【作者】 贺海鹏；

【导师】 丁益宏；

【作者基本信息】 吉林大学 ， 物理化学， 2009， 博士

【摘要】 本文利用量子化学计算方法对包含五原子平面四配位碳分子、基于杂原子取代的平面分子、基于平面四配位分子的夹心组装及其稳定化等几类重要平面分子结构和稳定性做了详细的理论研究。在总结前人大量实验和理论工作的基础上。首次系统的考虑了配体为Al、Ga、Si、Ge的平面碳分子稳定体热力学及动力学稳定性;此外我们率先研究了以高周期元素Si、Ge、Sn、Pb为中心的非碳中心平面分子的稳定性;在我们以前大量的杂夹板计算基础上,首次计算了非碳中心的平面分子的杂夹板夹心组装及其稳定化的理论研究。我们将平面化学的概念进行了创新性的理解和发展,不仅将配体的从传统的Al、Si原子拓展到Ga、Ge,还将中心原子从C原子的发展到更高周期的Si、Ge、Sn、Pb原子,系统的研究了这一类分子的平面稳定性。我们的研究工作大大的丰富了平面化合物的概念,并且将其应用领域极大的推广。这为实验上设计和合成具有特殊结构和奇特性质的新型平面分子提供了有益的指导。最终为气相原子簇单元通向分子材料的应用奠定了理论基础。本文的主要成果包括以下几个方面:（1）利用B3LYP和CCSD（T）（单点）方法,首次研究了含Si、Ge、Sn、Pb的六原子体系[MAl₅]⁺中各个异构体的结构及稳定性。结果表明,尽管与[CAl₅]⁺一样也具有18个价电子,[MAl₅]⁺ （M=Si、Ge、Sn、Pb）体系并不存在具有平面五配位结构的异构体,其能量的全局极小点为具有Cs对称性的蝶形异构体int1,这是由于中心原子M （Si、Ge、Sn、Pb）较大的体积显著破坏了[MAl₅]⁺中平面五配位结构的稳定性。（2）在B3LYP计算水平下,使用混合基组6-311+G（d）&LANl2dz首次对含Sn、Pb的五原子平面四配位碳分子[CAl₃X]和[CAl₃X]^- （X=Sn,Pb）两个体系（分别具有17和18价电子）的异构体结构及能量进行了量子化学计算研究,并与文献已经报道的[CAl₃X]和[CAl₃X]^- （X=Si、Ge）作了比较。结果表明,具有平面四配位碳结构的异构体int1是能量的全局最小点。相对于17e的[CAl₃X]体系来说,在得到一个电子以后形成18e的[CAl₃X]^- int1异构体在热力学上变得更稳定。本项研究将进一步丰富五原子平面四配位碳化学。（3）五原子的平面四配位碳分子的理论及实验研究是当今分子科学的热点问题之一。首次对含Si的pptC单元CAl₂Si₂首次开展了夹心组装的理论研究。我们发现,当CAl₂Si₂与碱金属及碱土金属（M=Li,Na,K,Be,Mg,Ca）组装成夹心化合物时,由于CAl₂Si₂之间强烈的熔合作用,不能采取传统的“同夹板夹心”方式,即[（CAl₂Si₂）M（CAl₂Si₂）]^q+,而我们近期提出的组装形式——“杂夹板夹心”([CpM （CAl₂Si₂）] ^q+)更适合CAl₂Si₂的组装。“杂夹板夹心”组装方案和离子性相互作用对于CAl₂Si₂的组装和稳定化起着重要作用。在组装的过程中,CAl₂Si₂的电子和结构特征得到很好的保持。因此,平面四配位碳单元CAl₂Si₂可以作为“建筑单元”来构建大尺寸含平面中心碳的化合物。更多还原

【Abstract】 It is fascinating to see and to understand the chemical structure of molecules. The chemical structure is a consequence not only of their constituent elements but also of the way those atoms are connected to each other, and what their special arrangement is. Any change in the spatial distribution of the nuclei will modify the nature of the chemical bond and vice versa.That the tetracoordinate tetravalent carbon atom prefers a tetrahedral arrangement of its four ligands was first recognized independently by J. H. van’t Hoff and J. A. LeBel in 1874. This contribution marks a milestone in understanding the structure and sterochemistry of carbon compounds. Almost a century after the publication of the van’t Hoff-LeBel model, Hoffmann et al. suggested rules to stabilize molecules containing a planar tetracoordinate carbon （ptC） atom in 1970, challenging the second structural foundation of Organic Chemistry. There are two approaches, to achieving this goal. The electronic approach involves selecting substituents that preferentially stabilize a planar disposition of the carbon bonds over the normal tetrahedral arrangement. The alternative approach is based on using mechanical molecular strain forces exerted by the surrounding ligands to the carbon atom. Inspired on Hoffmann’s ideas, several groups have successfully suggested and experimentally characterized molecules containing ptCs. The main results are summarized as follows:（1）Very recently, theoretical chemists have found that the hexa-atomic system [CAl₅]⁺ has a planar pentacoordinate carbon structure as the most stable form. In this paper, we attempt to further such topic. By means of the B3LYP and CCSD（T） （single-point） methods, we for the first time investigate the isomeric structures and thermodynamic stability of four hexa-atomic systems [MAl₅]⁺ （M=Si,Ge,Sn,Pb）. The results show that although bearing the same 18-valence electrons as [CAl₅]⁺,all the [MAl₅]⁺ （M=Si, Ge, Sn, Pb） systems do not have a planar pentacoordinate M isomer. Instead, the global structure is a Cs-symmetrized butterfly isomer int1.This can be rationalized that the bulkier central atom M （Si, Ge, Sn, Pb） than C has significantly destructed the stability of the planar pentacoordinate structure of [MAl₅]⁺.（2）The isomeric structures and energetics of two Sn,Pb-containing penta-atomic planar tetracoordinate carbon molecules [CAl₃X] and [CAl₃X]^- （X=Sn, Pb） （with 17 and 18 valence electrons, respectively） were studied by using the B3LYP method combined with the mixed basis set 6-311+G（d）&LANl2dz for the first time. The results were compared with the previously reported [CAl₃X] and [CAl₃X]^- （X=Si, Ge）. It was shown that the isomer int1 with the planar tetracoordinate carbon structure was the global minimum point. Relative to the 17e system [CAl₃X], achieving an additional electron to form the 18e system [CAl₃X]^- int1 becomes thermodynamically more stable. The present work would enrich the penta-atomic planar tetracoordinae carbon chemistry.（3）One of the focuses of molecular science is the theoretical and experimental investigations on the pentatomtic planar coordinated carbon （ptC） molecules. This paper for the first time reported the design of sandwich-like compounds based on a Si-containing ptC unit CAl₂Si₂. We found that due to the strong fusion interaction between CAl₂Si₂ decks, the assembly of CAl₂Si₂ with the alkali and alkaline earth metals（M=Li,Na, K, Be ,Mg,Ca）in form of the traditional“homo-deckered sandwich”scheme to form [（CAl₂Si₂）M（CAl₂Si₂）]^q+ is unstable. Instead, our recently proposed“hetero-decked sandwich”scheme can be effectively applied to CAl₂Si₂ to form [CpM （CAl₂Si₂）]^q+). Both the“hetero-decked sandwich”and the ionic interaction play important roles in the assembly and stabilization of CAl₂Si₂. During the assembly, the electronic and structural features of CAl₂Si₂ are well kept。Thus, the ptC molecule CAl₂Si₂ can act as a“building block”to construct large-scale compounds that contain planar coordinated carbon centers.更多还原