Platinum Tetra-iodide, PtI₄

Platinic Iodide, Platinum Tetra-iodide, PtI₄, is readily prepared in a variety of ways. It is deposited on addition of hydriodic acid, or of sodium (or potassium) iodide to a warm solution of chlor-platinic acid, and allowing to stand at the ordinary temperature. The solution becomes turbid and finally deposits crystals of iodide.

The salt may also be obtained by direct union of the components, as, for example, by heating finely divided platinum and iodine in sealed tubes. It results when iodo-platinic acid is heated to 100° C., and when platinum sponge is dissolved in a solution of iodine in aqueous hydriodic acid. The dark red solution is evaporated to dryness, raised to 180° C., and washed with boiling water.

Platinic iodide is a blackish brown, amorphous powder, which evolves iodine vapour when placed in vacuo even at ordinary temperatures. When warmed to 130° C. in air, iodine is evolved.

The heat of formation of platinic iodide solution is given as:

[Pt] + 2[I₂] = [PtI₄] + 17.4 Cals.

[Pt] + 2(I₂) = [PtI₄] + 39.0 Cals.

Although insoluble in water, platinic iodide dissolves in alcohol. Its molecular conductivity in ethyl alcohol at 25° C. increases with dilution until the concentration has been reduced to 0.25 gram molecule in 600 litres, when it becomes constant.