THERMODYNAMIC STUDY OF THE BINDING OF DIBENZO-18-CROWN-6 WITH AG+, PB2+ AND CD2+ IN ACETONITRILE-WATER SOLVENTS

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, Lambda, 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, Lambda(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 Delta H-0 and Delta S-0 in the present work has been discussed.