Nuclear magnetic resonance study of the stoichiometry and stability of several Li+-crown ether complexes in various acetonitrile-nitrobenzene mixtures

Lithium-7 NMR spectrometry was used to study the complexation reaction betw een lithium ions and several 12-, 15- and 18-membered crown ethers in a num ber of binary acetonitrile-nitrobenzene mixtures. Formation constants of th e resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift-mole ratio data. There is an inverse relationship between the complex stability and the amount of acetonitrile in the mixed solvent. Among different sized crown ethers used, 15-crowns we re found to form the most stable Li+ complexes in the series. The influence of substitution on the macrocyclic rings on the stability of the resulting complexes is discussed.