Study of the complex formation between 18C6 crown ether and Tl(+), Pb(2+) and Cd(2+) in binary non-aqueous solvents using differential pulse polarography

Complexation of the Tl(+), Pb(2+) and Cd(2+) ions with macrocyclic ligand 18-crown-6 (18C6) was studied in various binary solvent mixtures of propylencarbonate (PC)/dimethylformamide (DMF) and acetonitrile (AN)/dimethylsulfoxide (DMSO) systems at 22 degrees C using the differential pulse polarographic technique. The stoichiometry of the complexes was found to be 1:1 and the complexation constants increased with decreasing amounts of dimethylsulfoxide and dimethylformamide in these binary systems. In all cases, the variation of the stability constant with composition of the solvents was monotonic and showed good correlation with the inherent solvation ability of the neat solvents which form the mixture. In all of the solvent systems, the selectivity order for 18C6 complexes is Tl(+) > Pb(2+) > Cd(2+).