Synthesis and complexation properties of 1,3-alternate calix[4]arene-bis(crown-6) derivatives

Abstract

Calix[4]arene-bis(crown-6) was converted into its di- and tetra-carboxy and hydroxy derivatives as water-soluble receptors. The complexation properties of these ionophores were studied for alkali cations in methanolic and aqueous media. Stability constants were calculated by UV–Vis spectroscopy. All ligands showed a more or less pronounced affinity for the larger cations. Cs⁺/Na⁺ selectivity is enhanced by the number and the nature of the substituents. Compound 7 represents the most selective ligand for the Cs⁺ cation in methanol and in basic aqueous media. For selective Cs⁺/Na⁺ separation, the efficiency of the ligands was evaluated by means of a nanofiltration system.