conductometric studies of the thermodynamics of complexation of zn2+, ni2+, co2+, pb2+, mn2+, cu2+ ions with 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane in binary solvent mixtures

the complexation reaction between 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (kryptofix5) ligand with zn2+, ni2+, co2+, pb2+, mn2+ and cu2+ ions were studied conductometrically in different acetonitrile-nitromethane (an-nm) and acetonitrile-methanol (an-meoh) mixtures. the formation constants of the resulting 1:1 complexes were calculated from the computer fitting of the molar conductance in various mole ratios. the enthalpy and entropy changes of the complexation reactions were derived from conductometric titrations in different an-nm mixtures at various temperatures. the results revealed that kryptofix5 forms very stable 1:1 complexes with mentioned cations in all an-nm and an-meoh mixtures. it was found that the stability of the resulting complexes decreased with increasing nitromethane or methanol in the solvent mixture. the tδs° vs. δh° plot of all thermodynamic data obtained shows a fairly good linear correlation indicating the existence of enthalpy-entropy compensation in the complexation reactions.