On the electrostatic nature of electrides.

The nature of electron localization in electrides is explored by examining their electrostatic features. Ab initio investigations of three experimentally synthesized and two theoretically modeled organic electrides are performed in order to unveil the characteristics of the trapped electron and to understand the reason for their low thermal stability. A single molecular unit of the electride extracted from the crystal structure shows an unusually deep minimum in its electrostatic potential, located far away from its van der Waals surface. A comparison of electrostatic features of the usual electron localization such as lone pairs has been drawn against those of the trapped electron in the crystal voids of electrides. Further characterization of the MESP minimum brings out the isotropic behavior of the trapped electrons as compared to the lone-pair minimum which is strongly directional. The analysis of single molecular behavior of an electride has been extended to the set of molecules in the unit cell of the crystal lattice. The present study also suggests the criteria for ligands to achieve thermally stable organic electrides.