Bifluoride
| Bifluoride | |
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Other names
Hydrogen(difluoride) |
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| Identifiers | |
| CAS number | 18130-74-0 |
| Jmol-3D images | Image 1 |
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| Properties | |
| Molecular formula | HF2 |
| Molar mass | 39 g mol−1 |
 (verify) (what is:  / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
The bifluoride, or hydrogen(difluoride) ion is the species HF2−. This centrosymmetric triatomic anion features the strongest known hydrogen bond, with an F−H length of 114 pm[1] and a bond strength of >155 kJ mol−1.[2] A molecular orbital diagram reveals the atoms to be held together by a 3-center 4-electron bond.[3] Hydrogen(difluoride) is written as one word because it is an anion. Hydrogen difluoride would imply an electrically neutral compound, HF2, which does not exist. It is isoelectronic with the hypothetical compound helium difluoride, HeF2, which also does not exist, and the fluoroheliate anion, FHeO−, whose existence is suspected.
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[edit] Salts
Some HF2− salts are common, examples include potassium hydrogen fluoride, KHF2, and [NH4][HF2]. Many salts claimed to be anhydrous sources of fluoride (e.g. tetra-n-butylammonium fluoride) can decompose yielding bifluoride.
[edit] Autodissociation of pure HF
The bifluoride ion also contributes to the unusually high auto-protolysis constant of liquid anhydrous hydrogen fluoride, which autodissociates in a manner similar to the self-ionization of water. This equilibrium can be denoted as
- HF
H+ + F−
H+ + F−However, both the H+ and F− ions are solvated by HF, so a better descriptive equation is
- 3HF H2F+(HF) + HF2−(HF)
[edit] See also
[edit] References
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Wikimedia Commons has media related to: bifluoride ion |
- ^ Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0080379419.
- ^ Emsley, J., "Very Strong Hydrogen Bonds", Chemical Society Reviews, 1980, 9, 91-124.
- ^ Pimentel, G. C. The Bonding of Trihalide and Bifluoride Ions by the Molecular Orbital Method. J. Chem. Phys. 1951, 19, 446-448. doi:10.1063/1.1748245
