Theoretical studies have been carried out on Fe-3(CS)(3)(CO)(n) (n = 9, 8, 7, 6) derivatives. The lowest energy structure for Fe-3(CS)(3)(CO)(9) has one of the edge of the Fe3 triangle bridged by two CS groups analogous to the known structure for Fe-3(CO)(12). The lowest energy structures for the unsaturated Fe3(CS)3(CO)(n) (n = 8, 7, 6) have four- and six-electron donor bridging thiocarbonyl groups and Fe-Fe single bonds in preference to structures with formal iron-iron multiple bonds.