Spectrophotometric Study of the Thermodynamics of Complexation of Lithium and Sodium Ions With Dibenzo-24-Crown-8 in Binary Dimethylformamide-Acetonitrile Mixtures Using Murexide as a Metallochromic Indicator

Complexation of Li+ and Na+ with dibenzo-24-crown-8 has been studied in dimethylformamide-acetonitrile mixtures by means of a competitive spectrophotometric technique using murexide as metal ion indicator. Stabilities of the resulting 1:1 complexes were investigated at various temperatures and enthalpies and entropies of complexation were determined from the temperature dependence of the formation constants. Sodium forms a more stable complex with the crown ether than lithium. There is an inverse linear relationship between log Kf and the mole fraction of DMF in the solvent mixtures. The ΔH°-TΔS° plot of all thermodynamic data, obtained for both crown complexes in different solvent mixtures, shows a fairly good linear correlation, indicating the existence of an enthalpy-entropy compensation effect in complexation.