美国加州大学伯克利分校Jeffrey R. Long团队取得一项新突破。他们实现了三重态苯双阴离子的分离。相关论文发表在2021年7月19日出版的《自然化学》杂志上。

该研究组的研究表明，困难的苯双自由基双阴离子键可以通过建立一个双核配体来实现严格约束的逆三明治结构和直接的磁性交换耦合来稳定。具体来说，该课题组研究人员报道了化合物[K(18-冠-6)(THF)₂]₂[M₂(BzN₆-Mes)] (M=Y, Gd;BzN₆-Mes=1,3,5-三[2',6'-(N-三甲基)二甲氨基-4'-叔丁基苯基]苯)，其特征是一个三方配体，在中心苯双阴离子的每个表面结合一个三价金属离子。Gd³⁺化合物中的反铁磁交换优先稳定了三重态，使其成为分子基态。单晶x射线衍射数据和非核化学位移计算支持芳香度，符合贝尔德规则。

研究人员表示，根据贝尔德规则，具有4n π电子的分子在三重态中应该是芳香的，但是这种电子基态的简单环系统的实现受到了这些分子倾向于扭曲成具有大单三重态间隙的结构的阻碍。

附：英文原文

Title: Isolation of a triplet benzene dianion

Author: Colin A. Gould, Jonathan Marbey, Veacheslav Vieru, David A. Marchiori, R. David Britt, Liviu F. Chibotaru, Stephen Hill, Jeffrey R. Long

Issue&Volume: 2021-07-19

Abstract: Baird’s rule predicts that molecules with 4n π electrons should be aromatic in the triplet state, but the realization of simple ring systems with such an electronic ground state has been stymied by these molecules’ tendency to distort into structures bearing a large singlet–triplet gap. Here, we show that the elusive benzene diradical dianion can be stabilized through creation of a binucleating ligand that enforces a tightly constrained inverse sandwich structure and direct magnetic exchange coupling. Specifically, we report the compounds [K(18-crown-6)(THF)2]2[M2(BzN6-Mes)] (M=Y, Gd; BzN6-Mes=1,3,5-tris[2′,6′-(N-mesityl)dimethanamino-4′-tert-butylphenyl]benzene), which feature a trigonal ligand that binds one trivalent metal ion on each face of a central benzene dianion. Antiferromagnetic exchange in the Gd3+ compound preferentially stabilizes the triplet state such that it becomes the molecular ground state. Single-crystal X-ray diffraction data and nucleus-independent chemical shift calculations support aromaticity, in agreement with Baird’s rule.

DOI: 10.1038/s41557-021-00737-8

Source: https://www.nature.com/articles/s41557-021-00737-8