Complexation Ability of Dibenzo-24-crown-8 with Cs+ Cation in Binary Mixed Non-Aqueous Solvents

Abstract

The complexation reaction of macrocyclic ligand, dibenzo-24-   crown-8 (DB24C8) with Cs+ cation was studied in acetonitrile-methanol   (AN-MeOH), acetonitrile-ethanol (AN-EtOH), acetonitrile-dimethylformamide   (AN-DMF) and nitromethane-methanol (NM-MeOH) binary   mixtures at different temperatures using the conductometric method.   The conductance data show that in all the solvent systems, the stoichiometry   of the complex formed between DB24C8 and Cs⁺ cation is 1:1   (ML). It was found that the stability of (DB24C8.Cs)⁺ complex decreases   with increasing temperature. The stability constant of the resulting 1:1   complex in pure non-aqueous solvents decreases in the order: EtOH >   MeOH > DMF and in binary mixed solutions, it follows the order: ANEtOH   > AN-MeOH > AN-DMF. A non-linear behaviour was observed   for changes of log K_f of (DB24C8.Cs)⁺ complex versus the composition   of the binary mixed solvents. The obtained results show that the stability   of the complex is quite sensitive to the composition of the mixed solvents.   The values of thermodynamic quantities (ΔHº_c and ΔSº_c) for formation   of (DB24C8.Cs)⁺ complex were obtained from temperature dependence   of the stability constant using the van't Hoff plots. The results show that   in all cases the complex is enthalpy stabilized but, in most cases entropy   destabilized and both parameters are affected by the nature and composition   of the mixed solvents.