LITHIUM-7 AND SODIUM-23 NMR STUDIES OF THE COMPLEXATION OF Li+ AND Na+ IONS WITH 1,13-DIBENZO-24-CROWN-8 IN BINARY NITROMETHANE-ACETONITRILE MIXTURES

7 Li, 23 Na and 13 C NMR measurements were used to study the stoichiometry and stability of Li + and Na + complexes with dibenzo2-4-crown-8 in binary nitromethane-acetonitrile mixtures. The resulting chemical shift-mol ratio data clearly reveal the formation of both 1:1 and 2:1 (metal/ligand) complexes in solution. Formation of the two adducts in nitromethane and acetonitrile solutions was further supported by monitoring the molar conductance of Li + and Na + solutions as a function of macrocycle/metal ion mol ratio. Stepwise formation constants of the 1:1 and 2:1 complexes were evaluated from computer fitting of the NMR mol ratio data to equations which relate observed metal ion chemical shifts to formation constants. In all solvent systems, sodium forms more stable complexes with the crown ether than lithium. There is an inverse linear relationship between the logarithms of the stability constants and the mol fraction of acetonitrile in the solvent mixtures.