A competitive polarographic study of complexation of ammonium,anilinium, hydrazinium and pyridinium ions with some macrocyclic ligands in binary ethanol-water mixtures using a Pb(II)/Pb(Hg) couple as an electrochemical probe

The formation of ammonium, anilinium, hydrazinium and pyridinium ion complexes with the crown ethers 18-crown-6 (18C6) and 1,10-diaza-18-crown-6 (C22) and the cryptand C222 in different binary ethanol-water mixtures has been studied by a competitive polarographic method using a Pb²⁺/Pb(Hg) couple as a sensitive electro-chemical probe. Lead ion was found to form very stable complexes with the ligands used, in all solvent mixtures studied; Pb²⁺–C222 cryptate revealed a pronounced cryptate effect compared to the corresponding complexes with the monocyclic crown ethers used. In all solvent mixtures studied, the stability of the resulting 11 complexes between the protonated amines and macrocyclic ligands used vary in the order C22>C222>18C6. The observed selectivity order of each macrocyclic ligand used for different protonated amines is discussed based on the chemical and structural features of the host-guest partners in solution. In all cases studied there is an inverse linear relationship between the complex formation constants and the mole fraction of water in the mixed solvent.