Disproportionation of the Uranyl(V) Coordination Complexes in Aqueous Solution through Outer-Sphere Electron Transfer
Krishnamoorthy Arumugam1, Neil A Burton1
1Department of Chemistry, School of Natural Sciences, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
Inorganic Chemistry
|November 30, 2021
Summary
Uranyl(V) species are unstable and disproportionate in aqueous solution, forming uranyl(VI) and U(IV) complexes. This process requires H+ and is influenced by ligands, with outer-sphere electron transfer being probable for anionic complexes.
Area of Science:
- Inorganic Chemistry
- Computational Chemistry
- Environmental Chemistry
Background:
- Uranyl(V) species are unstable linear actinyl(VI/V) cations.
- They undergo H+ promoted disproportionation in aqueous solution.
- This reaction forms stable uranyl(VI) and U(IV) complexes.
Purpose of the Study:
- Investigate reduction free energies (RFEs) for [UO2]2+/+ to [UIVO2].
- Explore the stability of uranyl(V) complexes in aqueous solution.
- Compute disproportionation free energies (DFEs) for outer-sphere electron transfer.
Main Methods:
- Density Functional Theory (DFT) calculations.
- Conductor-like polarizable continuum model (CPCM).
- Calculated RFEs and DFEs for aqua, chloride, acetate, and carbonate complexes.
Main Results:
- Computed RFEs for aqua complex agree well with experimental data.
- DFEs confirm H+ is essential for disproportionation.
- Alkali cations offer minor favorability; anionic complexes favor outer-sphere electron transfer.
Conclusions:
- The presence of H+ is imperative for uranyl(V) disproportionation.
- Ligand type and charge significantly influence reaction feasibility.
- Outer-sphere electron transfer is a probable mechanism for anionic uranyl(V) complexes.
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