The Lewis acidity of bismuth(III) halides: a DFT analysis

The Lewis acidity of BiX₃ (X=Cl, Br, I) is explored using density-functional theory (DFT) studies of simple complexes with various alcohol and carbonyl substrates. The calculated relative energies of the complexes follow the trend of hardness for BiX₃ (Cl>Br>I). The observed halogen exchange reaction of BiCl₃ with alcohols and alkyl halides is discussed in terms of the computational results as well as theories of hardness and carbocation stability. The DFT results predict similar activation of substrates by molecular BiI₃ relative to BiBr₃, which is inconsistent with experimental results, which show no reactivity for the iodide in nonpolar solvents. However, the molecular form is unlikely in these solvents as BiI₃ is an ionic salt in contrast to the chloride and bromide, which are covalent solids.     

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.     

Kristallpackungen mit linear koordinierten Atomen

Crystal Packings with Linearly Coordinated Atoms Formally, crystal structures containing linearly coordinated atoms can be derived from simple structure types in various ways. In a systematic way, this can be done with the aid of crystallographic group‐subgroup relationships. One way is shown for K₂HgO₂ and KAgO, the structures of which result from the NaCl type by vacating certain Cl positions. Another way is the expansion of a crystal packing in order to obtain linearly coordinated atoms from octahedral coordination. This way, α‐HgO₂ results from the pyrite type, HgBr₂ and HgI₂ from SnS₂‐4H, HgCl₂ from diaspore (AlOOH), and HgO from NaCl. Na₂PdC₂ results from the NiAs type, when half of the Ni atoms are substituted by acetylide groups and the structure is expanded perpendicular to c . A third procedure is to formally insert an atom between two adjacent atoms, such as the insertion of O atoms between the metal atoms of the polonium structure to obtain the ReO₃ structure. Insertion of Au atoms into the NaCl type results in the KAuS structure, and insertion of Cu atoms between O atoms of anatase results in the SrCu₂O₂ type. Further insertion products are LiAg₃O₂ (Ag inserted in the SiS₂ type) and NaHgPO₄ (Hg inserted in the CrVO₄ type). Insertion of atoms between spheres of the body‐centered cubic structure yields the structures of PtHg₄, Cu₂O, AuCl and CS₂. Insertion of Cu atoms into the O—O bonds of β‐O₂ and simultaneous occupation of the octahedral voids with Fe atoms results in the delafossite structure (FeCuO₂), which is also adopted by oxide‐hydroxides like CrOHO and by LiFHF and NaN₃. Insertion of Hg atoms between the chalcogen atoms of the α‐Se structure results in the cinnabar structure (HgS); however, due to the widening of the spiral chains, the S atoms then adopt a different packing, and the structure is more adequately described by a hexagonal sphere packing of spheres having coordination number 10 and Hg atoms occupying certain voids. The quartz structure can also be derived from this sphere packing (of Si atoms) by inserting O atoms.     

Investigation of Poly(ether-b-amide)/Nanosilica Membranes for CO2/CH4Separation

The results of molecular dynamics （MD） simulations on transport process of CO2 and CH4 gases in poly（ether-b- amide） （PEBAX）/nanosilica membranes are discussed. The diffusion coefficients for CH4 and CO2 gases at 6 cases with different amounts of nanosilica loading in the simulation boxes are presented. The results show that diffusion coefficients for CO2 gas in all cases are larger than those for the CH4 one. Moreover 10% nanosilica loading case shows maximum effects on diffusion coefficients and improves them by more than 68% and 157% for CO2 and CH4 gases, respectively. Additionally, the results of 3-D Cartesian trajectories and displacements curves are presented and the jumping attempt of CO2 is significantly more than that of CH4. Due to the rubbery state of PEBAX membranes in ambient temperature, the results confirm that channel lifetimes are very short and then back diffusion is not observed for this polymer.     

十六烷基三甲基溴化铵插层氧化石墨结构的分子模拟

利用分子模拟方法研究了十六烷基三甲基溴化铵(C16TAB)分子数对C16TAB/GO插层复合物的结构变化,探讨了C16TAB在GO层间的排列方式,并通过实验数据进行验证。模拟结果表明,优化后GO结构模型的层间距为0.849 nm;C16TAB/GO插层复合物的层间距随着C16TAB分子数的增加呈5个阶梯状逐渐增大,层间距分别为1.56、1.98、2.33、2.76和3.40 nm,插层饱和时C16TAB分子达到28个。实验结果显示,随着C16TAB分子数的增加,C16TAB/GO插层复合物的层间距逐渐增大,插层饱和时为3.40 nm,实验结果与模拟结果能够很好地吻合。C16TAB在GO层间可能的排列方式为1~5层平躺排列或单层平躺、单层倾斜和单层直立,从能量和结构的角度探明了C16TAB在GO层间的最优排列为1~5层平躺排列。     

十六烷基三甲基溴化铵插层氧化石墨结构的分子模拟

利用分子模拟方法研究了十六烷基三甲基溴化铵(C₁₆TAB)分子数对C₁₆TAB/GO插层复合物的结构变化,探讨了C₁₆TAB在GO层间的排列方式,并通过实验数据进行验证.模拟结果表明,优化后GO结构模型的层间距为0.849 nm;C₁₆TAB/GO插层复合物的层间距随着C₁₆TAB分子数的增加呈5个阶梯状逐渐增大,层间距分别为1.56、1.98、2.33、2.76和3.40 nm,插层饱和时C₁₆TAB分子达到28个.实验结果显示,随着C₁₆TAB分子数的增加,C₁₆TAB/GO插层复合物的层间距逐渐增大,插层饱和时为3.40 nm,实验结果与模拟结果能够很好地吻合.C₁₆TAB在GO层间可能的排列方式为1~5层平躺排列或单层平躺、单层倾斜和单层直立,从能量和结构的角度探明了C₁₆TAB在GO层间的最优排列为1~5层平躺排列.     

Ion pair chromatography on reversed-phase layers

The results of investigations with ion pair chromatography on RP₂, RP₈ and RP₁₈ thin layers are described. Heptane sulphonic acid is used as ion pair former. The best results are achieved on RP₁₈-layers with the counter ion in the mobile phase.     

Dynamisch thermische analyse der Zersetzung von K2SiF6

Thermal decomposition of K₂SiF₆ is a complicated process depending on several parameters, the combination of which cause difficulty in comparing the results obtained from different methods. An experimental method for the study of small quantities of material is described. This allows direct comparison with thermoanalytical results. The influence of experimental conditions is discussed. The decomposition of K₂SiF₆ is a model for other complexes which produce easily hydrolysed products during thermal reaction. The course of thermal decomposition of K₂SiF₆ is described up to complete vaporisation of the products at 1200°C.     

A Computational Study of the Combinatorial Addition of Oxygen to Buckminsterfullerene

All possible isomers of C₆₀O _x have been investigated for x=1, 2, and 3. The method used is a modified extended Hückel method. There is a single C₆₀O isomer, 8 unique C₆₀O₂ isomers, and 47 unique C₆₀O₃ isomers. It is found that a single C₆₀O₂ isomer is much more stable than the remaining 7 and that 3 C₆₀O₃ isomers are more stable than the remaining 44. A qualitative reason for these results is proposed. The results indicate that the three lowest-energy C₆₀O₃ isomers should exist in equilibrium at room temperature.     

The Use of Laser Induced Breakdown Spectroscopy (LIBS) to Study Catalyst Deactivation of V2O5/γ‐Al2O3 as Compared to Inductively Coupled Plasma Optical Emission Spectrometry

Laser Induced Breakdown Spectroscopy (LIBS) method is introduced as a novel approach in this work to study catalyst deactivation of V₂O₅/γ‐‐Al₂O₃ for gas‐phase dehydration of glycerol and producing acrolein. The LIBS results of V₂O₅/γ‐Al₂O₃ samples are compared with those data that are obtained by Inductively Coupled Plasma Optical Emission Spectrometry (ICP‐OES). Experimental data of LIBS data specify that line intensities of vanadium are decreased by deactivation of V₂O₅/γ‐Al₂O₃ catalyst. A comparison between the results of LIBS test as well as ICP‐OES analysis shows that the amount of vanadium is decreased in the catalyst. Moreover, coke formation changes the surface of the catalyst. The results of deactivation of V₂O₅/γ‐Al₂O₃ are also compared with Pd/C catalyst deactivation.     

A CNDO study of the electronic structure of oxyanions XO4n− with X = Si,P, S,Cl, Ge,As, Se and Br

The orbital order, the bonding properties of the orbitals and the orbital populations are discussed. It is concluded that the orbital order in the valence shell in all the ions is 1a₁, 1t₂, 2a₁, 2t₂, 1e, 3t₂ and 1t₁. The results are compared when possible with experimental data and ab initio results.     

Calculation of the valence shell correlation effects on ionization potentials. A test on N2, C2N2 and H2NN

Two schemes for the definition of the valence space from an extended basis are proposed and tested for the calculation of ionic states in N₂, C₂N₂ and H₂NN. Good results are obtained with a projection scheme, leading to a 2h-1v model reproducing the essential features of the full basis 2h-1p results. Notably excellent agreement with experiment is obtained for the main ionization potentials in N₂ and C₂N₂. Unsatisfactory results are instead given by a simple extension of the minimal basis set SCF space, indicating the importance of employing accurate occupied orbitals as a starting point.     

An ab initio reinvestigation of the geometric and electronic structure of boron trioxide

In an attempt to resolve the controversy over the structure of the boron trioxide (B₂O₃) molecule an ab initio molecular orbital study employing a minimal STO-3G basis set with complete geometry optimization is reported. Our results indicate that B₂O₃ is a planar “w” shaped molecule with a rather small inversion barrier around the central atom and a quite important coupling between BOB and OBO angles. The computed bond distances are consistent with previous electron diffraction results, whereas the apex angle is in better agreement with the most recent IR study. The results obtained by the MNDO method are in good agreement with the ab initio ones. The electronic structure of B₂O₃ is discussed by means of Walsh diagrams and Mulliken population analysis.     

Relativistic and Non‐Relativistic Electronic Molecular‐Structure Calculations for Dimers of 4p‐, 5p‐, and 6p‐Block Elements

We report results of non‐relativistic and two‐component relativistic single‐reference coupled‐cluster with single and double and perturbative triple excitations [CCSD(T)] treatments for the 4p‐block dimers Ga₂ to Br₂, the 5p‐block dimers In₂ to I₂, and their atoms. Extended basis sets up to pentuple zeta are employed and energies extrapolated to the complete basis‐set limit. Relativistic and non‐relativistic results for the dissociation energy D_e are in close agreement with each other and previously published data, provided non‐relativistic or scalar‐relativistic results are corrected for spin–orbit contributions taken from the literature. An exception is Te₂ where theoretical results scatter by 0.085 eV. By virtue of this agreement it is unexpected that comparison with the experimental D₀ or D_e dissociation energies (zero‐point vibrational effects are negligible in this context) reveal errors larger than 0.1 eV for Ga₂, Ge₂, and Sb₂. Only relativistic treatments are presented for the 6p‐block cases Tl₂ to At₂. Sufficient agreement with experimental data is found only for Pb₂ and Bi₂, the deviation of the computed and experimental D₀ values for Po₂ is again larger than 0.1 eV. Deviations of 0.1 eV between the computed and experimental D₀ values are a major reason for concern and call for additional investigations in both fields to clarify the situation.     

Effect of hydrogen gas impurities on the hydrogen dissociation on iron surface

A small addition of oxygen to hydrogen gas is known to mitigate the hydrogen embrittlement (HE) of steels. As atomic hydrogen dissolution in steels is responsible for embrittlement, catalysis of molecular hydrogen dissociation by the steel surface is an essential step in the embrittlement process. The most probable role of oxygen in mitigating HE is to inhibit the reactions between molecular hydrogen and the steel surface. To elucidate the mechanism of such surface reaction of hydrogen with the steel in the presence of oxygen, hydrogen, and oxygen adsorption, dissociation, and coadsorption on the Fe(100) surface were investigated using density functional theory. The results show that traces of O₂ would successfully compete with H₂ for surface adsorption sites due to the grater attractive force acting on the O₂ molecule compared to H₂. The H₂ dissociation would be hindered on iron surfaces with predissociated oxygen. Prompted by the notable results for H₂ + O₂, other practical systems were considered, that is, H₂ + CO and CH₄. Calculations were performed for the CO chemisorption and H₂ dissociation on iron surface with predissociated CO, as well as, CH₄ surface dissociation. The results indicate that CO inhibition of H₂ dissociation proceeds via similar mechanism to O₂ induced inhibition, whereas CH₄ traces in the H₂ gas have no effect on H₂ dissociation. © 2014 Wiley Periodicals, Inc.     

Co/AlPO4-5催化剂中Co的状态及其作用

本文用IR,TEM,FABMS,ESCA,XRD以及还原度的测定等方法,描述了Co/AlPO_4-5上Co_3O_4在氢作用下变成Co°,CoO以及未还原的Co_3O_4三种状态的还原过程和钴的颗粒分布的变化,并表明在还原过程中,可能有钴的簇状物生成,导致B酸形成。     

Condensation reaction of C4H4 with pyridine

C₄H₄⁺ reacts with pyridine (C₅H₅N) via the channels of proton transfer, charge transfer and condensation with H-elimination. The condensation reaction is of general interest in terms of basic chemistry and is the focus of the present study. By means of theoretical calculations and Fourier transform mass spectrometer experiments using deuterated pyridine and substituted pyridines, the structure of the product ion and the reaction pathways are investigated. From the experimental results we find that the H atom that is eliminated can originate from either pyridine or C₄H₄⁺. The experiments show that elimination of an H atom from C₄H₄⁺ is preferred and that there is an observable kinetic isotope effect. By replacing H atoms with methyl groups in ortho positions of pyridine, the experimental results also suggest possible steric blocking to the condensation. Based on the experimental observations and results of theoretical calculations of several possible structures of intermediates, transition states, and final product ions, a possible reaction scheme for the condensation-H-elimination is discussed.     

Comment on Numerical Treatment of GPC Data

Abstract

The numerical treatment of a chromatogram to obtain the various molecular weight averages is discussed. The method used by Cooper and Matzinger to calculate the influence of the number of data points on M_n and M_w, is criticized. Another model function is proposed. Calculations then show that the results obtained for M_n, M_w and M_z are approaching the theoretical values more and more by increasing the number of data points as it should be expected. This is in contradiction with the results of Cooper and Matzinger. The influence of the base-line correction is evaluated too.     

水浴法制备CdS薄膜产生的本征缺陷对光电学性质的影响

采用化学水浴沉积法(CBD)在钠钙玻璃衬底上制备硫化镉(CdS)薄膜,研究不同硫酸镉(CdSO_4)浓度下产生的本征缺陷对CdS薄膜光电学性质的影响。采用光致发光光谱、紫外-可见分光光度计及霍尔效应测试系统对薄膜的本征缺陷、光学及电学性质进行分析,发现CdS薄膜主要存在镉间隙(Cdi)及硫空位(VS)等本征缺陷,且VS随CdSO_4浓度的降低而逐渐减少。同时,VS缺陷的减少有利于薄膜透过率的提高,但在一定程度上降低了薄膜的电导率。根据透过率及其相关公式可知,半导体材料中透过率与电导率成e指数反比关系,适当减小薄膜的电导率可以使其透过率得到大幅度的提高,理论解释与实验结果相一致。     

Applications of ESCA to polymer chemistry: Studies of some nitroso rubbers

Molecular core binding energies of the polymers formed by copolymerization of CF₃NO with CF₂?CF₂, CF₂?CFCl, and CF₂?CFH, respectively, have been studied by means of ESCA. The results are interpreted in terms of CNDO/2 SCF MO calculations on some model systems. Some evidence for structural irregularity is found for the copolymers with CF₂?CFCl and with CF₂?CFH. The reaction mechanism for the polymerization is also discussed in terms of the experimental results and INDO SCF MO calculations.