Side Arm Effects on Cyclen−Alkali Metal Cation Complexation: Highly Selective and Three-Dimensional Encapsulation of Na+ Ion

Abstract

A variety of armed cyclens were prepared in which ester, amide, nitrile, and pyridine moieties were attached as cation-ligating side arms to a 12-membered ring. Ester-, amide-, and pyridine-armed cyclens nicely accommodated a Na⁺ ion in a three-dimensional fashion and clearly discriminated the cation from Li⁺ and K⁺ ions. They extracted Na⁺ ion more efficiently and selectively than common Na⁺ ion-selective ligands. X-ray diffraction, FAB-MS, ²³Na NMR binding studies, and computer modeling experiments demonstrated that the cyclens having ester-, amide-, and pyridine-functionalized side arms formed highly selective encapsulated Na⁺ complexes via a cooperative action of parent cyclen and side arms.