A newtype of macrobicyclic compound, which was prepared by the reaction of 2,9-bis[(ethylamino)methyl]-15-crown-5 with sebacoyl dichloride, has shown a selective complexation property toward K+ and Ba2+ cations based on data obtained with potentiometric titration and solvent extraction. This finding was reasonably explained by considering the cooperative binding of the amide moieties and the crown