Tetrachlor-palladites, M₂PdCl₄

Palladium dichloride combines with chlorides of certain other metals to yield chlor-palladites, of general formula M₂PdCl₄. These are analogous to the chlor-platinites, M₂PtCl₄, the potassium salts of the two series being isomorphous.

Potassium Chlor-palladite, K₂PdCl₄, the most important salt of this series, is readily obtained by concentrating a solution of palladous chloride with excess of potassium chloride.

Insoluble in absolute alcohol, the crystals readily dissolve in water, yielding a reddish brown solution. Heated to 100° C. they still retain some water, and begin to decompose at 105° C., a fact which renders it difficult to obtain the crystals in a perfectly dry condition. At red heat, potassium chloride and metallic palladium are formed.

When boiled with excess of water potassium chlor-palladate, K₂PdCl₆, is formed. The boiling solution is reduced by alcohol and by sulphur dioxide. With ammonia, an ammoniate is produced.

Ammonium Chlor-palladite, (NH₄)₂PdCl₄, is obtained in an analogous manner to the potassium salt, and is interesting since it yields, upon heating in hydrogen, a residue of spongy palladium in a condition particularly suitable for catalytic activity.

The salt yields dark green prisms, soluble in water but insoluble in absolute alcohol.

Caesium Chlor-palladite, Cs₂PdCl₄, is precipitated on mixing concentrated solutions of caesium chloride and palladous chloride as a light brown deposit, which upon recrystallisation from hot water yields needles of the same colour.

Rubidium Chlor-palladite, Rb₂PdCl₄, prepared in an analogous manner to the preceding salt, crystallises from hot water in light brown silk-like needles.