Higher Oxidation States of Iron in Solid State: Synthesis and Their Mssbauer Characterization
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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 Mssbauer spectroscopic technique for identifying valence forms of elements in complex oxygencontaining compounds is emphasized. Sodium ferrate(IV), Na4FeO4, is highly hygroscopic and decomposes to Fe(VI) and Fe(III) upon contact with water. The basic Mssbauer parameter, isomer shift, 8, 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 -Fe). This suggests a weak influence of the outer ions on iron bound in an oxygen tetrahedron. The Mssbauer spectra of unknown oxoferrate ions with oxidation states of Fe5+ and Fe8+ 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. 2008 American Chemical Society.