Sulfur-Bridged Dimeric Complexes of Iron (III)

Iron(III) dimers of general formula [Fe(S₂CSR)₂(SR)]₂, R = C₂H₅, n-C₃H₇,n-C₄H₉, C₆H₅CH₂, have been synthesized. Under identical conditions, only the known monomeric compound [Fe(S₂CSR)₃] has been isolated for R = t-C₄H₉. Molecular weight and proton nmr spectral studies of the diamagnetic dimers in solution have been carried out. The pmr spectrum of the ethyl dimer, assigned on the basis of spin-decoupling experiments, is consistent with a structure which contains bridging ethyl sulfide and both bridging and terminal ethyl thioxanthate ligands. Cyclic voltammetric and conventional polarographic studies of the metal-metal bonded dimers reveal a two-electron reduction wave and a one-electron oxidation wave, both irreversible. Tris(t-butylthioxan-thato)iron(III) is monomeric in solution and exhibits reversible one-electron oxidation and one-electron reduction waves. The complex contains low-spin iron(III) with an effective moment of 2.46 BM at room temperature in the solid and over the limited temperature range, 210° < T < 293 °K, in dichloromethane solution. The solid-state reflectance and solution electronic spectra of all the dimers are nearly identical, implying similar structures, but differ significantly from the corresponding spectra of the t-butyl monomer. Infrared spectra are reported and discussed.