Potassium osmate is the

inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

with the formula K₂ sO₂(OH)₄ This diamagnetic purple

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

contains osmium in the VI (6+) oxidation state. When dissolved in water a red solution is formed. When dissolved in dilute alcohols, the salt gives a pink solution, and it gives a blue solution when dissolved in methanol. The salt gained attention as a catalyst for the asymmetric dihydroxylation of olefins.

Structure

The complex anion is

octahedral In geometry, an octahedron (: octahedra or octahedrons) is any polyhedron with eight faces. One special case is the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at each vertex. Many types of i ...

. Like related d² dioxo complexes, the oxo ligands are trans. The Os=O and Os-OH distances are 1.75(2) and 1.99(2) Å, respectively. It is a relatively rare example of a metal oxo complex that obeys the 18e rule.

Preparation

The compound was first reported by Edmond Frémy in 1844. Potassium osmate is prepared by reducing

osmium tetroxide Osmium tetroxide (also osmium(VIII) oxide) is the chemical compound with the formula OsO4. The compound is noteworthy for its many uses, despite its toxicity and the rarity of osmium. It also has a number of unusual properties, one being that the ...

with ethanol: :2 OsO₄ + C₂H₅OH + 5 KOH → CH₃CO₂K + 2 K₂ sO₂(OH)₄Alkaline oxidative fusion of osmium metal also affords this salt.

Reactions

Potassium osmate reacts with acids to produce osmyl salts, such as potassium osmyl chloride and the osmyl bromide. It reacts with

oxalic acid Oxalic acid is an organic acid with the systematic name ethanedioic acid and chemical formula , also written as or or . It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name i ...

to produce potassium osmyl oxalate. :: + 4HCl → + 4 :: + 2 → + 4 It also reacts with

potassium nitrite Potassium nitrite (distinct from potassium nitrate) is the inorganic compound with the chemical formula . It is an ionic salt of potassium ions K+ and nitrite ions NO2−, which forms a white or slightly yellow, hygroscopic crystalline powder that ...

to yield potassium osmyl nitrite.

Applications

Potassium osmate is used for the oxidative hydroxylation of organic compounds, notably the Sharpless dihydroxylation of olefins, as well as a catalyst for other asymmetric syntheses, such as carboranylated diols. It is also used for the synthesis of active pharmaceutical ingredients. Other uses include the stereoselective synthesis of β-N-glycopyranosides, and the preparation of osmium complexes for the voltammetric analysis of polysaccharides.

Related compounds

Other osmates are known, such as the highly water soluble sodium osmate, and insoluble osmates such as those of barium, strontium, calcium, and lead.

Images

Osmate solution2.png, Osmate dissolved in water Osmate alcohol.png, Osmate complexed with alcohol

References

{{Osmium compounds Osmium compounds Oxides Potassium compounds Transition metal oxyanions