Monocarbonyl Platinum Dichloride, PtCl₂.CO

Monocarbonyl Platinum Dichloride, PtCl₂.CO, obtained by heating the di- and sesqui-carbonyls to 250° C., yields golden yellow crystals, melting at 195° C. to an orange-red liquid. The crystals are hygroscopic and are decomposed by water, the main reaction consisting in the deposition of platinum and liberation of carbon dioxide and hydrochloric acid; thus:

PtCl₂.CO + H₂O = CO₂ + Pt + 2HCl.

This reaction cannot, however, represent the whole of the changes taking place, since although on adding a drop of water to crystals of the monocarbonyl derivative a black deposit is obtained, the deposit is soluble both in concentrated hydrochloric acid and in concentrated nitric acid. It cannot, therefore, be merely platinum.

When heated to 300° C. the carbonyl decomposes, yielding platinum and phosgene, COCl₂.

Carbonyl platinum dichloride has a distinctly basic character. It dissolves in excess of hydrochloric acid to a lemon-yellow solution, due, perhaps, to the formation of a soluble hydrochloride, PtCl₂.CO.HCl. This solution is a powerful reducing agent, effecting the reduction of silver, gold, and mercury from their salts. The monocarbonyl unites with soluble metallic chlorides, such as those of the alkali metals, to yield yellow, crystalline double salts. These, however, are so readily soluble and so easily decomposed that their satisfactory isolation has proved difficult. With the chlorides of certain organic bases, however, well-defined compounds have been obtained.