The complexation reaction between Y3+ Cation with N-phenylaza-15-crown-5(Ph-N15C5) was studied at different temperatures in acetonitrile–methanol (AN/MeOH), acetonitrile–propanol (AN/PrOH), acetonitrile–1,2 dichloroethane (AN/DCE) and acetonitrile–water (AN/H2O) binary mixtures using the conductometric method. The results show that in all cases, the stoichiometry of the complex is 1:1 (ML). The values of formation constant of the complex which were determined using conductometric data, show that the stability of (Ph-N15C5.Y)3?complex in pure solvents at 25 _Cchanges in the following order: PrOH[AN[MeOH and in the case of binary mixed solutions at 25 _C it follows the order: AN–DCE[AN–PrOH[AN–MeOH[AN–H2O. The values of standard thermodynamic quantities (DHc _ and DSc _ ) for formation of (Ph-N15C5.Y)3? complex were obtained from temperature dependence of the formation constant using the van’t Hoff plots. The results show that in most cases, the complex is entropy and enthalpy stabilized and these parameters are influenced by the nature and composition of themixed solvents. Inmost cases, a non-linear behaviorwas observed for variation of logKf of the complex versus the composition of the binary mixed solvents. In all cases, an enthalpy–entropy compensation effect was observed for formation of (Ph-N15C5.Y)3+ complex in the binary mixed solvents.

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