硼基反三明治Ta2B6团簇的化学成键模型

刘芳林; 翟华金

doi:10.13451/j.sxu.ns.2024067

山西大学学报(自然科学版) ›› 2025, Vol. 48 ›› Issue (04) : 775 -783. DOI: 10.13451/j.sxu.ns.2024067

化学

硼基反三明治Ta₂B₆团簇的化学成键模型

刘芳林 ,
翟华金

作者信息 +

Chemical Bonding of Boron-based Inverse Sandwich Ta₂B₆ Cluster Revisited

Fanglin LIU ,
Huajin ZHAI

Author information +

文章历史 +

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摘要

硼基反三明治团簇是一类新型复合团簇。团簇Ta₂B₆是其中一个典型体系，已报道的化学成键图像存在缺陷。本文运用一系列现代化学键分析工具详尽地研究团簇Ta₂B₆的化学成键和芳香性。研究结果表明：该团簇具有6π/6σ双重芳香性，它们均符合休克尔（4n+2）电子计数规则。该结论区别于文献中相关的12π/4σ电子计数。每个Ta中心保留2个近似非键5d电子，但不是孤对。团簇中没有显著的金属间相互作用。同时，团簇中B-B骨架σ键显示一定程度的棱形Ta-B₂-Ta四中心两电子特征，而不是经典路易斯两中心两电子键，这种成键现象在分子体系中是鲜见的。本工作提出的成键模型有望拓展至其他反三明治团簇体系。

Abstract

Boron-based inverse sandwich clusters are a new class of compound systems, for which D_6h Ta₂B₆ cluster is a typical example. However, the existing chemical bonding model of inverse sandwich Ta₂B₆cluster has fundamental flaws and an indepth revisiting of the system is warranted. In this work, chemical bonding and aromaticity of Ta₂B₆ cluster are studied computationally using an array of modern quantum chemistry tools, which include canonical molecular orbital (CMO) analysis, adaptive natural density partitioning (AdNDP), electron localization functions (ELFs), and nucleus-independent chemical shifts (NICSs). The concerted results reveal 6π/6σ double aromaticity in the cluster, conforming to the (4n + 2) Hückel rule. The observation differs distinctly from the prior 12π/4σ electron counting in the literature. Each Ta center maintains two 5d electrons that are essentially nonbonding, albeit they do not form a lone pair. There is not direct Ta Ta bonding in the system. The skeleton σ framework along B₆ ring is shown to possess a certain extent of rhombic Ta B₂ Ta four-center two-electron (4c-2e) character. It does not have strict Lewis-type σ single bonds, which is rare in molecular systems. The present bonding model may be extended to other inverse sandwich clusters.