Evidence for Uranium(VI/V) Redox Supported by 2,2′-Bipyridyl-6,6′-dicarboxylate

• Published in: Inorganic chemistry 2023-10, Vol.62 (39), p.16131-16148
• Main Authors: Mikeska, Emily R., Ervin, Alexander C., Zhang, Kaihua, Benitez, Gabriel M., Powell, Samuel M. R., Oliver, Allen G., Day, Victor W., Caricato, Marco, Comadoll, Chelsea G., Blakemore, James D.
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.3c02397

The 2,2′-bipyridyl-6,6′-dicarboxylate ligand (bdc) has been shown in prior work to effectively capture the uranyl­(VI) ion, UO2 2+, from aqueous solutions. However, the redox properties of the uranyl complex of this ligand have not been addressed despite the relevance of uranium-centered reduction to the nuclear fuel cycle and the presence of a bipyridyl core in bdc, a motif long recognized for its ability to support redox chemistry. Here, the bdc complex of UO2 2+ (1-UO 2 ) has been synthetically prepared and isolated under nonaqueous conditions for the study of its reductive chemical and electrochemical behavior. Spectrochemical titration data collected using decamethylcobaltocene (Cp*2Co) as the reductant demonstrate that 1e– reduction of 1-UO 2 is accessible, and companion near-infrared and infrared spectroscopic data, along with theoretical findings from density functional theory, provide evidence that supports the accessibility of the U­(V) oxidation state. Data obtained for control ruthenium complexes of bdc and related polypyridyl dicarboxylate ligands provide a counterpoint to these findings; ligand-centered reduction of bdc in these control compounds occurs at potentials more negative than those measured for reduction of 1-UO 2 , further supporting the generation of uranium­(V) in 1-UO 2 . Taken together, these results underscore the usefulness of bdc as a ligand for actinyl ions and suggest that it could be useful for further studies of the reductive activation of these unique species.