Merino-García María Del Rosario, Soriano-Agueda Luis Antonio, Guzmán-Hernández Juan de Dios, Martínez-Otero Diego, Landeros Rivera Bruno, Cortés-Guzmán Fernando, Barquera-Lozada José Enrique, Jancik Vojtech
Centro Conjunto de Investigación en Química Sustentable UAEM-UNAM, Carretera Toluca-Atlacomulco, km. 14.5, Toluca, Estado de México C.P. 50200, México.
Universidad Nacional Autónoma de México, Instituto de Química, Ciudad Universitaria, Circuito Exterior s/n, Ciudad de México 04510, México.
Inorg Chem. 2022 May 9;61(18):6785-6798. doi: 10.1021/acs.inorgchem.1c03923. Epub 2022 Apr 26.
Although benzene and borazine are isoelectronic and isostructural, they have very different electronic structures, mainly due to the polar nature of the B-N bond. Herein, we present an experimental study of the charge density distribution obtained from the multipole model formalism and Hirshfeld atom refinement (HAR) based on high-resolution X-ray diffraction data of borazine BNH () and ,',″-trichloroborazine () crystals. These data are compared to those obtained from HAR for benzene () and 1,3,5-trichlorobenzene () and further compared with values obtained from density functional theory calculations in the gas phase, where ,',″-trichloroborazine () was also included. The results confirm that, unlike benzene, borazines are only weakly aromatic with an island-like electronic delocalization within the BN ring involving only the nitrogen atoms. Furthermore, delocalization indices and interacting quantum atom energy for bonded and non-bonded atoms were found to be highly suitable indicators capable of describing the origin of the discrepancies observed when the degree of aromaticity in and is evaluated using common aromaticity indices. Additionally, analysis of intermolecular interactions in the crystals brings further evidence of a weakly aromatic character of the borazines as it reveals surprising similarities between the crystal packing of borazine and benzene and also between ,',″-trichloroborazine and 1,3,5-trichlorobenzene.
尽管苯和硼嗪是等电子体且结构相同，但它们具有非常不同的电子结构，这主要归因于B-N键的极性。在此，我们基于硼嗪BNH（）和，'，″-三氯硼嗪（）晶体的高分辨率X射线衍射数据，展示了从多极模型形式主义和 Hirshfeld 原子精修（HAR）获得的电荷密度分布的实验研究。这些数据与从苯（）和1,3,5-三氯苯（）的HAR获得的数据进行比较，并进一步与气相中密度泛函理论计算获得的值进行比较，其中也包括，'，″-三氯硼嗪（）。结果证实，与苯不同，硼嗪仅具有弱芳香性，在BN环内具有仅涉及氮原子的岛状电子离域。此外，发现键合和非键合原子的离域指数和相互作用量子原子能量是非常合适的指标，能够描述在使用常见芳香性指数评估和中的芳香性程度时观察到的差异的起源。此外，对晶体中分子间相互作用的分析进一步证明了硼嗪的弱芳香性，因为它揭示了硼嗪和苯的晶体堆积之间以及，'，″-三氯硼嗪和1,3,5-三氯苯之间令人惊讶的相似性。
