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 C has been investigated by means of potentiometric titrations. The following complex stability constants have been evaluated (pK(a) = 8.590 +/- 0.008): log beta(AlL)=8.59 +/- 0.01, log beta(AlL2) = 16.34 +/- 0.03, log beta(AlL3) = 23.11 +/- 0.05, log beta(AlL3)H(-1)=13.85 +/- 0.04. The qualitative and quantitative results obtained have been confirmed in part by UV spectrophotometry and H-1 NMR spectroscopy. Some potentiometric titrations were executed at 37 degrees C as well, and the following stability constants were obtained (pK(a)=8.452 +/- 0.004): log beta(AlL)=8.19 +/- 0.02, log beta(AlL2)=16.03 +/- 0.04, log beta(AlL3)=21.77 +/- 0.08, and log beta(AlL3)H(-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.