Trinuclear, Oxo-Bridged, Mixed-Valence Iron Mercaptocarboxylates

Mixed carboxylates and mercaptocarboxylates of mixed-valence FeIIFeIII with general formula [FeII-FeIII2O(OOCR)3(OOCR′SH)3L3](where R = C13H27, C15H31 or C17H35; R′= CH2 or C6H4 and L = pyridine) were successfully prepared by substitution of [FeIIFeIII2O(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 νasym(OCO) and νsym(OCO) vibrations of the bridging carboxylate and mercaptocarboxylate ligands along with the νasym(Fe3O) vibrations. Mössbauer spectroscopic studies revealed two resolved quadrupole doublets due to FeII and FeIII 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.