Chloroosmic acid

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]

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

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]