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

<p>A new series of superalkaline-earth-metal compounds Al<sub>14</sub>X (X = F<sub>2</sub>, Cl<sub>2</sub>, Br<sub>2</sub>, I<sub>2</sub>, (OH)<sub>2</sub>, O, S) has been investigated at the TPSS/Def2-TZVPP level. It is found that both interaction position and mode between Al<sub>14</sub> and X ligands influence isomer stability of the resulting superatom compounds. On the one hand, the top and bottom sites of Al<sub>14</sub> have higher reactivity relative to middle ones. On the other hand, different ligands favour different binding patterns when combining with Al<sub>14</sub>. For example, the halogen ligands prefer to occupy on-top sites of Al<sub>14</sub>. In contrast, the end-on bound configurations are the least favourable ones for Al<sub>14</sub> oxide. Natural population analysis indicates that the Al<sub>14</sub> cluster donates electrons to X ligands. Atoms in molecules analysis also suggests ionic bond character of the connection(s) between Al<sub>14</sub> and X moieties. Thus, the Al<sub>14</sub>X compounds are much like divalent salts where superatom Al<sub>14</sub> 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.</p>