The first reports of anionic electrons were detailed for solutions of alkali metals, however attempts to crystallise these systems with the electron remaining off-atom proved difficult. The first successful solid system containing anionic electrons was an organic complex condensed from such a solution by Dye et al. in 1983, and given the name electride. However, the material was extremely unstable at room temperature. It was not until the first purely inorganic electride was synthesised around 20 years later, that it was demonstrated that electrides could be stable with respect to temperature and pressure. The inorganic electride was synthesised by chemical treatment of the mineral mayenite (12𝐶𝑎𝑂 • 7𝐴𝑙 2 𝑂 3 ) to remove the oxygen ions from crystallographic cages, creating