Uncommon complex stoicheiometry in solvent extraction: solution-phase dicationic complex formation of crown ethers

Abstract

A solvent extraction study with 18-crown-6, 24-crown-8, and their dibenzo-derivatives has revealed that the following ligand–cation combinations give dicationic complexes in the solution phase: 18-crown-6 with Li⁺; 24-crown-8 with Li⁺, Na⁺, K⁺; dibenzo-24-crown-8 with Na⁺, K⁺, Ag⁺, Sr²⁺. The facile formation of dicationic complexes in the solvent extraction is attributed to the effective charge-shielding co-ordination by the bulky, lipophilic picrate anions in the contact ion-pair complex extracted.