From my understanding, the basic notions of acidity can be explained by considering a cup of pure water, and then adding a substance to it which creates either free $\ce{H+}$, or free $\ce{H3O+}$ and $\ce{H5O2+}$ etc...

And these ions are free to react and give rise to what we consider acidic behavior. The classic example is hydrogen chloride characterized with the following reaction

$$\ce{HCl +H2O = H3O+ + Cl-} $$

Whereas $\ce{H3O+}$ is our famous hydrochloric acid.

I wonder if it is possible for an analogous reaction to happen with other polar molecules. For example liquid $\ce{Li2O}$ (I believe it melts around 1438 Celsius) should be a polar liquid for the same reasons that $\ce{H2O}$ is (though maybe not as strongly polar), and therefore: $\ce{LiCl}$ should dissolve in molten $\ce{Li2O}$ to create positive charged lithium ion species such as $\ce{Li3O+}$. Which ought to function as an "acid" of sorts, in that they react with most thing which are dissolved/reacted by hydrochloric acid by acting as a positive charge donor (clearly not a proton donor since we are using lithium and not hydrogen to do the deed here)

Is my line of reasoning sound and has this been experimentally detected before?

  • $\begingroup$ I'm not sure if you want more then that Li cation is obviously Lewis acid $\endgroup$
    – Mithoron
    Dec 22 '20 at 2:23
  • $\begingroup$ (so I can get the terminology right) our $\text{Li}_2 \text{O}$ fluid with dissolved $\text{Li}\text{Cl}$ is a Lewis acid? $\endgroup$ Dec 22 '20 at 2:25
  • $\begingroup$ $\ce{Li+}$ is a Lewis acid that might coordinate to $\ce{Li2O}$ base forming an adduct. I highly doubt you can get much $\ce{Li2O}$ molecules outside of vapor phase, thogh. $\endgroup$
    – Mithoron
    Dec 22 '20 at 2:30

A complex of lithium ion with lithium hudroxide is known as the salt $\ce{[Li2OH]^+[ClO4]^-}$ [1]. As with the hydronium salt, this requires an essentially nonbasic counterion; with a chloride counterion a double salt is obtained with no evidence of a complex cation. From the abstract (some evident faults in translation from Russian have been corrected):

An effort is made to obtain salts of Li2OH+ and Li3O+ cations, belonging to a series of simple oxonium compound cations H3O+, LiOH2+, Li2OH+, Li3O+, where proton and lithium replace each other. Binary compounds of lithium hydroxide with lithium chloride and perchlorate are obtained: LiOH·LiClO4, LiOD·LiClO4, LiOH·LiCl, LiOD·LiCl and LiClO4·2LiOH. A conclusion is made by IR absorption spectra, that an adduct with perchlorate can be built of ClO4 anions and complex [Li2OH]+ cations. For adducts with chloride, equivalence of hydroxide and chloride anions with regular alternation of the anions in the crystal lattice is most probable.


1. Nikitina, Z. K., Nikitina, N. I., Rosolovskii, V. Y., "Complexing Lithium Salts and Lithium Oxide or Hydroxide: Synthesis and Characterization of a New Cation-Lithiumhydroxonium Li~2OH^+", Russian Journal of Inorganic Chemistry 42(9), 1295-1298 (1997).


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