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Iron metals oxidize to rust, losing electrons and gaining positive charge. Iron metals typically exist in an oxidation state of +2 or +3 (2 or 3 electrons less than a neutral iron atom). However, chemists have long thought that iron compounds with even higher oxidation states play important roles in enabling chemical reactions in metal-containing proteins. In recent years, scientists have been able to synthesize and characterize numerous iron +4 compounds [written Fe(IV)], but knew little about iron +5, Fe(V), compounds. Now researchers, using SSRL, have characterized a genuine Fe(V) species, which is even more oxidized and more positively charged than the iron in rust [Fe(III)] or Fe(IV).
Frank Neese, Karl Wieghardt, and co-workers, including SSRL's Serena DeBeer George, used X-ray absorption spectroscopy (XAS), combined with other spectroscopic and computational results, to describe the compound. Tuned to be sensitive to iron, XAS can pick up the amount of charge on the iron atom. The XAS "K-edge" corresponds to the excitation of the most tightly bound electrons in the iron atom. As the iron atom becomes more oxidized, the K-edge increases in energy, providing a signature for Fe(V). This study represents the first characterization of an Fe(V) species by XAS and serves as an important experimental marker for characterization of other Fe(V) species.
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