Infrared photodissociation spectroscopic and theoretical study of homoleptic dinuclear chromium carbonyl cluster cations with a linear bridging carbonyl group.

Infrared spectra of mass-selected homoleptic dinuclear chromium carbonyl cluster cations Cr(2)(CO)(n)(+) with n = 7-9 are measured via infrared photodissociation spectroscopy in the carbonyl stretching frequency region in the gas phase. The structures are established by comparison of the experimental spectra with the simulated spectra derived from density functional calculations. The Cr(2)(CO)(n)(+) cluster cations are characterized to have the (OC)(5)Cr-C-O-Cr(CO)(n-6)(+) structures with a linear bridging carbonyl group bonded to one chromium atom through its carbon atom and to the other chromium atom through its oxygen atom. The cluster cations all have a sextet ground state with the positive charge and the unpaired electrons located on the Cr(CO)(n-6) moiety. The formation of the linear bridging structures without Cr-Cr bonding can be rationalized that chromium forms strong Cr-CO bonds but weak Cr-Cr bonds.