Polarographic Study of the Interactions between Thallium and Lead Ions and Some Crown Ethers in 90% Acetonitrile and 90% Ethanol Solutions

The complexation reactions between Tl+ and Pb2+ ions and crown ethers 12-crown-4(12C4), 15-crown-5 (15C5), benzo-15-crown-5 (B15C5), 18-crown-6 (18C6), dicyclohexyl-18-crown-6 (DC18C6) and aza-18-crown-6 (A18C6) were studied in 90% acetonitrile and 90% ethanol solutions at 25 °C, using an a.c. polarographic technique. The stoichiometry and stability of the complexes were determined by monitoring the shift in peak potential of the polarographic waves of metal ions against the crown concentration. The stability of the resulting 1:1 complexes of Tl+ and Pb2+ ions, in both solvent systems used, was found to vary in the order 18C6>DC18C6>18C6>15C5>B15C5>12C4. In 90% ethanol, Pb2+ ion complexes wih all crown ethers used were more stable than the corresponding Tl+ complexes. The influence of substituents in the polyether ring and of the nature of solvent and metal ions on the stability of a number of complexes is discussed.