2010 publications citing ADF
First author: Jones, Travis E., Topological Catastrophe and Isostructural Phase Transition in Calcium, PHYSICAL REVIEW LETTERS, 105, , (2010)
Abstract: We predict a quantum phase transition in fcc Ca under hydrostatic pressure. Using density functional theory, we find, at pressures below 80 kbar, the topology of the electron charge density is characterized by nearest neighbor atoms connected through bifurcated bond paths and deep minima in the octahedral holes. At pressures above 80 kbar, the atoms bond through non-nuclear maxima that form in the octahedral holes. This topological change in the charge density softens the C’ elastic modulus of fcc Ca, while C-44 remains unchanged. We propose an order parameter based on applying Morse theory to the charge density, and we show that near the critical point it follows the expected mean-field scaling law with reduced pressure.
First author: Miro, Pere, On the Origin of the Cation Templated Self-Assembly of Uranyl-Peroxide Nanoclusters,JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 17787, (2010)
Abstract: Uranyl-peroxide nanoclusters display different topologies based on square, pentagonal and hexagonal building blocks. Computed complexation energies of different cations (Li+, Na+, K+, Rb+, and Cs+) with [UO2(O-2)(H2O)](n) (n = 4, 5, and 6) macrocycles suggest a strong cation templating effect. The inherent bent structure of a U-O-2-U model dimer is demonstrated and justified through the analysis of its electronic structure, as well as of the inherent curvature of the four-, five-, and six-uranyl macrocyles. The curvature is enhaced by cation coordination, which is suggested to be the driving force for the self-assembly of the nanocapsules.
First author: Williams, Bryan N., Group 3 Metal Complexes of Radical-Anionic 2,2 ‘-Bipyridyl Ligands, INORGANIC CHEMISTRY, 49, 11493, (2010)
Abstract: A new method for generating group 3 metal complexes containing radical-anionic 2,2′-bipyridyl (bipy) ligands is described that relies on hydrogen-atom abstraction from dearomatized biheterocyclic complexes. This method does not involve electron transfer to neutral 2,2′-bipyridyl or salt metathesis between the lithium salt of the 2,2′-bipyridyl radical anion and group 3 metal halides. The new metal complexes were characterized by single-crystal X-ray diffraction, electron paramagnetic resonance, and absorption spectroscopy. Density functional theory (DFT) calculations were used to probe the electronic structure of these compounds. All these methods support the radical-anionic character of bipy in all bipy compounds presented.
First author: Wu, Xia, Photoelectron Imaging and Theoretical Studies of Group 11 Cyanides MCN (M = Cu, Ag, Au),JOURNAL OF PHYSICAL CHEMISTRY A, 114, 12839, (2010)
Abstract: Photodetachment of group 11 cyanide anions MCN- (M = Cu, Ag, Au) has been investigated using photoelectron velocity-map imaging. The electron affinities (EAs) of CuCN (1.468(26)) and AgCN (1.602(22)) are larger, while that of AuCN (2.066(8)) is smaller than those of the free atoms. This intriguing observation was confirmed by theoretical studies and was assigned to the transition between ionic and covalent bond properties. The harmonic frequencies of the extended vibrational progressions in the M-C stretching mode are 460(50), 385(27), and 502(10) cm(-1), respectively, which suggests a stronger bond for Au-CN than for Ag-CN. Electronic structure analysis and model calculations suggest that all M-C bonds in group 11 cyanides are best described as single bonds. A model has been proposed to explain how the relativistic effects influence the Au-C bond strength in AuCN.
First author: Kuhn, Annemarie, Electrochemical and density functional theory study of bis(cyclopentadienyl) mono(beta-diketonato) titanium(IV) cationic complexes, ELECTROCHIMICA ACTA, 56, 257, (2010)
Abstract: The electrochemical behaviour of fluorinated bis(cyclopentadienyl) mono(beta-diketonato) titanium(IV) complexes, of general formula [Cp2Ti(R’COCHCOR)]+ClO4- with Cp=cyclopentadienyl and R’, R=CF3, C4H3S; CF3, C4H3O; CF3, Ph (C6H5): CF3, CH3; CH3, CH3; Ph, Ph and Ph, CH3 is described. Both metal and ligand based redox processes are observed. The chemically and electrochemically reversible Ti-IV/Ti-III couple is followed by an irreversible ligand reduction at a considerably more negative (cathodic) potential. A comparison of the ligand reduction in its free and chelated state indicates that the beta-diketonato ligand (R’COCHCOR)(-) in [Cp2Ti(R’COCHCOR)+ClO4- is electroactive at more negative potentials. A theoretical density functional theory (OFT) study shows that a highly localized metal centred frontier orbital dominates the Ti-IV/Ti-III redox chemistry resulting in a non-linear relationship between the formal redox potential (E-o’) and the sum of the group electronegativities of the R and R’ groups. chi(R) + chi(R’), of the ligand. Linear relationships, however, are obtained between the OFT calculated electron affinity (EA) of the complexes and chi(R) + chi(R’), the pK(a) of the free beta-diketones R’COCH2COR and the carbonyl stretching frequency, v(co), of the complexes. The DFT calculated electronic structure of the second reduced species [Cp2Ti(beta-diketonato)](-) shows that it is best described as Ti(III) coupled to a beta-diketonato radical.
First author: Flisak, Zygmunt, Structural Flexibility of Bis(phenoxyimine) Titanium Complexes in the Early Stages of Olefin Polymerization Process: A DFT Study, ORGANOMETALLICS, 29, 6196, (2010)
Abstract: The behaviors of three structurally similar salan- and phenoxyimine-based catalysts activated by perfluorophenylborate were compared in the early stages of ethylene polymerization. It was found that moderate modification of the ligand structure can dramatically reduce the interactions between the cationic active site and the counteranion and, as a result, decrease the theoretically calculated upper bound to the ion separation barrier from 15 to 2 kcal/mol. The interactions between the ions in the ion pair have further repercussions on the structure of the active sites (octahedral vs square pyramid), transition states and thus the insertion barriers.
First author: Nabavizadeh, S. Masoud, Oxidative Addition of Ethyl Iodide to a Dimethylplatinum(II) Complex: Unusually Large Kinetic Isotope Effects and Their Transition-State Implications, ORGANOMETALLICS, 29, 6359, (2010)
Abstract: The mechanism of oxidative addition of ethyl iodide to [PtMe2(2,2′-bipyridine)], 1, has been investigated by product analysis and by study of secondary deuterium kinetic isotope effects (KIEs), using the reagents C2H5I, C2D5I, CH3CD2I, and CD3CH2I. The reactions in acetone and benzene give [PtIMe2Et(bipy)], mostly as the product of trans oxidative addition, but with some of the isomeric product of cis oxidative addition and some [PtIMe3(bipy)], resulting from methyl group transfer. The reaction in benzene is light-sensitive, giving additional major products [PtI2Me2(bipy)] and [PtI2Me2-(OOEt)(bipy)], as well as several minor products indicative of a photochemically initiated free-radical reaction. No H/D exchange within the ethyl group was observed in any of the products. The dark reactions in acetone and benzene follow second-order kinetics, with large negative values of the entropy of activation, indicating the S(N)2 mechanism of oxidative addition of ethyl iodide to 1. However, for reaction with C2H5I vs C2D5I, values of the KIE k(H)/k(D) range from 1.32 to 1.72 in acetone and from 1.44 to 1.90 in benzene solution, and studies with CH3CD2I and CD3CH2I show that alpha- and beta-deuterium KIEs make about equal contributions to the overall KIE. These are the first reports of isotope effects on the rate of oxidative addition reactions of ethyl halides, and the high values of the secondary deuterium KIE were unexpected for the SN2 mechanism. Possible reasons for these observations are discussed.
First author: Wu, Jianguo, The Reaction of Carbon Dioxide with Palladium-Allyl Bonds, ORGANOMETALLICS, 29, 6369, (2010)
Abstract: A family of palladium allyl complexes of the type (2-methylally1)(2)Pd(L) (L = PMe3 (1), PEt3 (2), PPh3 (3), NHC (4); NHC = 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene) have been prepared through the reaction of (2-methylally1)2Pd with the appropriate free ligand. Compounds 1-4 contain one eta(1)- and one eta(3)-2-methylallyl ligand, and 3 was characterized by X-ray crystallography. These complexes react rapidly with CO, at low temperature to form well-defined unidentate palladium carboxylates of the type (eta(3)-2-methylallyl)Pd(OC(O)C4H7)(L) (L = PMe3 (6), PEt3 (7), PPh3 (8), NHC (9)). The structure of 9 was elucidated using X-ray crystallography. The mechanism of the reaction of 1-4 with CO2 was probed using a combination of experimental and theoretical (density functional theory) studies. The coordination mode of the allyl ligand is crucial, and whereas nucleophilic eta(1)-allyls react rapidly with CO2, eta(3)-allyls do not react. We propose that the reaction of palladium eta(1)-allyls with CO2 does not proceed via direct insertion of CO2 into the Pd-C bond but through nucleophilic attack of the terminal olefin on electrophilic CO2, followed by an associative substitution at palladium.
First author: Ess, Daniel H., Electrophilic, Ambiphilic, and Nucleophilic C-H Bond Activation: Understanding the Electronic Continuum of C-H Bond Activation Through Transition-State and Reaction Pathway Interaction Energy Decompositions,ORGANOMETALLICS, 29, 6459, (2010)
Abstract: The potential energy and interaction energy profiles for metal- and metal ligand-mediated alkane C-H bond activation were explored using B3LYP density functional theory (DFT) and the absolutely localized molecular orbital energy decomposition analysis (ALMO-EDA). The set of complexes explored range from late transition metal group 10 (Pt and Pd) and group 11 (Au) metal centers to group 7-9 (Ir, Rh, Ru, and W) metal centers as well as a group 3 Sc complex. The coordination geometries, electron metal count (d(8), d(6), d(4), and d(0)), and ligands (N-heterocycles, O-donor, phosphine, and Cp*) are also diverse. Quantitative analysis using ALMO-EDA of both directions of charge-transfer stabilization (occupied to unoccupied orbital stabilization) energies between the metal ligand fragment and the coordinated C-H bond in the transition state for cleavage of the C-H bond allows classification of C-H activation reactions as electrophilic, ambiphilic, or nucleophilic on the basis of the net direction of charge-transfer energy stabilization. This bonding pattern transcends any specific mechanistic or bonding paradigm, such as oxidative addition, sigma-bond metathesis, or substitution. Late transition metals such as Au(III), Pt(II), Pd(II), and Rh(III) metal centers with N-heterocycle, halide, or O-donor ligands show electrophilically dominated reaction profiles with forward charge-transfer from the C-H bond to the metal, leading to more stabilization than reverse charge transfer from the metal to the C-H bond. Transition states and reaction profiles for d6 Ru(II) and Ir(III) metals with Tp and acac ligands were found to have nearly equal forward and reverse charge-transfer energy stabilization. This ambiphilic region also includes the classically labeled electrophilic cationic species Cp*(PMe3)Ir(Me). Nucleophilic character, where the metal to C-H bond charge-transfer interaction is most stabilizing, was found in metathesis reactions with W(II) and Sc(III) metal center complexes in reactions as well as late transition metal Ir(I) and Rh(I) pincer complexes that undergo C-H bond insertion. Comparison of pincer ligands shows that the PCP ligand imparts more nucleophilic character to an Ir metal center than a deprotonated PNP ligand. The PCP and POCOP ligands do not show a substantial difference in the electronics of C-H activation. It was also found that Rh(T) is substantially more nucleophilic than Ir(I). Lastly, as a qualitative approximation, investigation of transition-state fragment orbital energies showed that relative frontier orbital energy gaps correctly reflect electrophilic, ambiphilic, or nucleophilic charge-transfer stabilization patterns.
First author: Liao, Meng-Sheng, Structure, Bonding, and Linear Optical Properties of a Series of Silver and Gold Nanorod Clusters: DFT/TDDFT Studies, JOURNAL OF PHYSICAL CHEMISTRY A, 114, 12701, (2010)
Abstract: DFT/TDDFT calculations have been carried out for a series of silver and gold nanorod clusters (Ag-n, Au-n, n = 12-120) whose structures are of cigar-type. Pentagonal Ag-n clusters with n = 49-121 and hexagonal Au-n clusters with n = 14-74 were also calculated for comparison. Metal-metal distances, binding energies per atom, ionization potentials, and electron affinities were determined, and their trends with cluster size were examined. The TDDFT calculated excitation energies and oscillator strengths were fit by a Lorentz line shape modification, which gives rise to the simulated absorption spectra. The significant features of the experimental spectra for actual silver and gold nanorod particles are well reproduced by the calculations on the clusters. The calculated spectral patterns are also in agreement with previous theoretical results on different-type Ag-n clusters. Many differences in the calculated properties are found between the Ag-n and Au-n clusters, which can be explained by relativistic effects.
First author: Jia, Jianfeng, Structure and Stability of Tube and Cage Ge60H60, JOURNAL OF PHYSICAL CHEMISTRY A,114, 12755, (2010)
Abstract: A tube Ge60H60, isomer in D-5d symmetry with fused five-membered rings located at the ends of the tube is more stable than the fullerene-like I,, cage isomer at the B3LYP/cc-pVDZ level of theory. Introducing endo Ge-H bonds increases the stability of both cage and tube isomers. The most stable tube isomer can admit six endo Ge-H bonds. The cage isomer can admit 10-12 endo Ge-H bonds (H-10@Ge60H50 and H-12@Ge60H48),and they also represent the most stable Ge60H60 isomers. The stability order and structural patterns of Ge60H60 are the same as those found for the corresponding Si60H60 isomers. Moreover, it is found that the 6-31G(d,P) basis set fails to predict the relative energies of the Ge60H60 isomers and the Ge6H6 isomers.
First author: Mohakud, Sasmita, Ambipolar Charge Transport in alpha-Oligofurans: A Theoretical Study, JOURNAL OF PHYSICAL CHEMISTRY C, 114, 20436, (2010)
Abstract: The molecular scale charge transport has been investigated in a few recently synthesized molecular crystals of alpha-oligofuran via thermally activated hopping mechanism described by the semiclassical Marcus theory. The microscopic order parameters such as reorganization energy and hopping matrix elements, governing charge transfer phenomena, are estimated accurately using quantum chemical calculations. The dispersion corrected density functional calculations are carried out to capture the weak van der Waal interactions between the pi-stacked molecules. The hopping matrix elements or charge transfer integrals are computed as the off-diagonal elements of Kohn-Sham matrix using fragment orbital approach which explicitly considers the spatial overlap between the molecular orbitals. Our study reveals that such oligofuran molecular crystals are excellent conductors for both charge carriers, However, the hole mobility is found to be slightly larger than electron mobility in smaller oligofuran molecular crystals, whereas the reverse holds true for larger molecule. Such ambipolar organic crystals with higher electron mobility show the possibility of sophisticated device fabrication in advanced electronics. In addition, we compare all our results with analogous oligothiophene crystals by performing the same level of calculations.
First author: Herrmann, Carmen, Local Pathways in Coherent Electron Transport through Iron Porphyrin Complexes: A Challenge for First-Principles Transport Calculations, JOURNAL OF PHYSICAL CHEMISTRY C, 114, 20813, (2010)
Abstract: We investigate the coherent electron transport properties of a selection of iron porphyrin complexes in their low-spin and high-spin states, binding the system to metallic electrodes with three different substitution patterns. We use a study of the local transmission through the complexes and their molecular orbitals to show the role of the various components of the molecular structure in mediating electron transport. While there are energies where the metal center and the axial ligands participate in transport, in the off-resonant energy range, these components simply form a scaffold, and the transport is dominated by transmission through the porphyrin macrocyle alone. This is still true when going from the low-spin to the high-spin state, except that now, an additional iron-centered MO contributes to transport in the formerly off-resonant region. It is found that while the choice of the exchange-correlation functional can strongly influence the quantitative results, our qualitative conclusions hold irrespective of the functional employed.
First author: Cozzolino, Anthony F., Supramolecular Chromotropism of the Crystalline Phases of 4,5,6,7-Tetrafluorobenzo-2,1,3-telluradiazole, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 17265, (2010)
Abstract: The remarkable effect that secondary bonding interactions can have on the macroscopic properties of a material is illustrated by two polymorphs of the title compound. The phase which is most stable under ambient pressure and temperature consists of puckered supramolecular ribbon polymers assembled by Te-N secondary bonding interactions and displays a characteristic red-orange color. A second yellow phase consists of ribbons with alternating short and long intermolecular Te-N secondary bonding distances and is metastable; at 127 degrees C the material undergoes an exothermic irreversible transition to the red polymorph. A third phase consists of pyridine-solvated supramolecular dimers; it is also yellow and transforms into the red phase after the crystals effloresce. Computational DFT studies indicate that the observed changes in optical properties are related to intermolecular mixing pi orbitals enabled by the supramolecular interactions and the symmetry of the supramolecular synthon.
First author: Skipper, Claire V. J., Computational Study of Silica-Supported Transition Metal Fragments for Kubas-type Hydrogen Storage, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 17296, (2010)
Abstract: To verify the role of the Kubas interaction in transition metal grafted mesoporous silicas, and to rationalize unusual rising enthalpy trends with surface coverage by hydrogen in these systems, computational studies have been performed. Thus, the interaction of H-2 with the titanium centers in molecular models for experimentally characterized mesoporous silica-based H-2 absorption materials has been studied quantum chemically using gradient corrected density functional theory. The interaction between the titanium and the H-2 molecules is found to be of a synergic, Kubas type, and a maximum of four H-2 molecules can be bound to each titanium, in good agreement with previous experiments. The average Ti-H-2 interaction energies in molecules incorporating benzyl ancillary ligands (models of the experimental systems) increase as the number of bound H-2 units increases from two to four, in agreement with the experimental observation that the H-2 adsorption enthalpy increases as the number of adsorbed H-2 molecules increases. The Ti-H-2 interaction is shown to be greater when the titanium is bound to ancillary ligands, which are poor pi-acceptors, and when the ancillary ligand causes the least steric hindrance to the metal. Extension of the target systems to vanadium and chromium shows that, for molecules containing hydride ancillary ligands, a good relationship is found between the energies of the frontier molecular orbitals of the molecular fragments, which interact with incoming H-2 molecules, and the strength of the M-H-2 interaction. For the benzyl systems, both the differences in M-H-2 interaction energies and the energy differences in frontier orbital energies are smaller than those in the hydrides, such that conclusions based on frontier orbital energies are less robust than for the hydride systems. Because of the high enthalpies predicted for organometallic fragments containing hydride ligands, and the low affinity of Cr(III) for hydrogen in this study, these features may not be ideal for a practical hydrogen storage system.
First author: de Oteyza, D. G., Copper-phthalocyanine based metal-organic interfaces: The effect of fluorination, the substrate, and its symmetry, JOURNAL OF CHEMICAL PHYSICS, 133, 17296, (2010)
Abstract: Metal-organic interfaces based on copper-phthalocyanine monolayers are studied in dependence of the metal substrate (Au versus Cu), of its symmetry [hexagonal (111) surfaces versus fourfold (100) surfaces], as well as of the donor or acceptor semiconducting character associated with the nonfluorinated or perfluorinated molecules, respectively. Comparison of the properties of these systematically varied metal-organic interfaces provides new insight into the effect of each of the previously mentioned parameters on the molecule-substrate interactions.
First author: Wang, Yan, Consistent Aromaticity Evaluations of Methylenecyclopropene Analogues, JOURNAL OF ORGANIC CHEMISTRY, 75, 8252, (2010)
Abstract: Quantitative evaluations of the aromaticity (antiaromaticity) of neutral exocyclic substituted cyclopropenes (HC)(2)C=X (X = BH to InH (group 13), CH, to SnH2 (group 14), NH to SbH (group 15), O to Te (group 16)) by their computed extra cyclic resonance energies (ECRE, via the block-localized wave function method) and by their aromatic stabilization energies (ASEs, via energy decomposition analyses) correlate satisfactorily (R-2 = 0.974). Electronegative X-based substituents increase the aromaticity of the cyclopropene rings, whereas electropositive substituents have the opposite effect. For example, (HC)(2)C=O is the most aromatic (ECRE = 10.3 kcal/mol), and (HC)(2)C=InH is the most antiaromatic (ECRE = -15.0 kcal/mol). The most refined dissected nucleus-independent chemical shift magnetic aromaticity index, NICS(0)(pi zz) also agrees with both energetic indexes (R-2 = 0.968, for ECRE; R-2 = 0.974, for ASE), as do anisotropy of the induced current density plots.
First author: Alegret, Nuria, Bingel-Hirsch Reactions on Non-IPR Gd3N@C-2n (2n=82 and 84), JOURNAL OF ORGANIC CHEMISTRY, 75, 8299, (2010)
Abstract: The Bingel-Hirsch reactions on non-isolated pentagon rule (non-IPR) Gd3N@C-2n (2n = 82, 84) are studied. Computational results show that the two metallofullerenes display similar reactivity according to their related topologies. Long C-C bonds with large pyramidalization angles lead to the most stable adducts, the [5,6] bonds in the adjacent pentagon pair being especially favored. The lesser regioselectivity observed for Gd3N@C-82 is probably due to the activation of some C-C bonds by means of the metal cluster.
First author: Yalovega, G. E., LOCAL AND ELECTRONIC STRUCTURE OF FREE NaCl CLUSTERS AS THE CLUSTER SIZE FUNCTION: ANALYSIS BY XANES AND DFT METHODS, JOURNAL OF STRUCTURAL CHEMISTRY, 51, 1070, (2010)
Abstract: Changes in the atomic and electronic structures of free NaCl clusters as the cluster size function are analyzed based on density functional theory and the finite difference method. It is shown that the geometric atomic structure of clusters distorts more with decreasing size. Along with this, an increase in the HOMO-LUMO gap is observed.
First author: Mizuhata, Yoshiyuki, The first observation of (1)J(Sn-C) coupling constants in tin-carbon double-bond compounds, APPLIED ORGANOMETALLIC CHEMISTRY, 24, 902, (2010)
Abstract: The (1)J(Sn-C)s in the tin-carbon double-bond systems were determined for the first time. These results were supported by theoretical calculations, showing the high s-character of the Sn-C double bonds. The new findings obtained will be of great use in the development of tin-containing functionalized materials.
First author: Adhikary, Chandan, Structural and magnetic studies on copper(II) azido complexes, COORDINATION CHEMISTRY REVIEWS, 254, 2933, (2010)
Abstract: The azide ligand has been receiving intense attention in the rapid growth of literature in the field of molecular magnetism Primarily azide ion functions as a bridging ligand and magnetic coupler of paramagnetic metal ions This review is centered on the study of diverse structural and magnetic properties of copper(II) azido complexes Some of the trends identified could serve as a privileged starting point for the further development of this promising area
First author: Sherman, David M., Surface complexation of Cu on birnessite (delta-MnO2): Controls on Cu in the deep ocean, GEOCHIMICA ET COSMOCHIMICA ACTA, 74, 6721, (2010)
Abstract: Hexagonal birnessite (delta-MnO2) is a close analogue to the dominant phase in hydrogenetic marine ferromanganese crusts and nodules. These deposits contain similar to 0.25 wt.% Cu which is believed to be scavenged from the overlying water column where Cu concentrations are near 0.1 mu g/L. Here, we measured the sorption of Cu on delta-MnO2 as a function of pH and surface loading. We characterized the nature of the Cu sorption complex at pH 4 and 8 using EXAFS spectroscopy and find that, at pH 4, Cu sorbs to birnessite by inner-sphere complexation on the {0 0 1} surface at sites above Mn vacancies to give a three to four-fold coordinated complex with 6 Mn neighbors at similar to 3.4 angstrom. At pH 8, however, we find that some Cu has become structurally incorporated into the MnO2 layer by occupying the vacancy sites to give 6 Mn neighbors at similar to 2.91 angstrom. Density functional calculations on CuMn18O24(OH)(30) (H2O)(3)(-4) and CuMn18O21(OH)(33)(H2O)(3)(-1) clusters predict a threefold coordinated surface complex and show that the change from surface complexation to structural incorporation is a response to protonation of oxygens surrounding the vacancy site. Consequently, we propose that the transformation between sorption via surface complex and vacancy site occupancy should be reversible. By fitting the Cu sorption as a function of surface loading and pH to the formation of the observed and predicted surface complex, we developed a surface complexation model (in the basic Stern approximation) for the sorption of Cu onto birnessite. Using this model, we demonstrate that the concentration of inorganic Cu in the deep ocean should be several orders of magnitude lower than the observed total dissolved Cu. We propose that the observed total dissolved Cu concentration in the oceans reflects solubilization of Cu by microbially generated ligands.
First author: Segala, Maximiliano, K-shell core-electron binding energies for phosphorus- and sulfur-containing molecules calculated by density functional theory, JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA,182, 141, (2010)
Abstract: In this paper, 1s ionization energies for P- and S-containing molecules were calculated using energy-difference method by OFT. Using observed core-electron binding energies (CEBEs) as reference, we found that the Becke00x(xc) exchange-correlation functional (E-xc) is the best choice for CEBEs(P1s), with an average absolute deviation (AAD) of 0.20 eV, and that the best choice for CEBEs(S1s) is E-xc = BmTau1, with an average absolute deviation (AAD) of 0.22 eV. However, the best single functional for calculation of both P and S is E-xc =VS98, resulting in the weighted AAD of 0.43 eV. Our results are also showing that the quality of AAD changes slightly with the apparent orbital hybridization of the atom.
First author: Makowska-Janusik, M., Mesoporous Silica Functionalized by Cyclam-Metal Groups: Spectroscopic Studies and Numerical Modeling, JOURNAL OF INORGANIC AND ORGANOMETALLIC POLYMERS AND MATERIALS, 20, 761, (2010)
Abstract: Mesoporous silica functionalized by cyclam-metal molecules were investigated by spectroscopic methods including Raman, IR, UV-VIS absorption and EPR technique. To analyse quantitatively the physical features, numerical models were developed using the density functional theory method. Thus, the construction of molecular geometries and their optimisation analysis were achieved on the cyclam-metal molecules in vacuum as well as constrained by the host mesoporous silica matrixes. In this context and with regard to the paramagnetic nature of the metals chelated by cyclam molecules, EPR technique allows probing the metal environments which can be compared to theoretical results inferred from numerical models. The vibrational and optical properties were exhaustively investigated and the assignment of the main features was quantitatively discussed thanks to the carried out numerical analyses. The developed approach point out the possibility to define a targeted application of such functional materials based on the possibility to fine tune the absorption features in a wide wavelength range by stabilizing defined configurations of the cyclam-metal groups.
First author: Ellis, Paul D., Solid-State Mn-55 NMR Spectroscopy of Bis(mu-oxo)dimanganese(IV) [Mn2O2(salpn)(2)], a Model for the Oxygen Evolving Complex in Photosystem II, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 16727, (2010)
Abstract: We have examined the antiferromagneticly coupled bis(mu-oxo)dimanganese(IV) complex [Mn2O2(salpn)(2)] (1) with Mn-55 solid-state NMR at cryogenic temperatures and first-principle theory. The extracted values of the Mn-55 quadrupole coupling constant, C-Q, and its asymmetry parameter, eta(Q), for 1 are 24.7 MHz and 0.43, respectively. Further, there was a large anisotropic contribution to the shielding of each Mn4+, i.e. a Delta sigma of 3375 ppm. Utilizing broken symmetry density functional theory, the predicted values of the electric field gradient (EFG) or equivalently the C-Q and eta(Q) at ZORA, PBE QZ4P all electron level of theory are 23.4 MHz and 0.68, respectively, in good agreement with experimental observations.
First author: Burger, Marga R., A comparison of experimental and DFT calculations of Pt-195 NMR shielding trends for [PtXnY6-n](2-) (X, Y = Cl, Br, F and I) anions, MAGNETIC RESONANCE IN CHEMISTRY, 48, S38, (2010)
Abstract: A comparison between experimental and calculated gas-phase as well as the conductor-like screening model DFT Pt-195 chemical shifts of a series of octahedral [PtX6-nYn](2-) complexes for X = Cl, Br, F, I was carried out to assess the accuracy of computed NMR shielding and to gain insight into the dominant sigma(dia), sigma(para) and sigma(SO) shielding contributions. The discrepancies between the experimental and the OFT-calculated Pt-195 chemical shifts vary for these complexes as a function of the coordinated halide ions, the largest being obtained for the fluorido-chlorido and fluorido-bromido complexes, while negligible discrepancies are found for the [PtCl6-nBrn](2-) series; the discrepancies are somewhat larger where a significant deviation from the ideal octahedral symmetry such as for the geometric cis/trans or fac/mer isomers of [PtF6-nCln](2-) and [PtF6-nBrn](2-) may be expected. The discrepancies generally increase in the order [PtCl6-nBrn](2-) <[PtBr6-nIn](2-) < [PtCl6-nIn](2-) < [PtF6-nBrn](2-) approximate to [PtF6-nCln](2-), and show a striking correlation with the increase in electronegativity difference Delta(chi) between the two halide ligands (X(-)and Y-) bound to Pt(IV) for these anions: 0.09 < 0.52 < 0.63 < 1.36 approximate to 1.27, respectively. The computed Pt-195 sensitivity to Pt-X bond displacement, partial derivative(delta Pt-195)/partial derivative(Delta Pt-X), of these complexes is very large and depends on the halide ion, decreasing from 24800, 18 300, 15 700 to 12 000 ppm/angstrom for [PtF6](2-), [PtCl6](2-), [PtBr6](2-) and [Ptl(6)](2-), respectively.
First author: Rastrelli, Federico, Predicting the H-1 and C-13 NMR spectra of paramagnetic Ru(III) complexes by DFT,MAGNETIC RESONANCE IN CHEMISTRY, 48, S132, (2010)
Abstract: Nuclear shieldings, including the Fermi-contact and pseudocontact terms, have been calculated with density functional theory (DFT) (nonrelativistic and relativistic) methods in several Ru(III) complexes, thereby predicting H-1 and C-13 paramagnetic shifts. A fair agreement with experimental values is observed. Structural, magnetic and dynamic parameters have also been input to the Solomon-Bloembergen equation in order to predict signal lineshapes. It is shown that DFT-predicted paramagnetic shifts can greatly aid in obtaining and understanding NMR spectra of paramagnetic Ru(III) complexes.
First author: Tit, Nacir, Effects of the passivating coating on the properties of silicon nanocrystals, MATERIALS CHEMISTRY AND PHYSICS, 124, 927, (2010)
Abstract: The effects of the hydrogen-coating of silicon nanocrystals (Si H NCs) on the chemical and physical properties are theoretically investigated The empirical tight-binding (TB) method within the minimal sp(3)-basis set and second nearest-neighbor interaction scheme is employed to calculate the electronic structures oscillator strength (OS) and recombination rates (RR) The coating is found to Induce numerous effects (i) the full chemical passivation of the dangling bonds existing on the surface of the silicon NCs (ii) the charge-carrier quantum-confinement (QC) enhancement which yields direct bandgap character distinguished with strong and fast photoluminescence (PL) emissions In this perspective based on the modeling of the PL data the QC rules are derived and found to be power-low like similar to the case of a single particle confined in a 3D box and (iii) the enhancement of the optical properties (i e OS and RR) Furthermore to deepen our understanding of the coating effects we have considered the Si29NC under three different situations (a) un-coated (b) the surface-dangling bonds being partially hydrogenated and the rest being dimerized (i e Si29H24 NC) (c) all the surface-dangling bonds being fully hydrogenated (i e Si29H36 NC) Using the density-functional-theory (DFT) the total energy calculation has confirmed that the occurrence of to hydrogenization is more probable than the dimerization (i e Si29H36 has lower energy and is thus more stable than Si29H24) On one hand these results corroborate the experimental findings presenting the enhancement of the optical efficiency with the increasing hydrogen content On the other hand the atomic relaxation is also shown to further enhance the optical properties and this should in turn corroborate the results of the experimental heat treatment of Si H NC films recently reported in literature
First author: Gonzalez, Emmanuel, Density Functional Theory Calculations on Ruthenium(IV) Bis(amido) Porphyrins: Search for a Broader Perspective of Heme Protein Compound II Intermediates, JOURNAL OF PHYSICAL CHEMISTRY B,114, 15380, (2010)
Abstract: Presented herein is a first density functional theory (DFT) (ZORA, STO-TZP) survey of ruthenium(IV) porphyrins with monoanionic nitrogen ligands, modeled after experimentally observed ruthenium porphyrin bis(amido), bis(methyleneamido), and bis(pyrazolato) complexes. Three exchange correlation functionals-PW91, OLYP, and B3LYP, which often behave somewhat differently-provide good, consistent descriptions of the lowest singlet and triplet states. For ruthenium porphyrin bis(amido) and bis(methyleneamido) complexes, the calculations reproduce the experimentally observed S = 0 ground states, with the triplet states only a few tenths of an electron-volt higher in energy. The singlet-triplet energy gaps decrease somewhat along the series PW91 > OLYP > B3LYP. Molecular orbital (MO) analyses also provide a qualitative explanation for the singlet ground states of these complexes, which may be contrasted with the triplet states of heme protein compound II intermediates and their synthetic iron(IV) models. Amido and methyleneamido ligands have a single pi-lone pair, unlike hydroxide, alkoxide, and thiolate ligands, which have two. The former therefore engage in a single pi-bonding interaction with one of the Ru d(pi) orbitals, resulting in an S = 0 d(4) electronic configuration. In contrast, the O or S ligands present in compound II engage in pi-bonding with both d(pi) orbitals, resulting in an S = I ground state. For the ruthenium(IV) bis(methyleneamido) complexes, our MO analysis indicates a somewhat different bonding description, relative to that proposed by the experimental researchers, who invoked Ru(d(pi)) -> N-methyleneamido(pi*) backbonding to explain Ru-N-methyleneamido multiple bond character. Instead, we found that the metal-methyleneamido pi-bonding almost exclusively involves N-to-Ru pi-donation and thus is qualitatively very similar to metal-amido pi-bonding. Ruthenium(IV) bis(pyrazolato) complexes provide rare examples of ruthenium(IV) centers with all-nitrogen ligation that are paramagnetic. OLYP successfully captures this “inverse” spin state energetics; PW91 and B3LYP do so less well.
First author: Lukose, Binit, On the reticular construction concept of covalent organic frameworks, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 1, 60, (2010)
Abstract: The concept of reticular chemistry is investigated to explore the applicability of the formation of Covalent Organic Frameworks (COFs) from their defined individual building blocks. Thus, we have designed, optimized and investigated a set of reported and hypothetical 2D COFs using Density Functional Theory (DFT) and the related Density Functional based tight-binding (DFTB) method. Linear, trigonal and hexagonal building blocks have been selected for designing hexagonal COF layers. High-symmetry AA and AB stackings are considered, as well as low-symmetry serrated and inclined stackings of the layers. The latter ones are only slightly modified compared to the high-symmetry forms, but show higher energetic stability. Experimental XRD patterns found in literature also support stackings with highest formation energies. All stacking forms vary in their interlayer separations and band gaps; however, their electronic densities of states (DOS) are similar and not significantly different from that of a monolayer. The band gaps are found to be in the range of 1.7-4.0 eV. COFs built of building blocks with a greater number of aromatic rings have smaller band gaps.
First author: Stander-Grobler, Elzet, Pyridine-Derived N-Heterocyclic Carbenes: An Experimental and Theoretical Evaluation of the Bonding in and Reactivity of Selected Normal and Abnormal Complexes of Nickel(II) and Palladium(II),ORGANOMETALLICS, 29, 5821, (2010)
Abstract: We report a thorough investigation of a series of isomeric complexes with the general formula trans-(pyridylidene)M(PPh3)(2)Cl (M = Pd, Ni). For the first time, a systematic comparison of normal, abnormal, and remote bonding modes is presented. X-ray structural and C-13 NMR data indicate the importance of carbenoid mesomeric contributions in their compound class.. The catalytic performance of the palladium complexes trans-(pyridylidene)Pd(PPh3)(2)Cl as precursors in Suzuki-Miyaura-type cross-coupling suggests a correlation of remote bonding with catalyst robustness and effectivity. When metal precursors M(PPh3)(4) are reacted with 2,4-dichloropyridinium salts, preferential formation of remote carbene complexes occurs and indications are that electronic parameters rather than steric influences are responsible for the observed selectivity. Calculations at the BP86/TZ2P level of theory support interpretation of the results.
First author: Aguirre-Etcheverry, Paulina, Synthesis, Structure, and Ligand Exchange Reactions of Tetramethyleneethane Complexes of Cobalt, ORGANOMETALLICS, 29, 5847, (2010)
Abstract: The synthesis of (eta(3):eta(3)-TME)[Co(CO)(3)](2) (1) was achieved using 2,3-bis(bromomethyl)-1,3-butadiene (TMEBr2) as the tetramethyleneethane (TME) ligand precursor and Na[Co(CO)(4)]. Solution NMR studies suggested an eta(3):eta(3)-configuration, which has been confirmed in the solid state by single-crystal X-ray diffraction studies. The series of complexes (eta(3):eta(3)-TME)[Co(CO)(2)PR3](2) (R = Me, 2; R = Et, 3; R = n-Bu, 4; R = Ph, 5; R = OPh, 6) were also synthesized by ligand exchange reactions, demonstrating that only one carbonyl may be exchanged for a phosphine group on each metal center. The eta(3):eta(3)-configuration of the tetramethyleneethane ligand in these complexes was determined by crystallographic studies. The effect of the electron-donating properties of PR3 was studied by cyclic voltammetry (CV) and infrared spectroscopy. The greatest degree of electron donation was seen when R = Et (3) and lowest when R = Ph (5) or R = OPh (6). Electronic communication between the metal centers was observed by CV. The chemical oxidation of 1 resulted in a highly unstable species that decomposed to {[(CO)(2)Co]TME[Co(CO)(3)]}(+)[BF4](-) (1(+)d), determined by its crystal structure. The synthesis of (eta(4):eta(4)-TME)[CoCp*](2) (7) has been achieved using a dipotassium 2,3-bis(methylene)-1,3-butanediyl (TMEK2) synthon. NMR studies suggested that 7 adopts an unusual eta(4):eta(4)-configuration, which was confirmed with the aid of crystallographic studies. DFT calculations were performed in order to rationalize the bonding for 1, 7, and hypothetical (eta(4):eta(4)-TME)[CoCp](2) (8). The large energy difference between the two coordination isomers 1 and la confirmed the eta(3):eta(3)-configuration. For isomers 7/7a and 8/8a, the energy difference between the two isomers (ca. 15 kJ mol(-1)) is in favor of the eta(4):eta(4)-configuration. For complexes 1(+) and 8(+), the calculations suggested complete delocalization on the system when one electron was removed.
First author: Coletti, Cecilia, Rhenium Allenylidenes and Their Reactivity toward Phosphines: A Theoretical Study,ORGANOMETALLICS, 29, 5982, (2010)
Abstract: Density functional and local MP2 calculations have been performed to study the electronic structure of the rhenium(I) allenylidene [(triphos)(CO)(2)Re(=C=C=CRR’)(+) species [triphos = MeC(CH2PPh2)(3); R, R’ = aryl group] and its reactivity toward tertiary phosphines. The calculated electronic structure shows a relatively electron-rich nature of the [(triphos)(CO)(2)Re](+) synthon in agreement with the experimental behavior of the corresponding allenylidene complex [(triphos)(CO)(2)Re(=C=C=CPh2)](+) (R = R’ = Ph). Both the kinetics and the thermodynamics of the nucleophilic addition of tertiary phosphines PMe3-xPhx, (x = 0, 1, 2, and 3) have been considered. The results indicate lower activation energies for the phosphine attack to C-gamma, which leads, however, to products higher in energy than those of the attack to C-alpha. The computed behavior agrees with the experimental evidence showing that the products of the attack to C-gamma are kinetically favored, while the products of the attack to C-alpha are thermodynamically favored. Finally, we addressed the mechanism of phosphine migration from C-gamma to C-alpha, finding a low-energy path corresponding to an incomplete detachment of the phosphine moiety that then shifts from the C-gamma to the C-alpha atoms while remaining weakly bound to the allenylidene unit.
First author: Yu, Insun, Phosphine-Tethered Carbene Ligands: Template Synthesis and Reactivity of Cyclic and Acyclic Functionalized Carbenes, ORGANOMETALLICS, 29, 6065, (2010)
Abstract: Reaction of the phosphine-tethered isocyanide iron(II) complex 1, [CpFe(CO)(PCN)]I, with primary and secondary amines forms the corresponding acyclic (diamino)carbene complexes [CpFe(CO)(PCXNE)]I; X = n-butylamine (4), 4-methylaniline (5), dihexylamine (6). Five- and six-membered cyclic (diamino)carbene complexes [CpFe(CO)(PCNHN-nCy)}1 (n = 5 (9), 6 (10)) are generated in two steps from the reaction of 1 with 2-chloroethyl and 3-chloropropylamine, first forming acyclic diaminocarbene complexes [CpFe(CO)(PCNXNH)]I (X = chloroethyl (7), chloropropyl (8)), respectively, followed by deprotonation and intramolecular cyclization. This methodology is not effective for alcohols; however, acyclic (oxy)(amino)carbene complexes are produced in two steps by the reaction of 1 with potassium methoxide, ethoxide, and isopropoxide to form the corresponding ylidene complexes CpFe(CO)(PCO(X)N) (X = Me (11), Et (12), i-Pr (13)), which, in the second step, can be protonated with an equimolar amount of HBF4 to form acyclic (oxy)(amino)carbene complexes [CpFe(CO)(PCO(X)NH)]BF4 (X = Me (14), Et (15), i-Pr (16)). Five and six-membered cyclic (oxy)(amino)carbene complexes [CpFe(CO)(PCNO-nCy)]Cl (n = 5 (17), 6 (18)) are formed by the concerted reaction of 1 with 2-chloroethoxide and 3-chloropropoxide followed by intramolecular cyclization. The reversible conversion of acyclic (silyl)(amino)carbene complex [CpFe(CO)(PPhCSi(Ph)3NH)]BF4)] (20) to its ylidene precursor CpFe(CO)(PPhCSi(Ph)3N) (19) via slow deprotonation with an equivalent of NaHB(OAc)(3) is demonstrated, and the structure of 20 is reported. All complexes were characterized by IR and NMR spectroscopy and, where possible, by single-crystal X-ray diffraction. DFT calculations were used to support the electronic structure of complexes deduced from structural and spectroscopic data.
First author: Potter, Robert G., Thermochemistry of Lewis Adducts of BH3 and Nucleophilic Substitution of Triethylamine on NH3BH3 in Tetrahydrofuran, INORGANIC CHEMISTRY, 49, 10512, (2010)
Abstract: The thermochemistry of the formation of Lewis base adducts of BH3 in tetrahydrofuran (THF) solution and the gas phase and the kinetics of substitution on ammonia borane by triethylamine are reported. The dative bond energy of Lewis adducts were predicted using density functional theory at the B3LYP/DZVP2 and B3LYP/6-311+G** levels and correlated ab initio molecular orbital theories, including MP2, G3(MP2), and G3(MP2)B3LYP, and compared with available experimental data and accurate CCSD(T)/CBS theory results. The analysis showed that the G3 methods using either the MP2 or the B3LYP geometries reproduce the benchmark results usually to within similar to 1 kcal/mol. Energies calculated at the MP2/aug-cc-pVTZ level for geometries optimized at the B3LYP/DZVP2 or B3LYP/6-311+G** levels give dative bond energies 2-4 kcal/mol larger than benchmark values. The enthalpies for forming adducts in THF were determined by calorimetry and compared with the calculated energies for the gas phase reaction: THFBH3 + L -> LBH3 + THF. The formation of NH3BH3 in THF was observed to yield significantly more heat than gas phase dative bond energies, predict, consistent with strong solvation of NH3BH3. Substitution of NEt3 on NH3BH3 is an equilibrium process in THF solution; (K approximate to 0.2 at 25 degrees C). The reaction obeys a reversible bimolecular kinetic rate law with the Arrhenius parameters: log A = 14.7 +/- 1.1 and E-a = 28.1 +/- 1.5 kcal/mol. Simulation of the mechanism using the SM8 continuum solvation model shows the reaction most likely proceeds primarily by a classical S(N)2 mechanism.
First author: Takahata, Yuji, Accurate calculation of C1s core electron binding energies of some carbon hydrates and substituted benzenes, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 959, 106, (2010)
Abstract: Approaches, using density functional theory (DFT), to calculate accurate adiabatic and vertical carbon is core electron binding energies (CEBE) of some alkanes, alkenes, alkynes and methyl- and fluorine-substituted benzenes are investigated.The approaches tested can be schematized as follows; Delta E-KS(PW86 x -PW91c/TZP + C-rel)//DFT(PW86 x -PW91c/TZP) where Delta E-KS is the difference between the Kohn-Sham total energy of the core-hole cation M+, E-KS(M+), and the Kohn-Sham total energy of the neutral ground state molecule M, E-KS(M). The geometry of M is optimized with DFT(PW86x-PW91c/TZP). For the adiabatic C1s CEBE calculation, the geometry of M+ is optimized whereas, for the vertical C1s CEBE calculation, the geometry of M+ is identical to the neutral ground state molecule M. C-rel represents relativistic corrections. We tested two cases; C-rel = 0 eV, and C-rel = 0.05 eV. The relativistic correction turned out to be not necessary, because inclusion of the relativistic correction always increased deviation. The current results suggest a systematic error in the calculations that is fortuitously offset by the neglect of relativistic effects. The best approach resulted in average absolute deviations (maximum absolute deviations) from adiabatic experimental values of 0.045 eV (0.130 eV) for calculations of the corresponding C1s CEBE of the alkanes, alkenes, and substituted benzenes for 120 cases. The absolute uncertainty in the experimental measurements is estimated to be 0.03 eV. The average absolute deviation of 0.045 eV is close to the magnitude of the experimental uncertainty. Agreement between theory and experiment is better for adiabatic C1s CEBE than for vertical C1s CEBE.
First author: Salvi, Nicola, Ion pairing in NHC gold(I) olefin complexes: A combined experimental/theoretical study,JOURNAL OF ORGANOMETALLIC CHEMISTRY, 695, 2679, (2010)
Abstract: The relative anion-cation orientation in [(NHC) Au(alkene)] BF4 ion pairs [NHC _ N-Heterocyclic Carbene 1,3-bis(di-iso-propylphenyl)-imidazol-2-ylidene (IPr) and 4,5-dimethyl-N, N’-bis(2,6-diiso-propylphenyl)- imidazol-2-ylidene ((IPr)-I-Me); alkene 4-methyl-1-pentene, 2,3-methyl-2-butene and 4-methylstyrene] has been investigated by combining F-19, H-1-HOESY NMR spectroscopy in (CDCl2)-Cl-2 and a detailed analysis of the Coulomb potential of the cationic fragment through DFT calculations. Two main orientations have been found where the anion locates close to the imidazole ring (NHC-side) and close to the olefin (olefin-side). The NHC-side orientation is always predominant (65-83%) while the exact position of the anion in the olefin-side is finely tuned by the nature of olefin substituents. In all cases, the counterion resides far away from the gold site, the latter carrying only a small fraction of the positive charge.
First author: Vijayakumar, M., Nuclear magnetic resonance studies on vanadium(IV) electrolyte solutions for vanadium redox flow battery, JOURNAL OF POWER SOURCES, 195, 7709, (2010)
Abstract: The vanadium(IV) electrolyte solutions with various vanadium concentrations are studied by variable temperature H-1 and O-17 nuclear magnetic resonance (NMR) spectroscopy. The structure and kinetics of vanadium(IV) species in the electrolyte solutions are explored with respect to vanadium concentration and temperature. It was found that the vanadium(IV) species exist as hydrated vanadyl ion, i.e. [VO(H2O)(5)](2+) forming an octahedral coordination with vanadyl oxygen in the axial position and the remaining positions occupied by water molecules. This hydrated vanadyl ion structure is stable in vanadium concentrations up to 3 M and in the temperature range of 240-340 K. The sulfate anions in the electrolyte solutions are found to be weekly bound to this hydrated vanadyl ion and occupies its second-coordination sphere. The possible effects of these sulfate anions in proton and water exchange between vanadyl ion and solvent molecules are discussed based on H-1 and O-17 NMR results.
First author: Srebro, Monika, On Conformational Flexibility of Half-Titanocene Catalysts with Aryloxy Ligands for High-Temperature Olefin Polymerization Processes: Static and Dynamic Theoretical Studies, ORGANOMETALLICS, 29, 5341, (2010)
Abstract: The static DFT calculations and Car-Parrinello molecular dynamic simulations were performed for a series of half-metallocene ethylene-polymerization catalysts based on Ti(I V) complexes with aryloxy ligands, varied in cyclopentadienide Cp/Cp* and 2,6-di-/2-monosubstituted phenoxy ligand combinations. The results confirm the more pronounced conformational flexibility of the monosubstituted systems, demonstrated by a relatively easy rotation of the aryloxy ligand. In the case of the complex with a 2-phenylphenoxy ligand, a substantial decrease in rotational barrier is observed due to the secondary interactions between the phenyl substituent and the methyl protons of Cp*. In the catalytically active species derived from the corresponding precatalysts, the barrier for the ligand rotation is decreased compared to the precatalysts. For the monosubstituted aryloxy complexes such an easy rotation allows for the transition between the “nonreactive” and “reactive” propagation pathways (anti and son), which can lead to an increase in their catalytic activity.
First author: Kovyrshin, Arseny, State-selective optimization of local excited electronic states in extended systems,JOURNAL OF CHEMICAL PHYSICS, 133, 5341, (2010)
Abstract: Standard implementations of time-dependent density-functional theory (TDDFT) for the calculation of excitation energies give access to a number of the lowest-lying electronic excitations of a molecule under study. For extended systems, this can become cumbersome if a particular excited state is sought-after because many electronic transitions may be present. This often means that even for systems of moderate size, a multitude of excited states needs to be calculated to cover a certain energy range. Here, we present an algorithm for the selective determination of predefined excited electronic states in an extended system. A guess transition density in terms of orbital transitions has to be provided for the excitation that shall be optimized. The approach employs root-homing techniques together with iterative subspace diagonalization methods to optimize the electronic transition. We illustrate the advantages of this method for solvated molecules, core-excitations of metal complexes, and adsorbates at cluster surfaces. In particular, we study the local pi -> pi* excitation of a pyridine molecule adsorbed at a silver cluster. It is shown that the method works very efficiently even for high-lying excited states. We demonstrate that the assumption of a single, well-defined local excitation is, in general, not justified for extended systems, which can lead to root-switching during optimization. In those cases, the method can give important information about the spectral distribution of the orbital transition employed as a guess.
First author: Poltev, Valeri I., DFT Study of Polymorphism of the DNA Double Helix at the Level of Dinucleoside Monophosphates, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 110, 2548, (2010)
Abstract: We apply DFT calculations to deoxydinucleoside monophosphates (dDMPs) which represent minimal fragments of the DNA chain to study the molecular basis of stability of the DNA duplex, the origin of its polymorphism and conformational heterogeneity. In this work, we continue our previous studies of dDMPs where we detected internal energy minima corresponding to the “classical” B conformation (BI-form), which is the dominant form in the crystals of oligonucleotide duplexes. We obtained BI local energy minima for all existing base sequences of dDMPs. In the present study, we extend our analysis to other families of DNA conformations, successfully identifying A, BI, and BII energy minima for all dDMP sequences. These conformations demonstrate distinct differences in sugar ring puckering, but similar sequence-dependent base arrangements. Internal energies of BI and BII conformers are close to each other for nearly all the base sequences. The dGpdG, dTpdG, and dCpdA dDMPs slightly favor the BII conformation, which agrees with these sequences being more frequently experimentally encountered in the BII form. We have found BII-like structures of dDMPs for the base sequences both existing in crystals in BII conformation and those not yet encountered in crystals till now. On the other hand, we failed to obtain dDMP energy minima corresponding to the Z family of DNA conformations, thus giving us the ground to conclude that these conformations are stabilized in both crystals and solutions by external factors, presumably by interactions with various components of the media. Overall the accumulated computational data demonstrate that the A, BI, and BII families of DNA conformations originate from the corresponding local energy minimum conformations of dDMPs, thus determining structural stability of a single DNA strand during the processes of unwinding and rewinding of DNA.
First author: Jung, Sunghan, Noncovalent Binding between Fullerenes and Protonated Porphyrins in the Gas Phase,JOURNAL OF PHYSICAL CHEMISTRY A, 114, 11376, (2010)
Abstract: Noncovalent interactions between protonated porphyrin and fullerenes (C-60 and C-70) were studied with five different meso-substituted porphyrins in the gas phase. The protonated porphyrin fullerene complexes were generated by electrospray ionization of the porphyrin fullerene mixture in 3:1 dichloromethane/methanol containing formic acid. All singly protonated porphyrins formed the 1:1 complexes, whereas porphyrins doubly protonated on the porphine center yielded no complexes. The complex ion was mass-selected and then characterized by collision-induced dissociation with Xe. Collisional activation exclusively led to a loss of neutral fullerene, indicating noncovalent binding of fullerene to protonated porphyrin. In addition, the dissociation yield was measured as a function of collision energy, and the energy inducing 50% dissociation was determined as a measure of binding energy. Experimental results show that C-70 binds to the protonated porphyrins more strongly than C-60, and electron-donating substituents at the meso positions increase the fullerene binding energy, whereas electron-withdrawing substituents decrease it. To gain insight into pi-pi interactions between protonated porphyrin and fullerene, we calculated the proton affinity and HOMO and LUMO energies of porphyrin using Hartree-Fock and configuration interaction singles theory and obtained the binding energy of the protonated porphyrin fullerene complex using density functional theory. Theory suggests that the protonated porphyrin fullerene complex is stabilized by pi-pi interactions where the protonated porphyrin accepts pi-electrons from fullerene, and porphyrins carrying bulky substituents prefer the end-on binding of C-70 due to the steric hindrance, whereas those carrying less-bulky substituents favor the side-on binding of C-70.
First author: Kachmar, Ali, New Insights in the Electrocatalytic Proton Reduction and Hydrogen Oxidation by Bioinspired Catalysts: A DFT Investigation, JOURNAL OF PHYSICAL CHEMISTRY A, 114, 11861, (2010)
Abstract: In this paper, we present a DFT study of the proton reduction mechanism catalyzed by the complex [Ni((P2N2H)-N-H)(2)](2+), bioinspired from the hydrogenases. A detailed analysis of the reactive isomers is discussed together with the localizations of the transitions states and energy minima. The reactive catalytic species is a biprotonated Ni(0) complex that can show different conformations and that can be protonated on different sites. The energies of the different conformations and biprotonated species have been calculated and discussed. Energy barriers for two different reaction mechanisms have been identified in solvent and in gas phase. Frequency calculations have been performed to check the nature of the energy minima and for the calculations of entropic energetic terms and zero point energies. We show that only one conformation is mostly reactive. All the others species are nonreactive in their original form, and they have to pass through conformational barriers in order to transform in the reactive species.
First author: Delgado, Marco, Alumina as a Simultaneous Support and Co Catalyst: Cationic Hafnium Complex Evidenced by Experimental and DFT Analyses, JOURNAL OF PHYSICAL CHEMISTRY C, 114, 18516, (2010)
Abstract: Electron-poor transition metal complexes are of high interest in polymerization or oligomerization, but they require the use of a Lewis acid cocatalyst in order to reach the cationic active structure. The structure of the surface complexes obtained by grafting Hf(CH(2)tBu)(4), 1, on gamma-alumina has been resolved by a combined experimental (mass balance analysis, labeling, in situ IR, NMR) and theoretical (DFT calculations) study. Thermolysis, oxidation, and hydrogenolysis reactions have unambiguously proved the presence of two kinds of neopentyl-metal bonds: Hf-CH(2)tBu and Al-CH(2)tBu. Three coexisting surface complexes have been fully characterized and quantified: a monoaluminoxy [( AlIVO)Hf(CH(2)tBu)(3)] a neutral bis-aluminoxy [( AlIVO)(AlsO)Hf(CH(2)tBu)(2)], and a zwitterionic bis-aluminoxy complex [( AlIVO)(AlsO)Hf(CH(2)tBu)(2)](+)-[(CH(2)tBu)Al-s](-) in 40%, 26%, and 34% yield, respectively. In C-13 NMR calculations the important effect of spin-orbit coupling has been underlined on the chemical shifts of the carbon atoms directly linked to hafnium. Hence, a large fraction of the grafted complex is in a cationic structure, explaining why this system is active in polymerization (> 10(3) kg of PE/mol of Hf.h.atm) without the need of a cocatalyst, since alumina plays the dual role of solid support and Lewis acid.
First author: Seldenthuis, Johannes S., An All-Electric Single-Molecule Motor, ACS NANO, 4, 6681, (2010)
Abstract: Many types of molecular, motors have been proposed and Synthesized in recent years, displaying different kinds of motion and fueled by different driving forces such as light, heat, or chemical reaction. We propose a new type of molecular motor based on electric field actuation and electric current detection of the rotational motion of a molecular dipole embedded in a three-terminal single-molecule device. The key aspect of this all-electronic design is the conjugated backbone of the molecule, which simultaneously provides the potential landscape of the rotor orientation and a real time measure of that orientation through the modulation of the conductivity. Using quantum chemistry calculations, we show that this approach provides full control over the speed and continuity of motion, thereby combining electrical and mechanical control at the molecular level over a wide range of temperatures. Moreover, chemistry can be used to change all key parameters of the device enabling a variety of new experiments on molecular motors
First author: Takagi, Nozomi, On the nature of homo- and hetero-dinuclear metal-metal quadruple bonds – Analysis of the bonding situation and benchmarking DFT against wave function methods, CANADIAN JOURNAL OF CHEMISTRY-REVUE CANADIENNE DE CHIMIE, 88, 1079, (2010)
Abstract: Homo- and hetero-dimetallic (d-d)(8) analogues of the formally quadruply bonded [Re(2)Cl(8)](2-) system with the general formula [MM’Cl(8)](x) (M, M’ = Tc, Re, Ru, Os, Rh, Ir and x = -2, -1, 0, +1, +2) have been calculated with the density functional theory (DFT) functionals SVWN, BLYP, BP86, PBE, OLYP, OPBE, HCTH, B3LYP, O3LYP, X3LYP, BH&HLYP, TPSS, VSXC, TPPSh, and ab initio methods (CASPT2, CCSD(T)) using basis sets of triple-zeta quality. The performance of the functionals for the description of the metal-metal bond distance and the bond dissociation energy as well as the singlet-triplet gap was evaluated with respect to ab initio data at the CASPT2 level. Generally, the generalized gradient approximation (GGA) functionals, BLYP, BP86, and PBE, show good performance in the description of the metal-metal bond distance and for the dissociation energy. Hybrid functionals are not to be used for compounds of the type discussed here as they lead to increasingly too short and too weak bonds with the amount of exact exchange included. All functionals underestimate the singlet-triplet gap, with the GGA functionals BLYP, BP86, PBE being the closest to the CASPT2 values. The bonding situations of the [MM’Cl(8)](x) compounds were analyzed at the DFT level (BP86) using the natural bond orbital (NBO) method and the energy decomposition analysis. The M-M bond in homodimetallic compounds, [MMCl(8)](x), becomes weaker from group 7 to group 8 to group 9 metals and the bond is weaker for 4d metal systems than for 5d transition metal compounds. The M-M bonds have approximately 50% covalent and 50% electrostatic character and the covalent contribution is dominated by the p orbitals, whereas the delta orbitals do not contribute significantly to the covalent bonding. Heterodimetallic systems, [MM’Cl(8)](x), have significantly stronger metal-metal bonds than the homodimetallic compounds. This comes from weaker Pauli repulsion and stronger electrostatic attraction. The most stable heterodimetallic bonds are observed for 5d-5d metal pairs.
First author: Zhou, Chuanyao, Site-specific photocatalytic splitting of methanol on TiO2(110), CHEMICAL SCIENCE, 1, 575, (2010)
Abstract: Clean hydrogen production is highly desirable for future energy needs, making the understanding of molecular-level phenomena underlying photocatalytic hydrogen production both fundamentally and practically important. Water splitting on pure TiO2 is inefficient, however, adding sacrificial methanol could significantly enhance the photocatalyzed H-2 production. Therefore, understanding the photochemistry of methanol on TiO2 at the molecular level could provide important insights to its photocatalytic activity. Here, we report the first clear evidence of photocatalyzed splitting of methanol on TiO2 derived from time-dependent two-photon photoemission (TD-2PPE) results in combination with scanning tunneling microscopy (STM). STM tip induced molecular manipulation before and after UV light irradiation clearly reveals photocatalytic bond cleavage, which occurs only at Ti4+ surface sites. TD-2PPE reveals that the kinetics of methanol photodissociation is clearly not of single exponential, an important characteristic of this intrinsically heterogeneous photoreaction.
First author: Chen, Lin X., X-ray snapshots for metalloporphyrin axial ligation, CHEMICAL SCIENCE, 1, 642, (2010)
Abstract: Axial ligation mechanisms of a metalloporphyrin, nickel(II) tetramesitylporphyrin (NiTMP), were investigated by static and transient X-ray absorption spectroscopy at Ni K-edge (8.333 keV). A surprisingly broad (i.e. similar to 1.4 eV) linewidth for the Is -> 3d(x2-y2) transition in the ground state was attributed to strong geometry dependent 3d molecular orbital (MO) energies due to coexisting conformers in solution. The broad distribution of 3d MO energy levels enables transient degeneracy of the 3d(z2) and 3d(x2-y2) MOs to produce a temporary vacancy in the 3d(z2) MO which favors axial ligation. Photoexcitation also induces the vacancy in the 3d(z2) MO, leading to a more than two-fold enhancement in the axial ligated species. Therefore, a unified axial ligation mechanism for both the ground and excited state is proposed based on the elucidation of the excited state structural dynamics, which will have a broad impact in understanding and controlling axial ligation in enzymatic reactions and molecular catalysis involving transient axial ligation.
First author: Cozzolino, Anthony F., Engineering Second-Order Nonlinear Optical Activity by Means of a Noncentrosymmetric Distortion of the [Te-N](2) Supramolecular Synthon, CRYSTAL GROWTH & DESIGN, 10, 4959, (2010)
Abstract: Moderate steric repulsion within the supramolecular ribbon chains assembled by 1,2,5-telluradiazole derivatives causes a distortion of the [Te-N](2) supramolecular synthon which removes the inversion center from the four-membered virtual ring. This geometrical feature can propagate through the lattice, creating a noncentrosymmetric crystal with second-order nonlinear optical (NLO) properties. This principle was demonstrated in the cases of 3,4-dicyano-1,2,5-telluradiazole and 5,6-dichlorobenzo-2,1,3-telluradiazole. The second harmonic generation efficiency of these materials, however, is modest because the molecular dipole moments have a nearly antiparallel arrangement in the ribbons. The structure of 5-benzoylbenzo-2,1,3-telluradiazole demonstrates that it is indeed possible to extend this strategy to generate acentric crystals of benzo-2,1,3-telluradiazoles featuring pendant groups (including NLO chromophores) and in this way design more efficient NLO materials.
First author: Wang, Shi, Case Study on a Rare Effect: The Experimental and Theoretical Analysis of a Manganese(III) Spin-Crossover System, INORGANIC CHEMISTRY, 49, 9839, (2010)
Abstract: The six-coordinated mononuclear manganese(III) complex [Mn(5-Br-sal-N-1,5,8,12)]ClO4 has been synthesized and isolated in crystalline form. Magnetic measurements and variable-temperature single-crystal X-ray crystallography corroborated with theoretical analysis provided firm evidence for the spin-crossover effects of this system. The monomeric complex cations are made by a hexadentate mixed-donor Schiff base ligand imposing a distorted octahedral geometry and subtle structural effects determining the manifestation of the variable spin properties of the manganese(III) centers. The spin crossover in [Mn(5-Br-sal-N-1,5,8,12)]ClO4 has resulted in an unprecedented crystallographic observation of the coexistence of high-spin (HS; S = 2) and low-spin (LS; S = 1) manganese(III) complex cations in equal proportions around 100 K. At room temperature, the two crystallographically distinct manganese centers are both HS. Only one of the two slightly different units undergoes spin crossover in the temperature range similar to 250-50 K, whereas the other remains in the HS state down to 50 K. The density functional theory calculations, performed as relevant numerical experiments designed to identify the role of orbital and interelectron effects, revealed unedited aspects of the manganese(III) spin-conversion mechanisms, developed in the conceptual frame of ligand-field models.
First author: Semrouni, David, Assessment of density functionals for predicting the infrared spectrum of sodiated octa-glycine, INTERNATIONAL JOURNAL OF MASS SPECTROMETRY, 297, 152, (2010)
Abstract: The sodiated peptide GGGGGGGG-Na+ or G(8)-Na+ has a remarkable structure with a highly coordinated sodium ion and an acidic OH that is strongly hydrogen-bound with the N-terminus. The presence of the sodium ion makes this hydrogen bond unusually strong and makes proton transfer easy, leading to an equally stable, salt bridge isomer. The performances of a variety of density functionals in describing the geometries, energetics and infrared spectra of these two isomers were investigated. Usual density functionals were tested and moreover, more recent functionals such as dispersion-corrected ones and Truhlar’s M06 series were also considered. The computed infrared spectra are compared with ab initio results and InfraRed Multiple Photon Dissociation (IRMPD) experiments. Two functionals in the M06 series have been proved to be quite efficient. A large number of functionals seems to be inadequate to compute infrared spectra for peptide in the amide N-H stretching region. In addition, a detailed analysis of the sodium-peptide interaction and of the hydrogen bond between the two peptide terminations points out a distinct electronic structure for the two isomers.
First author: Johansson, Mikael P., Magnetizabilities at Self-Interaction-Corrected Density Functional Theory Level,JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 6, 3302, (2010)
Abstract: Using a recent high-quality ab initio coupled cluster benchmark set for magnetizabilities, we assess the performance of a set of density functionals, representing different levels of complexity, from the local density approximation (LDA), via generalized gradient approximations (GGA’s) to kinetic energy density including meta-GGA’s. The effect of self-interaction correction (SIC) is remarkable and, in most cases, leads to a significant error reduction, revealing the sensitivity of magnetizability toward a physically sound exchange-correlation potential.
First author: Tit, Nacir, Origins of visible-light emissions in hydrogen-coated silicon nanocrystals: Role of passivating coating, JOURNAL OF LUMINESCENCE, 130, 2226, (2010)
Abstract: We present a theoretical investigation of the electronic and optical properties of hydrogen-coated silicon nanocrystals (Si:H NCs). On one hand, the density-functional theory (DFT) is used to both calculate the total energy and relax the NCs. On a second hand, the tight-binding method, which includes the minimal sp(3)-basis set within the second-nearest-neighbor interaction scheme, is applied to calculate the electronic structures, oscillator strength (OS) and recombination rate (RR) versus the NC size, coating and atomic relaxation. Three main findings are reported: (i) The quantum confinement in these NCs do follow similar rule to the case of a single-particle in a box, where the confinement energy decays in power-law with the increasing NC’s size. (ii) The coating is shown to play the essential role in creation of large band-gap energy lying within the visible-light energy spectrum. (iii) The surface atomic relaxation is found to reduce the band-gap energy by about 150 meV and enhance both OS and RR. Our claims are corroborated by the available experimental data.
First author: Mitoraj, Mariusz P., Theoretical description of hydrogen bonding in oxalic acid dimer and trimer based on the combined extended-transition-state energy decomposition analysis and natural orbitals for chemical valence (ETS-NOCV),JOURNAL OF MOLECULAR MODELING, 16, 1789, (2010)
Abstract: In the present study we have analyzed hydrogen bonding in dimer and trimer of oxalic acid, based on a recently proposed charge and energy decomposition scheme (ETS-NOCV). In the case of a dimer, two conformations, alpha and beta, were considered. The deformation density contributions originating from NOCV’s revealed that the formation of hydrogen bonding is associated with the electronic charge deformation in both the sigma-(Delta rho(sigma)) and pi-networks (Delta rho(pi)). It was demonstrated that sigma-donation is realized by electron transfer from the lone pair of oxygen on one monomer into the empty rho(H-O)*orbital of the second oxalic acid fragment. In addition, a covalent contribution is observed by the density transfer from hydrogen of H-O group in one oxalic acid monomer to the oxygen atom of the second fragment. The resonance assisted component (Delta rho(pi)), is based on the transfer of electron density from the pi-orbital localized on the oxygen of OH on one oxalic acid monomer to the oxygen atom of the other fragment. ETS-NOCV allowed to conclude that the sigma(O—HO) component is roughly eight times as important as pi (RAHB) contribution in terms of energetic estimation. The electrostatic factor (Delta E-elstat) is equally as important as orbital interaction term (Delta E-orb). Finally, comparing beta-dimer of oxalic acid with trimer we found practically no difference concerning each of the O-HO bonds, neither qualitative nor quantitative.
First author: Wang, Yi-Lei, Photoelectron Imaging and Spectroscopy of MI2- (M = Cs, Cu, Au): Evolution from Ionic to Covalent Bonding, JOURNAL OF PHYSICAL CHEMISTRY A, 114, 11244, (2010)
Abstract: We report a combined experimental and theoretical investigation of MI2- (M = Cs, Cu, Ag, Au) to explore the chemical bonding in the group IA and IB diiodide complexes. Both photoelectron imaging and low-temperature photoelectron spectroscopy are applied to MI2- (M = Cs, Cu, Au), yielding vibrationally resolved spectra for CuI2- and AuI2- and accurate electron affinities, 4.52 +/- 0.02, 4.256 +/- 0.010, and 4.226 +/- 0.010 eV for CsI2, CuI2, and AuI2, respectively. Spin-orbit coupling is found to be important in all the diiodide complexes and ab initio calculations including spin-orbit effects allow quantitative assignments of the observed photoelectron spectra. A variety of chemical bonding analyses (charge population, bond order, and electron localization functions) have been carried out, revealing a gradual transition from the expected ionic behavior in CsI2- to relatively strong covalent bonding in AuI2-. Both relativistic effects and electron correlation are shown to enhance the covalency in the gold diiodide complex.
First author: Hadley, Allison, Thiolate Ligand Exchange Mechanisms of Au-1 and Subnanometer Gold Particle Au-11,JOURNAL OF PHYSICAL CHEMISTRY C, 114, 18134, (2010)
Abstract: Density functional theory is employed to examine the thiolate-for-thiolate ligand exchange mechanism of the undecagold Au-11(SR’)(3)(PH3)(7) particle with several incoming thiols HSR” (R’ = H, CH3; R” = H, CH3, CH2CH3, CH2CH2CH3, CH2CH(NH2)COOH). The reaction with cysteine is investigated as a representation for undecagold-protein binding. BP86 calculations using double-, triple-, and quadruple-zeta basis sets on a model Au-1 system show that the triple-zeta basis set predicts reaction energies and geometries in good agreement with the larger quadruple-zeta basis set, while barrier heights are underestimated by similar to 9 kJ/mol. Ligand exchange reaction on Au-11 is more endothermic than Au-1 and longer organic chains on the incoming thiol lead to increases in the reaction energy of up to 0.8 kJ/mol. The reaction of cysteine is more favorable than other ligands, and the reaction energy is predicted to be -5.0 kJ/mol with the Au-11(SCH3)(3)(PH3)(7) particle. Barrier heights are essentially constant for aliphatic ligands, while the barrier height is 10 kJ/mol higher for the incoming cysteine molecule.
First author: Garcia-Lastra, J. M., Communication: Systematic shifts of the lowest unoccupied molecular orbital peak in x-ray absorption for a series of 3d metal porphyrins, JOURNAL OF CHEMICAL PHYSICS, 133, 18134, (2010)
Abstract: Porphyrins are widely used as dye molecules in solar cells. Knowing the energies of their frontier orbitals is crucial for optimizing the energy level structure of solar cells. We use near edge x-ray absorption fine structure (NEXAFS) spectroscopy to obtain the energy of the lowest unoccupied molecular orbital (LUMO) with respect to the N-1s core level of the molecule. A systematic energy shift of the N-1s to LUMO transition is found along a series of 3d metal octaethylporphyrins and explained by density functional theory. It is mainly due to a shift of the N-1s level rather than a shift of the LUMO or a change in the electron-hole interaction of the core exciton.
First author: Lo, Andy Y. H., Multinuclear Solid-State Magnetic Resonance Study of In+ and Ag+ in Neutral Weakly Coordinating Environments, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 1, 3078, (2010)
Abstract: A comprehensive multinuclear solid-state magnetic resonance study of In(I) and Ag(I)bis(imino)pyridine systems is presented. Solid-state. In-115 and Ag-109 NMR experiments are utilized to probe the metal cation centers, which are very weakly coordinated to the bis(imino)pyridine ligands. Along with solid-state N-15 NMR data, it is shown that the metal cations interact with the N’atoms within the “pocket” of the ligands. Reasonable agreement between the measured and calculated In-115 NMR (electric field gradient and chemical shift) tensors is obtained. The relationship between the electric field gradient tensor and the arrangement of the metal center relative to the encumbered ligand is explored. The insights obtained aid in understanding the structure and bonding in these kinetically stable complexes of unstable metal ions and may assist in the rational design of other encumbered ligands for capturing reactive species.
First author: Sanchez-Carrera, Roel S., Interaction of Charge Carriers with Lattice Vibrations in Oligoacene Crystals from Naphthalene to Pentacene, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 14437, (2010)
Abstract: A key feature of organic pi-conjugated materials is the strong connection between their electronic and geometric structures. In particular, it has been recently demonstrated that nonlocal electron-vibration (electron-phonon) interactions, which are related to the modulation of the electronic couplings (transfer integrals) between adjacent molecules by lattice vibrations, play an important role in the charge-transport properties of organic semiconductors. Here, we use density functional theory calculations and molecular mechanics simulations to estimate the strength of these nonlocal electron-vibration couplings in oligoacene crystals as a function of molecular size from naphthalene through pentacene. The effect of each optical vibrational mode on the electronic couplings is evaluated quantitatively. The results point to a very strong coupling to both intermolecular vibrational modes and intramolecular (including high-frequency) modes in all studied systems. Importantly, our results underline that the amount of relaxation energy associated with nonlocal electron-phonon coupling decreases as the size of the molecule increases. This work establishes an original relationship between chemical structure and nonlocal vibrational coupling in the description of charge transport in organic semiconductor crystals.
First author: Phillips, Val, Electronic Influences on Metallophilic Interactions in [Pt(tpy)X][Au(C6F5)(2)] Double Salts,INORGANIC CHEMISTRY, 49, 9265, (2010)
Abstract: Four double salt compounds of the type [Pt(tpy)X][Au(C6F5)(2)], where tpy =2,2′:6′,2 ”-terpyridine and X = Cl, 3, Br, 4, I, 5, and CCPh, 6, and their platinum starting materials, [Pt(tpy)Br]Br center dot 2H(2)O, 1, and [Pt(tpy)(CCPh)]PF6 center dot DMF center dot H2O, 2, have been synthesized and characterized. Complex 2 is a solvated form of the known and structurally characterized [Pt(tpy)(CCPh)]PF6 species. All compounds were characterized by single-crystal X-ray diffraction, elemental analyses, and solution electronic spectra. Structural characterization shows that compounds 3 and 4 are similar in the solid state and form cation-anion stacking patterns while compounds 5 and 6 form chains of cations supported by metallophilic interactions with anion partners on either side of the chains. Solution studies (UV-vis and fluorescence) strongly suggest that there are no Pt center dot center dot center dot Au interactions in solution state. Electronic structure calculations with density functional theory (DFT) elucidate the subtle changes in the electronic scaffolding of the ions in these compounds and show that predictions of metallophilic interactions are not straightforward but can be understood in terms of orbital symmetry and the relative energies of the frontier orbitals.
First author: Shaw, Michael J., Facile Determination of the Spectra of Unstable Electrode Products Using Simultaneous Fiber-Optic Chronoabsorptometry and Chronoamperometry, INORGANIC CHEMISTRY, 49, 9590, (2010)
Abstract: A widely applicable fiber-optic UV-vis method to determine the spectra of in situ generated redox products and intermediates at or near an electrode surface is described mathematically and implemented experimentally. The quantitative spectral information obtained gives extinction coefficients (absorptivities) as a function of wavelength, requires no arbitrary subtraction of the spectrum of the starting material, and is relatively insensitive to path length and concentration during the spectroelectrochemical measurements. We demonstrate proof-of-concept of this methodology by reproducing the expected spectrum of the ferrocenium ion from electrooxidation of ferrocene in MeCN, and by reproducing the spectrum that reveals pi-radical cation formation from the electrooxidation of (T(p-OMe)PP)Co(NO) ((T(p-OMe)PP = 5,10,15,20-tetra(p-methoxyphenyl)porphyrinato dianion). Importantly, we demonstrate its use for the facile detection of unstable redox products not previously detected by current spectroelectrochemical methods. We obtain, for the first time, the experimental UV-vis spectrum of the short-lived fac-[(dppe)Mn(CO)(3)Br](+) cation, a hitherto uncharacterized intermediate that forms during the archetypal redox-induced fac-to-mer isomerization of (dppe)Mn(CO)(3)Br (dppe = diphenylphosphinoethane). Spectral features of the Mn-containing species have been verified by comparison to theoretical spectra calculated by time-dependent density functional theory methods.
First author: Zarate, Ximena, DFT study on the electronic structure, energetics and spectral properties of several bis(organohydrazido(2-)) molybdenum complexes containing substituted phosphines and chloro atoms as ancillary ligands, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 957, 126, (2010)
Abstract: A theoretical study of the geometrical and electronic structure of several structurally related bis(organohydrazido(2-))-molybdenum complexes containing substituted phosphines and chloro atoms as ancillary ligands, of formula [Mo(NNPh2)(2)Cl-2(PPh3)(2)] (1), [Mo(NNPh2)(2)Cl-2(PMePh2)(2)] (2), [Mo(NNPh2)(2)Cl-2(PMe2Ph)(2)] (3), [Mo(NNPh2)(2)Cl-2(PMe3)(2)] (4) and [Mo(NNPh2)(2)Cl-2(PH3)(2)] (5), was carried out. In order to analyze the electronic effects when the phosphines are changed, a decomposition energy analysis was performed, finding that the Mo-Cl interactions have long distance and ionic character with poor “p” antibonding contributions. Besides, the metal-phosphine interactions have little covalent character, while the Mo-hydrazido(-2) interaction with significant orbital contribution, indicates a strong covalent character with respect to the rest of the ligands. On the other hand, the calculated electronic transitions using the Time-Dependent Density Functional Theory (TDDFT) are also presented at GGA and B3LYP theoretical levels, and despite of the limitations of the first method, we obtained a good correlation with B3LYP analysis performed. Also, the calculated excitations are in good agreement with the experimental data for (2) and (3), moreover, we were able to predict the electronic transitions that could be observed in the proposed (1), (4) and (5) complexes and these results indicate that these compounds are stable and they should be able to be synthesized.
First author: Clayborne, Penee A., The applicability of three-dimensional aromaticity in BiSnn- Zintl analogues, JOURNAL OF CHEMICAL PHYSICS, 133, 126, (2010)
Abstract: Three-dimensional aromaticity is shown to play a role in the stability of deltahedral Zintl clusters and here we examine the connection between aromaticity and stability. In order to gain further insight, we have studied Zintl analogs comprised of bismuth doped tin clusters with photoelectron spectroscopy and theoretical methods. To assign aromaticity, we examine the ring currents induced around the cage by using the nucleus independent chemical shift. In the current study, BiSn4- is a stable cluster and fits aromatic criteria, while BiSn5- is found to fit antiaromatic criteria and has reduced stability. The more stable clusters exhibit an aromatic character which originates from weakly interacting s-states and bonding orbitals parallel to the surface of the cluster, while nonbonding lone pairs perpendicular to the surface of the cluster account for antiaromaticity and reduced stability. The effect of three-dimensional aromaticity on the electronic structure does not result in degeneracies, so the resulting variations in stability are smaller than those seen in conventional aromaticity.
First author: Fedorov, Alexey, Structure and Bonding of Isoleptic Coinage Metal (Cu, Ag, Au) Dimethylaminonitrenes in the Gas Phase, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 13789, (2010)
Abstract: Dimethylaminonitrene complexes of IMesM(+) (IMes =1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; M = Cu, Ag, Au) were prepared in the gas phase and structurally characterized by high-resolution infrared spectroscopy of the cold species, ion-molecule reactions, and DFT computations. We measured the binding energies of the nitrene fragment to the IMesM+ moiety by energy-resolved collision-induced dissociation experiments in the gas phase, affording a trend in bond strength of M = Cu approximate to Au > Ag. This trend is explained in terms of a detailed metal-nitrogen bonding analysis, from which relativistic effects on the bonding were assessed. Various density functionals were evaluated for reproducing the observed thermochemical data and Truhlar’s M06 functional was found to give the best agreement.
First author: Zuchowski, Piotr S., Ultracold RbSr Molecules Can Be Formed by Magnetoassociation, PHYSICAL REVIEW LETTERS, 105, 13789, (2010)
Abstract: We investigate the interactions between ultracold alkali-metal atoms and closed-shell atoms using electronic structure calculations on the prototype system Rb + Sr. There are molecular bound states that can be tuned across atomic thresholds with a magnetic field and previously neglected terms in the collision Hamiltonian that can produce zero-energy Feshbach resonances with significant widths. The largest effect comes from the interaction-induced variation of the Rb hyperfine coupling. The resonances may be used to form paramagnetic polar molecules if the magnetic field can be controlled precisely enough.
First author: Dethlefsen, Johannes R., Electron Paramagnetic Resonance Studies of Nitrosyl and Thionitrosyl and Density Functional Theory Studies of Nitrido, Nitrosyl, Thionitrosyl, and Selenonitrosyl Complexes of Chromium, INORGANIC CHEMISTRY, 49, 8769, (2010)
Abstract: The novel S = 1/2 thionitrosyl complexes Cr(NS)(CN)(5)(3-), Cr(NS)(dmso)(5)(2+), and Cr(NS)(nmf)(5)(2+) (dmso = dimethyl sulfoxide, nmf = N-methylformamide) have been prepared, and their optical and electron paramagnetic resonance (EPR) spectra were studied. The values of the isotropic and anisotropic hyperfine and superhyperfine coupling constants A(Cr-53), A(N-14), and A(C-13) and of g were determined from the EPR spectra at room temperature and at 66 K. The values of A(perpendicular to) and A(iso) in the thionitrosyl complexes were slightly higher than in the analogous nitrosyl complexes. A common feature in the optical absorption spectra of the thionitrosyl complexes in solution at 298 K is an absorption band around 600 nm with a vibronic structure whereas such a band is located around 450 nm in the analogous nitrosyl complexes. Density functional theory (DFT) studies of the series of complexes Cr(N)(H2O)(5)(2+), Cr(NO)(H2O)(5)(2+), Cr(NS)(H2O)(5)(2+), and Cr(NSe)(H2O)(5)(2+) show that the unpaired electron resides in a metal-based d(xy) orbital and that the electronic structure in the equatorial plane is similar in all four complexes and similar to Cr3+. The sigma donating ability was found in the order N3- >> NO < NS approximate to NSe and the pi accepting ability in the order NO > NS approximate to NSe. Time dependent DFT calculations gave in all four complexes a d(x2-y2) <- d(xy) transition energy around 17 500 cm(-1).
First author: Chaki, Nirmalya K., Controlling Band Gap Energies in Cluster-Assembled Ionic Solids through Internal Electric Fields, ACS NANO, 4, 5813, (2010)
Abstract: Assembling ionic solids where clusters are arranged in different architectures is a promising strategy for developing band gap-engineered nanomaterials. We synthesized a series of cluster-assembled ionic solids composed of [As-7-Au-2-As-7](4-) in zero-, one-, and two-dimensional architectures. Higher connectivity is expected to decrease the band gap energy through band broadening. However, optical measurements indicate that the band gap energy increases from 1.69 to 1.98 eV when moving from zero- to two-dimensional assemblies. This increase is a result of the local electric fields generated by the adjacent counterions, which preferentially stabilize the occupied cluster electronic states.
First author: Courcot, Blandine, Which Atomic Charges are Best Adapted to Describe Polyoxometalates?,INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 110, 2155, (2010)
Abstract: Studying several polyanions different atomic charges have been considered to determine which scheme can be trusted to describe their chemistry. Focussing on hexa, hepta and octa-anions, five types of charges evaluated with Density-functional methods have been compared and discussed: Mulliken, Quantum Theory of Atoms in Molecules (QTAIM), Hirshfeld, Voronoi Deformation Density (VDD), and the net total Voronoi (NTV) charges. It appears that the same two groups of atomic charges predict comparable values. The first group encompasses Mulliken, QTAIM and the NTV charges and the second one Hirshfeld and VDD charges. When the two groups are compared they present two different tendencies regarding the different types of oxygen atoms that can be isolated in the studied polyanions. The absolute value of the first group charges increases with the coordination number of the oxygen atom, whereas Hirshfeld and VDD charges display the opposite variation. These two different tendencies are enhanced by the number of metal atoms in the polyanion. Surprisingly, the NTV charges, which are rarely used in comparison with the VDD, show the same trend as the QTAIM charges which emphasizes the implication of the promolecule’s definition in the failure of the Hirshfeld and VDD methods in this study. The Coulomb potential shows that Hirshfeld and VDD atomic charges are not adapted to reproduce the electrostatic properties of the anions which leads to the conclusion that these two partitioning approaches can’t describe correctly the chemistry of polyanions and have to be considered with care when dealing with charged species.
First author: Swart, Marcel, Density Functional Calculations of E2 and S(N)2 Reactions: Effects of the Choice of Method, Algorithm, and Numerical Accuracy, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 6, 3145, (2010)
Abstract: Herein we provide a detailed account on how the potential energy surfaces of the E2 and S(N)2 reactions of X- + CH3CH2X (X = F, Cl) depend on various methodological and technical choices in density functional calculations. We cover a choice of density functionals (OLYP, various M06-types, and the new SSB-D), basis sets (up to quintuple- and quadruple-zeta for Gaussian- and Slater-type orbitals, respectively, plus polarization and diffuse functions), and other aspects of the computations (among others: nonrelativistic versus zeroth-order regular approximation relativistic; numerical integration accuracy; all-electron versus frozen core; self-consistent field (SCF) versus post-SCF). The program codes ADF and NWChem are used for calculations with Slater- and Gaussian-type basis sets, respectively. The fluoride systems (X = F) appear to not only depend extremely sensitively on the basis set size (especially the presence of diffuse functions) but also on other technical settings, especially in the case of hybrid meta-generalized gradient approximation functionals. This work complements a recent contribution (Y. Zhao, D. G. Truhlar, J. Chem, Theory Comput. 2010, 6, 1104) and provides recommendations for density functionals, basis sets, and technical settings.
First author: Srebro, Monika, On preference of insertion mechanism in the ethylene polymerization catalyzed by half-titanocene complexes with aryloxy ligands: Static and dynamic theoretical studies, MACROMOLECULAR RESEARCH,18, 960, (2010)
Abstract: The Ziegler-Rauk bond-energy decomposition analysis was performed for the frontside (FS) and backside (BS) transition states of ethylene insertion in the processes catalyzed by half-titanocenes with phenoxy ligands to rationalize the origin of the energetic preference of the backside insertion observed for the complexes with monosubstituted phenoxide(Type 4 catalysts). The final preference of the backside or frontside transition state comes as a balance between the electronic preference of the former, and the steric preference of the latter. The unique energetic preference of the backside insertion observed for Type 4 catalysts appears to be a result of reduced steric crowding. The openness near the metal center and conformational flexibility leads to enhanced catalytic activity of those systems. In addition, Car-Parinello molecular dynamic simulations were carried out to examine the influence of entropic effects on the preference of the insertion mechanism. For Type 4 catalysts, the spontaneous frontside insertion was observed. Therefore, at the free-energy level, frontside insertion becomes viable due to entropic destabilization of the backside transition state.
First author: Schuehly, Wolfgang, Dibenzocyclooctadiene lignans from Magnolia and Talauma (Magnoliaceae): Their absolute configuration ascertained by circular dichroism and X-ray crystallography and re-evaluation of previously published pyramidatin structures, PHYTOCHEMISTRY, 71, 1787, (2010)
Abstract: Twelve pyramidatins, i.e., dibenzocyclooctadiene-type lignans, together with Machilin G, were isolated from the dichloromethane extracts of aerial material of Talauma gloriensis, Magnolia fraseri, and Magnolia pyramidata (Magnoliaceae). These lignans contain a highly oxidized 7,9′-epoxy-2,2′-cyclolignane skeleton. Their structures were established using NMR spectroscopy (1D and 2D experiments) and mass spectrometry. The absolute configurations of five pairs of atropisomers (S(a)/R(a)-pyramidatins) and two single atropisomers (S(a)-pyramidatins) were determined by experimental and calculated circular dichroism (CD). In addition, the absolute configuration of (S(a))-3,3′,4,4′,5,5′-hexamethoxypyramidatin was confirmed using X-ray crystallography.Five pyramidatins, (R)-3,3′,4,4′,5,5′-hexamethoxypyramidatin, (R(a))-3,3′-dimethoxy-4,5:4′,5′-bis(methylenedioxy)pyramidatin, (S(a))-3,3′,4,5′-tetramethoxy-4,5-methylenedioxypyramidatin, ramethoxy-4,5-methylenedioxypyramidatin, and (R(a))-3,3′,4,5-tetramethoxy-4′,5′-methylenedioxypyramidatin are reported herein for the first time. In the current dataset, NMR values are in accordance with the observed and calculated CD values. These values are herein reported with particular reference to previously described data of pyramidatins, which have to be revised.
First author: Krapp, Andreas, Chemical bonding in “early-late” transition metal complexes [(H2N)(3)M-M'(CO)(4)] (M = Ti, Zr, Hf; M’ = Co, Rh, Ir), THEORETICAL CHEMISTRY ACCOUNTS, 127, 141, (2010)
Abstract: Quantum chemical DFT calculations at the BP86/TZ2P level have been carried out for the complex [HSi(SiH2NH)(3)Ti-Co(CO)(4)], which is a model for the experimentally observed compound [MeSi{SiMe2N(4-MeC6H4)}(3)Ti-Co(CO)(4)] and for the series of model systems [(H2N)(3)M-M'(CO)(4)] (M = Ti, Zr, Hf; M’ = Co, Rh, Ir). The Ti-Co bond in [HSi(SiH2NH)(3)Ti-Co(CO)(4)] has a theoretically predicted BDE of D (e) = 59.3 kcal/mol. The bonding analysis suggests that the titanium atom carries a large positive charge, while the cobalt atom is nearly neutral. The covalent and electrostatic contributions to the Ti-Co attraction have similar strength. The Ti-Co bond can be classified as a polar single bond, which has only little pi contribution. Calculations of the model compound (H2N)(3)Ti-Co(CO)(4) show that the rotation of the amino groups has a very large influence on the length and on the strength of the Ti-Co bond. The M-M’ bond in the series [(H2N)(3)M-M'(CO)(4)] becomes clearly stronger with Ti < Zr < Hf, while the differences between the bond strengths due to change of the atoms M’ are much smaller. The strongest M-M’ bond is predicted for [(H2N)(3)Hf-Ir(CO)(4)].
First author: Irfan, Ahmad, Toward rational designing of n-type materials: Theoretical investigations of mer-Alq3 derivatives, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 956, 61, (2010)
Abstract: The ground state geometries of the CN and OCH3 derivatives of the meridianal isomer of tris(8-hydroxyquinolinato)aluminum (mer-Alq3) were calculated by density functional theory. The absorption spectra were computed at the TD-PBE0/6-31G(*) level. We have observed that position for substitution plays important role for absorption properties. The cyano derivatives make the LUMO energy levels lower and the electron affinity increase, thus these derivatives would enhance the electron injection ability. The ionization potentials and electron affinities showed that cyano derivatives would be better hole blockers than methoxy derivatives. The reorganization energies indicate that CN derivatives would enhance the electron mobility while introduction of OCH3 has no effect in the enhancement of electron mobility. We explained the distribution of highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) on different individual ligands.
First author: Hodgson, Jennifer L., Side Reactions of Nitroxide-Mediated Polymerization: N-O versus O-C Cleavage of Alkoxyamines, JOURNAL OF PHYSICAL CHEMISTRY A, 114, 10458, (2010)
Abstract: Free energies for the homolysis of the NO-C and N-OC bonds were compared for a large number of alkoxyamines at 298 and 393 K, both in the gas phase and in toluene solution. On this basis, the scope of the N-OC homolysis side reaction in nitroxide-mediated polymerization was determined. It was found that the free energies of NO-C and N-OC homolysis are not correlated, with NO-C homolysis being more dependent upon the properties of the alkyl fragment and N-OC homolysis being more dependent upon the structure of the aminyl fragment. Acyclic alkoxyamines and those bearing the indoline functionality have lower free energies of N-OC homolysis than other cyclic alkoxyamines, with the five-membered pyrrolidine and isoindoline derivatives showing lower free energies than the six-membered piperidine derivatives. For most nitroxides, N-OC homolysis is normally favored above NO-C homolysis only when a heteroatom that is alpha to the NOC carbon center stabilizes the NO-C bond and/or the released alkyl radical is not sufficiently stabilized. As part of this work, accurate methods for the calculation of free energies for the homolysis of alkoxyamines were determined. Accurate thermodynamic parameters to within 4.5 kJ mol(-1) of experimental values were found using an ONIOM approximation to G3(MP2)-RAD combined with PCM solvation energies at the B3-LYP/6-31G(d) level.
First author: Cho, Herman, Comprehensive Solid-State NMR Characterization of Electronic Structure in Ditechnetium Heptoxide, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 13138, (2010)
Abstract: A relativistic density functional theory description of the electronic structure of Tc2O7 has been evaluated by comparison with solid-state Tc-99 and O-17 NMR spectroscopic data (the former isotope is a weak beta emitter). Every site in the molecule can be populated by a nucleus with favorable NMR characteristics, providing the rare opportunity to obtain a comprehensive set of chemical shift and electric field gradient tensors for a small molecular transition-metal oxide. NMR parameters were computed for the central molecule of a (Tc2O7)(17) cluster using standard ZORA-optimized all-electron QZ4P basis sets for the central molecule and DZ basis sets for the surrounding atoms. The magnitudes of the predicted tensor principal values appear to be uniformly larger than those observed experimentally, but the discrepancies were within the accuracy of the approximation methods used. The convergence of the calculated and measured NMR data suggests that the theoretical analysis has validity for the quantitative understanding of structural, magnetic, and chemical properties of Tc(VII) oxides in condensed phases.
First author: Matas, Inmaculada, Synthesis, Electronic Structure, and Reactivity of Strained Nickel-, Palladium-, and Platinum-Bridged [1]Ferrocenophanes, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 13279, (2010)
Abstract: The group 10 bis(phosphine)metalla[1]ferrocenophanes, [{Fe(eta(5)-C5H4)(2)}M(Pn-Bu-3)(2)] [M = Ni (4a), Pd (4b), and Pt (4c)], have been prepared by the reaction of Li-2[Fe(eta(5)-C5H4)(2)].tmeda (5, tmeda = N,N,N’,N’-tetramethylethylenediamine) with trans-[MCl2(Pn-Bu-3)(2)] [M = Ni (trans-6a) and Pd (trans-6b)] and cis-[PtCl2(Pn-Bu-3)(2)] (cis-6c), respectively. Single crystal X-ray diffraction revealed highly tilted, strained structures as characterized by a angles of 28.4 degrees (4a), 24.5 degrees (4b), and 25.2 degrees (4c) and a distorted square planar environment for the group 10 metal center. UV/visible spectroscopy and cyclic voltammetry indicated that all three compounds had smaller HOMO-LUMO gaps and were more electron-rich in nature than ferrocene and other comparable [1]ferrocenophanes. DFT calculations suggested that these differences were principally due to the electron-releasing nature of the M(Pn-Bu3)2 metal-ligand fragments. Attempts to induce thermal or anionic ring-opening polymerization of 4a- c were unsuccessful and were complicated by, for example, competing ligand dissociation processes or unfavorable chain propagation. In contrast, these species all reacted rapidly with acids effecting clean extrusion of the bis(phosphine)metal fragment. Carbon monoxide inserted cleanly into one of the palladium-carbon bonds of 4b to afford the ring-expanded, acylated product [{Fe(eta(5)-C5H4)(eta(5)-C5H4)(CO))Pd(Pn-Bu-3)(2)] (10). The nickel analogue 4a, however, afforded [Ni(CO)(2)(Pn-Bu-3)(2)] whereas the platinum-bridged complex 4c was inert. Remarkably, all compounds 4a-c were readily oxidized by elemental sulfur to afford the [5,5′]bicyclopentadienylidene (pentafulvalene) complexes [{eta(4):eta(0)-C5H4(C5H4)M(Pn-Bu-3)(2)] [M = Ni (11a)] and [(eta(2)-C10H8)M(pn-Bu-3)(2)] [M = pd (11b) and Pt (11c)] by a formal 4-electron oxidation of the carbocyclic ligands. Compounds 11b and 11c represent the first examples of [5,5′]bicyclopentadienylidene as a neutral eta(2)-ligand. The relative energies of eta(2)-coordination with respect to that of eta(4):eta(0) bonding were investigated for 11a -c by DFT calculations.
First author: Gourlaouen, C., Importance of backdonation in [M-(CO)](p+) complexes isoelectronic to [Au-(CO)](+),JOURNAL OF CHEMICAL PHYSICS, 133, 13279, (2010)
Abstract: In this contribution, we study several monocarbonyl-metal complexes in order to unravel the contribution of relativistic effects to the metal-ligand bond length and complexation energy. Using scalar density functional theory (DFT) constrained space orbital variation (CSOV) energy decomposition analysis supplemented by all-electron four-component DFT computations, we describe the dependency of relativistic effects on the orbitals involved in the complexation for the Au+ isoelectronic series, namely, the fully occupied 5d orbitals and the empty 6s orbitals. We retrieve the well-known sensitivity of gold toward relativity. For platinum and gold, the four-component results illustrate the simultaneous relativistic expansion of the 5d orbitals and the contraction of the 6s orbitals. The consequences of such modifications are evidenced by CSOV computations, which show the importance of both donation and backdonation within such complexes. This peculiar synergy fades away with mercury and thallium for which coordination becomes driven by the accepting 6s orbitals only, which makes the corresponding complexes less sensitive toward the relativistic effects.
First author: Rayon, Victor M., Structure and bonding in third-row main group dicarbides C2X (X=K-Br), JOURNAL OF CHEMICAL PHYSICS, 133, 13279, (2010)
Abstract: The molecular structures of third-row main group dicarbides C2X (X=K-Br) have been studied by theoretical methods. It is found that K, Ca, and Ga favor C-2v-symmetric (T-shape) ground states, whereas As, Se, and Br have linear or quasilinear ground states. In the case of germanium. a very flat potential energy surface is found and an L-shape structure seems to be the ground state. Dissociation energies into X+C-2 are relatively high. The main features of these compounds, in particular, the preference for linear or cyclic structures, have been rationalized in terms of the most relevant interactions between the third-row atom and dicarbon with the help of an energy decomposition analysis.
First author: Jablonski, Miroslaw, Influence of Confinement on Hydrogen Bond Energy. The Case of the FH center dot center dot center dot NCH Dimer, JOURNAL OF PHYSICAL CHEMISTRY A, 114, 10253, (2010)
Abstract: The influence of the external pressure on the energy of the intermolecular hydrogen bond is investigated by modeling the pressure effects with helium atoms located at fixed points in space around the hydrogen bonded dimer. Several methods of estimating the energy of the H center dot center dot center dot N hydrogen bond in the He center dot center dot center dot FH center dot center dot center dot NCH center dot center dot center dot He model system are proposed. They show that the energy of the H center dot center dot center dot N hydrogen bond in this confined dimer decreases continuously with the reduction of the He center dot center dot center dot He distance, thus with the increase of the pressure effect exerted on the confined dimer.
First author: Calhorda, Maria Jose, Heteropolynuclear Gold Complexes with Metallophilic Interactions: Modulation of the Luminescent Properties, INORGANIC CHEMISTRY, 49, 8255, (2010)
Abstract: Metalloligands of stoichiometry [AuCl(P-N)] have been obtained by the reaction of the heterofunctional phosphines P-N = PPh(2)py, PPh(2)CH(2)CH(2)py, or PPhpy(2) with [AuCl(tht)] (tht = tetrahydrothiophene). Reactions of these metalloligands with several metal compounds have afforded heteropolynuclear species which exhibit luminescent properties. The stoichiometries depend on the molar ratio and the heterometal. Thus, the reaction with [Cu(NCMe)(4)](+) in a molar ratio 2:1 gives the trinuclear compounds Au(2)CuCl(2)(P-N)(2)](+) in which the structure and Au…Cu interactions depend on the phosphine ligand. With rhodium and iridium derivatives the reactivity is different leading to complexes of the type [AuMCl(2)(cod)(P-N)] for P N = PPh(2)py, PPhpy(2), and [Au2M2C1(cod)2(P N)21C1 with PPh(2)CH(2)CH(2)py. Using [MCl2(NCPh)2] (M = Pd, Pt) in a 2:1 molar ratio yields [Au2MCI4(P N)21 and in a 1:1 molar ratio [AuPdC13(y3-PPhpy(2))]. Several compounds have been characterized by X-ray diffraction showing in many cases short Au…M distances. The luminescence of these derivatives has been studied. The metalloligands display bands assigned to intraligand (IL) transitions. For the bimetallic (Au/M) systems the luminescence depends on the heterometal present and on the metallophilic interactions. The most important excitations in the relevant energy range were assigned essentially a MMLCT character (from Rh/Ir and Au to ligands) based on density functional theory (DFT) calculations in selected complexes. The luminescence behavior in Rh/Ir [AuMC12(cod)(PPh2py)1 complexes was interpreted on the basis of the different nature of the half occupied orbitals in the triplet state.
First author: Severa, Godwin, Thermal Desorption, Vibrational Spectroscopic, and DFT Computational Studies of the Complex Manganese Borohydrides Mn(BH4)(2) and [Mn(BH4)(4)](2-), JOURNAL OF PHYSICAL CHEMISTRY C, 114, 15516, (2010)
Abstract: The mechanochemical reaction of LiBH4 with MnCl2 produces the neutral complex Mn(BH4)(2). Thermal desorption studies show that the mechanochemical reaction of NaBH4 with MnCl2 produces a different species, apparently Na2Mn(BH4)(4), that undergoes dehydrogenation of a much lower weight percent H at a similar to 20 degrees C higher temperature than the neutral Mn(BH4)(2). Vibrational spectroscopy also reveals that a complex manganese borohydride(s) in addition to Mn(BH4)(2) are formed from the mechanochemical reactions. Analysis of the vibrational spectra in conjunction with DFT calculations on a model Mn(BH4)(4)(2-) complex suggest bidentate binding of the [BH4](-) ligands to the Mn center in the anionic complex. The calculated highest frequencies of the B-H stretching modes (corresponding to the “free” B-H bonds) agree well with the experimental frequencies and support the presence of this structural feature.
First author: Pakiari, Ali Heidar, An insight into microscopic properties of aprotic ionic liquids: A DFT study, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 955, 47, (2010)
Abstract: The relationship between the structure of counter-ions and inter-ionic interaction in ion-pairs is systematically studied for 15 aprotic ionic liquids (AlLs) using density functional theory. Five different substituted imidazolium cations and three different polyatomic anions (PA) are taken into account. Theoretical calculations show that the inter-ionic interaction decreases as the vdW volume of the counter-ions increases. By means of a new decomposition scheme called ETS-NOCV [33], which decomposes the total interaction energy into different parts, it can be shown that there is a clear linear relationship between the electrostatic part of the interaction energy and the total interaction energy. Further, for a given PA the electrostatic interaction decreases with increase of the vdW volume of the cation as one would expect. A similar decrease is seen in the electrostatic interaction between a given imidazolium cation on the PAs as the PA vdW volume increases.
First author: Kulhanek, J., Optical Operation by Chromophores Featuring 4,5-Dicyanoimidazole Embedded within Poly(methyl methacrylate) Matrices, JOURNAL OF PHYSICAL CHEMISTRY A, 114, 9440, (2010)
Abstract: We have studied photoinduced absorption, birefringence, and optical second-harmonic generation in poly(methyl methacrylate) (PMMA) films doped by organic chromophores featuring 4,5-dicyanoimidazole in the weight content equal to 5%. The chromophores indicated as IM1-1M6 were synthesized from 2-bromo-1-methylimidazole-4,5-dicarbonitrile by either nucleophilic substitution or Suzuki-Miyaura cross-coupling reaction. The samples were obtained as films of several micrometers thickness by the spin-coating method on a quartz substrate. Measurements of the optically induced birefringence were done by the Senarmont method at wavelength 1150 nm, and photoinduced absorption was studied in the spectral range 250-700 nm under optical treatment by 300 mW cw 532 nm laser. Photoinduced optical effects were studied by bicolor 1064 and 532 nm coherent laser pulses. The maximal changes were observed for the ratio between fundamental and writing beam intensities equal to about 7:1. To interpret the observed experimental measurements, theoretical simulations of photoinduced optical properties were performed by quantum chemical computational methods.
First author: Liao, Meng-Sheng, Iron Porphyrins with Different Imidazole Ligands. A Theoretical Comparative Study,JOURNAL OF PHYSICAL CHEMISTRY A, 114, 9554, (2010)
Abstract: A theoretical comparative study of a series of five- and six-coordinate iron porphyrins, FeP(L) and FeP(L)(O-2), has been carried out using DFT methods, where P = porphine and L = imidazole (Im), 1-methylimidazole (1-MeIm), 2-methylimidazole (2-MeIm), 1,2-dimethylimidazole (1,2-Me(2)Im), 4-ethylimidazole (4-EtIm), or histidine (His). Two ligated “picket-fence” iron porphyrins, FeTpivPP(2-MeIm) and FeTpivPP(2-MeIm)(O-2), were also included in the study for comparison. A number of density functionals were employed in the computations to obtain reliable results. The performance of functionals and basis set effects were investigated in detail on FeP, FeP(Im), and FeP(Im)(O-2), for which certain experimental information is available and there are some previous calculations in the literature for comparison. Many subtle distinctions in the effects of the different imidazole ligands on the structures and energetics of the deoxy- and oxy iron porphyrins are revealed. While FeP(2-MeIm) is identified to be high spin (S = 2), the ground state of FeP(1-MeIm) may be an admixture of a high-spin (S = 2) and an intermediate-spin (S = 1) state. The ground state of FeP(L)(O-2) may be different with different L. A weaker Fe L bond more likely leads to an open-shell singlet ground state for the oxy complex. The 2-methyl group in 2-MeIm, which increases steric contact between the ligand and the porphyrinato skeleton, weakens the Fe-O-2 bond, and thus iron porphyrins with 2-MeIm mimic T-state (low affinity) hemoglobin. The calculated FeP(2-MeIm)-O-2 bonding energy is comparable to the FeTpivPP(2-MeIm)-O-2 one, in agreement with the fact that the picket-fence iron porphyrin binds O-2 with affinity similar to that of myoglobin but different from the result obtained by the CPMD scheme. Im and 4-EtIm closely resemble His, the biologically axial base, and so future computations on hemoprotein models can be simplified safely by using Im.
First author: Zhu, Jianfeng, A Solid-State O-17 NMR Study of L-Tyrosine in Different Ionization States: Implications for Probing Tyrosine Side Chains in Proteins, JOURNAL OF PHYSICAL CHEMISTRY B, 114, 11681, (2010)
Abstract: We report experimental characterization of O-17 quadrupole coupling (QC) and chemical shift (CS) tensors for the phenolic oxygen in three L-tyrosine (L-Tyr) compounds: L-Tyr, L-Tyr center dot HCl, and Na-2(L-Tyr). This is the first time that these fundamental O-17 NMR tensors are completely determined for phenolic oxygens in different ionization states. We find that, while the O-17 QC tensor changes very little upon phenol ionization, the O-17 CS tensor displays a remarkable sensitivity. In particular, the isotropic O-17 chemical shift increases by approximately 60 ppm upon phenol ionization, which is 6 times larger than the corresponding change in the isotropic C-13 chemical shift for the C-zeta nucleus of the same phenol group. By examining the CS tensor orientation in the molecular frame of reference, we discover a “cross-over” effect between delta(11) and delta(22) components for both O-17 and C-13 CS tensors. We demonstrate that the knowledge of such “cross-over” effects is crucial for understanding the relationship between the observed CS tensor components and chemical bonding. Our results suggest that solid-state O-17 NMR can potentially be used to probe the ionization state of tyrosine side chains in proteins.
First author: Ribas, Xavi, Facile C-H Bond Cleavage via a Proton-Coupled Electron Transfer Involving a C-H center dot center dot center dot Cu-II Interaction, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 12299, (2010)
Abstract: The present study provides mechanistic details of a mild aromatic C-H activation effected by a copper(II) center ligated in a triazamacrocylic ligand, affording equimolar amounts of a Cu-III-aryl species and Cu-I species as reaction products. At low temperatures the Cu-II complex 1 forms a three-center, three-electron C-H center dot center dot center dot Cu-II interaction, identified by pulse electron paramagnetic resonance spectroscopy and supported by density functional theory calculations. C-H bond cleavage is coupled with copper oxidation, as a Cum-aryl product 2 is formed. This reaction proceeds to completion at 273 K within minutes through either a copper disproportionation reaction or, alternatively, even faster with 1 equiv of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), quantitatively yielding 2. Kinetic studies of both reactions strongly implicate a rate-limiting proton-coupled electron transfer as the key C-H activation step, a mechanism that does not conform to the C-H activation mechanism in a Ni-II analogue or to any previously proposed C-H activation mechanisms.
First author: Alemayehu, Abraham B., Nonplanar, Noninnocent, and Chiral: A Strongly Saddled Metallocorrole,INORGANIC CHEMISTRY, 49, 7608, (2010)
Abstract: The first crystal structure of a copper beta-octabromo-meso-triarylcorrole exhibits a uniquely saddled corrole macrocycle, where adjacent pyrrole rings are tilted relative to each other by 60-80 degrees. Such strong nonplanarity may be contrasted with the essentially planar macrocycle conformations observed in the vast majority of metallocorrole crystal structures. Density functional theory calculations suggest that two effects, ligand noninnocence and peripheral overcrowding, acting in concert, are responsible for the unique, observed conformation.
First author: Klein, Susanne, Carbodicarbenes and Related Divalent Carbon(0) Compounds, CHEMISTRY-A EUROPEAN JOURNAL, 16, 10160, (2010)
Abstract: Quantum-chemical calculations using DFT and ab initio methods have been carried out for fourteen divalent carbon(0) compounds (carbones), in which the bonding situation at the two-coordinate carbon atom can be described in terms of donor-acceptor interactions L -> C <- L. The chargeand energy-decomposition analysis of the electronic structure of compounds 1-10 reveals divalent carbon(0) character in different degrees for all molecules. Carbone-type bonding L -> C <- L is particularly strong for the carbodi-carbenes 1 and 2, for the “bent allenes” 3a, 3b, 4a, and 4b, and for the carbo-carbenephosphoranes 7a, 7b, and 7c. The last-named molecules have very large first and large second proton affinities. They also bind two BH(3) ligands with very high bond energies, which are large enough that the bis-adducts should be isolable in a condensed phase. The second proton affinities of the complexes 5, 6, and 8-10 bearing CO or N(2) as ligand are significantly lower than those of the other molecules. However, they give stable complexes with two BH(3) ligands and thus are twofold Lewis bases. The calculated data thus identify 1-10 as carbones L -> C <- L in which the carbon atom has two electron pairs. The chemistry of carbones is different from that of carbenes because divalent carbon(0) compounds CL(2) are p donors and thus may serve as double Lewis bases, while divalent carbon(II) compounds are p acceptors. The theoretical results point toward new directions for experimental research in the field of low-coordinate carbon compounds.
First author: Farah, Sara, Theoretical investigation of the coordination of dibenzazepine to transition-metal complexes: A DFT study, POLYHEDRON, 29, 2722, (2010)
Abstract: DFT calculations with full geometry optimizations have been carried out on a series of hypothetical compounds of the CpM(C14NH11) and (CO)(3)M(C14NH11) (M = transition metal and C14NH11 = dibenzazepine ligand) type. A rationalization of the bonding in hypothetical complexes is provided. Depending on the electron count and the nature of the metal, the dibenzazepine ligand can bind to the metal through the eta(1), eta(2), eta(3), eta(4), eta(5), eta(6), or eta(7) coordination mode adopting structures of types a or b. In the investigated species, the most favored closed-shell count is 18-MVE except for the Sc and V models which prefer the 16-MVE configuration.
First author: Pakiari, A. H., Nature and Strength of M-S Bonds (M = Au, Ag, and Cu) in Binary Alloy Gold Clusters,JOURNAL OF PHYSICAL CHEMISTRY A, 114, 9212, (2010)
Abstract: The interactions of pure (Au(k), Ag(k), and Cu(k); k = 1-3) and binary alloy (Au(n)Ag(m) and Au(n)Cu(m); m + n = k <= 3) metal clusters with hydrogen sulfide (H(2)S) have been investigated by using density functional theory (BP86, B3LYP, and CAM-B3LYP) and ab initio methods (MP2 and CCSD(T)), with a focus on the nature of metal-sulfur bonds. Binding energy calculations indicate that for pure metal clusters, the tendency of metal to interact with H(2)S has the order of Au > Cu > Ag. In binary alloy clusters, alloying Au(k) with copper and silver decreases the attraction of Au toward H(2)S, while alloying Ag(k) and Cu(k) by gold increases the attraction of Ag and Cu toward H(2)S, significantly. Dissociation energy values for isolated metal clusters specify the more favorable formation of binary alloy clusters (Au(n)Ag(m) and Au(n)Cu(m)) over pure ones. The nature of M-S bonds (M = Au, Ag, and Cu) is also interpreted by means of the quantum theory of atoms in molecules (QTAIM), natural bond orbital (NBO), and energy decomposition analysis (EDA). According to these theories, the M-S bonds are found to be partially electrostatic and partially covalent. EDA results identify that these bonds have less than 35% covalent character and more than 65% electrostatic, and the covalent character increases in different metals in the order Au > Cu > Ag.
First author: Aikens, Christine M., Geometric and Electronic Structure of Au-25(SPhX)(18)(-) (X = H, F, Cl, Br, CH3, and OCH3), JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 1, 2594, (2010)
Abstract: Using density functional theory calculations, the geometric structure of Au-25(SPh)(18)(-) is found to have S-6 symmetry. The electronic structure of this particle is affected by a splitting of the superatom P-z orbital from the set of P-x and P-y orbitals: this leads to a double peak similar to the characteristic double peak of Au-25(SCH2CH2Ph)(18)(-) and related compounds. Para substituents shift the HOMO and LUMO orbital energies, but the HOMO-LUMO gap remains constant. The shifts correspond with Hammett substituent constants, with the exception of OCH3. Calculated optical absorption spectra are mostly unaffected by ligand substitution, although slight (0.1 eV) changes are evident in ligand-based transitions.
First author: Harb, Mohammad K., Synthesis and Characterization of [FeFe]-Hydrogenase Models with Bridging Moieties Containing (S, Se) and (S, Te), EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 1, 3976, (2010)
Abstract: [FeFe]-hydrogenase-active-site models containing larger chalcogens such as Se or Te have exhibited greater electron richness at the metal centers and smaller gas-phase ionization energies and reorganization energies relative to molecules containing S atoms. Diiron complexes related to the much-studied molecule [Fe-2(mu-SC3H6S)(CO)(6)] (1) have been prepared with one S atom replaced either by one Se atom to give [Fe-2(mu-SC3H6Se)(CO)(6)] (2) or by one Te atom to give [Fe-2(mu-SC3H6Te)(CO)(6)] (3). The molecules have been characterized by use of mass spectrometry and C-13{H-1} NMR, Se-77{H-1)}NMR, IR, and photoelectron spectroscopic techniques along with structure determination with single-crystal X-ray diffraction, electrochemical measurements, and DFT calculations. He I photoelectron spectra and DFT computations of 2 and 3 show a lowering of ionization energies relative to those of the all-sulfur complex 1, indicating increased electron richness at the metal centers that favors electrocatalytic reduction of protons from weak acids to produce H-2. However, chalcogen substitution from S to Se or Te also causes an increase in the Fe-Fe bond length, which disfavors the formation of a carbonyl-bridged “rotated” structure, as also shown by the photoelectron spectra and computations. This “rotated” structure is believed to be important in the mechanism of H-2 production. As a consequence of the competing influences of increased electron richness at the metals with less favorable “rotated” structures, the catalytic efficiency of the Se and Te molecules 2 and 3 is found to be comparable to that of molecule 1.
First author: Marques, Alberto D. S., Experimental and Theoretical Studies of 2-Amino-3-methylimidazo[4,5-f] quinoline Derivatives: Cooked-Food Mutagens, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 110, 2047, (2010)
Abstract: The UV absorption spectra of two potent mutagens, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and NO2-IQ, dissolved in ethanol, were observed at room temperature. General appearance of the two spectra is somewhat different. The absorption spectra show five bands in the region above 200 nm. The peak positions of the five bands are similar in the two spectra. The observed bands in the two molecules were assigned using transition energies calculated with time-dependent density functional theory with triple-zeta polarized basis set with the statistical average of orbital potentials exchange-and-correlation functional. The emission spectra of the two molecules dissolved in ethanol were obtained at 77 K. Only fluorescence emission was observed in IQ. No phosphorescence emission of the molecule was observed. Both fluorescence and phosphorescence emissions were observed in NO2-IQ. These observations were interpreted with the aid of the calculated transition energy spectra. Some lowest vertical ionization energies of the two molecules were also calculated. The first ionization energy of NO2-IQ is greater than that of IQ by 1.2 eV. Core electron binding energies (CEBEs) of the two molecules were calculated as well. Using CEBE shifts of atoms in the molecules, it was possible to observe the changes of chemical environment when substituent changes.
First author: Koval, Peter, A Parallel Iterative Method for Computing Molecular Absorption Spectra, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 6, 2654, (2010)
Abstract: We describe a fast parallel iterative method for computing molecular absorption spectra within TDDFT linear response and using the LOAD method. We use a local basis of “dominant products” to parametrize the space of orbital products that occur in the LOAD approach. In this basis, the dynamic polarizability is computed iteratively within an appropriate Krylov subspace. The iterative procedure uses a matrix-free GMRES method to determine the (interacting) density response. The resulting code is about 1 order of magnitude faster than our previous full-matrix method. This acceleration makes the speed of our TDDFT code comparable with codes based on Casida’s equation. The implementation of our method uses hybrid MPI and OpenMP parallelization in which load balancing and memory access are optimized. To validate our approach and to establish benchmarks, we compute spectra of large molecules on various types of parallel machines. The methods developed here are fairly general, and we believe they will find useful applications in molecular physics/chemistry, even for problems that are beyond TDDFT, such as organic semiconductors, particularly in photovoltaics.
First author: Castro, Abril Carolina, Scalar and Spin-Orbit Relativistic Corrections to the NICS and the Induced Magnetic Field: The case of the E-12(2-) Spherenes (E = Ge, Sn, Pb), JOURNAL OF CHEMICAL THEORY AND COMPUTATION,6, 2701, (2010)
Abstract: Can relativistic effects modify the NICS and the B-ind values? In this manuscript we evaluate the relativistic corrections incorporated via the zeroth-order regular approximation to the calculations of nucleus-independent chemical shifts and the induced magnetic field (B-ind) in the E-12(2-) spherenes (E = Ge, Sn, Pb). We found that both electron delocalization descriptors are strongly affected by the relativistic corrections. For instance, for plumbaspherene, the difference in values from the nonrelativistic to the relativity-included calculation is almost 40 ppm! Our results show that the changes observed in the NICS and B-ind values in the title cages are a consequence of the treatment of the relativistic effects. If these effects are included as scalar or spin orbit calculations, then we can establish the next trend: Ge-12(2-) is a nonaromatic species, Sn-12(2-) is a low aromatic species, and Pb-12(2-) is strongly aromatic, according to calculated NICS and B-ind values. Thus, any prediction of electron delocalization in molecules containing heavy elements without considering an adequate treatment for relativistic effects may lead to an erroneous chemical interpretation.
First author: Day, Paul N., Calculation of One- and Two-Photon Absorption Spectra of Thiolated Gold Nanoclusters using Time-Dependent Density Functional Theory, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 6, 2809, (2010)
Abstract: The one- (OPA) and two-photon (TPA) absorption spectra have been calculated for a gold dimer, for a monothiolated gold dimer anion, for a thiolated gold cluster [Au(25)(SH)(18)](-1), whose structure has been determined, and for a proposed cluster [Au(12)(SR)(9)](+1) using time-dependent density functional theory (TDDFT). Geometry optimization with different exchange-correlation (X-C) functionals yielded small differences which had significant consequences in the spectra calculations. The calculated excitation energies of Au(25)(SH)(18)(-1) are in excellent agreement with experiment when the local density approximation X alpha-optimized geometry is used with the B3LYP X-C functional. The CAMB3LYP and mCAM functionals yielded OPA results in good agreement with experiment for the dimer systems and the larger clusters. The super-atom theory was useful in analyzing the electronic transitions in the larger clusters. TPA was dominated by resonance effects, and the calculated cross-sections displayed a strong X-C functional dependence.
First author: Birk, Torben, Alkali metal cation complexation and solvent interactions by robust chromium(III) fluoride complexes, JOURNAL OF FLUORINE CHEMISTRY, 131, 898, (2010)
Abstract: Interaction of robust chromium(III) fluoride complexes with sodium or lithium cations in solution lead to hypsochromic spectral shifts of increasing magnitude along the series: trans-[CrF(2)(py)(4)](+), mer-[CrF(3)(terpy)], and fac-[CrF(3)(Me(3)tacn)]. Crystalline products isolated from solution exhibit mu(2)-bridging by the fluoride ligands in a linear fashion between Na(+)-ions and chromium centres in catena-[Na(H(2)O)(4)(mu-F)-trans-{CrF(py)(4))](HCO(3))(2) and in the dimers [Li(H(2)O)(n)(mu-F)-trans-{CrF(py)(4))}](2+) (n = 3, 4). The uncharged chromium complexes fac-[CrF(3)(Me(3)tacn)] and mer-[CrF(3)(terpy)] have been synthesized from mer-[CrF(3)(py)(3)] and shown to precipitate sodium salts from solution, of which 3[CrF(3)(Me(3-)tacn)]center dot 2Na(Bph(4)).solv and 6[CrF(3)(terpy)]center dot 4Na(Bph(4)).solv have been crystallographically characterized. In these clusters, the neutral fluoride complexes bring the Na(+) cation separation down to 3.610 angstrom and 3.369 angstrom, respectively, which is much closer than the inter-cation distance in NaCl and comparable to that of NaF. DFT calculations support the notion of a strong interaction between Na(+) ions and neutral chromium(III) fluoride complexes. The calculations reproduce the magnitude and the counter-intuitive sign of the spectral shifts induced by second sphere complexation in solution, which originates in a breakdown of the assumption of parameter transferability in ligand-field descriptions.
First author: Gruden-Pavlovic, Maja, DFT study of the Jahn-Teller effect in Cu(II) chelate complexes, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 954, 80, (2010)
Abstract: Density functional theory (DFT) in conjunction with the intrinsic distortion path (IDP) is employed to study the Jahn-Teller (JT) effect in all four diastereoisomers of tris(ethylenediamine)copper(II) ([Cu(en)(3)](2+)) and tris(ethyleneglycol)copper(II) ([Cu(eg)(3)](2+)) complexes. As a consequence of the JT effect all the isomers tetragonally elongate to the C-2 configurations. Although there are energy differences between the isomers of [Cu(en)(3)](2+), almost equal JT parameters suggest that chelate ring conformation does not have affect on the JT distortion. In a case of [Cu(eg)(3)](2+) JT effect causes additional hydrogen bond formation and these two effects define the overall geometry of isomers.
First author: Zlatar, Matija, Intrinsic Distortion Path in the analysis of the Jahn-Teller effect, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 954, 86, (2010)
Abstract: The multideterminental-DFT approach was performed in order to calculate the Jahn-Teller (JT) parameters for the JT active molecules. Within the harmonic approximation the JT distortion can be analysed as a linear combination of all totally symmetric normal modes in any of the low symmetry minimum energy conformation, which allows to calculate the Intrinsic Distortion Path (IDP), exactly from the high symmetry point to the low symmetry configuration. Results obtained by both methods are consistent and give direct insight into the coupling of electronic structure and nuclear movements. As examples, the results for Cu-3 cluster, cobaltocene and manganocene are reported.
First author: Senn, F., Calculation of Co-59 shielding tensor a using LF-DFT, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 954, 105, (2010)
Abstract: Co-59 NMR shielding tensor sigma calculation using perturbation theory within the framework of Ligand Field-Density Functional Theory (LF-DFT)[1] is implemented for transition-metal complexes as an extension of the LF-DFT methodology. We give some first results for absolute and relative shielding tensors, which are in a good agreement with experimental results as well as with other theoretical calculations.
First author: Elkechai, Aziz, A relativistic DFT study of the electron affinity of the biscyclopentadienyl uranium complexes Cp-2*UX2, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 954, 115, (2010)
Abstract: Electron affinities (EA) of a series of biscyclopentadienyl uranium complexes Cp-2*UX2 (X-2 = (BH4)(2), Me-2, (NEt2)Cl and (OEt)(2)) related to the U(III)/U(IV) redox system were calculated using Density Functional Theory (DFT) in the framework of the relativistic Zero Order Regular Approximation (ZORA) coupled with the Conductor-like Screening Model (COSMO) for a realistic solvation approach, implemented in the ADF (Amsterdam Density Functional) package. A good correlation (r(2) = 0.992-0.996) is obtained between the calculated EA values at the ZORA/BP86/TZP and ZORA/BP86/TZ2P levels and the measured half-wave potentials in THF for the series of complexes under consideration. The importance of spin-orbit coupling and solvent effect which must be taken into account in order to achieve the good agreement between theory and experiment, as well as the basis set extension, are brought to light. The influence of the non aromatic ligands X-2 on electron affinities was studied. The role of involved orbitals (singled occupied molecular orbital -SOMO- of anionic species or lowest unoccupied molecular orbital -LUMO- of neutral species) in the redox process is discussed.
First author: Parameswaran, Pattiyil, Chemical Bonding in Transition Metal Complexes with Beryllium Ligands [(PMe3)(2)M-BeCl2], [(PMe3)(2)M-BeClMe], and [(PMe3)(2)M-BeMe2] (M = Ni, Pd, Pt), JOURNAL OF PHYSICAL CHEMISTRY A,114, 8529, (2010)
Abstract: The equilibrium geometries and bond dissociation energies of the 14 valence electron (VE) complexes [(PMe3)(2)M-BeCl2], [(PMe3)(2)M-BeClMe], and [(PMe3)(2)M-BeMe2] with M = Nt, Pd, and Pt have been calculated using density functional theory at the BP86/TZ2P level. The nature of the M Be bond was analyzed with the NBO charge decomposition analysis and the EDA energy decomposition analysis. The theoretical results predict the equilibrium structures with a T-shaped geometry at the transition metal where the PMe3 ligands are in the axial positions The calculated bond dissociation energies show that the M E bond strengths are in the range of donor acceptor complexes of divalent beryllium compounds with ammonia. The bond strength decreases when the substituent at beryllium changes from Cl to CH3. The NBO analysis shows a negative charge at the BeX2 fragment, which indicates a net charge flow from the transition metal fragment to the beryllium fragment The energy decomposition analysis of the M-Be bonds suggests two donor acceptor bonds with sigma mid pi symmetry where the transition metal fragment is a double donor with respect to the beryllium ligand The pi component of the [Ni]-> BeXX’ donation is much smaller than the sigma component
First author: Kurczab, Rafat, Theoretical Analysis of the Resonance Assisted Hydrogen Bond Based on the Combined Extended Transition State Method and Natural Orbitals for Chemical Valence Scheme, JOURNAL OF PHYSICAL CHEMISTRY A, 114, 8581, (2010)
Abstract: We have analyzed hydrogen bonding in a number of species, containing from two to four hydrogen bonds. The examples were chosen in such a way that they would enable us to examine three different hydrogen bonds involving OH-O. NH-O, and NH-N A common feature of the investigated systems is that they all are expected to exhibit resonance assisted hydrogen bonding (RAHB) in the electronic pi-framework. Our analysis was based on a recently developed method that combines the extended transition state scheme with the theory of natural orbitals for chemical valence (ETS-NOCV) We find that hydrogen bonding is associated with charge rearrangement in both the electronic a-framework (Delta rho(sigma)) and the electronic pi-framework (47,). However the stabilization due to Delta rho(sigma) is four times as important as the stabilization (RAHB) due to Delta rho(pi). Stabilization due to the electrostatic interaction (Delta/E(elstat)) between the two monomers that are brought together to form the hydrogen bonds is also important However Delta E(el) cannot alone account for the strength of the hydrogen bonds as it is more than compensated for by the repulsive Pauli repulsion (Delta E(Pauli))When N’ is part of an aromatic ring, N’H-O and N’H-N bonds are similar in strength to OH-O links involving carboxylic groups. However, NH-O bonds involving amide groups (-NH(2)) are considerably weaker than the OH-O links mentioned above. In systems with different hydrogen bonds, their relative strength is determined collectively in such a way as to optimize the total interaction This can result in that one of the bonds (OH-O, NH-O, and NH-N) becomes particularly strong or exceptionally weak. Even within the same dimer two X’-HX bonds of the same type can show quite different strength
First author: Zhou, Jia, Ab Initio Molecular Dynamics Study of the Reaction between Th+ and H2O, JOURNAL OF PHYSICAL CHEMISTRY A, 114, 8613, (2010)
Abstract: The gas phase reaction of Th+ with H2O to produce HThO+ H and ThO+ + H-2 was investigated using density functional theory and coupled cluster methods. RRKM calculations of the branching ratio favor the H atomic elimination channel in disagreement with experiment Ab initio classical trajectory calculations were carried out to obtain a better model of the molecular dynamics. The molecular dynamics simulations yield a branching ratio of ca. 80% for the H-2 elimination channel to 20% for the H atomic elimination channel in qualitative agreement with the observed ratio of 65% to 35%.
First author: Xiao, Hai, Theoretical Investigations of Geometry, Electronic Structure and Stability of UO6: Octahedral Uranium Hexoxide and Its Isomers, JOURNAL OF PHYSICAL CHEMISTRY A, 114, 8837, (2010)
Abstract: The existence of a novel octahedral UO6 complex had been suggested by Pyykko et al [Pyykko, P.; Runeberg, N., Straka, M; Dyall, K. G Chem. Phys Lett 2000, 328, 415]. We have now investigated the stability, the geometric and electronic structures, and the vibrations of various UO6 molecules, using spin-orbit density functional and scalar-relativistic coupled-cluster approaches We find four different (meta-)stable species, namely D-3(2h)-UO2(eta(2)-O-2(center dot))(2) at lowest energy, C-3(2 nu)-UO4 center dot(eta(2)-O-2(center dot)) and D-1(3)-U(eta(2)-O-2)(3) at medium energies, and O-1(h)-UO6 at highest energy The decay of O-h-UO6 occurs via an activated spin-flip mechanism. The UO6 species correspond to local minima on singlet and triplet energy surfaces and might be trapped in noble gas matrices Experimentally, the four species might be identified through their vibrational spectra Uranium is best described as coordinated by oxygen atoms in various oxidation states as oxo O2-, oxido(I) O center dot-, peroxido O-2(2-), and superoxido O-2(center dot-) ligands. The occurrence of monovalent oxygen is remarkable The resulting characterization of the central ion as U-VI in all four cases does not fully reflect the electronic differences, nor the “valence-activity” of the U-6p(6) semicore shell
First author: Brewer, Kathryn E., TDDFT Investigation of Surface-Enhanced Raman Scattering of HCN and CN- on Ag-20,JOURNAL OF PHYSICAL CHEMISTRY A, 114, 8858, (2010)
Abstract: Density functional calculations at the BP86/TZP level of theory are employed to examine the structures, binding energies, and vibrational frequencies of HCN-Ag-20 and CN–Ag-20 complexes Excited states are calculated using time-dependent density functional theory. A short time approximation for the perturbed density matrix and an empirical damping factor are employed to calculate surface-enhanced Raman scattering (SERS) intensities that account for both chemical and electromagnetic enhancement effects. Chemical effects provide 1-2 orders of magnitude enhancement, whereas electromagnetic effects yield up to 6 orders of magnitude enhancement for CN- or 5 for HCN. The structures and SERS enhancement factors suggest that multiple bonding configurations may be observed in experiment.
First author: Morton, Seth Michael, A discrete interaction model/quantum mechanical method for describing response properties of molecules adsorbed on metal nanoparticles, JOURNAL OF CHEMICAL PHYSICS, 133, 8858, (2010)
Abstract: A new polarizable quantum mechanics/molecular mechanics method for the calculation of response properties of molecules adsorbed on metal nanoparticles is presented. This method, which we denote the discrete interaction model/quantum mechanics (DIM/QM) method, represents the nanoparticle atomistically which enables the modeling of the influence of the local environment of a nanoparticle surface on the optical properties of a molecule. Using DIM/QM, we investigate the excitation energies of rhodamine-6G (R6G) and crystal violet (CV) adsorbed on silver and gold nanoparticles of different quasispherical shapes and sizes. The metal nanoparticle is characterized by its static total polarizability, a reasonable approximation for frequencies far from the plasmon resonance. We observe that for both R6G and CV, the presence of the nanoparticle shifts the strongest excitation to the red similar to 40 nm and also increases the oscillator strength of that excitation. The shifts in excitation energies due to the nanoparticle surface are found to be comparable to those due to solvation. We find that these shifts decay quickly as the molecule is moved away from the surface. We also find that the wavelength shift is largest when the transition dipole moment is aligned with the edges of the nanoparticle surface where the electric field is expected to be the largest. These results show that the molecular excitations are sensitive to the local environment on the nanoparticle as well as the specific orientation of the molecule relative to the surface.
First author: Ziegler, Tom, On the calculation of charge transfer transitions with standard density functionals using constrained variational density functional theory, JOURNAL OF CHEMICAL PHYSICS, 133, 8858, (2010)
Abstract: It is well known that time-dependent density functional theory (TD-DFT) based on standard gradient corrected functionals affords both a quantitative and qualitative incorrect picture of charge transfer transitions between two spatially separated regions. It is shown here that the well known failure can be traced back to the use of linear response theory. Further, it is demonstrated that the inclusion of higher order terms readily affords a qualitatively correct picture even for simple functionals based on the local density approximation. The inclusion of these terms is done within the framework of a newly developed variational approach to excitation energies called constrained variational density functional theory (CV-DFT). To second order [CV(2)-DFT] this theory is identical to adiabatic TD-DFT within the Tamm-Dancoff approximation. With inclusion of fourth order corrections [CV (4) -DFT] it affords a qualitative correct description of charge transfer transitions. It is finally demonstrated that the relaxation of the ground state Kohn-Sham orbitals to first order in response to the change in density on excitation together with CV (4) -DFT affords charge transfer excitations in good agreement with experiment. The new relaxed theory is termed R-CV(4)-DFT. The relaxed scheme represents an effective way in which to introduce double replacements into the description of single electron excitations, something that would otherwise require a frequency dependent kernel.
First author: Han, Wen-Ge, Density Functional Theory Analysis of Structure, Energetics, and Spectroscopy for the Mn-Fe Active Site of Chlamydia trachomatis Ribonucleotide Reductase in Four Oxidation States, INORGANIC CHEMISTRY, 49, 7266, (2010)
Abstract: Models for the Mn Fe active site structure of ribonucleotide reductase (RNR) from pathogenic bacteria Chlamydia trachomatis(Ct) in different oxidation states have been studied in this paper, using broken-symmetry density functional theory (DFT) incorporated with the conductor like screening (COSMO) solvation model and also with finite-difference Poisson Boltzmann self-consistent reaction field (PB-SORE) calculations. The detailed structures for the reduced Mn(II)-Fe(II), the met Mn(III)-Fe(III), the oxidized Mn(IV)-Fe(III) and the superoxidized Mn(IV)-Fe(IV) states are predicted. The calculated properties, including geometries, Fe-57 Mossbauer isomer shifts and quadrupole splittings, and Fe-57 and Mn-55 electron nuclear double resonance (ENDOR) hyperfine coupling constants, are compared with the available experimental data. The Mossbauer and energetic calculations show that the (mu-oxo, mu-hydroxo) models better represent the structure of the Mn(IV) Fe(III) state than the di-mu-oxo models. The predicted Mn(IV) Fe(III) distances (2.95 and 2.98 angstrom) in the (mu-oxo, mu-hydroxo) models are in agreement with the extended X-ray absorption fine structure (EXAFS) experimental value of 2.92 angstrom (Younker et al. J. Am. Chem. Soc. 2008, 130, 15022-15027). The effect of the protein and solvent environment on the assignment of the Mn metal position is examined by comparing the relative energies of alternative mono-Mn(II) active site structures. It is proposed that if the Mn(II) Fe(II) protein is prepared with prior addition of Mn(II) or with Mn(II) richer than Fe(II), Mn is likely positioned at metal site 2, which is further from Phe127.
First author: Cerofolini, G. F., Assigning chemical configurations to the XPS features observed at pristine (100) Si surface resulting after etching in HF aqueous solution, APPLIED SURFACE SCIENCE, 256, 6330, (2010)
Abstract: While the analysis of the spectra resulting from energy- or angle-resolved X-ray photoelectron spectroscopy allows the in-depth atomic composition in the probed region to be determined even for complex samples, the determination of the bonding configuration is less trivial. In this paper it is shown that a description of the chemical shift in terms of partial charge and Madelung potential (as results from local modelling of the atom) can provide information even in complicate situations, like that characterizing the hydrogen-terminated (1 0 0) Si prepared by HF(aq) etching of the native oxide.
First author: Ruggera, Jose F., Towards a rational design of enantioselective heterogeneous catalysts: Modeling of chiral organotin precursors, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 953, 91, (2010)
Abstract: In this work, the modeling of organotin compounds of general formula Men-Sn-R-3 (Men = menthyl, R = alkyl or alkoxyalkyl) is carried out. These compounds can be employed as precursors for obtaining enantioselective heterogeneous catalysts, prepared by means of Surface Organometallic Chemistry on Metals techniques. Both Molecular Mechanics and Molecular Dynamics, as well as Density Functional Theory (DFT), were used to give an insight into the relative stability of the Sn-C bonds of several different organotin compounds. The calculations carried out on the molecules Men-Sn-(iso-Bu)(3) and Men-Sn-((1-OCH3)-Et)(3) showed that if these molecules are used as precursor compounds to prepare heterogeneous organobimetallic catalysts, the probability of losing the menthyl group in a dissociation process is lower, leading to a better performance of the resulting catalysts, in terms of enantiomeric excess.
First author: Farah, Sara, Electronic structure of bis-azepine transition-metal complexes: A DFT investigation, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 953, 143, (2010)
Abstract: DFT calculations with full geometry optimizations have been carried out on a series of hypothetical compounds of M(C6NH7)(2) (M = transition metal) type with an eclipsed and staggered conformations in order to understand their electronic structure. A rationalization of the bonding with respect to the electron count in all the investigated hypothetical complexes is provided. Depending on the electron count and the nature of the metal, the azepine ligands can bind to the metal through the (eta(7),eta(7)), (eta(6),eta(6)), (eta(7),eta(4)), (eta(6),eta(4)), (eta(4),eta(4)), (eta(4),eta(2)) and (eta(3),eta(3)) coordination modes.
First author: Conradie, Marrigje M., A density functional theory study of the oxidative addition of methyl iodide to square planar [Rh(acac)(P(OPh)(3))(2)] complex and simplified model systems, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 695, 2126, (2010)
Abstract: The transition state for the oxidative addition reaction [Rh(acac)(P(OPh)(3))(2)] + CH3I, as well as two simplified models viz. [Rh(acac)(P(OCH3)(3))(2)] and [Rh(acac)(P(OH)(3))(2)], are calculated with the density functional theory (DFT) at the PW91/TZP level of theory. The full experimental model, as well as the simplified model systems, gives a good account of the experimental Rh-ligand bond lengths of both the rhodium(I) and rhodium(III) beta-diketonatobis(triphenylphosphite) complexes. The relative stability of the four possible rhodium(III) reaction products is the same for all the models, with trans-[Rh(acac)(P( OPh)(3))(2)(CH3)(I)] (in agreement with experimental data) as the most stable reaction product. The best agreement between the theoretical and experimental activation parameters was obtained for the full experimental system.
First author: Acosta-Silva, Carles, Mutual Relationship between Stacking and Hydrogen Bonding in DNA. Theoretical Study of Guanine-Cytosine, Guanine-5-methylcytosine, and Their Dimers, JOURNAL OF PHYSICAL CHEMISTRY B, 114, 10217, (2010)
Abstract: The mutual relationship between stacking and hydrogen-bonding and the possible influence of stacking in the different behavior of cytosine (C) and 5-methylcytosine (C’) in DNA have been studied through complete DFT optimization of different structures of G-C and G-C’ dimers (i.e., G-C/C-G and G-C’/C’-G), using four different functionals. Our results show that stacking leads to an increase of the O-6 center dot center dot center dot H-N-4 hydrogen bond length and to a simultaneous decrease of the N-2-H center dot center dot center dot O-2 one, in such a way that both lengths approach each other and, in some cases, an inversion occurs These results suggest that stacking can be a factor to explain the disparity between theory and experiment on the relative strength of the two lateral hydrogen bonds. Regarding the difference between cytosine and 5-methylcytosine, we have shown that methylation enhances the stacking interactions, mainly due to the increase of polarizability Methylation also favors the existence of slid structures which can produce local distortions of DNA
First author: Chaur, Manuel N., Structural and Electrochemical Property Correlations of Metallic Nitride Endohedral Metallofullerenes, JOURNAL OF PHYSICAL CHEMISTRY C, 114, 13003, (2010)
Abstract: Structural and electrochemical property correlations of metallic nitride endohedral metallofullerenes (MN EMFs) were studied in detail. The electrochemical properties of these compounds are strongly dependent on the symmetry of the carbon cage and, except for the Sc3N cluster, are independent of the nature of the metallic cluster due to the localization of the HOMO and LUMO on the carbon cage. The X-ray structure of Gd3N@C-86 shows that the cage obeys the isolated pentagon rule and uses a cage with D-3 symmetry, in agreement with previously published data for Tb3N@C-86, the only other structurally characterized C-86 MN EMF. The electrochemical properties of different MN EMFs are used to probe the structural features of these compounds. Electrochemistry was used to determine the relative abundances of the D-5h and I-h isomers of M3N@C-80 compounds, whereas HPLC allowed the analysis of larger MN EMFs. The binding energies (BEs) were computed for different MN EMFs, and a strong correlation between the BE (of the cluster and fullerene cage) and the corresponding abundance of the given MN EMF was obtained. The results account for the different template stages and for the relative abundances observed for MN EMFs.
First author: Kaminski, Radoslaw, Constrained Excited-State Structure in Molecular Crystals by Means of the QM/MM Approach: Toward the Prediction of Photocrystallographic Results, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 1, 2349, (2010)
Abstract: The QM/MM method is applied to predict the excited triplet structure of a molecule embedded in a crystal. In agreement with experimental observation, it is found that conformation changes on excitation are severely restricted compared with geometry changes predicted for the isolated molecule. The results are of importance for understanding the photophysical properties of molecular solids.
First author: Mbomekalle, Israel-Martyr, Influence of the Heteroatom Size on the Redox Potentials of Selected Polyoxoanions, INORGANIC CHEMISTRY, 49, 7001, (2010)
Abstract: The apparent formal potentials for the one-electron redox process of most Keggin-type heteropolytungstates, XW12O40q-, have long been shown to linearly depend on their overall negative charges, in the absence of proton interference in the process. However, for a given overall negative charge, these formal potentials are also shown here to depend on the specific central heteroatom X. In the present work, cyclic voltammetry was used to study a large variety of Keggin-type anions, under conditions where their comparisons are straightforward. In short, apparent potential values get more negative (the clusters are more difficult to reduce) for smaller central heteroatoms within a given family of Keggin-type heteropolyanions carrying the same overall negative charge. Density functional theory calculations were performed on the same family of Keggin compounds and satisfactorily reproduce these trends. They show that internal XO4 units affect differently the tungstate oxide cage. The electrostatic potential created by each internal anionic unit in a fragment-like approach (XO4q-@W12O36) was analyzed, and it is observed that X atoms of the same group show slight differences. Within each group of the periodic table, X atoms with lower atomic numbers are also smaller in size. The net effect of such a tendency is to produce a more negative potential in the surroundings and thus a smaller capacity to accept electrons. The case of [BW12O40](5-) illustrates well this conclusion, with the smallest heteroatom of the Keggin series with group III central elements and a very negative reduction potential with respect to the other elements of the same group. Particularly in this case, the electronic structure of the Keggin anion shows the effects of the small size of boron: the highest occupied molecular orbitals of [BW12O40](5-) appear to be similar to 0.35 eV higher than those in the other clusters of the same charge, explaining that the BO4 unit is more unstable than AlO4 or GaO4 despite carrying the same formal charge.
First author: Radford, Robert J., Modular and Versatile Hybrid Coordination Motifs on alpha-Helical Protein Surfaces,INORGANIC CHEMISTRY, 49, 7106, (2010)
Abstract: We report here the construction of phenanthroline (Phen) and terpyridine (Terpy)-based hybrid coordination motifs (HCMs), which were installed on the surface of the four-helical bundle hemeprotein cytochrome cb(562). The resulting constructs, termed HPhen1, HPhen2, HPhen3, and HTerpy1, feature HCMs that are composed of a histidine ligand and a Phen or Terpy functionality located two helix turns away, yielding stable tri- or tetradentate coordination platforms. Our characterization of the tridentate HCMs indicates that they accommodate many divalent metal ions (Co2+, Ni2+, Cu2+, Zn2+) with nanomolar to femtomolar affinities, lead to significant stabilization of the a-helical protein scaffold through metal-mediated cross-linking, assert tight control over protein dimerization, and provide stable and high-affinity binding sites for substitution-inert metal probes. Our analyses suggest that such tridentate HCMs may be used modularly on any a-helical protein surface in a sequence-independent fashion.
First author: Hernandez-Marin, Elizabeth, A kinetic study of dimethyl sulfoxide reductase based on density functional theory, CANADIAN JOURNAL OF CHEMISTRY-REVUE CANADIENNE DE CHIMIE, 88, 683, (2010)
Abstract: We present a density functional theory study on the oxygen atom transfer (OAT) reaction of dimethyl sulfoxide (DMSO) with model complexes resembling a functional synthetic analogue of the molybdoenzyme DMSO reductase. The good agreement between our calculated Gibbs free energy profile and data derived from experimental kinetic parameters supports the reaction mechanisms of the oxygen atom transfer proposed in this study. When the mechanism involves the formation of a DMSO-bound intermediate, the calculations on the free energy surface provide valuable information that explains the origin of the apparent contradiction between the experimental findings and previous theoretical calculations with respect to the rate-limiting step of the reaction mechanism. The enzymatic mechanism of the OAT reaction is more complex than the mechanism of any synthetic analogue, mainly due to the formation of an enzyme-substrate adduct prior to the appearance of the substrate-bound intermediate. This study also presents a possible mechanism for the formation of such an adduct and the subsequent oxygen atom transfer. The mechanism involves a proton transfer to and from the substrate.
First author: Chong, Delano P., Density functional theory study on the electron spectra of naphthalene and azulene vapours, CANADIAN JOURNAL OF CHEMISTRY-REVUE CANADIENNE DE CHIMIE, 88, 787, (2010)
Abstract: The ionization and excitation spectra of valence and core electrons of naphthalene and azulene in the gas phase are studied with density functional theory. The results are compared with available experimental data and previous calculations. New estimates are proposed for the ionization energies of both valence and core electrons and the calculated excitation energies are consistent with experiment.
First author: Kukovec, Boris-Marko, Disappearing and Concomitant Polymorphism of Nickel(II) Complexes with 6-Hydroxypicolinic Acid. Structural and Density Functional Theory Studies, CRYSTAL GROWTH & DESIGN, 10, 3685, (2010)
Abstract: The recrystallization of the complex [Ni(6-OHpic)(2)(H(2)O)(2)](1) from a mixture of pyridine and acetone led to the formation of three different polymorphs of [Ni(6-OHpic)(2)(py)(2)]. The stable monoclinic polymorph 3 was obtained by evaporation of the solution, while the slow diffusion of acetone into the pyridine solution of I yielded the orthorhombic polymorph 2. Further attempts to prepare 2 again were unsuccessful (disappearing polymorph). The new pseudopolymorph [Ni(6-OHpic)(2)(py)(2)]center dot py (4) was obtained under the same conditions as 3, but again not reproducibly (concomitant and a disappearing polymorph). trans-[Ni(6-OHpic)(2)(py)(2)] formed one intramolecular O-H center dot center dot center dot O hydrogen bond and one intermolecular one to afford dimers (3) and infinite zigzag chains (2). When two intramolecular O-H center dot center dot center dot O hydrogen bonds were present, the dimers were held by pi-pi stacking (4). Density functional theory calculations showed trans-[Ni(6-OHpic)(2)(py)(2)] to be the most stable isomer. The hydrogen bonded dimers are the most stable motif, followed by pi-pi stacked dimers (9.6 kcal mol(-1)) and zigzag chains (24.7 kcal mol(-1)). Thermogravimetric studies showed the initial loss of two coordinated water molecules in 1 and pyridine in 3 in similar temperature ranges.
First author: Janjua, Muhammad Ramzan Saeed Ashraf, Quantum Chemical Design for Enhanced Second-Order NLO Response of Terpyridine-Substituted Hexamolybdates, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 10, 3466, (2010)
Abstract: A dramatic increase in the second-order nonlinear optical (NLO) response of terpyridine-substituted hexamolybdates has been observed from 886.55 x 10(-3) esu (system 1) to 4622.92 x 10(-3) esu (system 7). The dipole polarizabilities and second-order nonlinear optical (NLO) properties of terpyridine derivatives of hexamolybdates have been investigated by using time-dependent density functional theory (TDDFT). The quantum mechanical design suggests that [Mo(6)O(18)(N(4)C(25)H(14)(CF(3))(2) (CN)(2))](2-) (system 7) is the best choice among all studied systems to improve nonlinearity. The electron-withdrawing ability of electron-acceptor groups (F, Cl, Br, I, CF(3), and CN) at the end of the terpyridine ligand directs the charge transfer (CT) from the POM cluster to the terpyridine segment along the z axis, which leads to an efficient second-order NLO molecular design. These small changes in molecular composition by substitution may have disproportionately huge effects on the NLO properties, which can be attributed to the so-called “butterfly effect”.
First author: Song, Ping, A theoretical study on the efficient reversible redox-based switching of the second-order polarizabilities of two-dimensional nonlinear optical-active donor-acceptor phenanthroline-hexamolybdate, JOURNAL OF MOLECULAR GRAPHICS & MODELLING, 29, 13, (2010)
Abstract: The A-shaped phenanthroline-hexamolybdate compounds that are based on the reversible Mo-centered redox process were investigated. The attachment of hexamolybdate terminals to phenanthroline by a pi-conjugated phenylamine bridge generated the organic ligand-centered or Ni-centered HOMO and the transition metal Mo-centered LUMO. The population in HOMO and LUMO predicted the reversible Mo-VI/V redox process and the ligand-to-metal charge transfer (LMCT) to a polyanion acceptor, which consequently evoked a significant second-order nonlinear optical (NLO) response. Moreover, the electron transition of these compounds exhibited a large beta(zyy) tensor along the y-axis, which confirms a promising two-dimensional (2D) character with sizable anisotropy values. Interestingly, the addition of electrons into the high-valence Mo atom in the hexamolybdate acceptor evoked dramatic enhancements in the NLO response for the reduction states in contrast to the response of the corresponding oxidation states. The reduction states in system I exhibited second-order NLO responses about 200 times larger than the oxidation states. In addition, the attachment of the Ni atom in compound IIa(red) enhanced the NLO response to nearly 1019 times greater than the response of the corresponding oxidation state compound IIa. The Ni atom as the electron donor plays an important role in the major electron transition for the reduction states in system II. Therefore, the NLO response of such compounds can be reversibly switched through the transition metal Mo-VI/V redox that is effectively coupled with the LMCT transition. Thus, the NLO activity can be controlled by a one-electron redox process, and the redox-active phenanthroline-hexamolybdate compounds are promising candidates for 2D redox-switching NLO materials in novel optoelectronic applications.
First author: Ricciardi, Giampaolo, The role of the metal ion in the photophysical behavior of Co(II), Ni(II), and Cu(II) octabutoxynaphthalocyanines: insights from ultra-fast time-resolved spectroscopy and DFT/TDDFT calculations,JOURNAL OF PORPHYRINS AND PHTHALOCYANINES, 14, 689, (2010)
Abstract: The photo-deactivation mechanism of the MNc(OBu)(8) (M = Co, Ni, Cu) series of complexes is reviewed, with special emphasis on the role played by the central metal. Ultra-fast transient absorption experiments and Density Functional Theory and time-dependent Density Functional Theory calculations consistently show that the central metal modifies the photo-deactivation mechanism of the investigated complexes by inducing substantial changes in the nature and energy of the excited states lying between the photo-generated state and the ground state.
First author: Koval, Peter, Fast construction of the Kohn-Sham response function for molecules, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 247, 1841, (2010)
Abstract: The use of the linear combination of atomic orbitals method for excited states involves products of orbitals that are known to be linearly dependent. We identify a basis in the space of orbital products that is local for orbitals of finite support and with a residual error that vanishes exponentially with its dimension. As an application of our previously reported technique we compute the Kohn-Sham density response function chi(0) for a molecule consisting of N atoms in (NN omega)-N-2, operations, with N-omega the number of frequency points. We test our construction of chi(0) by computing molecular spectra directly from the equations of Petersilka-Gossmann-Gross in (NN omega)-N-2 operations rather than from Casida’s equations which takes N-3 operations. We consider the good agreement with previously calculated molecular spectra as a validation of our construction of chi(0). Ongoing work indicates that our method is well suited for the computation of the GW self-energy Sigma = iGW and we expect it to be useful in the analysis of exitonic effects in molecules.
First author: Tsalavoutis, John T., Density Functional Investigation and Bonding Analysis of Pentacoordinated Iron Complexes with Mixed Cyano and Carbonyl Ligands, JOURNAL OF COMPUTATIONAL CHEMISTRY, 31, 1969, (2010)
Abstract: The equilibrium structures and vibrational frequencies of the iron complexes [Fe(0)(CN)(n)(CO)(5-n)](n-1) and [Fe(II)(CN)(n)(CO)(5-n)](2-n) (n = 0-5) have been calculated at the BP86 level of theory. The Fe(0) complexes adopt trigonal bipyramidal structures with the cyano ligands occupying the axial positions, whereas corresponding Fe(2+) complexes adopt square pyramidal structures with the cyano ligands in the equatorial positions. The calculated geometries and vibrational frequencies of the mixed iron Fe(0) carbonyl cyanide complexes are in a very good agreement with the available experimental data. The nature of the Fe-CN and Fe-CO bonds has been analyzed with both charge decomposition and energy partitioning analysis. The results of energy partitioning analysis of the Fe-CO bonds shows that the binding interactions in Fe(0) complexes have 50-55% electrostatic and 45-50% covalent character, whereas in Fe(2+) 45-50% electrostatic and 50-55% covalent character. There is a significant contribution of the pi-orbital interaction to the Fe-CO covalent bonding which increases as the number of the cyano groups increases, and the complexes become more negatively charged. This contribution decreases in going from Fe(0) to Fe(2+) complexes. Also, this contribution correlates very well with the C-O stretching frequencies. The Fe-CN bonds have much less pi-character (12-30%) than the Fe-CO bonds.
First author: Loison, C., Additive Model for the Second Harmonic Generation Hyperpolarizability Applied to a Collagen-Mimicking Peptide (Pro-Pro-Gly)(10), JOURNAL OF PHYSICAL CHEMISTRY A, 114, 7769, (2010)
Abstract: Second harmonic generation (SHG) spectrometry has been recently applied to investigate the structure of proteins and sugars (collagen, myosin, starch, etc.). The interpretation of experimental data at the molecular length-scale remains often qualitative because of the difficulty to model the SHG signal of such large molecules. Simpson and co-workers proposed to estimate the hyperpolarizability of the peptide backbone as the sum of the individual hyperpolarizabilities of the peptide bonds.(49) This article discusses the hyperpolarizabilities obtained using such an additive model for a peptide (Pro-Pro-Gly)(10) modeling collagen, for which experimental hyperpolarizabilities have been measured and modeled recently.(46) To investigate possible parameters for the model, we performed time-dependent density functional theory (TDDFT) calculations of the hyperpolarizability of a few molecules containing one peptide bond. In a second step, the additive model is applied. The results produced using different input parameters are compared to each other and to experimental data. For the chosen peptide, the additive model using N-methylacetamide as a building block agrees qualitatively with hyper-Rayleigh scattering data. The results emphasize the need for more reference data to test the additivity hypothesis and the transferability of the parameters to other secondary structure of proteins.
First author: Craciun, Raluca, Electron Affinities, Fluoride Affinities, and Heats of Formation of the Second Row Transition Metal Hexafluorides: MF6 (M = Mo, Tc, Ru, Rh, Pd, Ag), JOURNAL OF PHYSICAL CHEMISTRY A, 114, 7571, (2010)
Abstract: High-level electronic structure calculations were used to evaluate reliable, self-consistent thermochemical data sets for the second row transition metal hexafluorides. The electron affinities, heats of formation, first (MF6 -> MF5 + F) and average M-F bond dissociation energies, and fluoride affinities of MF6 (MF6 + F- -> MF7-) and MF5 (MF5 + F- -> MF6-) were calculated. The electron affinities are higher than those of the corresponding third row hexafluorides, making them stronger one-electron oxidizers. The calculated electron affinities, in good agreement with the available experimental values, are 4.23 eV for MoF6, 5.89 eV for TcF6, 7.01 eV for RuF6, 6.80 eV for RhF6, 7.95 eV for PdF6, and 8.89 eV for AgF6. The corresponding pentafluorides are also very strong Lewis acids, although their acidities on the pF(-) scale are about one unit lower than those of the third row pentafluorides. The performance of a wide range of DFT exchange-correlation functionals was benchmarked by comparing them to our more accurate CCSD(T) results.
First author: Mulder, R. Joshua, Methyl Cation Affinities of Neutral and Anionic Maingroup-Element Hydrides: Trends Across the Periodic Table and Correlation with Proton Affinities, JOURNAL OF PHYSICAL CHEMISTRY A, 114, 7604, (2010)
Abstract: We have computed the methyl cation affinities in the gas phase of archetypal anionic and neutral bases across the periodic table using ZORA-relativistic density functional theory (DFT) at BP86/QZ4P/BP86/TZ2P. The main purpose of this work is to provide the methyl cation affinities (and corresponding entropies) at 298 K of all anionic (XHn-1-) and neutral bases (XHn) constituted by maingroup-element hydrides of groups 14-17 and the noble gases (i.e., group 18) along the periods 2-6. The cation affinity of the bases decreases from H+ to CH3+. To understand this trend, we have carried out quantitative bond energy decomposition analyses (EDA). Quantitative correlations are established between the MCA and PA values.
First author: Pan, Qing-Jiang, Binuclear Hexa- and Pentavalent Uranium Complexes with a Polypyrrolic Ligand: A Density Functional Study of Water- and Hydronium-Induced Reactions, INORGANIC CHEMISTRY, 49, 6509, (2010)
Abstract: Binuclear uranyl (VI) and (V) complexes of a Pacman-like polypyrrolic macrocycle (H4L) were investigated using relativistic density functional theory. The reactivity of the bis-uranyl(VI) complex (UO2)(2)(L) (2a) was explored computationally. Although 2a has not been obtained experimentally, its structural analogue (UO2)(OH)K(THF)(2)(H2LMe)] has been synthesized recently. The high reactive activity of 2a originates from its unique butterfly like cation cation structure, containing an active 0 center with easily broken U-O bonding and having unsaturated coordination sites of uranium(VI) along the equatorial plane. The present study indicates that 2a can react with water (Path 3) and hydronium (Path 4), which lead to the formation of a series of complexes with a triangle-like O=U=O=U=O skeleton. Path 3 results in an unusual complex containing a combined cis-uranyl/trans-uranyl cation cation structure, (cis-UO2)( trans-UO2)(H2O)(L) (4b), where the oxo atom of the trans-uranyl coordinates the uranium center of the cis-uranyl and the water bonds to the uranium of trans-uranyl in the equatorial plane. After a process of hydrogen transfer with an extremely low energy barrier (<1.5 kcal/mol), 4b is converted into a slightly more stable isomer (U2O3)(OH)(2)(L) (4a), where two hydroxyl groups link to two uranium atoms, respectively. In conjunction with previous studies, the free energies of reactions of 2a induced by isomerization (Path 1), proton (Path 2), water (Path 3), and hydronium (Path 4) were calculated in the gas phase and aqueous solution. Solvation stabilizes the free energy of the formation reactions of the neutral complexes but destabilizes that of the charged complexes. In these reactions, three pairs of isomers were obtained for binuclear uranium(VI) complexes, but only the most stable in each pair exists for the binuclear uranium(V) analogues.
First author: Tamura, Ryo, Conductance of telescoped double-walled nanotubes from perturbation calculations,PHYSICAL REVIEW B, 82, 6509, (2010)
Abstract: In a telescoped double-walled nanotube with the inner tube partially extracted from the outer tube, the total current is forced to flow between the layers. Considering the interlayer Hamiltonian as a perturbation, we can obtain an analytic formula for the interlayer conductance. The accuracy of the perturbation formula is systematically improved by including higher order terms. The interlayer interaction effective in the perturbation formula is the product of the interlayer Hamiltonian and the wave function. It clarifies the effects of the spatial range of the interlayer Hamiltonian and the band energy shift.
First author: Hernandez-Marin, Elizabeth, Density Functional Theory Study of the Magnetic Circular Dichroism Spectra of Molybdenyl Complexes, INORGANIC CHEMISTRY, 49, 6066, (2010)
Abstract: We report a density functional theory (DFT) study of the magnetic circular dichroism (MCD) spectra for four molybdenyl complexes: [MoOCl(4)](-), [MoO(S(2)C(2)H(4))(2)](-), [(Tp*)MoO(bdt)], and [(L3S)MoO(bdt)] (Tp* = hydrotris (3,5-dimethyl-1-pyrazolyl) borate; L3S = (2-dimethylethane-thiolate)bis(3,5-dimethylpyrazolyl)-methane; bdt =1,2-benzenedithiolate). The simulation of the temperature dependent MCD-bands (C-terms) that give rise to the spectra was performed using a method based on time-dependent DFT. In this method, the C-parameters are calculated by including spin orbit perturbations. On the basis of the theoretical calculations, new or additional assignments are made for the MCD spectra of the complexes; specially for [(L3S)MoO(bdt)], for which case only tentative assignments of the excitations have been proposed in recent years.
First author: Liu Kun, Interpretation of the Experimental Electron Momentum Spectra of 5e(1/2) and 5e(3/2) Orbitals of CF3I with Relativistic Calculations, CHINESE PHYSICS LETTERS, 27, 6066, (2010)
Abstract: With our newly developed method, we calculate the spin-orbit splitting states 5e(1/2) and 5e(3/2) of the CF3I molecule incorporating the relativistic effects. Our theoretical results agree excellently with the recent experimental observations. The present study shows that relativistic effects can evidently change the electron momentum distributions of molecular orbitals when a medium.. element is included, such as iodine.
First author: Zalis, Stanislav, Quantum chemical interpretation of redox properties of ruthenium complexes with vinyl and TCNX type non-innocent ligands, COORDINATION CHEMISTRY REVIEWS, 254, 1383, (2010)
Abstract: This review provides an overview of density functional theory (DFT) calculations in a consequence with spectroelectrochemical measurements on mononuclear and symmetrically or unsymmetrically bridged di- and tetranuclear ruthenium complexes of vinyl and TCNX ligands. The DFT approach is used for the calculations of molecular structures, vibrational frequencies, electronic and electron paramagnetic resonance (EPR) spectral data. OFT calculations enable us to identity the primary redox site and the electron and spin-density distribution between the individual components for the individual redox congeners. The DFT technique reproduces the spectral properties of the presented complexes and their radical ions. The generally close correspondence between experimental and quantum chemical results demonstrate that modern DFT is a powerful tool to address issues like ligand non-innocence and electron and spin delocalization in systems containing both redox-active metal ions and redox-active ligands.
First author: Jones, Travis E., The Bond Bundle in Open Systems, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 110, 1500, (2010)
Abstract: Much of modern chemistry is concerned with the properties and dynamics of chemical bonds. Although they have been described variously, the most familiar representation is that of a link connecting two atoms. However, no one has yet developed a scheme by which to partition a molecule into bond volumes with well-defined properties. As a consequence, the chemical bond is left as nothing more than a heuristic devise. Here, we show molecules can be partitioned into bond-bundles-volumes that share many of the properties associated with the conceptual bond. This partitioning follows naturally through an extension of Baders topological theory of molecular structure. Surprisingly, it also bounds regions of space containing nonbonding or lone-pair electrons and leads to bond orders consistent with those expected from theories of directed valance.
First author: Christe, Karl O., Selenium(IV) fluoride and oxofluoride anions, JOURNAL OF FLUORINE CHEMISTRY, 131, 791, (2010)
Abstract: The [((C(6)H(5))(3)P)(2)N](+), [(C(6)H(5))(4)P](+) and [N(CH(3))(4)](+) salts of SeF(5)(-), SeF(6)(2-) and SeOF(3)(-) and CsSeO(2)F were prepared and characterized. Crystal structures were obtained for [((C(6)H(5))(3)P)(2)N][SeF(5)] and [((C(6)H(5))(3)P)(2)N][SeOF(3)] CH(2)Cl(2). In contrast to oxygen-bridged dimeric TeOF(3)(-), the SeOF(3)(-) anion in [((C(6)H(5))(3)P)(2)N][SeOF(3)] CH(2)Cl(2) is monomeric and represents the first experimentally well determined molecular structure of a monomeric trifluoro-chalcogenite anion. Similarly, [((C(6)H(5))(3)P)(2)N][SeF(5)] represents the first example of a structure containing a well-isolated undistorted SeF(5)(-) anion. The NMR and the vibrational spectra and their assignments were re-examined and corrected by comparison with high-level theoretical calculations. Whereas the previously published normal coordinate analysis of SeF(5)(-) is correct, that for SeOF(3)(-) needs major revision.
First author: Conradie, Jeanet, Understanding the Unusually Straight: A Search For MO Insights into Linear {FeNO}(7) Units, JOURNAL OF PHYSICAL CHEMISTRY B, 114, 8517, (2010)
Abstract: Ferrous-nitrosyl {FeNO}(7) complexes, whether S = 1/2 or 3/2, generally exhibit bent FeNO angles of around 140-145 degrees. There are, however, a handful of exceptions, which are characterized by linear or quasi-linear FeNO units. Presented herein is a relatively comprehensive DFT-based MO analysis of these unusual {FeNO)(7) complexes. DFT-derived FeNO bending potentials indicate that the unusual, experimentally observed quasi-linear geometries indeed correspond to minimum-energy structures on the potential energy surfaces of the isolated molecules/ions. Walsh diagram analyses support our earlier suggestion that the linearity of the {FeNO}(7) units in question is most commonly attributable metal d(sigma)-p(sigma) mixing resulting from the lack of a ligand trans to the NO. Importantly, this effect explains the linearity of both S = 1/2 {FeNO}(7) complexes such as [Fe(CN)(4)(NO)](2-) and Fe(dtc-Me-2)(7)(NO) (dtc-Me-2 = NN-dimethyldithiocarbamate) and S = 3/2 complexes such as [Fe(S’Bu)(3)(NO)](-). However, Roussin’s black salt anion, (Fe-4(mu-S)(3)(NO)(7)](-), which also contains a linear {FeNO}(7) unit, entails additional, special metal-ligand orbital interactions. The well-known brown-ring complex [Fe(H2O)(5)(NO)](2+) also contains a linear {FeNO}(7) unit; the linearity in this case is attributable to the weakness of the trans water ligand.
First author: Ganesan, Aravindhan, Influence of functional groups on the C-alpha-C-beta chain of L-phenylalanine and its derivatives, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 619, 143, (2010)
Abstract: L-phenylalanine (L-phe) consists of three different functional groups, i.e., phenyl, carboxyl (-COON) and amino (-NH2), joining through the C-alpha-C-beta bridge. Substitution of these groups produces 2-phenethylamine (PEA) and 3-phenylpropionic acid (PPA). Electronic structures of L-phe, PEA and PPA together with smaller “fragments” L-alanine and benzene were determined using density functional theory (DFT), from which core and valence shell ionization spectra were simulated. Comparison of the spectra reveals that core shell ionization energies clearly indicate that the carbon bridge is significantly affected by their functional group substitutions particularly at the C, site. In the valence space, quite unexpectedly, the frontier orbitals are concentrated on the benzene group although some energy splitting is observed. The orbitals which significantly affect the C-alpha-C-beta carbon backbone are from the inner valence shell in the ionization energy region of 20-26 eV of the molecules.
First author: Kovacs, Attila, Bonding interactions in EDTA complexes, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 950, 93, (2010)
Abstract: The structural and bonding characteristics of the ethylenediaminetetraacetic acid (EDTA) complexes of 12 metal ions (Mg2+, Ca2+, Sr2+, Ba2+, Al3+, Ga3+, Sn2+, Pb2+, Cu2+, Zn2+, Cd2+, Hg2+) were investigated by means of density functional theory computations. The computed molecular geometries were compared to those in the crystal. The ionic vs. covalent contribution in the bonding was assessed by energy partitioning analysis, while the details of the donor-acceptor interactions were determined by natural bond orbital (NBO) analysis.
First author: Trueba, A., Pressure-induced changes in Cr3+-doped elpasolites and LiCaAlF6: Interpretation of macroscopic data, PHYSICAL REVIEW B, 81, 93, (2010)
Abstract: In the research of pressure effects on Cr3+-doped insulating lattices, it is crucial to understand the dependence of the 10Dq parameter on the sample volume, V. This problem is explored in the present work through ab initio calculations on Cr3+-doped K2NaScF6, Cs2NaYCl6, and (CsNaYBr6)-Na-2 elpasolite lattices as a function of pressure in the 0-5 GPa range. From the calculated values of the lattice parameter and the Cr3+-X- ( X=F, Cl, and Br) distance, R, it is found that R varies with the cell volume, upsilon(c), as upsilon((1/3 beta))(c) where beta lies around 2.6. These results allow one to understand quantitatively the 10Dq dependence on V-m/3 for LiCaAlF6:Cr3+ where the measured exponent m=2.3 is seemingly anomalous when compared to the values found for ruby (m=4.5) or NiO (m=5).
First author: Acosta-Ramirez, Alberto, Synthesis and Structural Studies of Chiral Indium(III) Complexes Supported by Tridentate Diaminophenol Ligands, INORGANIC CHEMISTRY, 49, 5444, (2010)
Abstract: Indium(III) dimethyl, dihalide, and alkoxy-bridged complexes bearing a chiral diaminophenoxy tridentate ligand [NNHO](-) were synthesized. The dimethyl complex (NNHO)InMe2 (1) was unreactive toward ethanol and 2-propanol and only partially reactive toward the more acidic phenol. The dihalide complexes (NNHO)InX2 (X = Cl (3), Br (4), 1 (5)) reacted with Na0Et to form robust alkoxy-bridged complexes with the formula {[(NNHO)InX](2)(mu-X)(mu-OEt) (X = Cl (6), Br (7), 1 (8)). The reaction of the alkoxy-bridged complexes with water produced hydroxy-bridged dinuclear indium compounds. The hydroxy-bridged complex bearing a chloride ligand [(NNHO)InCl(mu-OH)](2) (9) was significantly more reactive toward dissociation and formation of a pyridine adduct than the iodo analogue [(NNHO)Inl(mu-OH)](2) (10). All compounds were fully characterized in solution by NMR spectroscopy and in the solid state by single-crystal X-ray diffraction. In addition, DFT calculations were used to help explain the reactivity trends observed.
First author: Zhang, Fu-Qiang, On the Origin of the Inverted Stability Order of the Reverse-Keggin [(MnO4)(CH3)(12)Sb12O24](6-): A DFT Study of alpha, beta, gamma, delta, and epsilon Isomers, INORGANIC CHEMISTRY, 49, 5472, (2010)
Abstract: Density functional theory calculations have been carried out to investigate the alpha, beta, gamma, delta, and epsilon isomers of [(MnO4)Me12Sb12O24](6-) (Me = CH3) anions, which are simplified Baker-Figgis models of Keggin-type antimonate complexes in experiments. It is found that the stability order of the five isomers (alpha beta > gamma > delta > epsilon), despite their significant similarities in frameworks. On the basis of the building block decomposition method, the stabilizing effect of the edge-sharing [Sb-2(mu-O)(2)Me-2] fragment inside gamma, 6, and E structures is confirmed and found to originate from its two energy-favorable components rather than itself as an indivisible unit. Similar behavior is also held by the destabilizing [W-2(mu-O)(2)O-2] fragment in [PW12O40](3-); however, the well-accepted electrostatic repulsion between the short Irr -Wvi contacts cannot be taken as direct evidence. Notably, in the assembly of the [(MnO4)Me12Sb12O24](6-) structure, all of the octahedral building units incline to compress axially and elongate horizontally, and this is exactly opposite to the deformation pattern observed in the building blocks of Keggin tungstates, which tend to elongate axially and compress horizontally, thus giving rise to the inverted stability order. Furthermore, energy decomposition analysis reveals that the intrinsic property of the anion comes from the spatial arrangements of the metal-oxygen cage and does not change significantly with the type and charge of the encapsulated anion.
First author: Casella, Girolamo, A DFT study of the Karplus-type dependence of vicinal (3)J(Sn-C-X-C), X=N,O,S, in organotin(IV) compounds: application to conformationally flexible systems, ORGANIC & BIOMOLECULAR CHEMISTRY,8, 2711, (2010)
Abstract: ZORA relativistic and non-relativistic OFT protocols have been used to investigate vicinal coupling constants, (3)J(Sn-C-X-C), in several organotin(IV) compounds, with particular emphasis on cyclic alpha-aminoorganostannanes. The dependence of the coupling constant on the heteroatom X (X = N,O,S) in the coupling path, and, for X = N. its substituents, has been studied in detail. The electron-withdrawing strength of the N-substituents has been found to strongly affect the magnitude and shape of the Karplus-type curve. The results obtained for the simple model systems, having no or little conformational flexibility, have helped in rationalizing the data concerning real flexible cyclic systems recently investigated in the literature. For these intricate cases a population analysis of various conformers has allowed to obtain a very good agreement between calculated and experimental data. It is therefore established that NMR J couplings, together with OFT calculations, are a very useful tool to investigate conformational issues in solution by comparison of experimental and weighted average calculated values.
First author: Mallajosyula, Sairam S., Toward DNA Conductivity: A Theoretical Perspective, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 1, 1881, (2010)
Abstract: With most of the early experiments reporting a wide range of electronic properties for DNA, varying from insulating, semiconducting, and conducting to even induced superconductivity, the conductivity of DNA still remains a challenge. To this end, theoretical studies have greatly aided in explaining the observed conductance behaviour of DNA. Theoretical charge transfer studeis of DNA can be divided into two broad categories model calculations and ab initio calculations. In this Perspective, we discuss a few results from both categories and highlight the importance of both methods. The aim is to provide an overview of the theoretical methods that are used to study DNA conductivity highlighting their strengths and deficiencies.
First author: Lopez-Acevedo, Olga, Chirality and Electronic Structure of the Thiolate-Protected Au-38 Nanocluster,JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 8210, (2010)
Abstract: Structural, electronic, and optical properties of the thiolate-protected Au-38(SR)(24) cluster are studied by density-functional theory computations (R = CH3 and R = C6H13) and by powder X-ray crystallography (R = C12H25). A low-energy structure which can be written as Au-23@(Au(SR)(2))(3)(Au-2(SR)(3))(6) having a bi-icosahedral core and a chiral arrangement of the protecting gold thiolate Au,,(SR), units yields an excellent match between the computed (for R = C6H13) and measured (for R = C12H25) powder X-ray diffraction function. We interpret in detail the electronic structure of the Au-23 core by using a particle-in-a-cylinder model. Although the alkane thiolate ligands are achiral, the chiral structure of the ligand layer yields strong circular dichroism (CD) in the excitations below 2.2 eV for Au-38(SCH3)(24). Our calculated CD spectrum is in quantitative agreement with the previously measured low-energy CD signal of glutathione-protected Au-38(SG)(24). Our study demonstrates a new mechanism for the strong chiral response of thiolate-protected gold clusters with achiral metal cores and ligands.
First author: Paul, Frederic, Spin Distribution in Electron-Rich Piano-Stool Iron(III) Pyridylalkynyl Radical Cations Containing [(eta(2)-dppe)(eta(5)-C5Me5)FeC C](+) End Groups, ORGANOMETALLICS, 29, 2491, (2010)
Abstract: This experimental and theoretical contribution is aimed at investigating the electronic structure of cationic electron-rich ethynylpyridyl Fe(III) derivatives of the formula [(eta(2)-dppe)(eta(5)-C5Me5)FeC C(x-C5H4N)][PF6] (x = 4, 3, 2; 1a-c[PF6]) and [(eta(2)-dppe)(eta(5)-C5Me5)FeC C(2,5-C5H3NX)][PF6] (X = Cl, Br; 2a,b[PF6]). The Mossbauer, NMR, and ESR characterization of these paramagnetic species are reported and discussed in connection with DFT results. Special emphasis is put on the electronic effect of the nitrogen atom and of the halogen substituent on the spin distribution within the pyridyl unit. It is shown that H-1 NMR constitutes a straightforward empirical way to investigate the slight changes in spin distribution taking place on the heteroaryl ring.
First author: Monreal, Marisa J., Reversible C-C Coupling in a Uranium Biheterocyclic Complex, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 7676, (2010)
Abstract: The C-C coupling of two molecules of 1-methylbenzimidazole was effected by a neutral uranium dibenzyl complex supported by a ferrocene 1,1′-diamide ligand. The transformation involves the C-H activation of two heterocycles and the coupling of one eta(2)-N,C-imidazolyl fragment with a coordinated 1-methylbenzimidazole ligand. The solid-state structure of this product was studied by both single-crystal and powder X-ray diffraction methods and confirms the formation of the biheterocyclic moiety. In solution, the C-C coupling event was found to be reversible, as assessed by variable-temperature H-1 and H-2 NMR spectroscopy as well as DFT calculations and reactivity studies.
First author: Zhekova, Hristina R., A Magnetic and Electronic Circular Dichroism Study of Azurin, Plastocyanin, Cucumber Basic Protein, and Nitrite Reductase Based on Time-Dependent Density Functional Theory Calculations, JOURNAL OF PHYSICAL CHEMISTRY A, 114, 6308, (2010)
Abstract: The excitation, circular dichroism, magnetic circular dichroism (MCD) and electron paramagnetic resonance (EPR) spectra of small models of four blue copper proteins are simulated on the TDDFT/BP86 level. X-Ray diffraction geometries are used for the modeling of the blue copper sites in azurin, plastocyanin, cucumber basic protein, and nitrite reductase. Comparison with experimental data reveals that the calculations reproduce most of the qualitative trends of the observed experimental spectra with some discrepancies in the orbital decompositions and the values or the excitation energies, the g(parallel to) components of the g tensor, and the components of the A tensor. These discrepancies are discussed relative to deficiencies in the time-dependent density functional theory (TDDFT) methodology, as opposed to previous studies which address them as a result of insufficient model size or poor performance of the BP86 functional. In addition, attempts are made to elucidate the correlation between the MCD and EPR signals.
First author: Ferbinteanu, Marilena, Noncovalent effects in the coordination and assembling of the[Fe(bpca)(2)][Er(NO3)(3)(H2O)(4)]NO3 system, CENTRAL EUROPEAN JOURNAL OF CHEMISTRY, 8, 519, (2010)
Abstract: In this work we perform a detailed analysis of the non-covalent effects that build the lattice of the [Fe(bpca)(2)][Er(NO3)(3)(H2O)(4)]NO3 compound, made of cationic d units [Fe(bpca)(2)]+,(where Hbpca is bis(2-pyridilcarbonyl)amine), neutral f complexes [Er(NO3)(3)(H2O)(4)], and the NO3- counter-ion. All these units are interlinked by hydrogen bonds, their assembling benefiting also from electrostatic effects. A particularly interesting sub-ensemble of the crystal is the linear chain formed by the lanthanide units. Going beyond the usual qualitative description of the supramolecular assembling, we performed electron structure calculations on appropriate models related to the experimental structures. The formation energies of d and f coordination bonds are estimated in semi-quantitative manner, being compared with the intermolecular ones, due to hydrogen bonding and dipolar interactions.
First author: Farnaby, Joy H., Tris(pyrazolyl)borate half-sandwich complexes of trivalent uranium incorporating the [C8H6{(SiPr3)-Pr-i-1,4}(2)](2-) and [C8H4{(SiPr3)-Pr-i-1,4)(2)](2-) ligands, COMPTES RENDUS CHIMIE, 13, 812, (2010)
Abstract: The reaction of UI3 in THF with KTPme2 and the subsequent addition of [K2(C8H6{(SiPr3)-Pr-i-1,4)(2))] or [K-2(C8H4{(SiPr3)-Pr-i-1,4}(2))] yields dark red [U(K-3-T-P(Me2))(C8H6{(SiPr3)-Pr-i-1,4)(2))] 1and purple [U{K-3-T-P(Me2))(C8H4[(SiPr3)-Pr-i-1,4)(2))] 2, respectively The H-1 NMR of 1 at room temperature suggests a rigid structure, whereas 2 is fluxional in solution on the NMR timescale 1 is unreactive towards CO1 CO2 and MeNC under mild conditions: density functional calculations were used to compare the electronic and steric effects of the T-P(Me2) vs. CP* ligands in mixed sandwich complexes of the type [U(L)(C8H6{SiH3-1,4)2)] (L = Cp* Or (K-3-T-p(Me2))) On heating at 80 degrees C. 1 reacts with excess MeNC to yield [U(C8H6((SiPr3)-Pr-i-1,4)(2))(k(2)-dmpz)(2)(eta(1)-CNMe)] 3 The structures of 1-3 have been determined by single crystal X-ray diffraction.
First author: Elkechai, Aziz, Electron affinities of biscyclopentadienyl and phospholyl uranium(IV) borohydride complexes: Experimental and DFT studies, COMPTES RENDUS CHIMIE, 13, 860, (2010)
Abstract: Electron affinities (EAs) of a series of biscyclopentadienyl and phospholyl uranium(IV) complexes L2U(BH4)(2) [L-2 = Cp-2, (tmp)(2),(tBuCp)(2), (Cp*)(tmp) and Cp*(2)] related to the U(III)/U(IV) redox system were calculated using relativistic Density Functional Theory (DFT) based methods coupled with the Conductor-like Screening Model for Real Solvents (COSMO-RS) approach. Electrochemical measurements of half-wave potentials in solution (tetrahydrofuran THF) were carried out for all these compounds under the same rigorous conditions A good correlation (r(2) = 0 99) is obtained between the calculated EA values, at the ZORA/BP86/TZ2P level, and the half-wave reduction potentials measured by electrochemistry. The investigations bring to light the importance of spin-orbit coupling and solvent effect and the use of a large basis set in order to achieve such a good agreement between theory and experiment The study confirms the instability of the Cp2U(BH4)(2) complex during the reduction process The influence of the substituted aromatic ligand L2, namely their electron donating ability, on EA was studied. The role of Involved orbitals (singled occupied molecular orbital -SOMO- of anionic species or lowest unoccupied molecular orbital -LUMO- of neutral species) in the redox process was revealed
First author: Vetere, Valentina, Modulation of the unpaired spin localization in Pentavalent Uranyl Complexes, COMPTES RENDUS CHIMIE, 13, 876, (2010)
Abstract: The electronic structure of various complexes of pentavalent uranyl species, namely UO2, is described, using DFT methods, with the aim of understanding how the structure of the ligands may influence the localisation of the unpaired 5f electron of uranium (V) and, finally, the stability of such complexes towards oxidation Six complexes have been inspected. [UO(2)PYs] (1).[(UO2PY5)KI2] (2), [UO2(salan-(BU2)-B-t)(PY)K] (3), [UO2(salophen-Bu-t(2))(thf)K] (4), [UO2(salen-Bu-t(2))(py)K] (5), [and UO2-cyclo[6]pyrroler](1-) (6), chosen to explore various ligands. In the five first complexes, the UO2+ species is well identified with the unpaired electron localized on the 5f uranium orbital. Additionally, for the salan, salen and salophen ligands, some covalent interactions have been observed, resulting from the presence of both donor and acceptor binding sites. In contrast, the last complex is best described by a UO22+ uranyl (VI) coordinated by the anionic radical cyclopyrrole, the highly delocalized pi orbitals set stabilizing the radical behaviour of this ligand
First author: Jose Juarez-Perez, Emilio, The Role of C-H center dot center dot center dot H-B Interactions in Establishing Rotamer Configurations in Metallabis(dicarbollide) Systems, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 13, 2385, (2010)
Abstract: The aim of this work is to explore the self-interaction capability of the anion [3,3′-Co(1,2-C(2)B(9)H(11))(2)](-) through C(cluster)- H center dot center dot center dot H-B (C(c)-H center dot center dot center dot H-B) dihydrogen bonds. A set of theoretical and empirical data aiming to establish the main rules that account for the binding mode between the negatively charged borane framework made by [3,3′-Co(1,2-C(2)B(9)H(11))(2)](-) and the [NMe(4)](+) ions have been compiled. The interaction between cation and anion is mainly electrostatic but the covalent contribution is also proven and quantified. The existing intermolecular H center dot center dot center dot H short contacts have been studied and are compared with available data from the Cambridge Structural Database. The results show that the electronic configuration of the transition metal atom in the sandwich complex is not enough to define the preferred rotamer due to the influence of the anion environment and the H center dot center dot center dot H interactions present in the solid state. We present a methodology with widely used theoretical tools to study cation center dot center dot center dot cobaltabisdicarbollide interactions in the solid state.
First author: Antras, Frederic, Pauson-Khand Reaction of Allenic Hydrocarbons: Synthesis of 4-Alkylidenecyclopentenones, EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, 13, 3312, (2010)
Abstract: The carbonyldicobalt-mediated alkyne/allene/CO cocyclization gives 4-alkylidenecyclopentenones as the major [2+2+1] cycloadducts. The regio- and stereoselectivities depend mainly on the substitution pattern of both the alkyne and the allenic moieties, which can be rationalized using the Magnus mechanism. However, contrary to this model, and in agreement with more recent mechanistic studies, our results provide evidence that both initial pseudo-equatorial and pseudo-axial coordination modes of the allenic hydrocarbons onto one of the cobalt atoms of the primary alkyne dicobalt complex are involved. DFT calculations supporting both these coordination modes are given.
First author: Johnson, Olivia E., Spectroscopic and computational investigation of three Cys-to-Ser mutants of nickel superoxide dismutase: insight into the roles played by the Cys2 and Cys6 active-site residues, JOURNAL OF BIOLOGICAL INORGANIC CHEMISTRY, 15, 777, (2010)
Abstract: Nickel-dependent superoxide dismutase (NiSOD) is a member of a class of metalloenzymes that protect aerobic organisms from the damaging superoxide radical (O(2) (center dot-)). A distinctive and fascinating feature of NiSOD is the presence of active-site nickel-thiolate interactions involving the Cys2 and Cys6 residues. Mutation of one or both Cys residues to Ser prevents catalysis of O(2) (center dot-), demonstrating that both residues are necessary to support proper enzymatic activity (Ryan et al., J Biol Inorg Chem, 2010). In this study, we have employed a combined spectroscopic and computational approach to characterize three Cys-to-Ser (Cys -> Ser) mutants (C2S, C6S, and C2S/C6S NiSOD). Similar electronic absorption and magnetic circular dichroism spectra are observed for these mutants, indicating that they possess nearly identical active-site geometric and electronic structures. These spectroscopic data also reveal that the Ni(2+) ion in each mutant adopts a high-spin (S = 1) configuration, characteristic of a five- or six-coordinate ligand environment, as opposed to the low-spin (S = 0) configuration observed for the four-coordinate Ni(2+) center in the native enzyme. An analysis of the electronic absorption and magnetic circular dichroism data within the framework of density functional theory computations performed on a series of five- and six-coordinate C2S/C6S NiSOD models reveals that the active site of each Cys -> Ser mutant possesses an essentially six-coordinate Ni(2+) center with a rather weak axial bonding interaction. Factors contributing to the lack of catalytic activity displayed by the Cys -> Ser NiSOD mutants are explored.
First author: Neugebauer, Johannes, A Subsystem TDDFT Approach for Solvent Screening Effects on Excitation Energy Transfer Couplings, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 6, 1843, (2010)
Abstract: We present a QM/QM approach for the calculation of solvent screening effects on excitation-energy transfer (EET) couplings. The method employs a subsystem time-dependent density-functional theory formalism [J. Chem. Phys. 2007, 126, 134116] and explicitly includes solvent excited states to account for the environmental response. It is investigated how the efficiency of these calculations can be enhanced in order to treat systems with very large solvation shells while fully including the environmental response. In particular, we introduce a criterion to select solvent excited states according to their approximate contribution weight to the environmental polarization. As a model system, we investigate the perylene diimide dimer in a water cluster in comparison to a recent polarizable QM/MM method for EET couplings in the condensed phase [J. Chem. Theory Comput. 2009, 5, 1838]. A good overall agreement in the description of the solvent screening is found. Deviations can be observed for the effect of the closest water molecules, whereas the screening introduced by outer solvation shells is very similar in both methods. Our results can thus be helpful to determine at which distance from a chromophore environmental response effects may safely be approximated by classical models.
First author: Janjua, Muhammad Ramzan Saeed Ashraf, Prediction of robustly large molecular second-order nonlinear optical properties of terpyridine-substituted hexamolybdates: Structural modelling towards a rational entry to NLO materials, JOURNAL OF MOLECULAR GRAPHICS & MODELLING, 28, 735, (2010)
Abstract: We have explored an innovative, versatile, and novel molecular hybrid containing polyoxometalate (POM) cluster linked with terpyridine ligand via pi-bridged donor-acceptor (D-A) configuration. The dipole polarizabilities, density of states, and second-order nonlinear optical (NLO) properties of terpyridine-substituted hexamolybdates have been investigated by using time-dependent density functional response theory (TDDFT). This class of organic-inorganic hybrid compounds possesses a robustly large molecular second-order NLO response, especially [Mo6O18(N4C25H16I2)](2-) (system 5) and [Mo6O17(N4C25H16(CN)(2))(N4C25H16(CN)(2))](2-) (system 10) with the static second-order polarizability (beta(vec)) computed to be 1209.25 x 10(-30) esu and 1622.67 x 10(-30) esu respectively. Thus, these systems have the possibility to be excellent second-order nonlinear optical materials. Analysis of the major contributions to the beta(vec) value suggests that the charge transfer (a) from POM-cluster to terpyridine ligand (D-A) along the z-axis plays the key role in the NLO response, POM-cluster (hexamolybdates) acts as a donor (D) whereas terpyridine ligand acts as an acceptor (A) in all the studied systems. The computed beta(vec) values increase by the incorporation of electron acceptors (halogen = F, Cl, Br and I) at the terminus of terpyridine ligand. Furthermore, substitution of trifluoromethoxy (-OCF3), trifluoromethyl (-CF3), and cyanide (-CN) at the end of terpyridine ligand respectively enhances the optical nonlinearity. Orbital analysis shows that the degree of CT between POM and terpyridine segment was increased in 2D and organometallic/POM hybrid systems. The present investigation provides important and thought provoking insight into the robustly large NLO properties of terpyridine-substituted hexamolybdates.
First author: Capar, Can, beta-octabromo-meso-tris(pentafluorophenyl)corrole: reductive demetalation-based synthesis of a heretofore inaccessible, perhalogenated free-base corrole, JOURNAL OF PORPHYRINS AND PHTHALOCYANINES,14, 509, (2010)
Abstract: Long known in various metal-complexed forms, beta-octabromo-meso-tris(pentafluorophenyl) corrole, H-3[Br8TPFPC], has not been available as a free ligand until now. It can be prepared in high yield (86%) via reductive demetalation (conc. H2SO4, FeCl2) of Mn[Br8TPFPC]. Interestingly, the same conditions did not result in demetalation of the analogous copper complex, which may be contrasted to the behavior of many other copper corroles, which demetalate cleanly. X-ray crystallographic analysis revealed a unique “half-saddled” conformation, wherein two of the pyrrole rings on one side of the direct pyrrole-pyrrole linkage are strongly tilted up and down relative to each other, whereas the other two pyrrole rings are roughly in the mean plane of the macrocycle.
First author: Kavun, V. Ya., NMR and DFT study of chemical bonding of the titanyl ion in pentafluoro complexes (NH4)(3)TiOF5 and Rb2KTiOF5, JOURNAL OF STRUCTURAL CHEMISTRY, 51, 463, (2010)
Abstract: 19F NMR and DFT methods are used to study the electronic structure and chemical bonding of titanyl ions in pentafluoro titanyl complexes (NH4)(3)TiOF5 and Rb2KTiOF5. The experimental values of the anisotropy of F-19 NMR chemical shifts (CSs) are shown to be consistent with the calculated parameters within the DFT method. At normal temperatures orientational disordering of octahedral [TiOF5](3-) anions occurs, fluorine atoms steadily occupying cis- and trans-positions with respect to the O2- ion. In both complexes, trans-position is not fully occupied; the occupation ratio does not exceed similar to 4:0.9. When the temperature is decreased to 150 K, the value of the CS anisotropy of the fluorine atom resonance line in trans-position is found to be smaller than the dipole-dipole broadening, whereas the line from fluorine atoms in cis-positions transforms into an asymmetric broad line characterized by the triaxial anisotropy of the CS tensor. It is shown that the found anisotropy corresponds to violation of the axial symmetry of Ti-F cis bonds because of strong delocalization of the electron density of Ti-O bonds in the titanyl ion.
First author: Jung, S., An Elucidation of the Interaction Between Pt Particles and CeO2 Surfaces Using Tight-Binding Quantum Chemistry Method, TOPICS IN CATALYSIS, 53, 700, (2010)
Abstract: To investigate the interaction between Pt particle and CeO2 surface, we applied tight-binding quantum chemistry method to the study of electron and bonding state of Pt/CeO2 system. We observed that the electron transfer between Pt and CeO2 and the reduction of the Ce atoms influences the stability of Pt particle on CeO2 surface.
First author: Reber, Arthur C., Reactivity of Aluminum Cluster Anions with Water: Origins of Reactivity and Mechanisms for H-2 Release, JOURNAL OF PHYSICAL CHEMISTRY A, 114, 6071, (2010)
Abstract: The reactivity of aluminum anion clusters with water was found to exhibit variations with size, with some clusters exhibiting negligible reactivity, others absorbing one or more water, while even others releasing H-2 with addition of multiple waters. (Roach, P.J., Woodward, W.H. et al. Science, 2009, 323, 492). Herein, we provide further details on the role of complementary active sites in the breaking of the 0 H bond on the cluster. We examine the reactions of Al-n(-) + H2O where n = 7-18, and show how the complementary active sites may be best identified. The clusters with active sites are found to be reactive, and clusters with barriers to reactivity have an absence of paired active sites. The role of charge in the reactivity is considered, which could account for the observed increase in reactivity at large sizes. The H, release in the reactivity of Al-17 – with multiple water molecules is also studied by comparing multiple reaction pathways, and the selective H, production is explained by the first water inducing a new active site. A mechanism for transferring hydroxyl groups on the surface of the cluster is also discussed.
First author: Morita, Yasushi, Triple-Stranded Metallo-Helicates Addressable as Lloyd’s Electron Spin Qubits, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 6944, (2010)
Abstract: We have first achieved the synthesis of triple-stranded metallo-helicates composed of 4,4′:2′,2 ”:4 ”,4 ”’-quaterimidazole (Qim) and Mn(II) or Zn(II) ions, which serve as synthetic electron spin qubits (quantum bits). In the crystal structure, a hydrogen-bonding network through counteranions and/or crystal solvents was constructed by the outward N-H hydrogen-bonding functional groups intrinsic to the imidazole skeleton. Importantly, these helicates showed high stability even in a solution state at room temperature. These salient features of triple helicates of Qim are different from those of reported metallo-helicates. These chemical properties of the Qim-based triple helicates allow us to synthesize magnetically diluted single crystals composed of Mn(II) (S = 5/2) and diamagnetic Zn(II) complexes of Qim in an appropriate Mn(II)/Zn(II) ratio. The magnetically diluted crystals can afford to build up the prototype of electron-spin qubits of Lloyd’s one-dimensional periodic system, which gives a practical approach to scalable quantum computers/quantum information processing systems (QCs/QIPSs). The experiments have proven the practical capability of oligo(imidazole)s as a component of Lloyd’s system which has nonequivalent g-tensors within the helicate (g-engineering). The helical symmetry plays an important role in giving a prototype of the synthetic spin qubits of the formidable Lloyd model. This result links supramolecular chemistry to the field of QCs/QIPSs.
First author: Kudinov, Alexander R., Ferracarborane Benzene Complexes [(eta-9-L-7,8-C2B9H10)Fe(eta-C6H6)](+) (L = SMe2, NMe3): Synthesis, Reactivity, Electrochemistry, Mossbauer Effect Studies, and Bonding, ORGANOMETALLICS,29, 2260, (2010)
Abstract: The benzene complexes [(eta-9-L-7,8-C2B9R5H8)Fe(eta-C6H6)](+) (3a: L = SMe2, R = H; 3b: L = SMe2, R = Me; 3c: L = NMe3, R = H) were prepared by photochemical reaction of [(eta(5)-C6H7)Fe(eta-C6H6)]+ with carborane anions [9-L-7,8-C2B9R2H8](-) (1a-c) followed by treatment of’ the (eta-9-L-7,8-C2B9R2H8)Fe(eta(5)-C6H7) (2a c) ferracarboranes formed with HCl. Visible light irradiation of 3a with (BuNC)-Bu-t or P(OMe)(3) in acetonitrile results in replacement of the benzene ligand, giving the tris(ligand) derivatives (eta-9-SMe2-7,8-C2B9H10)Fe(ligand)3]+ (4, 5). The unsymmetrical carborane complex (eta-9-SMe2-7,8-C2B9H10) (eta-Fe(eta-9-NMe3-7,8-C2B9H10) (6) was obtained by photochemical reaction of 3a with 1c. The structures of 2a, 3aBPh(4), and 6 were determined by X-ray diffraction. Temperature-dependent Mossbauer spectroscopy has been used to elucidate the hyperfine parameters and metal atom vibrational amplitudes in a number of these complexes. The redox activity of the farracarboranes 2a,c. and 3a,c has been investigated! by electrochemical techniques and compared with that of the related cyclopentadienyl complexes. Electrochemistry gives evidence that the conversion of 2a c to 3a c can also be triggered by a two-electron oxidation followed by deprotonation. DFT calculations of the redox potentials and the respective geometrical changes were performed. Data on electrostatic potentials at iron nuclei suggest that anions la,c are stronger donors than Cp- in cationic complexes, but weaker donors in the neutral derivatives.
First author: Wooles, Ashley J., Synthesis and Characterization of Dysprosium and Lanthanum Bis(iminophosphorano)methanide and -methanediide Complexes, ORGANOMETALLICS, 29, 2315, (2010)
Abstract: Attempts to prepare [Dy{C(PPh(2)NSiMe(3))(2)}(1)(THF)(2)] (1) from in situ prepared “[Dy(Bn)(2)(I)(THF)(3)]” (“2”; Bn = C(6)H(5)CH(2)) and H(2)C(PPh(2)NSiMe(3))(2) resulted in the isolation of [Dy{CH(1)PPh(2)NSiMe(3))(2)}(1),(TH F.)] (3) and, on one occasion, a small quantity of [(Dy(CH[PPh(7)NSiMe(3)](2))(1)}2(mu-O)] (4). However, attempts to prepare 3 from [K{CH(PPh(2)NSiMe(3))(2)}(THF)(n)] and [Dy(1)(3)(THE)(3.5)] were unsuccessful. The corresponding reactions with [La(1)3(THF)4] were unsuccessful, and the reaction of [{Li(2)(C[PPh(2)NSiMe(3)](2)}(3)] and [La(I)(3)(THF)(4)] in a 1:1 ratio resulted in the isolation of [La(1)(3)Li(THF)(4)] were unsuccessful, and the (5). However, the potassium methanide complex [K{CH(PPh(3)NMeSi(2))}(Mes)(2)}- = 2,4,6-Me(3)C(6)H(2)) was found to react with [La(1)(3)(THF)(4)] to give [La{CH(PPh(2)NMes)(2)}(1),(THF)(4)] (6). Complex 6 reacts with 1 equiv of [K(Bn)] to afford the methanediide complex [La{C(PPh(2)NMes)(2)}(1)(THF)(3)] (7). A DFT study of 6 and 7 revealed an increased accumulation of charge at the endocyclic carbon following deprotonation and conversion of 6 to 7, and although the La C bond indices increase substantially upon a second deprotonation, the bonding remains highly ionic and is dominated by carbon 2p contributions with little orbital contribution from lanthanum. Compounds 1-7 have been variously characterized by X-ray crystallography, NM It spectroscopy, FTIR spectroscopy, CH N microanalyses, room-temperature solution magnetic moments, and, lbr 6 and 7, DFT calculations.
First author: Crisp, Jeffrey A., Indenyl Complexes of Manganese(II). Conformational Flexibility of the Manganese(II) (RnC9H7-n) Bond, ORGANOMETALLICS, 29, 2322, (2010)
Abstract: Bis(cyclopentadienyl) complexes (Cp2M) of the divalent first-row transition metals V-Ni have been known and used for over 50 years. For almost as long, an analogous series of compounds has been known with the indenyl ligand (i.e., Ind(2)M), with the conspicuous exception of M = Mn, Bis(indenyl) complexes of manganese(II), Ind(2)’,MnLn have now been synthesized by halide metathesis from MnCl2 and an appropriate potassium indenide. Depending on the indenyl ligand substituents and the presence of coordinated bases, a variety of structural motifs and bonding modes of the indenyl ligand are found in the resulting complexes. Single-crystal X-ray structures obtained for [2-(SiMe3)C9H6](2)Mn, [1,3(SiMe3),C9H5],Mn, and [1,3-(i-Pr)(2)C9H5],Mn confirm that they possess classic /75-bound sandwich structures. In contrast, the unsubstituted parent complex recrystallizes from THF as a disolvate with two differently bonded indenyl ligands: i.e., (eta(3)-C9H7)(eta(1)-C9H7)Mn(thf)(2). Without the coordinated solvent, density functional theory calculations suggest that the complex would have two slipped eta(5)-bound ligands. When methyl groups are present on the benzo portion of the indenyl ligand, specifically in the 4,7-positions, the corresponding manganese complex is isolated as a cyclic octomer, {(4,7-Me,C9H5),Mn}(8), containing both bridging and terminal indenyl ligands. In the presence of I,4-dioxane, however, attempted synthesis of (4,7-Me7C9H5)(5)Mn results in the isolation of the [K(dioxane)(1.5)][Mn(4,7-Me2C9H5)3) salt, in which each manganese atom is surrounded by a paddle-wheel of three eta(2)-bound 4,7-dimethylindenyl ligands. Cation pi bonding to the ‘Potassium and the presence of coordinated dioxane molecules generates a layered structure for the salt. Magnetic susceptibility measurements on the compounds indicate the presence of high-spin M n(II) centers in all cases. These compounds demonstrate the high degree of conformational flexibility in the M n(I I) indenyl bond.
First author: Song, Ping, Theoretical study of the impact factor on redox property and second-order nonlinear response for organoimido derivatives of [Mo6O19](2-): Electron donors with magnitude of conjugated groups or length of conjugated chain, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 947, 9, (2010)
Abstract: Mono- and multi-organoimido substituted derivatives for Lindqvist-type molybdate were carried out to search the preferred contribution factor on the redox property and the second-order nonlinear optical response. It was indicated that organic conjugated groups were much more sensitive to the redox property and nonlinear optical response than non-conjugated ones. The increment of NAr ligands, i.e. the greater net charge donation between organic segment and inorganic polyanion cluster, drove the first reduction potential dramatically negative. In contrast, the lengthening of conjugated chain resulted in remarkable improvement on second-order nonlinear optical response than in reduction potentials. In addition, Mo N in mono-organoimido substituted derivatives has localized the electrons for HOMO on pi-orbital of the first phenyl ring adjacent to N-1 together with small part of pi-pd orbital between Mo-1 and N-1, and the electron transition tends to transfer to organic conjugated groups. The two distinct paths may offer favorable direction for experiment.
First author: Seldenthuis, J. S., Electroluminescence spectra in weakly coupled single-molecule junctions, PHYSICAL REVIEW B, 81, 9, (2010)
Abstract: We have combined ab initio quantum chemistry calculations with a rate-equation formalism to analyze electroluminescence spectra in single-molecule junctions, measured recently by several groups in scanning tunneling microscope setups. In our method, the entire vibrational spectrum is taken into account. Our method leads to good quantitative agreement with both the spectroscopic features of the measurements and their current and voltage dependence. Moreover, our method is able to explain several previously unexplained features. We show that in general, the quantum yield is expected to be suppressed at high bias, as is observed in one of the measurements. Additionally, we comment on the influence of the vibrational relaxation times on several features of the spectrum.
First author: Thomas, S., A Comparative Study of Aromaticity in Substituted Tetracyclic and Hexacyclic Thiophenes,JOURNAL OF PHYSICAL CHEMISTRY A, 114, 5940, (2010)
Abstract: We have studied the nature of aromaticity in expanded porphyrinic analogues of thiophenes formed by four and six thiophenes. Using density functional theory (DFT) we have analyzed the aromaticity of both the macrocycle and individual molecular fragments. We find paramagnetic annulenic ring currents in the case of tetracyclic molecules and diamagnetic annulenic ring currents for hexacyclic molecules. We have also studied the effect of substitution of benzene rings within the macrocycle. We find that as the number of benzene rings is increased the aromaticity increases for tetracyclic systems and decreases for hexacyclic systems. All the results have been analyzed with various microscopic parameters, including geometry, excitation gap, and NMR criteria.
First author: Brik, M. G., Optical absorption measurements and quantum-chemical simulations of optical properties of novel fluoro derivatives of pyrazoloquinoline, CHEMICAL PHYSICS, 370, 194, (2010)
Abstract: The results of experimental research and quantum-chemical simulations of the absorption spectra of 1( 4-fluorophenyl)-3,4-diphenyl, 3-(4-fluorophenyl)-1,4-diphenyl, and 4-(4-fluorophenyl)-1,3-diphenyl-pyrazolo[3,4-b] quinoline are presented. Although the fluorine atom is located on different phenyl rings in these molecules, the absorption spectra do not differ significantly. Semi-empirical AM1, PM3 and RM1 methods, as well as ab initio ADF code-based calculations were used to optimize geometry, calculate the infrared and visible spectra of the afore mentioned compounds and analyze the molecular orbitals schemes. The results of calculations are in good agreement with the experimental data. It was also demonstrated that the positions of the fluorescence maxima depend significantly on the solvent (contrary to the absorption spectra), in which the molecules are embedded, which allows for manipulating with fluorescence properties of the synthesized molecules by changing the solvent.
First author: Santi, Saverio, Intervalence Charge Transfer in Cationic Heterotrinuclear Fe(III)-Rh(I)-Cr(0) Triads of the Polyaromatic Cyclopentadienyl-Indenyl Ligand, ORGANOMETALLICS, 29, 2046, (2010)
Abstract: The challenge to realize polymetallic assemblies of unambiguous structure and stereochemistry, in which the nature of the intervalence transition (IT) is rationalized, has been faced by investigating the syn and anti isomers of eta(6)-Cr(CO)(3){eta(5)-[(2-ferrocenyl)indenyl]Rh(CO)(2)} and their mixed-valence cations. Crystallographic studies and DFT calculations provide a detailed description of the structural and electronic features of these complexes, evidencing a significant difference in geometrical distortions and frontier MO composition between syn and anti isomers. Mixed-valence cations are generated and monitored by low-temperature spectroelectrochemistry in the visible, IR, and near-IR regions. The IT bands in the near-ER spectra are rationalized in the framework of Marcus Hush theory and at quantum chemistry level by density functional theory. Noteworthy, the results reported provide rare experimental evidence that the presence of a third metal center (Rh) increases the metal metal (Fe-Cr) interaction with respect to the structurally correlated binuclear system.
First author: Fernandez, Israel, Rate-Determining Factors in Nucleophilic Aromatic Substitution Reactions, JOURNAL OF ORGANIC CHEMISTRY, 75, 2971, (2010)
Abstract: Quantum chemical calculations (OPBE/6-311++G(d,p)) have been performed to uncover the electronic factors that govern reactivity in the prototypical SNAr reaction. It was found that intrinsic nucleophilicity-expressed as the critical energy (the energy required for forming the Meisenheimer structure Ph(X)(2)(-)) in the identity substitution reaction X- + PhX X -> + X- + PhX (Ph = phenyl) shows the following approximate trend: NH2- approximate to OH- approximate to F- >> PH2- approximate to SH- approximate to Cl- > AsH2- approximate to SeH- approximate to Br-. The periodic trends are discussed in terms of molecular properties (proton affinity of X- expressing Lewis basicity of the nucleophile and C(1s) orbital energy expressing Lewis acidity of the substrate) based on a dative bonding model. Furthermore, the stepwise progress of the reactions and the critical structures are analyzed applying energy decomposition analysis. Increased stability, and thereby increased intrinsic nucleophilicity, correlates with decreasing aromatic character of the Meisenheimer structure. This apparent contradiction is explained in consistency with the other observations using the same model.
First author: Kocherzhenko, Aleksey A., Charge Transfer Through Molecules with Multiple Pathways: Quantum Interference and Dephasing, JOURNAL OF PHYSICAL CHEMISTRY C, 114, 7973, (2010)
Abstract: Quantum interference effects occurring in molecules through which a charge can travel via multiple pathways can be the basis for new unconventional design principles in molecular scale electronics. However, these quantum interference effects can be reduced by interaction between the charge and molecular vibrations. In this work dephasing (decoherence) effects have been studied using a model that combines a (classical) molecular mechanics description of molecular vibrations with a quantum mechanical propagation of the charge. It is found that despite the clear effect of dephasing on the charge propagation, interference effects are largely retained at room temperature if vibrations are accounted for. Additionally, it is shown that taking electronic interactions between non-nearest neighbor atoms into account also diminishes interference effects but not sufficiently to destroy them completely. It is concluded that interference effects are strong enough to use them in a functional manner in molecular electronics. This opens up new ways to design molecular electronic components that exploit quantum interference.
First author: Munoz-Castro, Alvaro, Toward the Synthetic Control of the HOMO-LUMO Gap in Binuclear Systems: Insights from Density Functional Calculations, INORGANIC CHEMISTRY, 49, 4175, (2010)
Abstract: Computational methods based on density functional theory have been applied to address the design of tailored HOMO-LUMO gap bimetallic complexes. We focus our attention on the [Cp*Fe-(L)-FeCp*] system, where two ferrocenyl units are linked through the dianion of fused ring ligands such as pentalene, s-indacene, dicyclopenta-[b,g]-naphthalene, dicyclopenta-[b,l]-anthracene and dicyclopenta-[b,l]-tetracene Our DFT calculations on the title organometallic complexes suggest a controlled decrease in the HOMO-LUMO gap, which is desirable for studies on electron-transfer phenomena, as well as the design potential devices for molecular electronic purposes.
First author: Radford, Robert J., Controlled Protein Dimerization through Hybrid Coordination Motifs, INORGANIC CHEMISTRY, 49, 4362, (2010)
Abstract: Protein homodimerization is the simplest form of oligomerization that is frequently utilized for the construction of functional biological assemblies and the regulation of cellular pathways Despite its simplicity, dimerization still poses an enormous challenge for protein engineering and chemical maniupulation, owing to the large molecular surfaces involved in this process. We report here the construction of a hybrid coordination motif consisting of a natural (His) and a non-natural ligand (quinolate)-on the alpha-helical surface of cytochrome cb(562), which (a) simultaneously binds divalent metals with high affinity, (b) leads to a metal-induced increase in global protein stability, and importantly, (c) enables the formation of a discrete protein dimer, whose shape is dictated by the inner-sphere metal coordination geometry and closely approximates that of the DNA-binding domains of bZIP family transcription factors
First author: Janjua, Muhammad Ramzan Saeed Ashraf, A DFT study on the electronic and redox properties of [X8V14O50](n-) (X = Si-IV, Ge-IV, P-V, and As-V), CANADIAN JOURNAL OF CHEMISTRY-REVUE CANADIENNE DE CHIMIE, 88, 434, (2010)
Abstract: The electronic and redox properties of the title polyanions have been calculated by means of density functional theory (DFT). These were unrestricted open-shell systems with electronic configuration of d(I) of V. In this behalf, energies and compositions of alpha-LUMO, beta-LUMO, alpha-HOMO, and beta-HOMO were also analyzed. First of all, electronic and redox properties of vanadosilicate [Si8V14O50](12-) (system 1) were calculated and then Si-IV was substituted with Ge-IV, P-V, and As-V for further investigations of systems 2, 3, and 4, respectively. The substitution greatly modifies the electronic properties as alpha-LUMOs are quite different in all the studied systems. The alpha-LUMO is mainly composed of V and O in system 1, V and Ge in system 2, V and O in system 3, and As, O, and V in system 4. The alpha HOMO-LUMO energy gaps are greatly reduced in systems 2, 3, and 4 as compared with system 1. The system 4 [As8V14O50](4-) has minimal value of total bonding energy, whereas system 2 [Ge8V14O50](12-) has maximal, so energetically system 4 is more favourable than the others. After the first reduction, alpha-LUMO in [Si8V14O50](14-) is made up of V and Si, beta-LUMO in [Ge8V14O50](13-) is concentrated on V and Ge, beta-LUMO in [P8V14O50](5-) is composed of V only, whereas beta-LUMO in [As8V14O50](5-) is delocalized over V, O, and As with almost the same contribution of all three atoms.
First author: Sherman, D. M., Metal complexation and ion association in hydrothermal fluids: insights from quantum chemistry and molecular dynamics, GEOFLUIDS, 10, 41, (2010)
Abstract: Complexation by ligands in hydrothermal brines is a fundamental step in the transport of metals in the Earth’s crust and the formation of ore deposits. Thermodynamic models of mineral solubility require an understanding of metal complexation as a function of pressure, temperature and composition. Over the past 40 years, mineral solubilities and complexation equilibria under hydrothermal conditions have been predicted by extrapolating thermodynamic quantities using equations of state based on the Born model of solvation. However, advances in theoretical algorithms and computational facilities mean that we can now explore hydrothermal fluids at the molecular level. Molecular or atomistic models of hydrothermal fluids avoid the approximations of the Born model and are necessary for any reliable prediction of metal complexation. First principles (quantum mechanical) calculations based on density functional theory can be easily used to predict the structures and relative energies of metal complexes in the ideal gas phase. However, calculations of metal complexation in condensed fluids as a function of temperature and pressure require sampling the configuration degrees of freedom using molecular dynamics (MD). Simulations of dilute solutions require very large systems (thousands of atoms) and very long simulation times; such calculations are only practical by treating the interatomic interactions using classical two-or three-body interatomic potentials. Although such calculations provide some fundamental insights into the nature of crustal fluids, simple two-or three-body classical potentials appear to be inadequate for reliably predicting metal complexation, especially in covalent systems such as Sn(2+), Au(3+) and Cu(+). Ab initio MD (i.e. where the bonding is treated quantum mechanically, but the molecular motions are treated classically) avoids the use of interatomic potentials. These calculations are practical for systems with hundreds of atoms over short times (<10 psec) but enable us to predict complexation as a function of pressure, temperature and composition. In this paper, I provide an introductory outline of the computational methods and illustrations of their application to NaCl brines and the complexation of Cu, Au, Sn and Zn.
First author: Skachkov, Dmitry, The Calculation of NMR Chemical Shifts in Periodic Systems Based on Gauge Including Atomic Orbitals and Density Functional Theory, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 6, 1650, (2010)
Abstract: We present here a method that can calculate NMR shielding tensors from first principles for systems with translational invariance. Our approach is based on Kohn-Sham density functional theory and gauge-including atomic orbitals. Our scheme determines the shielding tensor as the second derivative of the total electronic energy with respect to an external magnetic field and a nuclear magnetic moment. The induced current density due to a periodic perturbation from nuclear magnetic moments is obtained through numerical differentiation, whereas the influence of the responding perturbation in terms of the external magnetic field is evaluated analytically. The method is implemented into the periodic program BAND. It employs a Bloch basis set made up of Slater-type or numeric atomic orbitals and represents the Kohn-Sham potential fully without the use of effective core potentials. Results from calculations of NMR shielding constants based on the present approach are presented for isolated molecules as well as systems with one-, two- and three-dimensional periodicity. The reported values are compared to experiment and results from calculations on cluster models.
First author: Wassenaar, Jeroen, Catalyst selection based on intermediate stability measured by mass spectrometry,NATURE CHEMISTRY, 2, 417, (2010)
Abstract: The power of natural selection through survival of the fittest is nature’s ultimate tool for the improvement and advancement of species. To apply this concept in catalyst development is attractive and may lead to more rapid discoveries of new catalysts for the synthesis of relevant targets, such as pharmaceuticals. Recent advances in ligand synthesis using combinatorial methods have allowed the generation of a great diversity of catalysts. However, selection methods are few in number. We introduce a new selection method that focuses on the stability of catalytic intermediates measured by mass spectrometry. The stability of the intermediate relates inversely to the reactivity of the catalyst, which forms the basis of a catalyst-screening protocol in which less-abundant species represent the most-active catalysts, ‘the survival of the weakest’. We demonstrate this concept in the palladium-catalysed allylic alkylation reaction using diphosphine and IndolPhos ligands and support our results with high-level density functional theory calculations.
First author: Bunnik, Bouke S., Symmetric Transition State Analysis: An Analysis of Dissociative Methane Adsorption on Rh{111} Using Quantum Chemical Calculations, TOPICS IN CATALYSIS, 53, 403, (2010)
Abstract: The chemical bonding aspects of the transition state (TST) of methane activation on a Rh{111} surface are analyzed. Three methods are compared: The barrier decomposition analysis of Hu et al. in which the bond between CH is assumed completely broken in the TST (Satterfield, Heterogeneous catalysis in industrial practice, 2nd ed., 1996; Chorkendorff and Niemantsverdriet, Concepts of modern catalysis and kinetics, 2003; Somorjai, Introduction to surface chemistry and catalysis, 1994); the activation strain model of Bickelhaupt in which the CH bond is assumed to be equal to the gasphase CH interaction energy (Christmann, Surface science reports, 1988; Norskov and Christensen, Science, 2006; Forsberg, Chemical engineering progress, 2005); and a model in which the interaction energies between CH, and of the H atom and CH3 with the catalyst are all given equal attention, the symmetric transition state analysis. This symmetric transition state analysis would not yield a result different from the traditional methods if all bonds were additive and decoupled. But, as our results show, that is not in general the case. The position of the maximum in non-additivity can be considered a descriptor for the position of the TST on the reaction coordinate. At the TST, we find that the three interactions are of comparable strength.
First author: Baccouche, Azza, Effects of the Metal Center and Substituting Groups on the Linear and Nonlinear Optical Properties of Substituted Styryl-Bipyridine Metal(H) Dichloride Complexes: DFT and TDDFT Computational Investigations and Harmonic Light Scattering Measurements, JOURNAL OF PHYSICAL CHEMISTRY A, 114, 5429, (2010)
Abstract: UV-visible absorption spectroscopy and harmonic light scattering measurements coupled with density functional theory (DFT) calculations have been carried out for a series of 4,4′-bis(X-styry1)-2,2′-bipyridine M(II) dichloride complexes (M = Co, Ni, Cu, Zn; X = H, OMe, SMe, NMe2, NEt2, CN, NO2). The roles of the metal and the substituent X on their coordination geometries, absorption, and quadratic nonlinear optical properties have been investigated. We show that these complexes all exhibit a high-spin configuration and display a distorted tetrahedral metallic environment except the copper ones, which are distorted squareplanar complexes. When X is a strong electron-donating group (X = NMe2, NEt2) TDDFT calculations clearly demonstrate that, whereas the Zn complexes show an ILCT transition in the visible range, the Co, Ni, and Cu complexes exhibit additional MLCT and LLCT transitions. These latter transitions are vectorially opposed to the ILCT and could contribute to the decrease of the experimental quadratic hyperpolarizability beta values, in the order Zn > Ni approximate to Cu > Co. The computation of the beta values using TDDFT for the whole series of the closed-shell Zn(II) complexes featuring different X substituents established that the NLO activity increases with the donating strength of X and more generally with the decrease of the HOMO-LUMO energy gap. When X is a strong withdrawing group, the drastic decrease of the NLO response is explained by the negligible participation of the HOMO-LUMO transitions.
First author: Munoz-Castro, A., Spin-orbit effects on electronic delocalization. Aromaticity in a discrete square tetrapalladium sandwich complex, JOURNAL OF CHEMICAL PHYSICS, 132, 5429, (2010)
Abstract: In this article, we report the relativistic electronic structure, including spin-orbit interaction, employing all-electron density functional theory calculations on the multimetallic sandwich compound [(CNT)Pd-4(COT)](1+) (1), which can be considered as a [Pd-4](2+) fragment flanked by two ring-ligands, namely, cyclononatetraenyl (CNT1-) and cyclooctatetraene (COT), as well as the dimer of 1, hereafter 2. The calculations suggest that the Pd-4-ligand interaction is mainly electrostatic, being the main responsible term for the stabilization of the almost fully occupied 4d shell [Pd-4](2+) fragment. The ring currents and electronic delocalization estimated via the nuclear independent chemical shifts indices and electron localization function, allow us to describe a significant sigma-aromaticity at the center of the Pd-4 square in 1, which in conjunction with the aromaticity arising from the ligands induce considerable aromatic character inside of the multimetallic metallocene.
First author: Olivier, Celine, “Chain-Like” Trimetallic Ruthenium Complexes with C-7 Carbon-Rich Bridges: Experimental and Theoretical Investigations of Electronic Communication Tuning in Five Distinct Oxidation States, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 5638, (2010)
Abstract: In this work, we report the synthesis and the electronic properties of the unique highly conjugated molecular wires trans-[Cl-(dppe)(2)Ru=C=C=(Ph)C-CH=(CH3)C-C C-(X)(2)Ru-C C-C(CH3)=CH-C(Ph)=C=C=Ru(dppe)(2)Cl](n+) (n = 2, X = dppe ([3a](OTf)(2)) and dppm ([3b](OTf)(2)) with three similar metal centers spanned by two odd-numbered unsaturated C-7 chains providing a 28 angstrom long conjugated path and displaying five well-separated redox states (n = 0-4). Successive one-electron transfer steps were studied by means of cyclic voltammetry, EPR and UV-vis-NIR-IR spectroelectrochemistry. The electronic and physical properties of the different states were further rationalized with the help of DFT-based calculations. Upon one-electron reduction (n = 1), the single electron is delocalized over the two carbon chains through the central metal atom to an extent driven by the rotations within and between the chains. The second reduction (n = 0) involves the whole carbon-rich conjugated path of the molecule in a spin polarized scheme: one electron is delocalized over each chain, and the two electrons are antiferromagnetically coupled with a coupling on the order of kT. Interestingly, oxidation processes strongly involve both the metal atoms and the bridging ligands. The combined investigations reveal that the mono-oxidized system (n = 3) presents a spin density uniformly distributed between the metal atoms and the carbon atoms of the chains, whereas in the second oxidation state (n = 4) the compounds show a strong antiferromagnetic coupling on the order of 4 kT between the two single electrons localized in two distinct delocalized spin orbitals implying all the carbon atoms of the bridges and the three metal atoms. Thus, for the first time, electronic communication was fully evidenced and tuned in homonuclear trimetallic oligomeric carbon-rich systems in either an oxidation or a reduction process.
First author: Spiegelhauer, Olivia, Cysteine as a Modulator Residue in the Active Site of Xenobiotic Reductase A: A Structural, Thermodynamic and Kinetic Study, JOURNAL OF MOLECULAR BIOLOGY, 398, 66, (2010)
Abstract: Xenobiotic reductase A (XenA) from Pseudomonas putida 86 catalyzes the NADH/NADPH-dependent reduction of various substrates, including 2-cyclohexenone and 8-hydroxycoumarin. XenA is a member of the old yellow enzyme (OYE) family of flavoproteins and is structurally and functionally similar to other bacterial members of this enzyme class. A characteristic feature of XenA is the presence of a cysteine residue (Cys25) in the active site, where in most members of the OYE family a threonine residue is found that modulates the reduction potential of the FMN/FMNH(-) couple. We investigated the role of Cys25 by studying two variants in which the residue has been exchanged for a serine and an alanine residue. While the exchange against alanine has a remarkably small effect on the reduction potential, the reactivity and the structure of XenA, the exchange against serine increases the reduction potential by +82 mV, increases the rate constant of the reductive half-reaction and decreases the rate constant in the oxidative half-reaction. We determined six crystal structures at high to true atomic resolution (d(min) 1.03-1.80 angstrom) of the three XenA variants with and without the substrate coumarin bound in the active site. The atomic resolution structure of XenA in complex with coumarin reveals a compressed active site geometry in which the isoalloxazine ring is sandwiched between coumarin and the protein backbone. The structures further reveal that the conformation of the active site and substrate interactions are preserved in the two variants, indicating that the observed changes are due to local effects only. We propose that Cys25 and the residues in its place determine which of the two half-reactions is rate limiting, depending on the substrate couple. This might help to explain why the genome of Pseudomonas putida encodes multiple xenobiotic reductases containing either cysteine, threonine or alanine in the active site.
First author: Weiss, Joseph W. E., A Solid-State B-11 NMR and Computational Study of Boron Electric Field Gradient and Chemical Shift Tensors in Boronic Acids and Boronic Esters, JOURNAL OF PHYSICAL CHEMISTRY A, 114, 5119, (2010)
Abstract: The results of a solid-state B-11 NMR study of a series of 10 boronic acids and boronic esters with aromatic substituents are reported. Boron-11 electric field gradient (EFG) and chemical shift (CS) tensors obtained from analyses of spectra acquired in magnetic fields of 9.4 and 21.1 T are demonstrated to be useful for gaining insight into the molecular and electronic structure about the boron nucleus. Data collected at 21.1 T clearly show the effects of chemical shift anisotropy (CSA), with tensor spans (Omega) on the order of 10-40 ppm. Signal enhancements of up to 2.95 were achieved with a DFS-modified QCPMG pulse sequence. To understand the relationship between the measured tensors and the local structure better, calculations of the B-11 EFG and magnetic shielding tensors for these compounds were conducted. The best agreement was found between experimental results and those obtained from GGA revPBE DFT calculations. A positive correlation was found between Omega and the dihedral angle (phi(CCBO)), which describes the orientation of the boronic acid/ester functional group relative to an aromatic system bound to boron. The small boom CSA is discussed in terms of paramagnetic shielding contributions as well as diamagnetic shielding contributions. Although there is a region of overlap, both Omega and the B-11 quadrupolar coupling constants tend to be larger for boronic acids than for the esters. We conclude that the span is generally the most characteristic boron NMR parameter of the molecular and electronic environment for boronic acids and esters, and show that the values result from a delicate interplay of several competing factors, including hydrogen bonding, the value of phi(CCBO), and the electron-donating or withdrawing substituents bound to the aromatic ring.
First author: Munoz-Castro, A., Electronic Delocalization, Energetics, and Optical Properties of Tripalladium Ditropylium Halides, [Pd-3(C7H7)(2)X-3](1-) (X = Cl-, Br-, and I-), JOURNAL OF PHYSICAL CHEMISTRY A, 114, 5217, (2010)
Abstract: Here we report relativistic electronic structure calculations employing all-electron density functional theory (DFT) including scalar and spin-orbit interaction, on the multimetallic sandwich compound [Pd-3(C7H7)(2)X-3](1-) (X = Cl- (1), Br- (2), and I- (3)), which can be considered as a [Pd3X3](3-) fragment flanked by two ring-ligands [(C7H7)(2)](2+). The calculations suggest that the [Pd3X3](3-)-ligand interaction is mainly arising from electrostatic contributions, where the formally zerovalent Pd atoms allows backdonation of charge from the halide X1- atoms to the [(C7H7)(2)](+2) ligands, resulting in a net charge of about +0.4 for each Pd atoms that decreases from 1 to 3. The electronic delocalization estimated via the NICS indexes and the ELF function allows us to describe a significant stabilizing sigma-aromaticity at the center of the Pd-3 triangle, which decreases from [Pd3Cl3](3-) to [Pd(3)l(3)](3) (1 to 3) due to the softer character of the iodine counterpart, that donates extra charge to the ligands. The calculated electronic transitions via TD.DFT are in reasonable agreement with the experimental data obtained in CH2Cl2 solution, indicating that the most intense transition involves a core-centered [Pd3X3](3) transition toward the [(C7H7)(2)](2+) ligands, with mainly X1- character in the former molecular spinor that is responsible for the variation of the observed lambda(max) according to the variation of X1-.
First author: Garcia-Lastra, J. M., Cr3+ in layered perovskites: do the electron paramagnetic resonance parameters only depend on the impurity-ligand distances?, JOURNAL OF PHYSICS-CONDENSED MATTER, 22, 5217, (2010)
Abstract: The actual value of axial, R-ax, and equatorial, R-eq, impurity-ligand distances for Cr3+ embedded in tetragonal K2MgX4 (X = F, Cl) lattices has been explored by means of density functional theory (DFT) calculations on clusters involving up to 69 ions using two different functionals. For K2MgF4:Cr3+ R-eq and R-ax are found to be coincident within only 0.5 pm. When the g tensor of K2MgF4:Cr3+ is derived considering only the CrF63- unit in vacuo at the calculated equilibrium geometry the g(perpendicular to) – g(parallel to) quantity fails to reproduce the experimental value by one order of magnitude. In contrast, when the active electrons localized in the CrX63- complex (X = F, Cl) are allowed to feel the anisotropic electric field coming from the rest of the lattice ions the splitting in the first excited state, T-4(2), increases by one order of magnitude. The present results thus show that the g tensor anisotropy and the zero-field splitting constant, D, observed for K2MgX4:Cr3+ (X = F, Cl) are not mainly due to a local deformation of the CrX63- octahedron but to the action of the internal electric field, often ignored when seeking the microscopic origin of electronic properties due to impurities in insulating lattices. Accordingly, serious doubts on the validity of the superposition model are cast by the present work.
First author: Chen, Fu, Solid-State In-115 and P-31 NMR Studies of Triarylphosphine Indium Trihalide Adducts,JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 5479, (2010)
Abstract: Solid-state In-115 and P-31 NMR spectroscopy, relativistic density functional theory (DFT) calculations, and single-crystal X-ray diffraction were used to investigate a series of triarylphosphine indium(III) trihalide adducts, X3In(PR3) and X3In(PR3)(2) (X = Cl, Br or I; PR3 = triarylphosphine ligand). The electric field gradient tensors at indium as well as the indium and phosphorus magnetic shielding tensors and the direct and indirect In-115-P-31 spin-spin coupling were characterized; for complexes possessing a C3 symmetry axis, the anisotropy in the indirect spin-spin coupling, AJ(In-115,31P), was also determined. The In-115 quadrupolar coupling constants, Co(In-115), range from +/-1.25 +/- 0.10 to -166.0 +/ -2.0 MHz. For any given phosphine ligand, the indium nuclei are most shielded for X = I and least shielded for X = Cl, a trend also observed for other group-13 nuclei in M(III) complexes. This experimental trend, attributed to spin-orbit effects of the halogen ligands, is reproduced by the DFT calculations. The spans of the indium magnetic shielding tensors for these complexes, delta(11) – delta(33), range from 40 +/- 7 to 710 +/- 60 ppm; those determined for phosphorus range from 28 +/- 1.5 to 50 +/- 3 ppm. Values of (1)J(In-115,P-31) range from 550 +/- 20 to 2500 +/- 20 Hz. For any given halide, the (up arrow)J(In-115,P-31) values generally increase with increasing basicity of the PR3 ligand. Calculated values of (up arrow)J(In-115,P-31) and Delta J(In-115,P-31) duplicate experimental trends and indicate that both the Fermi-contact and spin-dipolar Fermi-contact mechanisms make important contributions to the (1)J(In-115,P-31) tensors.
First author: Michelini, Maria del Carmen, Gas-Phase Reactions of Uranate Ions, UO2-, UO3-, UO4-, and UO4H-, with Methanol: a Convergence of Experiment and Theory, INORGANIC CHEMISTRY, 49, 3836, (2010)
Abstract: Bimolecular reactions of uranium oxide molecular anions with methanol have been studied experimentally, by Fourier transform ion cyclotron resonance mass spectrometry, and computationally, by density functional theory (DFT). The primary goals were to provide fundamental insights into mechanistic and structural details of model reactions of uranium oxides with organics, and to examine the validity of theoretical modeling of these types of reactions. The ions UO3-, UO4-, and UO4H- each reacted with methanol to give a singular product; the primary products each exhibited sequential reactions with two additional methanol molecules to again give singular products. The observed reactions were elimination of water, formaldehyde, or hydrogen, and in one case addition of a methanol molecule. The potential energy profiles were computed for each reaction, and isotopic labeling experiments were performed to probe the validity of the computed mechanisms and structures-in each case where the experiments could be compared with the theory there was concurrence, clearly establishing the efficacy of the employed DFT methodologies for these and related reaction systems. The OFT results were furthermore in accord with the surprisingly inert nature of UO2-. The results provide a basis to understand mechanisms of key reactions of uranium oxides with organics, and a foundation to extend DFT methodologies to more complex actinide systems which are not amenable to such direct experimental studies.
First author: Rosa, Angela, Is [FeO](2+) the Active Center Also in Iron Containing Zeolites? A Density Functional Theory Study of Methane Hydroxylation Catalysis by Fe-ZSM-5 Zeolite, INORGANIC CHEMISTRY, 49, 3866, (2010)
Abstract: Arguments are put forward that the active a-oxygen site in the Fe-ZSM-5 catalyst consists of the FeO2+ moiety. It is demonstrated that this zeolite site for FeO2+ indeed obeys the design principles for high reactivity of the FeO2+ moiety proposed earlier: a ligand environment consisting of weak equatorial donors (rather oxygen based than nitrogen based) and very weak or absent trans axial donor. The alpha-oxygen site would then owe its high reactivity to the same electronic structure features that lends FeO2+ its high activity in biological systems, as well as in the classical Fenton chemistry.
First author: Zouchoune, Fairouz, Electronic structure and vibrational frequencies in dehydroacetic acid (DHA) transition-metal complexes: A DFT study, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 945, 78, (2010)
Abstract: The density functional theory (DFT) calculations were carried out on Cu(DHA)(2)(DMSO)(2) [1], Zn(DHA)(2)(DMSO)(2) [2] and Cd(DHA)(2)(DMSO)(2) [3], where their structural arrangement of which consists of a slightly distorted octahedron centred by a transition-metal with bidentate DHA ligands situated in equatorial positions and solvent molecules in axial positions. Results reveal the presence of one MO in the middle of large gap in [1], which allows its oxidation and its reduction. Thus two redox couples are envisageables. The electronic structure of closed-shell anion [1](-) is calculated and compared to that of the related [2] and [3] complexes, where substantial HOMO-LUMO gaps are computed.A bonding analysis of these species shows the weakness of M-O (solvent) bonds compared to M-O (DHA) ones. The calculated vibrational data have been found in good agreement with experimental results. TD-DFT calculations rationalize the long-range electronic communication as a main characteristic of the DHA transition-metal species and as a key to improve MLCT and LMCT charge transfers.
First author: Palusiak, Marcin, On the nature of halogen bond – The Kohn-Sham molecular orbital approach, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 945, 89, (2010)
Abstract: The nature of halogen bonding is investigated for a set of H3C-X center dot center dot center dot O = CH2 and F3C-X center dot center dot center dot O = CH2 (X = Cl, Br, I) molecular complexes. The Kohn-Sham MO investigation indicates effective stabilizing charge transfer/polarization interaction, while electrostatic interaction contributes only slightly to the total bonding interaction, being systematically overbalanced by exchange repulsion. Thus, the covalent nature of halogen bonding may be expected on the basis of the obtained results. What is more, the halogen atom, being Lewis acid in halogen bonding, may simultaneously act as Lewis base in hydrogen bonding. The same mechanism of anisotropic charge distribution on halogen atom is responsible for this dual character.
First author: Wu, Gang, Solid-State O-17 NMR and Computational Studies of C-Nitrosoarene Compounds, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 5143, (2010)
Abstract: We report the first solid-state O-17 NMR determination of the O-17 quadrupole coupling (QC) tensor and chemical shift (CS) tensor for four O-17-labeled C-nitrosoarene compounds: p-[O-17]nitroso-N,N-dimethylaniline ([O-17]NODMA), SnCl2(CH3)(2)([O-17]NODMA)(2), ZnCl2([O-17]NODMA)(2), and [O-17]NODMA center dot HCl. The O-17 quadrupole coupling constants (C-Q) observed in these C-nitrosoarene compounds are on the order of 10-15 MHz, among the largest values found to date for organic compounds. The O-17 CS tensor in these compounds exhibits remarkable sensitivity toward the nitroso bonding scheme with the chemical shift anisotropy (delta(11) – delta(33)) ranging from just 350 ppm in [O-17]NODMA center dot HCl to over 2800 ppm in [O-17]NODMA. This latter value is among the largest O-17 chemical shift anisotropies reported in the literature. These extremely anisotropic O-17 NMR interactions make C-nitrosoarene compounds excellent test cases that allow us to assess the detection limit of solid-state O-17 NMR. Our results suggest that, at 21.14 T, solid-state O-17 NMR should be applicable to all oxygen-containing organic functional groups. We also show that density functional theory (DFT) calculations can reproduce reasonably well the experimental O-17 QC and CS tensors for these challenging molecules. By combining quantum chemical calculations with experimental solid-state O-17 NMR results, we are able to determine the O-17 QC and CS tensor orientations in the molecular frame of reference for C-nitrosoarenes. We present a detailed analysis illustrating how magnetic field-induced mixing between individual molecular orbitals (MOs) contributes to the O-17 shielding tensor in C-nitrosoarene compounds. We also perform a Townes Dailey analysis for the observed O-17 QC tensors and show that O-17 CS and QC tensors are intrinsically related through the pi bond order of the N=O bond. Furthermore, we are able for the first time to examine the parallelism between individual O-17 and N-15 CS tensor components in C-nitrosoarenes.
First author: Djukic, Jean-Pierre, One-Pot Generation of a Tris-cationic Homobimetallic Planar-Chiral Ruthenacycle,ORGANOMETALLICS, 29, 1675, (2010)
Abstract: The “one-pot” generation of a tris-cationic homobimetallic racemic planar-chiral ruthenacyclic ruthenium sandwich complex from a reaction of the metal-free chelating ligand with the (eta(6)-benzene)dichloridoruthenium(I I) dimer in acetonitrile is reported. This unexpected complex, which was characterized by structural X-ray diffraction analysis, is the product of a multistep process entailing first the cycloruthenation of the ligand, a ligand exchange reaction, and eventually the site-selective pi-bonding of a bis-cationic [(eta(6)-benzene)Ru](2+) moiety to a monocationic ruthenacyclic intermediate. Investigations of the underlying electronic structure and bonding scheme by resorting to quantum chemical methods of the density functional theory have revealed the key role played by the electron-donating NMe(2) substituent, which enables the a priori antagonistic a-coordination of the in situ-formed cationic ruthenacycle by a dicationic (eta(6)-arene) ruthenium(II) moiety. Experimental evidence indicates indeed that, in the absence of such an electron-donating group at the metalacycle, the pi-coordination of the [(eta(6)-benzene)Ru](2+) cannot take place.
First author: Korichi, Hanane, The Coordination Chemistry of Azulene: A Comprehensive DFT Investigation,ORGANOMETALLICS, 29, 1693, (2010)
Abstract: DFT calculations with full geometry optimization have been carried out on a series of real and hypothetical compounds of the type L(n)MAz, MAz(2), L(n)M(2)Az, and M(2)Az(2) (Az = azulene). The analysis of their electronic and molecular structures in relation to their electron counts allows a comprehensive rationalization of the bonding within this very large family of compounds. A very rich coordination chemistry of azulene is apparent, even much richer than one could determine from the avalaible experimental data. The reason for this diversity comes in part from the marked dissymmetry of azulene, which is made up of two fused rings of very different sizes. It comes also in large part from the very large electronic and structural flexibility of azulene (in contrast to its isomer naphthalene), which is able to adapt to the electronic demand of the metal(s). Any of the fused C(5) and C(7) rings of azulene can be coordinated in various hapticities and symmetries, depending on the nature of the ML(n) moiety (or moieties) they are bonded to. This flexibility favors the possibility of existence of several isomers (sometimes enantiomers) of similar energy and of their interconversion in solution, in particular through haptotropic shifts. The azulene asymmetry causes dinuclear complexes to exhibit very different coordination environments (sometimes different oxidation states). In some of them, M – M bonding is preferred over M – azulene bonding. Most of the investigated complexes are expected to exhibit a rich fluxional behavior.
First author: Meyer, Drew A., Characterization of charge transfer excitations in hexacyanomanganate(III) with Mn K-edge resonant inelastic x-ray scattering, JOURNAL OF CHEMICAL PHYSICS, 132, 1693, (2010)
Abstract: We use hard x-ray resonant inelastic x-ray scattering (RIXS) and density functional theory (DFT) calculations to characterize charge transfer excitations in K(3)Mn(CN)(6). The combination of RIXS measurements and DFT calculations allows us to characterize the strength of the ligand-metal electronic interaction and assign the Raman resonances in the RIXS spectra to charge transfer excitations. With x-ray excitation energies resonant with the T(2g) and E(g) pre-edge peaks derived predominantly from the Mn 3d orbitals, we observe Raman resonances in the energy transfer range from 2 to 12 eV, which results from the filling of the 1s core-hole from T(1u)-symmetry occupied orbitals. DFT calculations indicate that these orbitals exhibit primarily ligand character, supporting the assignment of the energy transfer resonances to ligand-to-metal charge transfer excitations. Our RIXS measurements and DFT calculations also indicate that the E(g)-orbital spin-splits by roughly 0.8 eV, though we do not cleanly resolve the two absorption peaks in the RIXS spectra. We also see evidence for a metal-to-ligand charge transfer (MLCT) excitation when exciting with a 6545.0 eV incident photon, roughly 4 eV above the E(g) absorption peaks. The 6545.0 eV resonant emission spectrum shows a 6.0 eV energy transfer resonance, which corresponds to a final state hole in the T(2g) partially occupied orbital. DFT calculations indicate that excitation at 6545.0 eV populates an unoccupied T(1u)-symmetry orbital of primarily ligand character. Given the predominantly metal character of the final state hole, we assign the 6.0 eV Raman resonance to a MLCT excitation. These measurements demonstrate the ability of hard x-ray RIXS to characterize the valence electronic structure of coordination compounds.
First author: Wang, Nan, Visible light photocatalytic reduction of Cr(VI) on TiO2 in situ modified with small molecular weight organic acids, APPLIED CATALYSIS B-ENVIRONMENTAL, 95, 400, (2010)
Abstract: Visible light photoreduction of toxic Cr(VI) over TiO2 was achieved through surface modification with small molecular weight organic acids (SOAs) as sacrificial organics. Because neat anatase TiO2 is active only under UV light irradiation (lambda < 387 nm), no photoreduction of Cr(VI) was observed in TiO2 dispersions being irradiated with visible light (lambda > 420 nm). However, when a small amount of colorless SOAs was added into the TiO2 dispersion, a charge-transfer-complex (CTC) was formed between TiO2 and SOA, which was sensitive to visible light irradiation and induced the photo-oxidation of SOA and photoreduction of Cr(VI). It was observed that about 95% of added Cr(VI) (0.2 mmol L-1) was removed in the visible light-illuminated TiO2 (1.0 g L-1) dispersions at pH 3.0 within 2 h by adding 0.2 mmol L-1 tartaric acid as a SOA. The SOA-induced photoreduction of Cr(VI) proceeded via a CTC-mediated path, being governed by chemical structures of sacrificial SOAs. A higher energy of the highest occupied molecular orbital or lower ionization potential of SOAs is favorable to electron transfer within TiO2-SOA complex, thereby accelerating the photoreduction of Cr(VI). The Cr(VI) removal was further enhanced by increasing SOA concentration and/or decreasing solution pH.
First author: Fedorov, Alexey, Experimental and Theoretical Study of a Gold(I) Aminonitrene Complex in the Gas Phase,CHEMPHYSCHEM, 11, 1002, (2010)
Abstract: Visible light photoreduction of toxic Cr(VI) over TiO2 was achieved through surface modification with small molecular weight organic acids (SOAs) as sacrificial organics. Because neat anatase TiO2 is active only under UV light irradiation (lambda < 387 nm), no photoreduction of Cr(VI) was observed in TiO2 dispersions being irradiated with visible light (lambda > 420 nm). However, when a small amount of colorless SOAs was added into the TiO2 dispersion, a charge-transfer-complex (CTC) was formed between TiO2 and SOA, which was sensitive to visible light irradiation and induced the photo-oxidation of SOA and photoreduction of Cr(VI). It was observed that about 95% of added Cr(VI) (0.2 mmol L-1) was removed in the visible light-illuminated TiO2 (1.0 g L-1) dispersions at pH 3.0 within 2 h by adding 0.2 mmol L-1 tartaric acid as a SOA. The SOA-induced photoreduction of Cr(VI) proceeded via a CTC-mediated path, being governed by chemical structures of sacrificial SOAs. A higher energy of the highest occupied molecular orbital or lower ionization potential of SOAs is favorable to electron transfer within TiO2-SOA complex, thereby accelerating the photoreduction of Cr(VI). The Cr(VI) removal was further enhanced by increasing SOA concentration and/or decreasing solution pH.
First author: Meskaldji, Samir, Density Functional Theory Investigations of the Homoleptic Tris(dithiolene) Complexes [M(dddt)(3)](-q) (q=3, 2; M = Nd3+ and U3+/4+) Related to Lanthanide(III)/Actinide(III) Differentiation, INORGANIC CHEMISTRY, 49, 3192, (2010)
Abstract: The structures of the homoleptic lanthanide and actinide tris(dithiolene) complexes [M(dddt)(3)](q-) (q = 3, M = Nd3+ and q = 3 or 2, M = U3+/4+) have been investigated using relativistic Density Functional Theory (DFT) computations including spin orbit corrections coupled with the COnductor like Screening Model (COSMO) for a realistic solvation approach. The dithiolene ligands are known to be very efficient at stabilizing metal high oxidation states. The aim of the work is to explain the peculiar symmetric folding of the three Mdddt metallacycles in these complexes, some of them existing under a polymeric form, in relation with the Ln(III)/An(III) differentiation. In the [M(dddt)(3)(py)](q-) species, where an additional pyridine ligand is linked to the metal center, the Mdddt moieties appear to be almost planar. The study brings to light the occurrence of a M center dot center dot center dot C=C interaction explaining the Mdddt folding of the [U(dddt)(3)](q-) uranium species, the metal 5f electrons playing a driving role. No such interaction appears in the case of the Nd(III) complex, and the folding of the rather flexible dddt ligands in the polymeric structure of this species should be mainly due to steric effects. Moreover, the analysis of the normal modes of vibration shows that the U(III) complex [U(dddt)(3)](3-), which has not yet been isolated, is thermodynamically stable. It appears that the X-ray characterized U(IV) complex [U(dddt)(3)](2-) should be less stable than the calculated U(III) complex in a polar solvent.
First author: Pascu, Sofia I., Synthesis and structural investigations of Ni(II)- and Pd(II)-coordinated alpha-diimines with chlorinated backbones, INORGANICA CHIMICA ACTA, 363, 1157, (2010)
Abstract: Novel square planar Pd(II) alpha-diimines [PdX2{ArN=C(Cl)}(2)], where Ar = C6H5, (2,6-Me2C6H3), (2,6-(Pr2C6H3)-Pr-i) and X = Cl or Br, and the octahedral Ni(II) complex [NiBr2{(C6H5)N=C(Cl)}(2)(THF)(2)] have been prepared and characterised by spectroscopic methods. For two of the Pd(II) complexes and the Ni(II) complex the crystal structures were determined by X-ray crystallography. A further insight into the geometry and electronic structure of [PdBr2{(2,6-Me2C6H3)N=C(Cl)}(2)] was gained using density functional theoretical calculations (DFT). This compound resembles structurally and electronically typical olefin polymerisation pre-catalysts supported by alpha-diimines incorporating methyl-and 1,8-naphtalenyl substituents at the ligand backbone. The chlorine-substituted backbone of the free ligand [2,6-Me2C6H3N=C(Cl)](2) can be employed in further alkylation reactions to generate new multifunctional ligand prototypes with potential uses as ansa-metallocene/diimines building blocks for catalytic applications of heterobimetallic complexes.
First author: Dumit, Veronica I., Mechanistic Insights into Ferredoxin-NADP(H) Reductase Catalysis Involving the Conserved Glutamate in the Active Site, JOURNAL OF MOLECULAR BIOLOGY, 397, 814, (2010)
Abstract: Plant-type ferredoxin-NADP(H) reductases (FNRs) are flavoenzymes harboring one molecule of noncovalently bound flavin adenine dinucleotide that catalyze reversible reactions between obligatory one-electron carriers and obligatory two-electron carriers. A glutamate next to the C-terminus is strictly conserved in FNR and has been proposed to function as proton donor/acceptor during catalysis. However, experimental studies of this proposed function led to contradicting conclusions about the role of this glutamate in the catalytic mechanism. In the present work, we study the titration behavior of the glutamate in the active site of FNR using theoretical methods. Protonation probabilities for maize FNR were computed for the reaction intermediates of the catalytic cycle by Poisson-Boltzmann electrostatic calculations and Metropolis Monte Carlo titration. The titration behavior of the highly conserved glutamate was found to vary depending on the bound substrates NADP(H) and ferredoxin and also on the redox states of these substrates and the flavin adenine dinucleotide. Our results support the involvement of the glutamate in the FNR catalytic mechanism not only as a proton donor but also as a key residue for stabilizing and destabilizing reaction intermediates. On the basis of our findings, we propose a model rationalizing the function of the glutamate in the reaction cycle, which allows reinterpretation of previous experimental results.
First author: Petz, Wolfgang, Reaction of Double Ylide C(PPh3)(2) with [W(CO)(6)] – Crystal Structures of [(CO)(5)W(CCPPh3)] and [(CO)(5)W{eta(1)-O2C2(PPh3)(2)}] and Bonding Analyses of [TM(CCPR3)] Compounds, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 397, 1872, (2010)
Abstract: The photochemically generated complex [(CO)(5)W(thf)] reacts with C(PPh3)(2) (1) to provide the salt (HC{PPh3}(2))(2)[W-2(CO)(10)] (5) in high yield by abstraction of a proton from the solvent thf. With [W(CO)(6)], a slow reaction in benzene occurs to give a mixture of [(CO)(5)W{O2C2(PPh3)(2)}] (6) and the heterocumulene (phosphonioacetylide) complex [(CO)(5)W(CCPPh3)] (7) by a Wittig type reaction. Both compounds were characterized by spectroscopic and X-ray diffraction analyses. Theoretical density functional calculations reveal that the ligand CCPPh3 in 7 and in similar complexes is a strong sigma-donor but weak pi-acceptor.
First author: Conradie, Jeanet, Bonding in Titanocenyl Complexes Containing O,O ‘-Cyclic Ligands, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 110, 1100, (2010)
Abstract: Density functional theory calculations show that the formal 16-electron count of d(0) [Cp2TiIV(O,O’-BID)](0/1) complexes containing a O,O’-chelated bidentate ligand O,O’-BID of different ring size, is increased via Ti <- O pi bonding when both the O donor atoms carry a formal negative charge. The Ti <- O pi bonding occurs by symmetry lowering of the complex by either symmetrical (C-s) or unsymmetrical (C-2) folding of the O,O’-BID ligand round the O center dot center dot center dot O axis. An NBO analysis confirms the Ti <- O pi charge transfer via back-bonding.
First author: Zhao, Yan, Density Functional Calculations of E2 and S(N)2 Reactions: Effects of the Choice of Density Functional, Basis Set, and Self-Consistent Iterations, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 6, 1104, (2010)
Abstract: We have computed stationary points on the potential energy surface for the anti-E2, syn-E2, and S(N)2 pathways of the reactions of F- and Cl- with CH3CH2F and CH3CH2Cl with fully self-consistent fields and Gaussian basis functions. We find large differences from previously reported [Bento, A. P.; Sola, M.; Bickelhaupt, F. M. J. Chem. Theory Comput. 2008, 4, 929] calculations with Slater-type orbitals. We revise the findings of the previous study; in particular, we find average absolute errors in kcal/mol compared to benchmark calculations of 20 stationary point energies (6 saddle points and 14 minima) of 0.9 for M06-2X, 1.2 for M08-SO, 1.4 for M06-HF, 2.0 for M06, 2.3 for B3LYP, 2.5 for OLYP, 2.7 for M06-L, and 3.5 kcal/mol for TPSS. We also compare the predictions of various density functionals for the partial atomic charges at the transition states.
First author: Kaim, Wolfgang, The 1,4-diazabutadiene/1,2-enediamido non-innocent ligand system in the formation of iridaheteroaromatic compounds: Spectroelectrochemistry and electronic structure, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 695, 1052, (2010)
Abstract: Oxidation of the unambiguously characterized iridium(III)-enediamido complex IrCp*(RNCHCHNR), R = 2,6-dimethylphenyl, with six cyclically arranged p electrons was investigated using EPR and UV-vis spectroelectrochemistry. In contrast to a corresponding iminocatecholato system reported recently by Rauchfuss et al. [27] the two one-electron oxidation steps are not completely reversible, depending on the solvent. We attribute the electrochemical behavior observed in weakly coordinating dichloromethane and propylene carbonate solvents to an enhanced propensity for ligand addition: while neutral IrCp*(RNCHCHNR) remains coordinatively unsaturated with the strongly sigma and pi donating enediamido(2-) ligand mitigating the electron deficit, the oxidation to the less donating radical anion ligand (RNCHCHNR)(center dot-) or even to neutral 1,4-diazabutadiene is considered to induce a strong tendency for quasi-hexacoordination in [IrCp*(L)(RNCHCHNR)], L = solvent, halide, substrate. The presence of excess chloride thus leads to formation of the precursor complex ion [IrCp*ClRNCHCHNR)](+) after oxidation. EPR spectroscopy of the one-electron oxidation intermediate [IrCp*(RNCHCHNR)](+) was successful only for a frozen solution in propylene carbonate/0.1 M Bu(4)NPF(6) which revealed an axial signal with sizeable g anisotropy. DFT calculation results for [IrCp*(RNCHCHNR)](n), n = 0, +, 2+ confirm the available structural and spectroelectrochemical data (UV-vis, EPR).
First author: Majumdar, D., Density Functional Theory Based Studies on the Nature of Raman and Resonance Raman Scattering of Nerve Agent Bound to Gold and Oxide-Supported Gold Clusters: A Plausible Way of Detection, JOURNAL OF PHYSICAL CHEMISTRY A, 114, 4340, (2010)
Abstract: A detailed theoretical investigation has been carried out at the density functional level of theories to investigate the nature of Raman intensities of the -P = O stretching mode of a model nerve agent DFP (diisopropylfluorophosphate) when bound to different gold (Au-8, Au-20) and oxide-supported gold (MgO center dot center dot center dot Au-4, CaO center dot center dot center dot Au-4, TiO2 center dot center dot center dot Au-4, Al2O3 center dot center dot center dot Au-4, M16O16 center dot center dot center dot Au-8, and [M16O15 center dot center dot center dot Au-8](2+), M = Ca, Mg) clusters. All of these clusters and the DFP-bound clusters are fully optimized, and the computed energetics shows that DFP attaches itself weakly to these clusters. The normal Raman spectra calculations on these clusters show that there is substantial enhancement of the -P = O stretching mode of DFP compared to file isolated species. This enhancement has been found to be due to the polarization of the -P = O bond of DFP when bound to the clusters. Significant enhancement in intensity has been observed in the case of Au-n center dot center dot center dot DFP (n = 8, 20), M16O16 center dot center dot center dot Au-8 center dot center dot center dot DFP, and [M16O15 center dot center dot center dot Au-8](2+)center dot center dot center dot DFP (M = Ca, Mg) clusters. The resonance Raman calculations on the Au-n center dot center dot center dot DFP (n = 8, 20) reveals that this enhancement could be made quite large and selective, which is a feature that is unique to the nerve agents and could be used as a property for detecting them.
First author: Kane, Krista A., Calculation of Absolute Resonance Raman Intensities: Vibronic Theory vs Short-Time Approximation, JOURNAL OF PHYSICAL CHEMISTRY C, 114, 5540, (2010)
Abstract: We present the absolute resonance Raman scattering (RRS) intensities of uracil, rhodamine 6G (R6G), and iron(II) porphyrin with imidazole and CO ligands (FePImCO) calculated using density functional theory (DFT). The spectra are calculated using both the vibronic theory and the short-time approximation. We find that the absolute RRS intensities calculated using the short-time approximation are severely overestimated, as compared with results obtained using the vibronic theory. This issue is attributed to the sensitivity of the absolute RRS intensities to the adjustable damping factor within the short-time approximation. This is illustrated for uracil, for which the relative intensities were predicted accurately using the short-time approximation, but the absolute intensities were still overestimated. Although intensities comparable to that obtained with the vibronic theory could be obtained using the short-time approximation, it requires a large damping factor, roughly twice that estimated from the absorption spectrum, to be used in the simulations. Furthermore, we find that DFT underestimates the absolute RRS intensities for R6G as compared to experiments, which is most likely clue to the neglect of solvent effects in the calculations. For R6G and FePImCO, vibronic effects are shown to enhance the low-frequency modes relatively more, improving the agreement with experiments.
First author: Onuma, Hiroaki, Quantum chemistry and QSPR study on relationship between crystal structure and emission wavelength of Eu2+-doped phosphors, JOURNAL OF THE SOCIETY FOR INFORMATION DISPLAY, 18, 301, (2010)
Abstract: The relationship between crystal structures and emission properties has been computationally investigated for Eu2+-doped phosphors. The electronic structure of the Eu2+-doped BaMgAl10O17 phosphor was analyzed by using the quantum chemistry method. The different effects of O and Ba atoms on the Eu 5d states were determined. The presence of O and Ba atoms increases and decreases the energy level of the Eu 5d orbital by forming anti-bonding and bonding interactions, respectively. According to the electronic-structure analysis, the structure index that represents the local geometrical information of the Eu atom was defined. The relationship between the crystal structures and the emission wavelengths of the 16 Eu2+-doped oxide phosphors were studied by using the quantitative structure-property relationship (QSPR). The QSPR model suggested that the both O and alkaline-earth atoms around the Eu atom are of importance in the determination of the emission wavelength. The interaction between the Eu and the nearest O atoms make the Eu2+ emission wavelength short. On the other hand, the interaction from the alkaline-earth atoms around the Eu atom lengthens the Eu2+ emission wavelength. This evaluation method is useful in selecting the host material that indicates a desirable emission wavelength of the Eu2+-doped phosphors.
First author: Neugebauer, Johannes, Chromophore-specific theoretical spectroscopy: From subsystem density functional theory to mode-specific vibrational spectroscopy, PHYSICS REPORTS-REVIEW SECTION OF PHYSICS LETTERS, 489, 1, (2010)
Abstract: Spectroscopy forms the bridge between theory and experiment in the analysis of structure, properties, and reactivity of functional molecules and molecular aggregates. Our knowledge on the basic working principles of systems such as photosynthetic units strongly relies on spectroscopic information, which is interpreted in terms of molecular or submolecular building blocks. To choose such entities as the essential ingredients in a quantum chemical framework is thus a promising route to the theoretical spectroscopy of complex systems.This work describes developments of chromophore-specific quantum chemical methods, which focus on relevant substructures without sacrificing the view on the entire system. A subsystem density-functional theory approach is analyzed that employs a real-space partitioning of the electron density for the description of complex aggregates in terms of simple fragments. This approach can be used as a chrotnophore-specific embedding method and allows for efficient and accurate analyses of environmental effects. However, it fails for phenomena caused by a collective response of an aggregate of molecules. The limitations of this embedding scheme can be overcome by a general subsystem approach to time-dependent density functional theory, which easily relates to phenomenological theories such as excitonic coupling models.Resonance Raman spectroscopy can be used to probe local excited states in larger molecules and is thus intrinsically chromophore-specific. It is shown that well-known approximations for resonance Raman calculations can efficiently be used with time-dependent density-functional theory methods to study photochemical and photophysical processes in large molecules such as artificial photosynthetic systems. Intensity-driven approaches to resonance Raman calculations can exploit the selectivity observed in experiments for an iterative determination of high-intensity spectral features. Applications of such schemes to biochemical building blocks are discussed.
First author: Hao, Yan, Thermal decomposition of allyl-imidazolium-based ionic liquid studied by TGA-MS analysis and DFT calculations, THERMOCHIMICA ACTA, 501, 78, (2010)
Abstract: Thermal stability of ionic liquids (ILs) is of great significance for their applications in dissolving cellulose at elevated temperature. A novel ionic liquid, 1-allyl-3-methylimidazolium chloride ([Amim]Cl), was found to be a powerful solvent for cellulose. However, the study about long-term isothermal stability, thermal decomposition mechanism and decomposition products of [Amim]Cl are scarce. Herein, we studied the thermal stability and degradation mechanism of [Amim]Cl using isothermal thermogravimetric analysis (TGA) experiments and density functional theory (DFT) calculations. The weight loss of [Amim]Cl at 100 C under air atmosphere within 15 days was only 1.9% and [Amim]Cl after long-term heating also had dissolving capability of cellulose, indicating that [Amim]Cl has high thermal stability and can be long-term used at the dissolving temperature of cellulose. Both TGA experiments and DFT calculations revealed [Amim]Cl decomposed along two channels and the main pyrolysis products of the proposed mechanisms were detected using thermogravimetric technique coupled with mass spectrometry (TGA-MS).
First author: Yan, Likai, Electronic Properties of Unprecedented Bridging Organoimido-Substituted Hexamolybdate: New Insights from Density Functional Theory Study, JOURNAL OF PHYSICAL CHEMISTRY B, 114, 3754, (2010)
Abstract: The organoimido functionalization of polyoxometalates (POMs) has drawn tremendous attention due to particular merits in fabricating POM-based hybrid materials with finely tunable properties. The electronic properties, orbital and bonding characters of unprecedented bridging organoimido-substituted hexamolybdate are investigated using density functional theory methods. Among the organoimido-bridged hexamolybdates, [Mo6O16(2,6-Me-2-NC6H3)(2)(mu(2)-2,6-Me-2-NC6H3)](2-) (3-Ar-l), which features two terminal and one bridging organoimido ligand, is more favorable. The calculations confirm that the three-center (3c). pi bond originates From the coplanarity of bridging nitrogen atom with two Mo atoms and the hybridization of bridging nitrogen. The 3c bond stabilizes the organoimido-bridged anion 3-Ar-l. Compared with cis-bifunctionalized organoimido derivative [Mo6O17(2,6-Me-2-NC6H3)(2)](2-) (2-Ar), the bonding interaction between terminal organoimido ligand and hexamolybdate cluster. in 3-Ar-l is strengthened by the bridging organoimido. The results are in good agreement with thin analysis of the Wiberg bond index of the Mo-N bond. The organoimido segment modifies the occupied molecular orbitals of organoimido hexamolybdates. The unoccupied molecular orbitals in 3-Ar-l are largely nonbonding O-p and Mo-d orbitals in character, which resemble those of 2-Ar.
First author: Laine, R. M., Synthesis and Photophysical Properties of Stilbeneoctasilsesquioxanes. Emission Behavior Coupled with Theoretical Modeling Studies Suggest a 3-D Excited State Involving the Silica Core, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 3708, (2010)
Abstract: A set of stilbene-substituted octasilicates [p-RStil(x)Ph(8-x)SiO(1.5)](8) (R = H, Me, MeO, Cl, NMe2 and x = 5.3-8) and [o-MeStilSiO(1.5)](8) were prepared. Model compounds were also prepared including the corner and half cages: [p-MeStilSi(OEt)(3)], [p-Me(2)NStilSi(OSiMe3)(3)], and [p-Me(2)NStilSi(O)(OSiMe)](4). These compounds were characterized by MALDI-TOF, TGA, FTIR, and H-1 NMR techniques. Their photophysical properties were characterized by UV-vis, two-photon absorption, and cathodoluminescence spectroscopy (on solid powders), including studies on the effects of solvent polarity and changes in concentration. These molecules are typically soluble, easily purified, and robust, showing T-d(5%) > 400 degrees C in air. The full and partial cages all show UV-vis absorption spectra (in THF) identical to the spectrum of trans-stilbene, except for [o-MeStilSiO(1.5)](8), which exhibits an absorption spectrum blue-shifted from trans-stilbene. However, the partial cages show emissions that are red-shifted by similar to 20 nm, as found for stilbene-siloxane macrocycles, suggesting some interaction of the silicon center(s) with the stilbene pi(star) orbital in both the corner and half cages. In contrast, the emission spectra of the full cages show red-shifts of 60-100 nm. These large red-shifts are supported by density functional theoretical calculations and proposed to result from interactions of the stilbene pi(star) orbitals with a LUMO centered within the cage that has 4A(1) symmetry and involves contributions from all Si and oxygen atoms and the organic substituents. Given that this LUMO has 3-D symmetry, it appears that all of the stilbene units interact in the excited state, consistent with theoretical results, which show an increased red-shift with an increase in the functionalization of a single corner to functionalization of all eight corners with stilbene. In the case of the Me2N- derivatives, this interaction is primarily a charge-transfer interaction, as witnessed by the influence of solvent polarity on the emission behavior. More importantly, the two-photon absorption behavior is 2-3 times greater on a per p-Me(2)Nstilbene basis for the full cage than for the corner or half cages. Similar observations were made for p-NH(2)stilbenevinyl(8)OS cages, where the greater conjugation lengths led to even greater red-shifts (120 nm) and two-photon absorption cross sections. Cathodoluminescence studies done on [p-MeStilSiO(1.5)](8) or [p-MeStilOS](8) powders exhibit essentially the same emissions as seen in solution at high dilution. Given that only the emissions are greatly red-shifted in these molecules, whereas the ground-state UV-vis absorptions are not changed from trans-stilbene, except for the ortho derivative, which is blue-shifted 10 rim. It appears that the interactions are only in the excited state. Theoretical results show that the HOMO and LUMO states are always the pi and pi(star) states on the stilbene, which show very weak shifts with increasing degrees of functionalization, consistent with the small changes in the UV-vis spectra.The band gap between the lowest unoccupied 4a1 symmetry core state localized inside the silsesquioxane cage and the highest occupied state (pi state on stilbene), however, is markedly decreased as the number of stilbene functional grups is increased. This is consistent with the significant red-shifts in the emission spectra. The results suggest that the emission occurs from the 4a1 state localized on the cage. Moreover, for the compounds [p-RStil(6-7)Ph(2-1)OS](8), the emissions are blue-shifted compared to those of the fully substituted compounds, suggesting the molecular symmetry is reduced (from cubic), thereby reducing the potential for 3-D delocalization and raising the energy of the LUMO. The implications are that these octafunctional molecules exhibit some form of 3-D interaction in the excited state that might permit their use as molecular transistors as well as for energy collection and dispersion as molecular antennas, for example, and for nonlinear optical applications.
First author: Frischmann, Peter D., Capsule Formation, Carboxylate Exchange, and DFT Exploration of Cadmium Cluster Metallocavitands: Highly Dynamic Supramolecules, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 3893, (2010)
Abstract: A family of molecular heptacadmium carboxylate clusters templated inside [3 + 3] Schiff base macrocycles has been isolated and studied by variable temperature solution and solid-state NMR spectroscopy, single-crystal X-ray diffraction (SCXRD), and density functional theory (DFT) calculations. These metallocavitand cluster complexes adopt bowl-shaped structures, induced by metal coordination, giving rise to interesting host-guest and supramolecular phenomena. Specifically, dimerization of these metallocavitands yields capsules with vacant coordination and hydrogen-bonding sites accessible to encapsulated guests. Strong host-guest interactions explain the exceptionally high packing coefficient (0.80) observed for encapsulated N,N-dimethylformamide (DMF). The guest-accessible hydrogen-bonding sites arise from an unusual mu(3)-OH ligand bridging three cadmium ions. Thermodynamic and kinetic studies show that dimerization is an entropy-driven process with a highly associative mechanism. In DMF the exchange rate of peripheral cluster supporting carboxylate ligands is intrinsically linked to the rate of dimerization and these two seemingly different events have a common rate-determining step. Investigation of guest dynamics with solid-state H-2 NMR spectroscopy revealed 3-fold rotation of an encapsulated DMF molecule. These studies provide a solid understanding of the host-guest and dynamic properties of a new family of metallocavitands and may help in designing new supramolecular catalysts and materials.
First author: Hocking, Rosalie K., Fe L-Edge X-ray Absorption Spectroscopy Determination of Differential Orbital Covalency of Siderophore Model Compounds: Electronic Structure Contributions to High Stability Constants, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 4006, (2010)
Abstract: Most bacteria and fungi produce low-molecular-weight iron chelators called siderophores. Although different siderophore structures have been characterized, the iron-binding moieties often contain catecholate or hydroxamate groups. Siderophores function because of their extraordinarily high stability constants (K-STAB = 10(30)-10(49)) and selectivity for Fe(Ill), yet the origin of these high stability constants has been difficult to quantify experimentally. Herein, we utilize Fe L-edge X-ray absorption spectroscopy to determine the differential orbital covalency (i.e., the differences in the mixing of the metal d-orbitals with ligand valence orbitals) of a series of siderophore model compounds. The results enable evaluation of the electronic structure contributions to their high stability constants in terms of sigma- and pi-donor covalent bonding, ionic bonding, and solvent effects. The results indicate substantial differences in the covalent contributions to stability constants of hydroxamate and catecholate complexes and show that increased sigma as well as pi bonding contributes to the high stability constants of catecholate complexes.
First author: Scarso, Alessandro, Highly Active and Selective Platinum(II)-Catalyzed Isomerization of Allylbenzenes: Efficient Access to (E)-Anethole and Other Fragrances via Unusual Agostic Intermediates, ORGANOMETALLICS, 29, 1487, (2010)
Abstract: Terminal alkene isomerization reactions can be efficiently catalyzed by Pt(II) complexes bearing a chelating diphosphine and an alkyl or, better, aryl moiety under mild experimental conditions. In particular diphosphines, such as dppb, characterized by a large bite angle in conjunction with a pentafluorophenyl residue coordinated to Pt enable quantitative conversion of the reagent into internal alkenes within few hours at 50 degrees C in CHCl(3) as solvent. E/Z selectivity can be as high as 98:2 for allylbenzene, and the catalytic system can be fruitfully applied to the preparation of E fragrances derived by isomerization of substituted allylbenzene derivatives. The selectivity increases during the progress of the reaction because of a Subsequent catalytic step where the Z alkene coordinates to the Pt and is converted into the E isomer. NMR investigation on the catalyst showed formation of agostic Pt center dot center dot center dot H intermediate species derived by insertion of the substrate into the Pt-aryl bond followed by beta-hydride elimination. Formation of such agostic species is promoted by the steric hindrance imparted by the diphosphine characterized by a large bite angle. Kinetic studies and DFT calculations on the possible agostic intermediates shed light on their structure and enable the formulation of a possible catalytic mechanism.
First author: Gourier, Didier, EPR, ENDOR, and HYSCORE Study of the Structure and the Stability of Vanadyl-Porphyrin Complexes Encapsulated in Silica: Potential Paramagnetic Biomarkers for the Origin of Life, JOURNAL OF PHYSICAL CHEMISTRY B, 114, 3714, (2010)
Abstract: The possibility of using vanadyl ions as paramagnetic biomarkers for the identification of traces of primitive life fossilized in silica rocks is studied by cw-EPR, ENDOR, HYSCORE, and DFT calculations. It is well-known that porphyrins, which are Common to all living organisms, form vanadyl-porphyrin complexes in sediments deposited in oceans. However, the stability of these complexes over a very long time (more than 3 billion years) is not known. By encapsulating vanadyl-porphyrin complexes in silica synthesized by a sol-gel method to mimic SiO2 sediments, We studied the Structure and stability of these complexes upon step heating treatments by monitoring the evolution of the g factor and of the hyperfine interactions with V-51, H-1, N-14, C-13, and Si-29 nuclei. It is found that vanadyl-porphyrin complexes are progressively transformed into oxygenated vanadyl complexes by transfer of the VO2+ ion from the porphyrin ring to the mineral matrix, The organic component is transformed into carbonaceous matter which contains paramagnetic centers (IOM center dot centers). To test the validity of this approach, we studied by EPR a 3490 million years old chert (polycrystalline SiO2 rock) containing some of the oldest putative traces of life. This rock contains oxygenated vanadyl complexes and IOM center dot centers very similar to those found in the synthetic analogues.
First author: Tangen, Espen, Electronic Structure of a Paramagnetic {MNO}(6) Complex: MnNO 5,5-Tropocoronand,INORGANIC CHEMISTRY, 49, 2701, (2010)
Abstract: Using density functional theory (OLYP/STO-TZP) calculations, we have investigated the electronic structure of [Mn(5,5-tropocoronand)(NO)], a rare paramagnetic {MNO}(6) complex. Experimental methods, including magnetic susceptibility measurements and high-field electron paramagnetic resonance spectroscopy, have not provided an unambiguous spin state assignment for this complex. In other respects, however, the compound was fully characterized, including by means of single-crystal X-ray structure determination. The optimized S = 1 OLYP geometry reproduced all key aspects of the trigonal-bipyramidal molecular structure, including a short Mn-N(O) distance (similar to 1.7 angstrom) and an essentially linear MnNO angle. In contrast, the S = 0 and S = 2 optimized structures disagreed with the crystal structure in critical respects. Moreover, three different exchange-correlation functionals (OLYP, B3LYP, and B3LYP*) indicated an S = 1 ground state by a clear margin of energy. An examination of the Kohn-Sham MOs of this state indicated a primarily d(xz)(2)d(yz)(2)d(XY)(1)d(x2)-(1)(z2) electronic configuration, where the z axis is identified with the nearly linear MnNO axis. The d(y2) orbital is formally unoccupied in this state, interacting, as it does, head-on with two tropocoronand nitrogens lying along the yaxis, the pseudo-3-fold axis of the trigonal bipyramid. The doubly occupied d(xz) and d(yZ) orbitals are in actuality d pi(Fe)- pi*(NO)-based pi-bonding molecular orbitals, the alpha and beta “components” of which are significantly offset spatially. This offset results in excess minority spin density on the NO unit. Thus, the OLYP/TZP atomic spin populations are Mn, 2,85; N(O), -0.52; and 0, -0.35.
First author: Grimme, Stefan, The Crucial Role of Dispersion in the Cohesion of Nonbridged Binuclear Os -> Cr and Os -> W Adducts, INORGANIC CHEMISTRY, 49, 2911, (2010)
Abstract: The concept of a dative metal-metal bond is generally used to designate the donor-acceptor (DA) interaction of an electron-saturated metal center with another electron-deficient-or unsaturated-metal center. This type of DA bonding extended to the field of coordination complexes constitutes a borderline case of weak metal-metal interaction, among which the so-called metallophilic interactions occurring with 4d, 5d, and other late-transition-m eta I complexes are the most documented and representative examples. From a general standpoint, the peculiar position of the so-called dative metal-metal bond in chemical bonding stems from its presumed covalent character, which contrasts with the situation encountered with metallophilic interactions, which are essentially supported by dispersion and electrostatic forces and somewhat sustained by relativistic effects. In this study, the nature of the metal-metal bond in nonbridged 5d-3d Os-Cr and 5d-5d Os-W adducts, i.e., (Me3P)(CO)(4)OS-M(CO)(5) (M=Cr, W) and (CO)(5)OS-Cr(CO)(5), was addressed by resorting to state-of-the-art quantum-chemical methods. Semilocal density functional theory (DFT) approximations like Becke-Perdew or TPSS, the double-hybrid B2PLYP functional, as well as the corresponding dispersion, including TPSS-D and B2PLYP-D functionals and the wave-function-based spin-component-scaled second-order perturbative Moller-Plesset theory (SCS-MP2), were used. Energy decomposition analysis combined with the analysis of pairwise interfragment correlation energies from Pipek-Mezey localized molecular orbitals in combination with SCS-MP2 led to a clear demonstration of the significant role of dispersion (London) forces in the stabilization of the title adducts, wherein the Os-metal DA bond bears a rather low covalent character. These results plead in favor of a systematic recourse to dispersion including DFT approximations when addressing organometallic and coordination complexes.
First author: Xu, Lai, Dynamics of 1,3-Dipolar Cycloadditions: Energy Partitioning of Reactants and Quantitation of Synchronicity, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 3029, (2010)
Abstract: The dynamics of 1,3-dipolar cycloadditions of nine 1,3-dipoles with ethylene and acetylene have been explored by quasiclassical trajectory and single trajectory calculations in the retro-cycloaddition direction to compute energy partitioning of reactants among relative translation, vibration, and rotation. The results are interpreted with an expanded version of Polanyi’s Rules for bimolecular reactions, and three trends are evident. (1) Relative translation of reactants is the main contributor to surmounting the barrier, since all transition states (TSs) are early with respect to sigma bond formation. (2) Vibrational excitation in the 1,3-dipole bending modes required for reaction is related to the lateness of the TS with respect to dipole bending: diazonium betaines (late TS, dipole bending required) > nitrilium betaines > azomethine betaines (early TS, dipole bending least important). This is also the order of the activation barriers (high -> low). (3) The previously reported linear correlation between activation barriers and the energy required to distort reactants to their TS geometries are understandable in terms of the requirements for vibrational excitation computed here. For the 1,3-dipolar cycloadditions, single trajectory calculations, which contain no zero point vibrational energy, give reasonable estimates of the mean energy partitioning of reactants derived from potential energy barrier release. The timing of bond formation and relative reactivities of different 1,3-dipoles are discussed.
First author: Himmel, Daniel, How Far Can We Go? Quantum-Chemical Investigations of Oxidation State plus IX,CHEMPHYSCHEM, 11, 865, (2010)
Abstract: The highest known oxidation state of any element is +VIII. After the recent discovery of Ir(VIII)O(4) under cryogenic conditions, we have investigated the stability of cationic species [MO(4)](+) (M=Rh,Ir,Mt). Such compounds would formally represent the new oxidation state +IX, which is experimentally unknown so far for the whole periodic table. [IrO(4)](+) is predicted to be the most promising candidate. The calculated spin-orbit (SO) coupling shows only minor effects on the stability of the iridium species, whereas SO-coupling increases enormously for the corresponding Eka-Iridium (Meitnerium) complexes and destabilizes these.
First author: Scheffelaar, Rachel, Scope and Limitations of an Efficient Four-Component Reaction for Dihydropyridin-2-ones, JOURNAL OF ORGANIC CHEMISTRY, 75, 1723, (2010)
Abstract: A broad range of isonitrile-functionalized 3,4-dihydropyridin-2-ones could be prepared using a four-component reaction between phosphonates, nitriles, aldehydes, and isocyanoacetates. The reaction involves initial formation of a 1-azadiene intermediate which is trapped in situ by an isocyanoacetate to give the desired heterocyclic scaffold through cyclocondensation. The full scope and limitations of this four-component reaction are described. Variation of the nitrile and aldehyde inputs proved to be extensively possible, but variation of the phosphonate input remains limited. Regarding the isocyanoacetate, alpha-aryl isocyanoacetates give moderate to high yields and result in a complete diastereoselectivity for the 3,4-cis isomer. alpha-Alkyl isocyanoacetates gave the corresponding dihyropyridin-2-ones in moderate yields, most of them as mixtures of diastereomers. Elevated temperatures during cyclocondensation generally increased the yield and resulted in a change of the diastereomeric ratio in flavor of the cis-diastereomer. In addition to isocyanoacetates, a limited number of other alpha-acidic esters resulted in the formation of dihyropyridin-2-ones, albeit in much lower yield. Computational studies show that the observed difference in yield cannot be simply correlated to specific physical properties (including acidity) of the different alpha-acidic esters.
First author: Bakken, Vebjorn, Bimetallic Cobalt/Rhenium Systems: Preferred Position of Rhenium Through an Interdisciplinary Approach, CATALYSIS LETTERS, 135, 21, (2010)
Abstract: Some commercial type Fischer-Tropsch catalysts are based on rhenium-doped cobalt. In an attempt to elucidate the preferred position of rhenium in the cobalt matrix, we have carried out experimental Low Energy Ion Scattering investigations of oxidized and reduced catalyst samples and computational DFT investigations of bimetallic Co/Re clusters. The results indicate that rhenium preferentially occupies subsurface sites, where it can coordinate to a maximum number of cobalt atoms.
First author: Bodensieck, Antje, Absolute Configuration of Eremophilane Sesquiterpenes from Petasites hybridus: Comparison of Experimental and Calculated Circular Dichroism Spectra, CHIRALITY, 22, 308, (2010)
Abstract: In-depth conformational analyses of 10 known eremophilane (= (IS,4a-R,7R,8aR)-decahydro-1,8a-dimethyl-7-(1-methylethyl)napththalene) sesquiterpenes,.1-10, from Petasites hybridus were performed with molecular mechanics as well as density functional theory methods. Electronic transition energies and rotational strengths of these eight eremophilane lactones and two petasins were calculated by time-dependent density functional theory (B3PW91/TZVP). The absolute configurations of the constituents could be assigned by comparison of their simulated and experimental circular dichroism (CD) spectra in methanol as (4S,5R,8S,10R) (1, 2), (2R,4S,5R,8S,10R) (3, 4, 5), (2R,4S,5R,8R,9R,10R) (6), (2R,4S,5R,8R,10R) (7, 8), and (3R,4R,5R) (9, 10). Single-crystal X-ray diffraction data of 8p-hydroxyeremophilanolide ((8S)-8-hydroxyeremophil-7(11)-en-12,8-olide) (1) served as starting point for the theoretical conformational calculations of the 8 beta-epimers of the eremophilane lactones. Experimental CD spectra as well as (1)H NMR spectra of compound 1 in methanol were considerably dependent on sample concentration.
First author: van der Wijst, Tushar, Differential stabilization of adenine quartets by anions and cations, JOURNAL OF BIOLOGICAL INORGANIC CHEMISTRY, 15, 387, (2010)
Abstract: We have investigated the structures and stabilities of four different adenine quartets with alkali and halide ions in the gas phase and in water, using dispersion-corrected density functional theory at the BLYP-D/TZ2P level. First, we examine the empty quartets and how they interact with alkali cations and halide anions with formation of adenine quartet-ion complexes. Second, we examine the interaction in a stack, in which a planar adenine quartet interacts with a cation or anion in the periphery as well as in the center of the quartet. Interestingly, for the latter situation, we find that both cations and anions can stabilize a planar adenine quartet in a stack.
First author: Li, Jia, Phosphane-stabilized gold clusters: investigation of the stability of [Au-13(PMe2Ph)(10)Cl-2](3+),JOURNAL OF MOLECULAR MODELING, 16, 505, (2010)
Abstract: The phosphane-stabilized gold cluster [Au-13(PMe2Ph)(10)Cl-2](3+) was studied using density functional theory. The extraordinary stability of the cluster has been attributed to the stability of the gold core and the protection conferred by ligands. Here, five stability factors of the gold core were explained and verified by investigating the Au (13) (5+) core in detail. Interactions between the gold core and several PR3 ligands (R = Me, H, I, Br, Cl, F) were investigated according to the different electron donor abilities of each ligand; bonding energy between the ligand and the gold core was found to increase with the electronegativity of the R substituent. Furthermore, two other aspects of the ligands were clarified: how the ligand stabilizes the Au (13) (5+) core, and which kind of ligand provides the best stabilization for the cluster.
First author: Ramirez-Tagle, Rodrigo, DEDICATED TO DR. PABLO DOBUD URQUETA, JOURNAL OF THE CHILEAN CHEMICAL SOCIETY, 55, 39, (2010)
Abstract: Relativistic time-dependent density functional (TDDFT) calculations including spin orbit interactions via the zero order regular approximation (ZORA) and solvent effects using the COSMO model were carried out on the [Re(6)Q(8)(NCS)(6)](4-), (Q = S. Se, Te) clusters. These calculations indicate that the lowest energy allowed electronic transitions are characterized by being of LMCT type. The calculated absorption maximum tends to shift to longer wavelengths as the face-capping chalcogenide ligand becomes heavier. Thus our calculations predict that the [Re6Te8(NCS)(6)](4-) cluster might be also luminescent. Due to the unusual properties exhibited by these and other isoelectronic and isostructural hexarhenium (III) chalcogenide clusters, hexamolybdenum halide clusters and hexatungsten halide clusters, we propose here the design of nanodevices, such as, molecular sensors and molecular nanocells for molecular electronics.
First author: Bickelhaupt, F. Matthias, C(CN)(5)(-): transition state or intermediate?, MENDELEEV COMMUNICATIONS,20, 72, (2010)
Abstract: Cyanide reacts with tetracyanomethane towards the tricyanomethyl anion via cyanophilic substitution; this is suggested by nitrogen isotope-labeling experiments and proven by density functional calculations at OLYP/TZ2P.
First author: Gao, Yi, Icosahedral Crown Gold Nanocluster Au43Cu12 with High Catalytic Activity, NANO LETTERS, 10, 1055, (2010)
Abstract: Structural and catalytic properties of the gold alloy nanocluster Au43Cu12 are investigated using a density-functional method. In contrast to the pure Au-55 nanocluster, which exhibits a low-symmetry C-1 structure, the 55-atom “crown gold” nanocluster exhibits a multishell structure, denoted by Au@Cu-12@Au-42, with the highest icosahedral group-symmetry. in addition, density functional calculations suggest that this geometric magic-number nanocluster possesses comparable catalytic capability as a small-sized Au-10 cluster for the CO oxidation, due in part to their low-coordinated Au atoms on vertexes. The gold alloy nanocluster also shows higher selectivity for styrene oxidation than the bare Au(111) surface.
First author: Guerra, Celia Fonseca, Adenine versus guanine quartets in aqueous solution: dispersion-corrected DFT study on the differences in pi-stacking and hydrogen-bonding behavior, THEORETICAL CHEMISTRY ACCOUNTS, 125, 245, (2010)
Abstract: We have investigated the performance of the dispersion-corrected density functionals (BLYP-D, BP86-D and PBE-D) and the widely used B3LYP functional for describing the hydrogen bonds and the stacking interactions in DNA base dimers. For the gas-phase situation, the bonding energies have been compared to the best ab initio results available in the literature. All dispersion-corrected functionals reproduce well the ab initio results, whereas B3LYP fails completely for the stacked systems. The use of the proper functional leads us to find minima for the adenine quartets, which are energetically and structurally very different from the C-4h structures, and might explain why adenine has to be sandwiched between guanine quartets to form planar adenine quartets.
First author: Han, Wen-Ge, Quantum cluster size and solvent polarity effects on the geometries and Mossbauer properties of the active site model for ribonucleotide reductase intermediate X: a density functional theory study, THEORETICAL CHEMISTRY ACCOUNTS, 125, 305, (2010)
Abstract: In studying the properties of metalloproteins using ab initio quantum mechanical methods, one has to focus on the calculations on the active site. The bulk protein and solvent environment is often neglected, or is treated as a continuum dielectric medium with a certain dielectric constant. The size of the quantum cluster of the active site chosen for calculations can vary by including only the first-shell ligands which are directly bound to the metal centers, or including also the second-shell residues which are adjacent to and normally have H-bonding interactions with the first-shell ligands, or by including also further hydrogen bonding residues. It is not well understood how the size of the quantum cluster and the value of the dielectric constant chosen for the calculations will influence the calculated properties. In this paper, we have studied three models (A, B, and C) of different sizes for the active site of the ribonucleotide reductase intermediate X, using density functional theory (DFT) OPBE functional with broken-symmetry methodology. Each model is studied in gas-phase and in the conductor-like screening (COSMO) solvation model with different dielectric constants epsilon = 4, 10, 20, and 80, respectively. All the calculated Fe-ligand geometries, Heisenberg J coupling constants, and the Mossbauer isomer shifts, quadrupole splittings, and the Fe-57, H-1, and O-17 hyperfine tensors are compared. We find that the calculated isomer shifts are very stable. They are virtually unchanged with respect to the size of the cluster and the dielectric constant of the environment. On the other hand, certain Fe-ligand distances are sensitive to both the size of the cluster and the value of epsilon. epsilon = 4, which is normally used for the protein environment, appears too small when studying the diiron active site geometry with only the first-shell ligands as seen by comparisons with larger models.
First author: Zbiri, Mohamed, Density functional calculations of potential energy surface and charge transfer integrals in molecular triphenylene derivative HAT(6), THEORETICAL CHEMISTRY ACCOUNTS, 125, 445, (2010)
Abstract: We investigate the effect of structural fluctuations on charge transfer integrals, overlap integrals, and site energies in a system of two stacked molecular 2,3,6,7,10,11-hexakishexyloxytriphenylene (HAT(6)), which is a model system for conducting devices in organic photocell applications. A density functional based computational study is reported. Accurate potential energy surface calculations are carried out using an improved meta-hybrid density functional to determine the most stable configuration of the two weakly bound HAT(6) molecules. The equilibrium parameters in terms of the twist angle and co-facial separation are calculated. Adopting the fragment approach within the Kohn-Sham density functional framework, these parameters are combined to a lateral slide, to mimic structural/conformational fluctuations and variations in the columnar phase. The charge transfer and spatial overlap integrals, and site energies, which form the matrix element of the Kohn-Sham Hamiltonian are derived. It is found that these quantities are strongly affected by the conformational variations. The spatial overlap between stacked molecules is found to be of considerable importance since charge transfer integrals obtained using the fragment approach differ significantly from those using the dimer approach.
First author: Cho, Herman, Probing the oxygen environment in UO22+ by solid-state O-17 nuclear magnetic resonance spectroscopy and relativistic density functional calculations, JOURNAL OF CHEMICAL PHYSICS, 132, 445, (2010)
Abstract: A combined theoretical and solid-state O-17 nuclear magnetic resonance (NMR) study of the electronic structure of the uranyl ion UO22+ in (NH4)(4)UO2(CO3)(3) and rutherfordine (UO2CO3) is presented, the former representing a system with a hydrogen-bonding environment around the uranyl oxygens and the latter exemplifying a uranyl environment without hydrogens. Relativistic density functional calculations reveal unique features of the U-O covalent bond, including the finding of O-17 chemical shift anisotropies that are among the largest for oxygen ever reported (>1200 ppm). Computational results for the oxygen electric field gradient tensor are found to be consistently larger in magnitude than experimental solid-state O-17 NMR measurements in a 7.05 T magnetic field indicate. A modified version of the Solomon theory of the two-spin echo amplitude for a spin-5/2 nucleus is developed and applied to the analysis of the O-17 echo signal of U O-17(2)2+.
First author: Liu, Z., On the nature of B-C-carbene bonding in a stable neutral diborene, JOURNAL OF CHEMICAL PHYSICS, 132, 445, (2010)
Abstract: We report the bonding interactions within [R(H)B=B(H)] and [R] (R=:C(NHCH)(2)) as a ligand in a newly synthesized stable neutral diborene. By using theoretical analyses, we have found the nature of the B-C-carbene bonding, and, more importantly, the key to realize multiple bonds for chemical elements. With character of almost equal covalency and ionicity, the stabilizing orbital interaction term, Delta E-orb, of B-C-carbene, is mainly given by sigma-symmetry orbital interactions; the donor-acceptor interaction is weak and contributes small to Delta E-orb. In the weak donor-acceptor interaction, the B -> C-carbene pi backdonation is stronger than the B -> C-carbene sigma donation. Thus, in effect, the bond emerges in the B(delta+)-C-carbene (delta-) dipole. Inspection of the correlation lines of the orbital correlation diagram for the B-C-carbene bonding indicates that the strength of the bonding orbitals in the central BB unit is weakened due to the coordination of the carbenes, and the center is unstabilized by the carbene ligand. This is contrary to the conventional view on the mechanism of coordination and the Dewar-Chatt-Duncanson model. However this unstabilizing effect should be responsible for the stability of the B=B double bond in the stable neutral diborene. This is because the very short bond lengths arising from multiple bonds will lead to a very strong Pauli repulsion, and, ultimately, destruction of chemical bonds. It can therefore be concluded that, actually, to prevent the very short bond lengths is the true reason for the successful realization of multiple bonds for main-group elements such as boron.
First author: Arendt, Cassandra S., Role of Transmembrane Domain 4 in Ligand Permeation by Crithidia fasciculata Equilibrative Nucleoside Transporter 2 (CfNT2), JOURNAL OF BIOLOGICAL CHEMISTRY, 285, 6024, (2010)
Abstract: Equilibrative nucleoside transporters play essential roles in nutrient uptake, cardiovascular and renal function, and purine analog drug chemotherapies. Limited structural information is available for this family of transporters; however, residues in transmembrane domains 1, 2, 4, and 5 appear to be important for ligand and inhibitor binding. In order to identify regions of the transporter that are important for ligand specificity, a genetic selection for mutants of the inosine-guanosine-specific Crithidia fasciculata nucleoside transporter 2 (CfNT2) that had gained the ability to transport adenosine was carried out in the yeast Saccharomyces cerevisiae. Nearly all positive clones from the genetic selection carried mutations at lysine 155 in transmembrane domain 4, highlighting lysine 155 as a pivotal residue governing the ligand specificity of CfNT2. Mutation of lysine 155 to asparagine conferred affinity for adenosine on the mutant transporter at the expense of inosine and guanosine affinity due to weakened contacts to the purine ring of the ligand. Following systematic cysteine-scanning mutagenesis, thiol-specific modification of several positions within transmembrane domain 4 was found to interfere with inosine transport capability, indicating that this helix lines the water-filled ligand translocation channel. Additionally, the pattern of modification of transmembrane domain 4 suggested that it may deviate from helicity in the vicinity of residue 155. Position 155 was also protected from modification in the presence of ligand, suggesting that lysine 155 is in or near the ligand binding site. Transmembrane domain 4 and particularly lysine 155 appear to play key roles in ligand discrimination and translocation by CfNT2.
First author: Smith, Elizabeth L., A Short Yet Very Weak Dative Bond: Structure, Bonding, and Energetic Properties of N-2-BH3, JOURNAL OF PHYSICAL CHEMISTRY A, 114, 2628, (2010)
Abstract: The structure, bonding, and energetic properties of the N-2-BH3 complex are reported as characterized by density functional theory (DFT) and post-Hartree-Fock (HF) calculations. The equilibrium structure of the complex exhibits a short B-N distance near 1.6 angstrom, comparable to that of a strong acid-base complex like H3N-BH3. However, the binding energy is only 5.7 kcal/mol at the CCSD(T)/6-311+G(2df,2dp) level of theory, which is reminiscent of a weak, nonbonded complex. Natural bond orbital (NBO) and atoms in molecules (AIM) analyses of the electron density from both DFT and post-HF calculations do indicate that the extent of charge transfer and covalent character in the B-N dative bond is only somewhat less than in comparable systems with fairly large binding energies (e.g., H3N-BH3 and OC-BH3). Energy decomposition analysis indicates key differences between the N-2, CO, and NH3 complexes, primarily associated with the natures of the lone pairs involved (Sp VS sp(3)) and the donor/acceptor characteristics of the relevant occupied and virtual orbitals, both sigma and pi. Also, CCSD/6-311+G(2df,2dp) calculations indicate that the B-N distance potential is rather anharmonic and exhibits a flat, shelf-like region ranging from 2.1 to 2.5 angstrom that lies about 1.5 kcal/mol above the minimum at 1.67 angstrom. However, this region is more sloped and lies about 2.5 kcal/mol above the equilibrium region according to the CCSD(T)/6-311+G(2df,2dp)//CCSD/6-311+G(2df,2dp) potential. A ID analysis of the vibrational motion along the B-N stretching coordinate in the CCSD/6-311+G(2df,2dp) potential indicates that the average B-N distance in the ground vibrational state is 1.71 angstrom, about 0.04 angstrom longer than the equilibrium distance. Furthermore, the vibrationally averaged distance obtained via ail analysis of the CCSD(T)/6-311+G(2df,2dp)//CCSD/6-311+G(2df,2dp) potential was found to be 0.03 angstrom longer than the CCSD(T)/6-311+G(2df,2dp) minimum.
First author: Bermudez, V. M., Ab Initio Study of the Interaction of Dimethyl Methylphosphonate with Rutile (110) and Anatase (101) TiO2 Surfaces, JOURNAL OF PHYSICAL CHEMISTRY C, 114, 3063, (2010)
Abstract: Density functional theory has been applied to an ab initio Study of the molecular and the dissociative adsorption of dimethyl methylphosphonate (DMMP) oil TiO2. Rutile (110)-(1 x 1) and anatase (101)-(1 x 1) Surfaces, free of defects and of OH, have been modeled using two-dimensionally periodic slabs (2-DPS) and also clusters with unsaturated edge atoms terminated with pseudohydrogen. Molecular adsorption Occurs via the formation of a Ti-5c center dot center dot center dot O=P dative bond at unsaturated, 5-fold-coordinated Ti Surface sites. C-H center dot center dot center dot O bonds between CH3 groups and surface 0 atoms also contribute, but dative bonding between methoxy O atoms and Ti-5c sites has no significant effect. In 2-DPS calculations, all TiO2 Surfaces considered give about the same adsorption energy (Delta E-ads)for molecular adsorption. There does, however, appear to be a small variation among the different Substrates whereby Delta E-ads increases with Surface energy. Two spectroscopic Signatures of molecular adsorption have been computed. One is a shift of -70 cm(-1), relative to the gas-phase value, in the nu(P=O) stretching frequency, and the other is a shift of 0.5 eV to higher bindind energy, relative to the gas-phase value, of the molecular HOMO. Several hypothetically possible products have been considered for the first step in dissociative adsorption. The most favorable is a (CH3)(CH3O)P(-O-)(2) bridge between two Ti-5c Sites together with a CH3 bonded to the O atom of a (Ti-)(2)O-2c site. This model is consistent with experimental results for DMMP adsorption oil OH-free rutile (110) surfaces. Oil all TiO2 Surfaces considered, dissociative adsorption is more exothermic than molecular adsorption. In 2-DPS calculations, Delta E-ads for dissociative adsorption is essentially the same for rutile (110) and anatase (101), but is smaller than that for anatase (010). The cluster models give results that are generally consistent with those of 2-DPS models; however, Delta E-ads is somewhat overestimated in the cluster Calculations.
First author: Yang, Xiao-Feng, Unusual Selectivity of Gold Catalysts for Hydrogenation of 1,3-Butadiene toward cis-2-Butene: A Joint Experimental and Theoretical Investigation, JOURNAL OF PHYSICAL CHEMISTRY C, 114, 3131, (2010)
Abstract: We report a combined experimental and theoretical investigation of the unusual catalytic properties of gold nanoparticles in file selective hydrogenation of 1,3-butadiene. It is found that nanogold catalysts exhibit a unique preference toward Forming cis-2-butene compared to the trans isomer, and the ratio of cis/trans isomers is structure-sensitive in terms of the size of gold nanoparticles. Our density functional theory calculations show that the cis-1,3-butadiene can be preferably adsorbed at the edges and corners of gold nanoparticles as compared to the trans-1,3-butadiene. Moreover, the transition state calculations indicate that the isomerization of trans-butadiene to cis-butadiene is kinetically favorable, with rather low energy barriers. These unique properties of gold nanoparticles toward 1,3-butadiene adsorption are discussed based oil orbital interaction analyses. It is found that Au-6s-based molecular orbitals prefer adsorption of cis-1,3-butadiene to the trans isomer due to spatial match. The catalytic selectivity of gold nanoparticles toward Formation of cis-2-butene has been further corroborated by comparable investigations oil silver and copper catalysts.
First author: Munoz-Castro, Alvaro, Inside a Superatorn: TheM(7)(q) (M = Cu, Ag, q=1+, 0, 1-) Case, CHEMPHYSCHEM,11, 646, (2010)
Abstract: All-electron relativistic density functional calculations are performed to obtain the electronic structure and nucleus-independent chemical shifts (NICS) of D-5h pentagonal-bipyramidal (PBP) CU7q and Ag-7(q) (q = 1 +,0,1-) clusters. Scalar and spin-orbit relativistic effects are taken into account at two levels: the two-component zero-order regular approximation (ZORA) Hamiltonian and fully relativistic four-component calculations via the Dirac equation. These clusters are treated by including the spin orbit effect in the jellium model, within the double-valued valued point group (D-sh*) establishing the symmetry correlations between the molecular and the atomic spinors given by the full rotation group. These clusters show highly spherical aromaticity Which is suggested to increase the hardness of the superatom. Thus, the calculations suggest that the paramagnetic CU7 ah.and Ag-7 clusters can be regarded as pseudohalogens.
First author: Li, Ping, Coupling Interactions between Sulfurous Acid and the Hydroperoxyl Radical, CHEMPHYSCHEM,11, 696, (2010)
Abstract: Radical-molecule complexes associated with hydroperoxyl radical (HOO) play an important role in atmospheric chemistry. Herein, the nature of the coupling interactions between sulfrous acid (H2SO3) and the HOO radical is systematically investigated at the B3LYP/6-311 ++G(3df3pd) level of theory in combination with the atoms in molecules (AIM) theory, the natural bond orbital (NBO) method, and energy decompostion analyses (EDA). Eight stable stationary points possessing double H-bonding features were located on the H2SO3 center dot center dot HOO potential energy surface. The largest binding energies of -12.27 NAD 011.72 kcal/mol(-1) are observed for the two most stable complexes where both of them possess strong double intermolecular H-bonds of partially covalence. Morever, the characteristics of the IR spectra for the two most stable complexes are discussed to provide some help for their possible eperimental identification.
First author: Carey, D. Mac-Leod, [Cp*Ru(s-indacene)RuCp*] and [Cp*Ru(s-indacene)RuCp*](+): Experimental and theoretical findings concerning the electronic structure of neutral and mixed valence organometallic systems,POLYHEDRON, 29, 1137, (2010)
Abstract: The reaction of 2,6-diethyl-4,8-dimethyl-s-indacenyl-dilithium (Li(2)Ic’) with [Cp*RuCl](4) gives the organometallic binuclear bis-pentamethylcyclopentadienyl-ruthenium-s-indacene complex, [{Cp*Ru}(2)Ic’] (1, Ic’ = 2,4-diethyl-4.8-dimethyl-s-indacene), in high yields. The subsequent oxidation of 1 with a ferricinium salt ([Fc](+)[BF4](-)) gives the mixed valence compound [{Cp*Ru}(2)Ic’](+)[BF4](-) (1(+)) Compound 1 was structurally characterized by X-ray crystallography, finding that both {Cp*Ru} fragments are coordinated to opposite sites of the Ic’ ligand The structural and electronic features of 1 and 1(+) have been rationalized by Density Functional Theory (DFT) calculations. which suggest that both metallic centers get closer to the Ic’ and subtle electronic reorganizations occurs when chemical oxidation takes place Cyclic voltammetry and ESR experiments suggest a high electronic interaction between the metallic centers mediated by the Ic’ bridging ligand Time dependent DFT (TD-DFT) calculations were carried out to understand and assign the intervalence band present in the mixed-valent specie (1(+)) The main achievement of this article IS to feature the relationship of the experimental data with the computational results obtained with the Amsterdam Density Functional package (ADF). Both experimental and theoretical facts demonstrate that the mixed valence system (1(+)) is a delocalized one, and it can be classified as a Class III system according to the Robin & Day classification
First author: Hernandez-Marin, Elizabeth, Density Functional Theory Study of the Electron Paramagnetic Resonance Parameters and the Magnetic Circular Dichroism Spectrum for Model Compounds of Dimethyl Sulfoxide Reductase,INORGANIC CHEMISTRY, 49, 1566, (2010)
Abstract: We report a density functional theory (DFT) study of electron paramagnetic resonance (EPR) parameters for complexes modeling the paramagnetic center Mo(V) of the molybdoenzyme dimethyl sulfoxide reductase. We pay special attention to the Mo-OH link to find the most likely geometry and orientation of the metal center in the enzyme and provide an analysis of the physical origin of the g-values in terms of magnetically induced orbital mixing. We also present a study of the magnetic circular dichroism (MCD) spectrum for a complex that models the Mo(V) center of the enzyme. The calculation of the MCD-parameters that give rise to the spectrum was performed using a newly implemented method based on time-dependent DFT. On the basis of the theoretical calculations, it was possible to give a full assignment of the bands of the MCD spectrum for the enzyme.
First author: Bercaw, John E., Electronic Structures of Pd-II Dimers, INORGANIC CHEMISTRY, 49, 1801, (2010)
Abstract: The Pd-II dimers [(2-phenylpyridine)Pd(mu-X)](2) and [(2-p-tolylpyridine)Pd(mu-X)](2) (X = OAc or TFA) do not exhibit the expected planar geometry (of approximate D-2h Symmetry) but instead resemble an open “clamshell” in which the acetate ligands are perpendicular to the plane containing the Pd atoms and 2-arylpyridine ligands, with the Pd atoms brought quite close to one another (approximate distance 2.85 angstrom). The molecules adopt this unusual geometry in part because of a d(8)-d(8) bonding interaction between the two Pd centers. The Pd-Pd dimers exhibit two successive one-electron oxidations: Pd-II-Pd-II to Pd-II-Pd-III to Pd-III-Pd-III. Photophysical measurements reveal clear differences in the UV-visible and low-temperature fluorescence spectra between the clamshell dimers and related planar dimeric [(2-phenylpyridine)Pd(mu-Cl)](2) and monomeric [(2-phenylpyridine)Pd(en)][Cl] (en = ethylenediamine) complexes that do not have any close Pd-Pd contacts. Density functional theory and atoms in molecules analyses confirm the presence of a Pd-Pd bonding interaction in [(2-phenylpyridine)Pd(mu-X)](2) and show that the highest occupied molecular orbital is a d(z2) sigma* Pd-Pd antibonding orbital, while the lowest unoccupied molecular orbital and close-lying empty orbitals are mainly located on the 2-phenylpyridine rings. Computational analyses of other Pd-II-Pd-II dimers that have short Pd-Pd distances yield an orbital ordering similar to that of [(2-phenylpyridine)Pd(mu-X)](2), but quite different from that found for d(8)-d(8) dimers of Rh, Ir, and Pt. This difference in orbital ordering arises because of the unusually large energy gap between the 4d and 5p orbitals in Pd and may explain why Pd d(8)-d(8) dimers do not exhibit the distinctive photophysical properties of related Rh, Ir, and Pt species.
First author: Avarvari, Narcis, Hybrid Organic/Inorganic Complexes Based on Electroactive Tetrathiafulvalene-Functionalized Diphosphanes Tethered to C-3-Symmetrized Mo(3)Q(4) (Q = S, Se) Clusters, INORGANIC CHEMISTRY,49, 1894, (2010)
Abstract: A two-step procedure for the preparation of hybrid complexes based on electroactive tetrathiafulvalene (TTF)-functionalized o-P-2 diphosphanes (o-P-2 = 3,4-dimethyl-3,4-bis(diphenylphosphino)tetrathiafulvalene) and inorganic C-3-symmetrized Mo(3)Q(4) (Q = S, Se) clusters, namely, [Mo3S4Cl3(o-P-2)(3)]PF6 ([1]PF6) and [Mo3Se4Cl3(o-P-2)(3)]PF6 ([2]PF6), is reported. Their molecular and electronic structures are also described on the basis of X-ray diffraction experiments and density functional theory (DFT) calculations aimed at understanding the interactions established between both the organic and the inorganic parts. Cyclic voltammograms of compounds [1]PF6 and [2]PF6 display reduction features associated to the Mo(3)Q(4) core and oxidation characteristics due to the TTF skeleton. The oxidation chemistry of [1]PF6 and [2]PF6 in solution is also investigated by means of in situ electrospray ionization (ESI) mass spectrometry, UV-vis, and, electron paramagnetic resonance (EPR) measurements. Upon addition of increasing amounts of NOPF6 (less than 3 equiv), the sequential formation of 1(n+) (n = 1-4) species was observed whereas addition of a 3-fold excess of NOPF6 allows to access the three-electron oxidized [Mo3S4Cl3(o-P-2)(3)](4+) (1(4+)) and [Mo3Se4Cl3(o-P-2)(3)](4+) (2(4+)) cations. These 1(4+) and 2(4+) cations represent still rare examples of complexes with oxidized TTF-ligands that are remarkably stable either toward diphosphane dissociation or phosphane oxidation. Polycrystalline samples of compound [1](PF6)(4) were obtained by oxidation of compound [1]PF6 using NOPF6 which were analyzed by solid state absorption, UV-vis, and Raman spectroscopies.
First author: Quintal, Susana, Silver(I) and copper(I) complexes with ferrocenyl ligands bearing imidazole or pyridyl substituents, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 695, 558, (2010)
Abstract: The reactions between five ferrocenyl derivatives containing both a C=O and at least an imidazole or pyridine nitrogen atom and AgPF6, AgOTf, or [Cu(NCCH3)(4)]PF6 precursors were studied. The ligand {[bis(2-pyridyl)amino]carbonyl} ferrocene (L3), derived from (2-pyridyl)amine, favored tetrahedral coordination of Ag+ (with two ligands) and of Cu+ (with two acetonitrile ligands left from the precursor). In all the other ligands, both metal centers coordinated linearly to two ligands, preferring the imidazole or pyridinic nitrogen to other nitrogen atoms (amine) or oxygen donors.When the counter anions were triflate, the crystal structure showed a dimerization of the complex, with the ferrocenyl moieties occupying cis positions, by means of a weak Ag center dot center dot center dot Ag interaction. This was shown experimentally in the crystal structure of complex [Ag(L1)(2)]OTf (L1 = ferrocenyl imidazole) and in the presence of peaks corresponding to {Ag-2(L-2)(3)(OTf)}(+) and {Ag-2(L-2)(4)(OTf)}(+) in the mass spectra of [Ag(L-2)(2)]OTf (L2 = ferrocenyl benzimidazole). In all complexes containing PF6, there was no evidence for dimerization. Indeed, in the crystal structure of [Ag(L-2)(2)]PF6, the ferrocenyl moieties occupy trans positions and the metal centers are far from each other. DFT calculations showed that the energy of the cis and trans conformers is practically the same and the balance of crystal packing forces leads to dimerization when triflate is present.
First author: Uray, Georg, On- and off column enantiomerization of 4,4 ‘-bisquinolin-2-ones: A comparison of Auto-, DHPLcy2k and DCXplorer calculated thermodynamic data generated by dynamic high, performance liquid chromatography with theoretically calculated data, JOURNAL OF CHROMATOGRAPHY A, 1217, 1017, (2010)
Abstract: Fast semipreparative HPLC enantioseparation of four axially chiral biscarbostyrils (4,4′-bisquinoline-2-ones) using ULMO as a pi-acidic Pirkle type chiral stationary phase leads to two racernizing pairs (1,2; k(obs) 1.6 x 10(-4) and 3.0 x 10(-4) s(-1) at 28 degrees C) and two stable ones (3,4).3 was stabilized by a crown ether linkage from pos. 6 to 6′, and 4 had sterically demanding bromo substituents in pos. 3 and 3′. On-column generated temperature-dependent chromatograms of 1 and 2 were fitted with Auto-DHPLCy2k and DCXplorer. For cpd 2 both programs delivered similar Delta G values of 90 and 93 kJ/mol, well comparable with the 99 kJ/mol calculated with the B3LYP/6-31G (d) procedure. At temperatures of high conversion DCXplorer delivered inconsistent series of rate constants for the more tailing and less resolved tetramethoxy derivative 1. We connect this problem with an almost impossible halfwidth calculation of tailing peak pairs which are weakly resolved. However, this problem could be observed only in the case of tetramethoxy derivative 1. Stochastic generated data of Auto-DHPLCy2k could be used at a lower percentage of conversion only while the theoretical plate model did not deliver useful data at temperatures of very low conversion but fitted well high conversion chromatogram series of 1 and 2.
First author: Provorse, Makenzie R., Origin of Intense Chiroptical Effects in Undecagold Subnanometer Particles,JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 1302, (2010)
Abstract: Time-dependent density functional theory (TDDFT) calculations are employed to examine the optical absorption and circular dichroism (CD) spectra of undecagold Au(11)L(4)X(2)(+) (X = Cl, Br) complexes and their Au(2)X(2)L precursors, where L is either 2,2′-bis(diphenylphosphino)-1,1′-binaphtyl (BINAP) or 1,4-diphosphino-1,3-butadiene (dpb). These systems exhibit intense and mirror-image Cotton effects in their CD spectra. Experimental peak positions are well reproduced in the calculations. The low energy peaks of Au(11)L(4)X(2)(+) arise primarily from transitions between delocalized metal superatom orbitals. Bidentate phosphine ligands have both a structural and electronic impact on the system. The lowest energy structure of Au(11)L(4)X(2)(+) has a chiral C(2) geometry, whereas monodentate phosphine ligands lead to a C(1) structure. In addition, the chiral core structure of Au(11)L(4)X(2)(+) is not sufficient to explain the strong Cotton effects, and the intensity of the CD spectrum is increased by the presence of the bidentate phosphine ligands.
First author: Asaduzzaman, Abu Md., Computational Studies of Structural, Electronic, Spectroscopic, and Thermodynamic Properties of Methylmercury-Amino Acid Complexes and Their Se Analogues, INORGANIC CHEMISTRY, 49, 870, (2010)
Abstract: Quantum chemical calculations have been carried out to study the structural, electronic, spectroscopic, and thermodynamic properties of five methylmercury-amino acid complexes and their selenium analogues. The structural properties of methylmercury-amino acids are very similar to their Se analogues except for those properties that are directly related to the Se atom which has a larger covalent radius. Characteristic stretching frequencies are observed for Hg-S/Se and Hg-C bonds. Electronic properties of both methylmercury-amino acids and their Se analogues are different from each other, with the S complexes showing stronger electrostatic attractions which leads to stronger bonds to mercury. The methylmercury complexes with selenoamino complexes, however, are thermodynamically more favorable (Delta G of formation from suitable model reactants) than those of the corresponding amino acid complexes. This can be traced to the lower stability of the reactant selenoamino acids, Such different stability and favorability of formation might be responsible for the different physiological activity in biological systems such as the Hg-Se antagonism.
First author: Craciun, Raluca, Third Row Transition Metal Hexafluorides, Extraordinary Oxidizers, and Lewis Acids: Electron Affinities, Fluoride Affinities, and Heats of Formation of WF6, ReF6, OsF6, IrF6, PtF6, and AuF6, INORGANIC CHEMISTRY, 49, 1056, (2010)
Abstract: High level electronic structure calculations were used to evaluate reliable, self-consistent thermochemical data sets for the third row transition metal hexafluorides, The electron affinities, heats of formation, first (MF6 -> MF5 + F) and average M-F bond dissociation energies, and fluoride affinities of MF6 (MF6 + F- -> MF7-) and MF5 (MF5 + F- -> MF6-) were calculated. The electron affinities which are a direct measure for the oxidizer strength increase monotonically from WF6 to AuF6, with PtF6 and AuF6 being extremely powerful oxidizers. The inclusion of spin orbit corrections is necessary to obtain the correct qualitative order for the electron affinities. The calculated electron affinities increase with increasing atomic number, are in good agreement with the available experimental values, and are as follows: WF6 (3.15 eV), ReF6 (4.58 eV), OsF6 (5.92 eV), IrF6 (5.99 eV), PtF6 (7.09 eV), and AuF6 (8.20 eV.). A wide range of density functional theory exchange-correlation functionals were also evaluated, and only three gave satisfactory results. The corresponding pentafluorides are extremely strong Lewis acids, with OsF5, IrF5, PtF5, and AuF5 significantly exceeding the acidity of SbF5. The optimized geometries of the corresponding MF7- anions for W through Ir are classical MF7- anions with M-F bonds; however, for PtF7- and AuF7- non-classical anions were found with a very weak external F-F bond between an MF6- fragment and a fluorine atom. These two anions are text book examples for “superhalogens” and can serve as F atom sources under very mild conditions, explaining the ability of PtF6 to convert NF3 to NF4+, CIF5 to CIF6+, and Xe to XeF+ and why Bartlett failed to observe XePtF6 as the reaction product of the PtF6/Xe reaction.
First author: Rota, Jean-Baptiste, Toward Verdazyl Radical-Based Materials: Ab Initio Inspection of Potential Organic Candidates for Spin-Crossover Phenomenon, INORGANIC CHEMISTRY, 49, 1230, (2010)
Abstract: The origin of magnetic interactions in verdazyl-based radical stackings is examined using ab initio, wave function and density functional theory (DFT) calculations. Starting from the reported crystal structure of the 1.1′-bis(verdazyl)ferrocene diradical compound, the singlet-triplet energy difference has been evaluated on the basis of mulfireference difference dedicated configurations interaction calculations and suggested the innocent role of the ferro,-ene spacer. Using the underlying pi-dimer verdazyl structures, the J variations and potential energy surfaces of para lel and antiparallel face-to-face arrangements have been studied with respect to the verdazyl-verdazyl separation to evaluate the Coulomb repulsion U and bandwidth W While coupled-cluster CCSD(T) calculations are suggestive of a weak bond formation in both dimer arrangements (similar to 40 kJ mol(-1)) the DFT approach fails to reproduce the bonding character. The intrinsically delocalized characterof the magnetic orbitals favors an S= 0 ground state, but importantly, the S = 1 spin state is also bound. A typical 0.4 A increase (i.e., 10%) of the verdazyl-verdazyl equil briurn distance accompanying a 16 kJ mol(-1) adiabatic energy difference is calculated between the S = 0 and S = 1 states. In this distance separation regime, we finally suggest that either a relative 1 2 angstrom slippage or a similar to 42 degrees relative orientation of the verclazyl rings is likely to give rise to a high-spin S = 1 ground state. These features are symptomatic of a bistable system, and an interpretation of the exchange interaction in verdazyl pi-dimer structures in terms of spin transition is proposed.
First author: Storchi, Loriano, An Efficient Parallel All-Electron Four-Component Dirac-Kohn-Sham Program Using a Distributed Matrix Approach, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 6, 384, (2010)
Abstract: We show that all-electron relativistic four-component Dirac-Kohn-Sham (DKS) computations, using G-spinor basis sets and state-of-the-art density fitting algorithms, can be efficiently parallelized and applied to large molecular systems, including large clusters of heavy atoms. The performance of the parallel implementation of the DKS module of the program BERTHA is illustrated and analyzed by some test calculations on several gold clusters up to Au-32, showing that calculations with more than 25 000 basis functions (i.e., DKS matrices on the order of 10 GB) are now feasible. As a first application of this novel implementation, we investigate the interaction of the atom Hg with the Au-20 cluster.
First author: Kolesnikov, V. I., Study of friction and wear in the wheel-rail system by X-ray electron and auger-electron spectroscopy and quantum chemistry, JOURNAL OF FRICTION AND WEAR, 31, 11, (2010)
Abstract: The article presents the results of joint application of modern experimental and theoretical methods to analyze interatomic interactions on friction surfaces and in subsurface layers. The wear resistance of the wheel-rail system is shown to experience the effect of grain-boundary segregation, and the methods of suppressing its negative consequences are discussed. Adsorption on the iron surface of heteropolyphosphates of alkali metals, representing a new type of additive to lubricants, is studied.
First author: Mitoraj, Mariusz P., Theoretical description of bonding in cis-W(CO)(4)(piperidine)(2) and its dimer,JOURNAL OF MOLECULAR MODELING, 16, 337, (2010)
Abstract: The gradient-corrected DFT calculations were applied to characterize the bonding in the cis-W(CO)(4)( piperidine)(2) complex and its dimer. The Nalewajski-Mrozek bond order analysis, the Ziegler-Rauk bond-energy partitioning and Natural Orbitals for Chemical Valence (NOCV’s) were applied in a description of the electronic structure of cis-W(CO)(4)(piperidine)(2). The results indicate that the metal-carbon bond trans to piperidine is stronger than that in the cis position, as a result of an increase in both, the ligand -> metal donation and metal -> ligand pi-back-bonding; this implies a weakening of the carbon oxygen bond. In the dimeric complex, modeling the interactions in the solid state, the C-O bond is further weakened resulting in the lowering the CO stretching frequencies, observed experimentally by Braunstein et al. (Angew. Chem. Int. Ed. (2004), 43:5922-5925).
First author: Trueba, A., High magnetic anisotropy of Fe+ ions in KTaO3 and SrCl2, PHYSICAL REVIEW B, 81, 337, (2010)
Abstract: The zero-field splitting constant, D, and the gyromagnetic tensor of the off-center systems KTaO3:Fe+ and SrCl2:Fe+ have been explored by means of calculations based on the density-functional theory at the C-4v local equilibrium geometry. The calculated D values for KTaO3:Fe+ (9 cm(-1)) and SrCl2:Fe+ (53 cm(-1)) are found to be much higher than typical figures measured for insulating compounds containing common 3d Kramers ions with a spin S > 1/2 in the ground state. This result together with the calculated g(perpendicular to) and g(parallel to) values concur with available experimental information. The high magnetic anisotropy derived for Fe+ in KTaO3 and SrCl2 is shown to be strongly related to the existence of a E-4 excited state lying only at about 3000 and 600 cm(-1), respectively, above the ground state. Implications of present findings in the search of new molecular magnets with high values of the magnetic anisotropy are discussed in some detail.
First author: Beyhan, S. Maya, The weak covalent bond in NgAuF (Ng=Ar, Kr, Xe): A challenge for subsystem density functional theory, JOURNAL OF CHEMICAL PHYSICS, 132, 337, (2010)
Abstract: We have assessed the accuracy of a representative set of currently available approximate kinetic-energy functionals used within the frozen-density embedding scheme for the NgAuF (Ng=Ar, Kr, Xe) molecules, which we partitioned into a Ng and a AuF subsystem. Although it is weak, there is a covalent interaction between these subsystems which represents a challenge for this subsystem density functional theory approach. We analyzed the effective-embedding potentials and resulting electron density distributions and provide a quantitative analysis of the latter from dipole moment differences and root-mean-square errors in the density with respect to the supermolecular Kohn-Sham density functional theory reference calculation. Our results lead to the conclusion that none of the tested approximate kinetic-energy functionals performs well enough to describe the bond between the noble gas and gold adequately. This observation contributes to the growing evidence that the current procedure to obtain approximate kinetic-energy functionals by reparametrizing functionals obtained via the “conjointness” hypothesis of Lee, Lee, and Parr [Phys. Rev. A 44, 768 (1991)] is insufficient to treat metal-ligand interactions with covalent character.
First author: Luber, Sandra, Enhancement and de-enhancement effects in vibrational resonance Raman optical activity,JOURNAL OF CHEMICAL PHYSICS, 132, 337, (2010)
Abstract: In this study, we investigate interference between several excited electronic states in resonance enhanced vibrational Raman optical activity (RROA) spectra. A gradient Franck-Condon model for the excited-state potential energy surface is applied in order to include vibronic effects in the description of the RROA intensities. Both sum-over-states and time-dependent expressions for the RROA intensities in case of close-lying excited states are given. As an example, we compare the calculated RROA and resonance Raman spectra of (S)-(+)-naproxen-OCD(3) to the experimental ones. Subsequently, we examine the excitation profiles of (S)-(+)-naproxen and study the vibration at 1611 cm(-1) in more detail in order to demonstrate how the consideration of a second excited electronic state can lead to significant changes in the RROA intensities.
First author: Wang, Yi-Lei, Vibrationally Resolved Photoelectron Spectroscopy of Di-Gold Carbonyl Clusters Au-2(CO)(n)(-) (n=1-3): Experiment and Theory, JOURNAL OF PHYSICAL CHEMISTRY A, 114, 1247, (2010)
Abstract: We report vibrationally resolved photoelectron spectroscopy (PES) of Au-2(CO)(n)(-) (n = 1-3), in combination with relativistic density functional theory (DFT) and ab initio Calculations. The ground-state transition in the spectrum of Au2CO- is broad, containing vibrational structures both in the bending and in the CO stretching modes and suggesting a large structural change from Au2CO- to Au2CO. The ground-state transitions for both n = 2 and 3 display a well-resolved vibrational progression in the CO stretching mode with frequencies of 2110 +/- 40 and 2160 +/- 40 cm(-1), respectively. The PES data show that chemisorption of the first two CO’s each induces a significant red-shift in the electron binding energies. The third CO is physisorbed, inducing only a slight increase in electron binding energies relative to Au-2(CO)(2). Relativistic DFT and ab initio calculations are performed to determine the ground-state structures for Au-2(CO)(n)(-) and Au-2(CO)(n), and the results agree well with the experiment. Au-2(CO), Au-2(CO)(2), and Au-2(CO)(2) are all found to be linear, while Au-2(CO)(-) is bent due to the Renner-Teller effect. A strong spin-orbit effect is found in Au-2(CO)(2) that quenches the Renner-Teller effect, keeping the linear structure for this anion. The physisorption in Au-2(CO)(3) is borne out in CCSD(T) calculations. However, a wide range of DFT methods tested fail to correctly predict the relative energies of the physisorbed versus chemisorbed isomers for Au-2(CO)(3).
First author: Rayon, Victor M., A computational study of arsenic dicarbide (C2As), CHEMICAL PHYSICS LETTERS, 485, 286, (2010)
Abstract: A computational study of arsenic dicarbide has been carried out. In agreement with the experimental evidence theoretical calculations predict a (2)Pi ground state. However, a cyclic B-2(2) species is found just about 3-4 kcal/mol higher in energy. The B-2(2) species is shown to be a true minimum with a predicted barrier for isomerization around 7-8 kcal/mol. An analysis of the bonding suggests that the B-2(2) state is a truly cyclic species. The preference for the linear arrangement appears to be due to weaker Pauli repulsion, since both electrostatic and orbital terms seem to favor the cyclic isomer.
First author: Alizadegan, R., A divide and conquer real space finite-element Hartree-Fock method, JOURNAL OF CHEMICAL PHYSICS, 132, 286, (2010)
Abstract: Since the seminal contribution of Roothaan, quantum chemistry methods are traditionally expressed using finite basis sets comprised of smooth and continuous functions (atom-centered Gaussians) to describe the electronic degrees of freedom. Although this approach proved quite powerful, it is not well suited for large basis sets because of linear dependence problems and ill conditioning of the required matrices. The finite element method (FEM), on the other hand, is a powerful numerical method whose convergence is also guaranteed by variational principles and can be achieved systematically by increasing the number of degrees of freedom and/or the polynomial order of the shape functions. Here we apply the real-space FEM to Hartree-Fock calculations in three dimensions. The method produces sparse, banded Hermitian matrices while allowing for variable spatial resolution. This local-basis approach to electronic structure theory allows for systematic convergence and promises to provide an accurate and efficient way toward the full ab initio analysis of materials at larger scales. We introduce a new acceleration technique for evaluating the exchange contribution within FEM and explore the accuracy and robustness of the method for some selected test atoms and molecules. Furthermore, we applied a divide-and-conquer (DC) method to the finite-element Hartree-Fock ab initio electronic-structure calculations in three dimensions. This DC approach leads to facile parallelization and should enable reduced scaling for large systems.
First author: Nemec, Norbert, Benchmark all-electron ab initio quantum Monte Carlo calculations for small molecules,JOURNAL OF CHEMICAL PHYSICS, 132, 286, (2010)
Abstract: We study the efficiency, precision and accuracy of all-electron variational and diffusion quantum Monte Carlo calculations using Slater basis sets. Starting from wave functions generated by Hartree-Fock and density functional theory, we describe an algorithm to enforce the electron-nucleus cusp condition by linear projection. For the 55 molecules in the G2 set, the diffusion quantum Monte Carlo calculations recovers an average of 95% of the correlation energy and reproduces bond energies to a mean absolute deviation of 3.2 kcal/mol. Comparing the individual total energies with essentially exact values, we investigate the error cancellation in atomization and chemical reaction path energies, giving additional insight into the sizes of nodal surface errors.
First author: Nocton, Gregory, Synthesis, Structure, and Bonding of Stable Complexes of Pentavalent Uranyl, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 495, (2010)
Abstract: Stable complexes of pentavalent uranyl [UO2(salan-Bu-t(2))(py)K](n) (3), [UO2(salan-Bu-t(2))(py)K(18C6)] (4), and [UO2(salophen-Bu-t(2))(thf)]K(thf)(2)}(n), (8) have been synthesized from the reaction of the complex {[UO(2)py(5)][KI(2)py(2)]}(n) (1) with the bulky amine-phenolate ligand potassium salt K-2(salan-Bu-t(2)) or the Schiff base ligand potassium salt K-2(salophen-Bu-t(2)) in pyridine. They were characterized by NMR, IR, elemental analysis, single crystal X-ray diffraction, UV-vis spectroscopy, cyclic voltammetry, low-temperature EPR, and variable-temperature magnetic susceptibility. X-ray diffraction shows that 3 and 8 are polymeric and 4 is monomeric. Crystals of the monomeric complex [(UO2)-O-v(salan-Bu-t(2))(py)][Cp-2*Co], 6, were also isolated from the reduction of [(UO2)-O-VI(salan-Bu-t(2))(py)], 5, with Cp-2*Co. Addition of crown ether to 1 afforded the highly soluble pyridine stable species [UO(2)py(5)]I.py (2). The measured redox potentials E-1/2 (U-VI/U-V) are significantly different for 2 (-0.91 and -0.46 V) in comparison with 3, 4, 5, 7 and 9 (in the range -1.65 to -1.82 V). Temperature-dependent magnetic susceptibility data are reported for 4 and 7 and give mu(eff) of 2.20 and 2.23 mu(B) at 300 K respectively, which is compared with a mu(eff) of 2.6(1) mu(B) (300 K) for 2. Complexes 1 and 2 are EPR silent (4 K) while a rhombic EPR signal (g(x) = 1.98; g(y) = 1.25; g(z) = 0.74 (at 4 K) was measured for 4. The magnetic and the EPR data can be qualitatively analyzed with a simple crystal field model where the f electron has a nonbonding character. However, the temperature dependence of the magnetic susceptibility data suggests that one or more excited states are relatively low-lying. DFT studies show unambiguously the presence of a significant covalent contribution to the metal-ligand interaction in these complexes leading to a significant lowering of the pi(u)*. The presence of a back-bonding interaction is likely to play a role in the observed solution stability of the [UO2(salan-Bu-t(2))(py)K] and [UO2(salophen-Bu-t(2))(py)K] complexes with respect to disproportionation and hydrolysis.
First author: Griffith, Olga Lobanova, Electronic Properties of Pentacene versus Triisopropylsilylethynyl-Substituted Pentacene: Environment-Dependent Effects of the Silyl Substituent, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 580, (2010)
Abstract: Energy measures of the intra- and intermolecular electronic effects of triisopropylsilylethynyl substitution on pentacene have been obtained from the combination of closely related gas phase and solid phase ultraviolet photoelectron spectroscopy (UPS) measurements along with solution electrochemical measurements. The results show that the shift to lower ionization energy that is expected with this substitution and observed in the gas phase measurements becomes negligible in solution and is even reversed in the solid phase. The principles that emerge from this analysis are supported by electronic structure calculations at the density functional theory level. The relation between the gas phase and solid phase UPS measurements illustrated here provides a general approach to investigating the electronic effects acting on molecules in the condensed phase, which in this case are greater than the direct substituent electronic effects within the molecule. Electronic properties such as lower ionization energies built into the single-molecule building blocks of materials and devices may be reversed in the solid state.
First author: Chattopadhyay, Swarup, Steric Titration of Arylthiolate Coordination Modes at Pseudotetrahedral Nickel(II) Centers, INORGANIC CHEMISTRY, 49, 457, (2010)
Abstract: Several derivatives of the pseudotetrahedral phenylthiolate complex Tp(Me,Me) Ni-SPh (1), Tp(Me,Me-) = hydrotris(3,5-dimethyl-1-pyrazolyl) borate, were prepared incorporating substituted arylthiolates, including a series of orthosubstituted ligands Tp(Me,Me)Ni-SR (R = 2,6-Me(2)C(6)H(3), 2: 2,4,6-Me(3)C(6)H(2), 3; 2,4,6- (i)Pr(3)C(6)H(2), 4; and 2,6-Ph(2)C(6)H(3), 5) and a series of para-substituted complexes (R = C(6)H(4)-4-OMe, 6; C(6)H(4)-4-Me, 7; and C(6)H(4)-4-Cl, 8). The products were characterized by (1)H NMR and UV-vis spectroscopy. Spectra of 6-8 were consistent with retention of a common structure across the para-substituted series with modest perturbation of the spectral features of 1 assisting their assignment. In contrast, spectra of 2-5 were indicative of a significant change in configuration across the ortho-disubstituted series. The structure of complex 5 was determined by X-ray crystallography and a distinctive arylthiolate ligation mode was found, in which the N(3)S ligand field was significantly distorted toward a sawhorse, compared to a more common trigonal pyramidal shape (e.g., 1). Moreover, the arylthiolate substituent rotated from a vertical orientation co-directional with the pyrazole rings and disposed between two of them in 1, to a horizontal orientation perpendicular to and over a single pyrazole ring in 5. This reorientation is necessary to accommodate the large ortho substituents of the latter complex. The divergent Ni-S coordination modes result in distinct (1)H NMR and electronic spectra that were rationalized by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. These results demonstrate rich coordination chemistry for arylthiolates that can be elicited by steric manipulation at the periphery of pseudotetrahedral ligand fields.
First author: Mitoraj, Mariusz P., sigma-Donor and pi-Acceptor Properties of Phosphorus Ligands: An Insight from the Natural Orbitals for Chemical Valence, INORGANIC CHEMISTRY, 49, 578, (2010)
Abstract: Several derivatives of the pseudotetrahedral phenylthiolate complex Tp(Me,Me) Ni-SPh (1), Tp(Me,Me-) = hydrotris(3,5-dimethyl-1-pyrazolyl) borate, were prepared incorporating substituted arylthiolates, including a series of orthosubstituted ligands Tp(Me,Me)Ni-SR (R = 2,6-Me(2)C(6)H(3), 2: 2,4,6-Me(3)C(6)H(2), 3; 2,4,6- (i)Pr(3)C(6)H(2), 4; and 2,6-Ph(2)C(6)H(3), 5) and a series of para-substituted complexes (R = C(6)H(4)-4-OMe, 6; C(6)H(4)-4-Me, 7; and C(6)H(4)-4-Cl, 8). The products were characterized by (1)H NMR and UV-vis spectroscopy. Spectra of 6-8 were consistent with retention of a common structure across the para-substituted series with modest perturbation of the spectral features of 1 assisting their assignment. In contrast, spectra of 2-5 were indicative of a significant change in configuration across the ortho-disubstituted series. The structure of complex 5 was determined by X-ray crystallography and a distinctive arylthiolate ligation mode was found, in which the N(3)S ligand field was significantly distorted toward a sawhorse, compared to a more common trigonal pyramidal shape (e.g., 1). Moreover, the arylthiolate substituent rotated from a vertical orientation co-directional with the pyrazole rings and disposed between two of them in 1, to a horizontal orientation perpendicular to and over a single pyrazole ring in 5. This reorientation is necessary to accommodate the large ortho substituents of the latter complex. The divergent Ni-S coordination modes result in distinct (1)H NMR and electronic spectra that were rationalized by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. These results demonstrate rich coordination chemistry for arylthiolates that can be elicited by steric manipulation at the periphery of pseudotetrahedral ligand fields.
First author: Horiuchi, Clay M., Adsorption and decomposition of gamma-butyrolactone on Pd(111) and Pt(111),SURFACE SCIENCE, 604, 98, (2010)
Abstract: The adsorption and thermal chemistry of gamma-butyrolactone (GBL) on the (1 1 1) surface of Pd and Pt has been investigated using a combination of high resolution electron energy loss spectroscopy (HREELS) and temperature programmed desorption (TPD). HREELS results indicate that GBL adsorbs at 160 K on both surfaces through its oxygenate functionality. On Pd(1 1 1), adsorbed GBL undergoes ring-opening and decarbonylation by 273 K to produce adsorbed CO and surface hydrocarbon species. On Pt(1 1 1), very little dissociation is observed using HREELS, with almost all of the GBL simply desorbing. TPD results are consistent with decarbonylation and subsequent dehydrogenation reactions on Pd(1 1 1), although small amounts Of CO2 are also detected. TPD results from Pt(1 1 1) indicate that a small proportion of adsorbed GBL (perhaps on defect sites) does undergo ring-opening to produce CO, CO2, and H-2. These results suggest that the primary dissociation pathway for GBL on Pd(1 1 1) is through O-C scission at the carbonyl position. Through comparisons with previously published studies of cyclic oxygenates, these results also demonstrate how ring strain and functionality affect the ring-opening rate and mechanism.
First author: Herrmann, Carmen, Ghost transmission: How large basis sets can make electron transport calculations worse, JOURNAL OF CHEMICAL PHYSICS, 132, 98, (2010)
Abstract: The Landauer approach has proven to be an invaluable tool for calculating the electron transport properties of single molecules, especially when combined with a nonequilibrium Green’s function approach and Kohn-Sham density functional theory. However, when using large nonorthogonal atom-centered basis sets, such as those common in quantum chemistry, one can find erroneous results if the Landauer approach is applied blindly. In fact, basis sets of triple-zeta quality or higher sometimes result in an artificially high transmission and possibly even qualitatively wrong conclusions regarding chemical trends. In these cases, transport persists when molecular atoms are replaced by basis functions alone (“ghost atoms”). The occurrence of such ghost transmission is correlated with low-energy virtual molecular orbitals of the central subsystem and may be interpreted as a biased and thus inaccurate description of vacuum transmission. An approximate practical correction scheme is to calculate the ghost transmission and subtract it from the full transmission. As a further consequence of this study, it is recommended that sensitive molecules be used for parameter studies, in particular those whose transmission functions show antiresonance features such as benzene-based systems connected to the electrodes in meta positions and other low-conducting systems such as alkanes and silanes.
First author: Munoz-Castro, Alvaro, Calculated Molecular Properties of Triangular Tribenzo and Perfluoro-Tribenzo Trimercuronin Macrocycles, JOURNAL OF PHYSICAL CHEMISTRY A, 114, 666, (2010)
Abstract: Trimeric perfluoro-ortho-phenylene mercury(II) cluster is a prototypical example of a macrocyclic multidentate Lewis acid. In this study we report the electronic structure, the calculated absorption and vibrational spectra via all-electron scalar and spin-orbit relativistic DFT calculations for [Hg(o-C6H4)](3) (1), [Hg(o-C6F4)](3) (2), and the dimeric form of 2, ([Hg(O-C6F4)](3))(2) (3). Due to the inclusion of the spin-orbit interaction, double point groups were used (D-3h* and D-3d*). The calculations suggest small paratropic ring currents at the center of 1 and being smaller for 2 due to the withdrawn properties of the perfluorated ligand. The luminescent properties of the solid state of 2 are well represented by the postulated model of dimer 3, which mimic the solid state, where the proposed mechanism involves a vibronically coupled emission process. The calculated lambda(max)(absorption) of 3 show an intense peak at 347 mn, which compares well with the reported band at 355 nm; also, the calculated lambda(emission) = 431 nm is close to the experimental value of 440 nm. Moreover, the calculated structural changes of the first excited state (3*) are reflected in the large value of the calculated Stoke shifts of 84 nm, which is in quite good agreement with the value of 85 nm extracted from the experimental data.
First author: Gueell, Mireia, Spin-state splittings of iron(II) complexes with trispyrazolyl ligands, POLYHEDRON, 29, 84, (2010)
Abstract: We report a computational study at the OPBE/TZP level on the chemical bonding and spin ground-states of mono-nuclear iron(H) complexes with trispyrazolylborate and trispyrazolylmethane ligands. We are in particular interested in how substitution patterns on the pyrazolyl-rings influence the spin-state splittings, and how they can be rationalized in terms of electronic and steric effects. One of the main observations of this study is the large similarity of the covalent metal-ligand interactions for both the borate and methane ligands. Furthermore, we find that the spin-state preference of an individual transition-metal (TM) complex does not always concur with that of an ensemble of TM-complexes in the solid-state. Finally, although the presence of methyl groups at the 3-position of the pyrazolyl groups leads to ligand-ligand repulsion, it is actually the loss of metal-ligand bonding interactions that is mainly responsible for shifts in spin-state preferences.
First author: Munoz-Castro, A., Relativistic electronic structure of cadmium(II) multidecker phthalocyanine compounds,POLYHEDRON, 29, 451, (2010)
Abstract: Cadmium phthalocyanines (Pc) give rise to multilayered compounds, which may have potential application in material science. The Cd(II) single macrocycle (1) (C-4v), double decker [CdPc2] (2) (D-4), triple decker [Cd2Pc3] (3) (D-4h) and quadruple decker [Cd3Pc4] (4) (D-4d), are already characterized experimentally. The electronic structures of the multidecker Compounds were compared against the single macrocycle (1) which is used as benchmark. Relativistic electronic structure were carried out via DFT calculations using the two components ZORA Hamiltonian including both scalar and spin-orbit effects. Double point groups were used to take into account the inclusion of the spin-orbit coupling, and their group correlation is shown. The calculations show that the quadruple decker is the most reactive and behaves like a one-dimensional molecular metal.
First author: Schreckenbach, Georg, Theoretical Actinide Molecular Science, ACCOUNTS OF CHEMICAL RESEARCH,43, 19, (2010)
Abstract: Interest in the chemistry of the early actinide elements (notably uranium through americium) usually results either from the nuclear waste problem or the unique chemistry of these elements that result from 5f contributions to bonding. Computational actinide chemistry provides one useful tool for studying these processes.Theoretical actinide chemistry is challenging because three principal axes of approximation have to be optimized. These are the model chemistry (the choice of approximate electron-electron correlation method and basis sets), the approximate relativistic method, and a method for modeling solvent (condensed phase) effects. In this Account we arrange these approximations in a three-dimensional diagram, implying that they are relatively independent of each other. A fourth level of approximation concerns the choice of suitable models for situations too complex to treat in their entirety. We discuss test cases for each of these approximations.Gas-phase data for uranium fluorides and oxofluorides such as UF(6) and UO(2)F(2). show that GGA functionals provide accurate geometries and frequencies while hybrid density functional theory (DFT) functionals are superior for energetics. MP2 is seen to be somewhat erratic for this set of compounds, and CCSD(T) gives the most accurate results. Three different relativistic methods, small-core effective core potentials (SC-ECP), ZORA, and all-electron scalar, provide comparable results. The older large-core ECP (LC-ECP) approach is consistently worse and should not be used. We confirmed these conclusions through studies of the actinyl aquo complexes [AnO(2)(OH(2))(5)](n+), (An = U, Np, or Pu and n = 1 or 2) that are also used to test solvation models. As long as the first coordination sphere of the metal is included explicitly, continuum solvation models are reliable, and we found no dear advantage for the (costly) explicit treatment of the second coordination sphere. Spin-orbit effects must be included to reproduce the correct trend in An(VI)/An(V) reduction potentials.We propose a multistep mechanism for the experimentally observed oxygen exchange of UO(2)(2+) cations in highly alkaline solutions present in tank wastes. This process involves an equilibrium between [UO(2)(OH)(4)](2-) and [UO(2)(OH)(5)](3-), followed by formation of the stable [UO(3)(OH)(3)](3-) intermediate that forms from [UO(2)(OH)(5)](3-) through intramolecular water elimination. The [UO(3)(OH)(3)](3-) intermediate facilitates oxygen exchange through proton shuttling. We explain the experimentally observed stabilization of the pentavalent oxidation state of actinyl ions by macrocyclic ligands (such as 18-crown-6) as an effect of solvation: the large macrocycle screens the positive charge of the ion from the polarizable solvent Alkyl-substituted isoamethyrin complexes are bent despite being aromatic because of steric factors, rather than fit/misfit criteria regarding the actinyl ion.By application of an efficient DFT code, actinide molecules with more than 100 atoms can now be studied routinely. “Real” chemical questions can be answered as long as we take great care to apply methods that are accurate with respect to the three axes of approximation described above. While the exclusive focus of this Account has been on the early actinide elements, these conclusions also apply elsewhere in the periodic table.
First author: Qian, Meichun, Cluster-Assembled Materials: Toward Nanomaterials with Precise Control over Properties,ACS NANO, 4, 235, (2010)
Abstract: One pathway toward nanomaterials with controllable band gaps is to assemble solids where atomic clusters serve as building blocks, since the electronic structures of clusters vary with size and composition. To study the role of organization in cluster assemblies, we synthesized multiple architectures incorporating As-7(3-) clusters through control of the countercations. Optical measurements revealed that the band gaps vary from 1.1-2.1 eV, even though the assemblies are constructed from the identical cluster building block. Theoretical studies explain this variation as being a result of altering the lowest unoccupied molecular orbital levels by changing the countercations, Additional variations in the gap are made by covalently linking the clusters with species of varying electronegativity to. alter the degree of charge transfer. These findings offer a general protocol for syntheses of nanoassemblies with tunable electronic properties.
First author: Seth, Michael, CALCULATION OF MAGNETIC CIRCULAR DICHROISM SPECTRA WITH TIME-DEPENDENT DENSITY FUNCTIONAL THEORY, ADVANCES IN INORGANIC CHEMISTRY: THEORETICAL AND COMPUTATIONAL INORGANIC CHEMISTRY, VOL 62, 62, 41, (2010)
Abstract: One pathway toward nanomaterials with controllable band gaps is to assemble solids where atomic clusters serve as building blocks, since the electronic structures of clusters vary with size and composition. To study the role of organization in cluster assemblies, we synthesized multiple architectures incorporating As-7(3-) clusters through control of the countercations. Optical measurements revealed that the band gaps vary from 1.1-2.1 eV, even though the assemblies are constructed from the identical cluster building block. Theoretical studies explain this variation as being a result of altering the lowest unoccupied molecular orbital levels by changing the countercations, Additional variations in the gap are made by covalently linking the clusters with species of varying electronegativity to. alter the degree of charge transfer. These findings offer a general protocol for syntheses of nanoassemblies with tunable electronic properties.
First author: Scherer, Wolfgang, On the Nature of Agostic Interactions in Transition-Metal Amido Complexes,ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 49, 2242, (2010)
Abstract: One pathway toward nanomaterials with controllable band gaps is to assemble solids where atomic clusters serve as building blocks, since the electronic structures of clusters vary with size and composition. To study the role of organization in cluster assemblies, we synthesized multiple architectures incorporating As-7(3-) clusters through control of the countercations. Optical measurements revealed that the band gaps vary from 1.1-2.1 eV, even though the assemblies are constructed from the identical cluster building block. Theoretical studies explain this variation as being a result of altering the lowest unoccupied molecular orbital levels by changing the countercations, Additional variations in the gap are made by covalently linking the clusters with species of varying electronegativity to. alter the degree of charge transfer. These findings offer a general protocol for syntheses of nanoassemblies with tunable electronic properties.
First author: Villiers, Claude, An Isolated CO2 Adduct of a Nitrogen Base: Crystal and Electronic Structures,ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 49, 3465, (2010)
Abstract: One pathway toward nanomaterials with controllable band gaps is to assemble solids where atomic clusters serve as building blocks, since the electronic structures of clusters vary with size and composition. To study the role of organization in cluster assemblies, we synthesized multiple architectures incorporating As-7(3-) clusters through control of the countercations. Optical measurements revealed that the band gaps vary from 1.1-2.1 eV, even though the assemblies are constructed from the identical cluster building block. Theoretical studies explain this variation as being a result of altering the lowest unoccupied molecular orbital levels by changing the countercations, Additional variations in the gap are made by covalently linking the clusters with species of varying electronegativity to. alter the degree of charge transfer. These findings offer a general protocol for syntheses of nanoassemblies with tunable electronic properties.
First author: Cooper, Oliver J., A Monomeric Dilithio Methandiide with a Distorted trans-Planar Four-Coordinate Carbon,ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 49, 5570, (2010)
Abstract: One pathway toward nanomaterials with controllable band gaps is to assemble solids where atomic clusters serve as building blocks, since the electronic structures of clusters vary with size and composition. To study the role of organization in cluster assemblies, we synthesized multiple architectures incorporating As-7(3-) clusters through control of the countercations. Optical measurements revealed that the band gaps vary from 1.1-2.1 eV, even though the assemblies are constructed from the identical cluster building block. Theoretical studies explain this variation as being a result of altering the lowest unoccupied molecular orbital levels by changing the countercations, Additional variations in the gap are made by covalently linking the clusters with species of varying electronegativity to. alter the degree of charge transfer. These findings offer a general protocol for syntheses of nanoassemblies with tunable electronic properties.
First author: Lin, Tzu-Pin, A Mercury -> Antimony Interaction, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 49, 6357, (2010)
Abstract: One pathway toward nanomaterials with controllable band gaps is to assemble solids where atomic clusters serve as building blocks, since the electronic structures of clusters vary with size and composition. To study the role of organization in cluster assemblies, we synthesized multiple architectures incorporating As-7(3-) clusters through control of the countercations. Optical measurements revealed that the band gaps vary from 1.1-2.1 eV, even though the assemblies are constructed from the identical cluster building block. Theoretical studies explain this variation as being a result of altering the lowest unoccupied molecular orbital levels by changing the countercations, Additional variations in the gap are made by covalently linking the clusters with species of varying electronegativity to. alter the degree of charge transfer. These findings offer a general protocol for syntheses of nanoassemblies with tunable electronic properties.
First author: Izarova, Natalya V., A Noble-Metalate Bowl: The Polyoxo-6-vanado(V)-7-palladate(II) [Pd7V6O24(OH)(2)](6-), ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 49, 7807, (2010)
Abstract: One pathway toward nanomaterials with controllable band gaps is to assemble solids where atomic clusters serve as building blocks, since the electronic structures of clusters vary with size and composition. To study the role of organization in cluster assemblies, we synthesized multiple architectures incorporating As-7(3-) clusters through control of the countercations. Optical measurements revealed that the band gaps vary from 1.1-2.1 eV, even though the assemblies are constructed from the identical cluster building block. Theoretical studies explain this variation as being a result of altering the lowest unoccupied molecular orbital levels by changing the countercations, Additional variations in the gap are made by covalently linking the clusters with species of varying electronegativity to. alter the degree of charge transfer. These findings offer a general protocol for syntheses of nanoassemblies with tunable electronic properties.
First author: Hinderberger, Dariush, Probing How Counterion Structure and Dynamics Determine Polyelectrolyte Solutions Using EPR Spectroscopy, APPLIED MAGNETIC RESONANCE, 37, 657, (2010)
Abstract: In this review article, we describe how methods of electron paramagnetic resonance (EPR) spectroscopy were used to investigate polyion-counterion interactions in polyelectrolyte solutions. This subject is usually treated experimentally by light, X-ray, or neutron scattering techniques. It is shown that a large arsenal of EPR spectroscopic methods-from various sophisticated methods of line shape analysis of continuous-wave EPR, via electron spin echo envelope modulation, nanoscale distance measurements through double electron-electron resonance to high-field pulse EPR-can be used to characterize the intrinsically complicated structures formed in polyelectrolyte solutions. We show that even polymer physical models such as scaling relations can be tested in this way. The distinguishing feature with respect to the numerous scattering studies in this area is that EPR techniques are local methods, and by employing spin-carrying (i.e., EPR-active) probe ions, it is possible to examine polyelectrolytes from the counterions’ point of view.
First author: Zbiri, M., Molecular Modelling of Ground- and Excited-States Vibrations in Organic Conducting Devices: Hexakis(n-hexyloxy)triphenylene (HAT(6)) as Case Study, AUSTRALIAN JOURNAL OF CHEMISTRY, 63, 388, (2010)
Abstract: In order to gain insight into fundamental aspects of organic photocell materials, we have calculated ground and excited electronic-state structures and molecular vibrations for an isolated HAT6 molecule (hexakis(n-hexyloxy)triphenylene). Excited-state calculations are carried out using time-dependent density functional theory and frequencies are evaluated analytically using coupled perturbed Kohn-Shame quations. These model calculations have been validated against new infrared and ultraviolet data on HAT(6) in solution. The main allowed valence excitation, having the largest oscillator strength, is chosen for the structural and vibrational investigations. Comparison with the ground-state vibrational dynamics reveals surprisingly large spectral differences. In addition, the alkoxy tails, which are usually considered to play only a structural role, are clearly involved in the molecular vibrations and the structural distortion of the excited electronic state compared with the ground state. The tails may play a more important role in charge separation, transport and excited-state relaxation than was previously thought. In this case, chemical modification of the tails would allow vibrational and related properties of organic photocell materials to be tailored.
First author: Janjua, Muhammad Ramzan Saeed Ashraf, Tuning Second-Order Non-linear (NLO) Optical Response of Organoimido-Substituted Hexamolybdates through Halogens: Quantum Design of Novel Organic-Inorganic Hybrid NLO Materials, AUSTRALIAN JOURNAL OF CHEMISTRY, 63, 836, (2010)
Abstract: The second-order non-linear optical (NLO) response of organoimido-substituted hexamolybdates has been tuned from 218.61 x 10(-30) to 490.10 x 10(-30) esu. The dipole polarizabilities and second-order nonlinear optical (NLO) properties of organoimido derivatives of hexamolybdates have been investigated by using the time-dependent density functional response theory (TDDFT). The electron withdrawing ability of F (fluorine) has played an important role in tuning the second-order NLO response in this class of organic-inorganic hybrid compounds; particularly system 6[Mo(6)O(18)(NC(16)H(8)F(2)(CF(3))(2)I)](2-) with the static second-order polarizability (beta(vec)) computed to be 490.10 x 10 (30) esu. Thus, our studied systems have the feasibility to be excellent tuneable second-order NLO materials. The analysis of the major contributions to the beta(vec) value suggests that the charge transfer (CT) from POM to organic ligand (D-A) along the z-axis has been enhanced with addition of F atoms at the end phenyl ring which directs head (POM) to tail (fluorinated ring) charge transfer. The computed beta(vec) values have been tuned by incorporation of different halogen atoms at the end phenyl ring of organoimido segment. Furthermore, substitution of two trifluoromethyl (-CF(3)) groups sideways along with iodine (I) at the terminus of end phenyl ring in the organoimido ligand has a striking influence on tuning the optical non-linearity, as CT from POM to the organoimido ligand was significantly increased. These systematic small changes in molecular composition by substitution of different halogen groups leads to a tuning the NLO response; the so-called ‘ripple effect’ catches this point nicely. Thus, the present investigation provides thought provoking insight into the tuneable NLO properties of organoimido-substituted hexamolybdates.
First author: Irfan, Ahmad, Designing of Disubstituted Derivatives of mer-Alq3: Quantum Theoretical Study, AUSTRALIAN JOURNAL OF CHEMISTRY, 63, 1283, (2010)
Abstract: Different disubstituted derivatives of tris(8-hydroxyquinolinato) aluminium (mer-Alq3) have been designed. An electron donating group (-CH3) has been substituted at position 4; along with electron withdrawing groups (-Cl, -CN, and -F) at position 5 (i.e. tris(4-X-5-Y-8-hydroxyquinolinato)aluminium), as well as the molecules arising from reversion of these substitutions. The designed systems have been optimized at the B3LYP/6-31G* and TD-B3LYP/6-31G* level of theories, in the ground and excited states, respectively. The absorption and emission spectra have been calculated at the TD-B3LYP/6-31G* level. A significant blue shift has been observed for tris(4-methyl-5-cyano-8-hydroxyquinolinato)aluminium (2), and red shifts for each of tris(4-methyl-5-fluoro-8-hydroxyquinolinato)aluminium (3), tris(4-chloro-5-methyl-8-hydroxyquinolinato)aluminium (4), and tris(4-cyano-5-methyl-8-hydroxyquinolinato)aluminium (5). The reorganization energy in solvent best elucidates the charge transport behaviour (p- or n-type), rather than the equivalent gas phase for mer-Alq3 and its derivatives. The reorganization energies indicate that these new derivatives have better or comparable mobility when compared to the parent molecule. The electrostatic surface potential study suggested that photostability would be enhanced. On the basis of energy decomposition analysis, we have explained the distribution pattern of frontier molecular orbitals.
First author: Carlsson, Hakan, Computational Modeling of the Mechanism of Urease, BIOINORGANIC CHEMISTRY AND APPLICATIONS, 63, 1283, (2010)
Abstract: In order to elucidate aspects of the mechanism of the hydrolytic enzyme urease, theoretical calculations were undertaken on a model of the active site, using density functional theory. The bridging oxygen donor that has been found in the crystal structures was determined to be a hydroxide ion. The initial coordination of urea at the active site occurs most likely through the urea oxygen to the nickel ion with the lowest coordination number. This coordination can be made without much gain in energy. The calculations also showed that weak coordination of one of the urea amine nitrogen atoms to the second nickel atom is energetically feasible. Furthermore, a proposed mechanism including a tetrahedral intermediate generated by hydrolytic attack on the urea carbon by the bridging hydroxide was modeled, and the tetrahedral intermediate was found to be energetically unfavorable relative to terminal coordination of the substrate (urea).
First author: Valore, Adriana, Luminescent cyclometallated Ir(III) and Pt(II) complexes with beta-diketonate ligands as highly active second-order NLO chromophores, CHEMICAL COMMUNICATIONS, 46, 2414, (2010)
Abstract: [Ir(ppy)(2)(RCOCR’COR)] and [Pt(ppy)(RCOCHCOR)] (ppy = cyclometallated 2-phenylpyridine; R = Me, Ph; R’ = H, 2,4-dinitrophenyl) complexes show an unexpected large second order non linear optical response, as evidenced by the EFISH technique, which can be attributed by an SOS-TDDFT investigation mainly to intraligand charge transfer transitions involving the cyclometallated ligands.
First author: Wen, Shuhao, Ultra-low resistance at TTF-TCNQ organic interfaces, CHEMICAL COMMUNICATIONS, 46, 5133, (2010)
Abstract: We have investigated the conduction mechanism at the TTF-TCNQ organic hetero-interface by means of quantum mechanical (QM) calculations. The calculated resistances at the TTF-TCNQ interface are 39-64 k Omega per square, which is in good agreement with the experimental values of 1-30 k Omega per square.
First author: Jacobsen, Heiko, Shifting Paradigms: Electrostatic Interactions and Covalent Bonding, CHEMISTRY-A EUROPEAN JOURNAL, 16, 976, (2010)
Abstract: The role of electrostatic interactions in covalent bonding of heavier main group elements has been evaluated for the exemplary set of molecules X2H2 (X = C, Si, Ge, Sn, Pb). Density functional calculations at PBE/QZ4P combined with energy decomposition procedures and kinetic energy density analyses have been carried out for a variety of different structures, and two factors are responsible for the fact that the heavier homologues of acetylene exhibit doubly hydrogen-bridged local minimum geometries. For one, the extended electronic core with at least one set of p orbitals of the Group 14 elements beyond the first long period is responsible for favorable electrostatic E-H interactions. This electrostatic interaction is the strongest for the isomer with two bridging hydrogen atoms. Secondly, the H substituent does not posses an electronic core or any bonding-inactive electrons, which would give rise to a significant amount of Pauli repulsion, disfavoring the doubly bridged isomer. When one of two criteria is not met the unusual doubly bridged structure no longer constitutes the energetically preferred geometry. The bonding model is validated in calculations of different structures of Si-2(CH3)(2).
First author: Pan, Qing-Jiang, Binuclear Uranium(VI) Complexes with a “Pacman” Expanded Porphyrin: Computational Evidence for Highly Unusual Bis-Actinyl Structures, CHEMISTRY-A EUROPEAN JOURNAL, 16, 2282, (2010)
Abstract: On the basis of uranyl complexes reacting with a polypyrrolic ligand (H4L), we explored structures and reaction energies of a series of new binuclear uranium(VI) complexes using relativistic density functional theory. Full geometry optimizations on [(UO2)(2)(L)], in which two uranyl groups were initially placed into the pacman ligand cavity, led to two minimum-energy structures. These complexes with cation-cation interactions (CCI) exhibit unusual coordination modes of uranyls: one is a T-shaped (T) skeleton formed by two linear uranyls {O-exo=U-2=O-endo -> U-1(=O-exo)(2)}, and another is a butterfly-like (B) unit with one linear uranyl coordinating side-by-side to a second cis-uranyl. The CCI in T was confirmed by the calculated longest distance and lowest stretching vibrational frequency of U-2=O-endo among the four U=O bonds. Isomer B is more stable than T, for which experimental tetrameric analogues are known. The formation of B and T complexes from the mononuclear [(UO2)H2L)(thf)] (M) was found to be endothermic. The further protonation and dehydration of B and Tare thermodynamically favorable. As a possible product, we have found a trianglelike binuclear uranium(VI) complex having a O=U=O=U=O unit.
First author: Osuna, Silvia, On the Mechanism of Action of Fullerene Derivatives in Superoxide Dismutation,CHEMISTRY-A EUROPEAN JOURNAL, 16, 3207, (2010)
Abstract: We have studied the mechanism of the antioxidant activity of C(60) derivatives at the BP86/TZP level with inclusion of solvent effects (DMSO) by using the COSMO approach. The reaction studied here involves degradation of the biologically relevant superoxide radical (O(2)(center dot-)), which is linked to tissue damage in several human disorders. Several fullerene derivatives have experimentally been shown to be protective in cell culture and animal models of injury, but precisely how these compounds protect biological systems is still unknown. We have investigated the activity of tris-malonyl C(60) (also called C(3)), which efficiently removes the superoxide anion with all activity in the range of several biologically effective, metal-containing superoxide dismutase mimetics. The antioxidant properties Of C(3) are attributed to the high affinity of C(60) to accept electrons. Our results show that once the superoxide radical is in contact with the surface Of C(3), its unpaired electron is transferred to the fullerene. This pro-cess, which converts the damaging O(2)(center dot-) to neutral oxygen O(2), is the rate-determining step of the reaction. Afterwards, another superoxide radical reacts with C(3)(center dot-) to form hydrogen peroxide and in the process takes up the additional electron that was transferred in the first step. The overall process is clearly exothermic and, in general, involves reaction steps with relatively low activation barriers. The capability of C(3) to degrade a highly reactive oxygen species that is linked to several human diseases is of immediate interest for future applications in the field of biology and medicine.
First author: Valore, Adriana, Cyclometalated Ir-III Complexes with Substituted 1,10-Phenanthrolines: A New Class of Efficient Cationic Organometallic Second-Order NLO Chromophores, CHEMISTRY-A EUROPEAN JOURNAL, 16, 4814, (2010)
Abstract: Cyclometalated cationic Ir-III complexes with substituted 1,10-phenanthrolines (1,10-phen), such as [Ir-(ppy)(2)(5-R-1,10-phen)]Y (ppy=cyclometalated 2-phenylpyridine; R = NO2, H, Me, NMe2; Y- = PF6-, C12H25SO3-, I-) and [Ir(ppy)(2)(4-R,7-R-1,10-phen)]Y (R = Me, Ph) are characterized by a significant second-order optical non linearity (measured by the electrical field induced second harmonic generation (EFISH) technique). This nonlinearity is controlled by MLCT processes from the cyclometalated Ir-III, acting as a donor push system, to pi* orbitals of the phenanthroline, acting as an acceptor pull system. Substitution of cyclometalated 2-phenylpyridine by the more pi delocalized 2-phenylquinoline (pq) or benzo[h]quinoline (bzq) or by the sulfur-containing 4,5-diphenyl-2-methyl-thiazole (dpmf) does not significantly affect the mu beta absolute value, which instead is affected by the nature of the R substituents on the phenanthroline, the higher value being associated with the electron-withdrawing NO2 group. By using a combined experimental (the EFISH technique and H-1 and F-19 PGSE NMR spectroscopy) and theoretical (DFT, time-dependent-DFT (TDDFT), sum over states (SOS) approach) investigation, evidence is obtained that ion pairing, which is controlled by the nature of the counterion and by the concentration, may significantly affect the mu beta values of these cationic NLO chromophores. In CH2Cl2, concentration-dependent high absolute values of mu beta are obtained for [Ir-(ppy)(2)(5-NO2-1,10-phen)]Y if Y is a weakly interacting anion, such as PF6-, whereas with a counterion, such as C12H25SO3- or I-, which form tight ion-pairs, the absolute value of mu beta is lower and quite independent of the concentration. This mu beta trend is partially due to the perturbation of the counterion on the LUMO pi* levels of the phenanthroline. The correlation between the mu beta value and dilution shows that the effect of concentration is a factor that must be taken into careful consideration.
First author: Couzijn, Erik P. A., Gas-Phase Energetics of Reductive Elimination from a Palladium(II) N-Heterocyclic Carbene Complex, CHEMISTRY-A EUROPEAN JOURNAL, 16, 5408, (2010)
Abstract: Energy-resolved collision-induced dissociation experiments using tandem mass spectrometry are reported for an phenylpalladium N-heterocyclic carbene (NHC) complex. Reductive elimination of an NHC ligand as a phenylimidazolium ion involves a barrier of 30.9(14) kcal mol(-1), whereas competitive ligand dissociation requires 47.1(17) kcal mol(-1). The resulting three-coordinate palladium complex readily undergoes reductive C-C coupling to give the phenylimidazolium pi complex, for which the binding energy was determined to be 38.9(10) kcal mol(-1). Density functional calculations at the M06-L//BP86/TZP level of theory are in very good agreement with experiment. In combination with RRKM modeling, these results suggest that the rate-determining step for the direct reductive elimination process switches from the C-C coupling step to the fragmentation of the resulting a complex at low activation energy.
First author: van Zeist, Willem-Jan, Comment on “The Interplay between Steric and Electronic Effects in S(N)2 Reactions”, CHEMISTRY-A EUROPEAN JOURNAL, 16, 5538, (2010)
Abstract: We respond to a paper by Fernandez. Frenking, and Uggerud (FFU: Chem. Eur. J. 2009, 15, 2166) in which they conclude that not steric hindrance but reduced electrostatic attraction and reduced orbital interactions are responsible for the S(N)2 barrier, in particular in the case of more highly substituted substrates, for example, F- + C(CH3)(3)F. We disagree with this conclusion, which we show is the result of neglecting geometry relaxation processes that are induced by increased Pauli repulsion in the sterically congested S(N)2 transition state.
First author: Kim, Tae-Jin, Sterically Less-Hindered Half-Titanocene(IV) Phenoxides: Ancillary-Ligand Effect on Mono-, Bis-, and Tris(2-Alkyl-/arylphenoxy) Titanium(IV) Chloride Complexes, CHEMISTRY-A EUROPEAN JOURNAL, 16, 5630, (2010)
Abstract: A series of mono-, his-, and tris(phenoxy)-titanium(IV) chlorides of the type [Cp*Ti(2-R-PhO)(n)Cl(3-n) (n=1-3; Cp*=pentamethylcyclopentadienyl) was prepared, in which R=Me, iPr, tBu, and Ph. The formation of each mono-, bis-, and tris(2-alkyl-/aryl-phenoxy) series was authenticated by structural studies on representative examples of the phenyl series including [Cp*Ti(2-Ph-PhO)Cl(2)] (1PhCl2), [Cp*Ti(2-Ph-PhO)(2)Cl] (2PhCl), and [Cp*Ti(2-Ph-PhO)(3)] (3 Ph). The metal-coordination geometry of each compound is best described as pseudotetrahedral with the Cp* ring and the 2-Ph-PhO and chloride ligands occupying three leg positions in a piano-stool geometry. The mean Ti-O distances, observed with an increasing number of 2-Ph-PhO groups, are 1.784(3), 1.802(4), and 1.799(3) angstrom for 1PhCl2, 2 PhCl, and 3Ph, respectively. All four alkyl/aryl series with Me, iPr, tBu, and Ph substituents were tested for ethylene homopolymerization after activation with Ph(3)C(+)[B(C(6)F(5))(4)](-) and modified methyaluminoxane (7% aluminum in iso-par E; mMAO-7) at 140 C. The phenyl series showed much higher catalytic activity, which ranged from 43.2 and 65.4 kg(mmol of Ti.h)(-1), than the Me, iPr, and tBu series (19.2 and 36.6kg(mmol of Ti-h)(-1)). Among the phenyl series, the bis(phenoxide) complex of 2PhCl showed the highest activity of 65.4 kg (mmol of Ti.h)(-1). Therefore, the catalyst precursors of the phenyl series were examined by treating them with a variety of alkylating reagents, such as trimethylaluminum (TMA), triisobutylaluminum (TIBA), and methylaluminoxane (MAO). In all cases, 2 PhCl produced the most catalytically active alkylated species, [Cp*Ti(2-Ph-PhO)MeCl]. This enhancement was further supported by DFT calculations based on the simplified model with TMA.
First author: Salvi, Nicola, On the Dewar-Chatt-Duncanson Model for Catalytic Gold(I) Complexes, CHEMISTRY-A EUROPEAN JOURNAL, 16, 7231, (2010)
Abstract: We provide a rigorous model-free definition and a detailed theoretical analysis of the electron-charge displacements making up the donation and back-donation components of the Dewar-Chatt-Duncanson model in some realistic catalytic intermediates of formula L-Au-I-S in which L is an N-heterocyclic carbene or Cl- and S is an eta(2)-coordinated Substrate containing a C-C multiple bond. We thus show, contrary to a widely held view, that the gold substrate bond is characterized by a large pi back-donation component that is comparable to, and often as large as, the sigma donation. The back-donation is found to be a highly tunable bond component and we analyze its relationship with the nature of the auxiliary ligand L and with structural (interdependent) factors such as metal substrate bond lengths and carbon pyramidalization.
First author: Ogino, Isao, A Zeolite-Supported Molecular Ruthenium Complex with eta(6)-C6H6 Ligands: Chemistry Elucidated by Using Spectroscopy and Density Functional Theory, CHEMISTRY-A EUROPEAN JOURNAL, 16, 7427, (2010)
Abstract: An essentially molecular ruthenium-benzene complex anchored at the aluminum sites of dealuminated zeolite Y was formed by treating a zeolite-supported mononuclear ruthenium complex, [Ru(acac)(eta(2)-C2H4)(2)](+) (acac = acetylacetonate, C5H7O2-), with (C6H6)-C-13 at 413 K. IR, C-13 NMR, and extended X-ray absorption fine structure (EXAFS) spectra of the sample reveal the replacement of two ethene ligands and one acac ligand in the original complex with one (C6H6)-C-13 ligand and the formation of adsorbed protonated acac (Hacac). The EXAFS results indicate that the supported [Ru(eta(6)-C6H6)](2+) incorporates an oxygen atom of the support to balance the charge, being bonded to the zeolite through three Ru-O bonds. The supported ruthenium benzene complex is analogous to complexes with polyoxometalate ligands, consistent with the high structural uniformity of the zeolite-supported species, which led to good agreement between the spectra and calculations at the density functional theory level. The calculations show that the interaction of the zeolite with the Hacac formed on treatment of the original complex with (C6H6)-C-13 drives the reaction to form the ruthenium-benzene complex.
First author: Wang, Shu-Guang, Antibond Breaking-The Formation and Decomposition of He@Adamantane: Descriptions, Explanations, and Meaning of Concepts, CHEMISTRY-A EUROPEAN JOURNAL, 16, 9107, (2010)
Abstract: The reaction path from the inclusion complex He@adamantane to its two separated fragments over the transition barrier is investigated by using quantum chemistry. The changes of structure and wavefunction are intuitively anticipated, accurately computed, and qualitatively rationalized. With the help of the traditional concepts of chemical bonding and nonbonding interactions, and with numerical results from a chemically oriented energy-partitioning approach, we can rationalize the details of the chemical process, and qualitatively predict and interpret the two chosen alternative descriptions: the energy-partitioning approach and the topological electron-density analysis. The meaning of bonding within these two approaches, and unsolved aspects of the latter tool are clarified.
First author: Arnold, Polly L., Covalency in Ce-IV and U-IV Halide and N-Heterocyclic Carbene Bonds, CHEMISTRY-A EUROPEAN JOURNAL, 16, 9623, (2010)
Abstract: Oxidative halogenation with trityl chloride provides convenient access to Ce-IV and U-IV chloroamides [M(N{SiMe3}(2))(3)Cl] and their N-heterocyclic carbene derivatives, [M(L)(N-{SiMe3}(2))(2)Cl] (L= OCMe2CH2(CNCH2-CH(2)NDipp) Dipp=2,6-iPr(2)C(6)H(3)). Computational analysis of the bonding in these and a fluoro analogue, [U(L)(N{SiMe3}(2))(2)F], provides new information on the covalency in this relative rare oxidation state for molecular cerium complexes. Computational studies reveal increased Mayer bond orders in the actinide carbene bond compared with the lanthanide carbene bond, and natural and atoms-in-molecules analyses suggest greater overall ionicity in the cerium complexes than in the uranium analogues.
First author: Hopmann, Kathrin H., Spin Coupling in Roussin’s Red and Black Salts, CHEMISTRY-A EUROPEAN JOURNAL, 16, 10397, (2010)
Abstract: Although DFT calculations have provided a first-order electronic-structural description for Roussin’s red and black salts, a detailed study of spin coupling in these species has yet to be reported. Such an analysis is presented here for the first time, based on broken-symmetry density functional theory (DFT, chiefly OLYP/STO-TZP) calculations. Both the Noodleman and Yamaguchi formulas were used to evaluate the Heisenberg coupling constants (J). Three nitrosylated binuclear clusters were studied: [Fe-2(NO)(2)(Et-HPTB)(O2CPh)](2+) (1; Et-HPTB = N,N,N’,N’-tetrakis-(N-ethyl-2-benzimi-dazolylmethyl)-2-hydroxy-1,3-diami no-propane), [Fe(NO)2{Fe(NO)(NS3))S,S’ (2), and Roussin’s red salt anion [Fe-2(NO)(4)(mu-S)(2)](2-) (3). Although the Heisenberg J for 1 is small (approximate to 10(2) cm(-1)), 2 and 3 exhibit J values that are at least an order of magnitude higher (approximate to 10(3) cm(-1)), where the J values refer to the following Heisenberg spin Hamiltonian: H=JS(A).S-B. For Roussin’s black salt anion, [Fe-4(NO)(7)(mu(3)-S)(3)](-) (4), the Heisenberg spin Hamiltonian describing spin coupling between the {FeNO}(7) unit (S-A=3/2) and the three {Fe(NO)(2)}(9) units (S-B=S-C=S-D=1/ 2) in [Fe-4(NO)(7)mu(3)-S)(3)](-) was assumed to have the form: H = J(12)S(A).S-B+S-A.S-C+S-A.S-D)+J(22)(S-B.S-C+S-B.S-D+S-C.S-D), in which J(12) corresponds to the interaction between the apical iron and a basal iron, and J(22) refers to that between any two basal iron centers. Although the basal-basal coupling constant J(22) was found to be small (approximate to 10(2) cm(-1)), the apical-basal coupling constant J(12) is some forty times higher (approximate to 4000 cm(-1)). Thus, the nitrosylated iron-sulfur clusters feature some exceptionally high J values relative to the non-nitrosylated {2Fe2S} and {4Fe4S} clusters. An analysis of spin-dependent bonding energies shed light on this curious feature. In essence, the energy difference between the high-spin (i.e., ferromagnetically coupled iron sites) and low-spin (i.e., maximum spin coupling) states of Roussin’s salts are indeed rather similar to those of analogous non-nitrosylated ironsulfur clusters. However, the individual Fe(NO)(x) (x = 1, 2) site spins are lower in the nitrosylated systems, resulting in a smaller denominator in both the Noodleman and Yamaguchi formulas for J, which in turn translates into the very high I values.
First author: Zhou, Binbin, Studies on the Reactivity of [Ge-9](4-) towards [Fe(cot)(CO)(3)]: Synthesis and Characterization of [Ge8Fe(CO)(3)](3-) and of the Anionic Organometallic Species [Fe(cot)(CO)(3)](-), CHEMISTRY-A EUROPEAN JOURNAL, 16, 11145, (2010)
Abstract: Reaction of cyclooctatetraene (COT) iron(II) tricarbonyl, [Fe-(cot)(CO)(3)], with one equivalent of K4Ge9 in ethylenediamine (en) yielded the cluster anion [Ge8Fe(CO)(3)](3-) which was crystallographically-characterized as a [K(2,2,2-crypt)](+) salt in [K(2,2,2-crypt)](3)[Ge8Fe(CO)(3)]. The chemically-reduced organometallic species [Fe(eta(3)-C8H8)(CO)(3)](-) was also isolated as a side-product from this reaction as [K(2,2,2-crypt)][Fe(eta(3)-C8H8)(CO)(3)]. Both species were further characterized by EPR and IR spectroscopy and electrospray mass spectrometry. The [Ge8Fe(CO)(3)](3-) cluster anion represents an unprecedented functionalized germanium Zintl anion in which the nine-atom precursor cluster has lost a vertex, which has been replaced by a transition-metal moiety.
First author: Van, Nguyen, Oxidative Perhydroxylation of [closo-B12H12](2-) to the Stable Inorganic Cluster Redox System [B-12(OH)(12)](2-/.-): Experiment and Theory, CHEMISTRY-A EUROPEAN JOURNAL, 16, 11242, (2010)
Abstract: Reaction of cyclooctatetraene (COT) iron(II) tricarbonyl, [Fe-(cot)(CO)(3)], with one equivalent of K4Ge9 in ethylenediamine (en) yielded the cluster anion [Ge8Fe(CO)(3)](3-) which was crystallographically-characterized as a [K(2,2,2-crypt)](+) salt in [K(2,2,2-crypt)](3)[Ge8Fe(CO)(3)]. The chemically-reduced organometallic species [Fe(eta(3)-C8H8)(CO)(3)](-) was also isolated as a side-product from this reaction as [K(2,2,2-crypt)][Fe(eta(3)-C8H8)(CO)(3)]. Both species were further characterized by EPR and IR spectroscopy and electrospray mass spectrometry. The [Ge8Fe(CO)(3)](3-) cluster anion represents an unprecedented functionalized germanium Zintl anion in which the nine-atom precursor cluster has lost a vertex, which has been replaced by a transition-metal moiety.
First author: Bollermann, Timo, Molecular Alloys: Experimental and Theoretical Investigations on the Substitution of Zinc by Cadmium and Mercury in the Homologous Series [Mo(M ‘ R)(12)] and [M(M ‘ R)(8)] (M = Pd, Pt; M ‘ = Zn, Cd, Hg),CHEMISTRY-A EUROPEAN JOURNAL, 16, 13372, (2010)
Abstract: The synthesis and structural characterization of novel, metal-rich, highly coordinated compounds [Mo(M’R)(12)] and [M(M’R)(8)] (M: Pd, Pt, Mo; M’: Zn, Cd; R: Me= CH3, Cp*= pentamethylcyclopentadienyl) are reported. Additionally, a description of the bonding situation of the new compounds by means of quantum-chemical calculations is presented including the Hg analogues. Reaction of [Pt(GaCp*)(4)] with CdMe2 results in the formation of the unprecedented all-Cd coordinated [Pt(CdMe)(4)(CdCp*)(4)] (1). Similarly, the treatment of the all-Zn coordinated [Pd(ZnMe)(4)(ZnCp*)(4)] with CdMe2 affords the novel Zn/Cd mixed compound [Pd(CdMe)(4)(ZnCp*)(4)] (2). The related Zn/Cd mixed compound [Mo(ZnCp*)(3)(CdMe)(9)] (3) is prepared by reaction of [Mo(ZnCp*)(4)(GaMe)(4)] with an excess amount of CdMe2. All compounds were analyzed by H-1 and C-13 NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction. The bonding situation of these highly coordinated, metal-rich molecules 1-3 were studied by quantum-chemical calculations using density functional theory (DFT) at the BP86/TZ2P+ level, atoms-in-molecules (AIM) analysis, and energy-decomposition analysis (EDA), as well as the its natural orbitals for chemical valence variation (EDA-NOCV) and including the hypothetically all-Hg-coordinated ana-logues. The results point out that the radial interactions M-M’ in the icosahedral compounds that have twelve ligands are best described as classical electron-pair-sharing covalent bonds, whereas the dodecahedral species, which have eight ligands, exhibit metal-ligand donor-acceptor bonds. The attractive interactions between the metal-ligand fragments M’R by means of M’-M’ bonds are weaker but not insignificant. All complexes fulfill the 18electron rule. The analysis clarifies the electronic structures as being distinctly different from typical endohedral clusters M@(M ” R)(n) that exhibit strong peripheral M”-M” interactions: The M’-M’ bonds are not strong enough to yield stable (M’R) n cages.
First author: Petrie, Simon, Hydration Preferences for Mn4Ca Cluster Models of Photosystem II: Location of Potential Substrate-Water Binding Sites, CHEMISTRY-A EUROPEAN JOURNAL, 16, 14026, (2010)
Abstract: Density functional theory calculations are reported on a set of three model structures of the Mn4Ca cluster in the water-oxidizing complex of Photosystem II (PSII), which share the structural formula [CaMn4C9H10N2O16](q+)center dot(H2O)(n) (q = -1, 0, 1, 2, 3; n = 0-7). In these calculations we have explored the preferred hydration sites of the Mn4Ca cluster across five overall oxidation states (S-0 to S-4) and all feasible magnetic-coupling arrangements to identify the most likely substrate water binding sites. We have also explored charge-compensated structures in which the overall charge on the cluster is maintained at q=0 or +1, which is consistent with the experimental data on sequential proton loss in the real system. The three model structures have skeletal arrangements that are strongly reminiscent, in their relative metal-atom positions, of the 2.9-, 3.7-, and 3.5 angstrom-resolution crystal structures, respectively, whereas the charge states encompassed in our study correspond to an assignment of (Mn-III)(3)Mn-II for S-0 and up to (Mn-IV)(3)Mn-II for S-4. The three models differ principally in terms of the spatial relationship between one Mn (Mn(4)) and a generally robust Mn3Ca tetrahedron that contains Mn(1), Mn(2), and Mn(3). Oxidation-state distributions across the four manganese atoms, in most of the explored charge states, are dependent on details of the cluster geometry, on the extent of assumed hydration of the clusters, and in some instances on the imposed magnetic-coupling between adjacent Mn atoms. The strongest water-binding sites are generally those on Mn(4) and Ca. However, one structure type displays a high-affinity binding site between Ca and Mn(3), the S-state-dependent binding-energy pattern of which is most consistent with the substrate water-exchange kinetics observed in functional PSII. This structure type also permits another water molecule to access the cluster in a manner consistent with the substrate water interaction with the Mn cluster, seen in electron spin-echo envelope modulation (ESEEM) studies of the functional enzyme in the S-0 and S-2 states. It also rationalizes the significant differences in hydrogen-bonding interactions of the substrate water observed in the FTIR measurements of the S-1 and S-2 states. We suggest that these two water-binding sites, which are molecularly close, model the actual substrate-binding sites in the enzyme.
First author: Hobbs, Matthew G., Anionic N-Heterocyclic Carbenes with N,N ‘-Bis(fluoroaryl) and N,N ‘-Bis(perfluoroaryl) Substituents, CHEMISTRY-A EUROPEAN JOURNAL, 16, 14520, (2010)
Abstract: A series of rhodium complexes, [Rh(cod)(NHC-F-x)(OH2)] (cod =1,5-cyclooctadiene; NHC=N-heterocyclic carbene), incorporating anionic N-heterocyclic carbenes with 2-tert-butylmalonyl backbones and 2.6-dimethylphenyl (x=0), 2,6-difluorophenyl (x=4). 2.4,6-trifluorophenyl (x=6), and pentafluorophenyl (x=10) N,N’-substituents, respectively, has been prepared by deprotonation of the corresponding zwitterionic precursors with potassium hexamethyldisilazide, followed by immediate reaction of the resulting potassium salts with [{RhCl-(cod)}(2)]. These complexes could be converted to the related carbonyl derivatives [Rh(CO)(2)(NHC-F-x)(OH2)] by displacement of the COD ligand with CO. IR and NMR spectroscopy demonstrated that the degree of fluorination of the N-aryl substituents has a considerable influence on the sigma-donating and pi-accepting properties of the carbene ligands and could be effectively used to tune the electronic properties of the metal center. The carbonyl groups on the carbene ligand backbone provided a particularly sensitive probe for the assessment of the metal-to-ligand pi donation. The ortho-fluorine substituents on the N-aryl groups in the carbene ligands interacted with the other ligands on rhodium, determining the conformation of the complexes and creating a pocket suitable for the coordination of water to the metal center. Computational studies were used to explain the influence of the fluorinated N-substituents on the electronic properties of the ligand and evaluate the relative contribution of the sigma- and pi-interactions to the ligand-metal interaction.
First author: Zlatar, Matija, Density Functional Theory for the Study of the Multimode Jahn-Teller Effect, CHIMIA, 64, 161, (2010)
Abstract: The Jahn-Teller (JT) theorem states that in a molecule with a degenerate electronic state, a structural distortion must occur that lowers the symmetry, removes the degeneracy and lowers the energy. The multideterminental-DFT method performed to calculate the JT parameters for JT active molecules is described. Within the harmonic approximation the JT distortion can be analyzed as a linear combination of all totally symmetric normal modes in any of the low symmetry minimum energy conformation, which allows the intrinsic distortion path (IDP) to be calculated, exactly from the high symmetry point to the low symmetry configuration. Results obtained by the approach described here give direct insight into the coupling of electronic structure and nuclear movements.
First author: Loginov, Dmitry A., THE FIRST METALLACARBORANE TRIPLE-DECKER COMPLEXES WITH A BRIDGING PENTAPHOSPHOLYL LIGAND, COLLECTION OF CZECHOSLOVAK CHEMICAL COMMUNICATIONS, 75, 981, (2010)
Abstract: Visible light irradiation of cations [(Carb)Fe(eta-C(6)H(6))](+) in the presence of Cp*Fe(eta-cyclo-P(5)) affords the mu-pentaphospholyl triple-decker complexes [(Carb)Fe(mu-eta:eta-cyclo-P(5))FeCp*](+) (Carb = 9-SMe(2)-7,8-C(2)B(9)H(10) (3a) and 1-t-BuNH-1,7,9-C(3)B(8)H(10) (3b)). Structures of 3a- and 3b[Co(eta-7,8-C(2)B(9)H(11))(2)] were determined by X-ray diffraction. Bonding in 3a, 3b and mononuclear building blocks was analyzed by energy decomposition analysis.
First author: Dastychova, Lenka, THEORETICAL AND EXPERIMENTAL STUDIES OF IR AND NMR SPECTRA OF gem-2,2-DIAMINO-4,4,6,6-TETRAPHENOXY-1,3,5-cyclo-TRIAZA-lambda(5)-PHOSPH ORINE, COLLECTION OF CZECHOSLOVAK CHEMICAL COMMUNICATIONS, 75, 1125, (2010)
Abstract: The vibrational spectra of gem-2,2-diamino-4,4,6,6-tetraphenoxy-1,3,5-cyclo-triaza lambda(5)-phosphorine were studied using density functional theory. Selected vibrational bands were assigned to normal modes on the basis of DFT calculation with the ADF program package. The H-1 and C-13 NMR spectra, the higher order P-31, P-31{H-1(am).(sel.)} and P-31{H-1(arom).(sel.)} NMR spectra were measured and the values of (1)J(C, H), (2)J(C, H) and (2)J(P-I, P-II) were found. Nearly the complete spin system (ABB’M4X4X4′) for the symmetry C-2 was simulated with the gNMR simulation program and the values of (2)J(P-I,H-am.), (4)J(P-II, H-am.), (4)J(P-II, H-arom.), (6)J(P-I, H-arom.) and (6)J(P-II,H'(arom).) were determined for the first time. The experimental NMR data were also compared with quantum chemical calculation results.
First author: Zang, Hong-Ying, Inorganic-organic hybrid compounds based on the co-existence of different isomers or forms of polymolybdate, CRYSTENGCOMM, 12, 3684, (2010)
Abstract: Three novel compounds co-existing isomers or forms of polymolybdate, namely, {[Ni(gamma-Mo(8)O(26))(H(2)L(1))(2)(H(2)O)(2)](gamma-Mo(8)O(26))(H(2)L(1 ))}center dot 2H(2)O (1), {[Co(gamma-Mo(8)O(26))(H(2)L(1))(2)(H(2)O)(2)](beta-Mo(8)O(26))[Co(H(2)O )(6)]}center dot 6H(2)O (2) and [Cu(6)(I)L(4)(2)(beta-Mo(8)O(26))(Mo(6)O(19))] (3), where L(1) = 1,1′-bis(pyridin-3-ylmethyl)-2,2′-biimidazole, L(2) = 3-((1H-1,2,4-triazol-1-yl)methyl)pyridine, have been successfully synthesized. Crystal structure analysis reveals that 1 is a 1D + 1D supramolecular structure containing both gamma-[Mo(8)O(26)N(2)] and gamma-[Mo(8)O(28)] units; 2 has gamma-[Mo(8)O(26)](4-) as well as beta-[Mo(8)O(26)](4-) anions and 3 is a (3,4,6)-connected 2D network containing both beta-[Mo(8)O(26)](4-) and [Mo(6)O(19)](2-) anions. According to quantum chemical calculations, the transformation from beta-[Mo(8)O(26)](4-) to [Mo(6)O(19)](2-) is spontaneous in aqueous solution. Furthermore, we have investigated the optical band gap of compounds 1 and 3, with 3 showing a lower band gap (1.69 eV). Additionally, the photoluminescent property of 3 is also studied, which can be assigned to metal-to-ligand charge transfer (MLCT).
First author: Cantalupo, Stefanie A., Three-coordinate late transition metal fluorinated alkoxide complexes, DALTON TRANSACTIONS, 39, 374, (2010)
Abstract: Homoleptic fluorinated alkoxide complexes have been prepared from KOC(4)F(9), 1, via salt metathesis routes. One four-coordinate K{K(18C6)}[Co(OC(4)F(9))(4)], 2, and four three-coordinate complexes: {K(18C6)}[Fe(OC(4)F(9))(3)], 3, {K(18C6)}[Co(OC(4)F(9))(3)], 4, {K(18C6)}[Cu(OC(4)F(9))(3)], 5, and {K(18C6)}[Zn(OC(4)F(9))(3)], 6, have been prepared and all except 5 have been characterized crystallographically. Compounds 3, 4, and 6 are very rare examples of monomeric, trigonal alkoxide complexes. All compounds have been characterized with UV-vis and IR spectroscopy, solution magnetic susceptibility, and elemental analysis. In solution, compound 2 exists in an equilibrium with 4 and 1, which has been probed with cyclic voltammetry, supporting energetically different Co(2+)/Co(3+) potentials in the three-coordinate (E(p,a) = similar to 1.2 V vs Fc/Fc(+)) and four-coordinate (E(p,a) = similar to 0.9 V) geometries. The ligand field engendered by the perfluoro-t-butoxide ligand has been studied with DFT calculations on 4 and the hypothetical [Co(OC(4)H(9))(3)](-) as well as the previously reported [Co(mes)(3)](-) and [Co{N(TMS)(2)}(3)](-) showing significant pi-type interactions in the xy plane as well as above and below for the two alkoxide species.
First author: Hiney, Rachel M., Using EPR to follow reversible dihydrogen addition to paramagnetic clusters of high hydride count: [Rh-6(PCy3)(6)H-12](+) and [Rh-6(PCy3)(6)H-14](+), DALTON TRANSACTIONS, 39, 1726, (2010)
Abstract: A combined structural/EPR/computational chemistry investigation is reported on the two paramagnetic hydrido-cluster salts [Rh-6(PCy3)(6)H-12][BAr4F] and [Rh-6(PCy3)(6)H-14][BAr4F], the latter being formed by reversible addition of H-2 to the former, [BAr4F](-) = [B{C6H3(CF3)(2)}(4)](-). The solid-state structure of [Rh-6(PCy3)(6)H-14][BAr4F] shows an expanded cluster core compared to previously reported [Rh-6(PCy3)(6)H-12][ BAr4F] indicative of the addition of hydrogen to the cluster surface. This expansion correlates well with the calculated (PH3 replaces PCy3) structures. EPR measurements on [Rh-6(PCy3)(6)H-12][BAr4F] indicate two isomers at low temperature, which are tentatively assigned as diastereomers that result from locked phosphine rotation and bridging hydride/semi bridging hydride tautomerism. The EPR signal disappears above 60 K which is suggested to occur due to fast Raman-type relaxation-a phenomenon consistent with the calculated small SOMO/SOMO-1 and SOMO/LUMO gaps. For [Rh-6(PCy3)(6)H-14][BAr4F] EPR measurements indicate two isomers, the proportion of which change with temperature and deuteration-one axial isomer and one rhombic isomer. DFT calculations on a number of plausible isomers give EPR parameters which fit the experimentally determined rhombic isomer to one in which there is an interstitial hydride in the cluster and thirteen hydride ligands on the surface, while the axial isomer has two dihydrogen-like ligands on the cluster surface. That these isomers lie close in energy comes from both the EPR measurements ( as measured from equilibrium constants over a variable temperature range) and DFT calculations. Deuteration of the hydrides should favour the isomer with the lowest zero-point energy and this is the case, with the axial isomer (two D-2 ligands on the surface) being favoured over the rhombic.
First author: Fankel, Stefan, Novel access to azaphosphiridine complexes and first applications using Bronsted acid-induced ring expansion reactions, DALTON TRANSACTIONS, 39, 3472, (2010)
Abstract: Synthesis of azaphosphiridine complexes 3a-e was achieved via thermal group transfer reaction using 2H-azaphosphirene complex 1 and N-methyl C-aryl imines 2a-e (i) or via reaction of transient Li/Cl phosphinidenoid complex 5 (prepared from dichloro(organo)phosphane complex 4) using 2a-c (ii), respectively. Reaction of complexes 3a,d and trifluoromethane sulfonic acid in the presence of dimethyl cyanamide led to a highly bond-and regioselective ring expansion yielding 1,3,4 sigma(3)lambda(3)-diazaphosphol-2-ene complexes 8a,d after deprotonation with NEt3. P-31 NMR reaction monitoring revealed that protonation of complex 3a yields the azaphosphiridinium complex 6a, unambiguously identified by NMR spectroscopy at low temperature. All isolated products were characterized by multinuclear NMR spectroscopy, IR and UV/Vis (for 3a, d, 6a, 8a, d), MS and single-crystal X-ray crystallography in the cases of complexes 3b-d, 8a and 8d. DFT studies on the reaction mechanism and compliance constants of the model complex of 6a are presented.
First author: Song, Ping, Theoretical study on the tetranuclear endohedral vanadyl carboxylates with guest-switchable redox properties and large polarizability, DALTON TRANSACTIONS, 39, 3706, (2010)
Abstract: The polarizability and redox properties for the tetranuclear vanadium-oxide-carboxylates have been investigated using density functional theory (DFT). These so-called inorganic crown ethers possess large polarizabilities, which are equivalent to fullerene and generate large polarization on the guest anions into the host. The dipole-induced dipole interaction between the host and the guest anions induces charge transfer from the guest to the host, which is enhanced with the increasing polarization. Moreover, the redox potentials are sensitive to different guests inside the host bowl, and they shift negatively as compared to the isolated host bowl. In contrast, the modi. cation of the methyl group by CH(2)tBu on the rim of the bowl has evoked higher polarizability (over 560 a. u.) with larger polarization on the guest anions and more negative redox potentials. The weak interaction energies in accord with the organic crown ether incorporating alkali metal ions indicate that the guest anions can move freely inside and outside the host bowl, so this kind of inorganic crown ether may exhibit potential guest-switchable redox properties based on reversible complexation-decomplexation and will be expected to find applications in ion recognition and selectivity studies based on the sensitivity to different guests.
First author: Cavigliasso, German, Activation and cleavage of the N-N bond in side-on bound [L2M-NN-ML2] (L = NH2, NMe2, (NPr2)-Pr-i, C5H5, C5Me4H) dinitrogen complexes of transition metals from groups 4 through 9, DALTON TRANSACTIONS, 39, 4529, (2010)
Abstract: The activation and cleavage of the N-N bond in side-on bound [L2M-NN-ML2] (L = NH2, NMe2, (NPr2)-Pr-i, C5H5, C5Me4H) dinitrogen complexes of transition metals in groups 4 through 9 have been investigated using density functional theory. Emphasis has been placed on Ti, Zr, and Hf (group 4) complexes due to their experimental relevance. Calculations on these species have shown that for cases when the structural configuration corresponds to the terminal [ML2] fragments adopting a perpendicular orientation with respect to the central [N-N] unit, a considerably higher degree of N-N activation is predicted relative to that observed in the experimentally characterized cyclopentadienyl analogues and in related systems involving end-on dinitrogen coordination. An examination of the orbital interactions between the metal-based fragments and the dinitrogen unit shows that both sigma and pi bonding are important in the side-on binding mode, in contrast to the end-on mode where metal-nitrogen p interactions are dominant. This analysis also reveals that the model amide systems possess the orbital properties identied as necessary for successful N-N hydrogenation. A significant result obtained for the amide complexes containing metals from groups 5 (V, Nb, Ta), 6 (Cr, Mo, W), and 7 (Mn, Tc, Re), is the presence of metal-metal bonding in configurations that are considerably distorted from planarity. As a consequence, these complexes exhibit strongly enhanced stability relative to species where metal-metal bonding is absent. In contrast, the d(2) metal-based configurations in the group 4 complexes of Ti, Zr, and Hf are unable to provide the six electrons required for complete reductive cleavage of the dinitrogen unit which is necessary to allow the metal centres to approach one another sufficiently for metal-metal bond formation.
First author: Sierra, Diego, Heterobimetallic Re=Pd complexes bridged by eta(1):eta(5)-Ph2PC5H4 ligand. Synthesis, electronic and crystal structure of (CO)(2)(PR3)(eta(5)-C5H4(PPh2)Re-P)over bardCl(2), R = Me and OMe, DALTON TRANSACTIONS, 39, 6295, (2010)
Abstract: The new rhenium complexes (eta(5)-C5H4PPh2) Re(CO)(2)(PR3) (R = Me (1) andOMe (2)) were prepared photochemically from (eta(5)-C5H4PPh2)Re(CO)(3) in the presence of PMe3 or P(OMe)(3). Further reaction of these ligands with PdCl2(NCPh)(2) in chloroform, produces the heterobimetallic complexes (CO)(2)(PMe3)(eta(5)-C5H4 <(PPh2)Re P)over bar>dCl(2) (3) and (CO)(2)(P(OMe)(3))(eta(5)-C5H4 <(PPh2)Re P)over bar>dCl(2) (4). IR spectroscopy reveals that both complexes possess a Re-Pd interaction which was confirmed by X-ray crystallography (Re-Pd bond distance = 2.762 angstrom in 3 and 2.774 angstrom in 4). Relativistic functional density theory calculations have also been carried out in order to probe the bonding in these compounds.
First author: Tassell, Matthew J., Covalency in AnCp(4) (An = Th-Cm): a comparison of molecular orbital, natural population and atoms-in-molecules analyses, DALTON TRANSACTIONS, 39, 6719, (2010)
Abstract: The geometric and electronic structures of the title compounds are calculated with scalar relativistic, gradient-corrected density functional theory. The most stable geometry of ThCp4 (Cp = eta(5)-C5H5) and UCp4 is found to be pseudo-tetrahedral (S4), in agreement with experiment, and all the other AnCp(4) compounds have been studied in this point group. The metal -Cp centroid distances shorten by 0.06 angstrom from ThCp4 to NpCp4, in accord with the actinide contraction, but lengthen again from PuCp4 to CmCp4. Examination of the valence molecular orbital structures reveals that the highest-lying Cp pi(2,3)-based orbitals split into three groups of pseudo-e, t(2) and t(1) symmetry. Above these levels come the predominantly metal-based 5f orbitals, which stabilise across the actinide series, such that in CmCp4, the 5f manifold is at more negative energy than the Cp pi(2,3)-based levels. The stability of the Cm 5f orbitals leads to an intramolecular ligand. metal charge transfer, generating a Cm(III) f(7) centre and increased Cm -Cp centroid distance. Mulliken population analysis shows metal d orbital participation in the e and t(2) Cp pi(2,3)-based orbitals, which gradually decreases across the actinide series. By contrast, metal 5f character is found in the t(1) levels, and this contribution increases four-fold from ThCp4 to AmCp4. Examination of the t(1) orbitals suggests that this f orbital involvement arises from a coincidental energy match of metal and ligand orbitals, and does not re. ect genuinely increased covalency (in the sense of appreciable overlap between metal and ligand levels). Atoms-in-molecules analysis of the electron densities of the title compounds (together with a series of reference compounds: C2H6, C2H4, Cp-, M(CO)(6) (M = Cr, Mo, W), AnF(3)CO (An = U, Am), FeCp2, LaCp3, LaCl3 and AnCl(4) (An = Th, Cm)) indicates that the An -Cp bonding is very ionic, increasingly so as the actinide becomes heavier. Caution is urged when using early actinide/lanthanide comparisons as models for minor actinides/middle lanthanides.
First author: Wong, Allison W., Reactions of aromatic N-heterocycles with a lutetium benzyl complex supported by a ferrocene-diamide ligand, DALTON TRANSACTIONS, 39, 6726, (2010)
Abstract: A comparison between the reactivity behavior of two lutetium benzyl complexes supported by different ferrocene-diamide ligands towards aromatic N-heterocycles, such as 1-methylimidazole, isoquinoline, and pyridines, is presented. The two ferrocene-diamide ancillary ligands differ in their nitrogen-donor substituent: adamantyl for one and t-butyldimethylsilyl for the other. The synthesis and characterization of the adamantyl-derived complex 1(Ad)-DME are reported. The ring opening of 1-methylimidazole by the THF analogue of 1(Ad)-DME, 1(Ad)-THF, was observed, analogously to the ring opening of the same substrate by the lutetium benzyl complex supported by the silyl-substituted ligand. Also, analogous products were observed in the reactions with isoquinoline.
First author: Pevny, Florian, How to elucidate and control the redox sequence in vinylbenzoate and vinylpyridine bridged diruthenium complexes, DALTON TRANSACTIONS, 39, 8000, (2010)
Abstract: Vinylbenzoate-bridged diruthenium complexes (RHC=CH)(CO)(P(i)Pr(3))(2)Ru(mu-4-OOCC(6)H(4)-CH=CH)-RuCl(CO)(P(i)Pr(3)) (2) (R = Ph, 3a or CF(3), 3b) and vinylpyridine-bridged (eta(6)-p-cymene)Cl(2)Ru(mu-NC(5)H(4)-4-CH=CH)RuCl(CO)(P(i)Pr(3))(2) (3c) have been prepared from their monoruthenium precursors and investigated with respect to the sequence of the individual redox steps and electron delocalization in their partially and fully oxidized states. Identification of the primary redox sites rests on the trends in redox potentials and the EPR, IR and Vis/NIR signatures of the oxidized radical cations and is correctly reproduced by quantum chemical investigations. Our results indicate that the trifluoropropenyl complex 3b has an inverse FMO level ordering (Ru1-bridge-Ru2 > terminal vinyl-Ru1 site) when compared to its styryl substituted counterpart 3a such that the primary oxidation site in these systems can be tuned by the choice of the terminal alkenyl ligand. It is further shown that the vinylbenzoate bridge is inferior to the vinylpyridine one with regard to charge and spin delocalization at the radical cation level. According to quantum chemical calculations, the doubly oxidized forms of these complexes have triplet diradical ground states and feature two interconnected oxidized vinyl ruthenium subunits.
First author: Zhang, Fu-Qiang, P6Mo18O73 heteropolyanion and its four-copper complex: theoretical and experimental investigation, DALTON TRANSACTIONS, 39, 8256, (2010)
Abstract: The non-classical KP6Mo18O73 heteropolyanion has been studied by the density functional theory (DFT) method, and the calculated geometry compares well with the experimental one. In fully oxidized [KP6Mo18O73](7-) state, the d(xy)-orbitals centered at eight “belt” Mo sites in the lower part of the “basket” are the major contributors to the LUMO and LUMO+1, while the LUMO+2 orbital is mostly focused on the two polar parts. In contrast, the HOMOs indicates that the coordination of the KP6Mo18 heteropolyanion to metal ions favorably occurs at the oxygen atoms from four external phosphates and two molybdates of the handle of the “basket”. Compared with Wells-Dawson [P2Mo18O62](6-), the HOMO-LUMO gap in fully oxidized [KP6Mo18O73](7-) is much smaller, indicating much easier reduction that is consistent with the cyclic voltammogram. Both frontier orbitals and Mulliken analysis indicate that two of three blue electrons in [KP6Mo18O73](10-) (KP6Mo18-3e) have spin alpha while third blue electron has spin beta, in agreement with magnetic data. The four-copper complex of the non-classical KP6Mo18-3e heteropolyanion has been synthesized and structurally characterized; its structure supports the theoretical results such as reactivity and basicity of external oxygen sites.
First author: Boulho, Cedric, The dehydrogenation of ammonia-borane catalysed by dicarbonylruthenacyclic(II) complexes, DALTON TRANSACTIONS, 39, 8893, (2010)
Abstract: The reactivity of ruthenacyclic compounds towards ammonia-borane’s dehydrogenation was investigated by considering both hydrolytic and anhydrous conditions. The study shows that the highly soluble mu-chlorido dicarbonylruthenium(II) dimeric complex derived from 4-tert-butyl, 2-(p-tolyl) pyridine promotes, with an activation energy E-a of 22.8 kcal mol(-1), the complete hydrolytic dehydrogenation of NH3BH3 within minutes at ca. 40 degrees C. The release of 3 eq. of H-2 entails the formation of boric acid derivatives and the partly reversible protonolysis of the catalyst, which produces free 2-arylpyridine ligand and a series of isomers of “Ru(CO)(2)(H)(Cl)”. Under anhydrous conditions, hydrogen gas release was found to be slower and the dehydrogenation of NH3BH3 results in the formation of conventional amino-borane derivatives with concomitant protonolysis of the catalyst and release of isomers of “Ru(CO)(2)(H)(Cl)”. The mechanism of the protonolysis of the ruthenacycle was investigated with state-of-the-art DFT-D methods. It was found to proceed by the concerted direct attack of the catalyst by NH3BH3 leading either to the formation of a coordinatively unsaturated “Ru(CO)(2)(H)(Cl)” species. The key role of “Ru(CO)(2)(H)(Cl)” species in the dehydrogenation of ammonia-borane was established by trapping and quenching experiments and inferred from a comparison of the catalytic activity of a series of dicarbonylruthenium(II) complexes.
First author: Kou, Hui-Zhong, Ferromagnetic coupling in oximato-bridged multi-decker Ni-II clusters, DALTON TRANSACTIONS, 39, 9604, (2010)
Abstract: Single-, double- and triple-decker oximato-bridged Ni(II) clusters based on pyridine-2-amidoxime (H(2)pyaox) have been synthesized and characterized. The decks have the same tetranuclear cationic units [Ni-4(Hpyaox)(2)(pyaox)(2)](2+) that are stably present in the reaction solution. Magnetic studies show that uncommon ferromagnetic exchange between the adjacent Ni(II) ions through the oxime bridges is operative in the compounds with the magnetic coupling constant (J) in the range 0.6-6.3 cm(-1) (H = -2JS(Ni1)S(Ni2)). Density function theoretical (DFT) calculations and the experimental data confirm that the N O bond distances of the bridging oxime group have a decisive effect in magnetic coupling. For the present Ni(II) species, the elongation of N-O bond distances are responsible for the switching from antiferromagnetic to ferromagnetic exchange with the critical bond distance of 1.394 angstrom.
First author: Durango-Garcia, Clara J., On the nature of the transition metal-main group metal bond: synthesis and theoretical calculations on iridium gallyl complexes, DALTON TRANSACTIONS, 39, 10588, (2010)
Abstract: The iridum-gallyl complex MeIr(PCy3)(2)(GaMe2)((ClGaMe3)-Ga-center dot) exhibits a short Ir-Ga bond length of 2.381(1)-2.389(2) angstrom. Theoretical calculations (ZORA BP86/TZ2P) support the presence of a Ir-Ga single bond but highlight a pi orbital contribution.
First author: Roy, Sayak, Tricarbonylrhenium(I) complexes of highly symmetric hexaazatrinaphthylene ligands (HATN): structural, electrochemical and spectroscopic properties, DALTON TRANSACTIONS, 39, 10937, (2010)
Abstract: The new mononuclear and dinuclear tricarbonylrhenium(I) complexes [(HATN)Re(CO)(3)Cl] (1-Cl) and [(mu-Me-6-HATN)[Re(CO)(3)Cl](2)] (2-Cl-2) of highly symmetric ligands HATN and Me-6-HATN were synthesized and structurally characterized. X-Ray crystal structures reveal identical strained aromatic systems and out of the plane fac-Re(CO)(3)Cl units for both complexes. The packing geometry in the unit cell of 1 suggests intermolecular pi-pi association. Infrared spectroelectrochemistry (SEC) experiments confirmed ligand-based reductions. To get more insight into the reduction mechanism the triflate salts, [(HATN)Re(CO)(3)](OTf) (1-OTf) and [(mu-Me(6)HATN){Re(CO)(3)}(2)](OTf)(2) (2-OTf2), were synthesized. Their electrochemical and spectroelectrochemical behavior also exhibits reduction of the aromatic systems. The electronic absorption spectral features of the one electron reduced species were studied by UV-vis-NIR spectroscopy, which shows a broad shoulder at 1500 nm, confirming intra-ligand charge transfer (ILCT). Density functional theory (DFT) calculations on the complexes 1-Cl and 2-Cl-2 for structural optimization show good agreement with experimental bond lengths and bond angles. The spin density plot shows a metal based HOMO and HATN ligand centered LUMO.
First author: Haghighi, Mohsen Golbon, Cyclometalated organoplatinum(II) complexes: first example of a monodentate benzo[h]quinolyl ligand and a complex with bridging bis(diphenylphosphino)ethane, DALTON TRANSACTIONS, 39, 11396, (2010)
Abstract: The cyclometalated complexes [Pt(ppy)R(SMe(2))] or [Pt(bhq)R(SMe(2))], where ppyH = 2-phenylpyridine, bhqH = benzo[h] quinoline and R = methyl or p-tolyl, react with bis(diphenylphosphino) ethane, dppe, in a 1 : 1 ratio to give the corresponding complexes [Pt(kappa(1)-C-ppy) R(dppe)] or [Pt(kappa(1)-C-bhq)R(dppe)], in which the ppy or bhq ligands are monodentate and dppe is chelating. The similar reaction in a 2 : 1 ratio gives the binuclear complexes [{Pt(ppy)R}(2)(mu-dppe)] or [{Pt(bhq)R}(2)(mu-dppe)], in which the dppe ligands are in the unusual bridging bidentate bonding mode.
First author: McGlone, Thomas, Assembly of titanium embedded polyoxometalates with unprecedented structural features, DALTON TRANSACTIONS, 39, 11599, (2010)
Abstract: Two titanium embedded polyoxometalates with unprecedented structural features are presented: a monotitanium containing tungstoantimonate Na13H3[TiO(SbW9O33)(2)]center dot 33H(2)O featuring a {Ti=O}(2+) moiety (1) and a hexatitanium containing tungstoarsenate K-6[Ti-4(H2O)(10)(AsTiW8O33)(2)]center dot 30H(2)O containing a {Ti-4(H2O)(10)}(16+) moiety (2). Both compounds have been fully characterised by single crystal X-ray diffraction, elemental analysis, IR and TGA. 1 is constructed from two alpha-B-{(SbW9O33)-W-III} fragments linked by five sodium cations and an unprecedented square pyramidal Ti(O)O-4 group with a terminal Ti O bond, and 2 exhibits a Krebs-type structure composed of two {AsTiW8O33} fragments, where one W(VI) centre has been substituted for a Ti(IV) centre in each, fused together via a belt of four additional Ti(IV) centres. This system represents the tungsten Ti-incorporated polyoxoanion with one of the highest Ti : W ratios so far reported. Additionally, 2 could also be isolated as an n-tetrabutylammonium salt and has been further characterised by electrochemistry and electrospray ionisation (ESI) MS studies. Due to the unique nature of these systems, both have been fully investigated using DFT calculations yielding highly interesting results. Structure 1 has been optimised with five sodium atoms in the belt position, which in addition to reducing the high charge of the cluster influence a stabilisation of the antimony lone pairs. Electrostatic potential calculations highlight the high electronegativity of the terminal oxygen on the titanium centre, enhancing real potentiality as a reactive site for catalysis.
First author: Schoene, Dana, A Distorted Trigonal Antiprismatic Cationic Silicon Complex with Ureato Ligands: Syntheses, Crystal Structures and Solid State Si-29 NMR Properties, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 39, 461, (2010)
Abstract: Insertion of phenyl isocyanate into the Si-N bond of N-(trimethylsilyl)diethylamine yields the N’-silylated N,N-diethyl-N’-phenylurea 1, which undergoes transsilylation with SiCl4 to yield the C-3-symmetric cationic hexacoordinate silicon complex 3s(+) [tris-K-O,N’-(N,N-diethyl-N’-phenylureato)siliconium] as chloride salt, which was characterized crystallographically. The cationic complex 3s(+) exhibits a distorted trigonal antiprismatic coordination sphere about the silicon atom with fac arrangement of the three N-atoms (and the three O-atoms) relative to one another. This C-3-symmetric complex undergoes isomerization into its asymmetric isomer 3a(+) (mer arrangement of NNN or OOO relative to one another) in CDCl3 solution. Hence, two Si-29 NMR signals appear and four sets of signals emerge in the H-1 and C-13 NMR spectra. Despite its pronounced axial symmetry, the Si-29 NMR shielding tensor of the cation 3s(+) in its chloride salt exhibits an unusually small span (less than 20 ppm), which was analyzed CP/MAS NMR spectroscopically and by computational methods.
First author: Conradie, Jeanet, Electronic Structure of an Iron-Porphyrin-Nitrene Complex, INORGANIC CHEMISTRY, 49, 243, (2010)
Abstract: Middle and late transition metal imido complexes (which may also be viewed as metal-nitrene adducts) are rather rare, especially for square-pyramidal and octahedral coordination geometries. However, an iron(II) porphyrin aminonitrene adduct, denoted here as Fe(Por)(NN), has been known for almost a quarter of a century. Unlike the corresponding S = 1 oxene and S = 0 carbene adducts, Fe(Por)(NN) exhibits an S = 2 ground state. DFT calculations reported herein provide a molecular orbital description of this unusual species as well as a rationale for its S = 2 ground state. The electronic configuration of Fe(Por)(NN) may be described as d(pi) (2)d(xy) (1)d(z2) (1)d(x2-y2) (1)d(pi’) (1), where the z direction corresponds to the Fe-NN axis. The stability and double occupancy of one of the d(pi) orbitals may be attributed to a pi-backbonding interaction with the N-N pi(star) orbital. The weak sigma-donor ability of the aminonitrene ligand results in a relatively low-energy d(z2) orbital and an overall d(z2) orbital splitting pattern that engenders a high-spin ground state.
First author: Cox, Hazel, Recent advances in the visible and UV spectroscopy of metal dication complexes,INTERNATIONAL REVIEWS IN PHYSICAL CHEMISTRY, 29, 555, (2010)
Abstract: Experimental techniques developed during the past 15 years have demonstrated that it is possible to prepare stable metal dication complexes, such as [Cu(NH3)N]2+ and [Ni(H2O)N]2+, in the gas phase. The significance of these complexes lies in the fact that they contain metal ions that are in their more common charge state, and therefore, a link between their properties and those found for the same ions in the condensed phase is readily accessible. In this review, we focus on one aspect of the study of these ion complexes, and that is their visible and ultraviolet (UV) spectroscopy. Current experimental techniques for recording spectra in the gas phase are discussed together with the theoretical methods required to interpret the spectra of metal dication complexes. An attempt is made to identify any barriers that might exist to measuring the optical spectra of metal dication complexes using current ion beam technology, where a typical experiment will involve measuring either photofragment yield or ion beam depletion as a function of laser wavelength. One very obvious area of spectroscopy to be explored, and one that is unique to transition metal complexes, is ligand field spectroscopy. Estimates of photofragment yields based on typical absorption cross sections and the kinetics of fragmentation highlight the difficulties involved in measuring such spectra. Of the theoretical techniques currently available for calculating spectral transitions, the method most commonly used for metal complexes is time-dependent density functional theory (TDDFT). Using selected examples, it is shown that although TDDFT is, for the most part satisfactory, extreme caution should be exercised when investigating the electronic states of open-shell complexes. An obvious conclusion to emerge is that a theoretical method that predicts the correct ground state geometry of an open-shell complex (and is free from spin contamination) does not necessarily yield the correct electronically excited states due to multi-electron character and/or spin contamination in the excited state manifold. It is anticipated that the development of experimental techniques that can record accurate electronic spectra will provide new and more demanding benchmarks for the refinement of theoretical methods.
First author: Shang, Honghui, Linear scaling electronic structure calculations with numerical atomic basis set,INTERNATIONAL REVIEWS IN PHYSICAL CHEMISTRY, 29, 665, (2010)
Abstract: We discuss in this review recent progress, especially by our group, on linear scaling algorithms for electronic structure calculations with numerical atomic basis sets. The principles of the construction of numerical basis sets and the Hamiltonian are introduced first. Then we discuss how to solve the single-electron equation self-consistently, and how to obtain electronic properties via post-self-consistent-field processes in a linear scaling way. The linear response calculation with linear scaling is also introduced. Numerical implementation is emphasized, with some applications presented for demonstration purposes.
First author: Woebkenberg, Paul H., Ambipolar organic transistors and near-infrared phototransistors based on a solution-processable squarilium dye, JOURNAL OF MATERIALS CHEMISTRY, 20, 3673, (2010)
Abstract: Implementation of organic transistors in low-end, large-volume microelectronics depends, greatly, on the level of performance that can be achieved, but also on the compatibility of the technology with low-cost processing methodologies. Here we examine the suitability of a family of solution-processable zwitterionic molecules, so-called squarilium dyes, for the fabrication of organic ambipolar transistors and their application in (opto)electronic circuits. Ambipolar organic semiconductors and transistors are interesting because they could deliver performance characteristics (i.e. noise margins and signal gain) similar to that of complementary logic, but with the fabrication simplicity associated with unipolar logic (i.e. single semiconductor material and single type of metal electrodes). By designing squarilium dyes with appropriate electrochemical characteristics we demonstrate single-layer organic transistors that exhibit ambipolar charge transport with balanced electron and hole mobilities. By integrating a number of these ambipolar transistors we are also able to demonstrate complementary-like voltage inverters with wide noise margin and high signal gain. Another interesting feature of the squarilium dyes studied here is their strong absorption in the near-infrared (NIR) region of the electromagnetic spectrum. By exploring this interesting property we are able to demonstrate NIR light-sensing ambipolar organic transistors with promising operating characteristics.
First author: Fu, Yi, Bonding and electronic structures in W@Au(12)AE complexes (AE= NO+, CO, BF, CN-, or BO-): analogies among ligands isoelectronic to carbon monoxide, JOURNAL OF MOLECULAR MODELING, 16, 9, (2010)
Abstract: A theoretical study on the geometries and electronic structures of W@Au(12)AE (AE=NO+, BF, CN-, or BO-) was carried out to gain insight into interactions between W@Au-12 and ligands isoelectronic with CO. The best configuration for the adsorption site is on-top type for all five complexes. After complexing with boron ligands (BF or BO-), the axial Au-W bond distance in W@Au-12 is lengthened notably, but NO+ has the opposite effect on the axial Au-W bond. A charge transfer and energy decomposition analysis shows that the metal-ligand bonds have enhanced sigma-donation strength from NO+ to BO-. Furthermore, the A-E bond strength in the complexes becomes weaker with stronger pi-back-donation interactions. Finally, W@Au12CO has the largest HOMO-LUMO gap, making it the most stable in terms of kinetic stability.
First author: Delgado-Jaime, Mario Ulises, Blueprint XAS: a Matlab-based toolbox for the fitting and analysis of XAS spectra, JOURNAL OF SYNCHROTRON RADIATION, 17, 132, (2010)
Abstract: Blueprint XAS is a new Matlab-based program developed to fit and analyse X-ray absorption spectroscopy (XAS) data, most specifically in the near-edge region of the spectrum. The program is based on a methodology that introduces a novel background model into the complete fit model and that is capable of generating any number of independent fits with minimal introduction of user bias [Delgado-Jaime & Kennepohl (2010), J. Synchrotron Rad. 17, 119-128]. The functions and settings on the five panels of its graphical user interface are designed to suit the needs of near-edge XAS data analyzers. A batch function allows for the setting of multiple jobs to be run with Matlab in the background. Aunique statistics panel allows the user to analyse a family of independent fits, to evaluate fit models and to draw statistically supported conclusions. The version introduced here (v0.2) is currently a toolbox for Matlab. Future stand-alone versions of the program will also incorporate several other new features to create a full package of tools for XAS data processing.
First author: Wu, Guohua, The UV photofragmentation spectroscopy of the metal dication complex [Mn(pyridine)(4)](2+),MOLECULAR PHYSICS, 108, 1199, (2010)
Abstract: A theoretical and experimental study has been undertaken of the gas phase UV photoexcitation spectrum of the metal dication complex [Mn(pyridine)(4)](2+). The ions have been prepared using a combination of the pick-up technique and high energy electron impact, and then held in a cold ion trap where they were excited with tuneable UV radiation. Spectra have been recorded by monitoring fragment ion yields as a function of laser wavelength following the excitation of [Mn(pyridine)(4)](2+) at wavelengths between 225 and 348 nm. For the range 225-263 nm the summation of photofragment ion intensities resulted in a spectrum that contained considerable structure. Although it has been possible to give regions of the spectrum a qualitative assignment to either metal-based or ligand-based transitions, a detailed comparison with results from the application of adiabatic time-dependent density functional theory (TDDFT) to provide an accurate assignment of the electronic transitions involved is considered unsound. This failure to model the excited state spectrum of the open-shell complex [Mn(pyridine)(4)](2+) is attributed to the significant double-and higher-excitation character of the excited states, which cannot be modelled by the strict single-electron excitations available from adiabatic TDDFT.
First author: Song, Ping, Theoretical investigation of electronic properties and redox properties for purely inorganic and aryloxide substituted Ti-containing POM derivatives, MOLECULAR PHYSICS, 108, 1553, (2010)
Abstract: DFT calculations have been performed to investigate the redox properties and electron transition for a series of purely inorganic and aryloxide substituted Ti-containing polyoxometalate (POM) derivatives. The modification of organic conjugated groups dramatically alters the HOMO population and decreases the energy gap. It is evident from redox analysis that Ti atoms are preferred redox centres in organic-inorganic hybrid Ti-containing POMs, and the incorporation of -conjugated groups evokes anodic shift for reduction potential. In contrast with mono-TiW5O18 derivatives, bi-TiW5O18 derivatives exhibit narrower energy gaps and more active redox properties. It is noteworthy that the attachment of -conjugated groups induces the low-energy electron transition to be a significant bathochromic-shift, and it has been dramatically red-shifted by 296 nm in compound 1c in contrast with that in compound 1a. When the two TiW5O18 units are covalently linked as terminals to construct bi-TiW5O18 derivatives, the low-energy electron transition presents further bathochromical shift compared with corresponding mono-TiW5O18 derivatives. In addition, the crucial charge transfer for the hybrid Ti-containing POMs are generated from -conjugated donor to d-Ti orbital with part of p-Oc orbitals. The incorporation of the organic substituents results in attached POMs by covalent linkage to the catalyst supports, which consequently enhances the ability of catalysis.
First author: Chong, Delano P., Density functional theory study on the electron spectra of 1,4-benzoquinone vapour,MOLECULAR PHYSICS, 108, 2459, (2010)
Abstract: The ionization and excitation spectra of valence and core electrons of 1,4-benzoquinone in the gas phase have been studied with density functional theory. The results are compared with available experimental data and previous calculations. New estimates and some new assignments are proposed for the ionization energies of both valence and core electrons and the calculated excitation energies agree well with experiment.
First author: Dunlap, Brett I., Variational fitting methods for electronic structure calculations, MOLECULAR PHYSICS, 108, 3167, (2010)
Abstract: We review the basics and the evolution of a powerful and widely applicable general approach to the systematic reduction of computational burden in many-electron calculations. Variational fitting of electron densities (either total or partial) has the great advantage, for quantum mechanical calculations, that it respects the stationarity property, which is at the heart of the success of the basis set expansion methods ubiquitous in computational chemistry and materials physics. The key point is easy. In a finite system, independent of whether the fitted charge distribution is constrained to contain the proper amount of charge, variational fitting guarantees that the quantum mechanical total energy retains the stationarity property. Thus, many-electron quantum mechanics with variational fitting of an electronic density in an incomplete density-fitting basis set behaves similarly as the exact quantum mechanical energy does when evaluated with an incomplete basis set to fit wavefunctions or spin-orbitals. Periodically bounded systems are a bit more subtle but the essential stationarity is preserved. This preservation of an exact property is quite distinct from truncation of the resolution of the identity in a basis. Variational fitting has proven to have benefits far beyond the original objective of making a Gaussian-orbital basis calculation of an early density functional computationally feasible. We survey many of those developments briefly, with guidance to the pertinent literature and a few remarks about the connections with Quantum Theory Project.
First author: Rejmak, Pawel, Electronic view on ethene adsorption in Cu(I) exchanged zeolites, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 12, 2321, (2010)
Abstract: Ethene adsorption on isolated Cu(I) sites in two types of zeolites (faujasite and MFI) is investigated by means of the embedded cluster method. Structures, energetic stabilities and C=C stretching vibrations in adsorption complexes are discussed. Furthermore, for interpretative purposes, the interaction energies are decomposed, using novel approaches based on so called natural orbitals for chemical valence. Ethene is always symmetrically bound to Cu(I) ion by both C atoms. In some cases two local minima of similar stability on the potential energy surface, differing by Cu(I) site relaxation can be found that may be simultaneously populated in equilibrium. Binding energies usually decrease with the degree of reconstruction of Cu(I) site after adsorption, however, in particular cases, a more distorted structure can be slightly more stable if favorable pi* back donation overwhelms the distortion effects. Calculated values of binding energies for Cu(I)-Y zeolite (about 80 kJ mol(-1)) agree well with microcalorimetric data. We predict that ethene binding in MFI is over two times stronger (to the best of our knowledge no experimental data are available). The C=C stretching frequency is not site specific, but depends only on the type of copper connectivity to oxygen nodes. The appearance of two C=C bands in IR spectra of Cu(I)-faujasite can be explained as the effect of coexistence of two types of adsorption complexes, with Cu(I) coordinated to one or two framework tetrahedrons, respectively. In Cu(I)-MFI, only one type of adsorption complex with Cu(I) ion coordinated to a single tetrahedron exists, as only a single C=C band is present in IR spectra.
First author: Li, Ping, The capture of H-center dot and (OH)-O-center dot radicals by vitamin C and implications for the new source for the formation of the anion free radical, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 12, 5256, (2010)
Abstract: To gain a better understanding of the antioxidation behaviors of vitamin C, the reactions between vitamin C (monoanionic form, AAH(-)) and two radicals, H-center dot and (OH)-O-center dot, have been investigated employing the B3LYP and BHandHLYP methods in combination with the atoms in molecules (AIM) theory and energy decomposition analyses (EDA). Both the radical additions to the five-membered ring of AAH(-) and H-abstraction reactions are explored. The reaction profiles of various reactions have been obtained. The most favorable active site to be attacked by radical addition has been confirmed to be the C2 site of AAH(-), which is different from that of the C3 site in the neutral vitamin C. The (OH)-O-center dot addition reactions are essentially diffusion-controlled processes, which is in contrast to the previous reports. A new source for the formation of the principal anion free radical (AFR) of AAH(-) has been observed in the (OH)-O-center dot attack process, i.e., AFR can be formed mainly from the H13 abstraction reaction involving two types of concerted proton-electron transfer (CPET) mechanisms. Moreover, the binding characters and formation mechanisms of the stable reaction complex formed during the formation of AFR have been systematically investigated.
First author: Villaume, Sebastien, Near sulfur L-edge X-ray absorption spectra of methanethiol in isolation and adsorbed on a Au(111) surface: a theoretical study using the four-component static exchange approximation, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 12, 5596, (2010)
Abstract: The relativistic four-component static exchange approach for calculation of near-edge X-ray absorption spectra has been reviewed. Application of the method is made to the Au(111) interface and the adsorption of methanethiol by a study of the near sulfur L-edge spectrum. The binding energies of the sulfur 2p(1/2) and 2p(3/2) sublevels in methanethiol are determined to be split by 1.2 eV due to spin-orbit coupling, and the binding energy of the 2p(3/2) shell is lowered from 169.2 eV for the isolated system to 167.4 and 166.7-166.8 eV for methanethiol in mono-and di-coordinated adsorption sites, respectively (with reference to vacuum). In the near L-edge X-ray absorption fine structure spectrum only the sigma*(S-C) peak at 166 eV remains intact by surface adsorption, whereas transitions of predominantly Rydberg character are largely quenched in the surface spectra. The sigma*(S-H) peak of methanethiol is replaced by low-lying, isolated, sigma*(S-Au) peak(s), where the number of peaks in the latter category and their splittings are characteristic of the local bonding situation of the sulfur.
First author: de Jong, Wibe A., Utilizing high performance computing for chemistry: parallel computational chemistry,PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 12, 6896, (2010)
Abstract: Parallel hardware has become readily available to the computational chemistry research community. This perspective will review the current state of parallel computational chemistry software utilizing high-performance parallel computing platforms. Hardware and software trends and their effect on quantum chemistry methodologies, algorithms, and software development will also be discussed.
First author: Wen, Shu-Hao, Revealing quantitative structure-activity relationships of transport properties in acene and acene derivative organic materials, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 12, 9267, (2010)
Abstract: The intermolecular electronic coupling (transfer integral) and the intramolecular vibronic coupling (reorganization energy) are key parameters determining the transport properties of organic electronic materials. Using quantum mechanism calculations, we revealed the correlation between the reorganization energies and the partial charge difference values on the conjugated acene backbone, which can be used to evaluate the reorganization energies for acene and acene derivative systems with the same conjugated backbone but different substitutional groups. We used rigorous quantitative functions to investigate the electronic coupling oscillation behavior in slipped-cofacial stacking acene and acene derivative molecules, and revealed characteristic parameters in the electronic coupling oscillation. We suggest using a similar strategy to establish the quantitative structure-activity relationship database for different families of organic semiconducting materials.
First author: Gabriel, Margaret A., Metallofullerenes as fuel cell electrocatalysts: A theoretical investigation of adsorbates on C59Pt, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 12, 9406, (2010)
Abstract: Nano-structured electrode degradation in state-of-the-art polymer electrolyte membrane fuel cells (PEMFCs) is one of the main shortcomings that limit the large-scale development and commercialization of this technology. During normal operating conditions of the fuel cell, the PEMFC lifetime tends to be limited by coarsening of the cathode’s Pt-based catalyst and by corrosion of the cathode’s carbon black support. Because of their chemical properties, metallofullerenes such as C59Pt may be more electrochemically stable than the Pt/C mixture. In this paper we investigate, by theoretical methods, the stability of oxygen reduction reaction (ORR) adsorbates on the metallofullerene C59Pt and evaluate its potential as a PEMFC fuel cell catalyst.
First author: Huix-Rotllant, Miquel, Assessment of noncollinear spin-flip Tamm-Dancoff approximation time-dependent density-functional theory for the photochemical ring-opening of oxirane, PHYSICAL CHEMISTRY CHEMICAL PHYSICS,12, 12811, (2010)
Abstract: Under the usual assumption of noninteracting nu-representability, density-functional theory (DFT) together with time-dependent DFT (TDDFT) provide a formally exact single-reference method suitable for the theoretical description of the electronic excited-states of large molecules, and hence for the description of excited-state potential energy surfaces important for photochemistry. The quality of this single-reference description is limited in practice by the need to use approximate exchange-correlation functionals. In particular it is far from clear how well approximations used in contemporary practical TDDFT calculations can describe funnel regions such as avoided crossings and conical intersections. These regions typically involve biradical-like structures associated with bond breaking and conventional wisdom would seem to suggest the need to introduce explicit double excitation character to describe these structures. Although this is lacking in ordinary spin-preserving (SP) TDDFT, it is present to some extent in spin-flip (SF) TDDFT. We report our tests of Wang-Ziegler noncollinear SF-TDDFT within the Tamm-Dancoff approximation for describing the avoided crossing in the C-2v CC ring-opening reaction of oxirane and for describing the conical intersection relevant for the more physical asymmetric CO ring-opening reaction of oxirane. Comparisons are made with complete active space self-consistent field and quantum Monte Carlo benchmark results from two previous papers on the subject [J. Chem. Phys., 2007, 127, 164111; ibid 129, 2008, 124108]. While the avoided crossing in the C-2v pathway is found to be reasonably well described, the method was found to be only partially successful for the conical intersection (CX) associated with the physically more important asymmetric pathway. The origin of the difficulties preventing the noncollinear SF-TDDFT method from giving a completely satisfactory description of the CX was traced back to the inability of SF-TDDFT based upon a single triplet reference state to correlate all potentially relevant configurations involving not just two but three nearly degenerate orbitals (n, sigma(CO), and sigma*(CO)). This article is also the first report of our implementation of SF-TDDFT within the DEMON2K program.
First author: Moens, Jan, A density functional theory study on ligand additive effects on redox potentials, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 12, 13174, (2010)
Abstract: Adiabatic energy differences Delta E-adiabatic are computed at density functional theory (DFT) level for the oxidation half reaction of [M(CO)(n)L6-n] complexes (M = Ru2+/3+, Os2+/3+, Tc2+/3+; L = CN-, Cl-, water, CH3CN, N-2 and CO). Linear trends in Delta E-adiabatic with respect to the substitution number n(CO) support the hypothesis of additive ligand effects on the redox potential. The values of the slope of these linear regression curves are shown to be independent of metal type (Ru, Os and Tc) and can therefore act as a ligand specific parameter. Based on these parameters, a computed electrochemical series was constructed, which was in good agreement with Pickett’s P-L, Lever E-L(L) and CEP parameters. The linearity in DEadiabatic is also reflected in the structural properties such as the M-CO bond distances of [M(CO)(n)L6-n] complexes. An energy decomposition analysis of the bond between the metal fragment and ligand gave an additional insight into the ligand’s bonding properties in terms of electrostatic and orbital contributions.
First author: Schmierer, T., Femtosecond spectroscopy on the photochemistry of ortho-nitrotoluene, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 12, 15653, (2010)
Abstract: The photo tautomerisations of ortho-nitrotoluene (oNT) and its methylated derivative ortho-ethylnitrobenzene (oENB) have been studied by means of femtosecond spectroscopy and (TD)-DFT computations. In UV/Vis transient absorption spectroscopy a band peaking at 400 nm is seen to rise in a bi-modal manner with time constants of 1-10 ps and 1500 ps. Femtosecond stimulated Raman experiments clearly identify aci-nitro forms as the spectroscopic carriers of the 400 nm band. The assignment of the Raman spectra is based on TD-DFT computations. The quantum yields of the aci-nitro forms after 3 ns are 0.08 (oNT) and 0.3 (oENB). The aci-nitro forms are formed via a singlet channel (1-10 ps) and a triplet channel (1500 ps). There are indications that the triplet channel involves a bi-radical intermediate. In between 3 ns and 1 ms the spectrum of the aci-nitro form shifts from 400 to 390 nm. This could indicate a tautomerisation from Z-aci-nitro to an E form.
First author: van Zeist, Willem-Jan, Halogen versus halide electronic structure, SCIENCE CHINA-CHEMISTRY, 53, 210, (2010)
Abstract: Halide anions X(-) are known to show a decreasing proton affinity (PA), as X descends in the periodic table along series F, Cl, Br and I. But it is also well-known that, along this series, the halogen atom X becomes less electronegative (or more electropositive). This corresponds to an increasing energy of the valence np atomic orbital (AO) which, somewhat contradictorily, suggests that the electron donor capability and thus the PA of the halides should increase along the series F, Cl, Br, I. To reconcile these contradictory observations, we have carried out a detailed theoretical analysis of the electronic structure and bonding capability of the halide anions X- as well as the halogen radicals X(center dot), using the molecular orbital (MO) models contained in Kohn-Sham density functional theory (DFT, at SAOP/TZ2P as well as OLYP/TZ2P levels) and ab initio theory (at the HF/TZ2P level). We also resolve an apparent intrinsic contradiction in Hartree-Fock theory between orbital-energy and PA trends. The results of our analyses are of direct relevance for understanding elementary organic reactions such as nucleophilic substitution (S(N)2) and base-induced elimination (E2) reactions.
First author: Muller, Alfred J., Characterization and Oxidative Addition Reactions of Different Rhodium and Iridium Triazolato Complexes, SOUTH AFRICAN JOURNAL OF CHEMISTRY-SUID-AFRIKAANSE TYDSKRIF VIR CHEMIE, 63, 11, (2010)
Abstract: A number of different rhodium(I) and iridium(I) triazolato complexes and their oxidative addition products (triazolate = 3,5-bis(pyridine-2-yl)-1,2,4-triazolate (bpt(-)) and 4-amino-3,5-bis(pyridine-2-yl)-1,2,4-triazolate (bpt-NH-)) were prepared and characterized by means of IR and H-1 NMR spectroscopy, elemental analysis and computational chemistry methods. The oxidative addition reactions of these complexes with iodomethane in different solvents indicated simple second-order kinetics with the faster reactions in the more polar solvents (1.44(7) x 10(-2) L mol(-1) s(-1) in dichloromethane compared with 9.2(5) x 10(-4) L mol(-1) s(-1) in benzene for iridium bpt-NH). H-1 NMR data and density functional theory calculations illustrate that the coordination of the metal centre in [M(bpt-NH)(cod)] (M = Rh or Ir) occurs via the amine moiety and a nitrogen of a pyridine ring.
First author: Petz, Wolfgang, Carbodiphosphoranes and Related Ligands, TRANSITION METAL COMPLEXES OF NEUTRAL ETA1-CARBON LIGANDS, 30, 49, (2010)
Abstract: The theoretical and experimental research on carbodiphosphoranes C(PR3)(2) and related compounds CL2, both as free molecules and as ligands in transition metal complexes, is reviewed. Carbodiphosphoranes are examples of divalent carbon(0) compounds CL2 which have peculiar donor properties that are due to the fact that the central carbon atom has two lone electron pairs. The bonding situation is best described in terms of L -> C <- L donor acceptor interactions which distinguishes CL2 compounds (carbones) from divalent carbon(II) compounds (carbenes) through the number of lone electron pairs. The structures and stabilities of transition metal complexes with ligands CL2 can be understood and predictions can be made considering the double donor ability of the carbone compounds.
First author: Breunig, Hans J., Reactions of Distibanes with [Fe-2(CO)(9)]: Synthesis, Structure and DFT Calculations of [(Et2Sb)(4)Fe-4(CO)(14)], [(nPr(2)Sb)(4)Fe-3(CO)(10)], [{(Me3SiCH2)(2)Sb}(4)Fe-2(CO)(6)], and [2-(Me2NCH2)C6H4SbFe2(CO)(8)], ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 636, 1090, (2010)
Abstract: The iron complexes [(Et2Sb)(4)Fe-4(CO)(14)] (1), [(nPr(2)Sb)(4)Fe-3-(CO)(10)] (2), [{(Me3SiCH2)(2)Sb}(4)Fe-2(CO)(6)] (3), and [2-(Me2NCH2)-C6H4SbFe2(CO)(8)] (4) were prepared by reactions of distibanes with Fe-2(CO)(9). Compounds 1-4 were characterized by X-ray diffraction, H-1-NMR and IR spectroscopy as well as mass spectrometry; complex 1 was additionally characterized by density functional calculations.