LITHIUM-7 NMR STUDY OF THE THERMODYNAMICS OF COMPLEXATION OF LI^± ION WITH TETRAETHYLENEGLYCOL-BIS-(8-QUINOLYL) ETHER IN NON-AQUEOUS SOLUTION

Abstract

⁷Li NMR measurements were used to study the stoichiometry and stability of Li^± complexes with tetraethyleneglycolbis-(8-quinolyl)ether (TEGQ) in nitromethane, acetonitrile and their 1:1 (mol:mol) mixture. The resulting chemical shift-mol ratio data revealed the formation of both 1:1 and 2:1 (metal/ligand) complexes in solution. Formation of the two complexes was further supported by monitoring the molar conductance of LiClO₄ solutions as a function of TEGQ/Li^± mol ratio. The stepwise formation constants of the 1:1 and 2:1 complexes were evaluated from the computer fitting of the mol ratio data to equations which relate observed ⁷Li chemical shifts to formation constants. The enthalpy and entropy of complexation in all three solvent systems used were determined from the temperature dependence of the formation constants. Values of ΔH° and ΔS° were found to be solvent dependent. While the stabilities of both 1:1 and 2:1 complexes are of enthalpic origin in nitromethane, they become of entropic origin in acetonitrile solution.

Key Words:

• TEGQ
• Li^±
• complexes
• formation constants
• thermodynamics
• ⁷Li NMR