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 HVO42– above pH 10.5.