Yan Gai-Ru, Liu Yu-Qian, Liu Xin-Bo, Wang Meng-Hui, Cui Zhong-Hua, Pan Sudip
Institute of Atomic and Molecular Physics, Jilin University, Changchun 130023, China.
Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), Jilin University, Changchun 130023, China.
J Chem Phys. 2023 Aug 7;159(5). doi: 10.1063/5.0157339.
Planar hexacoordination (ph) is only rarely reported in the literature. So far, only a few neutral and cationic molecules possessing phE (E = C, Si, B, Al, Ga) in the most stable isomer are predicted theoretically. Present electronic structure calculations report hitherto unknown anionic planar hexcoordinate beryllium and magnesium, phBe/Mg, as the most stable isomer. Global minimum searches show that the lowest energy structure of BeC6M3- (M = Al, Ga) and MgC6M3- (M = Ga, In, Tl) is the D3h symmetric phBe/Mg clusters, where beryllium/magnesium is covalently bonded with six carbon centers and M is located in a bridging position between two carbon centers. These global minimum phBe/Mg clusters are highly kinetically stable against isomerization, facilitating the experimental confirmation by photoelectron spectroscopy. Noteworthy is the fact that the phBe/Mg center is linked with carbon centers through three 7c-2e delocalized σ bonds and three 7c-2e π bonds, making the cluster double aromatic (σ + π) in nature. The bonding between the Be/Mg and outer ring moiety can be best expressed as an electron-sharing σ-bond between the s orbital of Be+/Mg+ and C6M32- followed by three dative interactions involving empty pπ and two in-plane p orbitals of Be/Mg. Furthermore, Lewis basic M centers of the title clusters can be passivated through the complexation with bulky Lewis acid, 9-boratriptycene, lowering the overall reactivity of the cluster, which can eventually open up the possibility of their large-scale syntheses.
平面六配位（ph）在文献中鲜有报道。到目前为止，理论上仅预测出少数几种最稳定异构体中具有phE（E = C、Si、B、Al、Ga）的中性和阳离子分子。目前的电子结构计算报告了迄今未知的阴离子平面六配位铍和镁，即phBe/Mg，为最稳定的异构体。全局最小值搜索表明，BeC6M3-（M = Al、Ga）和MgC6M3-（M = Ga、In、Tl）的最低能量结构是D3h对称的phBe/Mg簇，其中铍/镁与六个碳中心共价键合，M位于两个碳中心之间的桥连位置。这些全局最小值phBe/Mg簇在动力学上对异构化具有高度稳定性，便于通过光电子能谱进行实验验证。值得注意的是，phBe/Mg中心通过三个7c-2e离域σ键和三个7c-2eπ键与碳中心相连，使得该簇在本质上具有双芳香性（σ + π）。Be/Mg与外环部分之间的键合可以最好地表示为Be+/Mg+的s轨道与C6M32-之间的电子共享σ键，随后是涉及Be/Mg的空pπ和两个平面内p轨道的三个配位相互作用。此外，标题簇的路易斯碱性M中心可以通过与大体积路易斯酸9-硼三环辛烷络合而被钝化，降低簇的整体反应性，这最终可能为它们的大规模合成开辟可能性。
