When K₂[OsCl₄] is heated with NH₃ under pressure, compound A of composition Os₂Cl₅H₂₄N₉ is isolated. Treatment of a solution of A with HI precipitates a compound in which three of the five chlorines have been replaced by iodine. Treating 1mmol of A with KOH releases 9 mmol NH₃. Compound A is diamagnetic and none of the stronger absorption bands in the IR spectrum is Raman active. Suggest a structure for A and account for the diamagnetism.