are less applicable to these heavy elements. Furthermore, understanding the properties of transplutonium elements has been restricted by their radioactivity and scarcity. This is especially true for einsteinium, the heaviest element on the periodic table that can currently be generated in quantities sufficient to enable macroscale studies. Researchers from the Lawrence Berkeley National Laboratory and Los Alamos National Laboratory overcame these challenges by working with small quantities of einsteinium-254 to characterize its complex compound in solution and as a solid.
Einsteinium, a synthetic element with the symbol Es and atomic number 99, is a soft, silvery-white, paramagnetic metal.
It was discovered as a component of the debris of the first hydrogen bomb explosion in 1952, and named after Albert Einstein.
The high radioactivity and scarcity of einsteinium isotopes have precluded this element from receiving the same attention as its preceding neighbors within the actinide series, the bonding, electronic structure and chemical properties of which are assumed to be between those of the transition metals and the lanthanides.
Contemporary worldwide availability of einsteinium is restricted to small-scale quantities (nano- to micrograms) of one of its two long-lived isotopes, einsteinium-254 (half-life = 275.7 days), which is substantially more radioactive than its longer-lived transplutonium neighbor, californium-249.
However, there are some examples that demonstrate how the technical challenges associated with working with transplutonium elements can be overcome, even for less accessible elements such as einsteinium.
With less than 250 nanograms of einsteinium-254, Berkeley Lab scientist Rebecca Abergel and colleagues synthesized and characterized a complex compound of this transplutonium element.
“There’s not much known about einsteinium,” Dr. Abergel said.
“It’s a remarkable achievement that we were able to work with this small amount of material and do inorganic chemistry.”
“It’s significant because the more we understand about its chemical behavior, the more we can apply this understanding for the development of new materials or new technologies, not necessarily just with einsteinium, but with the rest of the actinides too. And we can establish trends in the periodic table.”
The researchers used the Molecular Foundry at Berkeley Lab and the Stanford Synchrotron Radiation Lightsource at SLAC National Accelerator Laboratory to conduct luminescence spectroscopy and X-ray absorption spectroscopy experiments.
They able to measure a bond distance with einsteinium and also discovered some physical chemistry behavior that was different from what would be expected from the actinide series.
“Determining the bond distance may not sound interesting, but it’s the first thing you would want to know about how a metal binds to other molecules,” Dr. Abergel said.
“What kind of chemical interaction is this element going to have with other atoms and molecules?”
Once scientists have this picture of the atomic arrangement of a molecule that incorporates einsteinium, they can try to find interesting chemical properties and improve understanding of periodic trends.
“By getting this piece of data, we gain a better, broader understanding of how the whole actinide series behaves,” Dr. Abergel said.
“And in that series, we have elements or isotopes that are useful for nuclear power production or radiopharmaceuticals.”
The research also offers the possibility of exploring what is beyond the edge of the periodic table, and possibly discovering a new element.
“We’re really starting to understand a little better what happens toward the end of the periodic table, and the next thing is, you could also envision an einsteinium target for discovering new elements,” Dr. Abergel said.
The results were published in the journal Nature.
K.P. Carter et al. 2021. Structural and spectroscopic characterization of an einsteinium complex. Nature 590, 85-88; doi: 10.1038/s41586-020-03179-3