BICAPPED TETRAHEDRAL, TRIGONAL PRISMATIC, AND OCTAHEDRAL ALTERNATIVES IN MAIN AND TRANSITION GROUP 6 COORDINATION
BICAPPED TETRAHEDRAL, TRIGONAL PRISMATIC, AND OCTAHEDRAL ALTERNATIVES IN MAIN AND TRANSITION GROUP 6 COORDINATION
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DOI：
10.1021/ja00425a016
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发表时间：
1976-01-01
影响因子：
15
通讯作者：
ROSSI, AR
中科院分区：
文献类型：
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作者：
HOFFMANN, R;HOWELL, JM;ROSSI, AR
我们从理论上考察了二头四面体和三角棱镜作为六坐标主过渡基团化合物的共同八面体的替代品。六坐标硫对八面体几何结构的明显偏好通过分子轨道分析追溯到一对非键能级，其在非八面体几何结构中的高能量是由于配体-配体斥力的分子轨道等效。对于过渡元配合物，我们绘制了三角扭相互关联的八面体和三角棱柱极值的相关图。讨论了在电子较少的系统中三角棱镜的可能选择，以及降低三角棱镜对称条件下键合能量的策略。过渡金属配合物的二头四面体几何结构可以通过取代模式ML4D2来稳定，其中D是一个好的给体，M是一个d6金属中心。在主基团和过渡基团六坐标化合物中，八面体几何结构占主导地位。然而，在配位几何中，有越来越多的介于八面体和三棱柱体之间的三角棱柱配合物和结构。2®在六坐标锡和其他4族元素化学中发现了广泛的配位几何。有些六坐标过渡金属二氢化物，通式H2ML4，高度扭曲成双头四面体。目前存在一种独特的非氢化物，Fe (CO) 4 (Si (CH3) 3) 2，它表现出类似的畸变。我们还面临着六氟化氙令人着迷的结构问题。所有这些化合物本身都非常有趣，但到目前为止，它们加起来只是无数具有接近八面体几何形状的复合物中的一小部分。八面体或近八面体六坐标分子通常具有立体化学刚性。也许这通常是假设而不是证明，但我们在环境条件下分离了许多顺反同分异构体对ML4XY配合物，这是最直接的证明。在
We examine theoretically the bicapped tetrahedronand trigonal prism as alternatives to the common octahedron for six-coordinate mainand transition group compounds. The pronounced preference of six-coordinate sulfur for an octahe-dral geometry is traced by a molecular orbital analysis to a pair of nonbondinglevels, whose higher energy in the nonoctahe-dral geometries is due to the molecular orbital equivalent of a ligand-ligand repulsion. For transition element complexes we draw a correlation diagram for the trigonal twist interrelating octahedraland trigonal prismatic extremes. A possible prefer-ence for the trigonal prism in systems with fewd electrons is discussed, as well as a strategy for lowering the energy of the trigonal prismby symmetry-conditioned ir bonding. The bicapped tetrahedron geometry for transition metal complexes can be stabilized by a substitution pattern ML4D2 where D is a good donor and M is a d6 metal center.In main and transition group six-coordinate compounds the octahedral geometry predominates. There is, however, a growing class of trigonal prismatic complexes and structures intermediate between the octahedron and trigonal prism in coordination geometry. 2® In six-coordinate tin and other group 4 element chemistry a wide range of coordination geometries has been found. 2b Some six-coordinate tran-sition metal dihydrides, of the general formula H2ML4, are highly distorted toward a bicapped tetrahedron. 3 Presently there exists a unique non-hydride, Fe (CO) 4 (Si (CH3) 3) 2, which exhibits a similar distortion. 4 We also have the fasci-nating structural problem of xenon hexafluoride. 5 All these compounds, highly interesting in their own right, so far add up to but a small percentage of the myriad of complexes which assume a geometry close to octahedral. Octahedral or near-octahedral six-coordinate molecules are generally stereochemically rigid. Perhaps this is more often assumed than proven, but we have the most direct demonstration in the isolation, under ambient conditions, of many cis-trans isomeric pairs of ML4XY complexes. In