Halogen bonding motifs for anion recognition

The halogen bond is a powerful non-covalent interaction between the electron deficient sigma-hole region of a group 17 halogen element covalently bonded to electron withdrawing groups, and a Lewis base. The use of halogen bonding (XB) in anion recognition chemistry has rapidly expanded in recent decades, with a diverse range of host systems available for the selective complexation and detection of various anionic guest species in solution. These XB receptors have contrasting, and often superior anion binding affinities and properties when compared to their analogous hydrogen bonding receptors. This review summarises the development of these host systems to date, by first examining the various neutral and cationic XB donor motifs commonly employed and their integration into supramolecular acyclic and macrocyclic receptors. This is followed by a discussion of XB interactions in anion-binding mechanically interlocked hosts, which have proved to be effective receptors for a diverse range of anions in competitive aqueous solvent media, including biologically relevant chiral anions and dicarboxylates.