Preparation, characterization and pH-metric measurements of 4-hydroxysalicylidenechitosan Schiff-base complexes of Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Ru(III), Rh(III), Pd(II) and Au(III)

The 4-hydroxysalicylidenechitosan Schiff-base (2CS-Hdhba) was prepared by the condensation of 2,4-dihydroxybenzaldehyde with chitosan, and its metal complexes, [M(2CS-dhba)Cl2(H2O)2] (M(III) = Fe, Ru, Rh), [M′(2CS-dhba)(AcO)(H2O)2] (M′(II) = Co, Ni, Cu, Zn), [Pd(2CS-dhba)Cl(H2O)] and [Au(2CS-dhba)Cl2], are reported. These complexes were characterized by elemental analysis, by spectral data (FTIR, solid-phase 13C NMR, UV-vis and ESR spectroscopy), by morphological observations (SEM and XRD), and by magnetic and thermal measurements. The Schiff base (2CS-Hdhba) behaves as a bidentate chelate with a single negative charge. The azomethine nitrogen and the deprotonated 2-hydroxy centres with the pendant glucosamine hydroxy functionality play no role in coordination. The dissociation constants of 2CS-Hdhba and the stability constants of some of its metal complexes have been determined pH-metrically.