Extended Hückel molecular-orbital calculations on dodecahedral metalloboranes which do not conform to the polyhedral skeletal electron-pair theory

Abstract

Extended Hükel molecular-orbital calculations on the model complexes [B₄H₄(CoL₃)₄]⁴⁺ and B₄H₄(CoL₃)₄, where L = a two-electron σ-donor ligand, have established the electronic factors responsible for the breakdown of the polyhedral skeletal electron-pair theory when applied to B₄H₄[Co(η-C₅H₅)]₄ and B₄H₄[Ni(η-C₅H₅)]₄. In addition the observation that B₄H₄[Co(η-C₅H₅)]₄ and B₄H₄[Ni(η-C₅H₅)]₄ adopt alternative D_2d structures based on the dodecahedron has been rationalised in terms of the different electronic requirements for stabilising the flattened metal tetrahedral structure in B₄H₄[Co(η-C₅H₅)]₄ and the elongated metal tetrahedral structure in B₄H₄[Ni(η-C₅H₅)]₄.