A single π-bond captures 3, 4 and 5 atoms

Could more than two atoms be bound in such a way that a π-bond is the major bonding force without involving σ-bond at all? To answer this question, we have shown that 3, 4 or 5 metal atoms can be held together by a single π-bond in the Mg3−, NaMg3− and Na2Mg3 species. In both the NaMg3− and Na2Mg3 species, the basic structural unit is an unusual Mg32− trigonal planar cluster, which exhibits properties of aromaticity, because it satisfies the 4n + 2 rule for π-electrons and it is an equilateral triangle. Natural population analysis shows that the Na atomic orbitals contribute to formation of the π-bonding MO and thus all four in NaMg3− or all five in Na2Mg3 atoms are involved in chemical bonding. In these clusters, π-aromaticity occurs without initial formation of the σ-framework.