Structure and bonding of molecular stirrers with formula B₇M₂^- and B₈M₂ (M = Zn, Cd, Hg)

In this work, we systematically explored clusters with formula B₇M₂^- and B₈M₂ (M = Zn, Cd, Hg). The putative global minima are formed by an M₂ dimer and a disk-shaped boron wheel. Moreover, the chemical bonding analysis revealed that charge transfer from the metal atoms to the boron motifs resulted in (B₇)^3-(M₂)²⁺ and (B₈)^2-(M₂)²⁺ complexes with double (σ + π) aromatic boron wheels and a single bond for the metallic dimer. Above all, the computed rotational barriers of the M-M fragment with respect to the boron disk and molecular dynamics simulations indicate a virtually barrierless spin, resembling a magnetic stirrer on a baseplate.