Conductance Study of Complexation of Lead Ions by Several 18-Membered Crown Ethers in Acetonitrile-Dimethyl Sulfoxide Mixtures Between 25 and 55 deg C

摘要

A conductance study of the interaction between Pb~(2+) ion and 18-crown-6 (18C6), benzo-18-crown-6 (B 18C6), dicyclohexy1-18-crown-6 (DC18C6), aza-18-crown-6 (DBPy18C6), diaza-18-crown-6 (DAI8C6), dibenzopyridino-18-crown-6 (DBPy 18C6), and dibenzyldiaza-18-crown-6 (DBzDA18C6) in acetonitrile-dimethyl sulfoxide mixtures was carried out at various temperatures. The formation constants of the resulting 1:1 complexes were determined from the molar conductance-mole ratio data and found to vary in the order DA18C6 > A18C6 > DBzDA18C6 > DC18C6 > 18C6 > B18C6 > DBPy18C6. The enthalpy and entropy of complexation reactions were determined from the temperature dependence of the formation constants. In all cases, the resulting complexes are enthalpy stabilized, but entropy destabilized. A linear relationship is observed between log K_f of different complexes and mole fraction of acetonitrile in the solvent mixtures. The T#DELTA#S~o vs. #DELTA#H~o plot of all thermodynamic data obtained shows a fairly good linear correlation indicating the existence of an enthalpy-entropy compensation in the complexation reactions.