N,N-dimethylhydroxamidovanadium(V). Interactions with sulfhydryl-containing ligands: V(V) equilibria and the structure of a V(IV) dithiothreitolato complex

The major aqueous equilibrium complexation reactions of vanadate in the presence of N,Ndimethylhydroxylamine (DMHA) and with dithiothreitol (DTT), β-mercaptoethanol, glycine, or cysteine in solution have been studied using 51V NMR spectroscopy. Previously unreported DMHA complexes of 2:1 and 2:3 V:DMHA stoichiometry were observed and characterized. Concentration studies showed that, for the three sulphur-containing ligands, the major product of sulphur coordination has a 1:2:1 stoichiometry of vanadate to dimethylhydroxylamine to heteroligand. These products do not carry a charge in neutral to moderately basic solution. A second product type of 1:1:1, V to DMHA to heteroligand, stoichiometry is also formed. These products carry a single negative charge. A reductive reaction between vanadate and excess DTT to form a V(IV) complex was also observed and a solid product was isolated. This product could also be obtained by direct reaction of vanadyl sulphate with DTT. It was characterized by X-ray diffraction studies. Crystal structure of [{VO(SCH2CHOHCHOCH2S)}2] [AsPh4]2: monoclinic, space group P21/n, Z = 2, a = 10.1607(18) Å, b = 17.8255(42) Å, c = 15.1520(33) Å, β = 104. 000(15)°, V = 2662.8 Å3, RF = 0.038 for 2327 data (Io ≥ 2.5σ(Io)) and 325 variables.