Lithium Platinicyanide, LiPt(CN)₄

Lithium Platinicyanide, LiPt(CN)₄, is obtained as the copper-coloured double salt, LiPt(CN)₄.2LiPt(CN)₄, on warming hydrogen peroxide solution with lithium platinocyanide acidulated with sulphuric acid. If the platinocyanide solution is very concentrated or, better, if the hydrogen peroxide is replaced by perhydrol, pure lithium platinicyanide is obtained, free from admixed or combined platinocyanide.

The anhydrous salt is white, and is readily obtained by gently heating one of its hydrates.

The monohydrate, LiPt(CN)₄.H₂O, is obtained by evaporation of an aqueous solution of the trihydrate and of sodium sulphate, and gently warming the residue. The sodium sulphate hydrates itself at the expense of the lithium salt, and the yellow monohydrated salt is obtained. The monohydrate is also produced on simply warming either the trihydrate or dihydrate.

The dihydrate, LiPt(CN)₄.2H₂O, may be prepared by gently warming the trihydrate, or by cooling it in liquid air. It is orange-red in colour, but readily dissolves in water to a colourless solution.

The trihydrate LiPt(CN)₄.3H₂O, is obtained by evaporation of the aqueous solution at 40° to 50° C. to the crystallising point and suddenly cooling to 15° C. It yields needle-shaped crystals, which are colourless, but exhibit a slight lavender fluorescence.