金属团簇的超原子分子理论

选取合适的金属团簇(超原子)作为结构基元,进而组装形成新的团簇或晶体材料是团簇科学中一个有趣且充满挑战的课题,受到了实验和理论研究者的广泛关注.通过超原子组装这种"自下而上"的组装方式,可以获得具有特定物理化学性质的新材料.但是,长久以来针对如何进行超原子组装并无清晰、统一的理论认识,超原子组装基本等同于超原子的任意堆砌或拼接.那么,超原子能否像原子那样通过特定化学键形成分子或晶体?超原子间如何成键?超原子组装是否有一定模式可循?为了回答这些问题,我们提出了一个唯象理论:超原子分子理论.该理论的核心是构建超原子间的成键规则,将涉及超原子的"超级化学键"概括为3种类型,即超级共价键、超级杂化键和超级非键.超原子可以通过超级化学键结合形成超原子分子或超原子晶体.同时,超原子分子理论指出,超原子具有几何结构不同但电子结构相似的异构体,这些异构体称为"等同超原子".等同超原子同样可以作为组装基元,通过超级化学键进行结合.另外,针对包含复杂成键类型的团簇体系,超原子分子理论概括出了两种超原子组装模式,分别称为超原子网络和杂化超原子网络.综上所述,超原子分子理论包含了对超原子间成键规则的理解,对超原子组装基元的思考以及对超原子组装模式的认识.超原子分子理论的相关内容不仅可以为超原子组装提供系统的理论依据,而且可以对特殊团簇结构的稳定性给出合理解释,还可以为新型团簇的结构设计以及实验合成提供理论指导.     

电负性平衡与A—B键离子性百分数的估算

电负性平衡与Ａ—Ｂ键离子性百分数的估算海邦胜（华东冶金学院，２４３００２）众所周知，在化学中化学键的特征对认识化合物的物理和化学性质占有重要地位，化学键的特征又是成键原子的价电子运动状态变化的反映，这种反映可以用成键元素原子的电负性来表征。自３０年代...     

二元化合物鍵的极性程度的计算

分子中原子间化学键的极性程度,是指两个成键原子之间的电子偏移的数量,即与共价键相比较电子云(指价电子而言)重心从原子间距离的中心偏移的百分率。这数值可以用来表示化学键的极性程度,Pauling称之为“离子性百分率”,也可以叫做键极性指数。关于键的极性程度的计算,三十年来,提出的经验     

成键能力大的杂化轨道形成共价键的键能也大吗?

在我们的许多教科书中,当讲到原子轨道杂化的原因时,都是这样叙述的:杂化轨道具有更强的方向性,伸展得更远,可以与其他原子的原子轨道进行更大程度的重迭,从而提高成键能力,形成更牢固的化学键,使分子更加稳定。于是给学生形成了这样一个“基本概念”,“杂化轨道的成键能力越大,形成的共价键键能     

过渡金属络合物成键本质分析的常用方法

过渡金属络合物中过渡金属与配体间所形成的化学键的成键本质,可以在理论化学基础上,采用定量的方法进行分析。本文重点以铁羰基络合物为例,对常用的分析方法,如自然键轨道方法(NBO)、电荷分解分析(CDA)、分子中的原子(AIM)拓扑分析方法以及ETS和EDA能量分解方法等,在应用中的优缺点进行了分析和评述。借助于这些方法提供的电荷、能量和电子密度等配分项可以深刻认识和理解过渡金属-配体间形成的化学键的成键本质。     

Eu2+掺杂硼酸盐系列发光晶体化学键参数的计算

利用复杂晶体化学键理论对Eu^2 掺杂的硼酸盐晶体Ba2LiB5O10,Ba2MgB2O6,Ba2Be2B2O6,BaLiBO3,SrB4O7和SrAl2B2O7的化学键参数进行了理论计算，结果表明，在不同的晶体中掺杂离子与配位原子间形成的共价键的键性是不同的，这种差异的产生是由于成键原子的性质、配位数以及键长的不同而造成的。     

α-Al2O3(0001)表面吸附ZnO的DFT研究

建立了α-Al2O3(0001)2×1表面薄片吸附模型,采用基于DFT动力学赝势方法,对ZnO分子的吸附生长进行了计算.详细地研究了ZnO分子在表面吸附的成键方式以及表面化学键特性.在较稳定的吸附位上,ZnO化学键[(0.185±0.01)nm]与最近邻的表面Al—O键有30°的偏转角度,Zn在表面较稳定的化学吸附位置偏离表面O六角对称约30°.通过吸附能量、原子布居数和态密度的分析,ZnO的O2-与表面上的Al3+形成的化学键表现出强离子键特征;而Zn2+同基片表面O2-形成的化学键有明显的共价键成分.     

关于原子轨道杂化及有关化学现象的讨论

本文根据多原子分子中键角、键的共价强度及键长等化学结构数据和事实,总结其间的变化规律及联系,说明了原子间的共价成键作用及成键过程中的电子相关作用是原子轨道杂化的原因和动力。据此讨论和解释了多原子分子中的杂化类型和一些分子的异常立体构型,对惰性电子对效应的概念和原因提出新的看法。     

基于计算化学的探究式共价键教学设计

针对共价键教学中存在的问题,探讨了将计算化学技术作为探究工具,引入到共价键探究教学过程中。通过共价键形成过程中轨道重叠程度、键长和体系能量变化等数据,深刻揭示共价键成键的本质,给学生专家级的探究体验。同时强调化学学科方法思想和知识准备的作用,使探究活动更具科学价值。     

键连接性指数的建构及其在有机体系中的应用研究

以化学键为基础建构了键连接性指数及分子键连接性指数，该指数同时考虑顶 点原子的化学特征及键的性质．对于任意化学键，键连接性指数Si＝1+△I/R·[（ Z1-h1)m2/n1+(Z2-h2)m1/n2]，分子键连接性指数S为∑i=1^m√Si或∑i=1^m1/√ Si，其中，Z1，Z2为化学键键连原子的价电子数；n1，n2成键原子的价层最高主量 子数；m1，m2为成键原子的氧化数；h1，h2为与成键原子相连的氢原子个数；△I 为成键原子的电负性差(△I≥0)；R为化学键的相对键长．与以顶点为基础的价连 接性指数不同，该指数不仅能方便而有效地应用于饱和碳氢体系亦能有效地应用于 含多重键的不饱和体系及含杂原子的有机体系．研究了饱和碳氢体系标准生成焓， 不饱和碳氢体系和酮、醚、酯体系在水中的溶解度和辛醇/水分配系数，卤代甲烷 体系的标准生成焓，卤代苯体系辛醇/水分配系数，均取得比较满意的结果。     

Bismuth in Dynamic Covalent Chemistry: Access to a Bowl-Type Macrocycle and a Barrel-Type Heptanuclear Complex Cation

Dynamic covalent chemistry (DCvC) is a powerful and widely applied tool in modern synthetic chemistry, which is based on the reversible cleavage and formation of covalent bonds. One of the inherent strengths of this approach is the perspective to reversibly generate in an operationally simple approach novel structural motifs that are difficult or impossible to access with more traditional methods and require multiple bond cleaving and bond forming steps. To date, these fundamentally important synthetic and conceptual challenges in the context of DCvC have predominantly been tackled by exploiting compounds of lighter p-block elements, even though heavier p-block elements show low bond dissociation energies and appear to be ideally suited for this approach. Here we show that a dinuclear organometallic bismuth compound, containing BiMe₂ groups that are connected by a thioxanthene linker, readily undergoes selective and reversible cleavage of its Bi−C bonds upon exposure to external stimuli. The exploitation of DCvC in the field of organometallic heavy p-block chemistry grants access to unprecedented macrocyclic and barrel-type oligonuclear compounds.     

Substituent Effects on the Hydrogen Bonding Between Phenolate and HF, H2O and NH3

IntroductionSubstituent effects have been well known forthe covalently bonded systems for many years,they have found tremendous applications in medicalchemistry,biochemistry,organic chemistry,andmaterial chemistry[1] . In fact,the studies ofsubstituent effects have greatly contributed to ourunderstanding of chemical mechanisms,and theestablishments of many chemical theories haveheavily relied on the observed substituent effects.However,it turns out that little have beenknown so far the substit…     

质子酸的酸性强弱比较

酸碱质子理论是大学无机化学教学中最重要的概念之一,溶液中的酸碱强弱的比较虽然可以通过查找酸碱解离常数来得到,但在数据缺失情况下的定性比较酸碱强弱在教学中也很重要,而且这种比较可以帮助学生理解物质结构与性质之间的相关性。本文根据质子酸碱的化学组成和分子结构分析它们的酸碱性,并主要根据分子结构信息,包括键的极性、键的强度、键的离域、氢键、分子中键的环境等,推导、比较它们酸碱性的相对强弱。     

On Electrostatics,Covalency, and Chemical Dashes: Physical Interactions versus Chemical Bonds

The increasing availability of real-space interaction energies between quantum atoms or fragments that provide a chemically intuitive decomposition of intrinsic bond energies into electrostatic and covalent terms [see, for instance, Chem. Eur. J. 2018 , 24, 9101] provides evidence for differences between the physicist's concept of interaction and the chemist's concept of a bond. Herein, it is argued that, for the former, all types of interactions are treated equally, whereas, for the latter, only the covalent short-range interactions have actually been used to build intuition about chemical graphs and chemical bonds. This has led to the bonding role of long-range Coulombic terms in molecular chemistry being overlooked. Simultaneously, blind consideration of electrostatic terms in chemical bonding parlance may lead to confusion. The relationship between these concepts is examined herein, and some notes of caution on how to merge them are proposed.     

Integrating replication-based selection strategies in dynamic covalent systems

In the past 15 years, the chemistry of reversible covalent bond formation (dynamic covalent chemistry (DCC)) has been exploited to engineer networks of interconverting compounds known as dynamic combinatorial libraries (DCLs). Classically, the distribution of library components is governed by their relative free energies, and so, processes that manipulate the free energy landscape of the DCL can influence the distribution of library members. Within the same time frame, the design and implementation of molecules capable of copying themselves--so-called replicators--has emerged from the field of template-directed synthesis. Harnessing the nonlinear kinetics inherent in replicator behavior offers an attractive strategy for amplification of a target structure within a DCL and, hence, engendering high levels of selectivity within that library. The instructional nature of replicating templates also renders the combination of replication and DCC a potential vehicle for developing complex reaction networks; a prerequisite for the development of the emerging field of systems chemistry. This Concept article explores the role of kinetically and thermodynamically controlled processes within different DCC frameworks. The effects of embedding a replicating system within these DCC frameworks is explored and the consequences of the different topologies of the reaction network for amplification and selectivity within DCLs is highlighted.     

Observing the 3D Chemical Bond and its Energy Distribution in a Projected Space

Our curiosity-driven desire to “see” chemical bonds dates back at least one-hundred years, perhaps to antiquity. Sweeping improvements in the accuracy of measured and predicted electron charge densities, alongside our largely bondcentric understanding of molecules and materials, heighten this desire with means and significance. Here we present a method for analyzing chemical bonds and their energy distributions in a two-dimensional projected space called the condensed charge density. Bond “silhouettes” in the condensed charge density can be reverse-projected to reveal precise three-dimensional bonding regions we call bond bundles. We show that delocalized metallic bonds and organic covalent bonds alike can be objectively analyzed, the formation of bonds observed, and that the crystallographic structure of simple metals can be rationalized in terms of bond bundle structure. Our method also reproduces the expected results of organic chemistry, enabling the recontextualization of existing bond models from a charge density perspective.     

Density functional energy decomposition into one- and two-atom contributions

The present work provides a generalization of Mayer's energy decomposition for the density-functional theory (DFT) case. It is shown that one- and two-atom Hartree-Fock energy components in Mayer's approach can be represented as an action of a one-atom potential V(A) on a one-atom density rho(A) or rho(B). To treat the exchange-correlation term in the DFT energy expression in a similar way, the exchange-correlation energy density per electron is expanded into a linear combination of basis functions. Calculations carried out for a number of density functionals demonstrate that the DFT and Hartree-Fock two-atom energies agree to a reasonable extent with each other. The two-atom energies for strong covalent bonds are within the range of typical bond dissociation energies and are therefore a convenient computational tool for assessment of individual bond strength in polyatomic molecules. For nonspecific nonbonding interactions, the two-atom energies are low. They can be either repulsive or slightly attractive, but the DFT results more frequently yield small attractive values compared to the Hartree-Fock case. The hydrogen bond in the water dimer is calculated to be between the strong covalent and nonbonding interactions on the energy scale.     

HF,Ne等电子体系对内对间电子相关能的比较研究

采用MELD程序ROHF－OPT1方法在MP2/6-311++G(d)水平上,计算了HF分子基态1^∑和Ne原子基态1^S的对内对间电子相关能,并对两等电子体系的对相关能进行了分析和比较,深入研究两等电子体系对内对间相关能所具有的共同规律和存在的差异性,通过比较说明分子内的化学键是影响电子相关能的重要因素之一。HF分子和Ne原子两体系三重激发和四重激发对体系电子相关能的贡献的计算结果表明高激发项对电子相关能的贡献在精确量子化学计算中是不可以忽略的。     

H2XP…SHY复合物中磷键与硫键的理论研究

用从头算量子化学方法MP2 与CCSD(T)研究了H₂XP和SHY (X, Y=H, F, Cl, Br)分子的P与S之间形成的磷键X―P…S与硫键Y―S…P的本质与规律以及取代基X与Y对成键的影响. 计算结果表明, 硫键比磷键强, 连接在Lewis 酸上的取代基的电负性增大导致形成的磷键或硫键增强, 键能增大, 对单体的结构和性质的影响也增大; 而连接在Lewis 碱上的取代基效应则相反. 硫键键能为8.37-23.45 kJ·mol^-1, 最强的硫键结构是Y 电负性最大而X 电负性最小的HFS…PH₃, CCSD(T)计算的键能是16.04 kJ·mol^-1; 磷键键能为7.54-14.65 kJ·mol^-1, 最强的磷键结构是X 电负性最大而Y 电负性最小的H₂FP…SH₂, CCSD(T)计算的键能是12.52 kJ·mol^-1. 对磷键与硫键能量贡献较大的是交换与静电作用. 分子间超共轭lp(S)-σ^*(PX)与lp(P)-σ^*(SY)对磷键与硫键的形成起着重要作用, 它导致单体的极化, 其中硫键的极化效应较大, 从而有一定的共价特征.     

Why are the Homoleptic Diyl Complexes M(InR)4 with M = Ni and Pt Stable Compounds while only Ni(CO)4 but not Pt(CO)4 can become Isolated? A Theoretical Study of M(EMe)44 and M(CO)4 (M = Ni,Pd, Pt; E = B,Al, Ga,In, Tl)

The equilibrium geometries and first bond dissociation energies of the homoleptic complexes M(EMe)₄ and M(CO)₄ with M = Ni, Pd, Pt and E = B, Al, Ga, In, Tl have been calculated at the gradient corrected DFT level using the BP86 functionals. The electronic structure of the metal‐ligand bonds has been examined with the topologial analysis of the electron density distribution. The nature of the bonding is revealed by partitioning the metal‐ligand interaction energies into contributions by electrostatic attraction, covalent bonding and Pauli repulsion. The calculated data show that the M‐CO and M‐EMe bonding is very similar. However, the M‐EMe bonds of the lighter elements E are much stronger than the M‐CO bonds. The bond energies of the latter are as low or even lower than the M‐TlMe bonds. The main reason why Pd(CO)₄ and Pt(CO)₄ are unstable at room temperature in a condensed phase can be traced back to the already rather weak bond energy of the Ni‐CO bond. The Pd‐L bond energies of the complexes with L = CO and L = EMe are always 10 — 20 kcal/mol lower than the Ni‐L bond energies. The calculated bond energy of Ni(CO)₄ is only D_o = 27 kcal/mol. Thus, the bond energy of Pd(CO)₄ is only D_o = 12 kcal/mol. The first bond dissociation energy of Pt(CO)₄ is low because the relaxation energy of the Pt(CO)₃ fragment is rather high. The low bond energies of the M‐CO bonds are mainly caused by the relatively weak electrostatic attraction and by the comparatively large Pauli repulsion. The σ and π contributions to the covalent M‐CO interactions have about the same strength. The π bonding in the M‐EMe bonds is less than in the M‐CO bonds but it remains an important part of the bond energy. The trends of the electrostatic and covalent contributions to the bond energies and the σ and π bonding in the metal‐ligand bonds are discussed.