Redetermination of μ-oxido-bis[bis(N,N-diethylhydroxylaminato)oxidovanadium(V)]

In comparison with the previous determination [Saussine, Mimoun, Mitschler & Fisher (1980 ▶). Nouv. J. Chim. 4, 235–237] of the title compound, [V2(C4H10NO)4O3], the current study reports an improved precision of the derived geometric parameters, along with the deposition of all coordinates and displacement parameters. The two VV atoms are each surrounded by two deprotonated N,O-bidentate diethylhydroxylaminate groups, and a terminal and a bridging oxide ligand, in a distorted octahedral coordination geometry. The crystal packing is accomplished by van der Waals interactions.

In comparison with the previous determination [Saussine, Mimoun, Mitschler & Fisher (1980). Nouv. J. Chim. 4,[235][236][237] of the title compound, [V 2 (C 4 H 10 NO) 4 O 3 ], the current study reports an improved precision of the derived geometric parameters, along with the deposition of all coordinates and displacement parameters. The two V V atoms are each surrounded by two deprotonated N,O-bidentate diethylhydroxylaminate groups, and a terminal and a bridging oxide ligand, in a distorted octahedral coordination geometry. The crystal packing is accomplished by van der Waals interactions.

Comment
The crystal structure of the title compound, [(VO(C 4 H 10 NO) 2 ) 2 O], was first reported by Saussine et al. (1980). However, because atomic coordinates and displacement parameters have not been deposited (or are available) with the previous study, it is of interest to the public domain that this structure has been re-determined and to have access to the fully reported data.
Peroxidovanadium complexes are good insulin-mimetic compounds (Posner et al., 1994;Zhou et al., 2000). Studies suggest that the insulin-mimetic properties of peroxidovanadates are related to its oxidation at an active-site cysteine of the phosphatase (PTPs) that negatively regulate insulin receptor activation and signaling (Huyer et al., 1997). Hydroxylamine is related to hydrogen peroxide and it forms some complexes with vanadium that are structurally similar to those formed with hydrogen peroxide. It is also reported that the vanadium-hydroxylamine complex, bis(N,Ndimethylhydroxamido)hydroxooxovanadate (DMHAV), is a potent inhibitor of the protein tyrosine phosphatase-1B (PTP1B), and that this inhibition does not involve an oxidative process. Molecular modelling studies suggest that the main stabilizing interaction of DMHAV in PTP1B are a cyclic H-bonded structure involving the conserved active site aspartate and hydrophobic stabilization interactions with the methyl groups of DMHAV (Nxumalo et al., 1998). To gain further insight into the insulin mimetic actions of hydroxylamine complex, we have synthesized a group of vanadium-hydroxylamine complexes, including vanadium-aminoacids and vanadium-carboxylic acid hydroxylamido complexes (Zhang et al., 2009;2010)2. Here we report the synthesis and the redetermination of the structure of the title compound, [(VO(C 4 H 10 NO) 2 ) 2 O].
The title compound was synthesized from ammonium metavanadate, DL-valine and sodium hydroxide. Compared to reported synthetic steps, the use of an aqueous reaction system and the vanadium source all simplifies the synthesis procedure; DL-valine may play a buffer role.
The molecular structure is shown in Fig. 1. In the crystal, no intermolecular separations significantly less than the sums of the appropriate van der Waals radii (Bondi, 1964) are found. The two vanadium atoms are six-coordinate within a considerably distorted octahedral coordination geometry defined by two deprotonated N,O-bidentate diethylhydroxylamine groups, an terminal and a bridging oxide ligand. In order to compare the difference of the previous determination and our work, some important bond length and bond angles are listed in Table 1. A structurally similar dimethylhydroxamidovanadium(V) complex was previously prepared in a nonaqueous solvent system (Paul et al., 1997;Wieghardt et al., 1981).

Experimental
To a solution of sodium hydroxide (0.2390 g,5.975 mmol) in H 2 O (10 ml), ammonium metavanadate (0.2142 g,1.831 mmol) and DL-valine were added under stirring. The resulting colorless solution was stirred for approximately two minutes in an ice bath. 2 ml of N,N-diethylhydroxylamine (25.9 mmol) were added dropwise. The mixture was stirred for approximately five minutes, and after filtration of the solution, yellow crystals were obtained by slow evaporation of a mixture of the filtrate and ethanol at 277 K over a period of a few days.
supplementary materials sup-2 Refinement H atoms were placed in calculated positions, with C-H = 0.93 Å for phenyl, 0.96 Å for methyl and 0.97 Å for methylene H atoms, and refined as riding, with U iso (H) = 1.2U eq (C) for phenyl and methylene H, and 1.5U eq (C) for methyl H atoms. Fig. 1. The molecular structure of the title compound with displacement parameters shown at the 30% probability level.