Potassium Osminitrite, K₂0s(NO₂)₅

Potassium Osminitrite, K₂0s(NO₂)₅, is obtained by the action of excess of potassium nitrite on a solution of potassium chlorosmate at a temperature of about 80° C.:

K₂OsCl₆ + 7KNO₂ = K₂Os(NO₂)₅ + 6KCl + KNO₃ + NO.

It is necessary to carry out the operation away from air, as otherwise large quantities of osmyl oxynitrite are formed.

The crystals obtained are flattened parallelopipeds, canary yellow in colour, and readily soluble in water.