Thermodynamic studies of 18-crown-6 with La3+, Ce3+, Pr3+ and Nd3+ Complexes in acetonitrile-water binary solvent systems at 298.15 K, 308.15 K and 318.15 K by conductometric method

The complexation reactions between 18-crown-6 (18C6) with La3+, Ce3+, Pr3+ and Nd3+ cations were studied in acetonitrile-water (AN-H2O) binary solvent systems at different temperatures by the conductometric method. In all the cases, 18C6 forms a 1:1 complex with La3+, Ce3+, Pr3+ and Nd3+ cations. The results show that the selectivity order of 18C6 for the metal cations in AN–H2O binary solvent systems at 298.15 K is : La3+>Ce3+> Pr3+ >Nd3+. The values of stability constants of complexes, which were obtained from conductometric data, show that the stability of complexes is affected by the nature and composition of the binary mixed solvents. The corresponding thermodynamic parameters (∆H, ∆S and ∆G) were obtained from the temperature dependence of the stability constants using van’t Hoff plots. The results show that the values and also the sign of these parameters are influenced by the nature and composition of the mixed solvents.