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Hexachlor-palladates, M2PdCl6

Although palladium tetrachloride, PdCl4, analogous to platinic chloride, PtCl4, is not known in the free state, salts known as chlor-palladates, M2PdCl6, corresponding to, and isomorphous with, the chlor-platinates, M2PtCl6, have been prepared. They are much less stable than the platinum derivatives, but the fact that they can exist at all, when nickel yields no such compounds, affords an interesting link between palladium and platinum, and further justifies the intermediate position of palladium between nickel and platinum in the third vertical column in Group VIII of the Periodic Table.

Potassium Chlor-palladate, K2PdCl6

Potassium Chlor-pallaadate, K2PdCl6 is the most important salt of the series, and is conveniently obtained by passing chlorine through an aqueous, saturated solution of potassium chlor-palladite. The same salt is produced on dissolving palladium in aqua regia or in water saturated with hydrogen chloride and chlorine, and adding a saturated solution of potassium chloride. The liquid is evaporated to dryness, the residue washed with potassium chloride solution and finally with ice-water. Scagliarini and Berti-Ceroni prepared it by warming the chlor-palladite with potassium persulphate in the presence of hydrochloric acid. The salt precipitates out on cooling.

The crystals obtained in this way are red in colour, and isomorphous with the corresponding chlor-platinate. Density 2.738. On heating they turn black, but regain their red colour on cooling. They are readily reduced on warming in a current of hydrogen gas, whilst ignition converts them first into the chlor-palladite and finally into potassium chloride and metallic palladium.

Potassium chlor-palladate dissolves in water, but is only slightly soluble in ice-water, and is insoluble both in saturated potassium chloride solution and in alcohol. The aqueous solution undergoes partial dissociation, and on boiling with excess of water, potassium chlor-palladite is formed. Aqueous hydrochloric acid dissolves the salt without decomposition, whilst ammonia converts it into an ammoniate.

Caesium Chlor-palladate, Cs2PdCl6

Caesium Chlor-palladate, Cs2PdCl6, may be obtained in an analogous manner to the potassium salt, namely, by chlorinating an aqueous solution of caesium chlor-palladite. A brownish yellow crystalline precipitate results, which is very stable and almost insoluble in cold water. On boiling with water chlorine is evolved; it attacks ammonia, evolving nitrogen; concentrated sulphuric acid when warmed with the salt causes an evolution of chlorine and hydrogen chloride.

Rubidium Chlor-pailadate, Rb2PdCl6

Rubidium Chlor-pailadate, Rb2PdCl6 is obtained as a yellowish red precipitate in a similar manner to the preceding salt. Insoluble in cold water, it is decomposed by boiling water, and in its other properties closely resembles the caesium analogue.
The chlor-palladates of the following metals have been described: ammonium, (NH4)2PdCl6; glucinum, GlPdCl6.8H2O; magnesium, MgPdCl6.6H2O; zinc, ZnPdCl6.6H2O; nickel, NiPdCl6.6H2O; manganese, MnPdCl6. 6H2O.

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