Interrogation of Mn+-oxo Interaction Effects on Uranyl Bond Strength and Covalency

The uranyl cation, (UO2)2+ is the most stable form of uranium in aerobic and aqueous conditions, and therefore the most relevant species environmentally and industrially. This species features strong uranium-oxygen bonds, leading to relatively inert terminal oxygen atoms and restricting both reactivity and coordination geometries. The goal of this work was to develop a fundamental understanding of how these bonds can be weakened by studying engagement of the terminal oxygen atoms for the purposes of tuning reactivity. We present the synthesis and characterization of thirty-four compounds containing the uranyl cation and a secondary metal cation (Pb2+, Ag+, and Cd2+) connected by organic linkers. Spectroscopic characterization demonstrated that close metal-oxo interactions cause quenching of the uranyl luminescence, and red-shifting of the U=O symmetric stretching frequency in the Raman, which is indicative of bond weakening. Computational analyses (NBO, QTAIM) were used to rationalize the bond weakening, pointing to the population of antibonding U=O orbitals and depopulation of the bonding U=O orbitals. Harder metal cations (Cd2+ > Pb2+ > Ag+) had a stronger the influence on these interactions and greater bond weakening effects. A study of the equatorial coordination sphere in these compounds suggested that interactions at the oxo groups could be promoted by increasing electron donation into the uranium atom through equatorial coordination. This work makes substantive contributions for the control of Mn+-oxo interactions and subsequent tuning of U=O bond strengths, both of which may inform reactivity and spectroscopic trends. Control of these properties is relevant to applications in separations chemistry for nuclear waste clean-up and forensic detection of uranyl species.

Author

• Brager, Dominique

Language

• English

Keyword

• Actinide Chemistry
• Uranium
• Computational Chemistry
• Spectroscopy
• Crystallography

Date created

• 2024

Type of Work

• Dissertation

License

• All rights reserved

Rights statement

• In Copyright

GW Unit

• Chemistry

Degree

• Ph.D.

Advisor

• Cahill, Christopher L.

Committee Member(s)

• Kostal, Jakub
• Schofield, Mark H.

Persistent URL

•  https://scholarspace.library.gwu.edu/etd/b2773w64m