Unsaturation in binuclear cyclopentadienyliron carbonyl thiocarbonyls: Four-electron donor bridging thiocarbonyl groups versus metal-metal multiple bonds

► The cis-trans Cp2Fe2(CS)(CO)3 and Cp2Fe2(CS)2(CO)2 with two CE (E=O, S) bridges are essentially fluxional systems. ► The triply bridged Cp2Fe2(CS)(CO)2 and Cp2Fe2(CS)2(CO) are triplets with Fe=Fe double bonds. ► The doubly bridged Cp2Fe2(CS)(CO) and Cp2Fe2(CS)2 are singlets with FeFe triple bonds.