B₇Be₆B₇ : A Boron-Beryllium Sandwich Complex: A Boron-Beryllium Sandwich Complex

Planar boron clusters have often been regarded as “π-analogous” to aromatic arenes because of their similar delocalized π-bonding. However, unlike arenes such as C₅H₅⁻ and C₆H₆, boron clusters have not previously shown the ability to form sandwich complexes. In this study, we present the first sandwich complex involving beryllium and boron, B₇Be₆B₇. The global minimum of this combination adopts a unique architecture having a D_6h geometry, featuring an unprecedented monocyclic Be₆ ring sandwiched between two quasi-planar B₇ motifs. The thermochemical and kinetic stability of B₇Be₆B₇ can be attributed to strong electrostatic and covalent interactions between the fragments. Chemical bonding analysis shows that B₇Be₆B₇ can be considered as a [B₇]³⁻[Be₆]⁶⁺[B₇]³⁻ complex. Moreover, there is a significant electron delocalization within this cluster, supported by the local diatropic contributions of the B₇ and Be₆ fragments.