(B₃CB₃)N₂ Monolayer Consisting of CO₂-Type Superatomic Molecules with Sandwich Hexacoordinate Carbons

Searching for a useful way to build stable hypercoordinate carbon species is a great way to enrich carbon-based chemical rules. Here, we extend the super valence bond model into superatom-atom superbonding to theoretically predict a two-dimensional (B₃CB₃)N₂ monolayer, which is the first design of a stable nonplanar hexacoordinate carbon containing material, featuring a sandwich B₃CB₃ configuration. Chemical bonding analyses indicate that its stability originates from the unique super CO₂ structures, where each tricoordinate B₃ unit has six delocalized electrons acting as a super oxygen (S²P⁴), and the B₃CB₃ unit mimics the bonding pattern of the CO₂ molecule via the superatom-atom super double bond. Thus, the (B₃CB₃)N₂ monolayer can be visualized as an assembly of super CO₂ units linked by N atoms. The calculated moderate direct band gap (∼1.71 eV) and high light absorption coefficient of the (B₃CB₃)N₂ monolayer make it a promising candidate for further applications in electronics and optoelectronics. This work provides a possible pathway to design hypercoordinate carbon materials via superatom-atom cluster assembly, which is expected to be applied across diverse fields.