Sacanamboy Dumer S, García-Argote Williams, Pumachagua-Huertas Rodolfo, Cárdenas Carlos, Leyva-Parra Luis, Ruiz Lina, Tiznado William
Doctorado en Fisicoquímica Molecular, Facultad de Ciencias Exactas, Universidad Andrés Bello, República 275, Santiago 837014, Chile.
Centro de Investigación para el Diseño de Materiales (CEDEM), Facultad de Ciencias Exactas, Departamento de Ciencias Químicas, Universidad Andrés Bello, Avenida República 275, Santiago 837014, Chile.
Molecules. 2025 Aug 31;30(17):3566. doi: 10.3390/molecules30173566.
The aromaticity of small boron clusters remains under scrutiny due to persistent inconsistencies between magnetic and electronic descriptors. Here, we reexamine B, B, B, B, and B using a multidimensional approach that integrates Adaptive Natural Density Partitioning, Electron Density of Delocalized Bonds, magnetically induced current density, and the z-component of the induced magnetic field. We introduce a model in which σ-aromaticity arises from two distinct delocalization topologies: a radial 2e σ-pathway and a tangential multicenter circuit formed by alternating filled and vacant sp orbitals. This framework accounts for the evolution of aromaticity upon oxidation or reduction, preserving coherence between electronic structure and magnetic response. B features cooperative radial and tangential σ-delocalization, together with a delocalized 2e π-bond, yielding robust double aromaticity. B retains σ- and π-aromaticity, but only via a tangential 6e σ-framework, leading to a more compact delocalization and slightly attenuated ring currents. In B, the presence of a radial 2e σ-bond and a 4c-2e π-bond confers partial aromatic character, while the tangential 8e σ-framework satisfies the 4n rule and induces a paratropic current. In contrast, B lacks the radial σ-component but retains a tangential 8e σ-circuit and a 2e 4c-2e π-bond, leading to a σ-antiaromatic and π-aromatic configuration. Finally, B, exhibits delocalized π- and σ-circuits, yielding consistent diatropic ring currents, which confirms its fully doubly aromatic nature. Altogether, this analysis underscores the importance of resolving σ-framework topology and demonstrates that, when radial and tangential contributions are correctly distinguished, Hückel's rule remains a powerful tool for interpreting aromaticity in small boron rings.
由于磁性和电子描述符之间一直存在不一致，小硼簇的芳香性仍在研究之中。在这里，我们使用一种多维方法重新审视B₂、B₃、B₄、B₅和B₆，该方法整合了自适应自然密度划分、离域键的电子密度、磁诱导电流密度和诱导磁场的z分量。我们引入了一个模型，其中σ-芳香性源于两种不同的离域拓扑结构：径向2e σ-途径和由交替填充和空的sp轨道形成的切向多中心回路。该框架解释了氧化或还原时芳香性的演变，保持了电子结构和磁响应之间的一致性。B₃具有协同的径向和切向σ-离域，以及一个离域的2e π键，产生了强大的双芳香性。B₄保留了σ-和π-芳香性，但仅通过切向6e σ-框架，导致更紧凑的离域和稍弱的环电流。在B₅中，径向2e σ键和4c-2e π键的存在赋予了部分芳香特征，而切向8e σ-框架满足4n规则并诱导顺磁电流。相比之下，B₆缺乏径向σ-成分，但保留了切向8e σ-回路和2e 4c-2e π键，导致σ-反芳香和π-芳香构型。最后，B₂表现出离域的π-和σ-回路，产生一致的抗磁环电流，这证实了其完全双芳香的性质。总之，该分析强调了解析σ-框架拓扑的重要性，并表明，当正确区分径向和切向贡献时，休克尔规则仍然是解释小硼环中芳香性的有力工具。
