Tungsten Oxychlorides

Two oxychlorides of tungsten, respectively WO₂Cl₂ and WOCl₄, are known.

Tungsten dioxydichloride (tungstyl chloride), WO₂Cl₂, was originally considered to be a chloride of tungsten, and was obtained, although mixed with a certain amount of the oxytetrachloride, by interaction of chlorine with tungsten dioxide. In attempting to prepare tungsten hexa-chloride by the action of sulphur chloride upon tungsten trioxide, Bourion found that the product of the reaction was a mixture of the two oxychlorides only. Further, it is produced by heating tungsten hexachloride with oxalic acid.

This oxychloride forms stable yellow crystals which readily sublime, but which also melt at 259° C.; at much higher temperatures the substance largely dissociates into tungstic anhydride and the oxytetrachloride. Partial decomposition is also effected by warming with water. Tungsten oxytetrachloride, WOCl₄, is obtained by heating tungsten pentachloride or hexachloride in oxygen, by heating the penta-chloride with oxalic acid, by interaction of phosphorus pentachloride with tungsten trioxide; together with the oxychloride, WO₂Cl₂, by heating tungsten trioxide in a current of sulphur chloride vapour, by heating the trioxide or oxychloride, WO₂Cl₂, in the vapour of the hexachloride alone or mixed with chlorine, or by passing dry chlorine over a heated mixture of tungsten trioxide and carbon, the main product being then the oxytetrachloride, which may be obtained in a moderately pure state by taking advantage of its greater volatility than that of the dioxydichloride. It is also formed, together with small quantities of the hexachloride and probably of the pentachloride, when carbonyl chloride is passed over heated tungsten powder.

Tungsten oxytetrachloride forms splendid transparent, ruby-red, needle-shaped crystals which melt at 210° C. and boil at 227.5° C., giving a red vapour of normal density. By water it is decomposed, giving first the yellow oxychloride, and further, hydrochloric and tungstic acids. A certain amount of the yellow oxychloride is also formed from it by loss of chlorine on sublimation in air or oxygen.