STUDIES ON SPECIATION OF ALUMINUM COMPLEXES WITH MALIC-ACID BY HIGH-FIELD AL-27 NMR-SPECTROSCOPY

High field variable pH Al-27 NMR spectral studies of AlCl3-malic acid system show the formation of as many as four complex species in the pH range 2-8. The binding of malate to aluminium takes place through the hydroxyl and carboxyl groups resulting in five- and six-membered chel ate rings with deprotonation of the hydroxyl group. Malate functions e ither as a bidentate or a tridentate ligand. The 1: 1 Al-malate chelat e has been isolated and characterised by elemental analysis, potentiom etric titration and IR spectroscopy. The results indicate deprotonatio n of hydroxyl group and bidentate nature of carboxylate groups. A brid ged polymeric structure has been proposed for the chelate.