Predicted instability of binuclear iron carbonyl thionyls towards carbon dioxide elimination to give a novel iron carbonyl sulfide

The iron carbonyl thionyl Fe2(SO)(CO)8 is predicted by density functional theory to have a triply bridged structure analogous to Fe2(CO)9. However, it is disfavored by more than 30 kcal/mol with respect to CO2 elimination to give Fe2(S)(CO)7, predicted to have a very unsymmetrical bridging sulfur atom forming an Fetriple bond; length of mdashS triple bond with one iron atom and a Fesingle bondS single bond with the other iron atom.