Structural studies coupling X-ray diffraction and high-energy X-ray scattering in the UO2(2+)-HBr(aq) system
Richard E Wilson1, S Skanthakumar, C L Cahill
1Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, USA. rewilson@anl.gov
Inorganic Chemistry
|September 28, 2011
Summary
Structural chemistry of uranium(VI) in hydrobromic acid solutions reveals distinct uranyl complexes in solution versus solid states. High-energy X-ray scattering shows a lower U-Br coordination number in solution compared to crystallized salts.
Area of Science:
- Inorganic Chemistry
- Structural Chemistry
- Solution Chemistry
Background:
- Uranium(VI) chemistry is crucial for nuclear fuel cycles and waste management.
- Understanding uranyl speciation in concentrated halide media is vital for predicting behavior.
Purpose of the Study:
- To elucidate the structural chemistry of uranium(VI) in concentrated aqueous hydrobromic acid.
- To compare uranium(VI) complex structures in solution with those in crystallized salts.
Main Methods:
- Single crystal X-ray diffraction for solid-state structures.
- Synchrotron-based high-energy X-ray scattering (HEXS) for solution structures.
- Quantitative analysis of HEXS data for coordination numbers.
Main Results:
- Crystal structures of Cs(2)UO(2)Br(4), Rb(2)UO(2)Br(4)·2H(2)O, K(2)UO(2)Br(4)·2H(2)O, and (NH(4))(2)UO(2)Br(4)·2H(2)O determined.
- A molecular uranium(VI) dimer, (UO(2))(2)(OH)(2)Br(2)(H(2)O)(4), was identified.
- Solution studies revealed an average U-Br coordination number of 1.9(2).
- Significant differences observed between solid-state and solution structures.
Conclusions:
- Uranyl tetrabromide salts exhibit a U-Br coordination number of 4 in the solid state.
- In concentrated hydrobromic acid solution, uranium(VI) exhibits a lower average U-Br coordination number.
- Structural discrepancies highlight the importance of in-situ solution studies for understanding uranyl speciation.
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