Tungsten Hexachloride, WCl₆

In the entire absence of air and of moisture, tungsten heated to redness combines with chlorine to form the hexachloride, but it is extremely difficult to prevent simultaneous formation of the readily volatile oxychloride WOCl₄; the reaction is accelerated catalytically by the presence of platinum black. The hexachloride may also be obtained by the action of chlorine on the crystalline disulphide. The compound is a violet substance crystallising, e.g. from solution in carbon disulphide, in the cubic system; it is only slowly decomposed by water, although as usually prepared it fumes in moist air and is decomposed by cold water owing to the presence of oxychlorides. It melts at 275° C. and boils at 346° C.; its mean vapour density at 440° C. is 168.8, a value which points to dissociation of the molecule at this temperature. As a matter of fact, dry carbon dioxide passed through the fused salt liberates chlorine from the hexachloride, but not from the pentachloride.

Reduction with hydrogen converts the Tungsten Hexachloride, WCl₆, into lower chlorides and even into the metal, while with oxygen, oxychlorides are formed. With halogen hydracids, lower halides and mixed halides are formed.