Macrocyclic Polyethers and Their Complexes

The most important, and almost unique, property of the macrocyclic polyethers (“crown compounds”) is their tendency to form complexes with alkali metal salts and salts with similar cations. Such complexes are held together by electrostatic attraction between the cation and the negative end of the CO dipoles. The stability of the polyether complexes depends primarily upon how well the cation fits into the polyether ring; other factors are the charge density of the cation and—in solution—the solvating power of the medium. Cyclic polyethers have been successfully employed, inter alia, in experiments with ionic compounds in organic solvents and in studies of ion transport in biological systems.