Characterisation of superalkaline-earth-metal halides, hydroxide and chalcogenides

A new series of superalkaline-earth-metal compounds Al₁₄X (X = F₂, Cl₂, Br₂, I₂, (OH)₂, O, S) has been investigated at the TPSS/Def2-TZVPP level. It is found that both interaction position and mode between Al₁₄ and X ligands influence isomer stability of the resulting superatom compounds. On the one hand, the top and bottom sites of Al₁₄ have higher reactivity relative to middle ones. On the other hand, different ligands favour different binding patterns when combining with Al₁₄. For example, the halogen ligands prefer to occupy on-top sites of Al₁₄. In contrast, the end-on bound configurations are the least favourable ones for Al₁₄ oxide. Natural population analysis indicates that the Al₁₄ cluster donates electrons to X ligands. Atoms in molecules analysis also suggests ionic bond character of the connection(s) between Al₁₄ and X moieties. Thus, the Al₁₄X compounds are much like divalent salts where superatom Al₁₄ behaves just like an alkaline-earth-metal atom. Furthermore, considerable dissociation energies and large highest occupied molecular orbital and lowest unoccupied molecular orbital gaps confirm stability of these superatom compounds.