Infrared photodissociation spectroscopy of mass-selected homoleptic cobalt carbonyl cluster cations in the gas phase.

Infrared spectra of mass-selected homoleptic cobalt carbonyl cluster cations including dinuclear Co2(CO)8(+) and Co2(CO)9(+), trinuclear Co3(CO)10(+) and Co3(CO)11(+), as well as tetranuclear Co4(CO)12(+) are measured via infrared photodissociation spectroscopy in the carbonyl stretching frequency region. The geometric structures of these complexes are determined by comparison of the experimental spectra with those calculated by density functional theory. The Co2(CO)8(+) cation is characterized to have a Co-Co bonded structure with Cs symmetry involving a bridging CO ligand. The Co2(CO)9(+) cation is determined to be a mixture of the CO-tagged Co2(CO)8(+)-CO complex and the Co(CO)5(+)-Co(CO)4 ion-molecular complex. The Co3(CO)10(+) cation is the coordination-saturated trinuclear cluster, which is characterized to have a triangle Co3 core with C2 symmetry involving two edge-bridging and eight terminal CO ligands. The Co3(CO)11(+) cation is a weakly bound complex involving a Co3(CO)10(+) core ion. The Co4(CO)12(+) cluster cation is deduced to have a tetrahedral Co4(+) core structure with three edge-bridging and nine terminal carbonyls.