A convenient route to iron(III)-thiolates: synthesis and characterization of low-spin (S = ½) iron(III) complexes having the chromophore FeN₂S₂S₂ (S* = thioether)

Abstract

Three air-stable iron(III) complexes with homoleptic hexadentate ligands with the donor set N₂S*₂S₂ (S* = thioether, S = thiolate) have been isolated. The two thiol groups present in each ligand are initially protected as their t-butyl derivatives. When iron(III) chloride is allowed to reflux with any of these thiol-protected ligands the S¤ But linkages are cleaved forming the corresponding iron(III)-thiolates in high yields. The complexes are characterized by electronic absorption, EPR and room-temperature Mossbauer spectroscopic as well as room-temperature magnetic susceptibility studies. As the spectral data indicate each complex has a pseudo-octahedral coordination geometry around the metal ion. The effective magnetic moment values at 300 K lie in the range 2.24-2.30, corresponding to low-spin iron(III) (S =½ ) complexes with significant orbital contribution. One of the complexes exhibits a quasi-reversible Fe^III/Fe^II couple at E_f = 1.66 V (vs S.C.E.), while another complex shows a quasi-reversible Fe^IV/Fe^III couple at E_f = 0.86 V (vs S.C.E.).