New water-soluble calix[4]arene-bis(benzocrown-6) for caesium–sodium separation by nanofiltration–complexation

Calix-bis(benzocrown-6) and were converted into the water-soluble receptors , , and by introducing hydroxy, carboxy, sulfato or diethanolamino groups at the para position of the phenolic ring and/or on the benzo-ether moieties. The complexation properties of these ionophores were studied for all alkali cations in methanolic and aqueous media. Stability constants were calculated by UV–Vis spectroscopy. All ligands showed a more or less affinity for the larger cations, depending on the nature and the position of the substituents grafted on the benzo-ether chain only or both on the calixarene ring and the benzo-ether loop. For selective Cs+/Na+ separation, the efficiency of the ligands was evaluated by means of a nanofiltration system. In comparison with the known tetrahydroxylated bis-crown-6 calix[4]arene , compounds , and represent the most selective ligands for the Cs+ cation in a moderate salted medium ([NaNO3]=85 g/L).