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

The interaction between aluminium ion (AI) and quinolic acid (L) in acidic aqueous solution was investigated by potentiometry and C-13 and Al-27 NMR s pectroscopy. In the Al-27 NMR spectra, two peaks were observed at 8 and 15. 6 ppm, which were assigned to AlL and AlL2 complexes, respectively. The C-1 3 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 a djacent carboxylic group to form a chelate complex with a five-membered rin g. From a potentiometric study, the formation constants (log beta(1) and lo g beta(2)) for the AlL and AlL2 complexes were estimated to be 4.52+/-0.02 and 7.99+/-0.05, respectively.