Bonding in clusters. Part 7.—Protonation of six-apex closo-boranes and closo-carboranes: an ab initio calculational study

Abstract

Geometry optimised ab initio(STO-3G) calculations on the molecules 1,6-C₂B₄H₆ and 1,6-C₂B₄H⁺₇ are shown to produce a proton affinity in good agreement with experiment. The differences in the geometries of 1,6-C₂B₄H⁺₇, CB₅H₇, B₆H^–₇ and 1,2-C₂B₄H⁺₇ are shown to be due to the different distribution of the HOMO of the unprotonated molecules, and are predictable on symmetry grounds. The energies of protonations are shown to be due largely to approach of the proton to the unprotonated molecule, and very weakly bonding character is determined for the HOMO of the unprotonated molecules.