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Potassium osmate
Chemical compound

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. 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.

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Structure

The complex anion is octahedral. Like related d2 dioxo complexes, the oxo ligands are trans.5 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 1844.6 Potassium osmate is prepared by reducing osmium tetroxide with ethanol:7

2 OsO4 + C2H5OH + 5 KOH → CH3CO2K + 2 K2[OsO2(OH)4]

Alkaline oxidative fusion of osmium metal also affords this salt.8

Reactions

Potassium osmate reacts with acids to produce osmyl salts, such as potassium osmyl chloride and the osmyl bromide. It reacts with oxalic acid to produce potassium osmyl oxalate.910

K2[OsO2(OH)4] + 4HCl → K2(OsO2)Cl4 + 4H2O K2[OsO2(OH)4] + 2H2C2O4 → K2(OsO2)(C2O4)2 + 4H2O

It also reacts with potassium nitrite to yield potassium osmyl nitrite,11 and it reacts with ammonium salts to produce osmyl tetra-ammine compounds such as [OsO2(NH3)4]Cl2.12

Potassium osmate can be reduced to osmium dioxide with alcohol.13

K2[OsO2(OH)4] + C2H5OH → OsO2•2H2O + 2KOH + CH3CHO

Potassium osmate can be used to be prepare many other compounds. If potassium osmate is refluxed with HCl, it can be reduced to hexachloroosmic acid.14 It reacts with hydrogen sulfide to produce osmium disulfide, OsS2, and with sulfurous acid to form potassium osmium sulfite.1516

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.1718

Other uses include the stereoselective synthesis of β-N-glycopyranosides, and the preparation of osmium complexes for the voltammetric analysis of polysaccharides.19

Other osmates are known, such as the highly water soluble sodium osmate, and insoluble osmates such as those of barium, strontium, calcium, and lead.2021

When osmium tetroxide is treated with an alkali hydroxide, or even when potassium osmate is oxidized in alkaline medium, the perosmate anion is formed, [OsO4(OH)2]²⁻. When treated with alcohol or heating, perosmates are reduced to osmates, [OsO2(OH)4]²⁻2223

When osmium tetroxide is dissolved in anhydrous methanol containing potassium hydroxide, dipotassium tetramethyl osmate (DTMO) is obtained. DTMO was used as staining agent for electron microscopy.24

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See also

References

  1. F. Albert Cotton; Geoffrey Wilkinson (1966). Advanced Inorganic Chemistry: A Comprehensive Treatise. New York, Interscience Publishers. p. 1007. /wiki/F._Albert_Cotton ↩

  2. F. Albert Cotton; Geoffrey Wilkinson (1966). Advanced Inorganic Chemistry: A Comprehensive Treatise. New York, Interscience Publishers. p. 1007. /wiki/F._Albert_Cotton ↩

  3. Prakash Satya (2013). "Platinum Metals-IV:Osmium". Advanced Chemistry of Rare Elements, 5th Ed. India: S Chand and Company Limited. pp. 611–622. ↩

  4. Li, Guigen; Chang, Han-Ting; Sharpless, K. Barry (1996). "Catalytic Asymmetric Aminohydroxylation (AA) of Olefins". Angew. Chem. Int. Ed. Engl. 35 (4): 451–4. doi:10.1002/anie.199604511. /wiki/K._Barry_Sharpless ↩

  5. 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. doi:10.1524/ncrs.2002.217.jg.303 /wiki/Z._Kristallogr._NCS ↩

  6. Frémy, E. "Ueber das Osmium" Journal für Praktische Chemie 1844 vol.33, 406-416. doi:10.1002/prac.18440330160 /wiki/Edmond_Fr%C3%A9my ↩

  7. John M. Malin (1980). "Potassium Tetrahydroxodioxoosmate(VI) and trans ‐Bis(Ethylenediamine)Dioxoosmium(VI) Chloride". Potassium Tetrahydroxodioxoosmate(VI) and trans-Bis(Ethylenediamine)Dioxoosmium(VI) Chloride. Inorganic Syntheses. Vol. 20. pp. 61–63. doi:10.1002/9780470132517.ch18. ISBN 9780470132517. 9780470132517 ↩

  8. F. Albert Cotton; Geoffrey Wilkinson (1966). Advanced Inorganic Chemistry: A Comprehensive Treatise. New York, Interscience Publishers. p. 1007. /wiki/F._Albert_Cotton ↩

  9. Prakash Satya (2013). "Platinum Metals-IV:Osmium". Advanced Chemistry of Rare Elements, 5th Ed. India: S Chand and Company Limited. pp. 611–622. ↩

  10. J. Newton Friend (1920). "Osmium and its compounds". A textbook of inorganic chemistry, vol.IX Part I Cobalt, Nickel, and The Elements of The Platinum Group (PDF). London: Charles Griffin and Company, Limited. pp. 223–225. Retrieved 3 July 2025. https://dn790003.ca.archive.org/0/items/textbookinorgani00libg_516/textbookinorgani00libg_516.pdf ↩

  11. Prakash Satya (2013). "Platinum Metals-IV:Osmium". Advanced Chemistry of Rare Elements, 5th Ed. India: S Chand and Company Limited. pp. 611–622. ↩

  12. Prakash Satya (2013). "Platinum Metals-IV:Osmium". Advanced Chemistry of Rare Elements, 5th Ed. India: S Chand and Company Limited. pp. 611–622. ↩

  13. Prakash Satya (2013). "Platinum Metals-IV:Osmium". Advanced Chemistry of Rare Elements, 5th Ed. India: S Chand and Company Limited. pp. 611–622. ↩

  14. Chiririwa, Haleden; Muzenda, Edison (November 2014). "The Preparation and Characterisation of Osmium (IV), Osmium (II), and Osmium (0) Complexes from Refinery Materials" (PDF). International Conference on Chemical Engineering & Advanced Computational Technologies (ICCEACT): 32–33. Retrieved 19 June 2025. https://iieng.org/images/proceedings_pdf/9367E1114015.pdf ↩

  15. Prakash Satya (2013). "Platinum Metals-IV:Osmium". Advanced Chemistry of Rare Elements, 5th Ed. India: S Chand and Company Limited. pp. 611–622. ↩

  16. J.W. Mellor (May 1936). "Osmium". A comprehensive treatise on inorganic and theoretical chemistry, Volume 15. London: Longmans, Green and Co. p. 706. Retrieved 22 June 2025. https://archive.org/details/Mellor13/Mellor_15/page/n706/mode/2up?q=%5BOsO%28NH3%292%5D%28OH%292 ↩

  17. "Potassium osmate". Heraeus Precious Metals. Retrieved 5 July 2025. https://www.heraeus-precious-metals.com/en/products-solutions-by-metal/osmium/potassium-osmate/ ↩

  18. "Potassium osmate(VI) dihydrate". Sigma Aldrich. Retrieved 5 July 2025. https://www.sigmaaldrich.com/US/en/product/aldrich/209104?srsltid=AfmBOoo70UVoCh0tPlvnhz4p8gcUuZPP8kvUXMLr0iA2qbS00c0MrLtw ↩

  19. "Potassium osmate(VI) dihydrate". Sigma Aldrich. Retrieved 5 July 2025. https://www.sigmaaldrich.com/US/en/product/aldrich/209104?srsltid=AfmBOoo70UVoCh0tPlvnhz4p8gcUuZPP8kvUXMLr0iA2qbS00c0MrLtw ↩

  20. Prakash Satya (2013). "Platinum Metals-IV:Osmium". Advanced Chemistry of Rare Elements, 5th Ed. India: S Chand and Company Limited. pp. 611–622. ↩

  21. J.W. Mellor (May 1936). "Osmium". A comprehensive treatise on inorganic and theoretical chemistry, Volume 15. London: Longmans, Green and Co. p. 706. Retrieved 22 June 2025. https://archive.org/details/Mellor13/Mellor_15/page/n706/mode/2up?q=%5BOsO%28NH3%292%5D%28OH%292 ↩

  22. Prakash Satya (2013). "Platinum Metals-IV:Osmium". Advanced Chemistry of Rare Elements, 5th Ed. India: S Chand and Company Limited. pp. 611–622. ↩

  23. McFadzean, Belinda (December 2007). The Kinetics and Associated Equilibra of High Oxidation State Osmium Complexes (PDF) (PhD thesis). Port Elizabeth, South Africa: Nelson Mandela Metropolitan University. Retrieved 3 July 2025. https://core.ac.uk/download/pdf/145052548.pdf ↩

  24. Hinckley, C.; Murphy, Judith (13 August 1974). "Dipotassium Tetramethyl Osmate: A Stain for Electron Microscopy". Journal of Histochemistry and Cytochemistry. 23 (2): 123–127. Retrieved 6 July 2025. https://journals.sagepub.com/doi/pdf/10.1177/23.2.1167876 ↩