Thermodynamic study of the binding of dibenzo-18-crown-6 with Ag+, Pb2+ and Cd2+ in acetonitrile–water solvents

Abstract

Thermodynamic data for the binding of Ag⁺, Pb²⁺ and Cd²⁺ nitrates with dibenzo-18-crown-6 in acetonitrile–water solvents have been obtained in the temperature range 288–308 K using a conductometric technique. The observed molar conductivities, Λ, were found to decrease significantly for mole ratios less than unity. The conductivity data have been analysed using a model involving 1 : 1 stoichiometry. The stability constant, K, and the limiting molar conductivity, Λ_c, for each 1 : 1 complex have been obtained from the measured conductivities by using a non-linear least-squares curve-fitting procedure. The complexation sequence, based on the value of log K at 298 K, was found to be Pb²⁺ > Cd²⁺ > Ag⁺. The significance of the reported values of ΔH⁰ and ΔS⁰ in the present work has been discussed.