Vanadium(IV and V) Complexes of Schiff Bases and Reduced Schiff Bases Derived from the Reaction of Aromatic o-Hydroxyaldehydes and Diamines: Synthesis, Characterisation and Solution Studies

Abstract

Several sal2en-type reduced Schiff bases have been prepared from the reaction of 2 equiv. of salicylaldehyde (or derivatives) with ethylenediamine followed by reduction with NaBH4 and subsequently characterised. The water-soluble ligands (SO3-sal)2en and R(SO3-sal)2en (SO3-sal = salicylaldehyde-5-sulphonate) have been studied by pH potentiometry and 1H NMR spectroscopy and the protonation constants of R(SO3-sal)2en have been determined. The Schiff bases are more susceptible to hydrolysis than the corresponding reduced Schiff bases. The crystal structures of H2(o-van)2en and KH(o-van)2en (o-van = o-vanillin) have been determined by X-ray diffraction. The vanadium(IV) complexes have been prepared and characterised by magnetic measurements and IR, UV/Vis and EPR spectroscopy. The colours, magnetic susceptibilities and IR spectra of the new vanadium(IV) complexes of the reduced Schiff bases now obtained suggest oligomeric/polymeric structures for the compounds while the corresponding VIVO-Schiff-base complexes are monomeric.The complexation of [VIVO]2+ and [VVO2]+ with R(SO3-sal)2enin aqueous solution has been studied by pH potentiometry, UV/Vis as well as by EPR spectroscopy for the VIVO system and 1H and 51V NMR spectroscopy for the VVO2 system. Complex formation constants have been determined and binding modes have been proposed. N,Nprime-ethylenebis(pyridoxylaminato) (Rpyr2en) has also been obtained and the structure of Na[VVO2(Rpyr2en)]·CH3OH·3H2O determined by X-ray diffraction. The Rpyr2en2- ligand coordinates through both the N-amine and O-phenolate moieties in a symmetrical alpha-cis type coordination mode, i.e. with both O-phenolato donors cis to the O-oxo atoms and trans to each other. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)