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.
Structure
The complex anion is octahedral. Like related d2 dioxo complexes, the oxo ligands are trans.4 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 1844.5 Potassium osmate is prepared by reducing osmium tetroxide with ethanol:6
2 OsO4 + C2H5OH + 5 KOH → CH3CO2K + 2 K2[OsO2(OH)4]Alkaline oxidative fusion of osmium metal also affords this salt.7
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.89
K2[OsO2(OH)4] + 4HCl → K2(OsO2)Cl4 + 4H2O K2[OsO2(OH)4] + 2H2C2O4 → K2(OsO2)(C2O4)2 + 4H2OIt also reacts with potassium nitrite to yield potassium osmyl nitrite.10
Images
See also
References
F. Albert Cotton; Geoffrey Wilkinson (1966). Advanced Inorganic Chemistry: A Comprehensive Treatise. New York, Interscience Publishers. p. 1007. /wiki/F._Albert_Cotton ↩
F. Albert Cotton; Geoffrey Wilkinson (1966). Advanced Inorganic Chemistry: A Comprehensive Treatise. New York, Interscience Publishers. p. 1007. /wiki/F._Albert_Cotton ↩
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 ↩
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 ↩
Frémy, E. "Ueber das Osmium" Journal für Praktische Chemie 1844 vol.33, 406-416. doi:10.1002/prac.18440330160 /wiki/Edmond_Fr%C3%A9my ↩
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 ↩
F. Albert Cotton; Geoffrey Wilkinson (1966). Advanced Inorganic Chemistry: A Comprehensive Treatise. New York, Interscience Publishers. p. 1007. /wiki/F._Albert_Cotton ↩
Prakash Satya (2013). "Platinum Metals-IV:Osmium". Advanced Chemistry of Rare Elements, 5th Ed. India: S Chand and Company Limited. p. 617. ↩
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 ↩
Prakash Satya (2013). "Platinum Metals-IV:Osmium". Advanced Chemistry of Rare Elements, 5th Ed. India: S Chand and Company Limited. p. 617. ↩