σ-aromaticity and σ-antiaromaticity in alkali metal and alkaline earth metal small clusters

We extended the aromaticity concept to small a-aromatic alkali metal and alkaline earth metal clusters. We performed ab initio calculations (133LYP/6-311+G* and CCSD(T)/6-311+G*) on a selected group of triatomic and tetraatomic metal clusters. We have shown that the introduction of aromaticity and antiaromaticity in Li-3(+) and Li-3(-) ions, respectively, can be used to explain their relative stability and their structure. For the tetratomic 6sigma-electron Li2Mg2 species we predicted that the cyclic a-aromatic structures of Li2Mg2 are more stable than the classical linear Li-Mg-Mg-Li structure, thus showing the importance of the aromaticity in metal clusters. We believe that the further advancing of the aromaticity concept into metal clusters will be a useful tool in understanding chemical bonding in these species.