Kinetics of the Reaction of Abstracting Hydrogen from Ethylene by Hydrogen Atom

Hydrogen abstraction reaction, H C2H4 --H2 C2H2 was studied by using A initio SCF method. Ge-ometries were fully optimized at SCF level and energies were computed at STO-3G basis set for reactants and transition state. Vibrational analysis was performed thereupon. Finally, the rate constant calculations were carried out at different temperatures for all range of reaction temperature according to Eyring's sbwlute reaction rate theory. The calculated activation energy is 12. 68 kcal/mol, lower than observed value (H. S kcal/mol) by 1. 82 kcal/mol only. The agreement of the calculated rate constants with the experiments is satisfactory.     

纳米硅胶颗粒的制备及其对金属离子的识别

利用sol-gel方法制得了纳米级的硅胶悬浮液.通过表面化学修饰引入了具有发射荧光能力的萘基基团.在稳态荧光研究中清晰地观察到在微小粒子表面上萘基基团会因溶剂不同而发生重新排组,并呈现出激基缔合物发光.研究了不同过渡金属离子对粒子表面荧光的猝灭效应,发现只有Cu2＋对纳米微球荧光有强烈的猝灭特征,这种优良的选择能力使其有望发展成为一种分析检测Cu2＋的荧光化学敏感器.     

SiHCl3-H2气相外延生长Si单晶反应机理的理论研究

采用密度泛函理论计算方法, 在B3LYP/6-311G*水平下, 计算并得到了SiHCl3与H2反应各反应通道上各驻点的构型、振动频率和能量. 结果表明, 在气相中SiHCl3分解的通道d和SiHCl3与H2反应的通道c为竞争反应, 但其均未还原出Si原子, 只有衬底Si参与SiHCl3-H2的反应, Si原子才淀积在Si衬底上.     

过渡金属配合物连接的多金属钒酸盐[Co(o-phen)]V2O6·H2O的水热合成和晶体结构

多金属氧酸盐 ( POMs)由于结构新奇 ,物理性能优异 ,在催化、医药、材料和光化学等领域有应用前景 ,而受到人们广泛关注 [1～ 8] .近年来 ,水热技术和有机指导剂的引入促进了 POMs的有机 -无机杂化材料如 [N( CH3) 4]5V18O4 6 [2 ]和 [V4 O10 ( phen) 2 ][3]等研究的迅速发展 .以上化合物多数仅以有机胺为抗衡离子或直接配位连接到无机骨架上 .而以过渡金属配合物为结构导向剂的合成策略 ,最近才引起人们的重视[9～ 11] .本文以钒酸盐 -过渡金属配合物作为研究体系 ,在水热条件下合成了一种未见文献报道的由新型过渡金属配合物连接的…     

Beiträge zur Chemie der Alkylverbindungen von Übergangsmetallen. 58. Zur Kenntnis von 2-(Dimethylaminomethyl)ferrocenyl-Verbindungen des Vanadiums,Molybdäns,Wolframs, Thoriums und Urans

Contributions to the Chemistry of Transition Metal Alkyl Compounds. 58 On 2-(Dimethylaminomethyl)ferrocenyl Compounds of Vanadium, Molybdenum, Tungsten, Thorium, and Uranium Earlier results according to which dimethylaminomethylferrocenyl groups (FcN) are able to form stable organometallic chelate compounds were confirmed by synthesis of the heterobimetallic chelate compounds (FcN)₂VO · Li(acac) II , (FcN)MoO₂(acac) III , (FcN)WOCl₃ IV , (FcN)Th(acac)₃ V , and (FcN)UO₂(acac) VI from the corresponding metal acetylacetonates or oxidchlorides and (FcN)Li I . The new compounds were characterized by elemental analysis, the i.r., ¹H-n.m.r., and electron spectra and by their effective magnetic moments.     

A Theoretical Study of Amine Bonding in Titanium Alkoxide Adducts

Summary. DFT calculations were carried out on Ti₂(OCH₃)₈ (NH₂CH₃)₂ and Ti₂(OCH₃)₈(NH₃)₂, which are model compounds for the previously isolated amine adducts Ti₂(OR)₈(NH₂ R′)₂. The calculations show that the Ti–N bond strength is weak; however, coordination of the amine to the metal center is supported by a N–H···O hydrogen bond of the amine with the neighboring alkoxo ligand. The Ti–N interaction is purely σ in nature, while the Ti–O interactions include both σ and π contributions. The lowest unoccupied molecular orbitals are mainly localized on Ti t_2g-like orbitals.     

不同软段结构聚氨酯-酰亚胺嵌段共聚物的合成及热性能研究

用二步法合成了不同软段 (PPO ,PEG ,PEPA)聚氨酯 酰亚胺 (PUI)嵌段共聚物 ,FTIR光谱表征了所有合成PUI分子主链均含有酰亚胺链段 ,并研究了PUI嵌段共聚物的热性能受软段类型及长度的影响 .DSC研究表明聚酯型PUI的软硬段之间的相容性比聚醚型PUI好 ,随相同软段分子量的增加 ,PUI体系的软硬段兼容性变差 ,并显示了相分离的特征 ;热失重 (TGA)研究得出不同软段的PUI样品的热稳定性大小顺序为 :PEPA PUI >PEG PUI>PPO PUI ;动态力学 (DMTA)研究给出了所合成的PUI样品在 5 0～ 2 0 0℃范围内均出现了较长的模量平台显示出有较好的耐热性 ,且随硬段含量的升高其储能模量不断增强     

Density functional calculations of NMR chemical shifts and ESR g-tensors

An overview is given on recent advances of density functional theory (DFT) as applied to the calculation of nuclear magnetic resonance (NMR) chemical shifts and electron spin resonance (ESR) g-tensors. This is a new research area that has seen tremendous progress and success recently; we try to present some of these developments. DFT accounts for correlation effects efficiently. Therefore, it is the only first-principle method that can handle NMR calculations on large systems like transition-metal complexes. Relativistic effects become important for heavier element compounds; here we show how they can be accounted for. The ESR g-tensor is related conceptually to the NMR shielding, and results of g-tensor calculations are presented. DFT has been very successful in its application to magnetic properties, for metal complexes in particular. However, there are still certain shortcomings and limitations, e.g., in the exchange-correlation functional, that are discussed as well. Received: 24 October 1997 / Accepted: 19 December 1997     

On the automatic restricted-step rational-function-optimization method

The rational function optimization algorithm is one of the widely used methods to search stationary points on surfaces. However, one of the drawbacks of this method is the step reduction procedure to deal with the overstepping problem. We present and comment on a method such that the step obtained from the solution of the rational function equations possesses the desired correct length. The analysis and discussion of the method is mainly centered on the location and optimization of transition states. Received: 18 June 1998 / Accepted: 17 September 1998 / Published online: 23 November 1998     

Effect of conformational rigidity on the glass transition and initial decomposition temperatures of polyimides

The dependence of the glass transition and initial decomposition temperatures of polyperyleneimide and polynaphthylimide on the conformational rigidity was studied by the Monte Carlo, Kuhn segment, and quantum chemical AM1 methods. The corresponding linear plots can be used for estimation of the glass transition and initial decomposition temperatures when experimental determination is difficult.