Efficient and selective up-hill transport of anions by pH-induced affinity switching of a copper complex carrier

Abstract

The copper(II) complex of 6,6′-bis(4-hexylbenzoylamino)-2,2′-bipyridine served as a new type of functional carrier in efficient and selective up-hill transport of anions across an organic liquid membrane, Reversible deprotonation of the amide groups of the ligand regulated the uptake and release of anions by alteration of the anion affinity of the complex, and affinity switching of the carrier by the pH of external aqueous solutions induced efficient up-hill transport of SCN^– and toluene-p-sulfonate by coupling with a small pH difference across the membrane. The high thiocyanate selectivity of the carrier was ascribed to preferential axial co-ordination of SCN^– to the complex which possesses an N₂O₂ square-planar structure.