Bifluoride

Bifluoride

Bifluoride

Ion with formula HF2 and charge 1-

Not to be confused with Difluoride.

The bifluoride ion is an inorganic anion with the chemical formula [HF2]−. The anion is colorless. Salts of bifluoride are commonly encountered in the reactions of fluoride salts with hydrofluoric acid. The commercial production of fluorine involves electrolysis of bifluoride salts.

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Structure and bonding

The bifluoride ion has a linear, centrosymmetric structure (D∞h symmetry), with an F−H 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 (symmetrical hydrogen bond).[3]

Reactions

Salts, such as potassium bifluoride and ammonium bifluoride are produced by treating fluoride salts with hydrofluoric acid:

M+F− + HF → M+[HF2]−, where M+ = K+ or [NH4]+

Potassium bifluoride binds a second equivalent of HF:[4]

K[HF2] + HF → K[H2F3]

Heating these salts releases anhydrous HF.

References

Wikimedia Commons has media related to bifluoride ion.
  1. [1]
    Denne, W.A.; Mackay, M.F. (1971). "Crystal structure of p-toluidinium bifluoride". Journal of Crystal and Molecular Structure. 1 (5): 311–318. doi:10.1007/BF01200805. S2CID 101570657.
  2. [2]
    Emsley, J. (1980). "Very Strong Hydrogen Bonds". Chemical Society Reviews. 9: 91–124. doi:10.1039/CS9800900091.
  3. [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
  4. [4]
    Aigueperse, Jean; Mollard, Paul; Devilliers, Didier; Chemla, Marius; Faron, Robert; Romano, René; Cuer, Jean Pierre (2000). "Fluorine Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a11_307. ISBN 978-3527306732.
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