Tungsten dibromide

Tungsten dibromide [13470-10-5] WBr2, formed by the partial reduction of the pentabromide with hydrogen, is a black powder that decomposes at... 

Tungsten Dibromide, WBr., remains as a velvety bluish-black crystalline residue when the pentabroniide, heated in a bath of fused zinc chloride, is reduced by hydros end... 

CP Disproportionates at 450-500 °C into WBrs and WB2, and is soluble in water. Tungsten Dibromide VBr2... 

Dining preparation of tungsten(IV) dibromide oxide, appropriate proportions of reactants are heated in an evacuated sealed glass ampoule to 400-500°C. Initially only one end should be heated to prevent excessive pressure bursting the ampoule. See other GLASS INCIDENTS See other halogens, oxidants... 

The tube is sealed under vacuum and placed in a temperature gradient of 400/40°C. until the bromine has completely reacted. After this preliminary firing, the reaction tube is placed in a temperature gradient of 450/325°C. for 15 hours. The crude product is purified by a second sublimation. The more volatile impurities, WOBr4 and WBr5, are separated in the usual way, which leaves behind pure crystalline tungsten(VI) dibromide dioxide. The product yield is 15 g. (97%). Anal. Calcd. for W02Br2 W, 48.95 Br, 42.53 O, 8.52. Found W, 48.78 Br, 41.58 O, 8.65. 

Tungsten(VI) dibromide dioxide is sensitive to atmospheric moisture. It yields a clear, colorless solution in dilute and concentrated solutions of ammonia or sodium hydroxide. No reaction is observed with hot or cold concentrated hydrochloric acid, or dry organic solvents. 

The crude product contains a small amount of the less volatile tungsten(VI) dibromide dioxide as an impurity, which can be separated by sublimation at 120°C. under dynamic vacuum (10-3 torr). A yield of approximtely 15 g. (96%) of pure tungsten(VI) tetrabromide oxide is obtained after sublimation. Large crystals can be obtained by sublimation of the purified product in another tube with 1 mg. of bromine per milliliter of tube volume in a temperature gradient of 220/160°C. Anal. Calcd. for WOBr4 W, 35.40 Br, 61.52 O, 3.08. Found W, 35.37 Br, 61.56 O, 3.08. 

Tungsten(VI) dibromide oxide, first prepared by Tillack and Kaiser,10 forms well-crystallized, gray-black shiny needles. It is not attacked by water, dilute acids, ammonia, or organic solvents, such as ethanol, acetone, toluene, or trichloroethylene. Although the crystals appear unchanged in concentrated hydrochloric acid, a light-blue solution results. Concentrated nitric or sulfuric acid... 

FIGURE 6.27. Open-circuit photovoltage versus solution redox potential for n-Si and p-Si photoelectrodes in l.OM KCl/CHjOH solution. The redox couples used were (A) cobaltocene ° (B) A,W -dimenthyl-4, 4 -bipyridinium dichloride (C) V,V -dibenzyl-4,4 -bipyridinium dibromide (D) decamethylfer-rocene (E) Al,AI,N, AI -tetramethylphenylenediamine (F) dimethylferrocene" (G) ferrocene " (H) octyl-ferrocene ", A tungsten-halogen bulb was used to provide light intensities which yielded short-circuit photocurrent densities of 25-30 mA/cm After Lewis. (Reproduced by permission of The Electrochemical Society, Inc.)... 

Moly bdenum diazide tetrachloride, 4164 Silver azide chloride, 0009 Tin azide trichloride, 4146 Titanimn azide trichloride, 4147 Titanimn diazide dibromide, 0273 Tungsten azide pentabromide, 0297 Tungsten azide pentachloride, 4182 Uranimn azide pentachloride, 4181 Vanadimn azide tetrachloride, 4166 Vanadyl azide dichloride, 4090 See AMMINEMETAL AZIDES... 

U02Br2 URANIUM DIBROMIDE DIOXIDE 1749 W(CO)6[g] TUNGSTEN HEXACARBONYL (GAS) 1790... 

---