聚并苯的链间作用对其导电能力的影响

采用量子化学晶体轨道ＣＮＤＯ／ ２ 方法,在考虑聚并苯链间作用的基础上对聚并苯双链模型的电子结构进行计算和讨论．结果表明：聚并苯链处于不同相对位置的链间作用对聚并苯的电荷分布规律及能带结构均有一定影响,位置不同,影响不同．从聚并苯的能带结构可以得出：聚并苯是有较小能隙、良好本征导电性能的半导体材料,考虑链间作用,对能带结构特征未有大的改变,能隙等值略有修正,导电能力有所加强．利用此模型讨论,更接近于晶体的真实结构,对进行聚并苯导电材料的性能改进将有一定帮助．     

电荷转移复合物1-氮-甲基-苯并哒嗪TCNQ和2-氮-甲基-苯并哒嗪TCNQ的能带结构与电性质的研究

本文采用以EHMO为基础的紧束缚近似方法计算了同分异构复合物1-N-Mci TCNQ_2和2-N-Mci TCNQ_2的能带结构。通过计算谐振稳定能估算复合物中TCNQ的电荷。计算结果表明, 复合物晶体中的给体N-Mci对一维能带的前沿轨道无影响。1-N-Mci和2-N-Mci的几何形状不同, 在晶体堆积能量上影响TCNQ的排列, 使两个复合物的TCNQ堆积方式不同, 能带结构也就不一样了。1-N-Mci TCNQ_2复合物的TCNQ之间π-π轨道迭合较好, 能隙小。LU带色散大, LU轨道上的电子为末充满状态(δ≈1.77), 具有较好的导电性能。2-N-Mci TCNQ_2复合物中TCNQ二聚体之间π-π轨道重叠不好, 能隙大, LU带宽很窄, LU轨道上电子为半充满状态(δ≈1.0), 易于形成磁绝缘体, 其导电性比1-N-Mci TCNQ_2差, 这与实验结果是一致的。     

Guanine crystals: a first principles study

We report first principles density functional theory studies on the basic ground state characteristics, dynamic properties, and the electronic structure of guanine crystals. The effect of water molecules within the crystal is studied in detail, and we discuss their influence on the structural, vibrational, and electronic properties. The geometries calculated for various crystal structures are compared with gas-phase calculations and available experimental data. Phonon frequencies and eigenvectors are predicted for intermolecular and intramolecular lattice vibrations. Vibrational and electronic density-of-states are presented and analyzed. The electronic band structure near the fundamental gap is calculated from the Kohn-Sham approach. We find that the former molecular HOMO states form a dispersive band in the pi-pi stacking direction upon condensation resulting in a large bandwidth of 0.83 eV. Consequences for the charge transport in layered van der Waals bonded organic molecular crystals are discussed.     

Theoretical study on photophysical properties of phenolpyridyl boron complexes

Organoboron complexes have potential application in organic light-emitting devices (OLEDs). Our group has synthesized four phenolpyridyl boron complexes (Inorg. Chem. 2006, 45, 2788), which can function as an electron transport materials (ETM), white and blue emitters, and exhibit high efficiency and stability. To reveal the relationship between the properties and structures of these functional materials, theoretical analysis of spectral properties and electronic structures of these complexes was systematically characterized with the B3LYP and 6-31G* basis set. The calculated absorption and emission spectra of these systems are in good agreement with the experimental ones. It is clear seen that these transitions are charge transferred along 2,6-bis(2-hydroxyphenyl)pyridyl boron moiety, and the contribution of boron atom in these compounds to the main transition orbitals is vanishingly small. The substitution of methyl and methoxyl for hydrogen does not change the absorption wavelengths and transition natures, but influences the radioactive efficiencies and electron transport properties, which are observed and discussed in detail. Furthermore, large red shifts of fluorescence are caused by replacing the hydrogen with CN or NO2 groups, which indicates that they are potential candidates as green-light-emitting materials. These results are favorable to further understanding the photophysical properties of this kind of complexes.     

Molecular recognition of carbohydrates with artificial receptors: mimicking the binding motifs found in the crystal structures of protein-carbohydrate complexes

The binding motifs found in the crystal structures of protein-carbohydrate complexes have been successfully mimicked with simple acyclic pyridine- and pyrimidine-based receptors. A full discussion of the recognition motifs observed in the crystal structures of complexes of receptors 1 and 3 with glucopyranosides 4a and 4b is provided. A remarkable similarity of these motifs to those observed in the crystal structures of sugar-binding proteins and those found by molecular modeling is shown. In addition, the recognition properties of the new pyrimidine receptor 3 toward monosaccharides 4-6 are described. This molecule has been established as a highly effective receptor for beta-glucopyranosides.     

Correlation of crystal parameters with vibrational data of tetramethylammonium fluorocompounds

Examination of the solid state infrared spectra of the tetramethylammonium cation in ten salts shows correlation of infrared spectral properties with C-H…X hydrogen bonding and crystal habits in these tetramethylammonium salts. In this research a number of complexes of tetramethylammonium cation have been synthesized and the structures of five of them have been analyzed by X-ray single crystal diffraction. The IR predicted crystal habits are comprised by XRD data. The C-H stretching region characteristic hydrogen bonding shifts in the above salts. A good relation between two data has been found.     

Mo~2S~4(i-mnt)~2(Et~4N)~2和(Et~4N)~3K[Mo~2S~4(i-mnt)~2]~2 [i-mnt=S~2C (CN)^2^-]阴离子的能带结构研究

二核钼簇合物Mo~2S~4(i-mnt)~2(Et~4N)~2和(Et~4N)~3K[Mo~2S~4(i-mnt)~2]~2[i-mnt=S~2C(CN)^2^-]的阴离子在晶体中构成独特的链状结构,本文采用扩展的Huckel近似下的紧束缚能带方法,计算了它们的能带结构。结果表明,相邻簇阴离子间存在弱的相互作用,它是形成链状结构的基础。链状结构与晶体的半导体性质相关联。态密度和晶体轨道重叠布居反映了晶体中电荷分布状况及化学成键特点,与晶体结构分析、NMR谱学表征结果相符合。     

First principles study on the structure and electronic properties of 2‐nitrimino‐1‐nitroimidazolidine

The properties of 2‐Nitrimino‐1‐nitroimidazolidine are calculated by using SIESTA code, which adopts the standard Kohn‐Sham self‐consistent density functional method in the local density approximation. The structures and electronic properties are analyzed, and the factors that affect the impact sensitivity are discussed based on the crystal structure, band energy, and projected density of state. The reason for the smaller impact sensitivity compared to RDX (hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine) is also explored from several respects such as the weakest bond dissociation energy in single molecule, and hydrogen bond, band gap in the crystal. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

LiNiO2及掺杂化合物的结构与稳定性的第一性原理研究

应用第一原理局域密度泛函对LiNiO2及其掺杂化合物的晶体结构、能带结构和态密度进行了研究.结果表明:锂镍氧系正极材料是电子的良导体,在充放电过程中具有良好的稳定性,适合做锂离子电池的正极材料;在LiNiO2晶体中主要是O和Ni之间成键,镍离子和氧离子的相互作用比较强,Li在嵌入层状结构材料后部分失去电子,以离子状态存在.     

An attempt towards coordination supramolecularity from Mn(II), Ni(II) and Cd(II) with a new hexadentate [N4O2] symmetrical Schiff base ligand: Syntheses,crystal structures,electrical conductivity and optical properties

To explore the influence of non-covalent weak force interactions, mainly exerted by carboxylic groups, on the formation of supramolecular architectures of transition metal complexes and their electrical conduction processes, a new symmetrical [N₄O₂] hexadentate Schiff base ligand, 1,8-N-bis(3-carboxy)disalicylidene-3,6-diazaoctane-1,8-diamine, abbreviated to H₄fsatrien, and its complexes of Ni(II), Cd(II) and Mn(II) have been synthesized using in situ condensation of the ligand components in the presence of metal ions. The complexes were structurally characterized by elemental analyses, IR, UV–Vis, NMR, ESR, molar conductivity and magnetic measurements. The crystal structures of all the complexes have been determined by a single crystal X-ray diffraction study. The 1-D, 2-D and 3-D networks of the complexes are formed by π–π stacking, C–H?π interactions and mono or bifurcated H-bonding. The electronic structures of the complexes have been examined using the DFT method. Solid-state properties (e.g. electrical conductivity at different temperatures and optical properties) of the Ni(II) and Mn(II) complexes have also been studied and, depending on the temperature, the conductivity of the complexes is found to be insulating and semiconducting (intrinsic and extrinsic) in nature. The optical band gap (E_gd) of complexes (1) and (3) is found to be 2.57 and 2.30 eV, respectively.     

Roles of inter- and intramolecular vibrations and band-hopping crossover in the charge transport in naphthalene crystal

We calculate the hole and electron mobilities in naphthalene crystal from 10 to 300 K within the framework of the Holstein-Peierls model coupled with first-principles density-functional-theory-projected tight-binding band structures. All the electron-phonon coupling constants, including both local and nonlocal parts for inter- and intramolecular vibrations, have been taken into considerations through density functional theory. The band-hopping crossover transition temperature for the electron transport in the c' axis is calculated to be around 23 K. We have identified a few high frequency intramolecular vibrations which are very important to the charge transport in naphthalene crystal due to their comparatively large electron-phonon coupling constants. However, their contributions to the temperature dependence of mobility are minor because of the small phonon occupations and small nonlocal coupling strengths. The low frequency intermolecular modes (longitudinal optical modes) are found to be the major contributions to the temperature dependent charge transfer properties in naphthalene crystal. Even though the calculated qualitative temperature dependence is in agreement with experiment, the predicted absolute mobility is about one to two orders of magnitude larger.     

Photoluminescence properties of new BF2 complexes with pyrazolone ligands: Dependence on volume and electronic effect of substituents

Novel fluorine-boron complexes with donor-acceptor architecture in which pyrazoline-1,3-diones were chosen as electron donors have been synthesized and well characterized. Correlation of the luminescence properties of the complex 2c and its crystal structures was discussed. Well-ordered molecular packing in the crystal results in strong charge transfer interactions characterized by long excited-state lifetime. These fluorine-boron complexes show photophysical properties highly dependent on the solvent polarity and aggregation states. The substituents on the pyrazoline were found to have a significant impact on the solid-state luminescent properties. As a result, some significant differences in charge transfer modes were observed in the solid state among these complexes.     

Comparative first-principles study of structural and optical properties of alkali metal azides

A comparative first-principles study of the structural and optical properties of the alkali metal azides has been performed with density functional theory within the generalized gradient approximation. The crystal structures of the alkali azides compare well with experimental data. Their ionic character is manifested by the closeness of their internitrogen distances to the calculated N-N bond length for the free azide ion. An analysis of electronic structure, charge transfer, and bond order shows that the alkali azides are all wide-gap insulators and ionic compounds. The energy band and density of states for lithium azide and alpha-sodium azide are very similar, while these for potassium azide, alpha-rubidium azide, and alpha-cesium azide are alike, but some modifications are observed with the increment of alkali metals' electropositivity. These changes are closely related to the differences of the crystal structures. The general shapes of the real and imaginary parts of the dielectric function, adsorption coefficient, and electron energy-loss spectra are quite similar. The peaks originate from the electron transitions from the alkali metal s and p states to the conduction band. Our calculated optical properties for the alkali azides are found to be in good agreement with available experimental data. The absorption spectra of the alkali azides show a number of absorption peaks, which are believed to be associated with different exciton states, in the fundamental absorption region. In general, the electron energy-loss spectra have two plasma frequencies.     

Crystal structures of Ziegler-Natta catalyst supports

The crystal structures of three MgCl(2)·nEtOH complexes with n=1.5, 2.8, and 3.3 have been fully determined. Such complexes are the fundamental precursors for Ziegler-Natta polymerization catalysts used to produce polyolefins on a multimillion-ton scale worldwide. The ab initio structure solution showed that the structure of MgCl(2)·nEtOH complexes with n=1.5 and 2.8 are based on ribbons of metal-centered octahedra, whereas for n=3.3 this chainlike arrangement breaks into a threadlike structure of isolated octahedra linked by hydrogen bonds. A clear correlation between catalyst performance and the crystal structure of precursors has been found, and reveals the fundamental role of the latter in determining catalyst properties. The direct knowledge of building blocks in the precursor structures will help to develop more accurate models for activated catalysts. These models will not require the arbitrary and oversimplified assumption of locating the catalyst active sites on selected cut surfaces of the α-MgCl(2) crystal lattice.     

Ab initio and molecular dynamics studies of crystalline TNAD (trans-1,4,5,8-tetranitro-1,4,5,8-tetraazadecalin)

The structural and electronic properties of the energetic crystal TNAD (trans-1,4,5,8-tetranitro-1,4,5,8- tetraazadecalin) have been studied using plane-wave ab initio calculations based on the density function theory method with the ultrasoft pseudopotentials. It is found that the predicted crystal structure is in good agreement with experimental data and there are strong inter- and intramolecular interactions in bulk TNAD. Band structure calculations indicate that TNAD is an insulator with the band gap of ca. 3.3 eV. The hydrostatic compression effect on TNAD has been studied in the pressure range of 0-600 GPa. The results show that a pressure less than 10 GPa does not significantly change the geometric parameters, charge distributions, and electronic bands. When the pressure is over 10 GPa, increasing the pressure determines significant changes of the geometrical and electronic structures and large broadening of the electronic bands together with a sharp decrease of the band gap. Isothermal-isobaric molecular dynamics simulations at atmospheric pressure were further performed on the TNAD crystal in the temperature range 5-500 K. Average equilibrium lattice parameters and elastic properties as functions of temperature were determined. The thermal expansion coefficients calculated for the crystal indicate anisotropic behavior with the largest expansion along the b axis.     

meso-四(对烷氧苯基)卟啉金属配合物的合成和性能研究(II)

合成了Zn、Pb两个系列卟啉金属配合物12个,其中6个为未见文献报道的新化合物,用元素分析、IR、UV、^1HNMR、MS确证了其结构。总结了Zn、Pb与卟啉类配体配合的IR、UV、^1HNMR判据。研究了这两个系列化合物的液晶性能,发现9个化合物具有液晶性。     

Lead‐Free Halide Perovskite Nanocrystals: Crystal Structures,Synthesis, Stabilities,and Optical Properties

In recent years, there have been rapid advances in the synthesis of lead halide perovskite nanocrystals (NCs) for use in solar cells, light emitting diodes, lasers, and photodetectors. These compounds have a set of intriguing optical, excitonic, and charge transport properties, including outstanding photoluminescence quantum yield (PLQY) and tunable optical band gap. However, the necessary inclusion of lead, a toxic element, raises a critical concern for future commercial development. To address the toxicity issue, intense recent research effort has been devoted to developing lead‐free halide perovskite (LFHP) NCs. In this Review, we present a comprehensive overview of currently explored LFHP NCs with an emphasis on their crystal structures, synthesis, optical properties, and environmental stabilities (e.g., UV, heat, and moisture resistance). In addition, strategies for enhancing optical properties and stabilities of LFHP NCs as well as the state‐of‐the‐art applications are discussed. With the perspective of their properties and current challenges, we provide an outlook for future directions in this rapidly evolving field to achieve high‐quality LFHP NCs for a broader range of fundamental research and practical applications.     

NbX(X=C,N,O)的能带结构研究

本文采用EHT近似下的紧束缚能带方法,计算了NbX(X=C,N,O)的能带结构。结果表明,它们的能带结构相近,Nb—X间存在较强的成键作用,传导电子主要具有Nb的4d特征,Nb—Nb键与超导电性相关,从C到N,Nb—Nb键共价性削弱,Tc提高。尽管计算所得NbO中Nb—Nb键强度介于NbC和NbN之间,但其实际Tc却比NbC和NbN的都低,这是NbO的空位效应所致,这一结果可从我们对有序缺陷的Nb_(0.75)O_(0.75)晶体能带结构的计算得到验证。     

Effect of Two‐Dimensional Crystal Orbitals on Fermi Surfaces and Electron Transport in Three‐Dimensional Perovskite Oxides

Perovskite oxides are candidate materials in catalysis, fuel cells, thermoelectrics, and electronics, where electronic transport is vital to their use. While the fundamental transport properties of these materials have been heavily studied, there are still key features that are not well understood, including the temperature‐squared behavior of their resistivities. Standard transport models fail to account for this atypical property because Fermi surfaces of many perovskite oxides are low‐dimensional and distinct from traditional semiconductors. In this work, the low‐dimensional Fermi surfaces of perovskite oxides are chemically interpreted in terms of two‐dimensional crystal orbitals that form the conduction bands. Using SrTiO₃ as a case study, the d/p‐hybridization that creates these low‐dimensional electronic structures is reviewed and connected to its fundamentally different electronic properties. A low‐dimensional band model explains several experimental transport properties, including the temperature and carrier‐density dependence of the effective mass, the carrier‐density dependence of scattering, and the temperature dependence of resistivity. This work highlights how chemical bonding influences semiconductor transport.     

Interaction of Zn(II) with quinolone drugs: structure and biological evaluation

Zinc complexes with the third-generation quinolone antibacterial drugs levofloxacin and sparfloxacin have been synthesized and characterized. The deprotonated quinolones act as bidentate ligands coordinated to zinc ion through the pyridone and a carboxylato oxygen atom. The crystal structures of [bis(aqua)bis(levofloxacinato)zinc(II)], 1, and [bis(sparfloxacinato)(1,10-phenanthroline)zinc(II)], 3, have been determined by X-ray crystallography. The biological activity of the complexes has been evaluated by examining their ability to bind to calf-thymus DNA (CT DNA) by UV spectroscopy and viscosity measurements. UV studies of the interaction of the complexes with DNA have revealed that they can bind to CT DNA probably by the intercalative binding mode which has also been verified by DNA solution viscosity measurements. The DNA binding constants have been also calculated. A competitive study with ethidium bromide (EB) showed that the complexes exhibit the ability to displace the DNA-bound EB indicating that they bind to DNA in strong competition with EB for the intercalative binding site. The interaction of the complexes with human and bovine serum albumin proteins has been studied by fluorescence spectroscopy showing that the complexes exhibit good binding propensity to these proteins having relatively high binding constant values. The biological properties of the complexes have been evaluated in comparison to the previously reported Zn(II) complexes with the first- and second-generation quinolones oxolinic acid and enrofloxacin.