STUDIES ON COORDINATE BONDS IN POLYNUCLEAR COMPLEXES

多核配合物中桥接键的电子结构与其几何结构密切相关。考察了以下两种类型的配合物。采用杂化轨道、定域分子轨道、定域分子轨道的线性组合和非定域分子轨道等方法研究了R_2O_7^<n->型双核配合物中桥接键的电子结构与桥接氧键角的关系。在每种情况下，计算结果都显示出键角随中心(R)原子电负性的降低而增大的趋势，这与观察到的趋势一致。合理参数值计算得到的键角略小于实验键角。这种偏差被认为是键的部分离子特性的标志。在计算中使用的轨道类型中，在初等阶段应优先选择定域轨道；对于简单的离域分子轨道（没有模拟相互作用），键能仅轻微依赖于键角。研究了线性聚合物甲基桥[Be(CH_3)_2]_*、[Mg(CH_3)_2]_*和[LiAl(C_2H_5)_4]_*中五配位碳原子的特殊结构。由于碳的五共价不可能，首先研究了金属离子与CH_3^-(C_2H_5^-)配体的离子模型。在每个络合物中，离子之间的静电相互作用包括远程相互作用稳定了聚合物。然而，计算的ch_3桥的键角远大于观测值。另一方面，共价键能（相对值）的角度重叠处理使Be和Mg配合物的键角太小，而允许离子贡献的分子轨道处理使键角合理。在Li-Al配合物中，C-Al共价键比C-Li共价键强得多的模型，即Li^+[Al(CH_3)_4]_-所近似的模型，给出的键角与观测到的角一致。少

The electroinic structure of bridging bonds in polynuclear complexes was cprrelated with their geometrical structure. The two following types of complexes were examined.1. The relationship between the electronic structure of the bridging bond and the bond angle at the bridging oxygen in R_2O_7^<n->-type dinuclear complexes was examined by using hybridized orbitals, localized molecular orbitals, linear combinations of the localized molecular orbitals, and delocalized molecular orbitals. In every case, the results of calculation showed a tendency that the bond angle increases with decreasing electronegativity of the central (R) atom, in agreement with the observed tendency. The bond angles obtained from calculations with reasonable parameter values were slightly smaller than the experimental bond angles. This deviation was taken as a token of partial ionic character of the bonds. Among the types of orbitals used in the calculation, the localized ones should be preferred at an elementary … More stage ; with simple delocalized molecular obirtals (without cinfigulation interactions), the bond energy only slightly depended on the bond angle.2. The peculiar structure of five-coordinate carbon atom observed in the methy1 bridge of linear polymers, [Be(CH_3)_2]_*, [Mg(CH_3)_2]_*, and [LiAl(C_2H_5)_4]_*, was investtigated. Because of unlikeliness of five covalency of carbon, an ionic model with metal ions and CH_3^-(C_2H_5^-)ligands was first examined. In every complex, electrostatic interaction between ions including long-range interactions stabilized the polymer. However, the calculated bond angle of the CH_3-bridge was much greater than the observed. On the other hand, an angular overlap treatment of convalent bond energies (relative values) gave too small bond angles in the Be and Mg complexes, where a molecuar orbital treatment allowing for ionic contribution gave reasonable bond angles. In the Li-Al complex, a model where the C-Al covalent bond is much stronger than the C-Li one, i.e.a model approximated by Li^+[Al(CH_3)_4]_-, gave a bond angle consistent with the observed angle. Less