Infrared Photodissociation Spectroscopy of Mass-Selected Dinuclear Transition Metal Boride Carbonyl Cluster Cations.

The transition-metal-boron bonding interactions and geometric structures of heterodinuclear transition metal carbonyl cluster cations BM(CO) n + (M = Co, Ni, and Cu) are studied by a combination of the infrared photodissociation spectroscopy and density functional theory calculations at the B3LYP/def2-TZVP level. The BCu(CO) 5 + and BCo(CO) 6 + cations are characterized as an (CO) 2 B-M(CO) 3/4 + structure involving an σ-type (OC) 2 B → M(CO) 3,4 + dative bonding with end-on carbonyls, while for BNi(CO) 5,6 + complexes with a bridged carbonyl, a 3c-2e bond involving the 5σ electrons of the bridged carbonyl and an electron-sharing bond between the B(CO) 2 fragment and the Ni(CO) 2,3 + subunits were revealed. Moreover, the fundamental driving force of the exclusive existence of a bridged carbonyl group in the boron-nickel complexes has been demonstrated to stem from the desire of the B and Ni centers for the favorable 8- and 18-electron structures.