Potassium hexachloroosmate

Potassium hexachloroosmate

K2OsCl6 in an evaporating dish
Identifiers
CAS Number	16871-60-6  Y
3D model (JSmol)	Interactive image
ChemSpider	19990460
ECHA InfoCard	100.037.160
EC Number	240-893-6
PubChem CID	167580
UNII	3X55YB10CW
CompTox Dashboard (EPA)	DTXSID10276572
InChI InChI=1S/6ClH.2K.Os/h6*1H;;;/q;;;;;;2*+1;+4/p-6 Key: VGKQJCSDERXWRV-UHFFFAOYSA-H
SMILES [Cl-].[Cl-].[Cl-].[Cl-].[Cl-].[Cl-].[K+].[K+].[Os+4]
Properties
Chemical formula	K2OsCl6
Molar mass	481.13 g/mol
Appearance	Dark red to black solid
Density	2.03 g/cm3
Solubility in water	slightly soluble
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H301, H302, H311, H314, H331, H335
Precautionary statements	P260, P261, P262, P264, P264+P265, P270, P271, P280, P301+P316, P301+P317, P301+P330+P331, P302+P352, P302+P361+P354, P304+P340, P305+P354+P338, P316, P317, P319, P321, P330, P332+P317, P337+P317, P361+P364, P363, P403+P233, P405, P501
Related compounds
Other anions	Potassium hexachloroplatinate, Potassium hexachloropalladate(IV)
Other cations	Sodium hexachloroosmate, Ammonium hexachloroosmate(IV), Hexachloroosmic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Potassium hexachloroosmate is an inorganic chemical compound with the chemical formula K₂OsCl₆. It is a darkly colored solid with limited solubility in water.

Synthesis

There are several methods for producing potassium hexachloroosmate. The first involves reducing osmium tetroxide to chloroosmic acid with hydrochloric acid and alcohol, followed by addition of potassium chloride. ^[1]

It can also be obtained by heating finely divided osmium metal with potassium chloride and chlorine.

Addition of potassium chloride to a solution of sodium hexachloroosmate will precipitate this salt, and the last method involves treating potassium osmyl oxynitrite with hydrochloric acid. ^[2]

Properties

Crystals of K₂OsCl₆ viewed under a microscope

Potassium hexachloroosmate forms dark red octahedral crystals of the space group Fm3m, which produce a dark yellow color when dissolved in water. The crystal structure is isomorphic to the corresponding cations of palladium, platinum, and iridium. It is slightly soluble in water, and is insoluble in saline solutions as well as alcohol. ^{[3] [1]}

Potassium hexachloroosmate is most stable in acidic solutions, although with nitric acid it reacts to form osmium tetroxide. It slowly hydrolyses in water yielding osmium dioxide, and in strong alkali it also decomposes to the dioxide. ^{[4] [5]}

Reactions

Potassium hexachloroosmate reacts with a variety of reagents to produce different compounds. It reacts with pyridine and hydrazine to form Os(py)₂Cl₄ and Os(NH₃)₅N₂ respectively. When it reacts with a mixture of nitrogen dioxide, nitric oxide, and hydrochloric acid, Os(NO)Cl₅ is formed. Sodium phosphate and borax both react with it to yield the dioxide. ^{[6] [5]}

The reaction of K₂OsCl₆ with BrF₃ results in a stepwise substitution. ^[6]

OsCl²⁻
₆ → OsCl₅F²⁻
→ cis-OsCl₄F²⁻
₂ → fac-OsCl₃F²⁻
₃ → cis-OsCl₂F²⁻
₄ → OsClF²⁻
₅ → OsF²⁻
₆

The reaction time determines which isomers are obtained and in which ratio they're present. Advantageously, the stronger trans effect of the chloride ion can yield the following reaction: ^[6]

cis-OsCl₂F²⁻
₄ → mer-OsCl₃F²⁻
₃

References

1. Turner, A.G.; Clifford, A.F.; Ramchandra Rao, C.N. (October 1, 1958). "Potassium Hexachloroosmate, K2OsCl6, and Potassium Hexabromoosmate, K2OsBr6". Analytical Chemistry. 30 (10): 1708–1709. doi:10.1021/ac60142a602 . Retrieved 6 October 2025.
2. 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. p. 216. Retrieved 6 October 2025.
3. Fremy, Edmund. (1900). "Osmium". Encyclopédie chimique.Tome III.- Métaux. 17e cahier : platine et métaux qui l'accompagnent. Paris : Dunod. pp. 36–40. Retrieved 6 October 2025.
4. Jones, Terence (June 2002). "Electrodeposition of Osmium". Metal Finishing. 100 (6): 85. doi:10.1016/S0026-0576(02)80443-3 . Retrieved 7 October 2025.
5. J.W. Mellor (May 1936). "Osmium". A comprehensive treatise on inorganic and theoretical chemistry, Volume 15. London: Longmans, Green and Co. p. 718. Retrieved 7 October 2025.
6. Cotton, S. A. (1997). "Ruthenium and Osmium". Chemistry of Precious Metals (PDF). Rutland, UK: Blackie Academic & Professional. pp. 11–12. Retrieved 7 October 2025.