【摘要】 <正> 在讨论结构化学问题时,尽管人们都认识到成键的原子或原子团除了轨道相互作用外,它们的几何因素,如大小和形状也有着重要的影响.长期以来对这一问题进行定量而系统的研究却未受到应有的重视.由这些因素所带来的空间堆积作用在弱键化合物中的影响更为显著.f 电子组元素配合物与金属有机化合物的特点是:配位场稳定能低,主要呈离子键,方向性差和配位数高,因此配位体堆积相斥作用相对增强.近年来,这一领域的迅速发展为深入研究空间堆积效应准备了充分的条件.更多还原

【Abstract】 Two structural characters were found by mathematical treatment on more than130 structures of lanthanide coordination compounds.1.A region of packing saturation exists with the average SAS value 0.78 and thestandard deviation 0.05,thus demonstrating an equilibrium between steric effects andthe ligand field interaction.The former dominates above the“packing saturation”region and the compound tends to dissociate or to decompose.Bonding effect prevailsbelow the saturate region with effect of association,bridging or reactions which tend toincrease the steric crowding around the metal centre.2.The vector sums of coordinating ligands in each structures unacceptionallyapproach to zero with the average value of |(?)SAF·(?)| of the 130 struetures equal to 0.02and the standard deviation 0.015.It is therefore suggested that the gravity centre of thefirst order ligand packing tends to coincide with the metal centre.Such a phenomenoncould be explained that bonds between metal and the ligands are almost undirectionalwhereas steric repulsion among the ligands leads to a uniform distribution.It is thusreaching to a conclusion that,in weak bonding compounds,molecular geometry is notone which favours bonding to the maximum but rather one which reduces the localsteric tension to the least extent.更多还原