Rhenium trioxide

ReOj -I- 2BuLi — Li2Re03 -1- octane 2Li2Re03 -I- 2EtOH 2LiRe03 -1- 2LiOEt + H2 ReOj + excess Lil — Lio,2Re03 -1- Lil -I- L 

Three phases have been identified in the Lijle03 system. For x 0.35 the structure remains cubic. A line phase at x = 1.0 is rhombohedral, as is a phase at 1.8 X 2.0. 

Reaction and filtration operations are carried out in a helium-filled glove box. However, the procedures are easily adapted to the use of Schlenk techiiiques. The hexane used should be distilled from sodium, and the concentrated /z-BuLi 

The reaction mixture is filtered in the glove box and the LijReOj collected on a medium-porosity fritted-glass filter. The product is washed several times with hexane to ensure removal of any excess n-BuLi. The yield is quantitative. The filtrate and washings are then removed from the glove box after sufficient dilution with hexane and titrated for excess n-BuLi. 

The titration consists of addition of a few milliliters of distilled water and an excess of standard HCl (0.1 N), followed by back-titration with standard NaOH solution (0.1 N). The lithium stoichiometry is calculated on the basis of the titration results. It has been shown that this total base titration gives the same results as are obtained with active lithium reagent and atomic absorption analysis. 

Complete lithiation of the limiting lithium stoichiometry of Li oReOa may require more than one n-BuLi treatment. This can be due in part to dilution of n-BuLi as the reaction proceeds. On titrating the initial n-BuLi reaction solution, 10.491 mmol of Li remains from an original 3.0591V n-BuLi solution containing 12.SmL (38.238 mmol) of n-BuLi in hexane and 4.080 g (17.421 mmol) of ReOj. This indicates 1.59 mmol of Li per millimole of ReOj. Further lithiation and subsequent titration results in Li2.iRe03. X-ray powder diffraction data indicates the lithium composition, in excess of two Li per ReOs, is due to impurities in the ReOj. 

Confirmation of the lithium stoichiometry is determined by an iodine reaction that yields the amount of lithium removed from the structure. A titration (described in Section A) performed after reaction of Li ReOa with a standard iodine solution affords the stoichiometry Lii.99Re03. 

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A highly explosive red/orange solid, obtained from rhenium trioxide and hydrogen peroxide reacting in hexamethylphosphoramide as solvent, was tentatively assigned this structure. 

One of the simplest oxides is the rhenium trioxide (ReOs) structure shown in figure lA(b). It consists of an incomplete fee host lattice of with Re in one-quarter of the octahedral sites. (Crystallographic shear (CS) phases (discussed in 1.10.5) based on ReOs may be considered as consisting of the cubic MO2 structure.) Many oxides and fluorides adopt the ReOs structure and are used in catalysis. 

Button T. W., Me Colm I. J., Wilson S. J., 1979, Hardness anisotropy and its dependence on composition in sodium tungsten bronzes and rhenium trioxide single crystals, J. Mater. Sci., 14, 159-164. 

When the decomposition reaction is performed in silica or glass containers, Nb(0,F)3 results. These materials are gray-black to black, refractory materials having the rhenium trioxide type of cubic structure, with a cell constant varying from 3.889 to 3.917 A.2 These materials contain variable amounts of oxygen and have often been erroneously identified as NbF3. 

The rapid formation of the rhenium trioxide (Re03) and a gas chromatographic transport of Re03 governed by mobile adsorption processes to deposition temperatures of about 500 °C (deposition peak B in Figure 17). This behavior is observed if the employed quartz columns are pretreated in excess of 1000 °C with 02 and with 02, 02/H20, or H202 as reactive component of the carrier gas. 

Tungsten trioxide is a lemon yellow solid (mp 1200°C) it has a slightly distorted form of the cubic rhenium trioxide structure (Fig. 18-D-l). 

Li03Re, Lithium rhenium trioxide, 24 205 LiOsV2, Lithium divanadium pentaoxide, 24 202... 

M0O3 has, surprisingly, a layer lattice CrOg and WOg have the rhenium trioxide structure (Fig. 245). 

Rhenium trioxide, in almost quantitative yield, is given by the thermal decomposition of Re207(C4Hg02)3, the addition compound of Re207 with dioxan (Nechamkin, Kurtz and Hiskey, 1951). On heating, Re03 dispro-portionates ... 

R. Saladino, V. Neri, A. R. Pelhccia, R. Caminiti, C. Sadun, Preparation and structural characterization of polymer-supported methyl rhenium trioxide systems as efficient and selective catalysts for the epoxidation of olefins, J. Org. Chem. 67, 1323-1332 (2002). 

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