Bare and Ligand-Stabilized Planar Hexacoordinate Boron (phB) in ABeC₂B₄ (A = P, As, Sb, and Bi) Clusters

Planar hexacoordination is an extremely uncommon phenomenon for the atoms that belong to the main group. Within this article, we have analyzed the potential energy surfaces (PES) of ABeC₂B₄ (A = N, P, As, Sb, and Bi) clusters in neutral, monocationic, monoanionic, dicationic, and dianionic states using density functional theory (DFT). Among which PBeC₂B₄, PBeC₂B₄^-, AsBeC₂B₄^-, AsBeC₂B₄^2-, SbBeC₂B₄^-, and BiBeC₂B₄^- clusters contain a planar hexacoordinate boron (phB) atom in the global minimum energy structures with C symmetry. The global minima of the remaining clusters do not correspond to a phB atom. According to the results of the natural charge computations, a significant amount of negative charge is accumulated on the phB atom for each global minimum. Based on the values of the nucleus independent chemical shift (NICS), the phB structures are predicted to possess σ/π-dual aromaticity. The most intriguing aspect is that the planarity of the phB core is preserved in the complexes that are coupled to the N-heterocyclic carbene (NHC) ligand. The stability of these complexes has been depicted here for the first time. As a result, it is our hope that both bare and ligand-stabilized clusters are viable options for gas-phase observation and large-scale synthesis, respectively.