Designer Mg—Mg and Zn—Zn Single Bonds Facilitated by Double Aromaticity in the M₂B₇^- (M=Mg, Zn) Clusters^†

The simple homodinuclear M\begindocument - \enddocumentM single bonds for group II and XII elements are difficult to obtain as a result of the fulfilled s ^2 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, Mg _2 B _7 ^- and Zn _2 B _7 ^- , using density functional theory methods. The global minima of both of the clusters are in the form of M _2 ^2+ (B _7 ^3- ), where the M - M single bonds are positioned above a quasi-planar hexagonal B _7 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 B _7 ^3- moiety that is both \sigma and \pi aromatic. Vertical detachment energies of Mg _2 B _7 ^- and Zn _2 B _7 ^- are calculated to be 2.79 eV and 2.94 eV, respectively, for the future comparisons with experimental data.