Potassium osmate explained

Potassium osmate is the inorganic compound with the formula K₂[OsO₂(OH)₄]. This diamagnetic purple salt contains osmium in the VI (6+) oxidation state.^[1] When dissolved in water a pink solution is formed but when dissolved in methanol, the salt gives a blue solution.^[1] The salt gained attention as a catalyst for the asymmetric dihydroxylation of olefins.^[2]

Structure

The complex anion is octahedral. Like related d² dioxo complexes, the oxo ligands are trans.^[3] 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.^[4] Potassium osmate is prepared by reducing osmium tetroxide with ethanol:^[5]

2 OsO₄ + C₂H₅OH + 5 KOH → CH₃CO₂K + 2 K₂[OsO₂(OH)₄]Alkaline oxidative fusion of osmium metal also affords this salt.^[1]

See also

• Sodium hexachloroosmate

Notes and References

1. Book: Advanced Inorganic Chemistry: A Comprehensive Treatise. registration. F. Albert Cotton. F. Albert Cotton. Geoffrey Wilkinson. Geoffrey Wilkinson. 1966. 1007. New York, Interscience Publishers .
2. Li, Guigen . Chang, Han-Ting . . Catalytic Asymmetric Aminohydroxylation (AA) of Olefins. Angew. Chem. Int. Ed. Engl.. 1996. 35. 4 . 451–4. 10.1002/anie.199604511.
3. R. K. Murmann, C. L. Barnes "Redetermination of the crystal structure of potassium trans-(dioxo)-tetra(hydroxo)osmate(VI), K₂[Os(OH)₄(O)₂]" Z. Kristallogr. NCS 217, 2002, pp. 303–304.
4. [Edmond Frémy|Frémy, E.]
5. Book: Potassium Tetrahydroxodioxoosmate(VI) and trans-Bis(Ethylenediamine)Dioxoosmium(VI) Chloride. Inorganic Syntheses. 20. 1980. John M. Malin. Potassium Tetrahydroxodioxoosmate(VI) and trans ‐Bis(Ethylenediamine)Dioxoosmium(VI) Chloride . 61–63. 10.1002/9780470132517.ch18. 9780470132517.