The behavior of the aluminum trimer when combining with different superatom clusters.

The interaction between the aluminum trimer and representative (super)halogens X (X = F, LiF, BeF, BF) and (super)alkalis M (M = Li, FLi, OLi, NLi) has been theoretically investigated at the MP2/6-311+(3df) level. Various geometrical structures were obtained for the resulting Al-X and Al-M superatom compounds, respectively. Natural bond orbital analysis reveals that the Al moiety exists in a cationic state in Al-X while in an anionic state in Al-M compounds. And the charge transfer between Al and (super)atoms is found to be enhanced in either polar or nonpolar solvent. The studied superatom compounds feature large bond energies, binding energies, and HOMO-LUMO gaps, which not only reflect their stability but indicate strong interactions between Al and (super)atoms. Although the solvent effect is not significant for the stability of Al-X, the Al-superalkali compounds can be better stabilized in the presence of solvent molecules. In addition, these superatom compounds exhibit aromaticity both in the gas phase and in solution.