Oak Ridge Scientists Achieve Historic First: Promethium Chemistry Solved in Solution

Highlights

• Scientists at Oak Ridge National Laboratory successfully synthesized and characterized a promethium complex in aqueous solution, solving a 75-year chemistry challenge.
• The study provides unprecedented direct measurements of promethium’s bond lengths, electron distribution, and coordination geometry using advanced synchrotron spectroscopy.
• This breakthrough opens new possibilities for nuclear battery technologies, spacecraft applications, and beta radiation therapy by enhancing understanding of this elusive lanthanide element.

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In a groundbreaking study published in Nature, researchers at the U.S. Department of Energy’s Oak Ridge National Laboratory (ORNL) have achieved what chemists have failed to do for over 75 years: synthesize and fully characterize a promethium complex in aqueous solution. The advance finally brings the elusive 61st element into the experimental record of the lanthanides, completing a major missing link in f-block chemistry.

Led by Dr. Alexander S. Ivanov, the team used modern synchrotron spectroscopy and high-level quantum chemistry to confirm the structure of the [Pm(PyDGA)₃]³⁺ complex, formed with a newly synthesized ligand, bispyrrolidine diglycolamide (PyDGA). The experiment marks the first time that bond lengths, electron distribution, and coordination geometry of promethium have been directly measured in solution—data that had been inaccessible due to promethium’s radioactivity, synthetic origin, and isotopic scarcity.

Promethium’s measured bond length of 2.476 Å fits perfectly into a full experimental profile of lanthanide contraction, revealing that bond shortening accelerates from lanthanum to promethium and slows across the heavier elements. This experimental validation not only resolves longstanding theoretical predictions but also enhances models used in rare earth separation, nuclear fuel processing, and radiopharmaceutical development.

While trace contamination from promethium decay products (notably 147Sm) posed analytical challenges, the study’s agreement between EXAFS, ab initio simulations, and natural bond orbital analysis makes the conclusions robust. The research demonstrates that promethium, long considered too exotic to study in detail, can now be integrated into applied chemistry and strategic resource planning.

The implications are massive: with promethium used in nuclear batteries, spacecraft, and beta radiation therapy, understanding its chemistry unlocks more efficient extraction and potential synthetic control. More broadly, it signals a new era in rare earth science, where even the most inaccessible elements can be tamed by modern tools—offering strategic advantages in a world increasingly dependent on secure access to critical materials.