The History and the Current Revival of the Oxo Chemistry of Iron in its Highest Oxidation States: Fe^VI – Fe^VIII

Abstract

The history of the oxo compounds of iron in its highest oxidation states is reviewed and modern activities in this long neglected area of inorganic chemistry are highlighted. The chemistry of ferrates(VI) is the most rapidly advancing branch owing to several potential applications in diverse fields such as environmental chemistry and energy storage. Convenient and high‐yield preparations of ferrates(VI) in high purity are presented, followed by a coverage of the analytical, spectroscopic, and structural characterization in the solid and in solution, with a focus on the stability of these compounds, which had long been under‐estimated. Particular attention has been paid to the fascinating mechanisms that have been proposed for the intriguing “self‐decay” of the [FeO4]2– dianion. Redox processes with inorganic and organic substrates are summarized including fresh and waste water treatment on the one hand and “super‐iron batteries” on the other. Recent advances in the experimental and computational approach to ferrates(VII) [FeO4]– and the elusive “iron tetroxide” [FeO4] are described.

An Electrochemical Route for Hot Alkaline Blackening of Steel: A Nitrite Free Approach

“…We conclude that the formed black oxide layer is indeed magnetite (Fe 3 O 4 ), which is in agreement with the findings in literature [23]. purple colored electrolyte [28,31,32]. UV-VIS spectroscopy (Figure 4) could confirm the electrochemical formation of the ferrate(VI) ion, showing a band with an absorption maximum at 505 nm (green color, complementary of purple) [32][33][34].…”

“…T purple colored electrolyte [28,31,32]. UV-VIS spectroscopy (Figure 4) could confirm the electrochemical formation of the ferrate(VI) ion, showing a band with an absorption maximum at 505 nm (green color, complementary of purple) [32][33][34]. In order to confirm the chemical composition of the iron oxide overlayers that were formed by electrochemical blackening, the steel samples were examined by Auger electron spectroscopy.…”

“…Electrochemical blackening at temperatures below 80 • C by using more positive potentials was not successful. Apparently, ferrate(VI) ions (FeO 4 2− ) are formed at higher potentials, resulting in a purple colored electrolyte[28,31,32]. UV-VIS spectroscopy(Figure 4) could confirm the electrochemical formation of the ferrate(VI) ion, showing a band with an absorption maximum at 505 nm (green color, complementary of purple)[32][33][34].…”

Oxygen-evolution reaction by nickel/nickel oxide interface in the presence of ferrate(VI)

“…It displays that OER could occur by the mechanism of activation of K 2 FeO 4 using Ni ions (Fig. 8c) 31 .…”

Versatile Functionalization of Carbon Nanomaterials by Ferrate(VI)

“…Nature utilizes Fe IV =O and Fe V =O complexes as the active centers for a number of important enzymatic oxidations, which motivates many fundamental studies on the properties of high-valent iron compounds, especially their chemical and biological reactivities [1][2][3][4][5][6][7][8]. Fe VI , the highest accessible oxidation level of iron, generally exists in the form of ferrate(VI) ion (FeO 4 2− ) with four Fe VI =O bonds.…”