Macrocyclic compounds such as crown ethers are capable of forming complexes with metal cations viaelectrostatic attraction and encapsulation into the cavity[1]. Because of this ability, crown compounds have found applications in such areas as separation of metalcations [2] and phase transfer catalysis [3]. The study of various crown ethers in different solvent mixtures may indicate new approaches for developing pharmaceutical systems or a way to cross the blood organ barrier. Studies of crown ether complexes invarious solvents show that the thermodynamic and kinetic parameters for complexation processes are affected by the nature and composition of the mixed solvents [4,5].In this work, the complexation reactions between Mg2+, Ca2+, Sr2+ and Ba2+ cations with themacrocyclic ligand, dibenzo-18-crown-6 (DB18C6), inpure acetonitrile and dimethylformamide and theirbinary mixtures were studied at different temperature susing coductometric method. In all cases, DB18C6 forms 1:1 complexes with these cations. 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 and a non-linear behavior was observed for variation of logKf of the complexes versus the composition of the solvent systems. The values of thermodynamic parameters (ΔH°c and ΔS°c)for formation of complexes were obtained from temperature dependence of stability constants of complexes using van\\\\\\\'t Hoff plots. The results show that in all cases, the complexation reactions are enthalpy destabilized but entropy stabilized, and the values of these parameters are influenced by the natureand composition of the mixed solvents.

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