Photoelectron Spectroscopy of Size-Selected Bismuth-Boron Clusters: BiB ( = 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, BiB ( = 6-8). Well-resolved photoelectron spectra are obtained and are used to understand the structures and bonding of BiB in conjunction with theoretical calculations. Global minimum searches find that all three BiB clusters have planar structures with the Bi atom bonded to the edge of the planar B moiety via two Bi-B σ bonds as well as π bonding by the 6p orbital. BiB is found to consist of a double-chain B with a terminal Bi atom. Both BiB and BiB are composed of a Bi atom bonded to the planar global minima of the B and B clusters. Chemical bonding analyses reveal that BiB is doubly antiaromatic, whereas BiB and BiB are doubly aromatic. In the neutral BiB ( = 6-8) clusters, except BiB which has a planar structure similar to the anion, the global minima of both BiB and BiB are found to be half-sandwich-type structures due to the high stability of the doubly aromatic B and B molecular wheel ligands.