Complexing ability of a macrocyclic ligand, dibenzo-24-crown-8, with UO22+in some binary mixed non-aqueous solvents

Complexation between [image omitted] and dibenzo-24-crown-8 (DB24C8) was studied in acetonitrile-ethylacetate (AN-EtOAc), acetonitrile-dimethylformamide (AN-DMF), acetonitrile-methanol (AN-MeOH), acetonitrile-ethanol (AN-EtOH), and acetonitrile-propanol (AN-PrOH) binary solutions at different temperatures using conductometry. The conductance data show that in most cases the stoichiometry of the complex formed between DB24C8 and [image omitted] is 1 : 1 [M : L], but in pure EtOAc, a 1 : 2 [M : L2] complex is formed in the solution. In all cases, except in pure EtOAc, addition of DB24C8 to [image omitted] solutions causes a decrease in molar conductivity which indicates that the mobility of the complexed cation is lesser than that of the uncomplexed one. Non-linear behavior was observed for the changes of log Kf of (DB24C8 center dot UO2)2+ versus the composition of the binary mixed solvents. The stability order of the complex in binary mixed solvents at 25 degrees C was: AN-EtOAc AN-PrOH AN-EtOH AN-MeOH AN-DMF. The standard thermodynamic quantities ([image omitted] and [image omitted]) for the formation of (DB24C8 center dot UO2)2+ were obtained from the temperature dependence of the stability constant using van't Hoff plots. The results show that in most cases complexation between [image omitted] and DB24C8 is enthalpy and entropy stabilized and the values of these thermodynamic parameters are influenced by the nature and composition of the mixed solvents.