Infrared Photodissociation Spectroscopy of Mass Selected Homoleptic Copper Carbonyl Cluster Cations in the Gas Phase

Infrared spectra of mass-selected homoleptic copper carbonyl cluster cations including dinuclear Cu₂(CO)₆⁺ and Cu₂(CO)₇⁺, trinuclear Cu₃(CO)₇⁺, Cu₃(CO)₈⁺, and Cu₃(CO)₉⁺, and tetranuclear Cu₄(CO)₈⁺ are measured via infrared photodissociation spectroscopy in the carbonyl stretching frequency region. The structures are established by comparison of the experimental spectra with simulated spectra derived from density functional calculations. The Cu₂(CO)₆⁺ cation is characterized to have an unbridged <i>D</i>_3<i>d</i> structure with a Cu–Cu half bond. The Cu₂(CO)₇⁺ cation is determined to be a weakly bound complex involving a Cu₂(CO)₆⁺ core ion. The trinuclear Cu₃(CO)₇⁺ and Cu₃(CO)₈⁺ cluster cations are determined to have triangle Cu₃ core structures with <i>C</i>₂ symmetry involving two Cu­(CO)₃ groups and one Cu­(CO)_<i>x</i> group (<i>x</i> = 1 or 2). In contrast, the trinuclear Cu₃(CO)₉⁺ cluster cation is determined to have an open chain-like (OC)₃Cu–Cu­(CO)₃–Cu­(CO)₃ structure. The tetranuclear Cu₄(CO)₈⁺ cluster cation is characterized to have a tetrahedral Cu₄⁺ core structure with all carbonyl groups terminally bonded.