Equatorial Electronic Structure in the Uranyl Ion: Cs2UO2Cl4 and Cs2UO2Br4

Dumitru-Claudiu Sergentu; Frédéric Gendron; Eric D Walter; Sejun Park; Cigdem Capan; R Gian Surbella; Chuck Z Soderquist; Gabriel B Hall; Sergey I Sinkov; Jochen Autschbach; Herman Cho

doi:10.1021/acs.inorgchem.1c02832

Equatorial Electronic Structure in the Uranyl Ion: Cs₂UO₂Cl₄ and Cs₂UO₂Br₄

Inorg Chem. 2022 Mar 7;61(9):3821-3831. doi: 10.1021/acs.inorgchem.1c02832. Epub 2021 Nov 24.

Authors

Affiliations

¹ Department of Chemistry, University at Buffalo, State University of New York, Buffalo, New York 14260-3000, United States.
² Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99354, United States.
³ Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99354, United States.
⁴ Washington State University, Richland, Washington 99354, United States.
⁵ National Security Directorate, Pacific Northwest National Laboratory, Richland, Washington 99354, United States.
⁶ Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99354, United States.

PMID: 34817159
DOI: 10.1021/acs.inorgchem.1c02832

Abstract

Electric field gradient (EFG) tensors in the equatorial plane of the linear UO₂²⁺ ion have been measured by nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) experiments and computed by relativistic Kohn-Sham methods with and without environment embedding for Cs₂UO₂Cl₄ and Cs₂UO₂Br₄. This approach expands the possibilities for probing the electronic structure in uranyl complexes beyond the strongly covalent U-O bonds. The combined analyses find that one of the two largest principal EFG tensor components at the halogen sites points along the U-X bond (X = Cl, Br), and the second is parallel to the UO₂²⁺ ion; in Cs₂UO₂Cl₄, the components are nearly equal in magnitude, whereas in Cs₂UO₂Br₄, due to short-range bromide-cesium interactions, the equatorial component is dominant for one pair of Br sites and the axial component is larger for the second pair. The directions and relative magnitudes of the field gradient principal axes are found to be sensitive to the σ and π electron donation by the ligands and the model of the environment. Chlorine-35 NQR spectra of ²³⁵U-depleted and ²³⁵U-enriched Cs₂UO₂Cl₄ exhibited no uranium-isotope-dependent shift, but the resonance of the depleted sample displayed a 58% broader line width.