碱土金属Be_(n)(n=1~3)对B_(12)团簇结构的调控研究

Study on the Regulation of Alkali-earth Metal Be_(n)(n=1~3) on the Structure of B_(12) Clusters

基于第一性原理,系统地研究了Be_(n)(n=1~3)对B_(12)团簇结构的调控.结果表明:团簇BeB_(12)全局极小结构为Cs对称性准平面结构,而Be_(2)B_(12)和Be_(3)B_(12)最稳定的结构均为笼状结构,对称性分别为Cs和C_(2v).随着Ben(n=1~3)原子数的增加,团簇B_(12)由准平面结构过渡到笼状结构,且Be倾向内嵌在B_(12)笼状结构表面的B_(7)或B8单元环中,通过离子和共价作用形成稳定Be&B_(7)和Be&B8单元,从而稳定笼状结构.自然键轨道(NBO)分析表明,团簇Cs BeB_(12),Cs Be_(2)B_(12),C_(2v) Be_(3)B_(12)内部存在电子转移情况,Be原子2s轨道上失去电子,Be-B键主要以离子作用为主,同时也存在共价作用.成键分析显示Cs Be_(2)B_(12)和C_(2v) Be_(3)B_(12)的π键遵循球状芳香性2(n+1)^(2)(n=1)电子计数规则,表明该团簇具有球状芳香性.预测了三个结构的红外和拉曼光谱,为以后的合成实验和数据表征提供了理论基础.

Based on first-principles, we systematically study the regulation of Ben (n=1~3) on the structure of B_(12) clusters. For all the low energy isomers of BenB_(12) (n=1~3) searched at the PBE/DZVP level, we further use PBE0 and TPSSh methods to calculate their relative energy and select the most optimal structure, and then calculate its single point energy at CCSD(T)/6-311+G(d). The results show that the global minimum structure of BeB_(12) is quasi-planar and has Cs symmetry at the CCSD(T)/6-311+G(d) level. However, the most stable structures of Be_(2)B_(12) and Be_(3)B_(12) are cage-like structures, and their symmetries are Cs and C_(2v), respectively. Subsequently, with the increase of the number of Be atoms, B_(12) has a dramatic transition from quasi-planar structure to cage-like structure, and Be atoms tend to be embedded in the B_(7) or B8 unit ring on the surface of the cage-like structure of B_(12), forming stable Be&B_(7) and Be&B8 units through ionic and covalent interaction to stabilize the cage-like structure. Furthermore, at 400 K, Cs BeB_(12) and Cs Be_(2)B_(12) are kinetically stable, while some low-energy isomers of C_(2v) Be_(3)B_(12) can rheology each other. The natural bond orbital (NBO) analysis shows that the clusters Cs BeB_(12), Cs Be_(2)B_(12), and C_(2v) Be_(3)B_(12) have obvious electron transfer, and the 2s orbital of Be atom loses electrons. And the Be—B bonds are mainly ionic, covalent bonds exist at the same time. Adaptive natural density partitioning (AdNDP) reveals the bonding pattern of BenB_(12) (n=1~3), and we find that both the σ bonds and the multicenter π bonds promote the stability of the whole molecule. The results indicate that the π bonds of Cs BeB_(12) conform to the Hückel (4n+2) rule and is aromatic, while the π bonds of Cs Be_(2)B_(12), and C_(2v) Be_(3)B_(12) follow the spherical aromatic 2(n+1)^(2) (n=1) electron counting rule, with spherical aromaticity. In addition, we also predict the infrared and Raman spectra of the three structures in this text, which will provide theoretical basis for the experimentally synthesis and characterization of these structures in the future.