Ground and Excited Electronic Structures of Electride and Alkalide Units: The Cases of Metal-Tren, -Azacryptand, and -TriPip222 Complexes

TL;DR

This study systematically analyzes the electronic structures of molecular electrides and alkalides with various ligands, revealing their superatom characteristics, Aufbau order, and excitation energy trends, contributing to understanding superalkali behavior.

Contribution

It provides a comprehensive electronic structure analysis of electrides and alkalides with new insights into their superatom nature and excitation properties.

Findings

Electrides display diffused electron clouds and superatom characteristics.

Superatomic Aufbau order observed up to 1F level.

Excitation energies decrease from Tren to TriPip222 ligands.

Abstract

A systematic electronic structure analysis was conducted for M(L)$_n$ molecular electrides and their corresponding alkalide units M(L)$_n$M' (M/M' = Na, K and L = Tren, Azacryptand, TriPip222 and $n$ = 1, 2). All complexes belong to the superalkali category owing to their low ionization potentials. The saturated molecular electrides display M+(L)n-form with a greatly diffused quasispherical electron cloud. They were identified as superatoms considering the contours of populating atomic-type molecular orbitals. The observed superatomic Aufbau order of M(Tren)$_2$ is 1S, 1P, 1D, 1F, 2S, 2P, and 1G and it is consistent with those of M(Azacryptand) and M(TriPip222) up to the analyzed 1F level. Their excitation energies decrease gradually moving from M(Tren)$_2$ to M(Azacryptand) and to M(TriPip222). The studied alkalide complexes carry [M(L)$_n$]$^+$M'$^-$ ionic structure and their dissociation energies vary in the sequence of K(L)$_n$@Na > Na(L)$_n$N@a > K(L)$_n$@K > Na(L)$_n$@K. Similar to molecular electrides, the anions of alkalide units occupy electrons in diffuse Rydberg-like orbitals. In this work, excited states of [M(L)$_n$@M']$^{0,+,-}$ and their trends are also analyzed.