Osmium Sesquioxide, Os₂O₃

Osmium Sesquioxide, Os₂O₃, is obtained by heating salts of trivalent osmium with sodium carbonate in a current of carbon dioxide. It also results when an excess of osmium tetroxide is reduced by heating with finely divided osmium.

The sesquioxide is a dark powder, insoluble in acids. It is obtained in the hydrated condition, Os₂O₃.xH₂O, as a reddish brown precipitate on adding an alkali to an aqueous solution of an osmochloride.