Di-ionizable calix[4]arene-1,2-crown-5 and -crown-6 ethers in cone conformations: synthesis and divalent metal ion extraction

Di-ionizable calix[4]arene-1,2-crown-5 and -crown-6 ethers in the cone conformation exhibit selectivity for Ba2+ in competitive solvent extraction of alkaline earth metal cations and high extraction ability for Pb2+ and for Hg2+ in single species extraction.