A plier-shaped binary molecular wheel B7Mg4+ cluster: hybrid in-plane heptacoordination, double π/σ aromaticity, and electronic transmutation

Quantum chemical calculations in combination with unbiased global searches reveal a unique binary B7Mg4+ cluster, in which a vertically oriented Mg-2 dimer is incorporated into a ringent (or Pac-Man shaped) B-7 disk, forming a hybrid Mg2B7 molecular wheel with pseudo-seven-fold in-plane coordination. The hybrid wheel assumes a plier shape. The remaining Mg-2 dimer floats on the hybrid wheel via electrostatic interaction, with relatively minor covalent Mg-B bonding. The B7Mg4+ cluster can be described as a charge transfer [Mg-2](2+)[Mg2B7](-) complex. Chemical bonding analysis indicates double 6 pi/6 sigma aromaticity in B7Mg4+ cluster. The unique plier shape of the cluster is elucidated using the concept of electronic transmutation, in which the vertical Mg-2 dimer closely mimics the chemistry of an atomic B- or C site.

Automated summary

Combining quantum chemical calculations with unbiased global searches, a unique binary B7Mg4+ cluster has been revealed, in which a vertically oriented Mg-2 dimer is incorporated into a ringent B-7 disk, forming a hybrid Mg2B7 molecular wheel with pseudo-seven-fold in-plane coordination. The concept of electronic transmutation has been used to elucidate the unique plier shape of the cluster.