Antimony pentafluoride is the inorganic compound with the formula SbF<sub>5</sub>. This colorless, viscous liquid is a strong Lewis acid and a component of the superacid fluoroantimonic acid, formed upon mixing liquid HF with liquid SbF<sub>5</sub> in a 1:1 molar ratio. It is notable for its strong Lewis acidity and the ability to react with almost all known compounds.
Antimony pentafluoride is prepared by the reaction of antimony pentachloride with anhydrous hydrogen fluoride:
It can also be prepared from antimony trifluoride and fluorine.
In the gas phase, SbF<sub>5</sub> adopts a trigonal bipyramidal structure of D<sub>3h</sub> 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 [SbF<sub>4</sub>(ü-F)<sub>2</sub>]<sub>n</sub> ((ü-F) denotes the fact that fluoride centres bridge two Sb centers). The crystalline material is a tetramer, meaning that it has the formula [SbF<sub>4</sub>(ü-F)]<sub>4</sub>. The SbâÂÂF bonds are 2.02 àwithin the eight-membered Sb<sub>4</sub>F<sub>4</sub> ring; the remaining fluoride ligands radiating from the four Sb centers are shorter at 1.82 à. The related species PF<sub>5</sub> and AsF<sub>5</sub> are monomeric in the solid and liquid states, probably due to the smaller sizes of the central atom, which limits their coordination number. BiF<sub>5</sub> is a polymer.
Antimony pentafluoride is a very strong oxidizing agent. Phosphorus burns on contact with it.
SbF<sub>5</sub> increases the oxidizing power of Fluorine, making it able to oxidize oxygen:
SbF<sub>5</sub> has also been used in the first discovered chemical reaction that produces fluorine gas from fluoride compounds:
The driving force for this reaction is the high affinity of SbF<sub>5</sub> for , which is the same property that recommends the use of SbF<sub>5</sub> to generate superacids.
SbF<sub>5</sub> is a strong Lewis acid, exceptionally so toward sources of F<sup>âÂÂ</sup> to give the very stable anion [SbF<sub>6</sub>]<sup>âÂÂ</sup>, called hexafluoroantimonate. It is the conjugate base of the superacid fluoroantimonic acid. [SbF<sub>6</sub>]<sup>âÂÂ</sup> is a weakly coordinating anion akin to PF<sub>6</sub><sup>âÂÂ</sup>. Although it is only weakly basic, [SbF<sub>6</sub>]<sup>âÂÂ</sup> does react with additional SbF<sub>5</sub> to give a centrosymmetric adduct:
The [Sb<sub>2</sub>F<sub>11</sub>]<sup>âÂÂ</sup> anion is one of the ions found in HF/SbF<sub>5</sub> Mixture.
SbF<sub>5</sub> is highly corrosive to the skin and the eyes. It is extremely toxic and hazardous to health. Its lethal dose (LD<sub>50</sub>) is reported to be 270 mg/kg (mouse, subcutaneous) with lowest concentration (LC<sub>Lo</sub>) of 15 mg/m<sup>3</sup> or 1.69 ppm (rat, inhalation, 2 hours). Occupational exposure limit set by NIOSH stands at 50 mg/m<sup>3</sup> (5 ppm). It is considered to be Immediately dangerous to life and health at this concentration. Other than that, SbF<sub>5</sub> reacts violently with water along with many other compounds, often releasing dangerous hydrogen fluoride. It is a very strong oxidizer.