Li Rui, You Xue-Rui, Guo Jin-Chang, Zhai Hua-Jin
Nanocluster Laboratory, Institute of Molecular Science, Shanxi University, Taiyuan 030006, China.
J Phys Chem A. 2021 Jun 17;125(23):5022-5030. doi: 10.1021/acs.jpca.1c02764. Epub 2021 Jun 7.
Planar B global-minimum (GM) cluster is known as a molecular Wankel motor, featuring unique chemical bonding and structural fluxionality. While the geometry, bonding, and molecular dynamics of the cluster are documented in the literature, it remains warranted to fully understand its bonding nature and unravel the mechanism behind the structural dynamics. We shall offer herein an updated bonding model on the bases of canonical molecular orbital (CMO) analysis and adaptive natural density partitioning (AdNDP), further aided by natural bond orbital (NBO) analysis and orbital composition calculations. The computational data indicate that the B cluster has inner 2π/6σ and outer 10π/14σ concentric 4-fold π/σ aromaticity. Being spatially isolated from each other, the inner B disk supports 2π and 6σ subsystems, whereas the outer B double-ring ribbon has 10π and 14σ subsystems. All 4-fold π/σ subsystems are intrinsically delocalized and conform to the (4 + 2) Hückel rule for aromaticity. The change of Wiberg bond index (WBI) from GM to transition-state (TS) for radial B-B links is minimal and uniform, which offers a semiquantitative measure of structural dynamics and underlies the low energy barrier.
平面B全局最小（GM）簇被称为分子汪克尔发动机，具有独特的化学键合和结构流动性。虽然该簇的几何结构、键合和分子动力学已在文献中有所记载，但充分理解其键合本质并揭示结构动力学背后的机制仍很有必要。在此，我们将基于正则分子轨道（CMO）分析和自适应自然密度划分（AdNDP），并辅以自然键轨道（NBO）分析和轨道组成计算，提供一个更新的键合模型。计算数据表明，B簇具有内部2π/6σ和外部10π/14σ同心四重π/σ芳香性。内部B盘相互空间隔离，支持2π和6σ子系统，而外部B双环带具有10π和14σ子系统。所有四重π/σ子系统本质上都是离域的，符合（4 + 2）休克尔芳香性规则。径向B-B键从GM到过渡态（TS）的维伯格键指数（WBI）变化最小且均匀，这为结构动力学提供了一种半定量度量，并构成了低能垒的基础。
