Unveiling the Structure-Property Correlations of Acid-Stable Cyclic Imide Dioximes for Enhanced V(V) and U(VI) Sequestration.

Uranium and vanadium are critical minerals for sustainable energy, used in nuclear power and vanadium redox flow batteries, respectively. Extracting them from secondary sources is important for meeting global demand. The acid-stable, aromatic-based cyclic imide dioximes (Ar-CIDs) show great potential in this regard. In this study, we employed spectroscopic and thermodynamic analyses in methanol/water solutions to elucidate the coordination modes and stability constants of two Ar-CIDs, namely phthalimide dioxime (H2CIDII) and naphthalimide dioxime (H2CIDIII), with selected metal ions. Additionally, density functional theory (DFT) calculations were performed to examine the optimized coordination geometries and ligand structural deformation, providing structural insight into the experimentally observed coordination behavior. First, a structural modification in H2CIDII led to the formation of robust complexes with uranyl ions, UO22+, while impeding interaction with vanadate H2VO4-, due to a stretch in binding angle. Conversely, H2CIDIII exhibited experimentally determined stability constants for H2VO4- that were 1-4 orders of magnitude higher than those for other metal species. Notably, the robust chemical stability of H2CIDII and H2CIDIII in acidic environments, coupled with their capacity for selective metal complexation, offers potential as valuable extractants for UO22+ik and H2VO4- from secondary sources. These findings highlight the potential of Ar-CIDs in sustainable critical mineral extraction.