Osmium dioxide
Osmium dioxide is an inorganic compound with the formula. It exists as brown to black crystalline powder, but single crystals are golden and exhibit metallic conductivity. The compound crystallizes in the rutile structural motif, i.e. the connectivity is very similar to that in the mineral rutile.
Preparation
can be obtained by the reaction of osmium with a variety of oxidizing agents, including, sodium chlorate, osmium tetroxide, and nitric oxide at about 600 °C. Using chemical transport, one can obtain large crystals of, sized up to 7x5x3 mm3. Single crystals show metallic resistivity of ~15 μΩ cm. A typical transport agent is via the reversible formation of volatile :It can also be prepared by reducing osmium in higher oxidation states with alcohol, in which it forms a dihydrate. As opposed to the anhydrous dioxide, the dihydrate possesses a bluish black appearance.
Adding strong alkali to chloroosmic acid or its salts also yields the dihydrate.
Properties
Osmium dioxide does not dissolve in water, but it can be dissolved by strong acids such as hydrochloric acid.The crystals have rutile structure. Unlike osmium tetroxide, is not toxic.
Hexavalent osmium
Compounds of osmium in the +6 oxidation state are dominated by the osmyl species, in which exists as a radical trans-dioxo moiety. These osmyl compounds are all diamagnetic, and stabilized by strong σ-donor and π-donor ligands. Most osmyl compounds are mononuclear and have a linear O=Os=O structure.Examples of osmyl compounds include [potassium osmate|],, and [Potassium osmyl oxalate|], but many others are known.