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)

Abstract

The formation of complexes between aluminium(III) and 3-hydroxy-2(1H)-pyridinone (HL) in aqueous 0.6 m (Na)Cl at 25 °C has been investigated by means of potentiometric titrations. The following complex stability constants have been evaluated (pK_a = 8.590 ± 0.008): log β_AlL = 8.59 ± 0.01, log β_AlL2 = 16.34 ± 0.03, log β_AlL3 = 23.11 ± 0.05, log β_AlL3H–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 °C as well, and the following stability constants were obtained (pK_a = 8.452 ± 0.004): log β_AlL = 8.19 ± 0.02, log β_AlL2 = 16.03 ± 0.04, log β_AlL3 = 21.77 ± 0.08, and log β_AlL3H–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.