Electrides are among the most intriguing materials lately discovered. These ionic compounds have electrons occupying the anionic positions of solid compounds. Electrons in electrides act as separated individual entities, constituting the smallest possible anions in a molecule (actually these anions’ mass is 1820 times smaller than the smallest anion (H – ) reported thus far). All materials present defects at any temperature, due to misalignments or absences of atoms, the latter giving rise to vacancies that can be occupied by other particles. Farbe centers (from the German word Farben —color), commonly known as F centers, are vacancies occupied by electrons randomly displaced around the solid. The energy in the vacancy can undergo energetic excitations (in the UV-Vis range) that give rise to colors in e.g. gems. Electrides are actually stoichiometric F centers, i.e., isolated electrons are replicated in the solid structure according to the symmetry of the crystal. Therefore, unlike regular F centers, electride’s isolated electrons do feel each other’s presence. Electrides remind of alkaline metal solutions of ammonia, that form gold-blue colored materials that consist of positively charge alkaline metals and free electrons solvated by ammonia molecules. An important difference with electrides is that the latter occurs in the liquid (disordered) state, whereas electrides are solid (ordered) structures.
LIST OF PARTICIPANTS
 This compound really does stress-test what the molecular community considers to be a "bond". An analysis of the wavefunction leads to the following (non comprehensive) conclusions
So the challenge is this:
- Can this be a true compound of He, even if no conventional bonds/ionization of any type can be associated with the He atom?
- Might examples under ambient pressures exist?
Characterization and Identification of Molecular Electrides
The density due to the free electrons of electrides is not large enough to be located in the X-ray of the crystal structure. As a consequence, the evidence for these species is indirect and it comes from: (i) the similarity of this structure with analogue alkalide (i.e., the cationic structure) (ii) the chemical shift of the corresponding cation (133Cs), (iii) EPR studies, (iv) Density topology and ELF computational studies (v) Atomic-resolution scanning tunneling microscopy.
Electrides show particular magnetic (exalted susceptibilities that correlates with the channel area), chemical (organic synthesis, preparation of nanoscale metal and alloy particles), electric (an ideal electride should be a (Mott*) insulator) and optical properties (low optical spectra peaks as compared to alkali anions; huge nonlinear optical properties (NLOP), like large static first hyperpolarizabilities which make them of high interest due to their potential utilization in optical and optoelectronic devices).
Electrides are ionic compounds thus far occurring in the solid state, where the anionic part is constituted by isolated electrons. We show herein that molecular electrides in the gas phase can exist, provide an unambiguous computational means to characterize and identify these species as well as a recipe to design new electrides. We herein provide an unambiguous computational means to distinguish electrides from similar species, proving the existence of some electrides in the gas phase. We also put forward a recipe to design new electrides.
- X. Dong, A.R. Oganov, A.F. Goncharov, E. Stavrou, S. Lobanov, G. Saleh, G. Qian, Q. Zhu, C. Gatti, V.L. Deringer, R. Dronskowski, X. Zhou, V.B. Prakapenka, Z. Konôpková, I.A. Popov, A.I. Boldyrev, and H. Wang, Nature Chemistry, 2017, 9, 440-445, 2017. DOI:10.1038/nchem.2716
- For calculation details see DOI:10.14469/hpc/2156
- See J. A. Platts, J. Overgaard, C. Jones, B. B. Iversen and A. Stasch, J. Phys. Chem. A, 2011, 115, 194–200. DOI:10.1021/jp109547w for experimental detection of a non-nuclear attractor