Infrared photodissociation spectra are measured for mass selected cation complexes with a chemical formula [MC7O6](+) (M = Fe, Co, Ni) formed via pulsed laser evaporation of metal target in expansions of helium gas seeded by CO. The geometries of the complexes are determined by comparison of the experimental spectra with the simulated spectra from density functional calculations. All of these complexes are identified to have [M(CO)(4)(C3O2)](+) structures involving a carbon suboxide ligand, which binds the metal center in an eta(1) fashion. The antisymmetric CO stretching vibration of C3O2 is slightly red-shifted upon coordination. The donor-acceptor bonding interactions between C3O2 and the metal centers are analyzed using the EDA-NOCV method. The results show that M <- C3O2 sigma donation is stronger than the M -> C3O2 pi back-donation in these cation complexes.