INTERACTION OF N-HYDROXYACETAMIDE WITH VANADATE IN AQUEOUS-SOLUTION

The equilibria between aqueous vanadate and N-hydroxyacetamide (acetoh ydroxamic acid, HL, CH3CONHOH) have been studied at 25 degrees C in 0. 15 mol dm(-3) NaCl medium by combined potentiometric, spectrophotometr ic, V-51 and O-17 NMR methods. Complexes form in the range pH 3 to 11, and many of their formation constants have been determined. The neutr al species HV(HL) and HV(HL)(2) predominate below pH 4.5 and with HL:V > 2: 1, where V is an abbreviation for [H2VO4](-). These notional for mulae do not specify the possible co-ordination or loss of water molec ules from the complex anions and the charges shown are the overall spe cies charges rather than any algebraic sum. From pH 4.5 to 8.5 the mai n species are [V(HL)(2)](-) and, to a lesser extent, [V(HL)](-). Oxyge n-17 NMR data strongly suggest that [V(HL)(2)](-) has octahedral co-or dination, with a cis-VO2+ unit and two bidentate L- ligands, one of wh ich can lose another proton above pH 8.5 to form [VL(HL)](2-). The spe cies [V(HL)](-) also deprotonates above pH 9. The minor oligomeric spe cies [V-2(HL)(3)](n-) and [V-2(HL)(4)](n-) also form, at higher concen trations of V and HL.