碳碳键链接的二维共价有机框架研究进展

二维共价有机框架(Two-dimensional Covalent-Organic Frameworks, 2D COFs)是指一类由π-共轭构筑单元通过共价键连接形成的具有二维拓扑结构的晶态多孔材料.由于其独特的周期性多孔结构、高比表面积、优异的稳定性等特点在离子传输、光电材料、催化等领域展现出了巨大的应用潜力.其中,碳碳键链接的共价有机框架因兼具优异的稳定性和良好的结晶性,被认为是最具有前景的二维聚合物材料之一.近年来,基于不同的设计原则和合成策略涌现出了许多具有不同结构和优异性能的碳碳键链接共价有机框架.在这篇综述中,按照构筑单元的拓扑结构对碳碳键链接共价有机框架进行分类,并归纳总结了迄今为止C=C和C—C键链接的二维共价有机框架在合成方法、结构创新、性能提升以及实际应用领域的研究进展.该综述旨在为相关领域的研究人员更好地设计和合成具有多种功能的多孔结晶材料提供参考,从而促进碳碳键链接共价有机框架材料在光电领域的进一步发展和应用.     

镱硫属化合物的密度泛函理论研究

用密度泛函理论(DFT)研究镱硫属化合物的电子结构和性质,通过与实验比较考察了现有的几种近似密度泛函公式对镧系元素化合物的适用程度和相对论效应的影响.结果表明,用DFT计算的YbO键长对实验值的偏差约为0.002nm;但得到的键能即使在考虑梯度校正和相对论效应之后,仍比实验值高,在定域密度近似基础上引入交换梯度校正使键能计算值减小,其中PW86x使键能计算值减小稍多些,结果更接近实验值;相关梯度校正使键能计算值升高.相对论效应使键长缩短0.004～0.006nm,键能减小约0.5eV.计算结果的分析表明,Yb的5d轨道和配体的np轨道间形成σ键和π键.在所研究的分子体系中,配体原子从O到Te、Yb原子的5d轨道布后数依次减少,同键能减弱的顺序一致.相对论效应使键能减小的主要原因是在成键过程中发生了Yb的6s电子向5d轨道的转移,而相对论效应使该过程能量增加.偶极矩和电荷分布的计算表明,Yb-L键以共价性为主,相对论效应使共价性成份增加.     

键电荷与键共价性之间的关系研究(英文)

用一种半经验方法研究了固体材料中键电荷与键共价性的关系．这一理论方法是Ｐｈｉｌｉｐｓ，ＶａｎＶｅｃｈｔｅｎ，Ｌｅｖｉｎｅ，及Ｔａｎａｋａ等人提出的介电描述理论的推广．通过对一个例子ＲＭｎ２Ｏ５（Ｒ＝Ｌａ，Ｐｒ，Ｎｄ，Ｓｍ，Ｅｕ）的研究发现，键电荷越多，所产生的键共价性越大，与成键区域的电荷是键共价性形成的原因这一结论一致     

固态Nd化合物f-f跃迁的光声光谱研究

通过光声光谱对固态 Nd化合物的 f -f跃迁进行了研究。根据 Nd F3、Nd(sal) 3· H2 O和 Nd(sal) 3(phen) 2 的谱峰位置 ,计算了它们的电子云重排参数β、键合参数 b1/2 和 Sinha共价参数δ,表明三元配合物中钕离子形成键的共价程度最高 ,而 Nd F3中键的共价性最弱。通过光声支量表征了不同化合物中 Nd3+ 的 f -f跃迁光声强度的变化 ,证实了随着键的共价程度增加和配位数的增大 ,超灵敏跃迁强度显著增大     

第一性原理计算钛酸铅A位掺杂对其负热膨胀性的影响

近年来,实验发现钛酸铅基材料具有负热膨胀性,且其热膨胀程度会受到掺杂元素的影响.目前所研究的A位掺杂体系中,仅Cd原子掺杂能使钛酸铅负热膨胀性增强.所以研究A位掺杂钛酸铅,比较Cd原子与其他原子在掺杂钛酸铅时化学键的异同,有助于深刻理解钛酸铅负热膨胀的本质.本文利用第一性原理,分别优化了Sr、Ba、Cd掺杂钛酸铅的晶格常数,计算了它们的态密度和电荷密度.结果表明Cd―O键的共价性强于Pb―O键,而Ba―O键和Sr―O键几乎呈离子性,Ba/Sr对Pb的替代削弱了化合物的共价性,降低了自发极化强度.与实验测量的热膨胀系数对比可以发现,A位原子与氧原子之间的共价性增强,化合物负热膨胀程度升高;若A位原子与氧原子之间的共价性削弱,负热膨胀程度降低.可见A位原子与氧原子之间的共价性影响了钛酸铅基化合物负热膨胀性.     

第一性原理计算钛酸铅A位掺杂对其负热膨胀性的影响

近年来,实验发现钛酸铅基材料具有负热膨胀性,且其热膨胀程度会受到掺杂元素的影响. 目前所研究的A位掺杂体系中,仅Cd原子掺杂能使钛酸铅负热膨胀性增强. 所以研究A位掺杂钛酸铅,比较Cd原子与其他原子在掺杂钛酸铅时化学键的异同,有助于深刻理解钛酸铅负热膨胀的本质. 本文利用第一性原理,分别优化了Sr、Ba、Cd掺杂钛酸铅的晶格常数,计算了它们的态密度和电荷密度. 结果表明Cd―O键的共价性强于Pb―O键,而Ba―O键和Sr―O键几乎呈离子性,Ba/Sr对Pb的替代削弱了化合物的共价性,降低了自发极化强度. 与实验测量的热膨胀系数对比可以发现,A位原子与氧原子之间的共价性增强,化合物负热膨胀程度升高;若A位原子与氧原子之间的共价性削弱,负热膨胀程度降低. 可见A位原子与氧原子之间的共价性影响了钛酸铅基化合物负热膨胀性.     

f-类元素的有机衍生物——f-轨道成键及前景的探讨

本文就 f-类元素有机金属化学的进展叙述了对 f-轨道参与成键的长期探索过程。镧系有机化合物的可见光谱及磁性能的研究已表明,在镧系元素——碳σ键中似乎有比π键更大的共价性特征。最近的 ESCA(electronic spectrog-     

不饱和度·键数·C60多面体·数列--通过试题所给予的信息进行综合运用知识能力的培养

在学生已有的知识背景中 ,在学生已有的解题技能的基础上 ,综合利用有机试题所提供的信息 ,对其进行化学科内知识综合运用能力和跨学科知识的综合应用能力的提高训练 ,能增强其自学能力和提高其思维品质。　　题 1、2给予信息　不饱和度———有机化合物分子以烷烃组成作为参照标准来衡量其不饱和程度 ,每减少 2个氢原子就增加 1个不饱和度 ,常用Ω表示。烃ＣｎＨｍ其Ω =[(2ｎ +2 ) -ｍ]/ 2。键数———在粗略分析分子中原子间的共价结合方式时 ,键数指共价键的数目 ,此时不管 2原子是以共价单、双、叁键结合 ,键数均为 1,如 1个碳碳单键或…     

铍的夹心和半夹心化合物中铍原子的共价

用DV-XαSCC方法和自然键轨道法研究了CpBeH和Cp2Be的电子结构和成键情况,进而根据作者之一提出的共价定义研究了CpBeX(X=H, Cl, Br, CH3, C≡CH, ...)和Cp2Be等化合物中铍原子的共价。结果表明, 在这些化合物中, 铍原子的共价均为6。     

铍的夹心和半夹心化合物中铍原子的共价

用DV-XαSCC方法和自然键轨道法研究了CpBeH和Cp_2Be的电子结构和成键情况,进而根据作者之一提出的共价定义研究了CpBeX(X=H,Cl,Br,CH_3,C≡CH,……)和Cp_2Be等化合物中铍原子的共价.结果表明,在这些化合物中,铍原子的共价均为6.     

键能的分子轨道理论研究 1: 理论公式

从LCAO-MO出发, 给出了一个计算键能的近似方法, 即EAB(i)-∑∑CaiSabCbiεi为第i个占据分子轨道(MO)中的一对电子对A-B键键能的贡献。对所有分子轨道求和即为该键的键能: EAB=∑EAB(i)。按该方法, 不仅可以计算各种不同分子中每两个相键连原子间的键能, 还可以从MO及AO角度分析每一具体键, 如σ, π, δ键的键能以及各AO对键能的贡献。该方法虽有别于求键焓和平衡离解能De, 但计算结果和De的实验值甚相符合。通过对键能的分析研究, 能较好地揭示原子间的相互作用关系及化学键的强弱, 从而可进一步探讨化学反应活性, 反应速率等化学性质。     

Exploring the actinide-actinide bond: theoretical studies of the chemical bond in Ac2, Th2, Pa2, and U2

Multiconfigurational quantum chemical methods (CASSCF/CASPT2) have been used to study the chemical bond in the actinide diatoms Ac2, Th2, Pa2, and U2. Scalar relativistic effects and spin-orbit coupling have been included in the calculations. In the Ac2 and Th2 diatoms the atomic 6d, 7s, and 7p orbitals are the significant contributors to the bond, while for the two heavier diatoms, the 5f orbitals become increasingly important. Ac2 is characterized by a double bond with a 3Sigmag-(0g+) ground state, a bond distance of 3.64. A, and a bond energy of 1.19 eV. Th2 has quadruple bond character with a 3Dg(1g) ground state. The bond distance is 2.76 A and the bond energy (D0) 3.28 eV. Pa2 is characterized by a quintuple bond with a 3Sigmag-(0g+) ground state. The bond distance is 2.37 A and the bond energy 4.00 eV. The uranium diatom has also a quintuple bond with a 7Og (8g) ground state, a bond distance of 2.43 A, and a bond energy of 1.15 eV. It is concluded that the strongest bound actinide diatom is Pa2, characterized by a well-developed quintuple bond.     

IR spectral and quantum-chemical studies of binary extractants

The composition and ionic character of formation of binary extractants based on quaternary ammonium bases and organic acids were confirmed using spectral and quantum-chemical methods, the structures of the binary extractants were obtained. The energy of bond between cation and anion in molecules of the binary extractants was determined, it is by an order of magnitude higher than the energy of H bond and close to the energy of chemical (ionic) bond.     

Laplacian of the Hamiltonian Kinetic Energy Density as an Indicator of Binding and Weak Interactions

The kinetic energy is the center of a controversy between two opposite points of view about its role in the formation of a chemical bond. One school states that a lowering of the kinetic energy associated with electron delocalization is the key stabilization mechanism of covalent bonding. In contrast, the opposite school holds that a chemical bond is formed by a decrease in the potential energy due to a concentration of electron density within the binding region. In this work, a topographic analysis of the Hamiltonian Kinetic Energy Density (KED) and its laplacian is presented to gain more insight into the role of the kinetic energy within chemical interactions. This study is focused on atoms, diatomic and organic molecules, along with their dimers. In addition, it is shown that the laplacian of the Hamiltonian KED exhibits a shell structure in atoms and that their outermost shell merge when a molecule is formed. A covalent bond is characterized by a concentration of kinetic energy, potential energy and electron densities along the internuclear axis, whereas a charge-shift bond is characterized by a fusion of external concentration shells and a depletion in the bonding region. In the case of weak intermolecular interactions, the external shell of the molecules merge into each other resulting in an intermolecular surface comparable to that obtained by the Non-covalent interaction (NCI) analysis.     

EELS nanoanalysis for investigating both chemical composition and bonding of interlayers in composites

The paper is concerned with the application of analytical transmission electron microscopy (TEM) to characterize both chemical composition and bond state of the elements detected in interlayers in C- and SiC-fibre reinforced composites. The chemical bond state of nanometre-sized regions is characterized by means of electron energy loss spectroscopy (EELS), where respective information is gained by analysing energy loss near edge structures (ELNES). In this context results of Si-L₂₃ ELNES investigations are presented concerning the chemical bonding of silicon with carbon, nitrogen and oxygen. The specific bond state of silicon is revealed by recording series of EEL spectra at high energy resolution across the fibre/ matrix interlayers of interest. Moreover, the element distribution is imaged by energy-filtered TEM.Dedicated to Professor Dr. rer.nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Computational analyses of singlet-singlet and singlet-triplet transitions in mononuclear gold-capped carbon-rich conjugated complexes

Density functional theory and CASSCF calculations have been used to determine equilibrium geometries and vibrational frequencies of metal-capped one-dimensional pi-conjugated complexes (H3P)Au(C[triple chemical bond]C)(n)(Ph) (n = 1-6), (H3P)Au(C[triple chemical bond]CC6H4)(C[triple chemical bond]CPh), and H3P--Au(C[triple chemical bond]CC6H4)C[triple chemical bond]CAu--PH3 in their ground states and selected low-lying pi(pi)* excited states. Vertical excitation energies for spin-allowed singlet-singlet and spin-forbidden singlet-triplet transitions determined by the time-dependent density functional theory show good agreement with available experimental observations. Calculations indicate that the lowest energy 3(pi(pi)*) excited state is unlikely populated by the direct electronic excitation, while the low-lying singlet and triplet states, slightly higher in energy than the lowest triplet state, are easily accessible by the excitation light used in experiments. A series of radiationless transitions among related excited states yield the lowest 3(pi(pi)*) state, which has enough long lifetimes to exhibit its photochemical reactivities.     

Quantum chemistry aspects of the solvent effects on the ene reaction of 1‐Phenyl‐1,3,4‐triazolin‐2,5‐dione and 2‐methyl‐2‐butene

A density functional theory study was used to investigate the quantum aspects of the solvent effects on the kinetic and mechanism of the ene reaction of 1‐phenyl‐1,3,4‐triazolin‐2,5‐dione and 2‐methyl‐2‐butene. Using the B3LYP/6–311++ G(d,p) level of the theory, reaction rates have been calculated in the various solvents and good agreement with the experimental data has been obtained. Natural bond orbital analysis has been applied to calculate the stabilization energy of N18? H19 bond during the reaction. Topological analysis of quantum theory of atom in molecule (QTAIM) studies for the electron charge density in the bond critical point (BCP) of N18? H19 bond of the transition states (TSs) in different solvents shows a linear correlation with the interaction energy. It is also seen form the QTAIM analysis that increase in the electron density in the BCP of N18? H19, raises the corresponding vibrational frequency. Average calculated ratio of 0.37 for kinetic energy density to local potential energy density at the BCPs as functions of N18? H19 bond length in different media confirmed covalent nature of this bond. Using the concepts of the global electrophilicity index, chemical hardness and electronic chemical potentials, some correlations with the rate constants and interaction energy have been established. Mechanism and kinetic studies on 1‐phenyl‐1,3,4‐triazolin‐2,5‐dione and 2‐methyl‐2‐butene ene reaction suggests that the reaction rate will boost with interaction energy enhancement. Interaction energy of the TS depends on the solvent nature and is directly related to electron density of the bonds involved in the reaction proceeding, global electrophilicity index and electronic chemical potential. However, the chemical hardness relationship is reversed. Finally, an interesting and direct correlation between the imaginary vibrational frequency of the N18? H19 critical bond and its electron density at the TS has been obtained. © 2014 Wiley Periodicals, Inc.     

Spectroscopic calculation of CH bond dissociation energy in the series of chloro derivatives of methane, ethane, and propane

The bond-dissociation energy of CH bonds in chloro derivatives of methane, ethane, and propane has been determined by spectroscopic and quantum chemical methods. Spectroscopic values for CH bond dissociation energy were computed, basing on fundamental absorption bands in the anharmonic approximation, by the variational method with the use of the Morse anharmonic basis. Quantum chemical computations were performed using the basis 6-311G(3df, 3pd)/B3LYP. There are discussed the obtained regularities of changes in the bond dissociation energy when the structure of a molecule is changed.     

Spectroscopic calculation of CH bond dissociation energy for aliphatic derivatives from the ethylene series

The bond-dissociation energy of CH bonds in molecules of the ethylene homological series has been determined by spectroscopic and quantum chemical methods. Spectroscopic values for the CH bond dissociation energy were calculated based on the fundamental absorption bands in the anharmonic approximation by the variation method using the Morse anharmonic basis. Quantum chemical computations were performed with 6-311G(3d, 3p)/B3LYP basis. There are discussed the obtained regularities of changes in the bond dissociation energy when the structure of a molecule is changed.