The changes in the standard enthalpy (ΔH°c) for complexation of 4′NB18C6 with Y+3 cation were obtained from the slope of the van’t Hoff plots assuming that ΔCp is equal to zero over the entire temperature range investigated. In most cases, the van’t Hoff plots of LnKf versus 1/T were linear and a typical example of these plots is shown in Fig. 4. The changes in standard entropy ΔS°c were calculated from the relationship ΔG°c298.15 = ΔH°c − 298.15 ΔS°c. The thermodynamic data are summarized in Table 2. The changes of log Kf versus the solvent composition for (4′NB18C6.Y)3+ complex in AN-DMF binary system at different temperatures is shown in Fig. 3.