Can LiF3 exist? (1 lithium and 3 fluorines), and if so, what would the Lewis dot diagram look like?
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2Related: https://chemistry.stackexchange.com/questions/27920/why-is-nacl3-possible – Nilay Ghosh Dec 13 '21 at 02:08
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https://chemistry.stackexchange.com/questions/7800/can-fluorine-act-as-the-central-atom-in-interhalogen-compounds – Mithoron Dec 13 '21 at 15:40
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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 $\ce{LiF + F2}$.
Oscar Lanzi
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Perhaps at high pressures the trifluoride could be a stable compound, however there are certain technical difficulties involved in such an investigation. – Nicolau Saker Neto Dec 13 '21 at 02:30
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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.. – Oscar Lanzi Dec 13 '21 at 02:49
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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... – Mithoron Dec 13 '21 at 17:40
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@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. – Oscar Lanzi Dec 13 '21 at 18:56