¹³C and ²⁷Al NMR and potentiometric study on the interaction between aluminium ions and quinolic acid in acidic aqueous solutions

The interaction between aluminium ion (Al) and quinolic acid (L) in acidic aqueous solution was investigated by potentiometry and ¹³C and ²⁷Al NMR spectroscopy. In the ²⁷Al NMR spectra, two peaks were observed at 8 and 15.6 ppm, which were assigned to AlL and AlL₂ complexes, respectively. The ¹³C NMR spectra provide clear evidence that the L acts as a bidentate ligand and that the L coordinates with a nitrogen atom and an oxygen atom of the adjacent carboxylic group to form a chelate complex with a five-membered ring. From a potentiometric study, the formation constants (log β₁ and log β₂) for the AlL and AlL₂ complexes were estimated to be 4.52 ± 0.02 and 7.99 ± 0.05, respectively.