Antimony pentafluoride
Encyclopedia
Antimony pentafluoride is the inorganic compound
with the formula Sb
F
5. This colourless, viscous liquid is a valuable Lewis acid
and a component of the superacid
fluoroantimonic acid
, the strongest known acid. It is notable for its Lewis acid
ity and its ability to react with almost all known compounds.
with anhydrous hydrogen fluoride
:
It can also be prepared from antimony trifluoride and fluorine.
(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 [SbF4(μ-F)2]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 [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. The related species PF5 and AsF5 are monomer
ic 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.
SbF5 is a strong Lewis acid, exceptionally so toward sources of F− to give the very stable anion [SbF6]−, called hexafluoroantimonate. [SbF6]− 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
:
Antimony pentafluoride 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.
. It is corrosive to the skin and eyes.
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...
with the formula Sb
Antimony
Antimony is a toxic chemical element with the symbol Sb and an atomic number of 51. A lustrous grey metalloid, it is found in nature mainly as the sulfide mineral stibnite...
F
Fluorine
Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...
5. This colourless, viscous liquid is a valuable Lewis acid
Lewis acid
]The term Lewis acid refers to a definition of acid published by Gilbert N. Lewis in 1923, specifically: An acid substance is one which can employ a lone pair from another molecule in completing the stable group of one of its own atoms. Thus, H+ is a Lewis acid, since it can accept a lone pair,...
and a component of the superacid
Superacid
According to the classical definition superacid is an acid with an acidity greater than that of 100% pure sulfuric acid, which has a Hammett acidity function of −12. According to the modern definition, superacid is a medium, in which the chemical potential of the proton is higher than in pure...
fluoroantimonic acid
Fluoroantimonic acid
Fluoroantimonic acid is a mixture of hydrogen fluoride and antimony pentafluoride in various ratios. The 1:1 combination forms the strongest known superacid, which has been demonstrated to protonate even hydrocarbons to afford carbocations and H2....
, the strongest known acid. It is notable for its Lewis acid
Lewis acid
]The term Lewis acid refers to a definition of acid published by Gilbert N. Lewis in 1923, specifically: An acid substance is one which can employ a lone pair from another molecule in completing the stable group of one of its own atoms. Thus, H+ is a Lewis acid, since it can accept a lone pair,...
ity and its ability to react with almost all known compounds.
Preparation
Antimony pentafluoride is prepared by the reaction of antimony pentachlorideAntimony pentachloride
Antimony pentachloride is a the chemical compound with the formula SbCl5. It is a colourless oil, but typical samples are yellowish due to impurities...
with anhydrous hydrogen fluoride
Hydrogen fluoride
Hydrogen fluoride is a chemical compound with the formula HF. This colorless gas is the principal industrial source of fluorine, often in the aqueous form as hydrofluoric acid, and thus is the precursor to many important compounds including pharmaceuticals and polymers . HF is widely used in the...
:
- 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 D3h point group symmetrySymmetry group
The symmetry group of an object is the group of all isometries under which it is invariant with composition as the operation...
(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 [SbF4(μ-F)2]n ((μ-F) denotes the fact that fluoride centres bridge
Bridging ligand
A bridging ligand is a ligand that connects two or more atoms, usually metal ions. The ligand may be atomic or polyatomic. Virtually all complex organic compounds can serve as bridging ligands, so the term is usually restricted to small ligands such as pseudohalides or to ligands that are...
two Sb centres). The crystalline material is a tetramer, meaning that 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. The related species PF5 and AsF5 are monomer
Monomer
A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer; the term "monomeric protein" may also be used to describe one of the proteins making up a multiprotein complex...
ic 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.
SbF5 is a strong Lewis acid, exceptionally so toward sources of F− to give the very stable anion [SbF6]−, called hexafluoroantimonate. [SbF6]− reacts with additional SbF5 to give [Sb2F11]−:
- SbF5 + [SbF6]− → [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
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
:
- 2 SbF5 + F2 + 2 O2 → 2
Antimony pentafluoride has also been used in the first discovered chemical reaction that produces fluorine
Fluorine
Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...
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.
Safety
SbF5 reacts violently with many compounds, often releasing dangerous hydrogen fluorideHydrogen fluoride
Hydrogen fluoride is a chemical compound with the formula HF. This colorless gas is the principal industrial source of fluorine, often in the aqueous form as hydrofluoric acid, and thus is the precursor to many important compounds including pharmaceuticals and polymers . HF is widely used in the...
. It is corrosive to the skin and eyes.