A Bis-Imidazolium Receptor for the Selective Crystallization of Fluoride through Hydrogen Bonding

Selective recognition and separation of fluoride anions from other halides remain significant challenges in supramolecular chemistry due to the similar physicochemical properties of halide ions and the environmental concerns associated with fluoride contamination. We report a simple dicationic bis-imidazolium receptor with hydroxyethyl pendants that selectively binds fluoride ions over other halides through a selective “bidentate” hydrogen bonding mechanism involving C2–H···F– and O–H···F– interactions. This unique binding mode facilitates the crystallization of a fluoride complex from polar solvents containing chloride, bromide, or iodide ions. Despite minimal preorganization, the receptor exhibits size-matched binding pockets that selectively accommodate fluoride ions, enabling their separation from equimolar halide mixtures. This work introduces a new approach to fluoride recognition and offers potential applications in environmental remediation and industrial processes.