原子簇与有关分子的结构规则(Ⅰ)—(nxcπ)格式  

STRUCTURAL RULES OF CLUSTER COMPOUNDS AND RELATED MOLECULES (Ⅰ)

作　　者：徐光宪[1] Xu Guangxian(Department of Chemistry,Peking University,Beijing)

机构地区：[1]北京大学化学系

出　　处：《高等学校化学学报》1982年第S01期114-124,共11页Chemical Journal of Chinese Universities

摘　　要：包括原子簇在内的无机和有机分子可认为由若干分子片所组成,它们的结构类型可由四个数(nxcπ)来规定。文中提出七条结构规则来阐明原子簇及有关分子的结构和成键能力,并举例说明这些结构规则和(nxcπ)格式的应用,如由分子式估算结构类型,预测新的原子簇化合物及其可能的合成途径等。A number of structural rules and semi-empirical treatments have been proposed to elucidate the structure of cluster compounds. In the present paper I tried to use four numbers (nxcπ) to describe the structural types of clusters and related molecules.1. Organic and inorganic molecules including clusters are supposed to be composed of molecular fragments. A molecular fragment Mi consists of a central atom Ai and some ligands Lk attached to it, where i, j, k are numbers of valence electrons.2. Ligands are here defined as atomic groups attached to one or more central atoms. There are four types of bonds between the ligand and the central atom: (1) the ligand and the central atom each contributes one electron to form a covalent bond;(2) the ligand contributes a pair of electrons to the vacant orbital of the central atom to form a dative bond;(3) a pi ligand contributes all its pi electrons to form a bond with the central atom;(4) a bridging ligand may contribute one electron to form an electron-deficient three-center bond with two central atoms. Ligands may be classified according to the total number of valence electrons k they contribute to the central atom as shown in Table 1.3. Molecular fragments containing the same number of valence electrons i are called isoelectronic fragments and may be denoted by M1 and arranged in a form like the periodic table as shown in Table 2.4. The valency Vi of a fragment Mi is equal to the number of vacancies in the valence orbital of the fragment as shown in Table 3 and 4.5. The structural type of any molecule may be specified by a set of four numbers (nxcπ), wheren=no. of fragments, π=no. of pi bonds,c = no. of cycles in rings, polycyclic networks or clusters,x=Σxi, xi= 4-Vi= 4 +i-2(NVO)iTable 5 gives the formulas of x for various cases derived from the above general formula. Let B equal to the number of bonds between the n fragments in a molecule, then Table 6 summarizes the (xBcπ) values of n-fragment molecules of various structural types.6. In order to verify the above rule

关 键 词：结构规则 原子簇 分子片 成键能力 有机分子 合成途径 分子式 

分 类 号：O15[理学—数学]