Structural characterization and electrochemical behavior of oxovanadium(V) complexes with N-salicylidene hydrazides

The hydrazone ligands derived from salicylaldehyde and aliphatic carbonic acid hydrazides react with equimolecular amounts of ammonium metavanadate and 8-hydroxyquinoline in refluxing methanol to yield oxovanadium(V) complexes. The synthesis can alternatively be performed starting from [VO(acac)₂] followed by aerial oxidation to form the corresponding oxovanadium(V) complexes. The molecular structures determined by X-ray crystallography feature in all cases a oxovanadium(V) moiety in an distorted octahedral arrangement with an oxygen and nitrogen rich environment. The obtained compounds posses very good solubility in organic solvents, permitting electrochemical investigation. Square wave voltammetric measurements revealed two reversible one-electron reduction steps at 0.355 and −1.638 V. The reduction of the oxovanadium(V) complexes to the corresponding vanadium(IV) species occurs at relatively positive potential, which is independently verified by ESR spectroscopy. While the second reduction step appears to be accompanied by a pre-wave exhibiting an unusual frequency dependence which can be attributed to ligand addition/elimination equilibria related to the 8-hydroxyquinoline coligand. The oxovanadium(V) complexes can be converted into the corresponding cis-dioxovanadium(V) compounds by reaction with aqueous NaOH. ⁵¹V NMR monitoring of this reaction reveals that one equivalent of base results in a full conversion with the cis-dioxovanadium(V) complex being the only species present in solution.     

Oxovanadium(IV) complexes of carbohydrates: A brief overview

In this brief review the most recent studies and the most relevant aspects of the complexes generated by interaction of carbohydrates and related molecules with the oxovanadium(IV) cation, VO²⁺, are presented and discussed. The survey includes complexes of mono-, di- and polysaccharides, and of other molecules related to simple sugars. First studies with conduritols and related molecules are also described. Moreover, complexes of ascorbic and quinic acids and of some peculiar flavonoids are also included. Some comments on the general physicochemical properties of these complexes are made and their biological activities and effects are also briefly discussed.     

Structural characterization of pentadentate salen-type Schiff-base complexes of oxovanadium(IV) and their use in sulfide oxidation

Pentadentate Schiff-base complexes of oxovanadium(IV), the ligands of which were derived from salicylaldehyde derivatives with a variety of substituents and two kinds of amines (2,2^′-bis(aminoethyl)amine and 3,3^′-bis(aminopropyl)amine), were prepared, and their coordination geometries in the solid state were determined by X-ray diffraction and IR measurements and those in CH₂Cl₂ by EPR measurements. They were found to retain distorted octahedral coordination in the solid state. They showed the structural change depending on the type of the substituent. The complexes which reacted with tert-butylhydroperoxide converted methyl phenyl sulfide to the corresponding sulfoxide at lower rates of reaction than tridentate N-salicylidene-2-aminoethanolato oxovanadium(IV) ([VO(salae)]) and tetradentate (N,N^′-bis(salicylidene)ethylenediaminato)oxovanadium(IV) ([VO(salen)]).