Complexation of aluminium(III) with 3-hydroxy-2(1H)-pyridinone. Solution state study and crystal structure of tris(3-hydroxy-2(1H)-pyridinonato)-aluminium(III).

The formation of complexes between aluminium(III) and 3-hydroxy-2(1H)-pyridinone (HL) in aqueous 0.6 m (Na)Cl at 25 degrees has been investigated by means of potentiometric titrations. The following complex stability constants have been evaluated (pKa = 8.590 ± 0.008): log βAlL = 8.59 ± 0.01, log βAlL2 = 16.34 ± 0.03, log βAlL3 = 23.11 ± 0.05, log βAlL3H-1 = 13.85 ± 0.04. The qualitative and quantitative results obtained have been confirmed in part by UV spectrophotometry and 1H NMR spectroscopy. Some potentiometric titrations were executed at 37 degrees as well, and the following stability constants were obtained (pKa = 8.452 ± 0.004): log βAlL = 8.19 ± 0.02, log βAlL2 = 16.03 ± 0.04, log βAlL3 = 21.77 ± 0.08, and log βAlL3H-1 = 13.0 ± 0.2. Crystals of the complex AlL3 were obtained and analysed by X-ray diffraction. The neutral species is an octahedral six-co-ordinate complex with the ligand chelating in a bidentate fashion through the pyridinone oxygen and the deprotonated hydroxylic group.