Sodium-23 NMR study of the thermodynamics of complexation of Na+ with tetraethyleneglycol-bis-(8-quinolyl) ether in acetonitrile

Sodium-23 NMR measurements were used to investigate the stoichiometry and s tability of Na+ complexes with tetraethylenglycol-bis-(8-quinolyl) ether (T EGQ) in acetonitrile solution. The resulting chemical shift-mole ratio data revealed the formation of both 1:1 and 2:1 (metal/ligand) complexes in sol ution. Formation of the two complexes was further supported by monitoring t he molar conductance of sodium ion solutions as a function of the TEGQ/Namolar ratio. The stepwise formation constants of the 1:1 and 2:1 complexes were evaluated from the computer fitting of the mole ratio data to equation s which relate observed Na-23 chemical shift to formation constants. The en thalpy and entropy of complexation in acetonitrile solution were determined from 1:he temperature dependence of the formation constants. Both 1:1 and 2:1 complexes were found to be enthalpy stabilized, but entropy destabilize d.