Bismuth-Boron Multiple Bonding in BiB2 O- and Bi2 B<sup/>.

Despite its electron deficiency, boron is versatile in forming multiple bonds. Transition-metal-boron double bonding is known, but boron-metal triple bonds have been elusive. Two bismuth boron cluster anions, BiB2 O- and Bi2 B- , containing triple and double B-Bi bonds are presented. The BiB2 O- and Bi2 B- clusters are produced by laser vaporization of a mixed B/Bi target and characterized by photoelectron spectroscopy and ab initio calculations. Well-resolved photoelectron spectra are obtained and interpreted with the help of ab initio calculations, which show that both species are linear. Chemical bonding analyses reveal that Bi forms triple and double bonds with boron in BiB2 O- ([Bi≡B-B≡O]- ) and Bi2 B- ([Bi=B=Bi]- ), respectively. The Bi-B double and triple bond strengths are calculated to be 3.21 and 4.70 eV, respectively. This is the first experimental observation of Bi-B double and triple bonds, opening the door to design main-group metal-boron complexes with multiple bonding.