Photoelectron Spectroscopy of Size-Selected Bismuth–Boron Clusters: BiBn– (n = 6–8)

Because of its low toxicity, bismuth is considered to be a “green metal” and has received increasing attention in chemistry and materials science. To understand the chemical bonding of bismuth, here we report a joint experimental and theoretical study on a series of bismuth-doped boron clusters, BiBn– (n = 6–8). Well-resolved photoelectron spectra are obtained and are used to understand the structures and bonding of BiBn– in conjunction with theoretical calculations. Global minimum searches find that all three BiBn– clusters have planar structures with the Bi atom bonded to the edge of the planar Bn moiety via two Bi–B σ bonds as well as π bonding by the 6pz orbital. BiB6– is found to consist of a double-chain B6 with a terminal Bi atom. Both BiB7– and BiB8– are composed of a Bi atom bonded to the planar global minima of the B7– and B8– clusters. Chemical bonding analyses reveal that BiB6– is doubly antiaromatic, whereas BiB7– and BiB8– are doubly aromatic. In the neutral BiBn (n = 6–8) clusters, except BiB6 which has a planar structure similar to the anion, the global minima of both BiB7 and BiB8 are found to be half-sandwich-type structures due to the high stability of the doubly aromatic B73– and B82– molecular wheel ligands.