Fullerene C60 as a η5- and η6-ligand in sandwich-type π-complexes with transition metals

The molecular and electronic structures of some hypothetical sandwich-type -complexes of transition metals with fullerene C₆₀ were modeled. The M-C₆₀ bonds in ⁵-C₆₀MCp⁺ complexes (M = Fe, Ru, Os) are less strong than the M-Cp bonds in ferrocene, ruthenocene, and osmocene, respectively. The ⁶-C₆₀MC₆H₆ complexes (M = Cr, Mo, W) should be less stable than their classical analogs (C₆H₆)M(C₆H₆). The coordination of a metal atom with the fullerene at its pentagonal face is more energetically favorable than at a hexagonal face.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 598–601, April, 1994.We are grateful to V. I. Sokolov for discussion of the results obtained. This study was supported by the Russian Foundation for Basic Research (grants 93-03-4101 and 93-03-18725).     

Equilibrium structures of isolated (halogenated) fluorolithiomethanes

Equilibrium structures of isolated fluorolithiomethanes (1-3), chlorofluorolithiomethanes (4-6), bromofluorolithiomethanes (7-9), and bromochlorofluorolithiomethane (10) have been calculated at the HF/6-31+G(d,p) and MP2/6-31+G(d,p) levels. Depending on the number of halogens and the computational method employed, five distinct minimum structures could be recognized, viz. normal tetrahedral without coordination of halogen (T), trigonal bidentate with coordination of carbon and halogen to lithium (BCX), tetrahedral tridentate with coordination of carbon and two halogens to lithium (TCX2), quadrilateral bidentate with coordination of two halogens to lithium (BX2), and bipyramidal tridentate with coordination of three halogens to lithium (TX3).     

聚合物{[CuII(Hpb) (mal)]H2O}n :单体的量子化学计算和磁性研究

{[Cu^Ⅱ（Hpb）（mal）]H=O}n （Hpb=2-2＇-pyridylbenzimidazole, mal=maleic acid） is a helical chain-like polymer complex. In order to investigate the electronic structure of the complex, the monomer Cu^Ⅱ（Hpb）（mal） was obturated with different functional groups respectively. For these selective segments, the geometry optimizations were conducted by using hybrid DFT （B3LYP）methods to find that the structure obturated with H2O was better consistent with the experiment, and then this model would be used to latter calculations, such as the frontier molecular orbital and the NBO charge population analysis. In addition the magnetic behaviors of this complex were analyzed by experiments and the weak antiferromagnetic couple between copper（Ⅱ） ions was observed. The exchange coupling constant was calculated by DFT based on the spin broken symmetry formalism. The calculated coupling constants were in good agreement with the experimental data.     

Erratum: Separability between valence and conduction bands in transition metal clusters

Density Functional Theory (DFT) and direct ab initio molecular dynamics (MD) calculations were applied to the hydrogen molecule trapped in a water cluster composed of 12 water molecules (H₂O)₁₂. The static DFT calculation showed that the H₂ molecule is trapped in the center of mass of (H₂O)₁₂. The vibrational frequency of the H–H stretching mode of the H₂ molecule trapped in the water cluster was blueshifted from that in vacuo. On the other hand, the vibrational frequency of H₂ in water‐hydrogen 1:1 complex (H₂O–H₂) was redshifted. A direct ab initio MD calculation of H₂(H₂O)₁₂ at 50 K indicated that the H₂ molecule is rotated freely around the center of mass of the water cluster. The origin of the spectral shift of H₂ in water ice is discussed on the basis of the theoretical results. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Origin of visible-light-driven photocatalysis: A comparative study on N/F-doped and N-F-codoped TiO2 powders by means of experimental characterizations and theoretical calculations

An overall comparative study was carried out on N-doped, F-doped, and N-F-codoped TiO₂ powders (NTO, FTO, NFTO) synthesized by spray pyrolysis in order to elucidate the origin of their visible-light-driven photocatalysis. The comparisons in their experimentally obtained characteristics were based on the analysis of XPS, UV-Vis, PL, NH₃-TPD and ESR spectra. The comparisons in their theoretically predicted properties were based on the analysis of the calculated electronic structures. As the results, N-doping into TiO₂ resulted in not only the improvement in visible-light absorption but also the creation of surface oxygen vacancies. F-doping produced several beneficial effects including the creation of surface oxygen vacancies, the enhancement of surface acidity and the increase of Ti³⁺ ions. Doped N atoms formed a localized energy state above the valence band of TiO₂, whereas doped F atoms themselves had no influence on the band structure. The photocatalytic tests indicated that the NFTO demonstrated the highest visible-light activity for decompositions of both acetaldehyde and trichloroethylene. This high activity was ascribed to a synergetic consequence of several beneficial effects induced by the N-F-codoping.     

铂配位的腺嘌呤质子化的理论研究

用量子化学从头算研究一系列平面四方金属配体作用于腺嘌呤N₇位点对其质子化的影响。计算结果表明气相中，配合物质子化能力主要受长程静电效应影响，不同金属离子的影响差别甚微。综合考虑极性溶剂影响后长程静电效应影响显著降低。NBO电荷布居分析表明质子化位点电子云密度的变化直接影响该位点质子化能力。     

Carbon-Fluorine Bondings of Fluorinated Fullerene and Graphite

Carbon-fluorine bondings of fluorinated fullerenes and fluorine-graphite intercalation compound C_xF were investigated in detail on the basis of XPS data and the potential model using the charge distribution calculated by semiempirical method. It has been confirmed by the present study that two peaks in the C_1s spectra observed for fluorinated fullerenes are assigned to carbon atoms bonded to fluorine atoms and those unbound to fluorine atoms, and the small difference in charges and Madelung potentials of fluorine atoms in different circumstances well explains the single peak in F_1s spectra of fluorinated fullerenes. In the calculated structures of 1,3-C₆₀F₂ and 1,2-C₆₀F_x (x = 2?6) used as the models of C_xF, three kinds of carbon-fluorine bondings were observed corresponding to nearly ionic, semicovalent and covalent C? F bondings. The calculated result supports that the bi-intercalation structure of stage 1 C_xF consists of nearly ionic and semi-covalent fluorines.     

Semiempirical Molecular Orbital Studies of the Acylation Step in the Lipase‐Catalyzed Ester Hydrolysis

In this study, we present the results from the semiempirical molecular orbital calculations for the acylation step in the lipase‐catalyzed ester hydrolysis. The results reveal that the lowest energy path for the formation of the tetrahedral intermediate is for the serine residue of the catalytic triad to attack the substrate, followed by coupling heavy atom movement and proton transfer. The calculations of four active site models show that the cooperation of the aspartate group and the oxyanion hole is capable of lowering the activation energy by about 16 kcalmol^?1. Our results further suggest that the lipase‐catalyzed ester hydrolysis adopts the single proton transfer mechanism.     

环状芴基张力半导体拉曼光谱理论与实验研究

环状芴基张力半导体由于其特殊的分子结构，发射状排布的p轨道和纳米级空腔等诸多特点，引起了科学家广泛的关注.相对于直链型芴基半导体，环状芴基张力半导体展现出独特的光电性质.然而，迄今为止其振动性质没有被报道.对四元环芴的晶体与直链四聚芴粉末样品进行拉曼光谱表征和归一化处理，并结合理论计算.结果表明，与直链寡聚芴相比，环芴类似于碳纳米管的G峰发生了偏移，并且低频区域拉曼频移峰的峰强增加.其原因是由于张力的引入，改变了芴基主链的骨架和电子结构，加强芴骨架上π电子离域，同时使环芴中每个芴单元都参与到振动中.该研究结果为芴基张力半导体材料拉曼光谱的研究提供了一定的工作基础.     

Quantum chemistry study on B32 and B32H2–32

The structures of B32 and B₃₂H^2–₃₂ with I_h symmetry have been investigated by means of ab initio calculations at STO-3G level. The relationship between molecular orbitals of them has been analyzed and their bonding properties have been discussed. Then the possibility of their existence, as well as the similarity and difference between B₃₂ (B₃₂H^2–₃₂) and C₆₀ (C₆₀H₆₀) have been inferred.