Dominique Brager, Graduate Student, Cahill Lab, GW Department of Chemistry

The Department of Chemistry Presents:  Dominique Brager, Graduate Student, Cahill Lab, GW Department of Chemistry

The uranyl cation, (UO₂)²⁺ is the most stable form of uranium in aerobic and aqueous conditions, making it the most relevant species environmentally and industrially. Key features of this species include the strong uranium-oxygen bonds, and relative inertness of the terminal oxygen atoms, each of which restricts both reactivity and coordination geometries. Our focus, therefore, is to develop a fundamental understanding of how these bonds can be weakened, and a strategy for how the nominally terminal oxygen atoms may be engaged in further bonding. Our group has historically probed second-sphere interactions with the oxo groups as a means of influencing bonding character, and the current efforts focus on the effects of coordinated metal cations. As such, we have prepared synthesized structures containing the uranyl cation and a secondary metal cation (Pb²⁺, Ag⁺, and Cd²⁺) connected by anionic organic linkers. We found that close metal-oxo interactions cause significant quenching of the characteristic uranyl luminescence, and red-shifting of the U=O symmetric stretching frequency in the Raman, which are indicative of bond weakening. Computational analysis (NBO, QTAIM) indicates a population of antibonding U=O orbitals and a depopulation of bonding U=O orbitals, supporting the bond weakening seen in the spectroscopic data. We observe that the harder the metal cation (Cd²⁺ > Pb²⁺ > Ag⁺), the stronger the influence of these interactions and the greater the bond weakening effects are. Additionally, we determined 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 informs applications in separations chemistry for nuclear waste clean-up and forensic detection of uranyl species.

BIO

Dominique received her B.S. in Chemistry from American University in Washington, DC where she did undergraduate research under Dr. Douglas Fox, studying cellulose nanomaterials, and under Dr. Shouzhong Zou, studying catalysts for low temperature fuel cells. In 2019, Dominique joined Professor Christopher L. Cahill’s research group to pursue her interest in the field of nuclear chemistry where she studies heterometallic uranium/heavy metal hybrid materials.