Spectrophotometric Study of the Complexation Equilibria of Vanadium(V) with 3,5-Diaminoaza-Pyrazole Derivatives

Abstract

The acid-base characteristics of 3,5-diamino-4-[o-hydroxyphenylazo-] pyrazole (DAAZP) were studied spectrophotometrically in water dimethylsulphoxide media. The complexes of vanadium(V) with this reagent liable to occur in solutions are described and evaluated. The study of the behaviour uf vanadium in the presence of equimolar concentrations or in solutions containing metal or ligand excess gave evidence for the formation of two types of species with stoichiometric ratios 1 : 2 (M : L) depending on the pH of the medium. A spectrophotometric method for the determination of microamounts of vanadium (V) with DAAZP has been established at pH ═ 4.0 (λ_max ═ 450 nm, ∈ ═ 3.5 x 10⁴1 mol^–1 cm^–1).