Mbius规则预测，平面四元金属环可以是具有四个可移动电子的芳香环，但这样一个简单的环没有被识别，因为它通常有利于Hückel反芳香性。
该文中，研究人员报道了一种双Mbius芳香族的准正方形四元锕系化合物（Pa2B2）。化学键分析表明，这种二硼-精蛋白分子除了有四个离域σ电子外，还有四个离区π电子，满足σ和π组分的4n-Mbius规则。从能量上讲，块局域波函数法是从头算价键理论的最简单变体，它表明π和σ电子的离域能分别达到65.0和72.3 kcal/mol，而环外共振能（ECRE）达到45 kcal/mol。大的正ECRE值有力地证实了Pa2B2中前所未有的双Mbius芳香性。研究人员预计这种新型芳香分子可以丰富Mbius芳香性的概念，并为锕系化合物开辟一条新的途径。
附：英文原文
Title: Planar Four-Membered Diboron Actinide Compound with Double Mbius Aromaticity
Author: Xuhui Lin, Wei Wu, Yirong Mo
Issue&Volume: March 28, 2023
Abstract: The Mbius rule predicts that a planar four-membered metallacycle can be aromatic with four mobile electrons, but such a simple ring has escaped recognition because it usually favors Hückel anti-aromaticity. Here, we report that a quasi-square four-membered actinide compound (Pa2B2) is doubly Mbius aromatic. Chemical bonding analyses reveal that this diboron protactinium molecule has four delocalized π electrons in addition to four delocalized σ electrons, satisfying the 4n Mbius rule for both σ and π components. Energetically, the block-localized wavefunction method, which is the simplest variant of ab initio valence bond theory, shows that the delocalization energy for the π and σ electrons reaches up to 65.0 and 72.3 kcal/mol, respectively, while the extra cyclic resonance energy (ECRE) amounts to 45 kcal/mol. The large positive ECRE values strongly confirm the unprecedented double Mbius aromaticity in Pa2B2. We anticipate that this new type of aromatic molecule can enrich the concept of Mbius aromaticity and open a new avenue for actinide compounds.
DOI: 10.1021/jacs.3c00907
