On the electrostatic nature of electrides

Abstract

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.

Electrostatics for probing lone pairs and their interactions

“…Further, MESP analysis opens up new ways to classify, quantify, and characterize various types of lone pairs in chemical systems and provides a simple interpretation of chemical reactivity. MESP analysis has already shown its utility in the study of understanding electron localization/delocalization features and also for interpreting a wide range of chemical and biological phenomena …”

“…MESP analysis has already shown its utility in the study of understanding electron localization/delocalization features and also for interpreting a wide range of chemical and biological phenomena. [6,7,[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] The aim of the present study is to further expand the scope of the electrostatic viewpoint of lone pairs by studying a variety of lone-pair-bearing organic molecules as well as some inorganic ligands. The focus will be on the classification and quantification of lone pairs and providing a possible connection with the formal hybridization state of the lone pairbearing atom.…”

Electride: from computational characterization to theoretical design

“…The most direct computational characterization method is plotting the charge density and then performing a topological analysis. At the same time, useful insights can also be obtained from a scrutiny of other quantities, such as noncovalent interaction (NCI) index, electron localization function (ELF), and electrostatic potential (ESP) . In addition to ab initio characterization of existing electrides, theoretical design of new electride is also reported.…”

“…The ESP of electride is also an important quantity to study. As shown in four electride‐based model molecules, Li + (calix[4]pyrrole)e − , Li + (Cryptand‐2.1.1)e − , Na + (tri‐pip‐aza‐2.2.2)e − , and K + (Cryptand‐2.2.2)e − (Figure ), there is always a negative ESP minimum located far away from the positively charged molecular framework. Its near‐isotropic characteristics reveal that trapped electrons in electride can barely be associated with any specific atom in the nuclear framework.…”

“…on the van der Waals surfaces of (a) Li + (calix[4]pyrrole)e − , (b) Li + (Cryptand‐2.1.1)e − , (c) Na + (tri‐pip‐aza‐2.2.2)e − , and (d) K + (Cryptand‐2.2.2)e − . (Reproduced with permission from Ref . Copyright 2015.…”