三配位[CuCl_3]~-的电子结构、化学键和配位化学性质

用INDO法从正则分子轨道和定域分子轨道讨论了[CuCl_3]~-的电子结构和化学键,铜的4p轨道对成键贡献最大,3d轨道不参与成键。根据[CuCl_3]~-的HOMO和LUMO的原子轨道成份,讨论了它的配位化学性质。     

分子轨道成键性质及原子间化学键强度的成键能判据

本文定义了成键能Eb并用作分子轨道成键性质和分子中原子间化学键强度的判据。与Mulliken重叠布居Pb不同, 在成键能Eb中同时包含了原子轨道间的重叠因素和原子轨道的能量因素。对一些分子所作计算结果表明, 成键能判据较Mulliken重叠布居判据所得结论与实验更相符。     

定域分子轨道重心和分子结构的关系

本文讨论了定域分子轨道（ＬＭＯ）的重心和分子中化学键之间的关系，建立了利用定域分子轨道重心判断分子中成键情况及其化学键类型的方法，进而在ａｂ ｉｎｉｔｉｏ所得正则分子轨道（ＣＭＯ）定域化的基础上，计算了一些常见分子的ＬＭＯ重心；由此讨论了这些分子的化学键性质及其成键规律，探讨了一些化合物的反应性能。     

PdCO(OH)-体系中OH-助催化性能的成键能研究

本文使用相对论赝势从头计算方法和成键能判据[1 ] 研究了模型化合物 Pd CO(OH) -的电子结构 ,讨论了 OH-的助催化作用。得出 OH-对 Pd CO的助催化作用既可以通过其与金属 Pd形成化学键 (通过金属 )来实现 ,也可以通过空间电荷静电作用 (通过空间 )来实现。由分子轨道成键能分析指出 CO分子的强成键占据分子轨道 3σ和 1π的削弱是活化 CO的关键。     

镧系元素4f轨道在成键中的作用的理论研究

用密度泛函方法在冻结或不冻结4f轨道的条件下计算一系列含镧系元素双原子 分子,对结果进行分析,得出以下结论：镧系元素4f轨道按传统的化学键理论观点 是不直接参与成键的,但对成键有一定作用：通过与匹配物的轨道混合使键长变短 ,键能增加,一般可达百分之几。随着镧系原子序数的增加4f轨道对成键的贡献减 少。电负性高或价态高的匹配物对4f轨道的作用较强,4f轨道对成键的影响比较大 。对于重镧系元素,匹配物不是F或O时,4f轨道对成键的贡献相当小,可以看成芯 轨道,但对于轻稀土,在比较精确的计算中则应作为价轨道处理。镧系元素与氟结 合时,只有对靠近Yb的重镧系元素才可以把4f当作芯轨道,而与氧结合时即使对于 YbO把Yb4f作为芯轨道仍会带来较大误差。     

Ce(C_8H_8)_2和Ce(C_8H_8)_2~-的化学键性质

结合改进的重叠模型Xa-SW法和Ziegler过渡态法,通过将中心原子与配体的作用选成离子聚集、中心原子只有s和p轨道参与成键、中心原子只有d轨道参与成键、中心原子只有f轨道参与成键、中心原子的s、p、d和f轨道同时参与成键5种类型,从能量角度分析了Ce(C_8H_8)_2和Ce(C_8H_8)~-_2的化学键性质。     

硼烷缺电子多中心桥键的H-F力研究

Hellmann-Feynman静电力表现了分子中电荷分布及对各原子核的作用。H-F力的方向性可描述电子电荷的数量和位置,具有定量、形象和直观的特点,已在弯键的研究中显示出来。这一方法尚可用于多中心缺电子桥键的研究。 1 理论与方法 按LCAO-MO理论对H-F力进行分解,除有重叠力、极化力和屏蔽力外,还有一     

弱共价相互作用——不可忽略的分子间作用力

现有的化学教科书中将物质间的作用力分为化学键和分子间作用力。分子间作用力被描述为分子永久偶极和瞬间偶极引起的弱静电相互作用力。随着研究的深入,许多新的化学现象不能用现有的化学键和分子间作用力进行解释,而可以用原子轨道或分子轨道（用波函数描述）的弱重叠加以理解。文献中把这种既不同于普通化学键,又有别于教科书中所描述的分子间作用力的作用形式称为二级化学键,强调只在某些特别的物质中出现。本文通过对几种典型分子的结构和性质进行分析,认为二级化学键存在普遍性,可以看成是分子间的弱共价作用力,并认为这种弱共价作用是分子间作用力的重要组成部分。本文探讨了这种弱共价作用向化学键转化的可能性。     

PdCOM+(M=Li,Na,K)体系中M+的助催化性能的成键能研究

本文采用成键能判据探讨了模型化合物ＰｄＣＯＭ＾＋分子轨道成键性质和原子间化学键强度，进而说明Ｍ＾＋的助催化性能，得到与文献［２］和实验［３］相符的结论。     

稀土化合物化学键的共价性与4f轨道在其成键中的作用

稀土化学键的共价性和４ｆ 轨道在成键中的作用是化学界长期争论的问题之一。近年来的理论和实验研究结果表明,４ｆ 轨道参与了稀土化合物化学键的形成,稀土化学键具有相当大程度的共价性。４ｆ 轨道的参与比例和稀土化学键共价性成分的定量确定还需做大量的工作。     

希土冠醚配合物的电子结构

本文用INDO方法计算了希土冠醚配合物的分子构型、电子结构、电荷分布和键级,讨论了配位前后电荷分布特征,以及由于配位引起L→L_n电荷转移跟配合物电子结合能化学位移和配位活化的关系,解释了因冠醚内腔不同希土冠醚配合物呈现不同构型的内在原因。希土冠醚配合物的占据分子轨道以配位体轨道成分为主体(4f轨道除外),低空轨道以希土原子轨道成分为主体。其占据分子轨道可分为六组。冠醚环上引入苯环后配合物前线轨道呈现π键性质。其价键的主要贡献部份是5d轨道,其次是6p和6s。4f轨道基本上不参与成键。讨论了配合物的化学键性质及高配位数时稳定的因素。     

Topology and Chemistry

The determinants of chemical bonding are the chemical properties of the atoms and the constraints of three-dimensional (3-D) space into which the atoms must fit, but topology provides a convenient way of describing the resultant structure. This paper explores the topologies of various scalar fields associated with atoms in molecules and crystals and what they can tell us about chemical bonding. The scalar fields examined are the electron density, the electrostatic potential, and two simplified electrostatic potentials in which the contributions of the electron cores have been removed, namely the Madelung and the covalent field. Not all of the information contained in these fields is present in the topology but, since the topology is insensitive to the details of the field, it can often be determined using simplified calculations. Although the same topological model is used to explore all four fields, each field has its own distinctive topology and each provides different information about the nature of chemical bonding and structure. The analysis of these topologies, when combined with simple electrostatic theory and a few empirical observations, leads to a quantitative model of localized chemical bonding. In the process, the analysis provides insights into the nature of chemical bonding.     

Study on the covalence of Cu and chemical bonding in an inorganic fullerene-like molecule, [CuCl]_(20)[Cp~*FeP_5]_(12)[Cu-(CH_3CN)_2~+Cl~-]_5, by a density functional approach

The titled inorganic fullerene-like molecule (hereafter abbreviated as IFM) was recently synthe-sized by Bai et al.[1], which attracts a lot of interests from inorganic and organometallic chemists, and questions are raised for this smart molecule: (ⅰ) Why CuCl can react with Cp*FeP5 in solvent CH3CN to form IFM? (ⅱ) What is the nature of chemical bond-ing? (ⅲ) What is the covalence of Cu in this mole-cule? In this paper we intend to answer these questions in terms of the soft-hard …     

Role of core and valence atomic orbitals in the formation of chemical bonds

The general principles of the electronic structure of molecules and complexes are discussed. An analysis of photoelectron and x-ray photoelectron spectra reveals that in most cases, the interaction of the valence AO's results in the formation of delocalized MO's, which are populated by electrons, but are not bonding according to their energies (molecules with small atomic cores are exceptions). These MO's do not make a positive contribution to the exothermic effect of chemical bonding. The delocalization of the valence electrons in such MO's reduces their charge density in the region of the atomic cores and lowers the energy of the inner atoms-in-molecules levels as a result of the reduction of the internal shielding; the ESCA shifts of the inner electronic levels confirm this stabilization. In accordance with the virial theorem, the lowering of the energy of the core levels of the central atoms (with simultaneous, generally small changes in the energy of the core levels of the ligands and despite the significant destabilization of the delocalized MO's in comparison to the valence orbitals of the corresponding free atoms) makes up the main contribution to the energy of chemical bonds.This article is being published for purposes of discussion.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 5, pp. 572–578, September–October, 1986.     

Role of the electrons in inner valence MO's displayed in the x-ray photoelectron spectrum of the F2 molecule in its chemical bond

The results of a quantum-chemical calculation of the electronic structure of the F₂ molecule by the CNDO/2 and X-SW methods have been presented. The binding energies of the valence electrons calculated in accordance with Slater's transsition-state principle are in quantitative agreement with the experimental x-ray photoelectron data. The bonding character of the MO's has been evaluated on the basis of a calculation of the derivatives of the binding energy with respect to the internuclear distance and by determining the values of the orbital resonance energies, which characterize the covalent contribution of the electrons in different MO's to the chemical bonding in the molecule. It has been shown that the electrons in the inner valence 2_g MO make a significant contribution to the bonding of the atoms, which is only partially compensated by the antibonding properties of the 2_u* inner valence MO. The predominant participation of the 2s AO's of the fluorine atoms in the formation of the 2_g and 2_u* inner valence MO's has been established and is the reason for their significant stabilization and smaller energy splitting in comparison of other diatomic molecules, for example, N₂. The specific feature of these MO's determine the clearly expressed bonding character of the 3_g MO, which is caused by the predominant interaction of the fluorine 2p AO.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 2, pp. 211–217, March–April, 1985.     

外电场作用下三元环状水分子团簇的特性研究

The influence of an external field on the ground states energy and dipole moment of the cyclic water trimer is investigated. Employing the Hartree-Fork method with basis sets 3-21G. The field-induced H-F force including the internal and external forces and clusters equilibrium structures under balance of this force are analyzed. The external field is varied in the 0.001~0.01 a.u. range. It is shown that the magnitude of the external electric field has important effects on these characteristics of the cyclic water trimer. The energy was found to decrease and the dipole moment to increase with the increasing external field. The change of the electronic population of every atom leads the electrostatic field to vary accordingly.     

鸟嘌呤与氨基酸残基体系的极化力场

发展了应用于鸟嘌呤G和氨基酸残基体系的浮动电荷力场, 该力场明确定义了孤对电子和键的电荷和位置, 通过电荷随着环境的浮动来体现极化效应; 通过氢键拟合函数k_HB描绘了氢键键能. 应用量子化学方法, 对G与氨基酸残基体系从氢键、 几何结构及电荷分布3个方面展开计算及分析, 并以其为基准, 确定参数发展了适用于G与氨基酸残基氢键体系的ABEEMσπ PFF. 采用3种不同力场模拟目标分子的结构和性质. 模拟结果表明, 发展的ABEEMσπ PFF与量子化学方法具有最好的一致性, 可用于模拟生物大分子体系.     

原子力显微镜中化学成键对力的贡献

迄今非接触原子力显微镜已经成为一个非常强大的工具. 它不仅能够得到表面的原子周期结构,还能给出分子内部的化学键信息. 针尖和样品之间的相互作用是原子力显微镜的有效信号,主要包括三种,即范德瓦尔斯相互作用、静电相互作用和化学键相互作用. 本文在生长于Si(111)-7×7 的铅薄膜上测量了针尖和样品之间的化学键相互作用. 通过获取该相互作用随偏压的变化,并且利用抛物线拟合有效局域接触势的位置,我们发现它是随着针尖和样品之间距离的增大而减小的. 这种趋势来自于针尖和样品之间波函数的交叠. 从而可以得到电子的衰减长度. 我们还测量到了该衰减长度随着铅薄膜厚度的变化会发生振荡,这种振荡归因于平顶楔形铅岛内电子的量子尺寸效应.     

Exploring aromatic chemical space with NEAT: novel and electronically equivalent aromatic template

In this paper, we describe a lead transformation tool, NEAT (Novel and Electronically equivalent Aromatic Template), which can help identify novel aromatic rings that are estimated to have similar electrostatic potentials, dipoles, and hydrogen bonding capabilities to a query template; hence, they may offer similar bioactivity profiles. In this work, we built a comprehensive heteroaryl database, and precalculated high-level quantum mechanical (QM) properties, including electrostatic potential charges, hydrogen bonding ability, dipole moments, chemical reactivity, and othe properties. NEAT bioisosteric similarities are based on the electrostatic potential surface calculated by Brood, using the precalculated QM ESP charges and other QM properties. Compared with existing commercial lead transformation software, (1) NEAT is the only one that covers the comprehensive heteroaryl chemical space, and (2) NEAT offers a better characterization of novel aryl cores by using high-evel QM properties that are relevant to molecular interactions. NEAT provides unique value to medicinal chemists quickly exploring the largely uncharted aromatic chemical space, and one successful example of its application is discussed herein.