Spectrophotometric investigation of vanadyl phosphate equilibria in acid media

Abstract

The formation of vanadyl phosphate complexes in acidic LOM NaClO 4 solution was studied by spectrophotometry in the charge-transfer region of the optical spectrum. In the [H +] range studied, 0.4–13 mM, the principal species appear to be VO(H 2PO 4) + and VO(H 2PO 4) 2, formed with logarithmic stepwise formation constants of approximately 3.2 and 2.0, respectively. Both species are weakly acidic, ionizing to give VO(HPO 4) and VO(H 2PO 4)(HPO 4) − with pK a values on the order of 3–4. Results obtained for [H +] = 13 mM are anomalous and are not explained by these equilibrium constants.