COLUMBUS, Ohio -- Ohio State University chemists and their colleagues at the University of Virginia have created the first-ever compounds of uranium bonded to atoms of three so-called "noble gases" -- argon, krypton, and xenon.
In the last 40 years, scientists have only been able to form compounds from noble gases a handful of times. These chemical outcasts were once thought incapable of forming bonds with other elements, and until the 1960s were considered completely inert.
The chemists published their results Thursday, February 28, in the journal Science, available online via ScienceExpress.
The same technique that created these uranium compounds might be used to link noble gases to other metals, said Bruce Bursten, professor and chair of chemistry at Ohio State.
Bursten's coauthors include Jun Li, a former Ohio State research scientist now at Pacific Northwest National Laboratory, and Lester Andrews, professor of chemistry, and Binyong Liang, a chemistry graduate student, both of the University of Virginia.
The chemists created their first noble gas compound by chance, Bursten said, largely because of some unexpected results obtained by the Virginia group in some follow-up experiments.
"It's like that quote, 'luck is what happens when preparation meets opportunity,'" he said. "We got lucky. We were working hard to cover all bases on a different aspect of the chemistry, and when we got some strange results, we were able to recognize what was happening."
They were studying a molecule with the formula CUO, which is formed from the reaction of uranium atoms with carbon monoxide. The Ohio State and Virginia teams have been studying molecules like CUO in order to better understand how the radioactive metals react with small molecules, such as carbon monoxide, carbon dioxide, and water.
Using equipment at the University of Virginia, they produced molecules of CUO in the noble gas neon. For that experiment, the neon atoms simply formed a protective "cage" around the CUO at very low temperatures (4 Kelvin, about -270°C or -450°F) to preserve the molecules for study.
"We were studying the reactions of uranium atoms with carbon monoxide in solid neon," Andrews said. "When we repeated the experiments in solid argon, we got distinctly different spectra, which was our first clue that an unusually strong interaction was occurring between CUO and argon.
"We then turned to our collaborators at Ohio State to see whether theory predicted a different state for CUO in argon than in neon, and their calculations nicely explained our observations."
In an effort to dissect these strange results, the Ohio State portion of the research team began simulating the interaction of CUO and argon by using theoretical calculations on supercomputers at the Ohio Supercomputer Center and at the Pacific Northwest National Laboratory. Much to the chemists' astonishment, the simulations suggested that the uranium atoms in the CUO were forming bonds with the noble gas atoms.
"We didn't really believe that, so we tried every trick we knew to prove that it wasn't true," Bursten said.
Repeated experiments with mixtures of argon and neon, as well as xenon and krypton, showed that uranium-noble gas compounds were forming. The experimental observations were corroborated by additional theoretical calculations.
"These results expand the means in which the noble gases can form compounds with other elements and give us a new look at the ways in which chemical bonds can form," Bursten said.
The chemists are now investigating the possibility that other uranium compounds and other metals will bind with noble gases under these low-temperature conditions.
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