Lithium halide ion-pair recognition with halogen bonding and chalcogen bonding heteroditopic macrocycles.

A series of halogen bonding and chalcogen bonding phenanthroline containing heteroditopic macrocyclic receptors exhibit cooperative recognition of lithium halide (LiX) ion-pairs. Quantitative 1H NMR ion-pair titration experiments in CDCl3 : CD3CN (1 : 1, v/v) reveal a co-bound lithium cation switches on halide anion binding, most notably with the halogen bonding host system. The employment of bis- iodo- and telluromethyl-triazole sigma-hole donor motifs endows contrasting halide anion selectivity and binding affinity, with the halogen bonding ditopic host capable of exclusively binding lithium chloride whereas the chalcogen bonding ditopic receptor displays notable selectivity for lithium iodide over lithium bromide. Preliminary solid-liquid extraction experiments demonstrate the potential of sigma-hole mediated ion-pair recognition as a promising strategy for lithium salt recovery.