Jiang Zhi-Yu, Chen Teng-Teng, Chen Wei-Jia, Li Wan-Lu, Li Jun, Wang Lai-Sheng
Department of Chemistry and Key Laboratory of Organic Optoelectronics & Molecular Engineering of Ministry of Education, Tsinghua University, Beijing 100084, China.
Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States.
J Phys Chem A. 2021 Apr 1;125(12):2622-2630. doi: 10.1021/acs.jpca.1c01149. Epub 2021 Mar 19.
Inverse-sandwich structures have been observed recently for dilanthanide boride clusters, in which two Ln atoms sandwich a monocyclic B ring for = 7-9. An interesting question is if larger B rings are possible to form such inverse-sandwich clusters. Here we address this question by investigating LaB and LaB using photoelectron spectroscopy and quantum chemical calculations. Photoelectron spectra of LaB and LaB show complicated, but well-resolved, spectral features that are used to compare with theoretical calculations. We have found that global minimum structures of the two clusters are based on the octa-boron ring. The global minimum of LaB consists of two chiral enantiomers with symmetry, which can be viewed as adding a B unit off-plane to the B ring, whereas that of LaB can be viewed as adding a B unit in-plane to the B ring in a second coordination shell. Chemical bonding analyses reveal localized B-B bonds on the edge of the clusters and delocalized bonds in the expanded boron frameworks. The interactions between the La atoms and the boron frameworks include the unique (d-p)δ bonding, which was found to be the key for inverse-sandwich complexes with monocyclic boron rings. The current study confirms that the largest monocyclic boron ring to form the inverse-sandwich structures is B and provide insights into the structural evolutions of larger lanthanide boride clusters.
最近在二镧系硼化物簇中观察到了反夹心结构，其中两个镧系原子夹着一个单环硼环，n = 7 - 9。一个有趣的问题是，是否有可能形成更大硼环的这种反夹心簇。在这里，我们通过使用光电子能谱和量子化学计算来研究LaB₈和LaB₉来解决这个问题。LaB₈和LaB₉的光电子能谱显示出复杂但分辨良好的光谱特征，用于与理论计算进行比较。我们发现这两个簇的全局最小结构基于八硼环。LaB₈的全局最小值由两个具有C₂对称性的手性对映体组成，可以看作是在硼环平面外添加一个硼单元，而LaB₉的全局最小值可以看作是在第二配位层中在硼环平面内添加一个硼单元。化学键分析揭示了簇边缘的局域B - B键和扩展硼框架中的离域键。镧系原子与硼框架之间的相互作用包括独特的(d - p)δ键，这被发现是与单环硼环形成反夹心配合物的关键。当前的研究证实，形成反夹心结构的最大单环硼环是B₈，并为更大的镧系硼化物簇的结构演变提供了见解。
