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 D3d 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 C2 symmetry involving two Cu(CO)3 groups and one Cu(CO)x group
(x = 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.