Anion Receptors: A New Class of Amide/Quaternized Amine Macrocycles and the Chelate Effect

A new class of tetraamide macrocyclic receptors for anions with
two quaternized amine functionalities exhibited higher affinities for
anions compared with the corresponding neutral amides. In two
crystal structures of halide complexes of the prototypes with phenyl
and pyridine spacers, the anions are held by hydrogen bonding
with the amide hydrogens. The pyridine analogues display higher
affinities in general than the phenyl systems, a phenomenon which
is attributed to the anion version of the chelate effect.