Preparation and characterisation of vanadium complexes derived from salicylaldehyde or pyridoxal and sugar derivatives

By reaction of salicylaldehyde (Hsal) with the amino-sugars d-glucosamine (glsmN), d-galactosamine (galacN) or d-glucamine (glcN) in the presence of VOSO4 or VOCl2, Schiff base (SB) complexes were obtained. By using pyridoxal (pyr) instead of Hsal, a solid containing the SB derived from its reaction with glcN was isolated. The compounds were characterised in the solid state by elemental analyses, IR, EPR, CD and magnetic susceptibility measurements. The complexes are not simple monomers in the solid state and were formulated as {VIVO(sal–d-galacN)}n, {VIVO(sal–d-glsmN)}n, (VIVVVO3)(sal–d-glcN) and (VIVO)3(pyr–d-glcN)2, the SB ligands being coordinated through the imine–N, phenolato-O−, sugar–O− and sugar–OH moieties. The complexes 3–5 were studied in solution by UV–Vis and CD spectrophotometry. The CD band pattern and λmax are normally the same both in the solid state and in MeOH, indicating that the binding mode is mostly preserved. Complex 6 is only slightly soluble and the spectroscopic studies were not conclusive in this respect. Upon dissolution of complexes 3–6, the oxovanadium(IV) is progressively oxidized and the SB hydrolysed.