Multi-centre bonding in the carboranes: Anab initioand semi-empirical molecular orbital study

The electronic structures of the closo-carboranes 1,5-C2B3H5, 1,2-C2B4H6, 1,6-C2B4H6 and 2,4-C2B5H7 are discussed using the results of ab initio calculations in both minimal and extended bases of contracted gaussian type functions fitted to Slater type orbitals. A comparison is made with the results from semi-empirical INDO calculations, and the bonding in 1,7-C2B6H8, 1,6-C2B7H9, 5,9-C2B7H13, 1,6-C2B8H10 and the 1,2-, 1,7- and 1,12-isomers of C2B10H12 studied using the latter method. The delocalized molecular orbitals from both the ab initio and semi-empirical calculations are transformed to localized orbitals to provide an analysis of the multi-centre bonding in these electron-deficient molecules, which requires no prior assumptions about the nature of the bonding.