Mössbauer spectroscopic identification of thermal decomposition products in iron(III) carboxylates

Abstract

A series of carboxylatoferrate (III) complexes have been synthesized with monocarboxylic and dicarboxylic acids. Mössbauer spectra of all the complexes exhibit quadrupole doublets with ΔE_Q=0.36−0.88 mm s⁻¹, suggesting a distorted octahedral geometry. The complexes start decomposing at ≈100°C and finally yield a constant weight at <500°C. Mössbauer spectral studies of the intermediates and final products after heating at different temperatures yield a complex pattern, suggesting the formation of one or two magnetic phases. Mössbauer spectra of the final products show two, six or eight lines with a central doublet, all indicating the formation of α-Fe₂O₃ of different particle sizes. It is proposed that decarboxylation occurs first, followed by the loss of one or two ligands, depending on the nature of the carboxylate and the heating tempeature. The complex of pyridine-2,6-dicarboxylic acid shows an anomalous behavior.