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.