Ammonium hexachloroosmate(IV)

Ammonium hexachloroosmate(IV) is an inorganic chemical compound with the chemical formula (NH₄)₂OsCl₆.^[3][4]

Ammonium hexachloroosmate(IV)

Microcrystals of ammonium hexachloroosmate
Names
IUPAC name Ammonium hexachloroosmate(IV)
Identifiers
CAS Number	12125-08-5
3D model (JSmol)	Interactive image
ChemSpider	145801
ECHA InfoCard	100.031.977
EC Number	235-188-5
PubChem CID	11729867
CompTox Dashboard (EPA)	DTXSID70923737
InChI InChI=1S/6ClH.2H3N.Os/h6*1H;2*1H3;/q;;;;;;;;+4/p-4 Key: SRBXXQDKBKTWOC-UHFFFAOYSA-J
SMILES [NH4+].[NH4+].Cl[Os-2](Cl)(Cl)(Cl)(Cl)Cl
Properties
Chemical formula	Cl6H8N2Os
Molar mass	439.01 g·mol−1
Appearance	red crystals
Density	2.93 g/cm3
Melting point	170
Solubility in water	poorly soluble
Hazards
GHS labelling:
Pictograms	[1]
Signal word	Warning
NFPA 704 (fire diamond)	[2] 1 0 0
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Synthesis

Ammonium hexachloroosmate(IV) can be produced by the reduction of osmium tetroxide or potassium osmate with iron dichloride in hydrochloric acid in the presence of ammonium ions:^[5][6][7]

OsO₄ + 4FeCl₂ + 8HCl + 2NH₄Cl → (NH₄)₂[OsCl₆] + 3FeCl₃ + 4H₂O

K₂[OsO₂(OH)₄] + FeCl₂ + 2NH₄Cl ^{conc hcl}
_———→ (NH₄)₂OsCl₆ + FeCl₃ + 4H₂O + 2KCl

It can also be prepared by addition of an ammonium chloride solution to hexachloroosmic acid,^[8] or by addition of ammonium chloride to a solution of sodium hexachloroosmate.^[9]

Physical properties

Ammonium hexachloroosmate(IV) forms dark red crystals of the cubic system,^[10] space group Fm3m, cell parameters a = 0.9729 nm, Z = 4.

It is poorly soluble in cold water.^[11]

Chemical properties

The compound is reduced by hydrogen to metallic osmium:^[12][13]

3(NH₄)₂[OsCl₆] → 3Os + 2N₂ + 16HCl + 2NH₄Cl

(NH₄)₂[OsCl₆] + 2H₂ → Os + NH₄Cl + 4HCl

Similar to sodium hexachloroosmate, ammonium hexachloroosmate decomposes to osmium dioxide when exposed to strong alkali, and reacts with ammonia to produce osmium diammine hydroxide, OsO(NH₃)₂(OH)₂.^[9]

Ammonium hexachloroosmate is stable in hydrochloric acid, but it is oxidized by nitric acid, forming osmium tetroxide.^[14]

Reactions

Ammonium hexachloroosmate reacts with triphenylphosphine to form various complexes in which osmium is divalent.

(NH₄)₂OsCl₆ + 4PPh₃ ^{2-(2-methoxyethoxy)ethanol}
_{———————————→} OsHCl(CO)(PPh₃)₃ + 2NH₄Cl + 2PPh₃Cl₂

(NH₄)₂OsCl₆ + 6PPh₃ ^{2-methoxyethanol}
_{———————→} OsH₂(CO)(PPh₃)₃ + 2NH₄Cl + 3PPh₃Cl₂

It also reacts with triphenylphosphine in a solution of t-butyl alcohol and water to produce OsCl₂(PPh₃)₃.^[7]

When ammonium hexachloroosmate is refluxed with diethylphenylphosphine, OsCl₃(PEt₂Ph)₃ is formed.^[15]

Uses

The compound is used as a pharmaceutical, organic, and chemical intermediate.^[16]