Valence of elements in HgBa2Can-1CunO2n+2+d (n=1, 2, 3, 4)

Valence of elements in HgBa2Can-1CunO2n+2+d (n=1, 2, 3, 4) (both argon and oxygen annealed samples) were calculated. The result indicated for both argon and oxygen annealed samples, Hg had the lowest valence for the highest Tc sample. For fixed n, the valence of Cu in oxygen annealed samples was larger than that in argon annealed samples, indicating that oxygen annealed samples produce more carriers than argon annealed samples.     

Nucleus Independent Chemical Shift (NICS) at Small Distances from the Molecular Plane: The Effect of Electron Density

When close to the molecular plane, the behavior of nucleus independent chemical shift (NICS) as a function of the distance from the molecular plane deviates from its behavior at larger distances. By using a dense grid of NICS-probes (BQs) it is shown that, when close to the molecular plane, maximal (absolute) NICS values are obtained above the atoms. These maxima move towards the center as the grid is elevated until the (absolute) maximum NICS is obtained at the center and stay there when the grid is further elevated. It is shown that this behavior is a result of the current density, which is influenced by the electron density, according to the Biot-Savart law, which, in turn, causes the induced magnetic field measured by the NICS. It is thus concluded that if magnetic aromaticity is studied, the NICS calculations should be carried out at a large enough distance so that only the π-ring current affects the NICS. At distances ≥2 Å, NICS(r)_π,zz=A+B*C^r. Using non-linear correlation for obtaining A, B and C and extrapolate to NICS(1)_π,zz and NICS(1.7)_π,zz is recommended as measures for aromaticity.     

Aromaticity of N-heterocyclic carbene and its analogues: Magnetically induced ring current perspective

The N-heterocyclic carbene, imidazole-2-ylidene, and its main group (13-15) analogues contain cyclically conjugated 6π electrons. Experimental ¹H nuclear magnetic resonance (NMR) spectra suggest an increase in aromaticity along a period from left to right. Whereas the order along a group is as follows: period 2 > period 5 > period 4 > period 3 due to change in structure. To understand the order of aromaticity, the magnetically induced ring currents of the molecules are calculated using aromatic ring current shielding, gauge-including magnetically induced currents (GIMIC) method and Stanger's σ-model applying the gauge-including atomic orbitals NMR technique. It is found that GIMIC best describes the order of aromaticity especially along a group where current-profile changes on the bivalent atom down a group due to change in electron density. Moreover, the GIMIC provides the visualization of current by sign modulus and the anisotropy of the induced current density plots.     

Structures and Aromaticity of Planar XY2Z （X = Li,K, Y - P,As and Z = C,Si, Ge） Clusters

Clusters XY2Z species are theoretically investigated with density functional theory （DFT） method. The results show that for LiP2C, LiAs2Ge and KAs2C species, the C2v isomer is the most stable planar structure, while for other species the Cs isomer is the most stable planar structure at the B3LYP/6-311＋G＊ level. Wiberg Bond Index （WBI） and Nucleus-Independent Chemical Shift （NICS） values indicate the existence of delocalization in stable planar structures. A detailed Molecular Orbital （MO） analysis further reveals that planar isomers of these species have strong aromatic character, which strengthens the structural stability and makes them closely connect with the concept of aromaticity.     

四角锥形结构化合物BeB4X4(X=H，F，Cl)，HBB4H4与BB4H4+中B4平面环的半芳香性

选用6-311++G(3df,2p)基组,在二级微扰的理论下,对四角锥形结构化合物BeB4X4(X=H,F,Cl),HBB4H4与BB4H4+的分子振动频率,及原子间的相互作用进行了计算,作用能的计算使用了CCSD(T)方法。结果显示HBB4H4与BB4H4+是违反韦德规则的另两个特例,它们表现稳定的原因与芳香性有关。     

超价化合物NLin+4和OLin+4电子结构和性质

以6-3lG·基组利用HF、MP2和DFT方法优化了超价化合物NLin+4和OLn+4的几何构型.研究结果表明,MP2和DFT法计算出的OLi4分子解离出Li和Li2的反应能与已有的实验值吻合.对于NLi4分子,得到其解离出Li和Li2的反应能分别为191.78和515.37 kJ/mol(MP2值).并预测了OLin+4和NLin+4分子的基振动频率.     

叠氮二氢硼多聚体结构和性质的理论研究(英文)

本文采用DFT-B3LYP方法,以不同基组对叠氮二氢硼多聚体(H2BN3)n (n=1-4)进行计算研究.二聚体(H2BN3)2(C2h对称性)中含B2N2平面四元环结构.船式(Cs对称性)和椅式(C3v对称性)三聚体(H2BN3)3的结合能相近(-122 和 -126 kJ·mol-1),其中均含B3N3六元环结构.拥有B4N4八元环结构的四个四聚体的结合能只有稍微差别.与单体相比,簇合物的结构参数变化较大.由ΔG0T可知,298.2 K下单体形成二聚体在热力学上是不利的,而形成三聚体和四聚体是有利的.     

Structures, stabilities, electronic, and optical properties of C64 fullerene isomers, anions (C64(2-) and C64(4-)), metallofullerene Sc2@C64, and Sc2C2@C64

The 3465 classical isomers of C(64) fullerene have been investigated by quantum chemical methods PM3, and the most stable isomers have been refined with HCTH/3-21G//SVWN/STO-3G, B3LYP/6-31G(d)//HCTH/3-21G, and B3LYP/6-311G(d)//B3LYP/6-31G(d) level. C(64)(D(2):0003) with the lowest e(55) (e(55) = 2), the number of pentagon-pentagon fusions, is predicted to be the most stable isomer and it is followed by the C(64)(C(s):0077) and C(64)(C(2):0103) isomers within relative energy of 20.0 kcal/mol. C(64)(D(2):0003) prevails in a wide temperature range according to energy analysis with entropy contribution at B3LYP/6-31G(d) level. The simulated IR spectra and electronic spectra help to identify different fullerene isomers. All the hexagons in the isomers with e(55) = 2 display local aromaticity. The relative stabilities of C(64) isomers change with charging in ionic states. Doping also affects the relative stabilities of fullerene isomers as demonstrated by Sc(2)@C(64)(D(2):0003) and Sc(2)@C(64)(C(s):0077). The bonding of Sc atoms with C(64) elongates the C-C bond of two adjacent pentagons and enhances the local aromaticity of the fullerene cages. Charging, doping, and derativization can be utilized to isolate C(64) isomers through differentiating the electronic and steric effects.     

快速合成宽带激发、窄带发射白光LED用Li2CaSiO4∶Eu2+蓝-绿荧光粉

采用微波辅助法合成了蓝-绿色荧光粉Li2CaSiO4∶Eu2+,该荧光粉能很好的与紫外光及蓝光LED匹配。分别采用X射线衍射(XRD)、扫描电镜(SEM)和激发-发射光谱(PLE/PL)对样品进行了表征。X射线衍射数据与标准卡片PDF#27-290很好吻合。扫描电镜测试表明样品粒径在2~5μm。在紫外光和蓝光激发下,Li2CaSiO4∶1%Eu2+发射主峰位于478 nm,对应于Eu2+的t2g→8S7/2电子跃迁,半高峰宽31 nm。样品发光性能与Eu2+掺杂浓度有关,且Eu2+的最佳掺杂浓度为1%。合成的样品色坐标为(0.09,0.24),可作为白光LED用蓝-绿色荧光材料。     

纳米SrAl2O4:Eu2+,Dy3+长余辉发光材料的制备与性能

采用水热-均匀共沉淀法制备了纳米SrAl2O4:Eu2+,Dy3+长余辉发光材料.通过XRD、TEM、荧光光谱、热释光谱对其结构和性能进行分析.XRD结果表明所制备的SrAl2O4:Eu2+Dy3+纳米发光材料为单相,属单斜晶系.TEM测试表明纳米SrAl2O4:Eu2+,Dy3+发光材料为规则的球状粒子,粒径为50～80 nm,且分散性良好.激发和发射光谱测试表明,样品的激发光谱是峰值在356 nm 的连续宽带谱,发射光谱是峰值位于512 nm的宽带谱,与SrAl2O4:Eu2+,Dy3+粗晶材料相比,激发和发射光谱都出现了"蓝移"现象.样品的热释光峰值位于358 K,适合于产生长余辉.     

D6h‐Au42 Isomer: A Golden Aromatic Toroid Involving Superatomic π‐Orbitals that Follow the Hückel (4n+2)π rule

Recently, it has been shown that the superatom concept is intimately connected to relevant tools of great chemical significance, such as the Lewis structure model and the VSEPR theory, which has been employed to understand hybridized and dimeric‐like molecules. This suggests a potential rational construction of superatomic clusters mimicking more complex structures. Here, we extend another well‐employed concept to the superatomic clusters, to construct a novel Au₄₂ isomer with resemblance to cyclic aromatic molecules. It is shown that the Hückel (4n+2)π rule is ready to be applied, predicting aromatic behavior latterly supported by the favorable evaluation of the induced shielding cone formation. The D₆h isomer of Au₄₂ described here exhibits inherent characteristics mimicking aromatic hydrocarbon rings, displaying π‐superatomic orbitals and related properties. This new cluster is the first member of the superatomic clusters family to exhibit an aromatic π‐electron system.     

Reaction of ene-bis(phosphinylallenes): [2+2] versus [4+2] cycloaddition

Reaction of ene-bis(phosphinylallenes), derived from ene-bis(propargyl alcohols) and chlorodiphenylphosphine, was investigated. Benzene-bridged bis(phosphinylallenes) exclusively gave intramolecular [2+2] cycloadducts in the presence of dimethyl fumarate in sharp contrast to the reaction of benzene-bridged bis(sulfinylallenes), which gave the corresponding [4+2] cycloadducts. On the other hand, substituted ethylene- or five-membered heterocycle-bridged bis(phosphinylallenes) provided [4+2] cycloadducts. Reaction of benzene-bridged diallene bearing both a sulfinyl group and a phosphinyl group on the two allenyl groups was also described.     

Li_2SrSiO_4:Eu~(2+),Nd~(3+)中Eu~(2+)和Nd~(3+)的光谱性质和能量传递

在还原气氛下采用高温固相法制备了Li2SrSiO4:Eu2+,Nd3+发光材料,测量了它们的可见和近红外激发光谱和发射光谱及Eu2+的荧光寿命,研究了Eu2+和Nd3+掺入对其发光性质的影响。结果表明,当Eu2+的浓度为0.01,Nd3+的浓度为0.05时,样品的近红外发光强度最强;Eu2+的发射光谱和Nd3+激发光谱之间的光谱交叠范围较大,Eu2+和Nd3+之间存在着高效无辐射能量传递,能量传递效率约为55.7%,Eu2+的掺入可显著地敏化Nd3+的近红外发光。     

[4+2] Cycloaddition reactions of 4-sulfur-substituted 2-pyridones with electron-deficient dienophiles

[4+2] Cycloaddition reactions of 4-(phenylthio)-1-tosyl-2-pyridone (6a) and 4-(phenylsulfonyl)-1-tosyl-2-pyridone (6b) with electron-deficient dienophiles 7 (N-methylmaleimide, N-phenylmaleimide, and methyl acrylate) gave new isoquinuclidine products 8-10. The N-tosyl group of 6a and 6b was also efficiently converted to N-alkyl derivatives 6c-f, which showed different stereoselectivity toward reactions with dienophiles 7. Several other dienophiles 15 (dimethyl acetylenedicarboxylate, methyl vinyl ketone, ethyl vinyl ether, and methyl methacrylate) were found not to react with 6a or 6b, but led to the formation of tosyl migration products 4-(phenylthio)-O-tosyl-pyridinol (16a) and 4-(phenylsulfonyl)-O-tosyl-2-pyridinol (16b), respectively. The reactivity, regioselectivity, and stereoselectivity of the cycloaddition reactions were also compared with semi-empirical calculations.     

La2—xSrxCuO4和La2—xNdxCuO4＋y的键共价性计算

使用复杂晶体化学键理论计算了Ｌａ２－ｘＳｒｘＣｕＯ４和Ｌａ２－ｘＮｄｘＣｕＯ４＋ｙ中各键的健共价性,讨论了键性随着掺杂的变化规律,研究表明,对于２１４结构,没有发现明显的化学键性与超导温度的关系,因此２１４结构中有关超导现象产生的机理还有待于进一步研究。     

DFT calculations of the defect structures,electronic structures,and EPR parameters for three Rh2+ centers in AgCl

The local structures for various Rh²⁺ centers in AgCl are theoretically studied using density functional theory (DFT) with periodic CP2K program. Through geometry optimizing, the stable ground states with minimal energies and electronic structures are obtained for the tetragonally elongated (T_E), orthorhombically elongated (O_E), and tetragonally compressed (T_C) centers, and the corresponding g and hyperfine coupling tensors are calculated in ORCA level. The calculations reveal obvious Jahn–Teller elongation distortions of about 0.109 and 0.110 Å along [001] axis for T_E and O_E centers without and with 1 next nearest neighbor (nnn) cation vacancy V_Ag in [100] axis, respectively. Whereas T_C center with 1 nnn V_Ag along [001] axis exhibits moderate axial compression of about 0.066 Å due to the Jahn–Teller effect. For O_E and T_C centers with 1 nnn V_Ag, the ligand intervening in the central Rh²⁺ and the V_Ag is found to displace away from the V_Ag by about 0.028 and 0.024 Å, respectively. The present results are discussed and compared with those of the previous calculations based on the perturbation formulas by using the improved ligand field theory.     

4+1 and 4+2 coordinated complexes of magnesium phthalocyanine with dioxane

Two complexes of magnesium phthalocyanine with dioxane were obtained. They co-crystallise in the centrosymmetric space group of the triclinic system. One of them is biaxially ligated (4+2) complex MgPc(dioxane)₂ and the other is bridged μ-dioxane(MgPc)₂. The interaction of the bridged dioxane molecule with two MgPc molecules is stronger than the interaction of two dioxane molecules axially ligated to the metal center of MgPc on the both sides of the Pc-plane. The strength of the MgO bond in these complexes correlates with their thermal stability. Owing to the Mg?O interaction of the bridged dioxane molecule with two MgPc units and formation of the μ-dioxane(MgPc)₂ complex, the Mg atom is significantly displaced (0.357(3) Å) from the plane defined by four isoindole N atoms of Pc. This interaction causes a distortion of planar Pc(2-) macrocycle to the saucer-shape form. In biaxially ligated MgPc(dioxane)₂ molecule the Pc(2-) macroring exhibits the planar form. Due to the steric hindrance of the axial ligand, the crystals exhibit better solubility than the parent MgPc, since the structure is less stabilized by π-π interactions between the aromatic Pc(2-) macrorings than in the structure of MgPc. Ligation of MgPc by dioxane does not change the colouring properties compared with the MgPc pigment. The calculated 3D molecular electrostatic potential maps are helpful for understanding the organisation and arrangement of molecules in the crystal.     

Linear and nonlinear feature of electronic excitation energy in carbon chains HC2n+1H and HC2nH

Density functional theory has been used to investigate the geometries, bonding, and vibrational frequencies of HC_2nH (n = 1–13) and HC_2n+1H (n = 2–12). Vertical excitation energies for the X¹Σ → 1¹Σ transition of HC_2nH (n = 1–5) and for the X³Σ → 1³Σ transition of HC_2n+1H (n = 2–5) have been calculated by the time‐dependent density functional theory and ab initio second‐order multiconfiguration perturbation method, respectively. On the basis of the present calculations, explicit expressions for the size dependence of excitation energy in linear polyynes HC_2n+1H and HC_2n+1H are suggested. Such analytical λ ? n relationships show good agreement with experimental observations. Theoretical investigations of relevant excited states demonstrate that distinct linear and nonlinear spectroscopic features in such polyynes can be ascribed to similarity and difference in bonding between the ground and excited states in HC_2n+1H and HC_2nH. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Structural and Spectroscopic Properties of Linear Carbon Chains NC2nN and HC2n+1N (n = 1～10)

Using density functional theory, geometries and vibrational frequencies of linear chains NC2nN and HC2n+1N (n = 1～ 10) have been investigated.Time-dependent density functional theory (TD-DFT) has been used to calculate the vertical transition energies and oscillator strengths for the X 1∑+k → 11∑+u transition in NC2nN (n = 1 ～10) and X1∑+ → 11∑+ transition in HC2n+1N (n =1 ～7).On the basis of present calculations, the explicit expressions for the size dependence of the excitation energy and the first adiabatic ionization energy in both carbon chains have been suggested.