Antimony pentafluoride
Antimony pentafluoride is the inorganic compound with the formula SbF5. This colorless, viscous liquid is a strong Lewis acid and a component of the superacid fluoroantimonic acid, formed upon mixing liquid HF with liquid SbF5 in a 1:1 molar ratio. It is notable for its strong Lewis acidity and the ability to react with almost all known compounds.
Preparation
Antimony pentafluoride is prepared by the reaction of antimony pentachloride with anhydrous hydrogen fluoride: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 D3h point group symmetry. 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 n. The crystalline material is a tetramer, meaning that it has the formula 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.Antimony pentafluoride is a very strong oxidizing agent. Phosphorus burns on contact with it.
SbF5 increases the oxidizing power of Fluorine, making it able to oxidize oxygen:
SbF5 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 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 −, called hexafluoroantimonate. It is the conjugate base of the superacid fluoroantimonic acid. − is a weakly coordinating anion akin to PF6−. Although it is only weakly basic, − does react with additional SbF5 to give a centrosymmetric adduct:The − anion is one of the ions found in HF/SbF5 Mixture.