In an advance for promethium production, researchers get a new view of the element’s properties
Scientists characterize a promethium coordination complex for the first time, furthering the understanding of difficult-to-study lanthanide elements
image: Conceptual art showing the rare earth element promethium in a vial surrounded by an organic ligand. Scientists have discovered hidden features of promethium, opening a pathway for research on other lanthanide elements.
Credit: Image courtesy of Jacquelyn DeMink (art) and Thomas Dyke (photography), Oak Ridge National Laboratory
The Science
Unlike the vast majority of elements, the rare earth element promethium has no stable isotopes, which means that it is constantly decaying, making it difficult to study. In this research, scientists created a pure sample of the isotope promethium-147. They bonded it with a molecule to form a stable complex in water. Next, they used X-ray absorption spectroscopy to explore the structure of the compound and examine the way it chemically bonds.
The Impact
There is a growing demand for promethium, which is used in luminous paint, for lighting, and in nuclear batteries to power pacemakers, guided missiles, communications equipment, and other technology. It also has potential uses in radioactive imaging and cancer treatments. Promethium is one of a series of 15 metallic elements called lanthanides. These elements are difficult to separate from one another because they are so chemically similar. Knowing more about promethium’s chemical properties could lead to better separation methods and new applications. This would enable the production of purer, larger quantities of the element. The Department of Energy Isotope Program is currently the only global producer of promethium-147.
Summary
Scientists used an organic molecule known to form compounds with elements similar to promethium and bonded it to promethium in an aqueous solution. This created a stable compound, allowing the researchers to use X-ray absorption spectroscopy to measure the length of the bonds between promethium and the oxygen atoms it was linked to. The researchers were able to study the electronic structure of the promethium complex, providing new information about promethium’s chemical and physical properties and how those properties differ from those of the other lanthanides.
The differences between promethium and other lanthanides are especially important because scientists learned that in the lanthanide series, the bonds between elements and molecules get shorter as the atomic number increases – up to element 61, promethium. For promethium and lanthanides of higher atomic numbers, the contraction of the ionic radii slows, and the bond lengths decrease at a slower pace. Understanding this chemistry can lead to better separation methods that are needed to increase production of promethium.
Funding
This work was primarily co-sponsored by the Department of Energy (DOE) Office of Science, Office of Basic Energy Sciences’ Chemical Sciences, Geosciences and Biosciences Division and Materials Sciences and Engineering Division for ligand synthesis, lanthanide complexation studies, crystallization processes, spectroscopic analyses, and simulation efforts. The production, purification, and preparation of the promethium sample were supported by the DOE Isotope Program, managed by the Office of Isotope R&D and Production within the Office of Science. The single-crystal X-ray diffraction data collection and refinement were supported by the DOE Office of Science, Office of Basic Energy Sciences’ Chemical Sciences, Geosciences and Biosciences Division.