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

Several sal 2 en‐type reduced Schiff bases have been prepared from the reaction of 2 equiv. of salicylaldehyde (or derivatives) with ethylenediamine followed by reduction with NaBH 4 and subsequently characterised. The water‐soluble ligands (SO 3 ‐sal) 2 en and R(SO 3 ‐sal) 2 en (SO 3 ‐sal = salicylaldehyde‐5‐sulphonate) have been studied by pH potentiometry and 1 H NMR spectroscopy and the protonation constants of R(SO 3 ‐sal) 2 en have been determined. The Schiff bases are more susceptible to hydrolysis than the corresponding reduced Schiff bases. The crystal structures of H 2 ( o ‐van) 2 en and KH( o ‐van) 2 en ( 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 V IV O–Schiff‐base complexes are monomeric.The complexation of [V IV O] 2+ and [V V O 2 ] + with R(SO 3 ‐sal) 2 enin aqueous solution has been studied by pH potentiometry, UV/Vis as well as by EPR spectroscopy for the V IV O system and 1 H and 51 V NMR spectroscopy for the V V O 2 system. Complex formation constants have been determined and binding modes have been proposed. N , N ′ ‐ethylenebis(pyridoxylaminato) (Rpyr 2 en) has also been obtained and the structure of Na[V V O 2 (Rpyr 2 en)] · CH 3 OH · 3H 2 O determined by X‐ray diffraction. The Rpyr 2 en 2– ligand coordinates through both the N ‐amine and O ‐phenolate moieties in a symmetrical α‐ 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)