The electronic and geometrical structure of neutral and singly charged Fe4C2, Fe4C(CO), Fe-4(CO)(2), Fe4C2-CO, Fe4C(CO)(2), Fe4C3, and Fe-4(CO)(3) are studied using density functional theory with a generalized gradient approximation. It is found that the Fe4C2 and Fe4C2(CO) species possess two isomers with separated and dimerized carbon atoms. The latter isomers are lower in total energy by similar to0.3 eV. The Fe4C3 species possess three isomers corresponding to: a C-2 dimer and one separated carbon atom (the lowest energies), a C-3 trimer (intermediate energies), and three separated carbon atoms (the highest energies). The lowest energy dissociation channel corresponds to the loss of CO, except for Fe-4(CO)(2) and Fe4C(CO)(2)(+), where the loss of carbon dioxide is the lowest. The computed total energies are used to estimate the energetics of the Boudouard-like disproportionation reactions, Fe4Cn(CO)(m) + CO --> Fe4Cn+1(CO)(m-1) + CO2. It is found that the most exothermic reaction in the series is Fe4C(CO)(+) + CO --> Fe4C2+ + CO2 (by similar to0.3 eV).