Some theoretical and structural aspects of gold cluster chemistry

Abstract
The bonding in tertiary phosphine cluster compounds of gold is sufficiently straightforward to permit an effective interaction between theoretical concepts developed from semi-empirical molecular orbital calculations and synthetic and structural chemistry. At the simplest conceptual level the isolobal nature of the Au(PR 3 ) fragment and either the CH 3 or H radicals provides a basis for understanding the structures of a wide range of homonuclear and heteronuclear clusters, e.g. Os 3 (CO) 10 - H(AuPPh 3 ) and (OG) 5 VAu 3 (PPh 3 ) 3 . However, this simplified approach neglects some secondary gold-gold interactions between adjacent gold atoms, which arise from the availability of the higher-lying gold 6p orbitals. In low-nuclearity clusters tetrahedral fragments, which permit the effective formation of four-centre two electron bonds between the Au(PR 3 ) fragments, are preferred to larger deltahedra. In higher-nuclearity clusters the stabilities of the clusters depend on the presence of a central gold atom that provides strong radial gold-gold bonding. The relative importance of the radial and tangential components to the total bonding has been effectively demonstrated by a structural comparison of alternative Au 9 (PR 3 )3/8+ clusters. The predictive capability of the theoretical approach has been demonstrated by the synthesis and structural characterization of the icosahedral cluster [Au 13 Cl 2 (PMe 2 Ph) 10 ]3+.