Preparation and characterisation of oxovanadium(IV) complexes derived from 2,6-diformyl-4-methylphenol and l-His and l-Ala. Spectroscopic study of the system VIVO2+ + BDF–His

By reaction of 2,6-diformyl-4-methylphenol (BDF) with the amino acids l-His and l-Ala in the presence of VOCl2, two new oxovanadium(IV) complexes with the ligand obtained by the 1:2 condensation of BDF with the amino acids, BDF–His and BDF–Ala, were synthesised. The compounds were characterised in the solid state by elemental analyses, IR, CD and magnetic susceptibility measurements, and in the mother liquor by EPR. In water-containing solutions, BDF–Ala and BDF–His partially hydrolyse but the degree of Schiff base formation increases upon addition of VOSO4. The equilibria in the system VIVO2+ + BDF–His were studied by spectroscopic methods (EPR, CD and UV–Vis) in the pH range 1.5–12. The coordination behaviour of the ligand changes as the pH increases, leading to the formation of four main species all involving Ophen as donor atom. Plausible binding modes are discussed based on the spectroscopic results.