德国鲁普莱希特-卡尔斯-海德堡大学Greb Lutz团队报道了阳离子全金属σ-芳香{Bi₄}环的超分子俘获。相关研究成果发表在2024年5月17日出版的《自然—化学》。

有机分子中的芳香性是明确的，但它在纯金属环中的作用仍然存在争议。

该文中，研究人员介绍了阳离子{Bi₄}菱形在两个碗状二元杯[4]吡咯烷酸盐的对称电荷球内的超分子稳定方法。晶体学和光谱表征、量子化学分析和磁感应环电流表明，形式上的四价电子[Bi₄]⁴⁺环具有σ-芳香性。对其他p嵌段元素的计算筛选表明，平面菱形是16价电子四原子团簇的全局优选结构。

芳香族[Bi₄]⁴⁺与[Al₄]^4-是等电子的，这是先前在气相中的Li₃[Al₄]^-中观察到的反芳香基序。因此，电荷各向同性等微妙因素似乎决定了芳香性或反芳香性，建议在基于Hückel模型的讨论中谨慎行事——这一概念对第二行元素有效，但对较重的同系物不太确定。

附：英文原文

Title: Supramolecular trapping of a cationic all-metal σ-aromatic {Bi4} ring

Author: Yadav, Ravi, Maiti, Avijit, Schorpp, Marcel, Graf, Jrgen, Weigend, Florian, Greb, Lutz

Issue&Volume: 2024-05-17

Abstract: Aromaticity in organic molecules is well defined, but its role in metal-only rings remains controversial. Here we introduce a supramolecular stabilization approach of a cationic {Bi4} rhomboid within the symmetric charge sphere of two bowl-shaped dianionic calix[4]pyrrolato indinates. Crystallographic and spectroscopic characterization, quantum chemical analysis and magnetically induced ring currents indicate σ-aromaticity in the formally tetracationic 16-valence electron [Bi4]4+ ring. Computational screening for other p-block elements identifies the planar rhomboid as the globally preferred structure for 16-valence electron four-atomic clusters. The aromatic [Bi4]4+ is isoelectronic to the [Al4]4, a motif previously observed as antiaromatic in Li3[Al4] in the gas phase. Thus, subtle factors such as charge isotropy seem to decide over aromaticity or antiaromaticity, advising for caution in debates based on the Hückel model—a concept valid for second-row elements but less deterministic for the heavier congeners.

DOI: 10.1038/s41557-024-01530-z

Source: https://www.nature.com/articles/s41557-024-01530-z