A chemical containing the element iridium has set a new record for the highest recorded formal oxidation state in the periodic table of the elements. Formal oxidation state 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. The measurement is critical in many fields, for example, the chemical reactions that sustain batteries.

Previous work has reached an oxidation state of VIII with elements such as xenon, ruthenium, osmium, and plutonium. Researchers from China, Canada and Germany have now created a gaseous form of the iridium tetroxide cation ([IrO4]+) in which the iridium reaches an oxidation state of IX, the only element known to be able to do so.

This new record can be explained by relativistic effects which were first described by Albert Einstein.

Original research paper published in Nature on October 22, 2014.

Names and affiliations of selected authors

Mingfei Zhou, Fudan University, China,

Sebastien Riedel, Freie Universität Berlin, Germany

Gary J. Schrobilgen, Department of Chemistry, McMaster University, Ontario