Geometric supermolecules constructed by multi-ended acidic extractants and their coupling effect on the separation of lanthanides

Highlights • The self-assembly strategy of geometric supermolecules was applied to lanthanides separation. • 6-aniline carbonyl 2-pyridine carboxylic acid (SL1) provided tridentate coordination motif. • Based on SL1, a single-ended extractant (SE1) and four multi-ended extractants (MEs) were developed. • Upon coordinating Ln 3+ , SE1 yielded a mononuclear complex, while MEs formed geometric supermolecules. • The coupling effect of geometric supermolecules reduced Ln 3+ separation efficacy compared to mononuclear complex. Polynuclear supermolecules characterized by geometric structures exhibit distinct selective behavior for Ln 3+ during the assembly process, in contrast to mononuclear complexes, for the sake of coupling effect. While most studies about geometric supermolecules predominantly center on their assembly behaviors, overlooking their role in lanthanide separation. In this study, we bridge the gap between the behavioral study of geometric supermolecules and their application in separation processes by integrating these structures into the realm of solvent extraction. We report four cases of Multi-ended Extractants (MEs) and a case of Single-ended Extractant (SE1) serving as a control group. All these extractants are classified as acidic extractants. As designed, SE1 forms a mononuclear complex with Ln 3+ , whereas MEs assemble into geometric supermolecules with Ln 3+ . In the case of mononuclear complexes, Ln 3+ ions are not coupled. While in geometric supermolecules, Ln 3+ ions are interconnected through MEs, resulting in coupling between Ln 3+ ions. Although MEs bear the same coordination motif as SE1, coupling effect of geometric supermolecules weakens the separation efficiency towards light lanthanide ion pairs in comparison to corresponding mononuclear complex. These results deepen our comprehension of coupling effect of geometric supermolecules on separation and provide a foundation for subsequent studies on the impacts of such couplings on separation performance.