Antimony Pentafluoride

Antimony pentafluoride is the inorganic compound with the formula Sb F₅. This colourless, viscous liquid is a valuable Lewis acid and a component of the superacid fluoroantimonic acid, formed when mixing liquid HF with liquid SbF₅ in a 2:1 ratio. It is notable for its Lewis acidity and its ability to react with almost all known compounds.

Preparation

Antimony pentafluoride is prepared by the reaction of antimony pentachloride with anhydrous hydrogen fluoride:Sabina C. Grund, Kunibert Hanusch, Hans J. Breunig, Hans Uwe Wolf "Antimony and Antimony Compounds" in Ullmann's Encyclopedia of Industrial Chemistry 2006, Wiley-VCH, Weinheim.
:SbCl₅ + 5 HF → SbF₅ + 5 HCl
It can also be prepared from antimony trifluoride and fluorine.

Structure and chemical reactions

In the gas phase, SbF₅ adopts a trigonal bipyramidal structure of D_3h point group symmetry (see picture). The material adopts a more complicated structure in the liquid and solid states. The liquid contains polymers wherein each Sb is octahedral, the structure being described with the formula bF₄(μ-F)₂sub>''n'' ((μ-F) denotes the fact that fluoride centres bridge two Sb centres). The crystalline material is a tetramer, meaning that it has the formula bF₄(μ-F)sub>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. 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.

In the same way that SbF₅ enhances the Brønsted acidity of HF, it augments the oxidizing power of F₂. This effect is illustrated by the oxidation of oxygen:Shamir, J.; Binenboym, J. "Dioxygenyl Salts" ''Inorganic Syntheses'' 1973, XIV, 109-122.
:2 SbF₅ + F₂ + 2 O₂ → 2 ₂sup>+ bF₆sup>−
Antimony pentafluoride has also been used in the first discovered chemical reaction that produces fluorine gas from fluoride compounds:
:4 + 2 → 4 + 2 +

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

Hexafluoroantimonate

SbF₅ is a strong Lewis acid, exceptionally so toward sources of F⁻ to give the very stable anion bF₆sup>−, called hexafluoroantimonate. bF₆sup>− is a weakly coordinating anion akin to PF₆⁻.
Although it is only weakly basic, bF₆sup>− does react with additional SbF₅ to give a centrosymmetric adduct:
:SbF₅ + bF₆sup>− → b₂F₁₁sup>−

Safety

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

References

External links

WebBook page for SbF5National Pollutant Inventory - Antimony and compounds fact sheetNational Pollutant Inventory - Fluoride compounds fact sheet

{{DEFAULTSORT:Antimony Pentafluoride
Superacids
Antimony(V) compounds
Fluorides
Metal halides