Speciation and complexation in aqueous Al(III)-quinolinate solutions: a spectroscopic study

Aqueous solutions containing quinolinic acid (2,3-pyridinedicarboxylic acid ) and aluminum chloride were investigated using attenuated total reflection Fourier transform infrared spectroscopy, Al-27 nuclear magnetic resonance spectroscopy (Al-27 NMR), and potentiometry. Conditional equilibrium consta nts were acquired at an apparent ionic strength of 1.33 M for the formation of quinolinic acid (H2L), the HL- species, and each of the Al(III)-quinoli nate complexes (AlL+ and AlL2-). The resolved infrared spectra of the quino linate ion (L2-), the HL- species, and quinolinic acid were assigned and in terpreted with respect to the proton binding properties of the ligand. The assignments of the Al-27 NMR and infrared spectra of the Al(III)-quinolinat e complexes provide evidence that quinolinate preferentially chelates to Al (III) through both the nitrogen of the pyridine ring and one of the oxygens of a carboxylate substituent. (C) 2001 Elsevier Science Ltd. All rights re served.