Palladous salts

Paliadiumoxydul, n. palladous oxide, palladium-(II) oxide, -nitrat, n. palladous nitrate, palladium (II) nitrate, -salz, n. palladous salt, palladium (ID salt. 

Ammonia combines with palladium salts, yielding ammino-com-pounds. These are, however, mostly derivatives of the stable palladous salts. Thus the two principal groups of the ammino-derivatives of palladium are the pallados-ammines or diammino-palladium compounds, 1 Jorgensen, J. prald. Ohem., 1886, 34, 396. 2 Jorgensen, ibid., 1883, 27, 478. 

Those containing four molecules of ammonia, the tetrammino-palladous salts, of general formula [Pd(NH3)4]R2. 

Ammino-derivatives of the unstable palladic salts are unknown, but a series of compounds have been prepared where pyridine takes the place of ammonia in the complex, and these appear to be derivatives of palladic salts. Unlike the platinic salts, however, the co-ordination number in these substances is four instead of six. 

Palladous salts on treatment with excess of ammonia yield tetram-mino-palladous salts, from which on the addition of acid the corresponding diacido-diammino-compounds are precipitated. This method may be employed for the preparation of the chloro-, bromo-, and iodo-compounds, which are sparingly soluble in water, and the other members of the series are prepared from these by double decomposition. Ammonia transforms the compounds info tetrammino-palladous salts. 

Tetrammino-palladous Salts, [PdNH3)4]R2.—These are formed by exposing anhydrous palladium salts to the action of ammonia, or by treating an aqueous solution of the palladous salt, or the corresponding diammino-palladium derivative, with excess of ammonia. The solution formed is unstable and readily loses ammonia on evaporation, passing into the more stable series mentioned above. If, however, evaporation takes place in an atmosphere of ammonia the salts may be separated. In the dry state they slowly lose ammonia in air, more rapidly on heating or in vacuo. This series of compounds are almost colourless and are soluble in water. Acids transform them easily into the diammino-compounds. 

Ethylenediamine and propylenediamine may be substituted for ammonia in the diammino-palladous salts. This series is prepared by the action of ethylenediamine and analogous bases on palladous salts. A double palladous compound is first formed, which is decomposed on addition of excess of the base, yielding the single salt. 

Ammino-derivatives of palladic salts are unknown, but pyridine derivatives containing tetravalent palladium have been described. The substances are easily obtained by the oxidation of dichloro-di-pyridino-palladium. 

Palladous Salts likewise possess catalytic properties. For example, they accelerate the oxidation of oxalic acid by persulphates, and, to a less extent, by nitric acid. This is attributable to the alternate formation of a palladic salt by the oxidiser and its reduction by the oxalic acid. Ammonia is likewise oxidised by persulphates in the presence of a palladous salt.3... 

Three classes of palladium salts are known, namely, palladous salts, in which the metal functions as a divalent atom, and palladic salts, in which the metal is trivalent and tetravalent. The palladous salts are stable, but upon ignition yield metallic palladium. 

Palladic salts are less well known in the free state, being highly unstable, although, combined with other salts, they yield stable compounds. Examples of these are the chlor-palladates, of general formulae... 

Palladous salts are readily oxidised to palladie compounds, particularly when wanned. For example, a solution of palladous nitrate warmed with concentrated persulphate solution is oxidised to a brown, palladie compound, which decomposes hydrogen peroxide and ammonia vigorously, gaseous products being evolved. With hydrochloric acid it yields free chlorine. 

Ammonia is likewise oxidised by persulphates in the presence of a palladous salt. 

Palladous Oxide, PdO.—Palladous oxide was obtained by Berzelius by strongly heating palladium amalgam, by precipitating palladous salt solutions with alkali, as well as by fusing metallic palladium with alkalis.4... 

The colour of palladous oxide varies according to its method of preparation. Prepared by the action of alkali upon palladous salts in aqueous solution, it has a yellowish brown colour which becomes darker on prolonged boiling. The product obtained by the hydrolytic decomposition of the nitrate is almost black, and it may well be that the extent of hydration is responsible for these changes. 

On passing hydrogen sulphide through a solution of a palladous salt, a dark brown precipitate is obtained, which is presumably another form of palladous sulphide.5 It is insoluble in ammonium sulphide and in hydrochloric acid, but it dissolves both in nitric acid and in aqua regia. When heated in air, a basic sulphate is produced, whilst in chlorine palladous chloride is formed. Potassium cyanide gradually effects its solution. With sulphides of the alkali metals, sulpho- or thio-palladites, M2Pd3S4, are formed. 

Palladium combines with phosphorus at high temperatures, but definite phosphides do not appear as yet to have been isolated. Similarly, hydrogen phosphide causes the precipitation of a mass, containing both palladium and phosphorus, when passed into an aqueous solution of a palladous salt. Complex chlorophosphides have been prepared. ... 

Palladous salts oxidise the acid to phosphoric acid with deposition of palladium.6... 

Gayet, F. Marty, J.-D. and Lauth-de Viguerie, N. (2008). Palladate Salts from Ionic Liquids as Catalysts in the Heck Reaction. Arkiooc, 17,61-76. 

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