Interaction of 2-amino-N-hydroxypropanamide with vanadium(V) in aqueous solution

Abstract

The equilibria between vanadium(V) and 2-amino-N-hydroxypropanamide (HL or β-alaninehydroxamic acid, NH₂CH₂CH₂CONHOH) in aqueous solution have been studied at 25 °C in 0.10 mol dm^–3 NaClO₄ medium by combined potentiometric, spectrophotometric and ⁵¹V NMR methods. Complexes are formed between VO₂⁺ and the β-alaninehydroxamate anion (L^–) in the pH range 2.5–10.5, and many of their formation constants have been determined. Complexes with a 1∶1 and 2∶1 ligand∶metal ratio, depending on pH, can be either protonated or deprotonated, forming positively charged, neutral or negatively charged species: [VO₂HL]⁺ and [VO₂H₃L₂]²⁺ coexist below pH 3.5, with [VO₂HL]⁺ predominating over [VO₂H₃L₂²⁺]. From pH 3.5 to 7.0 the main species are [VO₂H₂L₂]⁺ and, to a lesser extent, [VO₂L]. Above pH 7, [VO₂H₂L₂]⁺ deprotonates to form [VO₂HL₂] and [VO₂L₂]^–. Above pH 9.5, the prevailing complex species are [VO₂H_–1L]^– and [VO₂H_–2L]^2–, being finally replaced by HVO₄^2– above pH 10.5.