On the structures and bonding in boron-gold alloy clusters: B6Au(n)- and B6Au(n) (n = 1-3).

Photoelectron spectroscopy and density-functional theory are combined to investigate the electronic and structural properties of a series of B-Au alloy clusters: B6Aun(-) and B6Aun (n = 1-3). Rich spectral features are observed for each species, and vibrational structures are resolved for numerous detachment transitions of B6Au(-) and B6Au2(-). Electron affinities of B6Aun (n = 1-3) are evaluated to be 2.70 ± 0.03, 2.91 ± 0.02, and 3.21 ± 0.05 eV, respectively. Global structural searches are performed for both the anions and their neutrals. The calculated electronic binding energies are compared with experimental measurements to establish the anion global-minimum structures and their corresponding neutral states. The ground-state structures of these clusters are shown to be planar or quasi-planar with an elongated B6 core, to which the first and second Au atoms are bonded terminally and the third Au in a bridging position. All three anion clusters are π antiaromatic. Natural bond orbital analyses show that the B-Au bonding is highly covalent, providing new examples for the Au∕H analogy in Au alloy clusters.