【作者】 张彩云；

【导师】 曹泽星；

【作者基本信息】 厦门大学 ， 物理化学， 2020， 硕士

【摘要】 具有“非经典”成键方式的平面分子由于其特殊的几何构型和电子结构,一直受到关注。1970年,Hoffmann提出的“平面四配位碳”概念,突破了人们对碳四面体成键模式的认知。采用空间限制和电子成键作用相结合的策略,可以获得分子稳定的平面构型,为平面结构分子的设计提供了思路。碳和硅均为第四主族的元素,其形成的化合物分别是有机世界和无机世界的重要组成部分,研究碳硅形成的新型分子结构和成键模式,有助于拓展功能材料的设计与开发。近年来,实验上已成功合成了一系列的平面四配位碳分子,结合广泛的理论计算,丰富了人们对平面四配位碳分子体系的认识。然而,目前对平面四配位硅化学还缺乏了解,有待理论和实验的进一步研究。本文通过密度泛函理论计算,设计并表征了一类新型的平面四配位分子,获得的主要结果如下:(1)通过密度泛函理论计算和动力学模拟,研究了平面四配位硅分子SiN4C8H8(Si-5555)、SiN2C10H10(Si-5656)、SiNC14H11(Si-5666)和SiN2C12H10(Si-4666)等的结构、稳定性及成键特征。这些稳定的平面四配位结构由四元环、五元环及六元环组成,均具有16个π电子。以Si-5555为例,详细地分析了其电子结构性质与稳定性。结果表明,Si-5555分子中心硅采用sp2d杂化与周围四个氮原子形成平面四配位硅结构(ptSi),剩下的3pz-空轨道与周围环上占据的π*反键轨道通过共轭相互作用,导致14个π电子满足休克尔规则。进一步的NICS和ACID计算,证实该分子具有较强的芳香性。此外,我们还研究了 ptSi的亲电和亲核特性,以及Si-5555双分子体系的结构和稳定性。(2)应用密度泛函理论方法,研究了一类新型含平面四配位碳、硅和锗化合物的结构、成键、稳定性和光谱性质。计算表明,这类化合物中含有平面四配位结构单元CB4、SiN4、GeN4、GeB4的分子具有稳定的电子和几何结构。这些稳定体系均存在中心原子与周围4个原子间的共轭π键,其中中心原子C为π电子给体,Si为π电子受体,而Ge可以是π电子受体也可以是给体。对于含平面四配位硅和锗的分子C20H16N4Si和C20H16N4Ge,中心原子采取sp2d杂化方式与周围N原子形成σ键,而由于C原子价层无d轨道且s和p轨道的能级差相对较小,近似采用sp2杂化与周围的B原子形成多中心σ键。(3)Si-5555中心的硅原子具有类卡宾特征,是一种强电子给体和弱电子受体。以Si-5555为单元,构建了其二聚体结构,讨论了其ptSi中心与CO2等小分子间的相互作用。计算表明,ptSi中心对CO2分子的吸附活化展现出非常高的活性,ptSi…CO2间显著的电荷转移相互作用是CO2吸附活化的驱动力。更多还原

【Abstract】 Planar molecules with the non-traditional bonding mode have been receiving considerable attention because of their special geometric and electronic structures.In 1970,Hoffmann put forward the concept of "planar tetracoordinate carbon",which broke through the conventional cognition of tetrahedral structure of carbon.The strategy to combine the spacial constraint and electron bonding interaction can maintain the stable planar structure of molecules,which provides a way for the design of planar tetracoordinate structure.Both carbon and silicon are the elements of the fourth main group,and their compounds are important parts of organic and inorganic worlds,respectively.In recent years,a series of planar tetracoordinate carbon compounds have been successfully synthesized experimentally and investigated theoretically,which enrich the understanding of planar tetracoordinate carbon molecular systems.However,the chemistry of planar tetracoordinate silicon is still unknown,and the further study is highly required,both theoretically and experimentally.In this dissertation,novel molecules containing planar tetracoordinate silicon are designed and characterized,based on extensive theoretical calculations.The main results are summarized as follows:(1)Structures,stabilities and bonding features of planar tetracoordinate silicon molecules SiN4C8H8(Si-5555),SiN2C10H10(Si-5656),SiNC14H11(Si-5666)and SiN2C12H10(Si-4666)were studied by DFT calculations and MD simulations.These stable planar tetracoordinate structures are composed of four membered rings,five membered rings and six membered rings,and they generally have 16 π electrons.Taking Si-5555 as an example,the electronic structure and stability are discussed in detail.The computational results show that the central Si of Si-5555 adopts sp2d hybridization to form planar tetracoordinate structure(ptSi)with its surrounding four nitrogen atoms,and the bonding interaction of the 3pz unoccupied orbital(Si)with the occupied π*orbital on the ring results in the net 14π electrons,which meets the 4n+2 Hückel rule for Si-5555.Further NICS and ACID calculations show that the Si-5555 molecule had strong aromaticity.In addition,we also studied the electrophilic and nucleophilic properties of ptSi,as well as the structure and stability of bimolecular systems of Si-5555.(2)Extensive density functional theory calculations have been used to explore structures,bonding features,stabilities and spectroscopic properties of a new type of molecules with the planar tetracoordinate carbon(ptC),ptSi and ptGc.These compounds with the planar CB4,SiN4,GeN4,and GeB4 moieties are predicted to be stable,both structurally and electronically,according to the structure optimizations and frequency analysis.There is generally a delocalized π bond between the central atom and its surrounding four atoms in such stable planar tetracoordinate compounds,in which C and Si behave as the π donor and acceptor,respectively,while Ge bears the character of both π donor and acceptor.In the compounds of C20H16N4X(X=Si and Ge),ptSi and ptGe adopt sp2d hybridization to form σ bonds with the N atoms.Since there is relatively small s-p energy splitting for C without the d orbital,an approximate sp2 hybridization is responsible for its σ bonding with surrounding B atoms.(3)The planar tetracoordinate silicon SiN4C8H8(Si-5555)has a carbenoid-type amphoteric center,behaving as a strong electron donor and weak electron acceptor.The dimer structure of Si-5555 was constructed,and the adsorption interactions between the ptSi site and CO2 as well as other small molecules were explored by DFT calculations.The present results indicate that the ptSi center shows remarkable activity towards adsorption and activation of CO2,which mainly arises from the significant charge transfer interaction within ptSi…CO2.更多还原