The frustratingly unreactive oxygen atoms in the water-soluble uranyl ion (UO2)2+ have now been shown to be capable of powerful chemistry—in the right environment.
Inorganic chemists Polly L. Arnold and Jason B. Love at Scotland's University of Edinburgh and colleagues show that when (UO2)2+ is enmeshed within an inflexible jaw-shaped ligand (shown), the ion's electronic structure is altered sufficiently to make its normally inert oxygens reactive enough to cleave Si-N and Si-C bonds (Nature 2008, 451, 315).
The discovery has potential for helping to solve problems of pervasive uranium contamination around nuclear power plants and might be generalized to include the uranyl ion's cousins, the radioactive plutonyl and neptunyl ions.
"This represents a sea change in uranium chemistry," notes James M. Boncella, an inorganic chemist at Los Alamos National Laboratory, in a piece accompanying the report.
Relativistic effects in the heavy uranium atom make some of its nonvalence electrons available for tight bonding with two oxygen atoms. For the most part, chemists have succeeded only in designing ligands that bind to the uranium atom.
However, Arnold and Love recently uncovered the ion's O-reacting potential, showing that a uranium-bound uranyl complex reacts with transition-metal silylamides (J. Am. Chem. Soc. 2006, 128, 9610). The uranium atom is coordinated within the upper portion of the open-jaw-shaped complex. One of the uranyl oxygens sticks up out of it, while the other oxygen sticks down into the mouth of the jaw and can form a bond with a transition-metal atom in the lower jaw segment.
The researchers now show that when the same uranium-bound uranyl complex reacts with potassium hydride, silanes, and transition-metal halides, the protruding oxygen becomes capable of abstracting and binding a Si(CH3)3 group.
The work "provides another example of an emerging body of research showing that a much broader envelope of actinide chemistry can be accessed than previously thought possible," says Gary S. Groenewold, an inorganic chemist at Idaho National Laboratory.