Nanocluster Laboratory, Institute of Molecular Science, Shanxi University, Taiyuan 030006, China.
Center for Applied Physics and Technology, School of Materials Science and Engineering, Peking University, Beijing 100871, China.
Molecules. 2023 Jun 12;28(12):4721. doi: 10.3390/molecules28124721.
Inverse sandwich clusters composed of a monocyclic boron ring and two capping transition metal atoms are interesting alloy cluster systems, yet their chemical bonding nature has not been sufficiently elucidated to date. We report herein on the theoretical prediction of a new example of boron-based inverse sandwich alloy clusters, VB, through computational global-minimum structure searches and quantum chemical calculations. This alloy cluster has a heptatomic boron ring as well as a perpendicular V dimer unit that penetrates through the ring. Chemical bonding analysis suggests that the inverse sandwich cluster is governed by globally delocalized 6π and 6σ frameworks, that is, double 6π/6σ aromaticity following the (4 + 2) Hückel rule. The skeleton B-B σ bonding in the cluster is shown not to be strictly Lewis-type two-center two-electron (2c-2e) σ bonds. Rather, these are quasi-Lewis-type, roof-like 4c-2e V-B-V σ bonds, which amount to seven in total and cover the whole surface of inverse sandwich in a truly three-dimensional manner. Theoretical evidence is revealed for a 2c-2e Lewis σ single bond within the V dimer. Direct metal-metal bonding is scarce in inverse sandwich alloy clusters. The present inverse sandwich alloy cluster also offers a new type of electronic transmutation in physical chemistry, which helps establish an intriguing chemical analogy between inverse sandwich clusters and planar hypercoordinate molecular wheels.
由单环硼环和两个封端过渡金属原子组成的反夹心簇是有趣的合金簇体系，但迄今为止，其化学键性质尚未得到充分阐明。我们通过计算全局最小结构搜索和量子化学计算，在此报告了硼基反夹心合金簇 VB 的新实例的理论预测。该合金簇具有作为七元硼环以及垂直 V 二聚体单元，其贯穿环。化学成键分析表明，反夹心簇由全局离域的 6π 和 6σ 框架控制，即遵循（4 + 2）Hückel 规则的双 6π/6σ 芳香性。表明簇中的骨架 B-B σ 键不是严格的路易斯型二中心二电子（2c-2e）σ键。相反，这些是准路易斯型，屋顶状的 4c-2e V-B-V σ 键，总共七个，以真正的三维方式覆盖反夹心的整个表面。理论证据表明 V 二聚体内存在 2c-2e 路易斯 σ 单键。反夹心合金簇中直接的金属-金属键很少。本反夹心合金簇还提供了物理化学中电子嬗变的新类型，这有助于在反夹心簇和平面超坐标分子轮之间建立有趣的化学类比。
