Platinum Dichloride, PtCl₂

Platinum Dichloride, PtCl₂, also known as Platinous Chloride, may be prepared by evaporating a solution of the tetrachloride to dryness and heating the residue to about 300° or 350° C. under constant stirring. Any unchanged platinic acid is removed by washing with water.

Platinum dichloride also results, mixed with a little tetrachloride, when platinum sponge or, better, platinum black, obtained by reduction of ammonium chlor-platinate by hydrogen gas at 100° C., is heated in chlorine to 360° C. It is obtained in a more pure condition by heating chlor-platinous acid, H₂PtCl₄, or the hydrated acid chloride, namely, trichlor-platinous acid, PtCl₂.HCl.2H₂O or H₂PtCl₃(OH)H₂O, to 100° C.

Platinum dichloride is a greenish grey or brown powder, its colour varying according to the method of preparation. Insoluble in water, it dissolves in hydrochloric acid to yield a solution of chlor-platinous acid, H₂PtCl₄, and in aqua regia to chlor-platinic acid, H₂PtCl₆. Caustic alkalies decompose it, yielding a black deposit of hydrated platinous oxide. With ammonia, complex ammino derivatives are formed.