium and the carbonyl oxygen as the extent of ligation increases. Similar trends were observed for [UO2(CH3CN)(n)](2+) complexes, although the uranyl asymmetric stretching frequencies were greater than those measured for acetone complexes having equivalent coordination, which is consistent with the fact that acetonitrile is a weaker nucleophile than is acetone. This conclusion was confirmed by the uranyl stretching frequencies measured for mixed acetone/acetonitrile complexes, which showed that substitution of one acetone for one acetonitrile produced a modest red shift of 3-6 cm(-1).

First author: Grundler, PV, Kinetic studies on the first dihydrogen aquacomplex, [Ru(H-2)(H2O)(5)](2+) : Formation under H-2 pressure and catalytic H/D isotope exchange in water, INORGANICA CHIMICA ACTA, 359, 1795, (2006)
Abstract: The ruthenium(II) hexaaqua complex [Ru(H2O)(6)](2+) reacts with dihydrogen under pressure to give the eta(2)-dihydrogen ruthenium(II) pentaaqua complex [Ru(H-2)(H2O)(5)](2+). The complex was characterized by H-1, H-2 and O-17 NMR: delta(H) = -7.65 ppm, J(HD) = 31.2 Hz, delta(O) = -80.4 ppm (trans to h(2)) and delta(O) = -177.4 ppm (cis to H-2). The H-H distance in coordinated dihydrogen was estimated to 0.889 angstrom from J(HD), which is close to the value obtained from DFT calculations (0.940 angstrom). Kinetic studies were performed by H-1 and H-2 NMR as well as by UV-Vis spectroscopy, yielding the complex formation rate and equilibrium constants: k(f) = (1.7 +/- 0.2) x 10(-3) kg mol(-1) s(-1) and K-eq = 4.0 +/- 0.5 mol kg(-1). The complex formation rate with dihydrogen is close to values reported for other ligands and thus it is assumed that the reaction with dihydrogen follows the same mechanisn (I-d). In deuterated water, one can observe that [Ru(H-2)(H2O)(5)](2+) Catalyses the hydrogen exchange between the solvent and the dissolved dihydrogen. A hydride is proposed as the intermediate for this exchange. Using isotope labeling, the rate constant for the hydrogen exchange on the eta(2)-dihydrogen ligand was determined as k(1) = (0.24 +/- 0.04) x 10(-3) s(-1). The upper and lower limits of the pK(a) of the coordinated dihydrogen ligand have been estimated:3 < pK(a) < 14.

First author: Mungur, SA, Titanium(IV) alkoxy-N-heterocyclic carbenes: Structural preferences of alkoxide and bromide adducts, ORGANOMETALLICS, 25, 1861, (2006)
Abstract: A series of titanium(IV) adducts of an amido-tethered N-heterocyclic carbene (NHC) of the form Ti(L)((OPr)-Pr-i)(n)(Br)(3-n) (n = 1-3, L = (BuNHCH2CH2)-Bu-t[C{(NBu)-Bu-t(CHCH)N}]) have been synthesized and characterized. Structural characterization of the n = 2 complex shows marked bending of the two ligands cis (and perpendicular) to the plane of the NHC group in the direction of the carbene, suggestive of a pseudo-back-bonding interaction between adjacent ligands and the carbene p orbital, consistent with a bonding model recently proposed for d(0) metal-NHC complexes. However, inspection of a space-filling model and the calculation of bond order using DFT methods suggest that the bending is due to repulsions between lone pairs on the adjacent pi-donor ligands in the complexes and not any specific interaction between the NHC and cis pi-donor ligands.

First author: Jacobsen, H, Tuning the palladium-silicon bond: Bond analysis of bisphosphine silyl palladium hydrides,ORGANOMETALLICS, 25, 1945, (2006)
Abstract: Density functional calculations (PW91) have been carried out for 33 complexes of the type (dhpe)M(H)Si(R-1)(R-2)(R-3) (dhpe = 1,2-bis(dihydrophosphino)ethane; M = Pd, Pt; R = H, Me, Ph, F, Cl). Bond snapping energies for the M-Si bond have been obtained, and the variation of silyl substitutents R allows one to tune the M-Si bond strength over a range of about 60 kJ/mol. On the basis of the results obtained from a Hirshfeld charge analysis, the Pd-Si bond is characterized by a sizable amount of charge transfer from the transition-metal fragment to the main-group ligand. This is reflected in the optimized Pd-Si bond length, which correlates well with the amount of charge transferred. Experimentally observed trends for the relative stability of bisphosphine silyl palladium hydrides can be successfully reproduced using a simplified approximation based on reaction energies derived from bond snapping energies. On average, the Pt-Si bond is stronger than the Pd-Si bond by 26 kJ/mol. The enhanced platinum bond strengths relative to those of palladium are attributed to relativistic effects.

First author: Belanzoni, P, Planar tetracoordinated silicon in silicon carbonyl complexes: A DFT approach, JOURNAL OF PHYSICAL CHEMISTRY A, 110, 4582, (2006)
Abstract: Recently, some works have focused attention on the reactivity of the silicon atom with closed-shell molecules. With CO, silicon may form a few relatively stable compounds, i.e., Si(CO), Si(CO)(2), and Si[C2O2], while the existence of polycarbonyl (n > 2) silicon complexes has been rejected by current literature. In this paper, the reaction of silicon with carbonyl has been reinvestigated by density functional calculations. It has been found that the tetracoordinated planar Si(CO)4 complex is thermodynamically stable. In Si(CO), silicon carbonyl, and Si(CO)(2), silicon dicarbonyl, the CO moieties are datively bonded to Si, and Si[C2O2], c-silicodiketone, is similar to the compounds formed by silicon and ethylene; Si(CO)4, silicon tetracarbonyl, may be viewed as a resonance between the extreme configurations (CO)(2)Si + 2CO and 2CO + Si(CO)(2). A detailed orbital analysis has shown that the Si bonding with four CO is consistent with the use of sp(2)d-hybridized orbitals on silicon, giving rise to a planar structure about Si.

First author: Makowska-Janusik, M, Origin of the photoinduced optical second harmonic generation arising in N-phenyl microcrystalline films, JOURNAL OF PHYSICAL CHEMISTRY B, 110, 6492, (2006)
Abstract: Photoinduced second-order nonlinear optical effects, particularly optical second harmonic generation (SHG) of N-phenyls with different numbers of aromatic rings deposited on glass substrates were studied. As a fundamental beam, a 5-ps pulsed Nd:YAG laser was used. Quantum chemical time-dependent density functional theory (TDDFT) simulations of the nonlinear optical properties were performed. The first-order hyperpolarizabilities of isolated molecules were calculated, under the influence of a polarized pumping beam, to evaluate the role played by the nanointerfaces separating the microcrystallites and the amorphous environment. Consideration was performed within a framework of steady-state Langevin order parameters for amorphous-like films. A strong dependence of the photoinduced SHG versus the number of aromatic rings determining the degree of film crystallinity was shown. A comparison of experimental data and theoretically evaluated results shows that for the photoinduced first-order nonlinear optical effect the dominant contribution is an amorphous-like structural component, unlike the transport properties, where the crucial role is played by the nanointerface region. This may reflect a specific feature of the multiphoton processes in such types of nanointerfaces because of nanoconfined effects.

First author: Poater, A, Molecular structure and bonding of copper cluster monocarbonyls CunCO (n=1-9), JOURNAL OF PHYSICAL CHEMISTRY B, 110, 6526, (2006)
Abstract: In this work we analyze CO binding on small neutral copper clusters, Cu-n (n = 1-9). Molecular structures and reactivity descriptors of copper clusters are computed and discussed. The results show that the condensed Fukui functions and the frontier molecular orbital theory are useful tools to predict the selectivity of CO adsorption on these small clusters. To get further insight into the CO binding to copper clusters, an energy decomposition analysis of the CO binding energy is performed. The CS symmetry of the formed CunCO clusters (n = 1-8) allows the separation between the orbital interaction terms corresponding to donation and back-donation. It is found that, energetically, the donation is twice as important as back-donation.

First author: Stevens, F, The Rh-ligand bond: RhX (X = C, N, O, F, P and Cl) molecules, CHEMICAL PHYSICS LETTERS,421, 281, (2006)
Abstract: Bond distances, vibrational frequencies and dipole moments of the RhX (X = C, N, O, F, P and Cl) molecules were studied by density functional theory (DFT) methods. For all molecules under consideration, spectroscopic properties are computed using various functionals. This study is the first systematic ab initio investigation of the RhX molecules and in those cases where comparison with experimental data can be made, good quantitative agreement is achieved when using the BP86 functional.

First author: Guerra, CF, Supramolecular switches based on the guanine-cytosine (GC) Watson-Crick pair: Effect of neutral and ionic substituents, CHEMISTRY-A EUROPEAN JOURNAL, 12, 3032, (2006)
Abstract: We have theoretically analyzed Watson-Crick guanine-cytosine (GC) base pairs in which purine-C8 and/or pyrimidine-C6 positions carry a substituent X = NH-, NH2, NH3+ (N series), O-, OH, or OH,1 (0 series), using the generalized gradient approximation (GGA) of density functional theory at the BP86/TZ2P level. The purpose is to study the effects on structure and hydrogen-bond strength if X = H is substituted by an anionic, neutral, or cationic substituent. We found that replacing X = H by a neutral substituent has relatively small effects. Introducing a charged substituent, on the other hand, led to substantial and characteristic changes in hydrogen-bond lengths, strengths, and hydrogen-bonding mechanism. In general, introducing an anionic substituent reduces the hydrogen-bond-donating and increases the hydrogen-bond-accepting capabilities of a DNA base, and vice versa for a cationic substituent. Thus, along both the N and O series of substituents, the geometric shape and bond strength of our DNA base pair can be chemically switched between three states, thus yielding a chemically controlled supramolecular switch. Interestingly, the orbital-interaction component in some of these hydrogen bonds was found to contribute to more than 49% of the attractive interactions and is thus virtually equal in magnitude to the electrostatic component, which provides the other (somewhat less than) 51% of the attraction.

First author: Corminboeuf, Clemence, The role of density functional theory in chemistry: Some historical landmarks and applications to zeolites, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 762, 1, (2006)
Abstract: Density functional theory (DFT) has progressively emerged in the last 40 years as a leading methodology for the modelling and simulation of chemical systems. In this paper, some historical landmarks in the development of this method are outlined, emphasizing on its main characteristic being an electron density-based theory. This is in contrast with wavefunction-based methodologies which were exclusively employed previously. Interestingly, DFT has been first applied to solids, with a rather late recognition by chemists and molecular scientists. After this historical survey, several applications of DFT to the structure and properties of zeolites are reviewed as a tribute to Dr Annick Goursot.

First author: Chermette, H, Trans effect and inverse trans effect in MLX5 complexes (M = Mo, U; L = O, S; X = Cl, Br): A rationalization within density functional theory study, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 762, 109, (2006)
Abstract: Trans effect in MLX5 complexes in which M is Mo or U metal, L is oxygen or sulphur and X a halide, are theoretically studied with density functional theory. In these octahedral complexes, the axial M-X bond length differs from the equatorial M-X one, and this difference depends on the relative electronegativity of the ligands, and of the total charge of the complexes (i.e. the oxidation degree of the metal). Fragment interaction energies, molecular orbital compositions and charge analysis are used to interpret the variation in the structures.

First author: Vargas, A, First principles study of the conformations of cinchonidine on a Pt(111) surface, JOURNAL OF CATALYSIS, 239, 220, (2006)
Abstract: The conformations of cinchonidine (CD) adsorbed on a Pt(111) surface were studied using first-principles methods. Eight conformationally different adsorption states due to different degrees of rotation around the tau(1) and tau(2) degrees of freedom were identified and their possible role in the formation of chiral surface sites relevant to enantioselective hydrogenation investigated in light of the currently existing experimental evidence. Comparison of the conformational behavior of CD in Solution and on platinum has revealed the effect of the metal surface on the internal mobility of the alkaloid. Although the study corroborates the outstanding role of-the adsorbed Open(3) conformer suggested previously, the rich conformational flexibility observed on the platinum surface points to the possibility that other conformers of CD also may be involved in enantiodifferentiation. Closed conformations of CD are found to play all important role in the conformational equilibria oil the surfacedue to their stability and are identified as precursors of the less stable, but presumably more active, open conformers. Although the open and closed conformers are closely related to the correspondent ones found in solution, surface species that are also adsorbed via quinuclidine moiety are characteristic of the metal-modifier interaction and should serve as precursors to catalytically active conformations.

First author: Conradie, Marrigje Marianne, A DFT overview of high-valent iron, cobalt and nickel tetraamidomacrocyclic ligand (TAML) complexes: The end of innocence?, JOURNAL OF INORGANIC BIOCHEMISTRY, 100, 620, (2006)
Abstract: Amidato-N ligands are normally viewed as classic, strongly a-donating, innocent ligands. However, when coordinated to high-valent transition metal centers, tetraamidomacrocyclic ligands are often substantially noninnocent, i.e., exhibit radical character involving the amido pi-systems. Even the so-called MAC* ligand, generally considered to be an innocent ligand, is noninnocent in several of its known complexes.

First author: Conradie, Jeanet, Trigonal bipyramidal iron(III) and manganese(III) oxo, sulfido, and selenido complexes. An electronic-structural overview, JOURNAL OF INORGANIC BIOCHEMISTRY, 100, 707, (2006)
Abstract: Using density functional theory calculations, we have carried out a broad survey of trigonal bipyramidal iron(III) and manganese(III) oxo, sulfido, selenido, and hydroxo complexes, with tripodal tetradentate “triurcidoamine” supporting ligands. The calculations reproduce the experimentally observed high-spin states of these compounds; a multifunctional analysis suggests that the high-spin nature of these species follows largely from their trigonal bipyramidal geometry. In conjunction with earlier calculations, the present study provides a broad overview of spin density profiles in iron-oxo species in general. Iron-oxo d(pi)-p(pi) interactions invariably result in a substantial spin density on the oxygen, which in turn may be significantly tuned by hydrogen bonding interactions. The oxygen spin densities are smaller in analogous manganese-oxo species, indicating that manganese is less adept at it-bonding than iron, which parallels earlier findings on porphyrin systems. The Fen(III)-S/Se spin density profiles provide one of the first confirmations in a transition metal context of Schleyer’s prediction that the heavier p-block elements are as effective as their second-row congeners in terms of their pi-donating ability.

First author: Han, Wen-Ge, Seven clues to the origin and structure of class-I ribonucleotide reductase intermediate X,JOURNAL OF INORGANIC BIOCHEMISTRY, 100, 771, (2006)
Abstract: Class-I ribonucleotide reductases (RNRs) are aerobic enzymes that catalyze the reduction of ribonuclectides to deoxyribonucleotides providing the required building blocks for DNA replication and repair. These riboiiLicleotide-to-deoxyribonucleotide reactions occur by a long range radical (or proton -coupled-electron-transfer) propagation mechanism initiated by a fairly stable tyrosine radical (“the pilot light”). When this pilot light goes out, the tyrosine radical is regenerated by a high-oxidation-state enzyme intermediate, called X. The active site of class-I RNR-X has been recognized as a spin coupled Fe(III)Fe(IV) center with S(total) = 1/2 ground state. Although several clues have been obtained from Mossbauer, (57)Fe, (1)H, (17)O(2), and H(2)(17)O ENDOR (electron-nuclear double resonance), EXAFS (extended X-ray absorption fine structure), and MCD (magnetic circular dichroism) experiments, the detailed structure of the intermediate X is still Unknown. In the past three years. we have been studying the properties of a set of model clusters for RNR-X using broken-symmetry density functional theory (DFT), and have compared them with the available experimental results. Based on the detailed analysis and comparisons, we have proposed a definite form for the active site structure of class-I RNR intermediate X. The puzzle is now set: can you find any flaws in the argument or evidence? Can you add anything further to the current experimental picture? The argument is formulated from seven experimental clues with associated calculations and models.

First author: Wang, XJ, A density functional investigation of charge transfer and structural distortions of cuprous(I) bis-phenanthroline under photo-induced excitation, JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, 179, 149, (2006)
Abstract: The charge transfer and structural distortions that occurred in the complexes cuprous(I) bis-phenanthroline (Cu(NN)(2)(+)) (NN denotes 1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline and 2,9-di(trifluoromethyl)-1,10-phenanthroline) upon excitation with an irradiation of light were studied by density functional theory (DFT). The calculations showed that the electrons transferred from central metal Cu to ligands with the transition of the complexes Cu(NN)(2)(+) from ground state to excited state. As a consequence, the central copper in the excited state of Cu(NN)(2)(+) exhibited similar electronic density to that in the corresponding complex Cu(NN)(2)(2+). Accompanying with this transfer process, the coordination polyhedra of CU(NN)(2)(+) became distorted upon excitation. The Structural distortion was significantly reduced by increasing the steric bulk of the 2- and 9-positions substituents in the ligands NN, which is helpful for the increase of the life time of the excited state.

First author: Fratiloiu, S, Electronic structure and optical properties of charged oligofluorenes studied by VIS/NIR spectroscopy and time-dependent density functional theory, JOURNAL OF PHYSICAL CHEMISTRY B, 110, 5984, (2006)
Abstract: The electronic structure and optical properties of charged oligofluorenes were studied experimentally and theoretically. Measurements of the optical absorption spectra of charged oligofluorenes in dilute solutions have been performed by using the pulse radiolysis technique. In addition, optical absorption spectra of radical cations and anions in a solid matrix were measured after gamma-irradiation at 77 K. The optical absorption spectra were measured in the range of 440-2100 nm (0.6-2.8 eV) and compared with results from time-dependent density functional theory (TDDFT) calculations. The calculated charge induced deformations and charge distribution do not indicate the occurrence of polaronic effects. The potential energy profiles for rotation around the inter-unit bond show that oligofluorenes are nonplanar in their neutral state, while they tend to more planar structures in their charged state. The optical absorption spectra of charged oligofluorenes are dependent on the angle between neighboring units. TDDFT absorption energies shift to lower values with increasing chain length, which suggests that the charge delocalizes along the oligomer chain.

First author: Lo Presti, L, On the interplay between CH…O and OH…O interactions in determining crystal packing and molecular conformation: An experimental and theoretical charge density study of the fungal secondary metabolite austdiol (C12H12O5), JOURNAL OF PHYSICAL CHEMISTRY B, 110, 6405, (2006)
Abstract: The total experimental electron density rho(r), its Laplacian del(2)rho(r), the molecular dipole moment, the electrostatic potential T(r), and the intermolecular interaction energies have been obtained from an extensive set of single-crystal X-ray diffracted intensities, collected at T = 70(1) K, for the fungal metabolite austdiol (1). The experimental results have been compared with theoretical densities from DFT calculations on the isolated molecule and with fully periodic calculations. The crystal structure of (1) consists of zigzag ribbons extended along one cell axis and formed by molecules connected by both (OHO)-O-… and (CHO)-O-… interactions, while in a perpendicular direction, adjacent molecules are linked by short (CHO)-O-… intermolecular contacts. An extensive, quantitative study of all the intra- and intermolecular (HO)-O-… interactions, based not only on geometrical criteria, but also on the topological analysis of rho(r), as well as on the evaluation of the pertinent energetics, allowed us (i) to assess the mutual role of (OHO)-O-… and (CHO)-O-… interactions in determining molecular conformation and crystal packing; (ii) to identify those (CHO)-O-… contacts which are true hydrogen bonds (HBs); (iii) to determine the relative hydrogen bond strengths. An experimental, quantitative evidence is given that (CHO)-O-… HBs are very similar to the conventional (OHO)-O-… HBs, albeit generally weaker. The comparison between experimental and theoretical electric dipole moments indicates that a noticeable charge rearrangement occurs upon crystallization and shows the effects of the mutual cooperation of HBs in the crystal. The total intermolecular interaction energies and the electrostatic energy contribution obtained through different theoretical methods are reported and compared with the experimental results. It is found that the new approach proposed by Spackman, based on the use of the promolecular charge density to approximate the penetration contribution to intermolecular electrostatic energies, predicts the correct relative electrostatic interaction energies in most of the cases.

First author: Diezi, S, The origin of chemo- and enantioselectivity in the hydrogenation of diketones on platinum,JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 4048, (2006)
Abstract: In the Pt-catalyzed hydrogenation of 1,1,1-trifluoro-2,4-diketones, addition of trace amounts of cinchonicline, O-methyl-cinchonidine, or (R,R)-pantoyl-naphthylethylamine induces up to 93% ee and enhances the chemoselectivity up to 100% in the hydrogenation of the activated carbonyl group to an OH function. A combined catalytic, NMR and FTIR spectroscopic, and theoretical study revealed that the two phenomena are coupled, offering the unique possibility for understanding the substrate-modifier-metal interactions. The high chemo-and enantioselectivities are attributed to the formation of an ion pair involving the protonated amine function of the chiral modifier and the enolate form of the substrate. DFT calculations including the simulation of the interaction of a protonated amine with the enolate adsorbed on a Pt 31 cluster revealed that only the C-O bond next to the CF(3) group of the substrate is in direct contact with Pt and can be hydrogenated. The present study illustrates the fundamental role played by the metal surface and indicates that also the enol form can be the reactive species in the hydrogenation of the activated ketone on chirally modified Pt.

First author: Guerra, CF, Adenine tautomers: Relative stabilities, ionization energies, and mismatch with cytosine,JOURNAL OF PHYSICAL CHEMISTRY A, 110, 4012, (2006)
Abstract: In this study, we have investigated 12 tautomers of the DNA base adenine at the BP86/TZ2P and BP86/QZ4P levels of density functional theory. The vertical and adiabatic ionization energies of all tautomers were determined as the difference in energy between the radical cation and the corresponding neutral system. Furthermore, an evaluation is made for the eigenvalue spectra calculated with the SAOP functional, which is shown to lead to substantial improvements for orbital energies compared to BP86. We have also explored the correlations between the Kohn-Sham orbitals of the different tautomers at the BP86/QZ4P and SAOP/QZ4P levels. Finally, we discuss implications of the existence of the tautomeric forms of adenine for the DNA replication.

First author: Sala, X, Atropisomeric discrimination in new Ru-II complexes containing the C-2-Symmetric didentate chiral phenyl-1,2-bisoxazolinic ligand, CHEMISTRY-A EUROPEAN JOURNAL, 12, 2798, (2006)
Abstract: A new family of Ru-II complexes containing the tridentate meridional 2,2′:6′,2″-terpyridine (trpy) ligand, a G-symmetric didentate chiral oxazolinic ligand 1,2-bis[4′-alkyl-4′,5′-dihydro-2′-oxazolyl]benzene (Phbox-R, R = Et or iPr), and a monodentate ligand, of general formula [Ru(Y)-(trpy)(Phbox-R)](n+) (Y = Cl, H2O py, MeCN, or 2-OH-py (2-hydroxypyridine)) have been prepared and thoroughly characterized. In the solid state the complexes have been characterized by IR spectroscopy and by X-ray diffraction analysis in two cases. In solution, UV/Vis, cyclic voltammetry (CV), and one-dimensional (1D) and two-dimensional (2D) NMR spectroscopy techniques have been used. We have also performed density functional theory (DFT) calculations with these complexes to interpret and complement experimental results. The oxazolinic ligand Phbox-R exhibits free rotation along the phenyloxazoline axes. Upon coordination this rotation is restricted by an energy barrier of 26.0 kcal mol(-1) for the case of [Ru-(trpy)(Phbox-iPr)(MeCN)](2+) thus preventing its potential interconversion. Furthermore due to steric effects the two atropisomers differ in energy by 5.7 kcal mol(-1) and as a consequence only one of them is obtained in the synthesis. Subtle but important structural effects occur upon changing the monodentate ligands that are detected by NMR spectroscopy in solution and interpreted by using their calculated DFT structures.

First author: Poater, J, Hydrogen-hydrogen bonding in planar biphenyl, predicted by atoms-in-molecules theory, does not exist, CHEMISTRY-A EUROPEAN JOURNAL, 12, 2889, (2006)
Abstract: Based on an Atoms-in-Molecules (AIM) analysis, Matta et a]. (Chem. Eur. J. 2003, 9, 1940) recently claimed evidence for the existence of hydrogen-hydrogen bonding between ortho-hydrogen atoms, pointing towards each other from adjacent phenyl groups in planar biphenyl. This AIM result is opposed to the classical view that nonbonded steric repulsion between the ortho-hydrogen atoms is responsible for the higher energy of the planar as compared to the twisted geometry of biphenyl. In the present work, we address the question if hydrogen-hydrogen bonding in biphenyl exists, as suggested by AIM, or not. To this end, we have analyzed the potential energy surface for internal rotation of biphenyl in terms of two interacting phenyl radicals using density functional theory (DFT) at BP86/TZ2P. A detailed analysis of the bonding mechanism and a quantitative bond energy decomposition in the framework of Kohn-Sham DFT show that Pauli (or overlap) repulsion, mainly between C-ortho-H-ortho phenyl MOs, prevents biphenyl from being planar and forces it to adopt a twisted equilibrium geometry. Furthermore, a derivative of biphenyl in which all four ortho-hydrogen atoms have been removed does adopt a planar equilibrium geometry. T’hus, our results confirm the classical view of steric repulsion between ortho-hydrogen atoms in biphenyl and they falsify the hypothesis of hydrogen-hydrogen bonding.

First author: Poater, J, A model of the chemical bond must be rooted in quantum mechanics, provide insight, and possess predictive power, CHEMISTRY-A EUROPEAN JOURNAL, 12, 2902, (2006)
Abstract: In this response to the preceding paper by Bader, we show that the core arguments and statements presented in the latter are flawed. We argue that it is insufficient for a model of the chemical bond to be rooted in quantum mechanics. A good model must in addition provide insight and possess predictive power. Our molecular orbital (MO) model of the chemical bond, in particular, the associated energy-decomposition approach satisfies all these conditions. On the other hand, Atoms-in-Molecules (AIM) theory is only rooted in quantum mechanics as far as its mathematical framework is concerned. The physical status of its central concepts is not so clear. In particular, “bond paths” and “bond critical points” are once more confirmed not to be indicators of a stabilizing interaction. Moreover, AIM theory lacks any predictive power. We also address specific questions raised in the preceding paper. Finally, interpreting chemical bonding implies choosing a perspective on this phenomenon. That there are many perspectives is a matter of fact and this is in no way unphysical. What is unscientific is to claim uniqueness and truth for one of these choices, namely AIM, and to dismiss on this ground all other approaches.

First author: Harris, KJ, Acetylenic carbon-13 chemical shift tensors for diphenylacetylene and (eta(2)-diphenylacetylene)Pt(PPh3)(2): A solid-state NMR and theoretical study, INORGANIC CHEMISTRY, 45, 2461, (2006)
Abstract: The structure of (eta(2)-diphenylacetylene)Pt(PPh3)(2), as well as those of its dichloromethane and benzene solvates, is determined via X-ray crystallography. An investigation of the chemical shift (CS) tensors of the C-13-labeled carbons in (PhC)-C-13=(CPh)-C-13 and (eta(2)-(PhC)-C-13 equivalent to(CPh)-C-13)Pt(PPh3)(2)center dot(C6H6) is carried out via analysis of C-13 NMR spectra from stationary solid samples. The principal components of the CS tensors as well as their orientations with respect to the 13C,13C internuclear vector are determined. DFT calculations of these CS tensors are in close agreement with the experimental values. For diphenylacetylene (tolane), the orientations and principal-component magnitudes of the alkynyl carbon CS tensors are comparable to those for other alkynyl carbons, although the CS tensor is not axially symmetric in this case. Coordination to platinum causes a change in the CS tensor orientation and a net increase in the isotropic chemical shift, resulting from a significant increase in two principal components (delta(11), and delta(33)) while the third (delta(22)) decreases only slightly. The measured carbon CS tensors in the platinum complex bear a striking similarity to those of the alkenyi carbons in trans-Ph(H)C=C(H)Ph, and a short theoretical discussion of these observations is presented.

First author: Poleshchuk, OK, SO3 complexes with nitrogen containing ligands as the object of nuclear quadrupole interactions and density functional theory calculations, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 761, 195, (2006)
Abstract: We have analyzed by means of DFT calculations of nitrogen nuclear quadrupole coupling constants of a range of SO3 center dot center dot center dot B complexes (n a pi type in Mulliken notation) formed between molecules SO3 and Lewis bases B. The geometrical parameters, the rotational constants and the nitrogen nuclear quadrupole coupling constants obtained by these calculations substantially agree with the data from microwave spectroscopy in the gas phase. A good correlation is found between the calculated bond strengths of these complexes and the lengthening of the S-O bond. The NBO partitioning scheme and the stabilizing orbital interaction term suggest that there are excellent correlations between the charge transfer and the bond strength. From electron partitioning analyses and Klopman’s approach, it follows that for the SO3 center dot center dot center dot B complexes the electrostatic contribution to the bonding is comparable to the covalent contribution.

First author: Fernandez, I, Correlation between Hammett substituent constants and directly calculated pi-conjugation strength, JOURNAL OF ORGANIC CHEMISTRY, 71, 2251, (2006)
Abstract: [GRAPHICS]The results of an energy decomposition analysis of ortho-, meta-, and para-substituted benzylic cations and para-substituted benzylic anions H2C-C6H4Rq (R = H, F, CN, Me, OH, NH2, NO2, CHO, CO2H; q = +, -) are presented and discussed. The calculated values for the pi bonding between CH2q and C6H4R show for substituents which have pi orbitals a linear correlation with the Hammett sigma(p), sigma(+)(p), and sigma(m) constants.

First author: Remko, M, Theoretical study of structure, pK(a), lipophilicity, solubility, absorption, and polar surface area of some centrally acting antihypertensives, BIOORGANIC & MEDICINAL CHEMISTRY, 14, 1715, (2006)
Abstract: The methods of theoretical chemistry have been used to elucidate the molecular properties of the Substituted imidazoline and oxazoline structures, a class of potent agonists and antagonists of imidazoline receptors. The geometries of various tautomers and isomers of 2-[2,6-dichlorophenylimino]imidazoline (clonidine), 1-(N-dicyclopropylmethyl)amino-2-oxazoline (rilmenidine), 4-chloro-N-(4,5-dihydro-1H-imidazol-2yl)-6-methoxy-2-methyl-5-pyrimidina mine (moxonidine), N-(dicyclopropylmethyl)-4,5-dihydro-1H-pyrrol-2-amine (arninopyrroline), N-dicyclopropylmethyl-4,5-dihydrothiazol-2-amine (aminothiazoline),4,5dihydro-2-(2-methoxyphenyl)-1H-imidazole (compound_6), 4,5-dihydro-2-(3-methylthiophen-2-yl)-1H-imidazole (compound-7), N-(2-chloro-4-iodophenyl)-4,5-dihydro-5-methyl-3H-pyrrol-2-amine (LNP-911), N-amidino-3,5-diamino-6-chloropyrazine-carboxamide (amiloride), 2-(1,4-benzodioxan-2-yl)-2-imidazoline (idazoxan), (+/-)-2-(2-ethyl-2,3-dihydro-2-benzofuranyl)-2-imidazoline (efaroxan), (4-aminobutyl)guaninine (agmatine), and 1-methyl-9H-pyrido[3,4-b]indole (harmane) have been studied using Becke3-LYP/6-3 I +G(d,p) and BP86/TZ2P DFT methods. The optimized geometries indicate that these molecules show a distinctly nonplanar configuration of the imidazoline and oxazoline moieties. In the gas-phase, rilmenidine and aminothiazoline exist in two forms (amino and imino), the amino tautomers being more stable by about 6 kJ/mol. The calculations showed, in agreement with experiments, that clonidine, moxonidine, and LNP-911 exist in a more stable imino tautomer. The tautomer containing the amino group is by about 30 kJ/mol less stable. Computations that include the effect of solvation indicated that also in water the relative stability order of individual tautomers (amino and imino forms) is preserved. The computed pK(a) values varied between 6.7 and 9.0, and correlate well with the available experimental pK(a)’s found in the literature. Among the clinically useful antihypertensives moxonidine exhibits the lowest basicity in water. At pH = 7.4 only about 50% of this drug exists in ionized form. The available experimental partition coefficients of compounds investigated Lire best reproduced by the CLOGP method. The computed partition coefficients varied between -1.80 (agmatine) and 5.35 (LNP_911) (CLOGP). Clonidine, rnoxonidine, and rilmenidine are moderately lipophilic compounds with lipophilicities between these two extreme values. The computed solubilities (about 0.1-4 g/L) show that the imidazoline and oxazoline derivatives Studied have very low water solubility. The analysis of molecular descriptors defined by Lipinski has shown that most of the compounds studied obey ‘rule of five’. Amiloride and aginatine ‘outlets’ exhibit also the lowest absorption. Therefore, in the early stages of the design of ligands acting oil inlidazoline binding sites, it is becoming more important to determine the pK(a), lipophilicity, water Solubility, polar surface area, absorption, and other physicochemical properties associated with a drug, before synthetic work is undertaken, with the aim of avoiding the synthesis of compounds that are predicted to have poor biopharmaceutical characteristics.

First author: Sojka, Z, DFT calculations of magnetic parameters for molybdenum complexes and hydroxymethyl intermediates trapped on silica surface, SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY, 63, 788, (2006)
Abstract: Density functional theory (DFT) calculations of EPR parameters and their structure sensitivity for selected surface paramagnetic species involved in oxidative dehydrogenation of methanol over silica grafted molybdenum catalyst were investigated. Two surface complexes, Mo-4c/SiO2 and {O–Mo4c}/SiO2, as well as (CH2OH)-C-center dot radical trapped on the SiO2 matrix were taken as the examples. The spin-restricted zeroth order regular approximation (ZORA) implemented in the Amsterdam Density Functional suite was used to calculate the electronic g tensor for those species. The predicted values were in satisfactory agreement with experimental EPR results. Five different coordination modes of the (CH2OH)-C-center dot radical on the silica surface were considered and the isotropic C-13, O-17, and H-1 hyperfine coupling constants (HFCC) of the resultant surface complexes were calculated. Structure sensitivity of the HFCC values was discussed in terms of the angular deformations caused by hydrogen bonding with the silica surface.

First author: Janik, MJ, A quantum chemical study of the decomposition of Keggin-structured heteropolyacids, JOURNAL OF PHYSICAL CHEMISTRY B, 110, 4170, (2006)
Abstract: Heterpolyacids (HPAs) demonstrate catalytic activity for oxidative and acid-catalyzed hydrocarbon conversion processes. Deactivation and thermal instability, however, have prevented their widespread use. Herein, ab initio density functional theory is used to study the thermal decomposition of the Keggin molecular HPA structure through the desorption of constitutional water molecules. The overall reaction energy and activation barrier are computed for the overall reaction HnXM12O40 -> Hn-2XM12O39 + H2O. and subsequently used to predict the effect of HPA composition on thermal stability. For example, the desorption of a constitutional water molecule is found to be increasingly endothermic in the order silicomolybdic acid (H4SiMO12O40) < phosphomolybdic acid (H3PMo12O40) < silicotungstic acid (H4SiW12O40) < phosphotungstic acid (H3PW12O40), in agreement with the experimental ordering of their thermal stability. The presence of an adjacent Keggin unit may stabilize the structural defect created by the water desorption, thus suggesting that constitutional water loss is an initial step toward the decomposition into a bulk mixed oxide. The equilibrium concentration of defective Keggin units is determined as a function of temperature and water partial pressure. It is concluded that the loss of constitutional water molecules is a plausible deactivation mechanism of the acid catalyst. The intermediate structures along the decomposition path are proposed as possible active sites for oxidation catalysis. The results presented herein provide molecular level insight into the dynamic nature of the heteropolyacid catalyst structure.

First author: Zhao, LL, Pyridine-Ag-20 cluster: A model system for studying surface-enhanced Raman scattering,JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 2911, (2006)
Abstract: This work presents a detailed analysis of enhanced Raman scattering of the pyridine-Ag-20 model system using time-dependent density functional theory. A consistent treatment of both the chemical and electromagnetic enhancements (EM) is achieved by employing a recently developed approach based on a short-time approximation for the Raman cross section. A strong dependence of the absolute and relative intensities on the binding site and excitation wavelength is found. The analysis of the Raman scattering cross sections shows the importance of different contributions to the enhancements, including static chemical enhancements (factor of 10), charge-transfer enhancements (10(3)), and EM enhancements (10(5)). The largest enhancement found (10(5)-10(6)) is due to the EM mechanism, with a small contribution from the chemical interaction. This suggests that the enhanced Raman scattering due to atomic clusters is comparable to findings on single nanoparticles. A combination of information about the vibrational motion and the local chemical environment provides a simple picture of why certain normal modes are enhanced more than others.

First author: Quinet, O, Time-dependent density functional theory simulation of hyper-Raman spectra, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 106, 599, (2006)
Abstract: Hyper-Raman spectra of several small systems have been simulated at the time-dependent density functional theory level of approximation and compared with their time-dependent Hartree-Fock analogues to address the effects of electron correlation. A numerical finite distortion scheme has been used to evaluate the first order-derivative of the dynamic first hyperpolarizability with respect to vibrational normal mode coordinates.

First author: Bridgeman, AJ, Bond orders between molecular fragments, CHEMISTRY-A EUROPEAN JOURNAL, 12, 2252, (2006)
Abstract: An extension of the Mayer bond order for the interaction between molecular fragments is presented. This approach allows the classical chemical concepts of bond order and valence to be utilised for fragments and the interactions between the fragments and symmetry-adapted linear combinations to be analysed. For high-symmetry systems, the approach allows the contribution from each irreducible representation to be assessed and provides a semiquantitative measure of the role of each bonding mode to interfragment interactions. The utility of this tool has been examined by a study of the bonding in symmetrical sandwich complexes. The validity of the frontier-orbital approach and the contributions from each frontier-orbital interaction can also be assessed within this model. As demonstrated by a study of a number of mixed-sandwich complexes, the model proves to be especially useful for low-symmetry systems in which separation of the sigma, pi and delta roles in bonding of the ligand is difficult to assess. ne fragment bond order describes the interaction between preoptimized fragment orbitals and is independent of the charges that are placed on these fragments. Although the method allows the chemist to define fragments in any way they choose, most insight is gained by using the same frontier orbitals employed so successfully in perturbational molecular-orbital approaches. The results are free from the influence of the electron-counting method used to describe fragments, such as the rings and metals in sandwich complexes.

First author: Zbiri, M, Asymmetric mu(2)-1,1-azido bridged copper(II) complex: Synthesis, X-ray structure, magnetic study and DFT calculations, INORGANICA CHIMICA ACTA, 359, 1193, (2006)
Abstract: A new rare variety asymmetric mu(2)-1,1-azido bridged copper(II) complex has been synthesized and characterized structurally and magnetically. The complex [Cu2L2(mu(2)-1,1-N-3)(2)]center dot H2O center dot CH3OH (L = 1-(N-ortho-hydroxyacetophenimine)-2-aminoethane) (1), crystallizes in monoclinic space group, P2(1)/n, with a = 9.469(4) angstrom, b = 12.526(8) angstrom, c = 12.899(10) angstrom, beta = 105.79(6)degrees, V = 1472.2(16) angstrom(3). X-ray study reveals that he Cu-N(azide)-Cu angles in this complex is 90.4 degrees. This is unusually low in comparison to that of the same angle in other end-on azido-bridged binuclear complexes. Though a strong ferromagnetic interaction between the metal centers is expected in the complex, the coupling has actually been found to be anti ferromagnetic (J = -4.2 cm(-1)), instead. To rationalize this paradoxical magnetic behavior, DFT calculation of this and other four complexes with very similar structure have been performed within broken symmetry framework. The calculated magnetic coupling constants (J) are in excellent agreement, both in sign and in the magnitude of the exchange interaction, with the experimental data, and the spin density map is correctly reproduced.

First author: Swart, M, Proton affinities of anionic bases: Trends across the periodic table, structural effects, and DFT validation, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 2, 281, (2006)
Abstract: We have carried out an extensive exploration of the gas-phase basicity of archetypal anionic bases across the periodic system using the generalized gradient approximation of density 14 functional theory (DFT) at BP86/QZ4P//BP86/TZ2P. First, we validate DFT as a reliable tool for computing proton affinities and related thermochemical quantities: BP86/QZ4PHBP86/TZ2P is shown to yield a mean absolute deviation of 1.6 kcal/mol for the proton affinity at 0 K with respect to high-level ab initio benchmark data. The main purpose of this work is to provide the proton affinities (and corresponding entropies) at 298 K of the anionic conjugate bases of all main-group-element hydrides of groups 14-17 and periods 2-6. We have also studied the effect of stepwise methylation of the protophilic center of the second- and third-period bases.

First author: de Jong, GT, Oxidative addition of the chloromethane C-Cl bond to Pd, an ab initio benchmark and DFT validation study, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 2, 322, (2006)
Abstract: We have computed a state-of-the-art benchmark potential energy surface (PES) for the archetypal oxidative addition of the chloromethane C-Cl bond to the palladium atom and have used this to evaluate the performance of 26 popular density functionals, covering LIDA, GGA, meta-GGA, and hybrid density functionals, for describing this reaction. The ab initio benchmark is obtained by exploring the PES using a hierarchical series of ab initio methods [HF, MP2, CCSD, and CCSD(T)] in combination with a hierarchical series of seven Gaussian-type basis sets, up to g polarization. Relativistic effects are taken into account through a full four-component all-electron approach. Our best estimate of kinetic and thermodynamic parameters is -11.2 (-10.8) kcal/mol for the formation of the most stable reactant complex, 3.8 (2.7) kcal/mol for the activation energy of direct oxidative insertion (OxIn), and -28.0 (-28.8) kcal/mol for the reaction energy (all energies relative to separate reactants, zero-point vibrational energy-corrected values in parentheses). Our work highlights the importance of sufficient higher angular momentum polarization functions for correctly describing metal-d-electron correlation. The best overall agreement with our ab initio benchmark is obtained by functionals from all three categories, GGA, meta-GGA, and hybrid DFT, with mean absolute errors of 0.8-3.0 kcal/mol and errors in activation energies for OxIn ranging from 0.0 to 1.2 kcal/mol. For example, three well-known functionals, BLYP, OLYP, and B3LYP, compare very reasonably with, respectively, an underestimation of the barrier for OxIn of -4.2 kcal/mol and overestimations of 4.2 and 1.6 kcal/mol. Interestingly, all important features of the CCSD(T) benchmark potential energy surfaces for the Pd-induced activation of C-H, C-C, C-F, and C-Cl bonds are reproduced correctly within a few kcal/mol by BLYP, OLYP, and B3LYP, while at the same time, none of these functionals is the “best one” in each individual case. This follows from an overall comparison of the results of the present as well as previous studies.

First author: Persson, P, Quantum chemical calculations of the influence of anchor-cum-spacer groups on femtosecond electron transfer times in dye-sensitized semiconductor nanocrystals, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 2, 441, (2006)
Abstract: Electronic properties of dye-sensitized semiconductor nanocrystals, consisting of perylene (Pe) chromophores attached to 2 nm TiO2 nanocrystals via different anchor-cum-spacer groups, have been studied theoretically using density functional theory (DFT) cluster calculations. Approximate effective electronic coupling strengths for the heterogeneous electron-transfer interaction have been extracted from the calculated electronic structures and are used to estimate femtosecond electron-transfer times theoretically. Results are presented for perylenes attached to the TiO2 via formic acid (Pe-COOH), propionic acid (Pe-CH2-CH2-COOH), and acrylic acid (Pe-CH=CH-COOH). The calculated electron transfer times are between 5 and 10 fs with the formic acid and the conjugated acrylic acid bridges and about 35 fs with the saturated propionic acid bridge. The calculated electron injection times are of the same order of magnitude as the corresponding experimental values and qualitatively follow the experimental trend with respect to the influence of the different substitutions on the injection times.

First author: Segala, M, Density functional theory calculation of 2p core-electron binding energies of Si, P, S, Cl, and Ar in gas-phase molecules, JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA, 151, 9, (2006)
Abstract: Density functional theory (DFT) calculations have been performed on the gas-phase 2p core-electron binding energies (CEBEs) of Si and Ar in 145 cases using the following procedure: AEKS (scalar-ZORA + E-xc)/TZP//HF/6-31G(d). Delta E-KS is the difference in the total Kohn-Sham energies of the 2p-ionized cation and the neutral parent molecule calculated by DFT using different exchange-correlation functionals E-xc with triple-zeta polarized basis set, at molecular geometry optimized by HF/6-31G(d), and relativistic effects have been estimated by scalar zeroth-order regular approximation. Among the 26 functionals tested, the form of E-xc giving the best overall performance was found to be the combination of OPTX exchange and LYP correlation functionals. For that functional, the average absolute deviation (AAD) of the 145 calculated CEBEs from experiment is 0.26 cV. There are seven other exchange-correlation functionals that led to AADs of less than 0.30 eV. Some functionals give lower AADs than E-xc=OPTX-LYP for some individual elements. In the case of Si, for example, the combination of either mPW91-PBE or Becke88-Perdew86 led to an AAD of only 0.10 eV for 56 silicon-containing molecules. Another example is the case of the argon atom, for which the choice of E-xc=OPTX-Perdew86 yields a value for CEBE equal to the experimental value.

First author: Declerck, R, First-principles calculation of the EPR g tensor in extended periodic systems, PHYSICAL REVIEW B, 73, 9, (2006)
Abstract: A method for the ab initio prediction of the EPR g tensor for paramagnetic defects in systems under periodic boundary conditions is presented. It is based on density functional theory and the pseudopotential approximation. The formalism is applicable to crystalline and amorphous insulators, as well as to isolated molecules using a supercell technique. The method is validated by comparison with a well-established theoretical approach and experimental data for a series of small isolated molecules. Finally the EPR parameters of an O-3(-) defect in a KCl lattice are evaluated following the new procedure, yielding results in good agreement with experiment and at an attractive computational cost.

First author: Deeth, RJ, Molecular modelling of Jahn-Teller distortions in Cu(II)N-6 complexes: elongations, compressions and the pathways in between, DALTON TRANSACTIONS, 73, 1092, (2006)
Abstract: Ligand Field Molecular Mechanics (LFMM) parameters have been optimised for six-coordinate Cu(II) complexes containing amine, pyridine, imidazole and pyrazine donors. As found in previous LFMM applications, the new parameters automatically generate distorted structures with the magnitudes of the Jahn-Teller elongations in good agreement with experiment. Here, we explore the rest of the potential energy surface. The introduction of axial strain drives the LFMM structures via rhombic geometries to the compressed structure, the latter corresponding to the saddle point between successive elongation axes. Calculated barrier heights between compressed and elongated geometries also agree well with available experimental data. In every case bar one, the LFMM predicts that the crystallographically observed elongation axis corresponds to the overall lowest energy well. The structural predictions are confirmed by independent density functional theory (DFT) optimisations. LFMM calculations on bis(2,5-pyrazolylpyridine)copper complexes display a smooth variation in structure as a function of pyrazolyl substituent from elongated for R = H through to fully compressed for R = Bu-t. This behaviour is driven by the steric interactions with the ground state varying smoothly as a linear combination of {d(x2-y2)}(1) and {d(z2)}(1).

First author: Poleshchuk, OK, HFI and DFT study of the bonding in complexes of halogen and interhalogen diatomics with Lewis base, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 760, 175, (2006)
Abstract: We have analyzed by means of DFT calculations with use of the pseudo-potential the nuclear quadrupole coupling constants of a range of (XYB)-B-… complexes (n a sigma type in Mulliken notation) formed between diatomic interhalogen molecules XY and Lewis bases B. The geometrical parameters, rotational and halogen nuclear quadrupole coupling constants obtained by these calculations substantially corresponded to the data of microwave spectroscopy in the gas phase. An analysis of the quality of the calculations that employ the pseudo-potential and the expanded basis set for the halogen compounds was carried out. The ZORA model is shown to be a viable alternative to the computationally demanding BH and HLYP model for the calculation of halogen and nitrogen coupling constants in molecules. In addition, the ZORA model, in contrast to the pseudo-potential model, leads to realistic values of iodine nuclear quadrupole coupling constants. From electron partitioning analyses and Klopman’s approach it follows that for the (ICIB)-B-… complexes the electrostatic bonding is predominant relative to covalent bonding,

First author: Bendjaballah, S, The versatility of pentalene coordination to transition metals: A density functional theory investigation, CHEMISTRY-A EUROPEAN JOURNAL, 12, 2048, (2006)
Abstract: DFT calculations with full geometry optimization have been carried out on a series of real and hypothetical compounds of the type [CpM-(C8H6)], [(CO)(3)M(C8H6)], [M(C8H6)(2)], [(CPM)(2)(C8H6)], [{(CO)(3)M}(2)(C8H6)], and [M-2(C8H6)(2)] (M=transition metal). The bonding in all the currently known compounds is rationalized, as well as in the (so far) hypothetical stable complexes. Depending on the electron count and the nature of the metal(s), eta(2) (predicted), eta(3), eta(5), eta(8), or intermediate coordination modes can be adopted. In the case of the mononuclear species, the most favored closed-shell electron counts are 18 and 16 metal valence electrons (NIVE). In the case of the dinuclear species, an electron count of 34 MVEs is most favored. However, other electron counts can be stabilized, especially in the case of dinuclear complexes. Coordinated pentalene should most often be considered as formally being a dianion, but sometimes as a neutral ligand. In the former case it can behave as an aromatic species made of two equivalent fused rings, as a C-5 aromatic ring connected to an allylic anion, or even as two allylic anions bridged by a C7=C8 double bond. In the latter case, it can behave as a bond-alternating cyclic polyene or as a C-5 aromatic ring connected to an allylic cation.

First author: Bridgeman, AJ, Computational study of solvent effects and the vibrational spectra of Anderson polyoxometalates, CHEMISTRY-A EUROPEAN JOURNAL, 12, 2094, (2006)
Abstract: The structures and vibrational frequencies of the type 11 Anderson heteropolyanions [TeMo6O24](6-) and [IMo6O24](5-) have been calculated by using density functional theory using a number of common functionals and basis sets. For the first time, Raman intensities have been calculated and the effect of solvent on the modeling has been investigated. The calculated IR and Raman spectral traces are in good agreement with experiment allowing the characteristic group frequencies for this class of polyoxometalate to be identified. The stretching vibrations of the molybdenum-oxygen bonds are predicted to occur at somewhat lower frequencies than in the type I polyoxometalates. Stretching of the heteroatom-oxygen bonds occurs at significantly lower frequencies than in the Keggin anions as a simple consequence of the higher coordination number of the central heteroatom in the Anderson systems. For the [Mo2O7](2-) and [Mo6O19](2-) ions, the relatively low negative charge leads to small structural changes when solvent is included. In these systems, solvent leads to an increase in the bond polarity and a decrease in the covalent bond orders, resulting in decreases in the calculated frequencies. For the Anderson anions, the higher negative charges leads to greater solvent effects with contraction of the clusters and increases in the frequencies of bands due to stretching of the two, cis-related molybdenum-oxygen bonds.

First author: Novozhilova, IV, Experimental and density functional theoretical investigations of linkage isomerism in six-coordinate {FeNO}(6) iron porphyrins with axial nitrosyl and nitro ligands, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 2093, (2006)
Abstract: A critical component of the biological activity of NO and nitrite involves their coordination to the iron center in heme proteins. Irradiation (330 < lambda < 500 nm) of the nitrosyl-nitro compound (TPP)Fe(NO)(NO2) (TPP = tetraphenylporphyrinato dianion) at 11 K results in changes in the IR spectrum associated with both nitro-to-nitrito and nitrosyl-to-isonitrosyl linkage isomerism. Only the nitro-to-nitrito linkage isomer is obtained at 200 K, indicating that the isonitrosyl linkage isomer is less stable than the nitrito linkage isomer. DFT calculations reveal two ground-state conformations of (porphine)Fe(NO)(NO2) that differ in the relative axial ligand orientations (i.e., GS parallel to and GS-perpendicular to). In both conformations, the FeNO group is bent (156.4 degrees for GS parallel to, 159.8 degrees for GS perpendicular to) for this formally {FeNO}(6) compound. Three conformations of the nitrosyl-nitrito isomer (porphine)Fe(NO)(ONO) (MSall, MSa perpendicular to, and MSa(L)) and two conformations of the isonitrosyl-nitro isomer (porphine)Fe(ON)(NO2) (MSbll and MSb perpendicular to) are identified, as are three conformations of the double-linkage isomer (porphine)Fe(ON)(ONO) (MSc parallel to, MSc perpendicular to, MSCL). Only 2 of the 10 optimized geometries contain near-linear FeNO (MSa(L)) and FeON (MSCL) bonds. The energies of the ground-state and isomeric structures increase in the order GS < MSa < MSb < Me. Vibrational frequencies for all of the linkage isomers have been calculated, and the theoretical gas-phase absorption spectrum of (porphine)Fe(NO)(NO2) has been analyzed to obtain information on the electronic transitions responsible for the linkage isomerization. Comparison of the experimental and theoretical IR spectra does not provide evidence for the existence of a double linkage isomer of (TPP)Fe(NO)(NO2).

First author: Moreno, M, Complexes in insulators: Role of the electric field from the host lattice, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 759, 195, (2006)
Abstract: Properties of a transition metal impurity M in an insulating lattice are usually explained in terms of the MXN complex formed with the N nearest anions. Along this work the importance of considering the electric field created by the rest of lattice ions on the complex is stressed. This electric field can play a relevant role for explaining optical, magnetic and structural properties of complexes embedded in insulators especially when the local symmetry around the impurity is not cubic. A first example showing the importance of such an electric field concerns the charge transfer transitions of the CuBr4(NH3)(2)(2-) centre formed in Cu2+-doped NH4Br where the local symmetry around Cu2+ is tetragonal. A second example deals with the compressed geometry inferred for the Jahn-Teller ion Cu2+ in layered perovskites like K2ZnF4. While for d(9) and d(7) ions in cubic halide lattices the equilibrium geometry is found to correspond to an elongated octahedron the tetragonal electric field in layered perovskites induces a gap between x(2) – y(2) and 3z(2) – r(2) d-orbitals of the CuF64- complex even when all ligands are at the same distance. The existence of this gap is shown to play a key role for understanding the surprising compressed geometry found for Cu2+ in tetragonal perovskites.

First author: Kovacs, A, A theoretical study of the structure and bonding of UOX4 (X = F, Cl, Br, I) molecules: The importance of inverse trans influence, CHEMPHYSCHEM, 7, 455, (2006)
Abstract: The structural and bonding properties of the uranium(vi) oxyhalides UOX4 (X=F, Cl, Br, I) have been investigated by quantum chemical calculations at three different levels of theory: quasi-relativistic density functional theory QFT) in conjunction with a triple-zeta all-electron basis set, as well as MP2 and the Becke3-Perdew-Wang91 exchange-correlation functional in conjunction with relativistic effective core potentials. The computations located four stationary points on the potential energy surface: a tetrogonal pyramid with the O atom in the apical position (C-4v), a trigonal bipyramid with the O atom in the equatorial position (C,), a trigonol bipyramid with the O atom in the axial position (C-3v) and a C-5 structure derived from C-3v by opening the X-eq-U-X-eq angle to near 180 degrees. The C-5 minimum, however, seems to be an artefact of the Becke-Perdew functional on the flat potential energy surface. In the C-3v structure, the linear X-ax-U=O moieties show clearly the geometrical consequences of the inverse trans influence (ITI) effect. This interaction can stabilise these sterically less favoured geometries. Two important trends are revealed by our computations: 1) UOX4 with the small X=F prefers the C-3v structure, whereas with increasing halogen size the stericolly less crowded C-2v structure is more important; and 2) MP2 theory accounts to a lesser extent for the IT/ effect with respect to DFT, which results in different structural preferences (MP2 for C-2v, DFT for C-3v) in the heavier halides. In addition, an important bonding property of the UOX4 molecules is the clear triple-bond character of the formally double U=O bonds.

First author: Garcia-Lastra, JM, Optical and vibrational properties of MnF64- complexes in cubic fluoroperovskites: insight through embedding calculations using Kohn-Sham equations with constrained electron density, JOURNAL OF PHYSICS-CONDENSED MATTER, 18, 1519, (2006)
Abstract: The local structure and optical and vibrational properties associated with Mn2+- doped cubic AMF(3) (A = K, Rb; M = Mg, Zn, Cd) fluoroperovskites are studied by means of embedding calculations using Kohn-Sham equations with constrained electron density. It is shown that while an electronic parameter like 10Dq essentially depends on the Mn2+-F- distance, the local vibration frequencies omega(i) (i = a(1g), eg modes) are dominated by the interaction between F- ligands and nearest M2+ ions lying along bonding directions. The high omega(a) values observed for KMgF3:Mn2+ and KZnF3:Mn2+, the huge variations Of we and omega(a) frequencies when the host lattice is changed, as well as the increase of Huang-Rhys factors and the Stokes shift following the host lattice parameter, are shown to be related to this elastic coupling of the MnF64- complex to the rest of the host lattice. The present results support the conclusion that the Stokes shift is determined by the interaction of the excited T-4(1g) state with a(1g) and e(g) local modes while the coupling with the t(2g) shear mode is not relevant. The variations of local vibrational frequencies and the Stokes shift induced by a hydrostatic pressure on a given system are shown to be rather different to those produced by the chemical pressure associated with distinct host lattices.

First author: Seyedsayamdost, MR, Mono-, di-, tri-, and tetra-substituted fluorotyrosines: New probes for enzymes that use tyrosyl radicals in catalysis, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 1569, (2006)
Abstract: A set of N-acylated, carboxyamide fluorotyrosine (FnY) analogues [Ac-3-FY-NH2, Ac-3,5-F2Y-NH2, Ac-2,3-F2Y-NH2, Ac-2,3,5-F3Y-NH2, Ac-2,3,6-F3Y-NH2 and Ac-2,3,5,6-F4Y-NH2] have been synthesized from their corresponding amino acids to interrogate the detailed reaction mechanism(s) accessible to FnY center dot S in small molecules and in proteins. These Ac-FnY-NH2 derivatives span a pK(a) range from 5.6 to 8.4 and a reduction potential range of 320 mV in the pH region accessible to most proteins (6-9). DFT electronic-structure calculations capture the observed trends for both the reduction potentials and pK(a)s. Dipeptides of the methyl ester of 4-benzoyl-L-phenylalanyl-F(n)Ys at pH 4 were examined with a nanosecond laser pulse and transient absorption spectroscopy to provide absorption spectra of FnY center dot S. The EPR spectrum of each FnY center dot has also been determined by UV photolysis of solutions at pH 11 and 77 K. The ability to vary systematically both pKa and radical reduction potential, together with the facility to monitor radical formation with distinct absorption and EPR features, establishes that F(n)Ys will be useful in the study of biological charge-transport mechanisms involving tyrosine. To demonstrate the efficacy of the fluorotyrosine method in unraveling charge transport in complex biological systems, we report the global substitution of tyrosine by 3-fluorotyrosine (3-FY) in the R2 subunit of ribonucleotide reductase (RNR) and present the EPR spectrum along with its simulation of 3-FY122 center dot. In the companion paper, we demonstrate the utility of FnYS in providing insight into the mechanism of tyrosine oxidation in biological systems by incorporating them site-specifically at position 356 in the R2 subunit of Escherichia coli RNR.

First author: Ellis, DE, Molecular squares, rectangles, and corners: Ground-state electronic structure and configurational properties, CHEMISTRY OF MATERIALS, 18, 620, (2006)
Abstract: A recently developed class of molecular squares based on octahedral ReCl(CO)(3)R-2 cornerposts has until now lacked a detailed theoretical description. We present an analysis of electronic structure of five of the simplest squares, rectangles, and related fragments; that is, those with pyrazine and bipyridine walls. We further consider a square containing Zn-porphyrin walls. The derived electronic charge distributions reveal bonding structure and spectral features of the class. We show that the analysis of conformational preferences can be greatly simplified by using a ” piecewise ” strategy, which enables us to make several generic statements about conformations of this class of macromolecules. To further illustrate advantages of this approach, we find the origin of metastability of the planar conformation of the bipyridine square.

First author: Herve, K, Iodine substituted tetrathiafulvalene radical cation salts with [M(isoq)(2)(NCS)(4)](-) anions where M = Cr-III, Ga-III: Role of I center dot center dot center dot S and S center dot center dot center dot S contacts on structural and magnetic properties, CHEMISTRY OF MATERIALS, 18, 790, (2006)
Abstract: The preparation, crystal structures, extended Huckel theory band structure, and density functional theory (DFT) calculations and conducting and magnetic properties of seven new charge-transfer salts, formulated as (D)(2)[M-III(isoq)(2)(NCS)(4)], where D = DIET (diiodo(ethylenedithio)tetrathiafulvalene), DIETS (diiodo(ethylenedithio)diselenadithiafulvalene), M = Cr, Ga, and isoq = isoquinoline, are reported. For each donor two different phases called a and b were obtained. Crystal data for (DIET)2[Cr(isoq)2(NCS)41 (1) are as follows: phase a, triclinic P1, a = 9.8645(6) (A) over circle, b = 10.3255(8) (A) over circle, c = 13.7712(8) (A) over circle, alpha = 87.905(5)degrees, beta = 75.981(5)degrees, gamma = 80.712(2)degrees; phase b, triclinic P1, a = 10.6760(5) (A) over circle, b = 11.3000(6) (A) over circle, c = 11.3930(9) (A) over circle, alpha = 101.256(2)degrees, beta = 96.755(2)degrees, gamma = 97.342(5)degrees. All compounds exhibit semiconductive behavior with room-temperature resistivity ranging from 2 x 10(3) to 5 x 10(4) Omega cm. Donors in the mixed-valence-state form dimers. They are connected to anions through very short I center dot center dot center dot S contacts (S2 center dot center dot center dot I2 = 3.248(2) (A) over circle for 1a). The magnetic measurements and spin density DFT calculations revealed that iodine atoms are good structural agents but are poor magnetic mediators to promote superexchange interactions between the donors and the inorganic anions. Our analyses reveal also that in these charge-transfer salts the magnetic interactions between spin carriers are mainly ensured by short intermolecular S center dot center dot center dot S contacts.

First author: Belanzoni, P, Reactivity of silicon carbonyl with ethylene, CHEMICAL PHYSICS LETTERS, 418, 383, (2006)
Abstract: The reaction of silicon atom with carbonyl has recently been investigated by density functional calculations. A few relatively stable silicon carbonyl compounds have been found. In this Letter, the reactivity of silicon tetracarbortyl with ethylene has been investigated by a density functional approach. The calculations predict this carbonylation procedure as an alternative to the use of highly toxic phosgene commonly required in addition reactions of carbonyl to unsaturated compounds.

First author: Corminboeuf, C, Scalar relativistic correction to nucleus-independent chemical shifts of coinage-metal compounds: How does the pseudopotential approximation perform?, CHEMICAL PHYSICS LETTERS, 418, 437, (2006)
Abstract: The performance of commonly used pseudopotentials for calculations of nucleus-independent chemical shifts (NICS) at the center of coinage-metal rings M4Li2 (D-4h), M = Cu, Ag, Au) is investigated. The scalar relativity, which has a non-negligible effect on NICS, is found to be accurately described by the pseudopotential approximation. Overall, good agreement is obtained with all-electron relativistic methods, however, careful comparisons with these calculations and consideration for large triple-zeta basis sets are recommended when aiming to accurately define the relative degree of diatropicity among a series of compounds.

First author: Bardaji, M, Synthesis, structural characterization, and theoretical studies of gold(I) and gold(I)-gold(III) thiolate complexes: Quenching of gold(I) thiolate luminescence, INORGANIC CHEMISTRY, 45, 1059, (2006)
Abstract: The gold(I) thiolate complexes [Au(2-SC6H4NH2)(PPh3)] (1), [PPN][Au(2-SC6H4NH2)(2)] (2) (PPN = Pph(3)= N = Pph(3)), and [{Au(2-SC6H4NH2)}(2)(mu-dppm)] (3) (dppm = PPh2CH2PPh2) have been prepared by reaction of acetylacetonato gold(l) precursors with 2-aminobenzenethiol in the appropriate molar ratio. All products are intensely photoluminescent at 77 K The molecular structure of the dinuclear derivative 3 displays a gold-gold intramolecular contact of 3.1346(4) angstrom. Further reaction with the organometallic gold(III) complex [Au(C6F5)(3)(tht)] affords dinuclear or tetranuclear mixed gold(I)-gold(III) derivatives with a thiolate bridge, namely, [(AuPPh3){Au(C6F5)(3)}(mu(2)-2-SC6H4NH2)] (4) and [(C6F5)(3)Au(mu(2)-2-SC6H4NH2)(AudppmAu) (mu(2)-SC6H4NH2)Au(C6F5)(3)] (5). X-ray diffraction studies of the latter show a shortening of the intramolecular gold(I)-gold(I) contact [2.9353(7) or 2.9332(7) angstrom for a second independent molecule], and short gold(l)-gold(III) distances of 3.2812(7) and 3.3822(7) angstrom [or 3.2923(7) and 3.4052(7) angstrom] are also displayed. Despite the gold-gold interactions, the mixed derivatives are nonemissive compounds. Therefore, the complexes were studied by DFT methods. The HOMOs and LUMOs for gold(l) derivatives 1 and 3 are mainly centered on the thiolate and phosphine (or the second thiolate for complex 2), respectively, with some gold contributions, whereas the LUMO for derivative 4 is more centered on the gold(III) fragment. TD-DFT results show a good agreement with the experimental UV-vis absorption and excitation spectra. The excitations can be assigned as a S -> Au-P charge transfer with some mixture of LLCT for derivative 1, an LLCT mixed with ILCT for derivative 2, and a S -> Au center dot center dot center dot Au-P charge transfer with LLCT and MC for derivative 3. An LMCT (thiolate -> Au-III mixed with thiolate Au-P) excitation was found for derivative 4. The differing nature of the excited states [participation of the gold(III) fragment and the small contribution of sulfur] is proposed to be responsible for quenching the luminescence.

First author: Wang, XJ, Investigation of charge transfer and structural distortions during photo-inducted excitation of cuprous bis-2,9-dimethyl-1, 10-phenanthroline complex by density functional theory, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 691, 551, (2006)
Abstract: This work reported the investigation of the structural distortions and charge-transfer processes that occurred in the complex of cuprous(I) bis-2,9-dimethyl-1,10-phenanthroline (Cu(dmp)(2)(+)) upon oxidation to copper(II), Cu(dmp)(2)(2+) through a excited state of Cu(dmp)(2)(+), by density functional theory. The intramolecular electronic transfer from central metal-to-ligand (MLCT) upon the irradiation of light energy is confirmed. Due to this MLCT excitation, the structure of the excited state of Cu(dmp)(2)(+) is distorted and reorga-nized to adapt with the change of charge in central metal. As a result, the excited state of Cu(dmp)(2)(+) is formed, which has the similar electronic and structural properties with Cu(dmp)(2)(2+). The bulky substituents in 2- and 9-positions of the phenanthroline ligands can restrain the structural distort and decrease nonradiative decay rate. Thus, the electronic and steric effects of the ligands in the cuprous photo-sensitive complexes have important consequences in the behavior of their excited state.

First author: Janczyk, A, Competition between metal-amido and metal-imido chemistries in the alkaline earth series: An experimental and theoretical study of BaNH, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 1109, (2006)
Abstract: The pure rotational spectrum of BaNH in its X-1 Sigma(+) ground electronic state has been recorded using millimeter/submillimeter direct absorption methods; data for the deuterium and barium 137 isotopomers have been measured as well. The molecules were produced by the reaction of ammonia or ND3 and barium vapor in the presence of a dc discharge. Transitions arising from the ground vibrational state and the excited vibrational bending (0110) and heavy atom stretching (100) modes were measured. The rotational spectrum indicates a linear structure, with B-0(BaNH) = 7984.549 MHz and B-0(BaND) = 7060.446 MHz. An r(m)((1)) structure has been determined, yielding r(BaN) = 2.077 +/- 0.002 angstrom and r(NH) = 1.0116 +/- 0.0006 A. Density functional calculations using an extensive Slater-type basis set with inclusion of scalar relativistic effects gives geometrical parameters and vibrational frequencies for BaNH in excellent agreement with those determined by experiment. The molecular orbital and natural bond order analyses of the BaNH wave function show Ba-N pi bonds formed by electron donation from the formally filled N 2p orbitals of the imido group to the empty Ba 5d orbitals. The multiple bonding between Ba and N stabilizes the linear geometry and, along with the relative ease of oxidation of the Ba atom, favors formation of the metal-imido species over that of the metal-amido species that have been found from similar studies with Mg, Ca, and Sr atoms in this group.

First author: Falzon, CT, Prediction of spectroscopic constants for diatomic molecules in the ground and excited states using time-dependent density functional theory, JOURNAL OF COMPUTATIONAL CHEMISTRY, 27, 163, (2006)
Abstract: Spectroscopic constants of the ground and next seven low-lying excited states of diatomic molecules CO, N-2, P-2, and ScF were computed using the density functional theory SAOP/ATZP model, in conjunction with time-dependent density functional theory (TD-DFT) and a recently developed Slater type basis set, ATZP. Spectroscopic constants, including the equilibrium distances r(e), harmonic vibrational frequency omega(e), vibrational anharmonicity omega(e)x(e), rotational constant B-e, centrifugal distortion constant D-e, the vibration-rotation interaction constant alpha(e), and the vibrational zero-point energy E-n(0), were generated in an effort to establish a reliable database for electron spectroscopy. By comparison with experimental values and a similar model with an established larger Slater-type basis set, et-QZ3P-xD, it was found that this model provides reliably accurate results at reduced computational costs, for both the ground and excited states of the molecules. The over all errors of all eight lowest lying electronic states of the molecules under study using the effective basis set are r(e)(+/- 4%), omega(e)(+/- 5% mostly without exceeding +/- 20%), omega(e)x(e)(+/- 5% mostly without exceeding 20%, much more accurate than a previous study on this constant of +/- 30%), B-e(+/- 8%), D-e(+/- 10%), alpha(e)(+/- 10%), and E-n(0)(+/- 10%). The accuracy obtained using the ATZP basis set is very competitive to the larger et-QZ3P-xD basis set in particular in the ground electronic states. The overall errors in r(e), omega(e)x(e) and alpha(e) in the ground states were given by +/- 0.7, +/- 10.1, and +/- 8.4%, respectively, using the efficient ATZP basis set, which is competitive to the errors of +/- 0.5, +/- 9.2, and +/- 9.1%, respectively for those constants using the larger et-QZ3P-xD basis set. The latter basis set, however, needs approximately four times of the CPU time on the National Supercomputing Facilities (Australia). Due to the efficiency of the model (TD-DFT, SAOP and ATZP), it will be readily applied to study larger molecular systems.

First author: Paul, F, Bonding and substituent effects in electron-rich mononuclear ruthenium sigma-arylacetylides of the formula [(eta(2)-dppe)(eta(5)-C5Me5)Ru(C C)-1,4-(C6H4)X][PF6](n) (n = 0, 1; X = NO2, CN, F, H, OMe, NH2),ORGANOMETALLICS, 25, 649, (2006)
Abstract: This study reports the isolation and the structural (X-ray), UV-vis, and NMR characterization of a series of electron-rich Ru(II) acetylide complexes of the formula (eta(2)-dppe)(eta(5)-C5Me5)Ru(C equivalent to X)-1,4-(C6H4)X (1a-f; X = NO2, CN, F, H, OMe, NH2) and (eta(2)-dppe)(eta(5)-C5Me5)Ru(C equivalent to C)-1,3-(C6H4)F (1c-m), as well as the spectroscopic (near-IR and ESR) in situ characterization of the corresponding elusive Ru(III) radical cations. The spectroscopic data are discussed in connection with DFT computations, and a consistent picture of the electronic structure of these Ru(11) and Ru(111) acetylide complexes is proposed. Notably, the strong reactivity of the Ru(Ill) radicals evidenced in this contribution constitutes a major difference with the relative stability of the known iron analogues.

First author: Hieringer, W, First hyperpolarizability of a sesquifulvalene transition metal complex by time-dependent density-functional theory, JOURNAL OF PHYSICAL CHEMISTRY A, 110, 1014, (2006)
Abstract: The first hyperpolarizability and electronic excitation spectrum of sesquifulvalene and a sesquifulvalene ruthenium complex have been computed and analyzed with use of time-dependent density-functional theory. A new orbital decomposition scheme is introduced that allows the computed first hyperpolarizability to be related to the electronic structure of complex molecules. The analysis shows that the first hyperpolarizability of sesquifulvalene is not associated with the first intense absorption, with HOMO-1 -> LUMO+1 character, but is dominated by the lowest energy transition, with HOMO -> LUMO character, despite its very low intensity. In the ruthenium complex, the analysis reveals that the strong enhancement of the nonlinear optical response compared to free sesquifulvalene should not be attributed to the effect of complexation on the hyperpolarizability of sesquifulvalene. The strong hyperpolarizability originates from MLCT transitions from ruthenium d-orbitals to an empty orbital located at the seven ring of sesquifulvalene, transitions that have no analogue in free sequifulvalene.

First author: David, J, Electronic structure and molecular properties of the heptacyanorhenate [Re(CN)(7)](3-) and [Re(CN)(7)](4-) complexes, JOURNAL OF PHYSICAL CHEMISTRY A, 110, 1072, (2006)
Abstract: We report scalar relativistic and Dirac scattered wave (DSW) calculations on the heptacyanorhenate [Re(CN)(7)](3-) and Re(CN)(7)(4-) complexes. Both the ground and lowest excited states of each complex split by spin-orbit interaction by about 0.3 eV. The calculated molecular electronegativities chi indicate that the open-shell complex is less reactive than the closed-shell complex, in agreement with experimental observations. The calculations indicate that the ground state spin density is highly anisotropic and that spin-orbit effects are responsible for the magnetic anisotropy of the molecular g tensor of the Re(CN)(7)(3-) complex. The calculated optical electronic transitions for both complexes with a polarizable continuum model using a time-dependent density functional (TDDFT)/B3LYP formalism are in reasonable agreement with those observed in the absorption spectrum.

First author: Figueroa, JS, A nitridoniobium(V) reagent that effects acid chloride to organic nitrile conversion: Synthesis via heterodinuclear (Nb/Mo) dinitrogen cleavage, mechanistic insights, and recycling, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 940, (2006)
Abstract: The transformation of acid chlorides (RC(O)Cl) to organic nitriles (RC equivalent to N) by the terminal niobium nitride anion [N equivalent to Nb(N[Np]Ar)(3)](-) ([1a-N](-), where Np = neopentyl and Ar = 3,5-Me2C6H3) via isovalent N for O(Cl) metathetical exchange is presented. Nitrido anion [1a-N](-) is obtained in a heterodinuclear N-2 scission reaction employing the molybdenum trisamide system, Mo(N[R]Ar)(3) (R = t-Bu, 2a; R = Np, 2b), as a reaction partner. Reductive scission of the heterodinuclear bridging N-2 complexes, (Ar[R]N)(3)Mo-(mu-N-2)Nb(N[Np]Ar)(3) (R = t-Bu, 3b; R = Np, 3c) with sodium amalgam provides 1 equiv each of the salt Na[1a-N] and neutral N equivalent to Mo(N[R]Ar)(3) (R = t-Bu, 2a-N; R = Np, 2b-N). Separation of 2-N from Na[1a-N] is readily achieved. Treatment of salt Na[1a-N] with acid chloride substrates in tetrahydrofuran (THF) furnishes the corresponding organic nitriles concomitant with the formation of NaCl and the oxo niobium complex O equivalent to Nb(N[Np]Ar)(3) (1a-O). Utilization of N-15-labeled N-15(2) gas in this chemistry affords a series of N-15-labeled organic nitriles establishing the utility of anion [1a-N](-) as a reagent for the N-15-labeling of organic molecules. Synthetic and computational studies on model niobium systems provide evidence for the intermediacy of both a linear acylimido and niobacyclobutene species along the pathway to organic nitrile formation. High-yield recycling of oxo 1a-O to a niobium triflate complex appropriate for heterodinuclear N2 scission has been developed. Specifically, addition of triflic anhydride (Tf2O, where Tf = SO2CF3) to an Et2O solution of 1a-O providesthe bistriflate complex, Nb(OTf)(2)(N[Np]Ar)(3) (1a-(OTf)(2)), in near quantitative yield. One-electron reduction of 1a-(OTf)(2) with either cobaltocene (Cp2Co) or Mg(THF)(3)(anthracene) provided the monotriflato complex, Nb(OTf)(N[Np]Ar)(3) (1a-(OTf)), which efficiently regenerates complexes 3b and 3c when treated with the molybdenum dinitrogen anions [N2Mo(N[t-Bu]Ar)(3)](-) ([2a-N-2](-)) or [N2Mo(N[Np]Ar)(3)](-) ([2b-N-2](-)), respectively.

First author: Palmer, EJ, Theoretical studies of pi-loading and structural diversity in Cp3MX (M = Zr, Hf; X = H, CH3, OR, NR2) compounds, POLYHEDRON, 25, 575, (2006)
Abstract: Density functional theory has been used to explore the bonding and geometric preferences of tris-Cp zirconium and hafnium compounds of the type Cp3MX. In most cases, two primary isomers were found: a “3-5” isomer, which contains three eta(5)-cp ligands, and a “2-5,1-1” isomer, which contains two eta(5)-Cp and one eta(1)-Cp ligands. The relative energies of these isomers are dependent upon the pi-donor ability of the X ligand. For the tris-Cp methyl compounds, the “3-5” isomers are more stable by 1-4 kcal/ mol. The “2-5,1-1” isomers of the tris-Cp alkoxide and amido compounds are more stable by 3-6 and 6-11 kcal/mol, respectively. Bonding analyses show these binding preferences can be understood in terms of pi-competition between the tris-Cp ligand set and the lone pair of the X ligand. pi-loading on the X ligand decreases the pi-donor ability of the “3-5” tris-Cp ligand set, which increases the preference for the “2-5,1-1” ground state geometry in the complexes with strong pi-donors. In addition, molecular orbital theory provides evidence for destabilization effects arising from filled-filled interactions between the “3-5” Cp3M fragment and the X lone pair.

First author: Tai, HC, Computational studies of the coordination stereochemistry, bonding, and metal selectivity of mercury, JOURNAL OF PHYSICAL CHEMISTRY A, 110, 452, (2006)
Abstract: Knowledge of the bonding, and selectivity of organic mercury, [H3C-Hg](+) (MeHg+), and inorganic Hg2+ for protein and DNA functional groups is important for understanding the mechanism of heavy metal poisoning. Herein, we elucidate (1) the differences between inorganic Hg2+ and organic MeHg+ in their interactions with different ligands of biological interest, (2) the protein and DNA functional groups that Hg2+ and MeHg+ target in aqueous solution, and (3) the likelihood of ” soft ” Hg2+ displacing the ” borderline ” Zn2+ bound to “harder” nitrogen/oxygen-containing side chains such as His and Asp/Glu. The results reveal that, relative to Hg2+, the lower positive charge on MeHg+ results in a longer and weaker bond with a given ligand, in accord with the observed kinetic liability of MeHg+ complexes. They also indicate that negatively charged or polar amino acid side chains containing S-/O-/S/N donors could coordinate to both organic MeHg+ and inorganic Hg2+. In addition, Gua and Cyt could also coordinate to MeHg+ and disrupt Gua(…)Cyt base pairing. A key novel finding is that Hg2+ is a far better electron acceptor than Zn2+, and can thus accept more negative charge from the Zn ligands than the native Zn2+, thus enhancing Hg-ligand interactions and enabling to displace the native cofactor from zinc essential enzymes and ” structural ” Zn proteins. The results herein support several possible mechanisms for Hg poisoning. Ways that mercury poisoning could be prevented in cells are discussed.

First author: Roy, LE, Magnetic coupling in dinuclear Gd complexes, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 568, (2006)
Abstract: A spin density functional (SDFT) study of carboxylate-bridged and diazenido-bridged dinuclear gadolinium compounds is presented. Calculated magnetic coupling constants for the carboxylate-bridged structures are in good agreement with experimental data, confirming the ability of the broken symmetry approach used in this work to predict magnetic behavior in such compounds. The systematic trend wherein symmetrically bridged complexes are antiferromagnetically coupled and asymmetrically bridged are ferromagnetically coupled is reproduced by the SDFT calculations. The mechanism underlying magnetic coupling in closed- and open-shell dinuclear complexes is described using a perturbative molecular orbital model that focuses the influence of the 4f(7)-5d exchange interaction on molecular orbitals with significant 5d-orbital character for the complex [{[(Me3Si)(2)N](2)(thf)Gd}(2)(N-2)]. Open-shell electronic configurations facilitate strong ferromagnetic coupling, whereas in closed-shell systems antiferromagnetic coupling is usually preferred.

First author: Segala, M, Geometry, solvent, and polar effects on the relationship between calculated core-electron binding energy shifts (Delta CEBE) and Hammett substituent (sigma) constants, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 758, 61, (2006)
Abstract: According to Lindberg et al. there exists an equation Delta CEBE=kappa sigma for substituted benzene derivatives. Core-electron binding energy shift (Delta CEBE) is the difference between the CEBE of a specific carbon in monosubstituted benzene derivatives (C6H5-Z) and in benzene (C6H5-H); K is related to a reaction constant and or is the experimental Hammett substituent constant. The object of the present work is to investigate geometry, solvent, and polar effects on Lindberg’s equation using theoretically calculated ACEBE. The CEBEs were calculated using DFT within the scheme Delta E-KS (PW86x-PW91c/TZP + C-rel). The geometry has only little effect on the CEBE values. A regression relation between ACEBE and 0, takes the form Delta CEBE = kappa sigma-C with K congruent to 1.17 and C congruent to 0.17. We estimated 69 sigma constants in water that have not been presented in the literature. Theoretical resonance (sigma(R)) and inductive (sigma(I)) effects were calculated using Taft equations. ACEBE (R) and ACEBE (1) effects on ACEBE were also calculated using Taft-like equations. The quality of the correlation to the resonance is better than that to the inductive effect, in water. The regression quality in aqueous organic solvent is poorer than in water in both Lindberg and Taft equations. The solvent effect is greater on the resonance than on the inductive effect.

First author: Wu, JZ, Tuning the photoinduced O-2-evolving reactivity of Mn4O47+, Mn4O46+, and Mn4O3(OH)(6+) manganese-oxo cubane complexes, INORGANIC CHEMISTRY, 45, 189, (2006)
Abstract: The manganese-oxo “cubane” core complex Mn4O4L61 (1, L-1 = Ph2PO2-), a partial model of the photosynthetic water oxidation site, was shown previously to undergo photodissociation in the gas phase by releasing one phosphinate anion, an O-2 molecule, and the intact butterfly core cation (Mn4O2L51+). Herein, we investigate the photochemistry and electronic structure of a series of manganese-oxo cubane complexes: [Mn4O4L62] (2), 1(+)(ClO4-), 2(+)(ClO4-), and Mn4O3(OH)L-6(1) (1H). We report the atomic structure of [Mn4O4L62](ClO4), 2(+)(ClO4-) [L-2 = (4-MeOPh)(2)-PO2-] UV photoexcitation of a charge-transfer band dissociates one phosphinate, two core oxygen atoms, and the Mn4O2L5+ butterfly as the dominant (or exclusive) photoreaction of all cubane derivatives in the gas phase, with relative yields: 1H >> 2 > 1 > 2(+) > 1(+). The photodissociation yield increases upon (1) reducing the core oxidation state by hydrogenation of a corner oxo (1H), (2) increasing the electron donation from the phosphinate ligand (L-2), and (3) reducing the net charge from +1 to 0. The experimental Mn-O bond lengths and Mn-O bond strengths and the calculated ligand binding energy explain these trends in terms of weaker binding of phosphinate L-2 versus L-1 by 14.7 kcal/mol and stronger Mn-(mu(3)-O)(core) bonds in the oxidized complexes 2(+) and 1(+) versus 2 and 1. The calculated electronic structure accounts for these trends in terms of the binding energy and antibonding Mn-O(core) and Mn-O'(ligand) character of the degenerate highest occupied molecular orbital (HOMO), including (1) energetic destabilization of the HOMO of 2 relative to 1 by 0.75 eV and (2) depopulation of the antibonding HOMO and increased ionic binding in 1(+) and 2(+) versus 1 and 2.

First author: Campanera, JM, Exohedral reactivity of trimetallic nitride template (TNT) endohedral metallofullerenes,JOURNAL OF ORGANIC CHEMISTRY, 71, 46, (2006)
Abstract: Fullerenes containing, a trimetallic nitride template (TNT) within the cage are a particularly interesting class of endohedral metallofullerenes. Recently two exohedral derivatives of the SC(3)N@C(80) fullerene have been synthesized: a Diels-Alder and a fulleropyrrolidine cycloadduct. The successful isolation, purification, and structural elucidation of these metallofullerenes derivatives have encouraged us to understand how the chemical reactivity is affected by TNT encapsulation. First of all, we predicted the most reactive exohedral sites, taking, into account the double bond character and the pyramidalization angle of the C-C bonds. For this purpose, a full characterization of all different types of C-C bonds of the following fullerenes was carried out: I(h)-C(60):1, D(3)-C(68):6140, D(3)-SC(3)N@C(68), D(5h)-C(70):1, D(3h)-C(78):5, D(3h)-S(C3)N@C(78), I(h)-C(80):7 and several isomers Of SC(3)N@C(80). Finally the exohedral reactivity of these TNT endohedral metallofullerenes, via [4 + 2] cycloaddition reactions of 1,3-butadiene, was corroborated by means of DFT calculations.

First author: Garipov, RR, Combined EPR and DFT study of the copper(II) complexes with N-phosphoryl thioureas,CHEMICAL PHYSICS, 320, 59, (2006)
Abstract: Copper(II) bis-complexes with N-phosphoryl thioureas, RN’HC(S) NP(O)(OPri)(2)(-) {R = phenyl (1), cyclohexyl (11)1, have been obtained and investigated in liquid and frozen toluene solutions, Equilibria between trans-S,N and cis-S,N -isomers have been revealed and described by EPR method. In contrast to more usual S,O-forms, trans-S,N-isomers demonstrate large superhyperfine splitting from N and P atoms simultaneously. From EPR spectra anisotropic hyperfine, superhyperfine, and g-tensor parameters obtained and the symmetry of the metal ion surrounding analyzed. Rhombic anisotropy of copper(II) hyperfine and axial symmetry of N and P superhyperfine splitting resolved. Structural, hydrodynamic, and magnetic characteristics of the complexes established experimentally were supported by DFT calculations. According to EPR. and DFT studies, tetrahedral distortion is higher in cis-S,N than in trans-S,N forms for steric reasons and slightly higher in I(S,N-trans) isomer than in II(S,N-trans) one due to the electrondonating effect of cyclobexyl substituent. The domination of S,N- over S,O-coordination is explained by the effects of the crystal field stabilization and the formation of the intramolecular hydrogen bonds.

First author: Petrie, S, Tertiary arsine adducts of iodoarsines: A structural and theoretical investigation,ORGANOMETALLICS, 25, 164, (2006)
Abstract: The Lewis acid-base adducts PhMe2As -> AsPhI2, PhMe2As -> AsMeI2, and PhMeEtAs -> AsMeI2 have been structurally characterized by single-crystal X-ray diffraction, and their structures and bonding investigated by density functional theory calculations at the PBE/TZP level of theory. The adduct PhMe2-As -> AsPhI2 crystallizes in the monoclinic space group Pna2(1). The coordination geometry around the arsenic atom of the iodoarsine in the adduct is distorted trigonal bipyramidal with the arsenic atom of the tertiary arsine being almost directly above the arsenic and orthogonal to the T-shaped iodoarsine at a distance of 2.456(1) angstrom. The nearest intermolecular neighbor to the arsenic of the iodoarsine in the structure is the phenyl group of the tertiary arsine of an adjacent molecule. The adduct PhMe2As -> AsMeI2 crystallizes in the monoclinic space group P2(1)/c. The core structure of this adduct is a dimer based on edge-sharing through iodine atoms in the basal MeAsI3 planes of two square pyramids in which the arsenic atoms of the tertiary arsines occupy the apical sites of the pyramids in a trans arrangement within the dimeric unit (As-As 2.4979(5) angstrom). The adduct PhMeEtAs -> AsMeI2 crystallizes in the space group Pbca. Intermolecular contacts between the arsenic of the T-shaped iodoarsine and an iodine of an adjacent molecule trans to the arsenic of the tertiary arsine generate helical -(-As-I-As-)-(n) chains of opposite helicity running through the unit cell. The calculations indicate that the molecular orbitals most directly associated with the As-As bonding in the adducts do not show any significant contribution from the virtual orbitals of either arsenic subunit. The theoretical results, which give As-As bond energies of 10-30 kJ mol(-1) for the three adducts, are consistent with the ready dissociation of the adducts in solution and the importance of intermolecular interactions in stabilizing the complexes in the solid state.

First author: Muller, J, 6-Nitro-1-deazapurine, ACTA CRYSTALLOGRAPHICA SECTION E-STRUCTURE REPORTS ONLINE, 62, O223, (2006)
Abstract: The title compound, C6H4N4O2, is a potential nucleobase surrogate. In the crystal structure, molecules are linked by intermolecular N-H center dot center dot center dot N hydrogen bonds [H center dot center dot center dot N = 1.88 (3) angstrom] to form one-dimensional chains in the b-axis direction.

First author: Bickelhaupt, FM, alpha-Stabilization of carbanions: Fluorine is more effective than the heavier halogens,ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 45, 823, (2006)
Abstract: The title compound, C6H4N4O2, is a potential nucleobase surrogate. In the crystal structure, molecules are linked by intermolecular N-H center dot center dot center dot N hydrogen bonds [H center dot center dot center dot N = 1.88 (3) angstrom] to form one-dimensional chains in the b-axis direction.

First author: Buchin, Beatrice, “Naked” Ga+ and In+ as pure acceptor ligands: Structure and bonding of [GaPt(GaCp*)(4)][BArF], ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 45, 5207, (2006)
Abstract: The title compound, C6H4N4O2, is a potential nucleobase surrogate. In the crystal structure, molecules are linked by intermolecular N-H center dot center dot center dot N hydrogen bonds [H center dot center dot center dot N = 1.88 (3) angstrom] to form one-dimensional chains in the b-axis direction.

First author: Santo, Ryoko, Diamagnetic-paramagnetic conversion of tris(2-pyridylthio)methylcopper(II) through a structural change from trigonal bipyramidal to octahedral, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 45, 7611, (2006)
Abstract: The title compound, C6H4N4O2, is a potential nucleobase surrogate. In the crystal structure, molecules are linked by intermolecular N-H center dot center dot center dot N hydrogen bonds [H center dot center dot center dot N = 1.88 (3) angstrom] to form one-dimensional chains in the b-axis direction.

First author: Rodriguez-Fortea, Antonio, Dancing on a fullerene surface: Isomerization of Y3N@(N-ethylpyrrolidino-C-80) from the 6,6 to the 5,6 regioisomer, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 45, 8176, (2006)
Abstract: The title compound, C6H4N4O2, is a potential nucleobase surrogate. In the crystal structure, molecules are linked by intermolecular N-H center dot center dot center dot N hydrogen bonds [H center dot center dot center dot N = 1.88 (3) angstrom] to form one-dimensional chains in the b-axis direction.

First author: Terreux, R, Interactions study between the copper II ion and constitutive elements of chitosan structure by DFT calculation, BIOMACROMOLECULES, 7, 31, (2006)
Abstract: Molecular modeling is particularly useful to understand interactions between various kinds of molecules and ions. This study is aimed at studying the interactions between one Cu2+ ion and one or several glucosamine residues. The geometries and the interaction energies of all of the complexes involving all of the dimers obtained from glucosamine and N-acetylglucosamine were computed by means of density functional theory (DFT) methods. In a first step, for the two dimers A-A and A-B (A for glucosamine and B for N-acetyl glucosamine), a starting geometry was built, and the energies were calculated using a rigid rotation of 30 degrees intervals for each of the dihedral angles (Phi and psi) of the glycosidic bond, spanning the whole angular range. These calculations allowed us to retrieve the minimal energy conformation and investigate all possible conformations. The results were compared to some experimental data. In a second step, we investigated the interactions of Cu2+ with the different possible coordination sites of A. For all complexes considered, the Cu2+ site was completed with H2O and/or OH- ligands to have a global neutral charge. The calculations confirmed that the most stable interactions involved the free amino site in a “pending complex”. Another pending form was possible considering the participation of the heterocyclic O site, but the latter was less favored. On the other hand, we also showed that glucosamine could not act as a bidentate ligand and that N-acetyl glucosamine was not coordinating with Cu2+. Finally, our results evidenced a cooperative fixation of Cu2+ ions when considering the complexation of two successive metal ions on the two consecutive glucosamine residues of the dimer A-A.

First author: Fernandez, Israel, pi-conjugation in donor-substituted cyanoethynylethenes: an EDA study, CHEMICAL COMMUNICATIONS, 7, 5030, (2006)
Abstract: pi-Conjugation in several donor-substituted cyanoethynylethenes was estimated using energy decomposition analysis (EDA); very good linear correlations between the Delta E-pi values and experimental data are found.

First author: Willans, MJ, An investigation of lanthanum coordination compounds by using solid-state La-139 NMR spectroscopy and relativistic density functional theory, CHEMISTRY-A EUROPEAN JOURNAL, 12, 159, (2006)
Abstract: Lanthanum-139 NMR spectra of stationary samples of several solid La-III coordination compounds have been obtained at applied magnetic fields of 11.75 and 17.60 T The breadth and shape of the La-139 NMR spectra of the central transition are dominated by the interaction between the La-139 nuclear quadrupole moment and the electric field gradient (EFG) at that nucleus; however, the influence of chemical-shift anisotropy on the NMR spectra is non-negligible for the majority of the compounds investigated. Analysis of the experimental NMR spectra reveals that the La-139 quadrupolar coupling constants (C-Q) range from 10.0 to 35.6 MHz, the spans of the chemical-shift tensor (Omega) range from 50 to 260 ppm, and the isotropic chemical shifts (delta(iso)) range from -80 to 178 ppm. In general, there is a correlation between the magnitudes of C-Q and Omega, and delta(iso) is shown to depend on the La coordination number. Magnetic-shielding tensors, calculated by using relativistic zeroth-order regular approximation density functional theory (ZORA-DFT) and incorporating scalar only or scalar plus spin-orbit relativistic effects, qualitatively reproduce the experimental chemical-shift tensors. In general, the inclusion of spin-orbit coupling yields results that are in better agreement with those from the experiment. The magnetic-shielding calculations and experimentally determined Euler angles can be used to predict the orientation of the chemical-shift and EFG tensors in the molecular frame. This study demonstrates that solid-state La-139 NMR spectroscopy is a useful characterization method and can provide insight into the molecular structure of lanthanum coordination compounds.

First author: Kozmon, Stanislav, DFT study on 3-substituted tetrahydropyran-2-yl radicals, COLLECTION OF CZECHOSLOVAK CHEMICAL COMMUNICATIONS, 71, 1453, (2006)
Abstract: A series of tetrahydropyran-2-yl radical ( 1) analogs was studied using density functional theory (DFT) to model conformational behavior of glycopyranosyl radicals. Calculations of the structure and stability of the C-4(1), C-1(4), B-2,B-5, B-O,B-3, and H-4(3) ring conformers for tetrahydropyran-2- yl radical ( 1) and for 3-fluoro- (2, 7), 3-hydroxy- (3, 8), 3-methoxy- (4, 9), 3-acetoxy( 5, 10), and 3-(benzyloxy) tetrahydropyran-2-yl (6, 11) derivatives showed that conformational behavior of the 3- substituted radicals depends on both the electronic character and orientation of the C3 substituent. The calculations show that radical 1 is slightly pyramidal and exists as an equilibrium mixture of the C-4(1) and C-1(4) conformers. Substituents at the C3 position force 2 – 11 radicals to adopt a chair conformation with the substituent in the axial orientation. Thus radicals 2 – 6 prefer the C-1(4) conformer though there are several ring conformers in equilibrium whereas for radicals 7 – 11 the C-4(1) conformer predominates. The calculated preferences are consistent with available ESR data. These results provide further support for the importance of quasi-homoanomeric interactions on stability of anomeric radicals.

First author: Cozzolino, AF, The effect of steric hindrance on the association of telluradiazoles through Te-N secondary bonding interactions, CRYSTAL GROWTH & DESIGN, 6, 181, (2006)
Abstract: DFT calculations were used to compare the magnitude of steric repulsion to the strength of secondary bonding interactions (SBIs) in the (Te-N)(2) supramolecular synthon to explain or predict the supramolecular structures assembled by two derivatives of the 1,2,5-telluradiazole ring: benzo-2,1,3-telluradiazole (4c) and 3,6-dibromobenzo-2,1,3-telluradiazole (5). The crystallographically determined structures were consistent with the computational predictions. In sharp contrast with the previously known structures of its sulfur and selenium analogues, 4c forms infinite ribbon chains in the solid state with 2.6;2(7)-2.720(7) angstrom Te-N SBIs. Steric hindrance in 5 restricted the supramolecular association to form discrete dinners with 2.697(8) angstrom Te-N SBIs. In addition to discrete dinners, the dibromo derivative crystallizes as solvated dimers in 5-DMSO with 2.834(5) angstrom Te-O SBIs. Other weaker SBIs were identified in the crystal lattices and were assessed by the computational method.

First author: Jimenez-Rodriguez, C, SPANphos: trans-spanning diphosphines as cis chelating ligands!, DALTON TRANSACTIONS, 6, 268, (2006)
Abstract: Several SPANphos ligands based on a spirobichroman backbone, introduced as a putative trans ligand, form compounds of the type [Rh(nbd)(SPANphos)] BF(4) (1 – 6) in which both norbornadiene and SPANphos act as cis chelating ligands. The cyclooctadiene rhodium chloride derivatives form bimetallic complexes. Crystal structures for several of these compounds and free ligands are reported. Semiemperical AM1 and DFT calculations show that spirobichroman can assume several conformations, some of which are suitable for the formation of cis chelating SPANphos. All calculations on SPANphos complexes of PdCl(2), PtCl(2) and Rh(CO) Cl show that the trans complex is more stable by 4 – 10 kcal mol(-1). The cis conformation in 1 – 6 is enforced by the cis chelating norbornadiene ligand.

First author: Poater, A, A trinuclear Pt(II) compound with short Pt-Pt-Pt contacts. An analysis of the influence of pi-pi stacking interactions on the strength and length of the Pt-Pt bond, DALTON TRANSACTIONS, 6, 1188, (2006)
Abstract: In this work we report the first example of a trinuclear Pt(II) complex with Pt-Pt-Pt bonds that are not facilitated by direct intervention of bridging ligands but are partially held by the attractive pi-pi stacking interaction between the phenyl units of the 4,4′-dimethyl- 2,2′-bipyridyl ligands. The effect of the pi-pi stacking interactions on the strength and length of the Pt-Pt bond has been discussed using reduced models of the interacting moieties in which the aromatic rings have been removed. The nature of the Pt-Pt bonds has been studied through energy decomposition and atoms-in-molecules analyses. The results indicate that the relatively strong (about 40 kcal mol(-1)) Pt-Pt metallic bond has similar covalent and ionic contributions.

First author: Schneider, SK, A first structural and theoretical comparison of pyridinylidene-type rNHC (remote N-heterocyclic carbene) and NHC complexes of Ni(II) obtained by oxidative substitution, DALTON TRANSACTIONS, 6, 1226, (2006)
Abstract: A series of cationic pyridinylidene and quinolinylidene complexes of chlorobis(triphenylphosphine)nickel(II) were prepared by oxidative substitution of Ni(PPh3)(4) with methylated chloropyridines or chloroquinolines. NMR as well as X-ray crystallographic studies confirmed the trans arrangement of the two phosphines in the products. Calculations, using suitable model compounds at the BP86/TZVP level, clearly differentiate between a standard imidazolylidene complex and new complexes of the NHC-type on the one hand, and new complexes classified as rNHC-types – with the heteroatom distant from the carbene carbon – on the other. The latter form significantly stronger bonds – mainly of an electrostatic nature – with the metal.

First author: Cavigliasso, G, Periodic trends in metal-metal interactions in face-shared [M(2)Cl(9)](z-) systems, DALTON TRANSACTIONS, 6, 2017, (2006)
Abstract: The periodic trends in metal-metal interactions in even-electron and mixed-valence [M(2)Cl(9)](z-) face- shared systems, involving transition metals in Groups 4 to 8 and electronic configurations ranging from d(1)d(1) through to d(5)d(5) and from d(1)d(2) through to d(4)d(5), have been investigated by calculating metal-metal bonding and spin polarization (exchange) effects using density functional theory. These two terms are in opposition to one another and their relative difference determines the extent to which the metal-based electrons are delocalized and thus the degree of metal-metal bonding. Remarkably strong linear correlations between the two terms, and between each term and the square of the spin density on the metal centres, have been obtained for all group and period series considered, and are discussed in terms of their dependence on the metal orbital properties and electron density.

First author: Ingram, Kieran I. M., Density functional theory investigation of the geometric and electronic structures of [UO(2)(H(2)O)(m)(OH)(n)](2-n) (n+m=5), DALTON TRANSACTIONS, 6, 2403, (2006)
Abstract: Gradient corrected density functional theory has been used to calculate the geometric and electronic structures of the family of molecules [UO(2)(H(2)O)(m)(OH)(n)](2-n) (n + m = 5). Comparisons are made with previous experimental and theoretical structural and spectroscopic data. r(U-O(yl)) is found to lengthen as water molecules are replaced by hydroxides in the equatorial plane, and the (nu) over tilde (sym) and (nu) over tilde (asym) uranyl vibrational wavenumbers decrease correspondingly. GGA functionals (BP86, PW91 and PBE) are generally found to perform better for the cationic complexes than for the anions. The inclusion of solvent effects using continuum models leads to spurious low frequency imaginary vibrational modes and overall poorer agreement with experimental data for (nu) over tilde (sym) and (nu) over tilde (asym). Analysis of the molecular orbital structure is performed in order to trace the origin of the lengthening and weakening of the U-O(yl) bond as waters are replaced by hydroxides. No evidence is found to support previous suggestions of a competition for U 6d atomic orbitals in U-O(yl) and U-O(hydroxide) pi bonding. Rather, the lengthening and weakening of U-O(yl) is attributed to reduced ionic bonding generated in part by the sigma-donating ability of the hydroxide ligands.

First author: Llewellyn, Simon A., Migratory insertion in N-heterocyclic carbene-containing Fe carbonyl complexes: an experimental and theoretical study, DALTON TRANSACTIONS, 6, 2535, (2006)
Abstract: The compound [Fe(eta-C5H5)(CO)(2)( Me)] reacts thermally with N-heterocyclic carbenes (L) to give both alkyl, [Fe(eta-C5H5)(L)(CO)(Me)], and acyl, [Fe(eta-C5H5)(L)(CO)(COMe)], derivatives. The reaction temperature has been shown to affect the product distribution. The alkyl and acyl derivatives exist in an equilibrium that is more easily perturbed than in the tertiary phosphine analogues. DFT studies on the reactivity of [Fe(eta-C5H5)(CO)(2)( Me)] with PH3 and dihydroimidazole-2-ylidene (IH) have shown that CO exchange is energetically favoured for IH, and energetically disfavoured for PH3. The products of CO-induced migratory insertion, [Fe(eta-C5H5)(L)(CO)(COMe)], are more stable than the parent alkyl, [Fe(eta-C5H5)(L)(CO)(Me)], compounds. This stabilisation is larger when L = IH than when L = PH3. Stabilisation of the transition state by agostic interactions was seen in both instances, but this was significantly more pronounced for L = IH.

First author: Koch, KR, Pt-195 NMR and DFT computational methods as tools towards the understanding of speciation and hydration/solvation of [PtX6](2-)(X = Cl-, Br-) anions in solution, DALTON TRANSACTIONS, 6, 3277, (2006)
Abstract: Pt-195 NMR together with DFT calculations and MD simulations, offer a powerful toolkit with which to probe the hydration shells of the [PtCl6](2-) anions, which may lead to a more profound understanding of the solute-solvent interactions of such complexes.

First author: Calhorda, Maria Jose, Group 11 complexes with the bis(3,5-dimethylpyrazol-1-yl) methane ligand. How secondary bonds can influence the coordination environment of Ag(I): the role of coordinated water in [Ag-2(mu-L)(2)(OH2)(2)](OTf)(2), DALTON TRANSACTIONS, 6, 4104, (2006)
Abstract: The complexation properties of the ligand bis(3,5-dimethylpyrazol-1-yl) methane ( L) towards group 11 metals have been studied. The reaction in a 1 : 1 molar ratio with [Cu(NCMe)(4)] PF6 or Ag(OTf) complexes gives the mononuclear [CuL(NCMe)] PF6 ( 1), with crystallographic mirror symmetry, or dinuclear [Ag-2(mu-L)(2)](OTf)(2) ( 2) ( OTf = trifluoromethanesulfonate) in which the ligand bridges both silver centres, an unprecedented mode of coordination for this type of ligands. Compound 2 crystallizes with two water molecules and forms a supramolecular structure through classical hydrogen bonding. The reaction in a 2 : 1 ratio affords in both cases the four-coordinated derivatives [ML2] X ( M = Cu, X = PF6 ( 3); Ag, X = OTf ( 4)). The treatment of [Ag(OTf)(PPh3)] with the ligand L gives [AgL(PPh3)] OTf (5). The gold( I) derivative [Au-2(C6F5)(2)(mu-L)] ( 6) has also been obtained by reaction of L with two equivalents of [Au(C6F5)( tht)]. These complexes present a luminescent behaviour at low temperature; the emissions being mainly intraligand but enhanced after coordination of the metal. Compounds 1 – 4 have been characterized by X-ray crystallography. DFT studies showed that, in the silver complex 2, coordination of H2O to Ag in the binuclear complex is favoured by formation of a hydrogen-bonding network, involving the triflato anion, and releasing enough energy to allow distortion of the Ag-2 framework.

First author: Ballivet-Tkatchenko, Danielle, Insertion reaction of carbon dioxide into Sn-OR bond. Synthesis, structure and DFT calculations of di- and tetranuclear isopropylcarbonato tin(IV) complexes, DALTON TRANSACTIONS, 6, 5167, (2006)
Abstract: The reaction of carbon dioxide with the stannane (n)Bu(2)Sn(O(i)Pr)(2) and distannoxane [(n)Bu(2)((i)PrO) Sn](2)O leads to the selective insertion into one Sn – O(i)Pr bond generating the corresponding (n)Bu(2)Sn(O(i)Pr)(OCO(2) (i)Pr) and (n)Bu(2)((i)PrO) SnOSn(OCO(2) (i)Pr)(n)Bu(2) species. Both compounds are characterised by multinuclear NMR, FT-IR and single-crystal X-ray crystallography. In the solid state, they adopt a dimeric arrangement with bridging isopropoxy and terminal isopropylcarbonato ligands. The X-ray crystal structure of the dinuclear stannane shows that the Sn(2)O(2) ring and the two Sn – OCO(2)C fragments are nearby coplanar. The same holds for the ladder-type tetranuclear distannoxane. The dimeric structures are also evidenced by solution NMR in non-coordinating solvents. Interestingly, the assignment of the exo and endo tin resonances of the dimeric distannoxane is unambiguous using a labeled (13)CO(2) experiment. The stability of the dimeric association has been probed in the stannane series on the basis of DFT calculations.

First author: Cavigliasso, German, Metal-metal bonding in molecular actinide compounds: electronic structure of [M2X8](2-) (M = U, Np, Pu; X = Cl, Br, I) complexes and comparison with d-block analogues, DALTON TRANSACTIONS, 6, 5476, (2006)
Abstract: Density functional and multiconfigurational ( ab initio) calculations have been performed on [M2X8](2-) (X = Cl, Br, I) complexes of 4d (Mo, Tc, Ru), 5d (W, Re, Os), and 5f (U, Np, Pu) metals in order to investigate general trends, similarities and differences in the electronic structure and metal-metal bonding between f-block and d-block elements. Multiple metal-metal bonds consisting of a combination of sigma and pi interactions have been found in all species investigated, with delta-like interactions also occurring in the complexes of Tc, Re, Np, Ru, Os, and Pu. The molecular orbital analysis indicates that these metal-metal interactions possess predominantly d(z2) (sigma), d(xz) and d(yz) (pi), or d(xy) and d(x2-y2) (delta) character in the d-block species, and f(z3) (sigma), f(z2x) and f(z2y) (pi), or f(xyz) and f(z) (delta) character in the actinide systems. In the latter, all three (sigma, pi, delta) types of interaction exhibit bonding character, irrespective of whether the molecular symmetry is D-4h or D-4d. By contrast, although the nature and properties of the sigma and p bonds are largely similar for the D-4h and D-4d forms of the d-block complexes, the two most relevant metal-metal delta-like orbitals occur as a bonding and antibonding combination in D-4h symmetry but as a nonbonding level in D-4d symmetry. Multiconfigurational calculations have been performed on a subset of the actinide complexes, and show that a single electronic configuration plays a dominant role and corresponds to the lowest-energy configuration obtained using density functional theory.

First author: Bagno, A, Relativistic DFT calculation of Sn-119 chemical shifts and coupling constants in tin compounds,JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 2, 37, (2006)
Abstract: The nuclear shielding and spin-spin coupling constants of Sn-119 in stannane, tetramethylstannane, methyltin halides Me4-nSnXn (X = Cl, Br, l; n = 1-3), tin halides, and some stannyl cations have been investigated computationally by DFT methods and Slater all-electron basis sets, including relativistic effects by means of the zeroth order regular approximation (ZORA) method up to spin-orbit coupling. Calculated Sn-119 chemical shifts generally correlate well with experimental values, except when several heavy halogen atoms, especially iodine, are bound to tin. In such cases, calculated chemical shifts are almost constant at the scalar (spin-free) ZORA level; only at the spin-orbit level is a good correlation, which holds for all compounds examined, attained. A remarkable ” heavy-atom effect ”, analogous to that observed for analogous alkyl halides, is evident. The chemical shift of the putative stannyl cation (SnH3+) has also been examined, and it is concluded that the spectrum of the species obtained in superacids is inconsistent with a simple SnH3+ structure; strong coordination to even weak nucleophiles such as FSO3H leads to a very satisfactory agreement. On the contrary, the calculated Sn-119 chemical shift of the trimesitylstannyl cation is in very good agreement with the experimental value. Coupling constants between Sn-119 and halogen nuclei are also well-modeled in general (taking into account the large uncertainties in the experimental values); relativistic spin-orbit effects are again quite evident. Couplings to C-13 and H-1 also fall, on the average, on the same correlation line, but individual values show a significant deviation from the expected unit slope.

First author: Volkov, A, Dependence of the intermolecular electrostatic interaction energy on the level of theory and the basis set, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 2, 81, (2006)
Abstract: As electrostatic forces play a prominent role in the process of folding and binding of biological macromolecules, an examination of the method dependence of the electrostatic interaction energy is of great importance. An extensive analysis of the basis set and method dependence of electrostatic interaction energies (E-es) in molecular systems using six test dimers of a-glycine is presented. A number of Hartree-Fock, Kohn-Sham, Moller-Plesset, configuration interaction (Cl), quadratic Cl, and coupled cluster calculations were performed using several double-, triple-, and quadruple-zeta-quality Gaussian- and Slater-type (Kohn-Sham calculations only) basis sets. The main factor affecting E-es was found to be the inclusion of diffuse functions in the basis set expansions. Moller-Plesset (even at second order), quadratic Cl, and coupled cluster calculations produce the most consistent results. Hartree-Fock and Cl methods usually overestimate the E-es while the Kohn-Sham approach tends to underestimate the magnitude of the electrostatic interaction. The combination of the transferable-pseudoatom databank and the exact potential and multipole moment method reproduces Kohn-Sham B3LYP/6-31G** results on which it is based, confirming the excellent transferability of the pseudoatom densities within the systems studied. However, because Kohn-Sham calculations with double-zeta-quality basis sets show considerable deviations from advanced correlated methods, further development of the databank using electron densities from such methods is highly desirable.

First author: Zhang, Yi-Quan, Magnetostructural correlations in the cyano-bridged CrNi, Cr2Ni and Cr2Ni6 complexes: density functional theory calculations, JOURNAL OF MATERIALS CHEMISTRY, 16, 4657, (2006)
Abstract: A theoretical density functional study of the magneto-structural correlations in a series of the cyano-bridged CrnNim systems is presented. Two approaches with several LDA and GGA functionals gave the result that the ferromagnetic coupling interactions between the nearest-neighbors CrNi weaken with the increase of the number of exchange interactions and the decrease of the Ni -N-brid-C(bri)d angles. Moreover, Kahn’s qualitative theory succeeded in being applied to interpret the relationships J approximate to n ( the number of exchange interactions) and J approximate to theta ( the Ni-N-brid-C-brid angle) through the overlap integral S-ij and the spin density populations on Cr( III) and Ni( II).

First author: Lillehaug, S, Catalytic clehydrogenation of ethane over mononuclear Cr(III)-silica surface sites. Part 2: C-H activation by oxidative addition, JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, 19, 25, (2006)
Abstract: Models of Cr(III)-silica were used to study C-H activation in ethane by oxidative addition as a possible route to catalytic dehydrogenation. This mechanism involves a formal double oxidation of chromium and a minimum energy crossing point (MECP) was located on the seam between the quartet spin potential energy surface of Cr(III) and the doublet spin potential energy surface of Cr(V). Subsequent to the change of spin state, the C-H activation path passes through a transition state on the doublet potential surface, leading to the formation of an ethylhydridochromium(V) complex. This complex represents only a shallow minimum on the potential energy surface and beta-hydrogen transfer to complete the catalytic cycle must therefore take place in the extension of the C-H activation step. The combination of a significant activation energy and a small pre-exponential factor in the rate constant makes C-H activation by oxidative addition an unlikely mechanism for dehydrogenation in this system.

First author: Makowska-Janusik, M., Interface effects on the NLO properties of guest-host materials, MATERIALS SCIENCE-POLAND, 24, 25, (2006)
Abstract: Electro-optical properties of silicon carbide (SiC) nano-sized clusters embedded into three different polymeric matrices, i.e., poly(methyl methacrylate, poly-N-vinylcarbazole and polycarbonate were investigated. Electric properties of SiC were calculated using time-dependent DFT methods considering an isolated cluster and environmental effects. The concept of the polymeric influence on optical properties of chromophores was executed by the local electric field approach. Electric field created by charge distribution of the surrounding polymer was calculated using guest-host structures obtained by the molecular dynamics simulations. Optical properties of SiC situated in polymeric environments differ from those of free clusters. It is seen more significantly for the hyperpolarizability than for the polarizability. The spatial distribution of SiC in the matrix depends on the kind of polymer and gives an important influence on the obtained local electric field value. The Si-C distances do not change with variation of the polymeric matrix. The geometry of 3C-SiC is very stable and does not change during MD simulations performed at 300 K.

First author: Takenaka, H, Guest atom displacements in silicon cluster Na-2@Si50H44, MATERIALS TRANSACTIONS,47, 63, (2006)
Abstract: We present the displacements of the guest sodium atoms in double caged Na-2@Si50H44 cluster. The cluster consists of a piece of clathrate II consisting of two adjacent Si-28 cages filled with guest sodium atoms, being hydrogenated in order to terminate the dangling bonds. Although in a single Si28H28 cage the endohedral sodium atom locates at the center, the sodium atoms in each of the double cage cluster displace about 0.06 nm away from cacti center of the cages to form a dimer between the endohedral sodium atoms. The displacements are attributed to the formation of covalent bond between the endohedral sodium atoms and the ionic bonding between the sodium atoms and the cage silicon atoms.

First author: Casellas, Helene, Crystallographic evidence of theoretically novel anion-pi interactions, NEW JOURNAL OF CHEMISTRY, 30, 1561, (2006)
Abstract: The reaction of Cu(NO3)(2)center dot 3H(2)O with the multidentate ligand N,N’,N ”,N”’- tetrakis{2,4-bis (di-2-pyridylamino)-1,3,5-triazin-6-yl} triethylenetetramine (dpatta) in acetonitrile at high temperature and pressure results in the formation of the tetranuclear coordination compound [Cu-4(dpatta)(NO3)(4)](NO3)(4)center dot 12H(2)O ( 1), whose crystal structure exhibits remarkable anion-pi interactions which have been calculated, considering the unexpected position of the anion toward the aromatic ring.

First author: Jacob, CR, Comparison of frozen-density embedding and discrete reaction field solvent models for molecular properties, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 8, 2349, (2006)
Abstract: We investigate the performance of two discrete solvent models in connection with density functional theory (DFT) for the calculation of molecular properties. In our comparison we include the discrete reaction field (DRF) model, a combined quantum mechanics and molecular\mechanics (QM/MM) model using a polarizable force field, and the frozen-density embedding (FDE) scheme. We employ these solvent models for ground state properties (dipole and quadrupole moments) and response properties (electronic excitation energies and frequency-dependent polarizabilities) of a water molecule in the liquid phase. It is found that both solvent models agree for ground state properties, while there are significant differences in the description of response properties. The origin of these differences is analyzed in detail and it is found that they are mainly caused by a different description of the ground state molecular orbitals of the solute. In addition, for the calculation of the polarizabilities, the inclusion of the response of the solvent to the polarization of the solute becomes important. This effect is included in the DRF model, but is missing in the FDE scheme. A way of including it in FDE calculations of the polarizabilities using finite field calculations is demonstrated.

First author: Willans, MJ, An NMR and relativistic DFT investigation of one-bond nuclear spin-spin coupling in solid triphenyl group-14 chlorides, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 8, 2733, (2006)
Abstract: A solid-state nuclear magnetic resonance and zeroth-order regular approximation density functional theory, ZORA-DFT, study of one-bond nuclear spin-spin coupling between group-14 nuclei and quadrupolar Cl-35/37 nuclei in triphenyl group-14 chlorides, Ph3XCl ( X = C, Si, Ge, Sn and Pb), is presented. This represents the first combined experimental and theoretical systematic study of spin-spin coupling involving spin- pairs containing quadrupolar nuclei. Solid-state NMR spectra have been acquired for all compounds in which X has a spin- 1/2 isotope-C-13, Si-29, ([117/119]) Sn and Pb-207-at applied magnetic fields of 4.70, 7.05 and 11.75 T. From simulations of these spectra, values describing the indirect spin-spin coupling tensor – the isotropic indirect spin – spin coupling constant, (1)J(X,Cl-35/37)(iso) and the anisotropy of the J tensor, Delta(1)J(X,Cl-35/ 37)-have been determined for all but the lead – chlorine spin- pair. To better compare the indirect spin – spin coupling parameters between spin- pairs, (1)J(iso) and Delta(1)J values were converted to their reduced coupling constants, K-1(iso) and Delta K-1. From experiment, the sign of K-1(iso) was found to be negative while the sign of Delta K-1 is positive for all spin- pairs investigated. The magnitude of both K-1(iso) and Delta K-1 was found to increase as one moves down group-14. Theoretical values of the magnitude and sign of K-1(iso) and Delta K-1 were obtained from ZORA-DFT calculations and are in agreement with the available experimental data. From the calculations, the Fermi-contact mechanism was determined to provide the largest contribution to K-1(iso) for all spin- pairs while spin- dipolar and paramagnetic spin – orbit mechanisms make significant contributions to the anisotropy of K. The inclusion of relativistic effects was found to influence K (Sn, Cl) and K(Pb, Cl).

First author: van Besien, Els, Electronic spectra of uranyl chloride complexes in acetone: a CASSCF/CASPT2 investigation, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 8, 4311, (2006)
Abstract: A theoretical study is presented of the electronic spectra of the complexes UO(2)Cl(2)ac(4), UO(2)Cl(2)ac(3), [UO(2)Cl(3)ac(2)](-) and [UO(2)Cl(3)ac](-) (ac = acetone) using perturbation theory based on a complete-active-space type wavefunction (CASSCF/CASPT2). Both scalar relativistic effects and spin-orbit coupling were included in the calculations. The calculated excitation energies and oscillator strength values have been compared to the experimental absorption spectrum for uranyl chloride complexes in acetone solution, for chloride-to-uranyl ratios between two and three. The main purpose of this work was to investigate the origin of the remarkable intensity increase observed in the lower part of the experimental absorption spectra, upon addition of chloride to uranyl complexes in acetone. The calculated excitation energies for the different complexes are similar and closely correspond to the experimental data. However, in none of the theoretical spectra, the high intensities observed in the lower part of the experimental spectrum are reproduced.

First author: Mayer, I., Energy partitioning schemes, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 8, 4630, (2006)
Abstract: The paper gives an overview, generalization and systematization of the different energy decomposition schemes we have devised in the last few years by using both the 3-D analysis (the atoms are represented by different parts of the physical space) and the Hilbert space analysis in terms of the basis orbitals assigned to the individual atoms. The so called “atomic decomposition of identity” provides us the most general formalism for analyzing different physical quantities in terms of individual atoms or pairs of atoms. (The “atomic decomposition of identity” means that we present the identity operator as a sum of operators assigned to the individual atoms.) By proper definitions of the atomic operators, both Hilbert-space and the different 3-D decomposition schemes can be treated on an equal footing. Several different but closely related energy decomposition schemes have been proposed for the Hilbert space analysis. They differ by exact or approximate treatment of the three-and four-center integrals and by considering the kinetic energy as a part of the atomic Hamiltonian or as having genuine two-center components, too. (Also, some finite basis correction terms may be treated in different manners.) The exact schemes are obtained by using the “atomic decomposition of identity”. In the approximate schemes a projective integral approximation is also introduced, thus the energy components contain only one- and two-center integrals. The diatomic energy contributions have also been decomposed into terms of different physical nature (electrostatic, exchange etc.) The 3-D analysis may be performed either in terms of disjunct atomic domains, as in the case of the AIM formalism, or by using the so called “fuzzy atoms” which do not have sharp boundaries but exhibit a continuous transition from one to another. The different schemes give different numbers, but each is capable of reflecting the most important intramolecular interactions as well as the secondary ones-e.g. intramolecular interactions of type C-H center dot center dot center dot O.

First author: Lumetta, Gregg J., Potential application of Klaui ligands in actinide separations, SEPARATIONS FOR THE NUCLEAR FUEL CYCLE IN THE 21ST CENTURY, 933, 201, (2006)
Abstract: We have undertaken a systematic experimental and computational study of the complexation of Cp*Co[P(O)(OR)(2)](3)(-) (Cp* = pentamethylcyclopentadienyl) ligands with f-block metal ions (i.e., lanthanides and actinides). As part of this work, the complexation of La 31 ion with Cp*Co[P(O)(OR)(2)](3)(-) ligands has been studied as the alkyl group was systematically varied from methyl to n-propyl (R = -CH3, -CH2CH3, and -CH2CH2CH3). For ligands in which R = -CH3 or -CH2CH3, complexes with ligand-to-La stoichiometries of 1: 1 and 2:1 were formed. In contrast, only the 1:1 complex was isolated when R=-CH2CH2CH3. Computational modeling indicates that the coordination number for La in the 1:1 and 2:1 complexes is 8 and 9, respectively. A prototypical extraction chromatography resin containing Cp*Co[P(O)(OEt)(2)](3)(-) (1b) has been prepared. The resin consists of 0.75 wt% 1b on Amberlite (R) XAD-7. This resin strongly sorbs Am3+ and Pu4+. The sorption of these ions decreases with increasing nitric acid concentration, but this effect is more pronounced for Am3+. This allows for convenient separation of Am3+ from Pu4+ by simple adjustments in the HNO3 concentration. The tripodal geometry of 1b disfavors the complexation Of UO22+, so sorption of U(VI) by the 1b-containing resin is weak.

First author: Reinen, Dirk, The binding properties of terminal and bridging fluoride and of aqua ligands – a semiempirical vibronic coupling and DFT study of mixed-ligand manganese(III) complexes, ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 632, 1375, (2006)
Abstract: A combined vibronic coupling and angular overlap analysis of M(III)L6 complexes, supplemented by basic DFT calculations, is performed where the 3d cations are Cru(III), Fe-III or the Jahn-Teller unstable Mn cation, and the ligands L fluoride – in terminal (F-t) or in bridging (F-b) function – or OH2. Our approach is mostly semiempirical and based on a novel ligand strain model, which utilises available structural and spectroscopic data and mostly deals with mixed-ligand Mn-III complexes, containing simultaneously F-t, F-b and H2O. Surveying the great number of published structural data, some interesting results concerning the differing binding properties are derived. While the total bond covalency is similar for the three ligands, the total bond strength – and hence also the ionic bond increment – follows the sequence: F-t >> OH2 > F-b. Partitioning the bond covalency into a part, which measures the ligand-to-metal charge flow (a), and an increment stemming from orbital (predominantly sigma-) overlap (b), one obtains: F-t >> F-b > OH, for (a) and the reverse sequence for (b).DFT model calculations on the [M-III(F-t)(6)](3-) polyhedra in a solvent continuum were the basis for the elucidation of reliable ground state potential energy surfaces also for the further investigated complexes. The sometimes only very small energy difference between the involved three minima, generated via the interaction with the Jahn-Teller active vibrational F, mode, led to various orthorhombic distortion conformers in the range between the tetragonal elongation and compression, depending on the strain magnitude imposed on the [Mn(F-t)(6)](3-) parent polyhedron by a F-t-by-F-b (or OH2) substitution. It is further remarkable, that the average bond length of the Jahn-Teller distorted octahedron varies significantly with the extent of the deformation and wether it is elongated or compressed – providing also computational evidence for the experimentally observed additional coupling to the totally symmetric alpha(1g) mode (E-g circle times(epsilon(g) + alpha(1)) vibronic interaction). The Jahn-Teller stabilisation energy of the D-4h-elongated [Mn-III(F-t)6]3- complex (absolute minimum) with respect to the regular octahedron can be defined as the difference between the non-Jahn-Teller restoring energy(approximate to 0.3 eV) and the vibronic energy (approximate to 0.6(5) eV). It is considerable (approximate to -0.3(5) eV) in comparison to the stabilisation in regard to the compressed D-4h-conformer (congruent to -0.075 eV).