The complexation reactions between K+,Ag+, N and Hg2+ cationsandthe macrocyclic ‎ligand, dibenzo -18- crown -6 ( DB 18 C 6), were studied in ethylacetate ( EtOAc )– ‎dimethylformamide ( DMF ) binary mixtures at different temperatures using the ‎conductometric method . The conductance data show that the stochiometry of all the ‎complexes is 1:1. A non-linear behavior was observed for the variation of of the ‎complexes versus the composition of binary mixed solvents, which was discussed in ‎terms of heteroselective salvation and solvent – solvent interactions in binary ‎solutions. It was found that the stability order of the complexes changes with ‎changing the composition of the mixed solvents. The sequence of stabilities for the ‎K+, Ag+, N and Hg2+ complexes with DB18C6 in tOAc–DMF binary solutions ‎‎(mol. % DMF 25.0) and (mol. % DMF 50.0 ) at 25°C is (DB18C6-Ag)+ > ‎‎(DB18C6-K)+ > (DB18C6-Hg)2+ > (DB18C6-NH4)+, but in the cases of pure DMF ‎and a binary solution of EtOAc–DMF (mol. % DMF 75.0) is (DB18C6-K)+ > ‎‎(DB18C6-Hg)2+ (DB18C6-Ag)+ ≈ (DB18C6- NH4)+. The values of thermodynamic ‎quantities (∆ ∆ ) for these complexation reactions have been determined from the ‎temperature dependence of the stability constants, and the results show that the ‎thermodynamics of the complexation reactions is affected by the nature and ‎composition of the mixed solvents and, in all cases, positive values of ∆ characterize ‎the formation of these complexes. In addition, the experimental results show that the ‎values of entropies for the complexation reactions between K+, Ag+, N and Hg2+ ‎cations and DB18C6 in EtOAc–DMF binary solutions do not change monotonically ‎with the solvent omposition.‎

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