Infrared photodissociation spectroscopy of transition metal carbonyl and metal oxide carbonyl cations

Abstract

Transition metal carbonyls and metal oxide carbonyls of the form M(CO)n+ and MOm(CO)n+ are produced in a molecular beam via laser vaporization in a pulsed nozzle source. Size-selected ions are investigated using infrared laser photodissociation spectroscopy in the carbonyl stretching region (2000−2300 cm-1) and in the metal oxide stretching region (800−1200 cm-1). The number of infrared active bands, their relative intensities, and band positions provide insight into the bonding, coordination and geometries of these complexes. Density Functional Theory calculations are conducted in support of the experimental data. The Y(CO)8+ ion was produced and characterized. This complex is the first eight-coordinate homoleptic transition metal carbonyl observed in the gas phase. The group IV metal carbonyls (M(CO)n+, M = Ti, Zr, Hf) prefer an n = 6 coordination number, and a systematic decrease in the C−O stretching frequency was observed going from titanium to hafnium. Cu(CO)n+ complexes display non-classical carbonyl bonding and the n = 4 complex is the fully coordinated species, similar to isoelectronic Ni(CO)4. All VOm(CO)n+ complexes have a six coordinate core similar to pure vanadium carbonyl and oxidation causes the carbonyl frequencies to blue-shift.