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.
