Vanadium (IV and V) Complexes of Reduced Schiff Bases Derived from the Reaction of Aromatic <i>o</i>‐Hydroxyaldehydes and Diamines Containing Carboxyl Groups

Abstract

Abstract The reduced Schiff bases of salicylaldehyde [and o ‐vanillin ( o ‐van)] with D , L ‐ and L ‐diaminopropionic acid (DPA), designated by salDPA, and L ‐2,4‐diaminopentanoic acid [ornithine (Orn)], designated by salOrn, as well as the V IV O 2+ and V V O 2 + complexes of salDPA were prepared. The compounds were characterised in the solid state and in solution. The structure of H 4 salDPA + Cl – was determined by X‐ray diffraction. Complexation of V IV O 2+ and V V O 2 + with salDPA and salOrn (only the V IV O system) in aqueous solution was studied by potentiometry, UV/Visible spectroscopy and circular dichroism, as well as by EPR spectroscopy for the V IV O–salDPA system and by 1 H‐ and 51 V NMR spectroscopy for the V V O 2 –salDPA system. Stoichiometries and complex formation constants were determined by potentiometry at 25 °C and I = 0.2 M KCl. Practically only 1:1 complexes were formed in both systems with composition (VO)LH 2 and(VO)L in the V IV O–salDPA system, and with composition(VO 2 )LH and (VO 2 )L in the V V O 2 –salDPA system. Spectroscopic data provided information about the most probable binding modes of each stoichiometry. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2006)