Antimony pentafluoride

Antimony pentafluoride
IUPAC name	antimony(V) fluoride
Other names	antimony pentafluoride pentafluoridoantimony
Identifiers
CAS number	7783-70-2 Y
UN number	1732
RTECS number	CC5800000
SMILES	[F-].[F-].[F-].[F-].[F-].[SbH3+3]
InChI	1/5FH.Sb.3H/h5*1H;;;;/q;;;;;+3;;;/p-5/r5FH.H3Sb/h5*1H;1H3/q;;;;;+3/p-5
InChI key	CCIMPPQYTRNALI-RNQIAQHSAI
ChemSpider ID	21172742
Properties
Molecular formula	SbF5
Molar mass	216.74 g/mol
Appearance	colorless oily liquid hygroscopic
Density	2.99 g/cm3 [1]
Melting point	8.3 °C, 281 K, 47 °F
Boiling point	149.5 °C, 423 K, 301 °F
Solubility in water	Reacts with water
Solubility	soluble in KF
Hazards
MSDS	ICSC 0220
EU Index	051-003-00-9
EU classification	Harmful (Xn) Dangerous for the environment (N)
R-phrases	R20/22, R51/53
S-phrases	(S2), S61
NFPA 704	0 3 1 W
Related compounds
Other anions	Antimony pentachloride
Other cations	Phosphorus pentafluoride Arsenic pentafluoride Bismuth pentafluoride
Related compounds	Antimony trifluoride
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Antimony pentafluoride is the chemical compound with the formula SbF₅. This colourless, viscous liquid is a valuable Lewis acid and a component of the superacid fluoroantimonic acid, the strongest known acid. Some features that give the compound scientific interest are its Lewis acidity and that it also reacts with almost all known compounds.^[2]

Preparation

Antimony pentafluoride is prepared by the reaction of antimony pentachloride with anhydrous hydrogen fluoride:

SbCl₅ + 5 HF → SbF₅ + 5 HCl

It may also be prepared from antimony trifluoride and fluorine, or by treating antimony pentoxide with aqueous hydrofluoric acid and evaporing water.

Structure and chemical reactions

In the gas phase, SbF₅ adopts a trigonal bipyramidal structure of D_3h point group symmetry (see picture). The structure is more complex in the liquid and solid state. The liquid contains polymers wherein each Sb is octahedral, the structure being described with the formula [SbF₄(μ-F)₂]_n. The crystalline material is tetrameric, i.e. it has the formula [SbF₄(μ-F)]₄. The Sb-F bonds are 2.02 Å within the eight-membered Sb₄F₄ ring; the remaining fluoride ligands radiating from the four Sb centers are shorter at 1.82 Å.^[3] The related species PF₅ and AsF₅ are monomeric in the solid and liquid states, probably due to the smaller sizes of the central atom, which limits their coordination number. BiF₅ is a polymer.^[4]

SbF₅ is a strong Lewis acid, exceptionally so toward sources of F⁻ to give the very stable anion [SbF₆]⁻. The latter reacts with additional SbF₅ to give [Sb₂F₁₁]⁻.

In the same way that SbF₅ enhances the Brønsted acidity of HF, it enhances the oxidizing power of F₂. This effect is illustrated by the oxidation of oxygen:^[5]

2 SbF₅ + F₂ + 2 O₂ → 2 [O₂]⁺[SbF₆]⁻

Antimony pentafluoride has also been used in the first discovered chemical reaction that produces fluorine gas from fluoride compounds:

4 SbF₅ + 2 K₂MnF₆ → 4 KSbF₆ + 2 MnF₃ + F₂

The driving force for this reaction is the high affinity of SbF₅ for F⁻, which is the same property which recommends the use of SbF₅ to generate superacids.

Safety

SbF₅ reacts violently with many compounds, often releasing dangerous hydrogen fluoride. It is also corrosive to the skin.

References

External links

• WebBook page for SbF5
• National Pollutant Inventory - Antimony and compounds fact sheet
• National Pollutant Inventory - Fluoride compounds fact sheet