The bifluoride ion is an inorganic anion with the chemical formula HF
2
.

Bifluoride
Hydrogendifluoride ion.svg
Hydrogendifluoride-3D-vdW.png
Names
Other names
Hydrogen(difluoride)
Bifluoride anion
Hydrogen difluoride anion
Identifiers
3D model (JSmol)
ChemSpider
Properties
HF2
Conjugate acid Hydrogen fluoride
Conjugate base Fluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Structure and bondingEdit

The bifluoride ion has a linear, centrosymmetric structure (D∞h symmetry), with a FH bond length of 114 pm.[1] The bond strength is estimated to be greater than 155 kJ/mol.[2] In molecular orbital theory, the atoms are modeled to be held together by a 3-center 4-electron bond.[3]

Acid-base properties and saltsEdit

In the reaction

HF
2
+ H+ ⇌ 2 HF

the ion is acting as a Brønsted–Lowry base. This reaction can occur in non-aqueous solution. On the other hand, in the reaction

HF
2
+ H2O ⇌ 2 F + H3O+

it is acting as an acid. Salts, such as potassium bifluoride and ammonium bifluoride can be made in the direct reaction

MF + HF → M(HF2)   M = K+ or NH+
4

ReferencesEdit

  1. ^ Denne, W.A.; Mackay, M.F. (1971). "Crystal structure of p-toluidinium bifluoride". Journal of Crystal and Molecular Structure. 1 (5): 311–318.
  2. ^ Emsley, J. (1980). "Very Strong Hydrogen Bonds". Chemical Society Reviews. 9: 91–124. doi:10.1039/CS9800900091.
  3. ^ 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