Efficient divalent metal cation extractions with di-ionizable calix[4]arene-1,2-crown-4 compounds

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