Tetrahedral AlO Cage: A Superchalcogen Atom.

Superatoms are stable clusters that mimic the chemical behavior of individual atoms in the periodic table. Many endeavors have been devoted to the design and characterization of various superatoms, while engineering superatoms to mimic the chemistry of chalcogens remains a challenge. In this paper, we present a new superchalcogen by evaluating a hollow tetrahedral AlO cluster with theoretical calculations. By comparing the AlO with its daughter dianion (AlO) in terms of stability, aromaticity, electronic properties, and chemical behavior in compounds, we find that this cluster tends to get two additional electrons to reach a more stable electronic state, which is the origin of the identity of superchalcogens. The adaptive natural density partitioning (AdNDP) analysis illustrates that this AlO cluster accommodates two electrons by a 4-center-2-electron bond formed between the four face-centered Al atoms. Moreover, the AlO cluster has exothermic first and second adiabatic electron affinity (EA), indicating that the dianion (AlO) is stable against spontaneous electron emission and fragmentation in the gas phase. This reflects the size advantage of superchalcogens when compared with chalcogens. Interestingly, we further study a cluster with one more electron than the superchalcogen AlO, namely, H@(AlO) and find that it is a superhalogen due to its large vertical and adiabatic EA.