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David Bradley ISSUE #70
November 2007
Lester Andrews
Organic Uranium

The first ever uranium methylidyne molecule has been synthesized by US chemists despite the reactivity of the heavy, heavy metal. The new structure contains a unique uranium-carbon triple-bond.

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Lester Andrews of the University of Virginia and colleagues have worked on uranium chemistry for fifteen years preparing dozens of different molecules. So, they know very well the extent of uranium's reactivity. To make this latest compound, however, required a focused pulsed laser to evaporate depleted uranium in a vacuum chamber and react the vapor with fluoroform (CHF3) molecules. But, that was not all, in order to trap the new triple-bonded compound they had to freeze it in an argon atmosphere at just 8 degrees above absolute zero. "The uranium atom went into a C-F bond and rearranged the other fluorine atoms to make the new molecule," Andrews explains. The team then used infrared spectroscopy to characterize this exotic and unstable triple bond between the uranium and carbon atoms.

Credit: Andrews/PNAS

After they did the IR spectroscopy, the team calculated the structure and bonding properties of the new compound and the simulation with the spectroscopic results. "The agreement was good enough for us to conclude we had in fact made the molecule that we set out to make," Andrews says.

Andrews points out that it is not only chemists who ought to know more about the properties of uranium compounds. "I think it's imperative for people to know more about uranium chemistry, particularly our policy makers," he adds, "People need to realize that you can't just dig up a shovelful of uranium ore and make a bomb from it. One has to go through a considerable amount of chemical process to win uranium from its ore. You have to refine the ore into metal and enrich the material in the hot isotope before it has uses as a nuclear material. This is highly complicated chemistry."

Proc Natl Acad Sci, 2007, 104, 18919-18924