Comparative density functional study of the complexes [UO2(CO3)3]4- and [(UO2)3(CO3)6]6- in aqueous solution
Florian Schlosser1, Lyudmila V Moskaleva, Alena Kremleva
1Technische Universität München, Department Chemie and Catalysis Research Center, 85747, Garching, Germany.
Dalton Transactions (Cambridge, England : 2003)
|May 26, 2010
Summary
Researchers studied uranium(VI) carbonate complexes, [UO(2)(CO(3))(3)](4-) and [(UO(2))(3)(CO(3))(6)](6-), in water. Calculations support the formation of the trinuclear complex in acidic uranyl carbonate solutions.
Area of Science:
- Inorganic Chemistry
- Computational Chemistry
- Environmental Chemistry
Background:
- Uranium speciation and transport in aqueous environments are critical for understanding its environmental fate.
- Anionic uranium(VI) carbonate complexes play a significant role in uranium behavior in water.
Purpose of the Study:
- To investigate the structures of mononuclear tris(carbonato) [UO(2)(CO(3))(3)](4-) and trinuclear hexa(carbonato) [(UO(2))(3)(CO(3))(6)](6-) uranium(VI) complexes in solution.
- To elucidate the formation mechanism of the trinuclear complex from mononuclear units.
Main Methods:
- Employed a relativistic all-electron density functional method for theoretical calculations.
- Applied a full solvation treatment, including explicit aqua ligands for short-range effects and a polarizable continuum model for long-range electrostatic interactions.
- Calculated structures, vibrational frequencies, and free energy changes.
Main Results:
- Structures and vibrational frequencies of "gas-phase" models with explicit aqua ligands showed the best agreement with experimental data.
- The polarizable continuum model slightly overestimated electrostatic interactions for these highly anionic species.
- The calculated free energy change for the association of three mononuclear complexes to form the trinuclear complex matched experimental values.
Conclusions:
- The study provides accurate structural and energetic insights into key uranium(VI) carbonate complexes.
- Results support the formation of the trinuclear hexa(carbonato) complex [(UO(2))(3)(CO(3))(6)](6-) upon acidification of uranyl carbonate solutions.
- The findings are crucial for predicting uranium speciation and transport in natural waters.
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