Brom-palladates, M₂PdBr₆

Although palladium tetrabromide is not known, compounds of the type M₂PdBr₆, termed brom-palladates, have been prepared. Of these the most important is:

Potassium Brom-palladate K₂PdBr₆, which is precipitated from a solution of potassium brom-palladite on passing through it a current of bromine vapour. It also results on oxidising a solution of the brom- palladite with potassium persulphate in the presence of hydrobromic acid. It crystallises in beautiful black octahedra, which dissolve sparingly in water, yielding a reddish brown solution.

Boiling water and hot concentrated sulphuric acid each decompose the salt, bromine being evolved. Ammonia is immediately decomposed by it, with evolution of nitrogen.

Ammonium Brom-palladate, (NH₄)₂PdBr₆, is obtained in a similar manner to the preceding salt, ice-cold solutions being employed. The salt crystallises in black, regular octahedra, which are stable in air and sparingly soluble in cold water, yielding a reddish brown solution. Upon heating in a dry tube, bromine vapour is at first evolved, ammonium bromide next sublimes, and a residue of palladium sponge remains behind. Towards hot water, sulphuric acid, and ammonia the salt behaves in an analogous manner to the preceding salt.