Can LiF3 exist? (1 lithium and 3 fluorines), and if so, what would the Lewis dot diagram look like?


1 Answer 1


Lithium with an oxidation state of +3 would seem beyond the pale, but all the halogens are known to form trihalide ions. Thus in principle one could imagine a salt, $\ce{Li^+(F3^-)}$.

However, trihalide ions are generally not stable in salts except with a bulky, essentially nonpolarizing cation or at GPa-level pressures; even caesium does not impart a perfectly symmetrical triiodide ion structure. Therefore, the proposed lithium trifluoride, with a small and relatively polarizing cation, would be expected to decompose to $\ce{LiF + F2}$.

  • $\begingroup$ Perhaps at high pressures the trifluoride could be a stable compound, however there are certain technical difficulties involved in such an investigation. $\endgroup$ Commented Dec 13, 2021 at 2:30
  • $\begingroup$ Agreed. I chose not to open that can of worms, partly because at least with caesium other (more fascinating) factors enter the picture. See Zhu et al.. $\endgroup$ Commented Dec 13, 2021 at 2:49
  • $\begingroup$ I wonder, if a Lewis adduct of LiF and F2 would be possible in gas phase. AuF5 is strong enough to make it, so maybe monomeric LiF also is... $\endgroup$
    – Mithoron
    Commented Dec 13, 2021 at 17:40
  • $\begingroup$ @mithoron I would not bet on it, AuF5 is a uniquely strong Lewis acid. F2 coordination seems not to be reported with other Lewis acids such as SbF5 or BF3. $\endgroup$ Commented Dec 13, 2021 at 18:56

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