Conductometric titrations have been performed in acetonitrile–ethylacetate (AN–EtOAc) binary solutions at 288, 298, 308, and 318 K to obtain the stoichiometry, the complex stability constants and the standard thermodynamic parameters for the complexation of Cd2+, Ni2+, and Ag+ cations with 4,13didecyl1,7,10,16tetraoxa4,13diazacyclooctadecane (cryptand 22DD). The stability constants of the resulting 1:1 complexes formed between the metal cations and the ligand were determined by computer fitting of the conductancemole ratio data. There is a nonlinear relationship between the logKf values of complexes and the mole fraction of ethylacetate in the mixed solvent system. In addition, the conductometric data show that the stoichiometry of the complexes formed between the Cd2+, Ni 2+, and Ag+ cations with the ligand changes with the nature of the solvent. The standard enthalpy and entropy values for the 1:1 [ML] complexation reactions were evaluated from the temperature dependence of the formation constants. Thermodynamically, the complexation processes of the metal cations with the C22DD, is mainly entropy governed and the values of ther modynamic parameters are influenced by the nature and composition of the binary mixed solvent solutions.

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