Molecular-orbital calculations on [Au6]2+ and [Aug9]3+ clusters have shown that the overlap of the gold 6s orbitals makes a dominant contribution to the bonding. Co-ordination of ligands to these ‘ bare ’ metal clusters encourages a more favourable hybridisation of the metal orbitals and results in stronger radial metal–metal bonding. The electronic factors responsible for the breakdown of the Polyhedral Skeletal Electron Pair rules when applied to the gold clusters are discussed.