Structural and Bonding Issues in Clusters and Nano-clusters

The study of gold cluster compounds origin/ated from Malatesta’s syntheses of tertiary phosphine derivatives in the 1960s and was greatly extended between 1970 and 2000. Single crystal X-ray studies defined the major structural classes and led to the development of a theoretical model which accounted for their closed shell requirements in terms of their topological features. This model proved to be sufficiently flexible to be extended to related heteronuclear cluster compounds. Since the turn of the century the range of gold cluster compounds has been greatly extended by the study of organothiolato-gold cluster compounds and unligated gold clusters. The structures of the organothiolato-compounds have revealed that some of the gold atoms combine with the ligands to generate a novel class of metallo-organothiolato-ligands which protect and stabilise the inner core of gold atoms. The smaller cluster cone angles of the organothiolato-based ligands have accessed clusters with higher nuclearities (>100 gold atoms) some of which have been structurally characterised. These developments originally suggested that the phosphine and organothiolato-clusters defined quite distinct classes of gold clusters, but recent structural and theoretical developments have reconciled many of these differences. This review summarises the structures of the clusters and suggests a unified theoretical model which accounts for the broad structural properties of the two classes of compound.