Ni+(CO2)(n), Ni+(CO2)(n)Ar, Ni+(CO2)(n)Ne, and Ni+(O-2)(CO2)(n) complexes are generated by laser vaporization in a pulsed supersonic expansion. The complexes are mass-selected in a reflectron time-of-flight mass spectrometer and studied by infrared resonance-enhanced photodissociation (IR-REPD) spectroscopy. Photofragmentation proceeds exclusively through the loss of intact CO2 molecules from Ni+(CO2)(n) and Ni+(O-2)(CO2)(n) complexes, and by elimination of the noble gas atom from Ni+(CO2)(n)Ar and Ni+(CO2)(n)Ne. Vibrational resonances are identified and assigned in the region of the asymmetric stretch of CO2. Small complexes have resonances that are blueshifted from the asymmetric stretch of free CO2, consistent with structures having linear Ni+-O=C=O configurations. Fragmentation of larger Ni+(CO2)(n) clusters terminates at the size of n=4, and new vibrational bands assigned to external ligands are observed for ngreater than or equal to5. These combined observations indicate that the coordination number for CO2 molecules around Ni+ is exactly four. Trends in the loss channels and spectra of Ni+(O-2)(CO2)(n) clusters suggest that each oxygen atom occupies a different coordination site around a four-coordinate metal ion in these complexes. The spectra of larger Ni+(CO2)(n) clusters provide evidence for an intracluster insertion reaction assisted by solvation, producing a metal oxide-carbonyl species as the reaction product. (C) 2004 American Institute of Physics.