Laser-ablated ruthenium and osmium atoms, cations and electrons have been reacted with CO molecules during condensation in excess neon. The Ru(CO)(x) and Os(CO)(x) (x = 1-5) molecules are formed during sample deposition or on annealing. The Ru(CO)(x)(-) and Os(CO)(x)(-) (x = 1-4) anions are formed by electron capture, and the RuCO+ and OsCO+ cations are produced by metal cation reactions and identified from (CO)-C-13 and (CO)-O-18 isotopic substitution, density functional calculations, and behavior on doping with CCl4 to serve as an electron trap. Density functional calculations predict these frequencies within 1% and the isotopic shifts for different C-O stretching modes within averages of 1 to 2 cm(-1) including vibrational modes for both C-3v and D-2d tetracarbonyl anion structures.