Solvent effects on uranium(VI) fluoride and hydroxide complexes studied by EXAFS and quantum chemistry

Area of Science:

• Inorganic Chemistry
• Computational Chemistry
• Structural Chemistry

Background:

• Uranium complexes exhibit diverse coordination geometries influenced by ligands and solvent environments.
• Understanding these structures is key to predicting reactivity and properties of uranium compounds.

Purpose of the Study:

• To investigate the structural differences between uranium(VI) fluoride and hydroxide complexes.
• To elucidate the role of solvent effects in determining the coordination geometry of these complexes.
• To validate computational methods for predicting uranium complex structures.

Main Methods:

• Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy for experimental structural determination.
• Wave function-based and Density Functional Theory (DFT) methods for theoretical investigations.
• Solvent modeling using discrete spheres and conductor-like polarizable continuum models (CPCM).

Main Results:

• Fluoride complexes (UO(2)F(n)(H(2)O)(5-n)(2-n)) adopt pentagonal bipyramid geometry.
• Hydroxide complexes (UO(2)(OH)(4)(2-)) exhibit square bipyramid geometry.
• CPCM solvent models accurately reproduced the experimentally observed geometries, unlike models without solvent.
• Calculated bond distances closely matched experimental data when appropriate solvent models were used.

Conclusions:

• Solvent effects are the primary drivers of structural variations between uranium(VI) hydroxide and fluoride complexes.
• Accurate prediction of uranium complex structures necessitates the inclusion of sophisticated solvent models.
• Computational methods, especially CPCM, are reliable tools for studying the structural chemistry of uranium complexes.