The diversity of iron−sulfur bonding in binuclear iron carbonyl sulfides

The potential accessibility of Fe2S(CO)n derivatives with 1:2 sulfur to iron ratios by the decarboxylation of iron carbonyl thionyls has led to their investigation using density functional theory. The lowest energy Fe2S(CO)n (n = 8, 7, 6) structures are predicted to be singlet structures with all terminal CO groups, a bridging sulfur atom, and a formal Fe–Fe single bond of length ∼2.5 Å. The Fe−S distances in these structures shorten from ∼2.3 to ∼2.1 Å as CO groups are lost, suggesting an increase in the formal Fe−S bond orders. The thermochemistry of CO dissociation suggests that both Fe2S(CO)8 and Fe2S(CO)7 are viable synthetic objectives. A similar density functional theory study of Fe2S2(CO)n derivatives (n = 7, 6, 5) finds the experimentally known Fe2S2(CO)7 structure with a bridging S2CO group and the Fe2S2(CO)6 structure with a bridging disulfide ligand to be the lowest energy structures by substantial margins of ∼17 and ∼21 kcal/mol, respectively. The low-energy structures for the unsaturated Fe2S2(CO)5 are derived from the low-energy Fe2S2(CO)6 structures by loss of a CO group in various ways with relatively little change in the underlying Fe2S2 framework.