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 pre sence of N,N-dimethylhydroxylamine (DMHA) and with dithiothreitol (DTT), be ta -mercaptoethanol, glycine, or cysteine in solution have been studied usi ng V-51 NMR spectroscopy. Previously unreported DMHA complexes of 2:1 and 2 :3 V:DMHA stoichiometry were observed and characterized. Concentration stud ies showed that, for the three sulphur-containing ligands, the major produc t of sulphur coordination has a 1:2:1 stoichiometry of vanadate to dimethyl hydroxylamine to heteroligand. These products do not carry a charge in neut ral 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 sing le 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. T his product could also be obtained by direct reaction of vanadyl sulphate w ith DTT. It was characterized by X-ray diffraction studies. Crystal structu re of [{VO(SCH2CHOHCHOCH2S)}(2)] [AsPh4](2): monoclinic, space group P2(1)/ n, Z = 2, a = 10.1607(18) Angstrom, b = 17.8255(42) Angstrom, c = 15.1520(3 3) Angstrom, beta = 104. 000(15)degrees, V = 2662.8 Angstrom (3), R-F = 0.0 38 for 2327 data (I-o >= 2.5 sigma (I-o)) and 325 variables.