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

Abstract

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 1∶1 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.