sodium hexammine electride

[Na(NH₃)₆]⁺e⁻

49/50 rare

Sodium hexammine electride is a salt featuring a solvated electron as the counterion. Among numerous other physicochemical eccentricities, salts formed with this 'electride' anion possess anomalously low densities compared to typical ionic compounds, as a solvated "electride" is virtually massless compared to anions in conventional salts. Created by dissolving sodium metal in liquid ammonia, electride salts exhibit highly distinctive coloration, shifting from a pale blue at low concentrations to an intensely deep blue-bronze at higher concentrations. The striking color arises from the solvated electrons themselves, which occupy cavities in the ammonia structure. These electrons are not bound to any atom, instead existing in a quantum mechanical "solvent cage" surrounded by ammonia molecules. The resulting [Na(NH₃)₆]⁺e⁻ complex exhibits exceptional electrical conductivity, as the electrons can go wherever the hell they want. As a result, the solvated electrons in electride salts act as powerful reducing agents. This power is brought to bear in the Birch reduction, a powerful synthetic method that selectively converts aromatic rings to 1,4-cyclohexadienes—a transformation vital in natural product synthesis and pharmaceutical development.