Osmiamic Acid, OsNO₃H

Osmiamic Acid, OsNO₃H, may be prepared by decomposing the barium salt with dilute sulphuric acid, or the silver salt with hydrochloric acid. The dilute aqueous solution thus obtained is fairly stable, but upon concentration it decomposes.

Joly suggested that osmiamic acid might well be represented as a nitroso compound by the formula OsO(NO)OH, derived from the unknown trihydroxv compound, Os(NO)(OH)₃, which corresponds to Ru(NO)(OH)₃.

Such a constitution is in harmony with certain reactions of, for example, its potassium salt, OsNO₃K. Thus reduction of the last named with acidulated stannous chloride yields the amide of potassium chlorosmate, namely, K₂Os(NH₂)Cl₅, the supposition being that the NH₂ group is formed by direct reduction of an NO group.

Werner and Dinklage, however, have pointed out that cooled hydrochloric acid reacts with potassium osmiamate, evolving chlorine and yielding a well-crystallised salt of composition K₂OsNCl₅. This is confirmed by Wintrebert. Now Werner and Dinklage regard it as improbable that a nitroso group can be present in the original acid, and suggest the formula:



the imido group replacing one atom of oxygen in the tetroxide.

To the potassium salt they give the tantomeric formula: