Osmiamic acid

Osmiamic Acid, OsNOsH, 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 8 suggested that osmiamic acid might well be represented as a nitroso compound by the formula OsO(NO)OII, derived from the unknown trihydroxv compound, Os(NO)(OH)s, which corresponds to Ru(NO)(OH)3. 

Os(VI) complexes of type [Os(VI)NX5]2- or [0s(VI)NX4H20]-(X = Cl, Br, CN, ox) are made by the action of the appropriate acid HX on potassium osmiamate (6, 11). The tendency to lose the ligand trans to the nitride and to substitute a water molecule is some evidence of a trans labilizing effect of jr-donor ligands. X-ray studies show a distorted octahedral structure with the osmium atom slightly out of the plane of the equatorial X atoms towards the nitride (1). The Os=N stretching frequency is around 1080 cm-1 (11) in such complexes. 

The osmiamate in is the source of most other osmium nitrido complexes. The free acid is said to be 0sN(0H)02 in the solid state and the Bu"4N, Ph4P+, Pli4As+, lithium, rhodium, potassium, rubidium, cesium, ammonium, silver, thallium, mercury, zinc, barium and lead salts are also known. The preparation of the potassium salt of OSO4 in concentrated KOH solution with NH4OH is a simple method for obtaining this useful starting material. ... 

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