Structure of a uranyl peroxo complex in aqueous solution from first-principles molecular dynamics simulations

Area of Science:

• Inorganic Chemistry
• Computational Chemistry
• Physical Chemistry

Background:

• Uranyl(VI) compounds exhibit diverse speciation.
• Understanding ligand coordination is crucial for uranyl chemistry.

Purpose of the Study:

• To investigate the relative stability of peroxo and hydroperoxo uranyl(VI) complexes.
• To elucidate the role of solvent effects on uranyl speciation.

Main Methods:

• Ab initio and density-functional theory computations.
• Car-Parrinello molecular dynamics simulations.
• Thermodynamic integration for free energy calculations.

Main Results:

• The hydroperoxo isomer is more stable in the gas phase.
• The peroxo isomer ([UO2(OH)(κ(2)-O2)(H2O)2](-)) is more stable in aqueous solution by ~32 kJ mol(-1).
• Solvation effects, hydration shells, and dipole moments stabilize the peroxo form.

Conclusions:

• Explicit solute-solvent interactions are critical for determining uranyl(VI) speciation.
• The stability of uranyl complexes is highly dependent on the aqueous environment.
• Computational methods accurately predict solution-phase stability.