Fluoronium Explained

The fluoronium ion is an inorganic cation with the chemical formula . It is one of the cations found in fluoroantimonic acid.^[1] The structure of the salt with the anion, has been determined.^{[2] [3]} The fluoronium ion is isoelectronic with the water molecule and the azanide ion.

The term can also refer to organyl substituted species of type H––R, R––R, or R₂C=F⁺. In contrast to the heavier halogens, which have long been known to form open-chain halonium ions (such as [Me₂Cl]⁺[Al(OTeF₅)₄]^–)^[4] as well as cyclic haliranium ions, fluorine was not believed to form fluoronium ions of type R––R until the recent characterization of a fluoronium ion locked in a designed cage structure by Lectka and coworkers.^[5] Recent solvolysis experiments and NMR spectroscopic studies on a metastable [C–F–C]⁺ fluoronium ion strongly support the dicoordinated fluoronium structure over the alternative rapidly equilibrating classical carbocation. Definitive structural proof of the symmetrical [C–F–C]⁺ was reported by Riedel, Lectka, and coworkers by single crystal X-ray diffraction analysis. Besides its synthesis and crystallographic characterization as the [Sb₂F₁₁]⁻ salt, vibrational spectra could be recorded and a detailed analysis concerning the nature of the bonding situation in this fluoronium ion and its heavier halonium homologues was reported.^[6]

Notes and References

1. Esteves. Pierre M.. Ramírez-Solís. Alejandro. Mota. Claudio J. A.. March 2002. The Nature of Superacid Electrophilic Species in HF/SbF5: A Density Functional Theory Study. Journal of the American Chemical Society. 124. 11. 2672–2677. 10.1021/ja011151k. 0002-7863. 11890818.
2. Mootz. Dietrich. Bartmann. Klemens. 1988. The Fluoronium Ions H₂F⁺ and : Characterization by Crystal Structure Analysis. Angewandte Chemie. 27. 3. 391–392. 10.1002/anie.198803911.
3. Diercksen. G. H. F.. von Niessen. W.. Kraemer. W. P.. SCF LCGO MO studies on the fluoronium ion and its hydrogen bonding interaction with hydrogen fluoride FH. Theoretical Chemistry Accounts: Theory, Computation, and Modeling. 31. 3. 205–214. 1973. 10.1007/BF00526510. 98637994.
4. Hämmerling. Sebastian. Thiele. Günther. Steinhauer. Simon. Beckers. Helmut. Müller. Carsten. Riedel. Sebastian. 2019. A Very Strong Methylation Agent: [Me2Cl][Al(OTeF5)4]]. Angewandte Chemie International Edition. en. 58. 29. 9807–9810. 10.1002/anie.201904007. 31050103 . 143434865 . 1521-3773.
5. Pitts. Cody Ross. Holl. Maxwell Gargiulo. Lectka. Thomas. 2018-02-12. Spectroscopic Characterization of a [C−F−C]⁺ Fluoronium Ion in Solution. Angewandte Chemie International Edition. en. 57. 7. 1924–1927. 10.1002/anie.201712021. 29316122.
6. Hoffmann. Kurt F.. Wiesner. Anja. Müller. Carsten. Steinhauer. Simon. Beckers. Helmut. Kazim. Muhammad. Pitts. Cody Ross. Lectka. Thomas. Riedel. Sebastian. 2021-09-06. Structural proof of a [C–F–C]+ fluoronium cation. Nature Communications. en. 12. 1. 5275. 10.1038/s41467-021-25592-6. 34489464 . 8421340 . 2041-1723.