Establishing a Molecular Basis for Rare Earth Separations: Progress Towards Rare Earth Recycling Through Coordination and Redox Chemistry

The rare earth elements (La–Lu, Sc and Y) are used in a variety of modern technologies due to their unique optical and magnetic properties. However, extraction and purification of individual rare earth elements is a challenging process that requires significant amounts of energy and generates large quantities of waste. This work focuses on the development of simple, single-step rare earth separation procedures that depend upon a tripodal nitroxide ligand framework. Optimization of solvent conditions for these separations was conducted for targeted rare earth combinations, demonstrating the tunability of the separation procedures. Derivatization of the tripodal ligand framework demonstrated that changing the electronic properties of the rare earth complexes led to modification of their underlying properties, allowing for efficient separations in greener alternative solvents. Preparation of a tris(nitroxide) tripodal, radical proligand was confirmed by magnetometry and electron paramagnetic resonance studies. Reaction of the isolated tri-radical species with different rare earth complexes revealed significantly different reaction rates that allowed for the development of a chelation-driven kinetic separation process for rare earth elements