The Structures and Bonding of Bismuth-Doped Boron Clusters: BiB₄^- and BiB₅^-

We present an investigation on the structures and chemical bonding of two Bi-doped boron clusters BiBn- (n = 4, 5) using photoelectron spectroscopy and theoretical calculations. The electron affinities of BiB4 and BiB5 are measured to be 2.22(2) eV and 2.61(2) eV, respectively. Well-resolved photoelectron spectra are obtained and used to compare with theoretical calculations to verify the structures of BiB4- and BiB5-. Both clusters adopt planar structures with the Bi atom bonded to the periphery of the planar B-n moiety. Chemical bonding analyses reveal that the B-n moiety maintains sigma and pi double-aromaticity. The Bi atom is found to induce relatively small structural changes to the B-n moiety, very different from transition metal-doped boron clusters.