In the present work the complexation process between UO22+cation and the macrocyclic ligand, dibenzo-18-crown-6 (DB18C6) was studied in ethylacetate–dimethylformamide (EtOAc/DMF), ethylacetate–acetonitrile (EtOAc/AN), and ethylacetate–tetrahydrofuran (EtOAc/THF) andethylacetate–propylencarbonate (EtOAc/PC) binary solutions at different temperatures using the conductometric method. The results show that the stoichiometry of the (DB18C6 . UO2)2+ complex in all binary mixed solvents is 1:1. A non-linear behavior was observed for changes of log Kf of this complex versus the composition of the binary mixed solvents. The stability constant of (DB18C6 .UO2)2+ complex in various neat solvents at 25oC decreases in order: THF>EtOAc>PC>AN>DMF, and in the binary solvents at 25oC is: THF–EtOAc>PC–EtOAc>DMF–EtOAc ~ AN–EtOAc. The values of thermodynamic quantities (DHoc, DSoc) for formation of this complex in the different binary solutions were obtained from temperature dependence of its stability constant and the results show that the thermodynamics of complexation reaction between UO22+cation and DB18C6 is affected strongly by the nature and composition of the mixed solvents.

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