Chemists at the University of California, Irving, have created a new stable oxidation state of uranium. The new +2 oxidation state, sought for over 30 years, has been seen fleetingly in the gas phase but until now it has not been observed in molecular species in solution. To make the new oxidation state, the team started with a tris(cyclopentadienyl) complex of U3+ and then reduced it with potassium, which forms a counter cation stabilised with a cryptand. The resulting complex with a U2+ ion is stable at room temperature for several days as a solid, or for about an hour and a half when solvated in THF. The chemistry and physical properties of this important metal are still being understood.
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