The complexation process between Y+3 cation with kryptofix 22DD was studied in ethylacetate-dimethylformamide (EtOAc-DMF) ,ethylacetate-methanol (EtOAc-MeOH), ethylacetate-nitromethane (EtOAc-NM) and ethylacetate-dimethylsulfoxide (EtOAc-DMSO) binary mixtures at different temperatures by using conductometric method.The conductance data show that in most cases, the stoichiometry of the complex is 1:1 [ML].But in the case of EtOAc/DMSO (mol%DMSO=90) binary mixture,a 1:2 (ML2) complex is formed in solution, which shows that the stoichometry of complexes may be changed by the nature of the medium.The values ofthermodynamic parameters (ΔHcº andΔScº) for formation of (kryptofix 22DD.Y)+3complex were obtained from temperature dependence of the stability constant using the van’t Hoff plots.The results show that in most cases, the(kryptofix 22DD.Y)+3complex is enthalpy and entropy stabilized and the values are and also the sign of thermodynamic parameters are influenced by the nature and composition of the mixed solvents.

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