Wikipedia

Potassium osmate

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.[4] It gained attention as a catalyst for the asymmetric dihydroxylation of olefins.[5]

Potassium osmate
Names
Other names
Potassium osmate(VI) dihydrate
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.157.189 Edit this at Wikidata
EC Number
  • 243-247-1
UNII
  • InChI=1S/2K.4H2O.2O.Os/h;;4*1H2;;;/q2*+1;;;;;2*-1;+4/p-4
    Key: DDTIHYGDUUGVNU-UHFFFAOYSA-J
  • [K+].[K+].[O-][Os](O)(O)(O)(O)[O-]
Properties
K2[OsO2(OH)4]
Molar mass 368.42 g/mol
Appearance Garnet red[1]
Soluble[2]
Solubility Insoluble in alcohol or ether
Hazards
GHS labelling:
GHS06: Toxic
Danger
H301, H311, H330, H331
P260, P264, P270, P271, P280, P284, P301+P310, P302+P352, P304+P340, P310, P311, P312, P320, P321, P330, P361, P363, P403+P233, P405, P501
NFPA 704 (fire diamond)
[3]
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilInstability 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazard OX: Oxidizer. E.g. potassium perchlorate
3
1
1
OX
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Properties

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Solid potassium osmate is stable in air. It is more stable in cold water under alkaline conditions, but hot water or acid accelerates decomposition. When exposed to sunlight for prolonged periods of time, it decomposes and produces a sooty powder along with the odor of the tetroxide. It is insoluble in alcohol and ether.[1][6][7]

Structure

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The complex anion is octahedral. Like related d2 dioxo complexes, the oxo ligands are trans.[8] 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

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The compound was first reported by Edmond Frémy in 1844.[9] Potassium osmate is prepared by reducing osmium tetroxide with ethanol:[10]

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

Reactions

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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.[7][1]

K2[OsO2(OH)4] + 4 HCl → K2[OsO2Cl4] + 4 H2O
K2[OsO2(OH)4] + 2 H2C2O4 → K2[OsO2(C2O4)2 + 4 H2O

Potassium osmate reacts with potassium nitrite to yield potassium osmyl nitrite, and it reacts with ammonium salts to produce osmyl tetra-ammine compounds such as [OsO2(NH3)4]SO4 and [OsO2(NH3)4]Cl2.[7][11]

Potassium osmate can be reduced to osmium dioxide with alcohol.[1][7]

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

It reacts with hydrogen sulfide to produce osmium disulfide, OsS2, and with sulfurous acid to form potassium osmium sulfite.[7][6]

Applications

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Potassium osmate is used as a catalyst for the Sharpless dihydroxylation of olefins. In this application, it shuttles to Os(VIII) derivative, which adds to the olefin. Osmium tetroxide functions equivalently.

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Other osmates are known, such as the highly water soluble sodium osmate, and insoluble osmates such as those of barium, strontium, calcium, and lead.[7][6]

When osmium tetroxide is treated with an alkali hydroxide, or even when potassium osmate is oxidized in alkaline medium, red perosmates are formed, [OsO4(OH)2]2-. When treated with alcohol, perosmates are reduced to osmates, [OsO2(OH)4]2-, yielding purple colored solutions. Perosmate salts share the same valency as osmium tetroxide, as opposed to perruthenates. The perosmates of sodium, potassium, rubidium, cesium, and barium are known.[12][13]

OsO4 + 2KOH → K2[OsO4(OH)2][14]

When osmium tetroxide is dissolved in anhydrous methanol containing potassium hydroxide, a blue solution of dipotassium tetramethyl osmate (DTMO) is obtained. DTMO was used as a staining agent for electron microscopy.[15]

OsO4 + 5CH3OH + 2KOH → K2[OsO2(OCH3)4] + H2CO + 4H2O

See also

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References

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  1. 1 2 3 4 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. 219–225, 231. Retrieved 3 July 2025.
  2. ↑ Comey, Arthur Messinger (1896). A Dictionary of Chemical Solubilities: Inorganic. Macmillan and Company. p. 275. Retrieved 6 July 2025.
  3. ↑ "Potassium osmate(VI) dihydrate". Chemical Book. Retrieved 6 July 2025.
  4. ↑ F. Albert Cotton; Geoffrey Wilkinson (1966). Advanced Inorganic Chemistry: A Comprehensive Treatise. New York, Interscience Publishers. p. 1007.
  5. ↑ 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.
  6. 1 2 3 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.
  7. 1 2 3 4 5 6 Prakash Satya (2013). "Platinum Metals-IV:Osmium". Advanced Chemistry of Rare Elements, 5th Ed. India: S Chand and Company Limited. pp. 611–622. Retrieved 24 July 2025.
  8. ↑ 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
  9. ↑ Frémy, E. "Ueber das Osmium" Journal für Praktische Chemie 1844 vol.33, 406-416. doi:10.1002/prac.18440330160
  10. ↑ 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.
  11. ↑ Burvikova, J. N.; Lin'Ko, I. V.; Venskovskiy, N. U.; Rybakov, V. B. (2007). "Crystal structure and properties of [OsO2(NH3)4]SO4 · H2O". Crystallography Reports. 52 (2): 221–225. doi:10.1134/S1063774507020095.
  12. ↑ Griffth, W.P. (1964). "Infrared Spectra and Structures of Osmium Oxy-complexes". Journal of the Chemical Society. 40: 245–246. Retrieved 21 November 2025.
  13. ↑ Griffith, William Pettit (1967). The Chemistry of the Rarer Platinum Group Metals. New York, London: Interscience Publishers. pp. 69–73. Retrieved 23 May 2026.
  14. ↑ Cotton, S. A. (1997). "Ruthenium and Osmium". Chemistry of Precious Metals (PDF). Rutland, UK: Blackie Academic & Professional. p. 20. Retrieved 11 July 2025.
  15. ↑ 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.
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