【作者】 孙丽莉；

【导师】 王荣顺；

【作者基本信息】 东北师范大学 ， 物理化学， 2009， 博士

【摘要】 根据IPR规则,富勒烯结构中的五元环要尽可能的分散,以此降低体系的张力能,增强体系的稳定性。C60是能够满足IPR规则的最小碳笼。碳原子数少于60的小富勒烯,和结构中含有除五元环、六元环之外的其他结构(如四元环或七元环)的准富勒烯,由于不满足IPR规则,结构中必然存在较大的张力,因此具有较高的化学活性,难以在实验中合成和分离。因此,对小富勒烯和准富勒烯衍生物的结构、稳定性和物理化学性质等方面进行详细的理论研究,对富勒烯化学的发展具有重要的意义。本论文采用量子化学方法,对C32、C50、C52小富勒烯和C58、C62准富勒烯衍生物进行理论研究,目的是为加深对这些富勒烯衍生物的了解,并为实验研究奠定理论基础、提供有效的信息。本论文的主要研究内容如下:1.采用密度泛函理论B3LYP/6-31G(d)方法,计算D3 C32富勒烯包合H、Li、Na、K、Be、Mg、Ca、B、Al、C、Si、N、P等13种原子和H+、Li+、Na+、K+、Be2+、Mg2+、Ca2+、B3+、Al3+等9种阳离子生成的内嵌衍生物。计算结果表明,包合粒子使D3 C32的体积增大,中性原子对C–C键长的影响大于相应的阳离子。中性富勒烯包合物的热力学稳定性由内嵌原子的电负性决定,与内嵌原子的体积无关。2.采用密度泛函理论B3LYP/6-31G(d)方法,计算D5h C50富勒烯包合H原子,碱金属原子和碱土金属原子生成的内嵌衍生物及其阳离子。计算结果表明氢原子内嵌对D5h C50的影响可以忽略,金属原子内嵌的影响较大。随着化合物上外加正电荷的增加,D5h C50包合Li、Na、K、Mg和Ca系列粒子的衍生物的结构扭曲参数增大,包合Be系列粒子的衍生物的结构扭曲参数减小。D5h C50内嵌衍生物的前线轨道能级主要由所带外加正电荷的大小决定。D3 C50内嵌衍生物的变化规律与D5h C50内嵌衍生物相同。3.依次采用PM3、HCTH/3-21G和B3LYP/6-31G(d)方法计算所有C2-C52H2异构体的相对稳定性。用卤原子取代HCTH/3-21G水平下最稳定的19个C2-C52H2异构体中的氢原子,得到C2-C52X2 (X = F, Cl)的基态候选结构,采用B3LYP/6-31G(d)方法进行计算。结果表明,最稳定的19个C2-C52X2 (X = H, F, Cl)异构体都是热力学稳定的,其中最稳定的5个异构体的加成位置均位于5/5键上。加成反应能够释放C52的结构张力,增强其化学稳定性。加成产物的热力学稳定性由加成基团的种类和加成位置共同决定。C2-C52X2 (X = H, F, Cl)是潜在的实验合成目标。4.采用密度泛函理论B3LYP/6-31G(d)方法,计算3种H2@C58Hn、6种CO@C58Hn和6种LiH@C58Hn (n = 0, 18)准富勒烯内嵌衍生物,并讨论内嵌分子的体积和极性对化合物结构和稳定性的影响。计算结果表明,C58Hn (n = 0, 18)包合非极性H2和弱极性CO是热力学不稳定的,包合强极性LiH是热力学稳定的。在C58Hn (n = 0, 18)中,非极性H2和弱极性CO的取向由内嵌分子与碳笼之间的空间排斥作用决定,强极性LiH分子的取向则由内嵌分子和碳笼之间的偶极–诱导偶极作用决定。5.依次采用AM1、HF/STO-3G、B3LYP/3-21G和B3LYP/6-31G(d)方法计算了所有hept-C62F2异构体的相对稳定性。用氯原子或溴原子取代B3LYP/6-31G(d)水平下最稳定的5个hept-C62F2异构体中的氟原子,得到hept-C62X2 (X = Cl, Br)的基态候选结构,并在相同水平下进行计算。结果表明,最稳定的5个hept-C62X2 (X = F, Cl, Br)加成衍生物都是热力学稳定的,加成反应能够释放hept-C62结构中的张力,增强其化学稳定性。加成位置相同时,加成产物的热力学稳定性随着加成原子体积的增大而降低。hept-C62F2具有很强的热力学稳定性,是潜在的实验合成目标。本论文的研究结果表明,小富勒烯内嵌衍生物的结构和稳定性受到内嵌原子(或分子)的电负性、极性、体积、及碳笼容积等因素的影响。一般而言,内嵌能够改善小富勒烯的电子结构,但不能显著释放小富勒烯结构中的张力,这也是小富勒烯内嵌衍生物难以合成分离的原因。氢/卤素的加成反应能够有效的释放小富勒烯和准富勒烯结构中的张力,增强其化学稳定性,因此其氢/卤化物具有较高的热力学稳定性,是潜在的实验合成目标。更多还原

【Abstract】 Since the discovery and macroscopic scaled synthesis of C60, the fullerenes have aroused tremendous scientific interest because of their novel and unusual physical and chemical properties, and were extensively studied. Geometries and stabilities of fullerenes are governed by the well-known isolated pentagon rule (IPR), and the Ih C60 is the smallest carbon cage fulfilling this rule. The smaller fullerenes C2n (2n < 60) violating IPR, inevitable suffer large strain energies and show high lability. Besides that, quasi-fullerenes violating the classical definition, contain rings of other size, for example 4 or 7, are expected to suffer extra local strain or/and further loss ofπdelocalization, and thus highly unstable. Most of smaller fullerenes and quasi-fullerenes are not experimentally approachable at present, and therefore, theoretical studies are significant for investigating their structures, stabilities and properties. In this thesis, derivatives of smaller fullerenes and quasi-fullerenes have been studied by quantum chemical method. The main results are summarized as follows.1. The endohedral complexes formed by D3 C32 and 13 atoms ranging fromⅠA toⅤA, including H, Li, Na, K, Be, Mg, Ca, B, Al, C, Si, N, and P, as well as 9 cations ranging fromⅠA toⅢA, including H+, Li+, Na+, K+, Be2+, Mg2+, Ca2+, B3+, and Al3+, were theoretically investigated using density functional theory at the B3LYP/6-31G(d) level. Theoretical studies reveal that size of all endohedral fullerenes is slightly enlarged due to encapsulation, and cage containing atom is larger than the cage containing corresponding cation. Thermodynamic stability of neutral endohedral complex is determined by electronegativity of the guest atom, and only Li, Na, and Ca atoms can be stably put into the cage.2. The endohedral complexes formed by D5h C50 and H, alkali metals, and alkaline-earth metals, as well as charged states of the endohedral complexes, were theoretically investigated using B3LYP/6-31G(d) method. Theoretical studies reveal that the encapsulated H hardly affects the D5h C50, but the encapsulated metals significantly distort the cage. As the extra charges on the complexes increase, the structural distortions decrease for Li, Na, K, Mg, Ca series derivatives, but increase for Be series derivatives. Both EHOMO and ELUMO of complexes are determined by the number of extra charges on them. The D3 endohedral complexes are found to change in the same way as the D5h isomers.3. PM3, HCTH/3-21G, and B3LYP/6-31G(d) methods were orderly used for searching the most stable C2-C52H2 isomer. C2-C52X2 (X = F and Cl) isomers being isostructural with the first 19 most stable C2-C52H2 isomers were considered as candidates of the most stable one, and optimized at the B3LYP/6-31G(d) level. Theoretical studies reveal that the first 19 most stable C2-C52X2 (X = H, F, and Cl) isomers are energetically favorable, and the attaching sites of the first 5 most stable isomers all locate the pentagon-pentagon fusions of C2-C52. The additional reactions release the strain energy of C2-C52, and enhance its chemical stability. Relative stability of C2-C52X2 (X = H, F, and Cl) isomers is determined by both attaching sites and properties of addends. The C2-C52X2 (X = H, F, and Cl) complexes are potential targets in experiments. 4. To investigate the influence of size and polarity of endohedral molecules on fullerene derivatives, three H2@C58Hn, six CO@C58Hn and six LiH@C58Hn (n = 0, 18) complexes were optimized using density functional theory at the B3LYP/6-31G(d) level. The results show that C58Hn (n = 0, 18) cages destabilize nonpolar H2 and weakly polar CO, and stabilize strongly polar LiH. For cage encapsulating H2 or CO, size of endohedral molecule is the main factor determining its orientation inside the cages. Orientation of LiH inside C58Hn (n = 0, 18) cages is determined by the dipole-induced dipole attractive interaction between them, which is especially significant in LiH@C58H18 complexes.5. AM1, HF/STO-3G, B3LYP/3-21G, and B3LYP/6-31G(d) methods were employed orderly to search the most stable hept-C62F2 isomer. The hept-C62X2 (X = Cl and Br) isomers, which are isostructural with the first 5 most stable hept-C62F2 isomers, were chosed as candidates of the most stable one, and optimized at the B3LYP/6-31G(d) level. From the results of the first 5 most stable hept-C62X2 (X = F, Cl, and Br) isomers, it is found that halogenations release the strain energy of hept-C62, and enhance its chemical stability. All 5 most stable hept-C62X2 (X = F, Cl, and Br) halogenated complexes are energetically favorable, and their thermodynamic stability decreases following with the increase of size of addends. The hept-C62F2 complexes are potential targets in experiments with high thermodynamic stability.In all, theoretical investigations in the thesis reveal that structures and stabilities of endohedral complexes of smaller fullerenes are influenced by factors such as electronegativity, polarity, size of endohedral spcies, and capability of fullerenes. The encapsulation usually can enhance the electronic structures of smaller fullerenes, but cannot release their strain energies effectively. That is the reason why experimental isolation for the endohedral complexes of smaller fullerenes is difficult. However, additional reactions of H2/halogens can significantly release the strain energies of smaller fullerenes and quasi-fullerenes, and enhance their chemical stability. Therefore, the corresponding hydrofullerenes and halofullerenes show high thermodynamic stability, and are potential targets in experiments.更多还原