Mechanism of Ion recognition by N-aryldibenzomonoazacrown ethers

Abstract

15-crown-5-ether preferentially captures Na⁺, which ion size fits the crown ring size, among Na⁺, Li⁺ and Mg²⁺. But N-aryl-monoaza-15-crown-5-ehters (ArN15C) preferentially captures Li⁺ and Mg²⁺ than Na⁺. It is considered four oxygens of ArN15C coordinates Li⁺ and Mg²⁺ because the nitrogen coordinating ability is reduced by electron-withdrawing aryl group. The ArN15C ring is probably twisted so that Li⁺ and Mg²⁺ may pull the four oxygens. So we synthesized N-aryl-dibenzo-monoaza 15-crown-5-ethers (DBArN15C) having two benzene rings in crown ring. Crown ring of DBArN15C is less flexible crown ring than ArN15C. We investigated the stability constants of DBArN15C-metal ion complexes. The stability constants was the order of Li⁺ > Na⁺ > Mg²⁺, and the selectivity of Na⁺ inclusion was improved.