Designer Mg−Mg and Zn−Zn single bonds facilitated by double aromaticity in the M2B7− (M=Mg, Zn) clusters

The simple homodinuclear M-M single bonds for group II and XII elements are difficult to obtain as a result of the fulfilled s2 electronic configurations, consequently, a dicationic prototype is often utilized to design the M+ −M+ single bond. Existing studies generally use sterically bulky organic ligands L− to synthesize the compounds in the L− −M+ −M+ −L− manner. However, here we report the design of Mg-Mg and Zn-Zn single bonds in two ligandless clusters, Mg2B7− and Zn2B7−, using density functional theory methods. The global minima of both of the clusters are in the form of M22+(B73−), where the M-M single bonds are positioned above a quasi-planar hexagonal B7 moiety. Chemical bonding analyses further confirm the existence of Mg-Mg and Zn-Zn single bonds in these clusters, which are driven by the unusually stable B73− moiety that is both σ and π aromatic. Vertical detachment energies of Mg2B7− and Zn2B7− are calculated to be 2.79 eV and 2.94 eV, respectively, for the future comparisons with experimental data.