Conductometric studies on complexation of Ag+ cation by C-thiophene calix[4]resorcinarene in pure and mixed non-aqueous solvent systems

Abstract

The present work relates to the complexation reaction between a new ionophore C-thiophenecalix[4]resorcinarene (C-TC[4]R) with Ag+ cation in pure acetonitrile (ACN), methanol (MeOH), ethanol (EtOH), dimethylformamide (DMF) and dimethylsulfoxide (DMSO) and their binary mixtures by conductometric method. The conductance data showed that the stoichiometry of the complexes formed in pure as well as binary solvent mixtures was 1:1 (Ag+: C-TC[4]R). The stability of C-TC[4]R complexes with Ag+ metal ion was observed to be sensitive to the nature of the solvent system. The results obtained show that the selectivity of C-TC[4]R for Ag+ cation in pure solvents followed the order MeOH > DMF > EtOH > DMSO > ACN. In binary solvent systems, there was a linear change in log K f values for all the binary mixtures (ACN–DMF, ACN–DMSO, MeOH–DMF, EtOH–DMF and EtOH–DMSO) except MeOH–DMSO. The results show that the complexation reactions were spontaneous and entropy (∆S°) as well as enthalpy (∆H°) stabilized in all the solvent systems except EtOH–DMSO, in which the complexes were entropy destabilized. A linear relationship between ΔH° and ΔS° values indicate the existence of entropy–enthalpy compensation in the formation of [Ag–C-TC[4]R]+ complex in all the solvent systems studied.