Double Chlorides of Trivalent Tungsten

Double Chlorides of Trivalent Tungsten, with those of potassium, ammonium, rubidium, caesium, and thallium, have been prepared by reduction with tin of a solution of potassium tungstate in concentrated hydrochloric acid. They are all anhydrous, of the type R^•₃W₂Cl₉, and are stable in the dry state. Conductivity and cryoscopic measurements show that the tungsten is present as part of a complex anion, and that in aqueous solution not more than four ions are produced by dissociation. The anion, W₂Cl₉''', is very stable, and the chlortungstates act as strong reducing agents on solutions of silver, gold, mercury, copper, and ferric salts; in the last case the reaction is quantitative. The following salts have been prepared:

Cr(NH₃)₆W₂Cl₉.2H₂O, dark green, microscopic, rectangular prisms;
Co(NH₃)₆W₂Cl₉.6H₂O, bright green, microcrystalline powder;
Cu(NH₃)₄NH₄W₂Cl₉.H₂O, and
Cu(NH₃)₄KW₂Cl₉.H₂O, green crystalline powders;
Cd(NH₃)₄NH₄W₂Cl₉;
Cd(NH₃)₄KW₂Cl₉;
[Ag(NH₃)₂]₃W₂Cl₉, unstable.

These are generally sparingly soluble in water, the concentrated solutions being green, the more dilute, yellow.

A solution of the free acid, H₃W₂Cl₉, is obtained by the action of hydriodic acid on a solution of the thallium salt; it has not, however, been isolated.