How Many Electrons Does a Molecular Electride Hold?

Abstract

Electrides are very peculiar ionic compounds where electrons occupy the anionic positions. In a crystal lattice, these isolated electrons often form channels or surfaces, furnishing electrides with many traits with promising technological applications. Despite their huge potential, thus far, only a few stable electrides have been produced because of the intricate synthesis they entail. Due to the difficulty in assessing the presence of isolated electrons, the characterization of electrides also poses some serious challenges. In fact, their properties are expected to depend on the arrangement of these electrons in the molecule. Among the criteria that we can use to characterize electrides, the presence of a non-nuclear attractor (NNA) of the electron density is both the rarest and the most salient feature. Therefore, a correct description of the NNA is crucial to determine the properties of electrides. In this paper, we analyze the NNA and the surrounding region of nine molecular electrides to determine the number of isolated electrons held in the electride. We have seen that the correct description of a molecular electride hinges on the electronic structure method employed for the analyses. In particular, one should employ a basis set with sufficient flexibility to describe the region close to the NNA and a density functional approximation that does not suffer from large delocalization errors. Finally, we have classified these nine molecular electrides according to the most likely number of electrons that we can find in the NNA. We believe this classification highlights the strength of the electride character and will prove useful in designing new electrides.

Room-Temperature-Stable Magnesium Electride via Ni(II) Reduction

“… 36 − 38 However, to the best of our knowledge, only eight organic electrides have been synthesized, of which only one is room-temperature-stable. 39 , 40 Remarkably, QTAIM reveals the presence of a non-nuclear attractor (NNA) with a charge of -0.48 in the center of [ 3-Mg 4 ] − , thus strongly advocating the notion that the latter is an electride. 41 The electride electron is topologically encaged by the interaction of 6,6′-hydrogen atoms of the bipyridine core within a capsule of an approximate length of 0.4 nm ( Figure 3 ), similar to previously known organic electrides.…”

“…Thus, we conclude that [ 3-Mg 4 ] − is unlikely to be a hydride; instead, the residual electron density observed in the middle of the cavity suggests the intriguing possibility of [ 3-Mg 4 ] − being an electride. Electrides are materials that hold a free electron in a cavity formed by cations. , Inorganic electrides such as [Ca 24 Al 28 O 64 ] 4+ 4e – have been shown to be room-temperature-stable and possess intriguing electronic properties such as high conductivity, and have even demonstrated applications as aqueous compatible reductants. − However, to the best of our knowledge, only eight organic electrides have been synthesized, of which only one is room-temperature-stable. , Remarkably, QTAIM reveals the presence of a non-nuclear attractor (NNA) with a charge of -0.48 in the center of [ 3-Mg 4 ] − , thus strongly advocating the notion that the latter is an electride . The electride electron is topologically encaged by the interaction of 6,6′-hydrogen atoms of the bipyridine core within a capsule of an approximate length of 0.4 nm (Figure ), similar to previously known organic electrides .…”

Impact of Van der Waals interactions on structural and nonlinear optical properties of azobenzene switches

“…45,46 I ND is proportional to the deviation from idempotency of the first-order reduced density matrix. 47,48 In all cases, I ND values are rather small compared to other multireference molecules 49 (see Table S5). All in all, we can conclude that these molecules present a rather mild multireference character and they can be reasonably well described with single-reference methods such as MP2 and CC2.…”

Molecular Electrides: An In Silico Perspective

“…The strength of the electride can be measured based on the probability of finding electron(s) within an NNA basin which was demonstrated by Matito and co-workers. [153] The probability of finding zero, one, and two electrons within the NNA basin is denoted as P 0 , P 1, and P 2 , respectively. The condition for finding at least one electron is (1-P 0 ) > 0.5.…”

“…Except for Mg 2 EP, and Mg 2 @C 60 , the probability of finding two electrons in the NNA basin is negligible. [153] To avoid spurious validation from the AIM analysis, one should be aware of the limitation of the density functional approximations (DFA) employed in the calculations. [153] Due to the factitious self-interactions, various DFAs have delocalization errors, which results in the overestimation of the electron delocalization in the system.…”