Brom-palladites, M₂PdBr₄

With bromides of the alkali metals palladous bromide yields pallado-bromides or brom-palladites, of general formula M₂PdBr₄, analogous to the chlor-palladites already considered.

Potassium Brom-palladite, K₂PdBr₄, is obtained by dissolving equivalent weights of the bromides of potassium and palladium in water containing hydrobromic acid. Upon evaporation the anhydrous salt crystallises in reddish brown needles, which are very stable.

Digestion of the aqueous solution of this salt with bromine at a temperature not exceeding 70° C. yields the dihydrate, K₂PdBr₄.2H₂O, which separates out in long, dark brown, shining needles. These upon exposure to air rapidly lose their lustre and acquire the reddish brown colour of the anhydrous salt. Owing to the rapidity with which they lose their combined water, complete analysis of the crystals is difficult.

Ammonium Brom-palladite, (NH₄)₂PdBr₄, may be prepared1 in a similar manner to the preceding salt. Its crystals are olive brown in colour, anhydrous, and very stable in air. They readily dissolve in water. Upon ignition a residue of palladium sponge is obtained.

Caesium Brom-palladite, Cs₂PdBr₄, is precipitated as a dark brown mass on mixing concentrated solutions of caesium bromide and palladous bromide. Upon recrystallisation from dilute hydrogen bromide solution, fine reddish brown needles are obtained, which are anhydrous, and very soluble in water.

Rubidium Brom-palladite, Rb₂PdBr₄, is obtained in a precisely similar manner to the caesium salt. It yields similar needle-shaped crystals, which are also reddish brown in colour.

Sodium Brom-palladite, 2Na₂PdBr₄.9H₂O, has been obtained by concentrating mixed solutions of the bromides of sodium and palladium over sulphuric acid in an evacuated desiccator. It separates out in large, deep red plates which are exceedingly deliquescent.