Conductance Study of the Thermodynamics of Dibenzo-21-crown-7 Complexes with Na+, K+, Rb+ and Cs+ Ions in Acetonitrile Solution

A conductance study of the interaction between Na+, K+, Rb + and Cs+ ions and dibenzo-21-crown-7 in acetonitrile solution has been carried out at various temperatures. The formation constants of the resulting 1:1 complexes were determined from the molar conductance-mole ratio data and, in the entire temperature range, found to vary in the order Rb+ >K+>Cs+>Na+. The enthalpy and entropy of complexation reactions were determined from the temperature dependence of the formation constants. In all cases, the resulting complexes were found to be both enthalpy and entropy stabilized.