Coordination and Spin States in Vanadium Carbonyl Complexes (V(CO)n+, n=1-7) Revealed with IR Spectroscopy

The vibrational spectra of vanadium carbonyl cations of the form V(CO)(n)(+), where n = 1-7, were obtained via mass-selected infrared laser photodissociation spectroscopy in the carbonyl stretching region. The cations and their argon and neon tagged analogues were produced in a molecular beam via laser vaporization in a pulsed nozzle source. The relative intensities and frequency positions of the infrared bands observed provide distinctive patterns from which information on the coordination and spin states of these complexes can be obtained. Density functional theory is carried out in support of the experimental spectra. Infrared spectra obtained by experiment and predicted by theory provide evidence for a reduction in spin state as the ligand coordination number increases. The octahedral V(CO)(6)(+) complex is the fully coordinated experimental species. A single band at 2097 cm(-1) was observed for this complex red-shifted from the free CO vibration at 2143 cm(-1).