Tetradentate Ligand's Chameleon-Like Behavior Offers Recognition of Specific Lanthanides

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Abstract

The surging demand for high-purity individual lanthanides necessitates the development of novel and exceptionally selective separation strategies. At the heart of these separation systems is an organic compound that, based on its structural features, selectively recognizes the lighter or heavier lanthanides in the trivalent lanthanide (Ln) series. 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 the unique ability to achieve peak selectivity in the light, medium, and heavy Ln regions. The structural rigidity of the bis-lactam-1,10-phenanthroline 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 (phenanthroline → bipyridine) results in the fast formation of complexes with light Lns, but, in the span of hours, the peak selectivity shifts toward middle Ln (Sm), resulting in time-resolved separation. As expected, at low nitric acid concentrations, the neutral tetradentate ligand complexes with Ln3+ ions. However, the change in extraction mechanism is observed at high nitric acid concentrations, leading to the formation and preferential extraction of anionic heavy Ln species, [Ln(NO3)x+3]x−, that self-assemble with two ligands that have undergone protonation, forming intricate supramolecular architectures. The tetradentate ligand that is structurally balanced with restrictive and unrestrictive motifs demonstrates unique, controllable selectivity for light, middle, and heavy Lns, underscoring the pivotal role of solvation and ion interactions within the first and second coordination spheres.

Original languageEnglish
JournalJournal of the American Chemical Society
DOIs
StateAccepted/In press - 2024

Funding

This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Separation Science program, and Materials Chemistry program under award no. DE-SC00ERKCG21 (J.T.D. was supported under award ERKCK60, and J.E. was supported under award ERKCC08). This research used resources of the Advanced Photon Source at beamline 12-BM, a DOE User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract DE-AC02-06CH11357. Portions of this research were carried out at National Synchrotron Light Source II (NIST beamline 6-BM), a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704.

FundersFunder number
Basic Energy Sciences
U.S. Department of Energy
Office of Science
Brookhaven National LaboratoryDE-SC0012704
Argonne National LaboratoryDE-AC02-06CH11357
Separation Science programERKCK60, ERKCC08, DE-SC00ERKCG21

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