Two oxybromides of tungsten, WO2Br2 and WOBr4, are known. When bromine vapour is passed over red-hot tungsten dioxide, when a mixture of bromine vapour and air is passed over metallic tungsten, or when the pentabromide is passed over heated tungsten trioxide, both oxybromides are formed, and are separated by taking advantage of the fact that the oxy bromide, WOBr4, is the more readily volatile.
The dioxydibromide, WO2Br2, forms light red, transparent, infusible crystals which yield a yellow powder; the vapour is slightly decomposed into the trioxide and the oxybromide, WOBr4. It is unacted upon by cold water.
The oxytetrabromide, WOBr4, forms readily fusible, dark brown, lustrous needles of melting-point 277° C. and boiling-point 327° C. It is deliquescent and is decomposed by water. |