Trinuclear,Oxo-Bridged,Mixed-Valence Iron Mercaptocarboxylates

Mixed carboxylates and mercaptocarboxylates of mixed-valence Fe^IIFe^III with general formula [Fe^II-Fe^III₂O(OOCR)₃(OOCRSH)₃L₃](where R = C₁₃H₂₇, C₁₅H₃₁ or C₁₇H₃₅; R= CH₂ or C₆H₄ and L = pyridine) were successfully prepared by substitution of [Fe^IIFe^III₂O(OAc)₆(H₂O)₃] with straight chain carboxylic acids and mercaptocarboxylic acids. The title products have been characterized by elemental analyses, molar conductances and magnetic susceptibility measurements, i.r., electronic and Mössbauer spectral data. The i.r. spectra showed resolved bands arising from the _asym(OCO) and _sym(OCO) vibrations of the bridging carboxylate and mercaptocarboxylate ligands along with the _asym(Fe₃O) vibrations. Mössbauer spectroscopic studies revealed two resolved quadrupole doublets due to Fe^II and Fe^III at 80, 200 and 295 K, confirming the valence-localized type of compound. This fact has also been supported by the observed electronic spectral bands in the complexes. Magnetic susceptibility measurements showed net anti-ferromagnetic coupling related to mixed-valence pairs. A structure for the complexes has been established on the basis of physico-chemical studies.