Structural and bonding patterns in gold clusters

The study of gold cluster compounds originated from Malatesta's syntheses of tertiaryphosphine 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 and 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. The structures of these compounds have revealed that the gold atoms combine with the organothiolato-ligands to generate a novel class of metallo-organothiolato-ligands which protect and stabilise the inner core of gold atoms. 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 all the clusters of gold and suggests a theoretical model which effectively unites the broad structural properties of the two classes of compound. This model is based on the united atom model for diatomics developed by Mulliken and the compression co-ordinate is related to the interpenetration of icosahedral and cuboctahedral pseudo-spherical clusters. The predicted closed shell requirements agree well with the results of structural determinations.