We present infrared spectra of [CoO(CO2)(n)](-) and [NiO(CO2)(n)](-) clusters and interpret them in the framework of computational results employing density functional theory. We find that both [CoO(CO2)n](-) and [NiO(CO2)n](-) clusters are generally composed of the same core isomers. The dominant isomers consist of an eta(2) CO2 ligand and a CO3 moiety that can be bound to the metal atom with monodentate (eta(1))) or bidentate (eta(2))) connectivity. Minor structural isomers observed are composed of a C2O4 moiety with a lone oxygen atom or a CO3 unit.