Density functional theory studies on Co-2(CS)(2)(CO)(8) show the structure with two bridging CS groups to be the global minimum. Unbridged Co-2(CS)(2)(CO)(8) structures lie at least 11 kcal/mol above this global minimum Co-2(mu-CS)(2)(CO)(6). The lowest energy unsaturated Co-2(CS)(2)(CO)(n) (n = 5, 4, 3) structures are predicted to contain four-electron donor bridging eta(2)-mu-CS groups, unlike the cot-responding homoleptic carbonyls Co-2(CO)(n+2), which contain only two-electron donor carbonyl groups.