Higher Oxidation States of Iron in Solid State: Synthesis and Their Mössbauer Characterization

Abstract

The solid state synthesis of iron ion in high oxidation states (≥+4) is briefly reviewed. Reactions in solid state are mainly considered through some unusual cases of obtaining iron ions with oxidation states of Fe(V), Fe(VI), Fe(VII), and Fe(VIII). The significance of the Mossbauer spectroscopic technique for identifying valence forms of elements in complex oxygen-containing compounds is emphasized. Sodium ferrate(IV), Na 4 FeO 4 , is highly hygroscopic and decomposes to Fe(VI) and Fe(III) upon contact with water. The basic Mossbauer parameter, isomer shift, 5, for alkali and alkaline earth metal ferrate(VI) changes in a very narrow range of -0.87 to -0.91 mm s -1 (with respect to α-Fe). This suggests a weak influence of the outer ions on iron bound in an oxygen tetrahedron. The Mossbauer spectra of unknown oxoferrate ions with oxidation states of Fe 5+ and Fe 8+ are reported. The isomer shift, which is a fundamental parameter decreases with increasing valence state. This tendency persists for all possible high oxidation states of iron.