The nido-Cage⋅⋅⋅π Bond: A Non-covalent Interaction between Boron Clusters and Aromatic Rings and Its Applications

Non-covalent interactions involving multicenter multielectron skeletons such as boron clusters are rare. Now, a non-covalent interaction, the nido-cage⋅⋅⋅π bond, is discovered based on the boron cluster C₂ B₉ H₁₂ ^- and an aromatic π system. The X-ray diffraction studies indicate that the nido-cage⋅⋅⋅π bonding presents parallel-displaced or T-shaped geometries. The contacting distance between cage and π ring varies with the type and the substituent of the aromatic ring. Theoretical calculations reveal that this nido-cage⋅⋅⋅π bond shares a similar nature to the conventional anion⋅⋅⋅π or π⋅⋅⋅π bonds found in classical aromatic ring systems. This nido-cage⋅⋅⋅π interaction induces variable photophysical properties such as aggregation-induced emission and aggregation-caused quenching in one molecule. This work offers an overall understanding towards the boron cluster-based non-covalent bond and opens a door to investigate its properties.