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 sigma-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 5 sigma 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.