S. Pramanik, A. Ivanov, D. Jiang, I. Popovs, S. Jansone-Popova
Oak Ridge National Laboratory,
United States
Keywords: ligands, preorganization, extraction, lanthanides, anions
Summary:
Due to their general applications in advanced technologies, lanthanides play a huge role in the US economy, energy, and national security. Separating lanthanides is a massive task due to costly methods and environmental challenges. Our recent results also represent the first example of radioactive Promethium complex using water soluble diglycolamides ligands. Our present work involves the design and synthesis of multidentate preorganized ligands for the selective separation of lanthanides. A series of ligands were designed and synthesized to effectively separate lanthanides with tunable selectivity. This work emphasizes the significant implications resulting from modifying the donor group configuration within an N, O-based tetradentate ligand and the changes in the solvation environment of Ln ions in the process of separating Lns, with a unique ability to achieve peak selectivity in the light, medium, and heavy Ln region. The structural rigidity of the bis-lactam-1,10-phenanthroline (BLPhen) ligand enforces size-based selectivity, displaying an exceptional affinity for Lns having larger ionic radii, such as La. Modifying the ligand by eliminating one preorganization element (bipyridine) results in the fast formation of complexes of BLBPy with light Lns, but after equilibrium, the peak selectivity shifts towards middle Ln (Sm)– resulting in time-resolved separation. As expected, the neutral tetradentate ligand complexes with Ln ions at low nitric acid concentrations. However, the change in extraction mechanism is observed at high nitric acid concentrations, leading to the formation and preferential extraction of anionic heavy Ln ensemble, [Ln(NO3)5]2-, that self-assemble with two ligands that have undergone protonation forming intricate supramolecular architectures. Lately, we have also been focusing on synthesizing redox-active DGA ligands, which could lead to the development of new environmentally friendly and efficient separation of trivalent lanthanides. This presentation will highlight our recent results in unraveling the synthesis, coordination, and selective methods to separate lanthanides.