Palladous Chloride, PdCl₂

Palladous Chloride, Palladium Bichloride, PdCl₂, is obtained in the anhydrous condition as a sublimate on heating spongy palladium to dull redness in dry chlorine. The monosulphide, PdS, when heated in chlorine is converted into the anhydrous chloride, and the same salt is produced by dehydrating the dihydrate, PdCl₂.2H₂O, at a slightly elevated temperature.

Palladium chloride can be distilled at a low red heat in a current of chlorine. It then yields a sublimate of dark red, needle-shaped crystals which deliquesce in the air.

When heated in air to 160° C. chlorine is evolved, and even at 100° C., after prolonged heating, traces of chlorine are driven off. When heated in an inert gas such as carbon dioxide, chlorine is evolved at 250° C. It is reduced by hydrogen in the cold.

When palladium dichloride is dissolved in water, and ammonia added in sufficient excess to dissolve the flesh-coloured precipitate, the diammoniate, PdCl₂.2NH₃, may be obtained as a precipitate by diluting with a large volume of water and acidulating with hydrochloric acid. It may be dried at 110° to 120° C., and has been used for the determination of the atomic weight of palladium. Density 2.5.

The dihydrate, PdCl₂.2H₂O, is obtained by crystallisation from the solution obtained by dissolving palladium in hydrochloric acid containing free chlorine, or in aqua regia. In the latter case the solution is first evaporated with hydrochloric acid in order to expel all the nitrogen products.

The salt crystallises as a brown, hygroscopic mass, which undergoes decomposition in excess of water, yielding a precipitate which possibly contains an oxychloride. Carbon monoxide passed into a solution of palladium dichloride effects its decolorisation, precipitating the metal as a black powder. The dilute solution is also completely reduced by hydrogen in twenty-four hours at ordinary temperature.