Disulfido iron–manganese carbonyl cluster complexes: Synthesis, structure, bonding and properties of the radical CpFeMn2(CO)7(μ3-S2)2

Two new compounds CpFeMn2(CO)7(μ3-S2)2 (2) and Cp3Fe3Mn(CO)4(μ3-S2)2(μ3-S) (3) were obtained by the treatment of [CpFeMn(CO)5(μ3-S2)]2 (1) with CO at room temperature in the presence of room light. Compound 2 contains two triply bridging disulfido ligands on opposite sides of an open FeMn2 triangular cluster. EPR and temperature-dependent magnetic susceptibility measurements show that it is paramagnetic with one unpaired electron per formula equivalent. The electronic structure of 2 was established by DFT and Fenske-Hall (FH) molecular orbital calculations which show that the unpaired electron occupies a low lying antibonding orbital that is located principally on the iron atom. The cyclic voltammogram of 2 exhibits one reversible one-electron oxidation wave at +0.34 V and one irreversible one-electron reduction wave at −0.66 V vs. Ag/AgCl. Compound 3 contains three iron atoms and one manganese atom with two triply bridging disulfido ligands and one triply bridging sulfido ligand and has no unpaired electrons. The molecular structures of compounds 2 and 3 were established by single crystal X-ray diffraction analyses.