On the chemical bonding of gold in auro-boron oxide clusters AunBO- (n = 1-3).

During experiment on Au-B alloy clusters, an auro-boron oxide cluster Au2BO- was observed to be an intense peak dominating the Au-B mass spectra, along with weaker signals for AuBO- and Au3BO-. Well-resolved photoelectron spectra have been obtained for the three new oxide clusters, which exhibit an odd-even effect in electron affinities. Au2BO- is shown to be a closed shell molecule with a very high electron detachment energy, whereas AuBO and Au3BO neutrals are shown to be closed shell species with large HOMO-LUMO gaps, resulting in relatively low electron affinities. Density functional calculations were performed for both AunBO- (n = 1-3) and the corresponding HnBO- species to evaluate the analogy between bonding of gold and hydrogen in these clusters. The combination of experiment and theory allowed us to establish the structures and chemical bonding of these tertiary clusters. We find that the first gold atom does mimic hydrogen and interacts with the BO unit to produce a linear AuBO structure. This unit preserves its identity when interacting with additional gold atoms: a linear Au-[AuBO] complex is formed when adding one extra Au atom and two isomeric Au2-[AuBO] complexes are formed when adding two extra Au atoms. Since BO- is isoelectronic to CO, the AunBO- species can be alternatively viewed as Aun interacting with a BO- unit. The structures and chemical bonding in AunBO- are compared to those in the corresponding AunCO complexes.