A research team involving University of Iowa chemists reports a new oxidation state for a rare earth chemical element, a discovery that could broaden its use and potential applications for society.

The chemical element is praseodymium. It is part of a group of 17 elements called rare earth elements (REE). REEs are central to a host of everyday products and uses, including smartphones, medical imaging, lasers, and wind turbines. Praseodymium also is one of the 15 REEs called lanthanides— a category of metals that are indispensable for advanced materials and technologies, driving innovations in computing performance, and smaller devices.

The discovery of a new oxidation state (five plus) for a lanthanide element traditionally thought to only be accessible in its three or four plus states, opens new possibilities for redox chemistry — or how elements gain or lose electrons between different types of metals — and broaden the technical applications of lanthanides in fields such as rare-earth mining and quantum technology. 

Chemists have long wondered about praseodymium in this oxidation state, in part because this group of metals might have characteristics similar to transition metals, which would broaden their uses and applications.

However, stabilizing praseodymium in this state — a necessary step for observing and proving its existence — has been challenging. Computational modeling can contribute to understanding why this is the case.

“When a metal becomes so positively charged, it tries to pull more electrons towards itself in a way that can be challenging to model, even with state-of-the-art methods. Our group had previously worked on copper complexes that, it turned out, had some similarities,” says Bess Vlaisavljevich, associate professor in the Department of Chemistry at Iowa and the study’s co-corresponding author. “I didn't expect to make comparisons between lanthanides and transition metals, but by comparing a broad spectrum of experiments with the modeling, we were able to make comparisons across the periodic table.”

Vlaisavljevich will team with researchers at other institutions to expand the scope of the work. 

“We hope to achieve more examples of pentavalent (+5) praseodymium while also using similar strategies to find new oxidation states in other lanthanides or actinides,” she says. 

The study, “Praseodymium in the Formal +5 Oxidation State” was published online April 7 in the journal Nature Chemistry.

Co-corresponding authors are Henry Storms La Pierre, from the Georgia Institute of Technology; and Ivan Popov, from Washington State University.

Contributing authors are Andrew Boggiano, Julie Niklas, Haruko Tateyama, Hongwei Wu, and Johannes Leisen, from Georgia Tech; Chad Studvick, from the University of Akron; Sabyasachi Roy Chowdhury, from Iowa; and Florian Kleemiss, from Aachen University, in Germany.

Vlaisavljevich’s work was funded by the U.S. Department of Energy, as an Early Career award, through the Office of Science, Basic Energy Sciences, Heavy Element Chemistry Program. The U.S. National Science Foundation also funded the research.