Nature of Bonding in Bowl‐Like B₃₆ Cluster Revisited: Concentric (6π+18π) Double Aromaticity and Reason for the Preference of a Hexagonal Hole in a Central Location

Abstract

The bowl-shaped C B cluster with a central hexagon hole is considered an ideal molecular model for low-dimensional boron-based nanosystems. Owing to the electron deficiency of boron, chemical bonding in the B cluster is intriguing, complicated, and has remained elusive despite a couple of papers in the literature. Herein, a bonding analysis is given through canonical molecular orbitals (CMOs) and adaptive natural density partitioning (AdNDP), further aided by natural bond orbital (NBO) analysis and orbital composition calculations. The concerted computational data establish the idea of concentric double π aromaticity for the B cluster, with inner 6π and outer 18π electron counting, which both conform to the (4n+2) Hückel rule. The updated bonding picture differs from existing knowledge of the system. A refined bonding model is also proposed for coronene, of which the B cluster is an inorganic analogue. It is further shown that concentric double π aromaticity in the B cluster is retained and spatially fixed, irrespective of the migration of the hexagonal hole; the latter process changes the system energetically. The hexagonal hole is a destabilizing factor for σ/π CMOs. The central hexagon hole affects substantially fewer CMOs, thus making the bowl-shaped C B cluster the global minimum.

Insight into The Nature of Rim Bonds in Coronene

“…Coronene C 12 H 24 is one of the most remarkable and intriguing molecules in organic chemistry. − Although it was first synthesized almost a century ago it is still in focus − , because of its unusual structure which remains a conundrum. As a big planar polycyclic molecule formally containing 24 π-electrons, coronene does not correspond to aromatic molecules which follow the 4 n + 2 Huckel’s rule so its well-known experimental stability could not be theoretically substantiated by simple counting of conjugated system π-electrons.…”

Electronic structure, stability, and aromaticity of M2B6 (M = Mg, Ca, Sr, and Ba): an interplay between spin pairing and electron delocalization

“…In the past two decades combined experimental and theoretical studies have been systematically undertaken to characterize the structure and bonding properties of size-selected boron clusters. [1][2][3][4] Bare boron clusters can adopt a diverse variety of geometric structures, such as planar, 1 quasi-planar, 1,4 bowl, 5,6 cage, 7 tubular, 8,9 multiple ring 10 and fullerene-like structures. 11 Isolated bare boron clusters exhibit different geometrical shapes from the clusters found as building blocks in the bulk phase of elemental boron.…”

Concentric Inner 2π/6σ and Outer 10π/14σ Aromaticity Underlies the Dynamic Structural Fluxionality of Planar B19– Wankel Motor Cluster

“…As the nearest neighbor of carbon in the periodic table, boron is a typical electron-deficient element, which leads to unique structures and chemical bonding for boron-based nanoclusters and low-dimensional nanomaterials. − Over the past 30 years, systematic experimental and computational studies have shown that boron clusters exhibit planar or quasi-planar (2D) structures in a wide range of sizes. For example, anionic 2D boron clusters were observed and characterized up to 40 atoms, B 40 – , via photoelectron spectroscopy (PES) in the gas phase, which coexists with cage-like borospherene .…”