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

The equilibria between vanadium(V) and 2-amino-N-hydroxypropanamide (HL or beta-alaninehydroxamic acid, NH2CH2CH2CONHOH) in aqueous solution have been studied at 25 degrees C in 0.10 mol dm(-3) NaClO4 medium by combined poten tiometric, spectrophotometric and V-51 NMR methods. Complexes are formed be tween VO2+ and the beta-alaninehydroxamate anion (L-) in the pH range 2.5-1 0.5, 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 proto nated or deprotonated, forming positively charged, neutral or negatively ch arged species: [VO2HL](+) and [VO2H3L2](2+) coexist below pH 3.5, with [VO2 HL](+) 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.