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

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.