【作者】 陈晨；

【导师】 崔中华；

【作者基本信息】 吉林大学 ， 原子与分子物理， 2022， 硕士

【摘要】 由于具有奇特的几何和成键方式,平面超配位分子是一类典型的非经典、反常规分子体系,尤其是近年来发现的潜在的物理化学特性使其受到广泛关注。经典的四配位饱和碳原子是立面体构型,然而在1970年,霍夫曼等人提出了针对于平面四配位碳（pt C）的电子稳定化策略,随后的几年里在理论上设计出基态的一些pt C分子。到目前为止,大量的具有高稳定性的pt C分子被理论设计,气相观测以及实验合成,突破了碳原子的成键能力并推动了人们对平面超配位分子的认知。碳原子的平面超配位研究激发了人们对于其他主族以及过渡金属平面超配位的探索和兴趣,尤其是高周期14主族原子（硅,锗等）。相对于丰富的平面超配位碳分子,其重主族原子的类似物是非常稀少的,尤其是高配位（五和六配位）体系的设计是非常具有挑战性的。本文基于对已报道的平面分子电子结构的理解结合高效的结构搜索程序,获得了几个平面六配位硅和锗分子,为突破传统分子几何和电子结构的认知提供重要的理论线索。本论文的具体研究内容如下:1.孤立的和配体保护的平面六配位硅分子的理论设计平面六配位分子体系是非常稀少的几何和电子结构,尤其是在主族原子体系中。本工作利用高效的结构搜索软件进行结构预测并在高精度水平进行结构优化和能量计算,发现了Si Sb₃M₃⁺（M=Ca,Sr,Ba）体系中平面六配位硅（ph Si）分子是全局极小值,且具有高D_3h（¹A₁（?））对称性。另外,通过动力学模拟发现其具有良好的动力学稳定性。电子结构分析表明:Si Sb₃M₃⁺（M=Ca,Sr,Ba）不仅是平面六配位硅分子,而且中心原子Si和配体原子间具有奇异的成键方式,即Si-Sb具有多重键特性,而Si-M（M=Ca,Sr,Ba）之间除了有良好的静电吸引还有M原子d轨道贡献。这是一种有趣的重碱土金属类比过渡金属成键行为。更重要的是,我们发现利用N-杂环卡宾（NHC）和苯（Bz）等配体保护的办法能够很好的保持平面六配位特性,这使得孤立的Si Sb₃M₃⁺和配体保护的Si Sb₃M₃⁺团簇均可以作为气相检测和大规模合成的候选簇。2.平面六配位硅和锗的设计和电子结构的理论研究通过系统的势能面搜索和高水平的耦合簇方法CCSD（T）能量确认,我们发现20个价电子的XBe₆Au₆²⁺（X=Si,Ge）团簇的全局极小值为平面六配位硅和锗（ph Si,ph Ge）原子。这类平面六配位分子具有D_6h对称性的“六芒星”形结构,且具有高的动力学稳定性。电子结构分析表明:双重的2π+6σ芳香性是稳定ph Si和ph Ge的重要驱动力,同时平面Si和Ge中心和周围Be₆Au₆配体环最优的尺寸匹配为其平面性实现提供了重要的几何结构因素。同时,在此类ph Si和ph Ge体系中,中心原子和配体间具有良好的共价和离子键特性,是目前报道的平面六配位主族体系中少有的成键方式,极大的丰富了平面超配位分子。更多还原

【Abstract】 Due to their peculiar geometry and bonding,planar hyper-coordinate molecules are typical class of non-classical,unconventional molecular systems,especially the potential physicochemical properties discovered in recent years have attracted widespread attention.The classical tetracoordinated saturated carbon atom is the elevation configuration,however,in 1970,Hoffman et al.proposed an electron stabilization strategy for planar tetracoordinate carbon（pt C）and theoretically designed ground-state pt C molecules in the following years.So far,a large number of highly stable pt C molecules have been theoretically designed,gas-phase observations and experimental synthesis,which has greatly promoted the bonding ability of carbon atoms and people’s understanding of planar hyper-coordinated molecules.The study of planar hyper-coordination of carbon atoms has stimulated the exploration and interest of other principal families and transition metal plane hyper-coordination,especially heavier 14principal group atoms（silicon,germanium,etc.）.Analogues of heavy host atoms are very rare relative to the abundance of planar hyper-coordinated carbon molecules,especially the design of high coordination（penta-and hexa-coordination）systems is very challenging.Through the understanding of the reported electronic structure of planar molecules,as well as the efficient structure search procedure,several planar hexacoordinate silicon and germanium molecules are obtained,which provides important theoretical clues for the cognition and understanding of breaking through the traditional molecular geometry and electronic structure.The main contents of this paper are as follows:1.Theoretical design of isolated and ligand-protected planar hexa-coordinated silicon moleculesPlanar hexa-coordinated molecular systems are very rare geometric and electronic structures,especially in principal group atomic systems.Through efficient structural search and high level of energy confirmation,it was found that the planar hexa-coordinated silicon（ph Si）molecule in the Si Sb₃M₃⁺（M=Ca,Sr,Ba）system is a global minimum value and has a high D_3h（¹A₁（?））symmetry.In addition,it was found to have good dynamic stability through dynamic simulation.Electron structure analysis shows that Si Sb₃M₃⁺（M=Ca,Sr,Ba）is not only a well-defined planar hexa-coordinated silicon molecule,but also has a strange bonding method between the central atom Si and the ligand atom,that is,Si-Sb has multiple bonding characteristics,and Si-M（M=Ca,Sr,Ba）has a good electrostatic attraction between M-M and M atomic d orbital contribution.This is an interesting heavy alkaline earth metal analogy transition metal bonding behavior.More importantly,we found that the use of ligand-protected methods such as N-heterocyclic carbine（NHC）and benzene（Bz）can maintain the planar six coordination characteristics very well,which makes the isolated Si Sb₃M₃⁺and ligand-protected Si Sb₃M₃⁺clusters can be used as candidate clusters for gas phase detection and large-scale synthesis.2.Design and electronic structure of planar hexa-coordinated silicon and germanium.Through the systematic potential energy surface search and the high-level coupling cluster method CCSD（T）energy confirmation,we found that the global minimum values of the XBe₆Au₆²⁺（X=Si,Ge）cluster of 20 valence electrons are planar hexa-coordinated silicon and germanium（ph Si,ph Ge）atoms.This type of planar hexa-coordinated molecule has a high,D_6h symmetry"hexacoordinate"shaped structure,and has a high dynamic stability.Electron structure analysis shows that dual2π+6σaromaticity is an important driving force for stabilizing ph Si and ph Ge,while the optimal size matching of the center of the plane Si and Ge and the surrounding Be₆Au₆ ligand ring provides an important geometric factor for its flatness realization.At the same time,in such ph Si and ph Ge systems,the central atoms and ligands have good covalent and ionic bonding characteristics,which is a rare bonding method in the currently reported planar hexa-coordinated master family system,which greatly enriches the bonding method in the geometry and electronic structure of planar hexa-coordinated molecules.更多还原