Freiburg Scientist Discovers New Oxidation State of Rhodium

Mayara da Silva Santos, doctoral candidate at the University of Freiburg’s Institute of Physics, has discovered a new oxidation state of rhodium. This chemical element is one of the most catalytically important platinum-group metals and is used, for example, in catalytic converters for automobiles. Rhodium is actually already well studied. What helped Silva Santos make the rare discovery of a surprisingly high oxidation state was a new approach: As part of her doctoral dissertation, she is studying unusual transition metal oxides. Her discovery of so-called rhodium(VII) has just been published as a very important paper in the journal Angewandte Chemie.

Oxides in an ion trap

“Discoveries are always exciting,” says the Freiburg chemist: “Our oxides are highly reactive but could play an important role as reactive intermediate states.” They can be observed in chemical reactions only with difficulty because they are very short-lived. “We were able to store the oxides in a special ion trap at low temperatures over an extended time period and thus study them undisturbed.”

Third-highest oxidation state of all elements

This interdisciplinary approach, combining physics and chemistry as well as experiment and theory, was the key to success, says Prof. Dr. Tobias Lau, professor at the University of Freiburg’s Institute of Physics: “The teamwork between different disciplines was very helpful in sample production, mass spectrometry, X-ray spectroscopy, and data analysis.”

An important finding of this interdisciplinary work is that more valance electrons than previously thought can take part in chemical bonds with rhodium and that rhodium can assume the third-highest oxidation state of all elements. This highest oxidation state of rhodium – rhodium(VII) – was previously unknown but could play a role in chemical reactions.

Fact sheet:

• Original publication: M. da Silva Santos, T. Stüker, M. Flach, O. S. Ablyasova, M. Timm, B. von Issendorff, K. Hirsch, V. Zamudio-Bayer, S. Riedel, J. T. Lau, The Highest Oxidation State of Rhodium: Rhodium(VII) in [RhO₃]⁺, Angew. Chem. Int. Ed. e202207688 (2022). DOI:10.1002/anie.202207688
• The research project was funded by the German Research Foundation (DFG) within the context of the research training group 2717 “Dynamics of Controlled Atomic and Molecular Systems (DynCAM)“ at the University of Freiburg and conducted at the synchrotron radiation source BESSY II at Helmholtz-Zentrum Berlin. Calculations were performed at the Free University of Berlin.
• Mayara da Silva Santos is an inorganic chemist and a doctoral candidate in the field of cluster and synchrotron spectroscopy at the University of Freiburg’s Institute of Physics as well as a member of the Department of Highly Sensitive X-ray Spectroscopy at Helmholtz-Zentrum Berlin. Prof. Dr. Tobias Lau is professor of experimental physics at the University of Freiburg and a department head at Helmholtz-Zentrum Berlin. Their research interests concern electronic and magnetic properties of metal centers in small clusters and coordination complexes as well as the development of new methods for X-ray spectroscopy.