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Identification of Formal Oxidation Stage IX for Chemical Compound

Researchers at Freie Universität Berlin Collaborated in Significant Research on Highest Possible Oxidation States

№ 372/2014 from Oct 24, 2014

Scientists at Freie Universität Berlin, Fudan University in Shanghai, and McMaster University in Hamilton, Canada, discovered a chemical compound with a higher oxidation state than those previously known. The chemistry professor Sebastian Hasenstab-Riedel from Freie Universität and an international group of researchers characterized a compound that reaches the formal oxidation number IX. Formal oxidation state − an important concept in chemistry − describes the number of electrons an atom loses or gains when it joins with other atoms in chemical compounds; the higher the oxidation state, the greater the number of electrons removed from the element. Until now, based on the position of the known 118 elements in the periodic table, the number was limited to values between I and VIII. The recently discovered iridium compound [IrO4]+ with the formal oxidation state IX belongs to the group of metal oxides and could be used in the future as a strong oxidizing agent for chemical reactions. The research results were published in Nature.

[IrO4]+ was detected in the gaseous state by photodissociation. The change from the oxidation state VIII to IX was possible because the element iridium has one more electron than its neighboring element osmium, which in the previously known analog connection OsO4 reaches the oxidation state VIII. OsO4 plays a role in a variety of chemical reactions, for example as a catalyst for oxidation reactions in organic chemistry.

Through quantum-chemical calculations, the scientists in Hasenstab-Riedel's group were able to show the possible existence of a compound with the oxidation state IX as early as 2010. Since these calculations also predicted stability in the solid state, the researchers are confident that [IrO4]+ can be transformed  to the solid state in the next step of the gas phase.

Further Information

Prof. Dr. Sebastian Hasenstab-Riedel, Institute of Chemistry and Biochemistry, Freie Universität Berlin, Tel.: +49 30 838-54071 and -59860, Email:


Guanjun Wang, Mingfei Zhou, James T. Goettel, Gary J. Schrobilgen, Jing Su, Jun Li, Tobias Schlöder, Sebastian Riedel: Beyond Oxidation State VIII: Discovery of the First Species in Formal Oxidation State I, In: Nature, DOI 10.1038/nature13795.