Molecular-orbital calculations on transition-metal cluster compounds containing six metal atoms

Abstract

Extended-Hückel calculations on model M6H6(M = Co or Ir) cluster compounds with octahedral, bicapped-tetrahedral, and trigonal-prismatic geometries are reported. The theoretical basis of the polyhedral skeletal electron-pair theory is discussed and the important role played by terminal and bridging ligands in such clusters is emphasised. The capping principle which has been used to rationalise the geometries of metal cluster compounds such as [Os6(CO)18] and [Os7(CO)21] is shown to have a quite general quantum-mechanical basis.