Tuning the Separation of Light Lanthanides Using a Reverse-Size Selective Aqueous Complexant.

Area of Science:

• Coordination Chemistry
• Separation Science
• Materials Chemistry

Background:

• Lanthanide ion separation is a critical challenge due to their similar chemical properties.
• Organic extractants are widely used, but aqueous complexants with distinct coordination chemistries are underexplored for enhancing intralanthanide separations.
• Novel macrocyclic ligands offer potential for selective metal ion binding.

Purpose of the Study:

• To investigate the lanthanide coordination chemistry of macrophosphi, a novel analogue of macropa.
• To evaluate macrophosphi's efficacy as an aqueous complexant for improving lanthanide separations.
• To demonstrate the potential of reverse-size selective aqueous complexants in lanthanide separation schemes.

Main Methods:

• Synthesis and characterization of macrophosphi, a novel macrocyclic ligand.
• Investigation of lanthanide coordination behavior with macrophosphi using binding affinity studies.
• Implementation of macrophosphi in a biphasic extraction system with bis(2-ethylhexyl)phosphoric acid.
• Determination of separation factors for lanthanide pairs, specifically Ce/La.

Main Results:

• Macrophosphi exhibits a dramatic enhancement in discriminating between light lanthanides compared to its analogue macropa.
• Macrophosphi shows a binding affinity for La³⁺ over 5 orders of magnitude higher than for Gd³⁺.
• Separation factors of up to 45 were achieved for the Ce/La pair using macrophosphi as an aqueous complexant in a biphasic system.
• Remarkable separation of adjacent lanthanides was demonstrated.

Conclusions:

• The substitution of pendent arms in macropa to create macrophosphi significantly improves lanthanide selectivity.
• Macrophosphi's distinct coordination chemistry enables efficient discrimination among light lanthanides.
• Reverse-size selective aqueous complexants like macrophosphi hold significant promise for advancing lanthanide separation technologies.