The complex formation between Na+, Li+, Hg2+, Tl+ and Cu2+ metal cations with macrocyclic ligand, Nphenylaza- 15-Crown-5 (PhA15C5) was studied inacetonitrile(AN)-methanol(MeOH) and Acetonitrile(AN)–Water(H2O) binary systems at different temperatures using conductometric method. The obtained results show that the stoichiometry of the complexes is 1:1(ML), but in the case of Hg2+ ,cation,at pure methanol and Tl+ cation, a 1:2(ML2) complex is formed in solutions. The stability constants of the complexes were obtained from fitting of molar conductivity curves using a computer program,Genplot. A non-linear behavior was observed for changes of logKf of the complexes versus the composition of AN-MeOH and AN – H2O binary solution. The results show that the selectivity of PhA15C5 for the metal cations changes with the composition of the mixed solvent. The values of standard enthalpy changes(ΔH°c) for complexation reactions were obtained from the slope of the van’t Hoff plots and the changes in standard entropy(ΔS°c) were calculated from the relationship: ΔG°c, 298.15=ΔH°c- 298.15 ΔS°c. The obtained results show that, in most cases the complexes are entropy stabilized but from the enthalpy view point, depending on the solvent system, the metal ion complexes are stabilized or destabilized, and the values of ΔH°c and ΔS°c depend strongly on the nature of the medium.

Keywords