Chloroosmic acid

Chloroosmic acid

Solution of chloroosmic acid
Names
IUPAC name Dihydrogen hexachloroosmate(2-)
Other names Hexachloroosmic acid
Identifiers
CAS Number	27057-71-2  Y
3D model (JSmol)	Interactive image
ChemSpider	21241340
ECHA InfoCard	100.043.797
EC Number	248-192-7
PubChem CID	56843362
InChI InChI=1S/6ClH.Os/h6*1H;/q;;;;;;+4/p-4 Key: UTIXXJBEMJZGFB-UHFFFAOYSA-J
SMILES [H+].[H+].Cl[Os-2](Cl)(Cl)(Cl)(Cl)Cl
Properties
Chemical formula	Cl6H2Os
Molar mass	404.95 g·mol−1
Appearance	Reddish-purple or black crystalline solid. [1] [2] Yields greenish yellow to reddish brown solutions [2] [3]
Density	5.3-5.65 g/cm3 (hexahydrate) [4]
Melting point	decomposes [1]
Solubility in water	very soluble
Solubility	Insoluble in organic solvents [2]
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H301, H311, H314, H331
Precautionary statements	P260, P261, P262, P264, P264+P265, P270, P271, P280, P301+P316, P301+P330+P331, P302+P352, P302+P361+P354, P304+P340, P305+P354+P338, P316, P317, P321, P330, P361+P364, P363, P403+P233, P405, P501
Related compounds
Other anions	Hexachloroplatinic acid
Other cations	Sodium hexachloroosmate, Potassium hexachloroosmate, Ammonium hexachloroosmate(IV)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Chloroosmic acid (also known as hexachloroosmic acid, and dihydrogen hexachloroosmate) is an inorganic chemical compound with the chemical formula H₂OsCl₆. It exists as a dark hygroscopic solid. It forms a hexahydrate. ^[5]

Synthesis

Hexachloroosmic acid can be prepared by reducing osmium tetroxide in hydrochloric acid with alcohol and heating. ^{[3] [6]} Ferrous chloride is sometimes used in place of alcohol. ^[7]

OsO₄ + 4FeCl₂ + 10HCl → H₂OsCl₆ + 4FeCl₃ + 4H₂O

Another way of preparing it is by dissolving osmium dioxide in hydrochloric acid. ^[8]

It can also be prepared by reducing potassium osmate with hydrochloric acid under heating. ^[2]

Properties

Solid crystals of hexachloroosmic acid have been described as reddish-purple in color, ^[2] while commercial vendors describe it as black. ^{[1] [5]} In solution, it exhibits colors ranging from yellowish green to reddish brown. ^{[6] [3] [2]} Owing to its highly hygroscopic nature, solutions of hexachloroosmic acid can be evaporated down to a syrup without crystallization. ^[3] As an acid, it is corrosive.

Reactions

When strong alkali is added to hexachloroosmic acid, it decomposes and precipitates osmium dioxide. ^{[8] [6]}

It also reacts with alkali chlorides to yield hexachloroosmate salts, such as ammonium hexachloroosmate(IV). ^[3]

References

1. "Dihydrogen Hexachloroosmate(IV) Hydrate". American Elements . Retrieved 19 June 2025.
2. 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.
3. Gilchrist, Raleigh (June 8, 1932). "A new determination of the atomic weight of Osmium" (PDF). Bureau of Standards Journal of Research. 9 (3): 279–290. doi:10.6028/jres.009.021 . Retrieved 19 June 2025.
4. "Dihydrogen hexachloroosmate (IV) hexahydrate". Cymit Quimica. Retrieved 19 June 2025.
5. "Dihydrogen hexachloroosmate (IV) hexahydrate". Strem Catalog. Retrieved 19 June 2025.
6. Gilchrist, Raleigh (1931). "A method for the separation and gravimetric determination of osmium" (PDF). J Res Bur Stand. 6 (3): 421–448. doi:10.6028/jres.006.028 . Retrieved 19 June 2025.
7. Buckingham, D.A. (1961). Preparation and Oxidation-Reduction Potentials of Some Osmium Compounds (PhD thesis). Australian National University. p. 4.
8. Stopinski, Orin (September 1977). "Platinum-Group Metals" (PDF). Environmental Health Effects Research Series. Washington, DC: Environmental Protection Agency: 85–86. Retrieved 19 June 2025.