REACTIONS OF VANADATE WITH N,N-DIMETHYLHYDROXYLAMINE - AQUEOUS EQUILIBRIA AND THE CRYSTAL-STRUCTURE OF THE UNCHARGED OXYGEN-BRIDGED DIMER OF BIS(N,N-DIMETHYLHYDROXAMIDO)HYDROXOOXOVANADATE

V-51 nuclear magnetic resonance spectroscopy has been utilized in the investigation of the reactions of vanadate with N,N-dimethylhydroxylam ine in aqueous medium. The major components of the reaction products w ere mono- and bisliganded mononuclear vanadate compounds with V-51 che mical shifts near -630 and -740 ppm, respectively. Variation of the co ncentration of the reactants enabled the determination of stoichiometr y and formation constants of the products. The two major signals near -740 ppm were assigned to two stereoisomers of a bisligand product. Th e proton stoichiometries and pK(a) values of the major products were d etermined from pH variation studies. A crystalline product of the type [V(O)(ONMe2)(2)](2)O was isolated from the reaction of vanadate with dimethylhydroxylamine and its structure determined from X-ray diffract ion studies. The compound possesses a dimeric ore-bridge structure wit h a six-coordinate vanadium core. The arrangement about each vanadium may be described as approximately tetrahedral considering the center o f the N-O bond in each dimethylhydroxamide ligand as one vertex. Hydro lysis of the crystalline solid in D2O provided two isomers that corres ponded to the two bisligand products. A variable temperature H-1 NMR s tudy in D2O and 50% D2O/(CD3)(2)CO mixture revealed the existence of r easonably fast chemical exchange between the two predominant isomers. The nature of coordination of these and related compounds is discussed . Crystal structure of [V(O)(ONMe2)(2)](2)O: orthorhombic, space group P22(1)2(1); Z = 2; a = 7.0955(9) Angstrom; b = 10.2313(12) Angstrom; c = 11.5942(11) Angstrom; V = 841.69 Angstrom(3); T = 213 K; R-F = 0.0 21 for 1141 data (I-0 greater than or equal to 2.5 sigma(I-0)) and 137 variables.