The C6B122− complex: A beautiful molecular wheel containing a ring of six planar tetracoordinate carbon atoms

We predicted by density functional theory (DFT) calculations the C-B binary wheel-like clusters: planar C6B122−, quasi-planar C6B12 and C6B122+ complexes. The C6B122− dianion with D6h symmetry has six equivalent planar tetracoordinate carbon atoms. Remarkably, its C6 unit is highly fluxional and rotates readily inside the boron perimeter. Based on our calculating results, we do not think that the Hückel 4n+2π electron rule is applicable to describe the aromaticity of the whole ring-in-ring systems, but suitable for each individual ring. Further analysis reveals that the multicenter σ bonding helps bind the outer boron ring to central C6 unit.