Inclusion Complexes of Halide Anions with Macrocyclic Receptors

This review highlights the binding and structural aspects of halide complexes with synthetic macrocyclic receptors with different functional groups including charged amine (protonated or quaternary form), amide, thioamide and pyrrole. Different binding modes in solution and solid states in terms of monotopic, ditopic, cascade and sandwich complexes of halides are discussed. The sizes and functional groups of the macrocycles, as well as solvents have been shown to play a critical role in binding and selectivity for anionic guests. In general, macrobicyclic or tricyclic hosts tend to form monotopic complexes with anions of comparable sizes, while an expanded cavity is needed for the higher degree of complexation (e.g., ditopic or cascade). On the other hand, the formation of a sandwich complex is favored by monocyclic ligands with hydrogen donor groups.