In Silico Design and Characterization of a New Molecular Electride: Li@Calix[3]Pyrrole

Abstract

Electrides, in which anionic electrons are localized independently of the atoms in the compound, have shown promise, especially as catalysts and optoelectronic materials. Here, we present a new computationally designed molecular electride, Li@calix[3]pyrrole (Li@C3P). Electron density and electron localization function analyses unequivocally confirm the existence of localized electride electron density, outside the system, independent of any specific atoms. Non-covalent interaction plots further validate the character of the isolated localized electron, suggesting that the system can be accurately represented by Li⁺@calix[3]pyrrole ⋅ e^-, denoting its distinct charge separation. The remarkable non-linear optical properties of Li@C3P, including average polarizability, $\bar{\alpha }$ =412.4 au, first hyperpolarizability, β=4.46×10⁴ au, and second hyperpolarizability, ${\gamma }_{\parallel }$ =18.40×10⁶ au, are unparalleled in the previously reported and similar Li@C4P molecular electride. Furthermore, energy decomposition analysis in combination with natural orbital for chemical valence theory sheds light on the mechanism of electron density transfer from Li to the C3P cage, yielding the charge-separated Li@C3P complex. In addition to the electron transfer, a key factor to its electride nature is the electronic structure of the CnP cage, which has its lowest unoccupied molecular orbital located in the void adjacent to the N-H groups at the back of the bowl-shaped CnP cage.

Keywords: Calixpyrrole; Electron Density Analysis; Electron Localization Function; Molecular Electride; Non-Nuclear Attractor.