Wang Ying-Jin, Feng Lin-Yan, Zhai Hua-Jin
Nanocluster Laboratory, Institute of Molecular Science, Shanxi University, Taiyuan, 030006, China.
Department of Chemistry, Xinzhou Teachers University, Xinzhou, 034000, Shanxi, China.
Chem Asian J. 2019 Sep 2;14(17):2945-2949. doi: 10.1002/asia.201900915. Epub 2019 Aug 1.
Typical salts are composed of positive and negative ions that appear alternatively, whereas decorated layered materials normally have ions anchored on the polygonal sites. In this way, the ions are spatially fixed and the system is stabilized on electrostatic grounds. Here we report on a unique boron-lithium cluster, B Li , which contains a disk-like B core, being sandwiched by a Li ring and an isolated Li atom. All Li centers are stacked exactly on the B atoms from top or bottom, rather than being anchored on triangular B sites. The cluster shows dynamic fluxionality, whose Li ring rotates freely on the B disk even at below room temperature (200 K), akin to a subnanoscale propeller. The rotation barrier is only 0.37 kcal mol at the single-point CCSD(T) level. The sandwich shape facilitates intramolecular charge-transfers, leading to a [Li ] [B ] [Li] salt complex. The [Li ] layer has 2σ aromaticity, while [B ] core is robust with both π and σ sextets. Three-fold π/σ aromaticity collectively stabilizes the system, as well as underlies its dynamic fluxionality. The interlayer bonding turns out to be strong, dominated by ionic interactions (of the order of 3-4 eV per Li /Li unit). The work demonstrates a propeller at the subnanoscale, which is dynamically fluxional despite strong covalent and ionic bonding.
典型的盐由正负离子交替出现组成，而修饰的层状材料通常有离子锚定在多边形位点上。通过这种方式，离子在空间上被固定，系统基于静电原理得以稳定。在此，我们报道一种独特的硼锂簇合物，B₃Li₃，它包含一个盘状的B₃核心，被一个Li环和一个孤立的Li原子夹在中间。所有的Li中心都从顶部或底部精确地堆叠在B原子上，而不是锚定在三角形的B位点上。该簇合物表现出动态流动性，即使在室温以下（200 K），其Li环也能在B盘上自由旋转，类似于一个亚纳米级的螺旋桨。在单点CCSD(T)水平下，旋转势垒仅为0.37 kcal mol⁻¹。这种夹心形状促进了分子内的电荷转移，形成了一种[Li⁺]₃[B₃³⁻][Li⁺]盐络合物。[Li⁺]层具有2σ芳香性，而[B₃³⁻]核心同时具有π和σ六重态，较为稳定。三重的π/σ芳香性共同稳定了该系统，并构成了其动态流动性的基础。层间键合很强，主要由离子相互作用主导（每个Li⁺/Li单元约为3 - 4 eV）。这项工作展示了一个亚纳米级的螺旋桨，尽管存在强共价键和离子键，但它仍具有动态流动性。
