Electride

  An electride is an ionic compound in which an electron is the anion.^[1] The first electrides to be studied in depth were solutions of alkali metals in ammonia.^[2] When sodium metal dissolves in ammonia, the result is a blue solution consisting of [Na(NH₃)₆]⁺ and solvated electrons. Such solutions are powerfully reducing, as demonstrated by their use in Birch Reductions. Evaporation of these blue solutions affords a mirror of Na. Such solutions slowly lose their colour as the electrons reduce ammonia:

[Na(NH₃)₆]⁺e^- + NH₃ → NaNH₂ + H₂

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Addition of 2,2,2-cryptand to a solution of [Na(NH₃)₆]⁺e^- affords [Na(2,2,2-crypt)]⁺e^-. Evaporation of these solutions yields a blue-black paramagnetic salt with the formula [Na(2,2,2-crypt)]⁺e^-. Such salts decompose above 240 K. In these salts, the electron is delocalized between the cations. Electrides are paramagnetic and Mott insulators.

References

J. L. Dye, M. J. Wagner, G. Overney, R. H. Huang, T. F. Nagy, and D. Tománek. Cavities and Channels in Electrides. J. Am. Chem. Soc. 118, 7329 (1996).