Study of complex formation between dicyclohexyl-18-crown-6 and UO2 2+ cation in some binary mixed non-aqueous solvents using conductometric method

Abstract

In the present work, the complexation process between UO2 2+ cation and the macrocyclic ligand, dicyclohexyl-18-crown-6 (DCH18C6) was studied in ethyl acetate/1,2-dichloroethane (EtOAc/DCE), acetonitrile/1,2-dichloroethane (AN/DCE), methanol/1,2-dichloroethane (MeOH/DCE) and ethanol/1,2-dichloroethane (EtOH/DCE) binary solutions at different temperatures using the conductometric method. The conductance data show that in most cases, the stoichiometry of the complex formed between DCH18C6 and UO2 2+ cation is 1:1 [M:L], but in some solvent systems also a 1:2 [M:L2] complex is formed in solutions. The values of stability constant of (DCH18C6·UO2)2+ complex which were obtained from conductometric data, show that the stability of the complex is affected by the nature and also the composition of the solvent system and in all cases, a non-linear behavior is observed for the variation of (log K f) of the (DCH18C6·UO2)2+ complex versus the composition of the binary mixed solvents. The values of thermodynamic quantities $$ \Updelta H_{c}^{\circ} $$ and $$ \Updelta S_{c}^{\circ} $$ for formation of (DCH18C6·UO2)2+ complex were obtained from temperature dependence of the stability constant using the van’t Hoff plots. The experimental results show that depending on the nature and composition of the solvent systems, the complex is enthalpy stabilized or destabilized, but in most cases, it is stabilized from entropy view point and both thermodynamic parameters are affected by the nature and composition of the binary mixed solutions.