A New Family of Bare and NHC‐Ligand‐Stabilized Planar Hexacoordinate Boron Species: Be 2 B 4 CE + ( E = N, P, and As) Clusters

The occurrence of planar hexacoordination is of interest for main‐group elements in the periodic table. In this study, we investigated the potential energy surfaces (PES) of Be 2 B 4 CE clusters ( E = N, P, As, Sb, and Bi) across their neutral, mono‐cationic, mono‐anionic, di‐cationic, and di‐anionic charge states using density functional theory (DFT). Among these, Be 2 B 4 CN + , Be 2 B 4 CP + , and Be 2 B 4 CAs + clusters exhibit a true planar hexacoordinate boron (phB) atom in their global minimum energy structures, all possessing C s symmetry. In the case of the phB structure for the Be 2 B 4 CN + system, the N atom is connected to the phB atom, whereas for other phB structures, there is no connection between the central boron atom and the E atoms. Natural charge analysis revealed that in the phB structure of the Be 2 B 4 CN + , the central boron atom is slightly negative, while it is notably negative for Be 2 B 4 CP + and Be 2 B 4 CAs + systems. Nucleus‐independent chemical shift (NICS) calculations confirm that the phB structures possess σ / π ‐dual aromaticity. The most intriguing finding is that the planar geometry of the phB center remains intact upon coordination with the N‐heterocyclic carbene (NHC) ligand.