Conductometric Studies of Complexation of Benzo-15-crown-5 Ether with Some Transition Metal Ions in Pure and Binary Non-aqueous Solvent Mixtures

The complexation reaction between Benzo-15-crown-5 Ether [B15C5] with Fe3+, Co2+, Ni2+ and Cu2+ cation was studied in pure acetonitrile (ACN), pure dimethyl-sulfoxide (DMSO) and in the binary solvent mixtures of ACN-DMSO at various temperatures by conductometric method. The conductance data showed that the stoichiometry of the complexes formed in pure as well as in the binary solvent mixtures was 1:1 ([Mn+]: [B15C5]). In binary solvent mixtures, the values of log Kf decrease with increase in temperature and with increase in the percentage of ACN. The values of thermodynamic parameters (ΔGo, ΔHo and ΔSo) for formation of complexes were obtained from temperature dependence of stability constant of complexes (L-Mn+) using the Van’t Hoff plots. The negative values of ΔGo show the spontaneous reaction, the positive values of ΔHo indicate that the complexation reactions are enthalpy destabilized. Besides this, the positive values of ΔSo indicate that entropy is a driving force for the complexation reaction. The values of ΔHo and ΔSo for formation of the complexes were obtained from temperature dependence of the stability constants. The findings indicate that the nature and composition of the mixed solvents have an impact on both the values and the sign of these parameters.