Complexing ability of a macrocyclic ligand, dibenzo-24-crown-8, with UO2 2+ in some binary mixed non-aqueous solvents

Abstract

Complexation between 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 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 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 K f of (DB24C8 · UO2)2+ versus the composition of the binary mixed solvents. The stability order of the complex in binary mixed solvents at 25°C was: AN–EtOAc > AN–PrOH ∼ AN–EtOH ∼ AN–MeOH > AN–DMF. The standard thermodynamic quantities ( and ) for the formation of (DB24C8 · 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 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.