Oxidoalkoxidovanadium(V) complexes: Synthesis, characterization and comparison of X-ray crystal structures

Abstract

The reaction of VO(acac)2 with the ONO-chelator obtained by the condensation of salicylaldehyde with 2-hydroxybenzoylhydrazine (H2L) in a monohydric alcohol (ROH) medium produces [VO(OR)L]-type oxidoalkoxido complexes (1–7) where R=Me, nPr, iPr, nBu, iBu, tBu and nPen. All the complexes show the metal atom to have a five-coordinate square pyramidal environment, although in some complexes there is an additional weak V⋯O interaction in the sixth axial position. In acetonitrile medium and in the presence of a cis-diol (ethylene glycol), H2L reacts with VO(acac)2 to form a six-coordinate complex, [VO(OCH2CH2OH)L] (8). When the reaction is carried out in acetonitrile medium in the presence of 2-amino ethanol, a completely different type of product containing the square pyramidal complex anion [VO2L]− associated with the cation [NH3CH2CH2OH]+ is obtained. It was noted previously that on being reacted with monodentate nitrogen donor bases B (which are stronger than pyridine), the [VO(OR)L] complexes react to form the same complex anion [VO2L]− associated with the corresponding cation [BH]+. The coordination environment around the V(V) acceptor center of the water soluble [BH]+[VO2L]− satisfies one of the several requirements for an efficient antidiabetic vanadium species such as water solubility, nature of donor atoms of the ligand and their disposition around the VO2+ acceptor center.