Advancing Understanding of Heavy Elements at the Edge of the Periodic Table

The Science

Researchers have for the first time examined in detail a compound of einsteinium (Es). Einsteinium is one of the synthetic elements—elements not found in nature. It is also the heaviest element currently available for classical chemistry studies. To examine this rare element, the researchers developed new methods for working with microscopic samples of einsteinium 254, a highly radioactive isotope of the element.

The Impact

This is the first chemical characterization of an einsteinium compound in more than 40 years. The analyses provide a glimpse into the fundamental properties of this element, suggesting that the chemistry of einsteinium is quite different from the other elements in the actinide series of the Periodic Table. The actinides include elements like uranium and plutonium. Most actinides are not found in nature, and all are radioactive. These experimental results chart the path to exploring the fundamental behavior of rare heavy elements. The results could transform chemistry, potentially pointing to a new understanding of chemistry across the Periodic Table.

Summary

Researchers prepared a coordination complex with einsteinium (Einsteinium-254) and an octadentate hydroxypyridinonate chelator, 3,4,3-LI(1,2-HOPO). They characterized the resulting molecular species through a combination of X-ray absorption and luminescence spectroscopies. XANES and EXAFS measurements provided an experimental measurement of the L3-absorption-edge energy of Es and of an Es bond distance. Luminescence spectroscopy results revealed Es sensitization, via the antenna effect, with a hypsochromic luminescence shift upon metal complexation. This is unprecedented for +3 actinide (and lanthanide) sensitized luminescence in similar systems. Combined with the EXAFS and XANES analyses, the sensitive EsIII luminescence underlines the potential differences between Es and the rest of the actinides, including an intermediate spin-orbit coupling scheme, in which j-j coupling is prevalent. As all data were collected with less than 200 ng of metal, these results highlight the potential to advance coordination chemistry across the actinide series and the periodic table when samples are available in only limited quantities.

Funding

This research was funded by the Department of Energy (DOE) Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division, Heavy Element Chemistry Program at Lawrence Berkeley National Laboratory (LBNL) and Los Alamos National Laboratory (LANL). The research was also funded in part by a DOE Integrated University Program graduate research fellowship, the Glenn T. Seaborg Institute at LANL, the DOE Office of Science Early Career Research Program, and the DOE Office of Science, Office of Workforce Development for Teachers and Scientists, Office of Science Graduate Student Research (SCGSR) program. The research made use of the Stanford Synchrotron Radiation Lightsource at SLAC National Accelerator Laboratory and instrumentation at the Molecular Foundry at LBNL, both DOE Office of Science user facilities.