Zur Kristallstruktur von Rb2C2 und Cs2C2

On the Crystal Structure of Rb₂C₂ and Cs₂C₂ By reaction of rubidium or caesium solved in liquid ammonia with acetylene AC₂H with A = Rb, Cs was obtained, which was subsequently converted into the binary acetylide A₂C₂ in vacuum at temperatures of 520 K (Rb₂C₂) and 470 K (Cs₂C₂) using a surplus of the respective alkali metal. The crystal structures of the very air sensitive compounds were solved and refined by a combination of both neutron and X‐ray powder diffraction data. Rb₂C₂ as well as Cs₂C₂ coexist in two modifications. The hexagonal modification (P 6 2m, Z = 3) crystallises in the known Na₂O₂ structure type with two crystallographic independent sites for the C₂^2– dumbbells. For the orthorhombic modification (Pnma, Z = 4) a new structure type was found, which is related to the PbCl₂ structure type with ordered C₂^2– dumbbells occupying the Pb sites. Temperature dependent investigations between 4 K and the decomposition temperature by the means of neutron and X‐ray powder diffraction resulted in a very complex dynamic disorder of the C₂ dumbbells, which is still not completely understood. The frequencies of the C–C stretching vibration determined by the help of Raman spectroscopy fit nicely to the results obtained for other alkali metal acetylides and alkali metal hydrogen acetylides. These results seem to indicate that the electronegativity of the alkali metal has a strong influence on the frequency of the C–C stretching vibration.     

Superconductivity in the intermetallic borocarbides YPd2B2C,YPt2B2C and LaPt2B2C

We report a detailed study of the thermodynamic properties of the conventional phonon-mediated superconductors YPd₂B₂C, YPt₂B₂C and LaPt₂B₂C. Our calculations conducted within the framework of the Migdal-Eliashberg formalism show that the experimental values of the critical temperature cannot be properly reproduced using commonly accepted value of Coulomb pseudopotential. Moreover, we proved that the values of universal ratios of conventional superconductivity appearing in the Bardeen-Copper-Schrieffer (BCS) theory are inconsistent with our results obtained from the investigated borocarbides. The observed differences are connected with the strong/medium-coupling and retardation effects existing in the studied systems.     

FeCl2-K2MoS4体系电催化还原乙炔为乙烯

采用控电位电解、循环伏安法和交流阻抗法研究了FeCl₂-K₂MoS₄体系对乙炔在石墨电极上还原为乙烯的电催化活性及反应机理。实验结果表明,当石墨阴极的电位控制在-1.50V(vs.SCE)时,FeCl₂+K₂MoS₄的DMF溶液对C₂H₂还原为C₂H₄表现出明显的电催化活性和高的选择性。在-0.5～-1.0V时Mo(Ⅵ)还原为Mo(Ⅴ);在按连串的电子传递机理进行的Mo(Ⅴ)→Mo(Ⅲ)反应的电位区间(-1.0～-1.50V)溶液中所形成的络合品种传递电子的能力更强。Mo(Ⅲ)可能是络合物的电活性成分。     

Incorporating C2 into C60 films

The material formed by depositing C(2)(-) anions onto/into thin C(60) films (on graphite) at room temperature has been studied by means of thermal desorption mass spectroscopy, ultraviolet photoionization spectroscopy, atomic force microscopy (AFM), and surface enhanced Raman spectroscopy. As-prepared, C(2)/C(60) films manifest thermal desorption behaviour which differs significantly from pure C(60) films. Whereas the latter can be fully sublimed, we observe decomposition of C(2)/C(60) films to a high-temperature-stable material while predominantly C(60), C(62), and C(64) are desorbed in parallel. Deposition of C(2)(-) also leads to significantly modified electronic and vibrational properties. Based on DFT model calculations of the Raman spectra, we suggest that as-prepared C(2)/C(60) films contain appreciable amounts of polymeric networks comprising -C(2)-C(60)-C(2)-C(60)- chains. Detection of sublimed C(62) and C(64) upon heating implies that thermal decomposition of C(2)/C(60) films involves addition/uptake of C(2) units into individual fullerene cages. Correspondingly, annealing films up to various intermediate temperatures results in significant modifications to valence-band UP spectra as well as to surface topographies as imaged by AFM. The novel carbonaceous material obtained by heating to T > 950 K has a finite density of states at the Fermi level in contrast to as-prepared C(2)/C(60). It comprises fused fullerene cages.     

An Ab Initio Study of C2H2.H2, C2H2.N2, and C2H2.Ar Complexes

Ab initio calculations at the post Hartree–Fock level were performed on complexes of acetylene with hydrogen, nitrogen, and argon. Total energies, optimum geometries, and binding energies were calculated, using the 6-311G** and the 6-31+G(2df,2pd) basis sets. Calculations showed the complexes to be more stable than the separate entities, with the exception of the acetylene–hydrogen complex.     

Na2C2 und K2C2: Synthese,Kristallstruktur und spektroskopische Eigenschaften

Na₂C₂ and K₂C₂: Synthesis, Crystal Structure, and Spectroscopic Properties By the reaction of sodium or potassium solved in liquid ammonia with acetylene and subsequent heating in high vacuum Na₂C₂ and K₂C₂ could be synthesised as single phase products. The crystal structures described by Föppl could be confirmed by X-ray and neutron diffraction experiments (K₂C₂) on powdered samples. Both compounds crystallise in a tetragonal structure (I4₁/acd, no. 142, Z = 8) which can be described as a distorted variant of the antifluorite-structure type. At temperatures above room temperature (Na₂C₂: 580 K, K₂C₂: 420 K) a reversible phase transition (1^st order transition) to a cubic modification (Fm 3 m, no. 225, Z = 4) has been observed, analogous to the alkaline earth metal acetylides. This high temperature modification represents an undistorted antifluorite structure with disordered C₂^2– dumbbells. The results of raman- and ¹³C-MAS-NMR-spectroscopic investigations are in agreement with acetylide dumbbells in the title compounds and allow a comparison to the respective monoalkalimetal and alkaline earth metal acetylides.     

Crossover Sorption of C2H2/CO2 and C2H6/C2H4 in Soft Porous Coordination Networks

Porous sorbents are materials that are used for various applications, including storage and separation. Typically, the uptake of a single gas by a sorbent decreases with temperature, but the relative affinity for two similar gases does not change. However, in this study, we report a rare example of “crossover sorption,” in which the uptake capacity and apparent affinity for two similar gases reverse at different temperatures. We synthesized two soft porous coordination polymers (PCPs), [Zn₂(L1)(L2)₂]_n (PCP-1) and [Zn₂(L1)(L3)₂]_n (PCP-2) (L1= 1,4-bis(4-pyridyl)benzene, L2=5-methyl-1,3-di(4-carboxyphenyl)benzene, and L3=5-methoxy-1,3-di(4-carboxyphenyl)benzene). These PCPs exhibits structural changes upon gas sorption and show the crossover sorption for both C₂H₂/CO₂ and C₂H₆/C₂H₄, in which the apparent affinity reverse with temperature. We used in situ gas-loading single-crystal X-ray diffraction (SCXRD) analysis to reveal the guest inclusion structures of PCP-1 for C₂H₂, CO₂, C₂H₆, and C₂H₄ gases at various temperatures. Interestingly, we observed three-step single-crystal to single-crystal (sc-sc) transformations with the different loading phases under these gases, providing insight into guest binding positions, nature of host–guest or guest-guest interactions, and their phase transformations upon exposure to these gases. Combining with theoretical investigation, we have fully elucidated the crossover sorption in the flexible coordination networks, which involves a reversal of apparent affinity and uptake of similar gases at different temperatures. We discovered that this behaviour can be explained by the delicate balance between guest binding and host–guest and guest-guest interactions.     

Gentamicin C: Separation of C1, C1a,C2, C2a and C2b components by HPLC using lsocratic ion-exchange chromatography and post-column derivatisation

Summary A HPLC system, using a strong cation exchanger and isocratic elution, was developed for the separation of the main, components of gentamicin (C₁, C_1a, C₂, C_2a) and C_2b (sagamicin) in less than 20 minutes. The detection was performed by post-column derivatisation with o-phthalaldehyde and a fluorescence detector. The detection limit was 10ng for gentamicin C₁. Some commercial gentamicin samples were analyzed.     

Effect of Jakyakgamcho-Tang Extracts on H2O2-Induced C2C12 Myoblasts

Oxidative stress is a major contributor to muscle aging and loss of muscle tissue. Jakyakgamcho-tang (JGT) has been used in traditional Eastern medicine to treat muscle pain. Here, we compared the total phenolic and flavonoid contents in 30% ethanol and water extracts of JGT and tested the preventive effects against oxidative stress (hydrogen peroxide)-induced cell death in murine C2C12 skeletal muscle cells. The total phenolic content and total flavonoid content in 30% ethanol extracts of JGT were higher than those of water extracts of JGT. Ethanol extracts of JGT (JGT-E) had stronger antioxidant activities of 2,2′-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) and 2,2′-diphenyl-1-picrylhydrazyl-scavenging activity (DPPH) than water extracts of JGT (JGT-W). JGT-E contained 19–53% (1.8 to 4.9-fold) more active compounds (i.e., albiflorin, liquiritin, pentagalloylglucose, isoliquiritin apioside, isoliquiritin, liquiritigenin, and glycyrrhizin) than JGT-W. The ethanol extracts of JGT inhibited hydrogen peroxide-induced cell death and intracellular reactive oxygen species generation more effectively than the water extract of JGT in a dose-dependent manner. For the first time, these results suggest that ethanol extract of JGT is relatively more efficacious at protecting against oxidative stress-induced muscle cell death.     

New calculations on the ion-molecule processes C2H2(+) + H2 --> C2H3(+) + H and C2H2(+) + H2 --> C2H4+

New high-level quantum chemical calculations have been undertaken to understand the rates and mechanisms of the reactive and associative channels for the reactants C2H2(+) + H2. The reactive channel, which produces C2H3(+) + H, has been shown to be slightly endothermic, confirming earlier calculations at a somewhat lower level and in agreement with some recent experimental work. The associative channel, leading to C2H4+, has been shown to proceed via a transition state with negative energy relative to the reactants, so that association is predicted to be efficient. This result is in conflict with an earlier theoretical study but in agreement with low-temperature experimental measurements.     

乙烷乙烯乙炔燃烧实验现象分析及其探讨

从键能、反应速率、含碳量、反应历程等方面分析探讨,得出乙烷乙烯乙炔在空气中燃烧现象不同是由分子结构中单双叁键活泼性不同造成的结论,否定了长期以来的含碳量评价标准,肯定了物质结构决定性质这一论断。     

Soot formation from C2H2 and C2H4 pyrolysis at different temperatures

A study of the pyrolysis of two hydrocarbons, C₂H₂ and C₂H₄, at different temperatures has been carried out in order to compare their behaviour in terms of soot and gas yields and gas composition. Pyrolysis experiments have been performed in the same conditions for both hydrocarbons: an inlet hydrocarbon concentration of 15,000 ppmv and a temperature range of 1000–1200 °C. For C₂H₂ and C₂H₄ pyrolysis tests, the results present the same trend when increasing the temperature: an increase in soot yield, a decrease in gas yield and a similar evolution of the outlet gases. Comparatively, it can be observed that acetylene is a more sooting hydrocarbon than ethylene for a given temperature. Additionally, the study of soot reactivity with O₂ and NO shows that the soot samples obtained from ethylene show a slightly higher reactivity towards O₂ and NO than the soot samples formed from acetylene.     

C2H4CnH2n

镍(Ni)基催化剂在低碳烯烃聚合领域具有重要的地位,也是该领域研究的热点.自Johnson等报道(J.Am.Chem.Soc.,1995, 117, 6414–6415)二亚胺配体络合的Ni(II)催化剂可有效降低烯烃聚合度,降低产物中非线性烯烃的选择性,甚至可以生成α-烯烃以来,掀起了Ni基催化剂在烯烃聚合领域的研究热潮.从均相到负载型多相Ni基催化剂,从载体类型到配体性质,从Ni纳米粒子的粒径调控到金属表面价态,关于Ni活性中心的研究工作一直存在争论.本课题组之前研究结果表明,曾明确了无定形硅铝(ASA)载体负载的Ni催化剂,经惰性气氛(N2)预处理得到的一价Ni是烯烃齐聚反应的主要活性中心(J.Chem. Soc. Chem. Commun., 1991, 126–127).本文进一步深入研究了不同Al2O3含量的ASA载体上Ni活性位点的结构及其在乙烯齐聚反应中的活性.27AlNMR结果表明,催化剂中的铝存在三种配位方式,分别为AlⅣ、AlⅤ和AlⅥ,其中AlⅣ含量随Al2O3含量的增加而增加.载体中铝配位方式的不同,导致其表面金属负载的金属Ni活性位点所处的结构亦不同.原位FTIR-CO和H2-TPR实验结果表明,催化剂表面存在两种不同结构分布的Ni位点,分别是接枝在弱酸性硅醇上的Ni2+阳离子和Si-(OH)-Al桥式羟基离子交换位置的Ni2+阳离子.多数研究者认为,位于离子交换位置处孤立的Ni阳离子是反应的活性中心.然而,近期有研究者提出负载在酸性硅烷醇表面孤立的Ni2+阳离子为反应的活性中心物质.本文研究发现,随着Al2O3负载量的降低,处于离子交换位置处的Ni2+离子含量逐渐减少,而处于硅醇缺陷位点处的Ni2+离子含量则逐渐增多.原位FTIR-CO分析结果表明,处于硅醇缺陷位点处的Ni2+离子物种在惰性气氛中更易于转化为活性中心Ni+.相应的催化反应结果表明,相比于离子交换位置的Ni2+物种,具有与硅醇缺陷位点相连的Ni2+离子结构更有利于表现出更高的乙烯齐聚化活性.由此可知,处于硅醇缺陷位点的Ni2+物种是乙烯齐聚反应的活性中心的前驱体.本文进一步研究了硅醇缺陷位点处的Ni2+离子物种更易于转化为活性中心Ni+的原因.H2-TPR结果表明,相比于离子交换位置的Ni2+物种,处于硅醇缺陷位点的Ni2+物种与载体之间的相互作用力更弱.C2H4-TPD结果进一步表明,具有这种相对较弱的金属载体间作用力结构的催化剂对反应物C2H4分子的吸附作用力相对更强,吸附量也相对增多,因此其乙烯齐聚的催化性能更优.本研究结果对理解活性中心结构和合理设计催化剂提供参考.     

Collisions of slow polyatomic ions with surfaces: dissociation and chemical reactions of C2H2+*, C2H3+, C2H4+*, C2H5+, and their deuterated variants C2D2+* and C2D4+* on room-temperature and heated carbon surfaces

Interaction of C2Hn+ (n = 2-5) hydrocarbon ions and some of their isotopic variants with room-temperature and heated (600 degrees C) highly oriented pyrolytic graphite (HOPG) surfaces was investigated over the range of incident energies 11-46 eV and an incident angle of 60 degrees with respect to the surface normal. The work is an extension of our earlier research on surface interactions of CHn+ (n = 3-5) ions. Mass spectra, translational energy distributions, and angular distributions of product ions were measured. Collisions with the HOPG surface heated to 600 degrees C showed only partial or substantial dissociation of the projectile ions; translational energy distributions of the product ions peaked at about 50% of the incident energy. Interactions with the HOPG surface at room temperature showed both surface-induced dissociation of the projectiles and, in the case of radical cation projectiles C2H2+* and C2H4+*, chemical reactions with the hydrocarbons on the surface. These reactions were (i) H-atom transfer to the projectile, formation of protonated projectiles, and their subsequent fragmentation and (ii) formation of a carbon chain build-up product in reactions of the projectile ion with a terminal CH3-group of the surface hydrocarbons and subsequent fragmentation of the product ion to C3H3+. The product ions were formed in inelastic collisions in which the translational energy of the surface-excited projectile peaked at about 32% of the incident energy. Angular distributions of reaction products showed peaking at subspecular angles close to 68 degrees (heated surfaces) and 72 degrees (room-temperature surfaces). The absolute survival probability at the incident angle of 60 degrees was about 0.1% for C2H2+*, close to 1% for C2H4+* and C2H5+, and about 3-6% for C2H3+.     

Efficient C2 functionalisation of 2H-2-imidazolines

Alkylation and oxidation of 2H-2-imidazolines, followed by regioselective deprotection, thionation and microwave-assisted Liebeskind-Srogl reaction, efficiently led to 2-aryl-2-imidazolines as new analogues of p53-hdm2 interaction inhibitors (Nutlins).     

Semiempirical calculation of harmonic force constants: CNDO/2 and MINDO/2 study of C2H6, C2H4 and C2H2

The complete quadratic force fields of ethane, ethylene and acetylene have been calculated from CNDO/2 and MINDO/2 wavefunctions by the force method. Agreement with experiment is satisfactory for both methods. In the CNDO method the stretching force constants must be scaled empirically to obtain realistic values. It is particularly significant that stretching-deformation and deformation-deformation coupling force constants are correctly reproduced by the CNDO method and with the exception of the rocking-rocking couplings, also by the MINDO method. It is concluded that such calculations may usefully contribute to the determination of force fields.     

OH+ C2H2N←C2H3 + NO→CH3 + NCO反应机理的密度泛函理论研究

应用密度泛函理论研究了反应通道(a)C2H3 NO→CH3 NCO和(b)C2H3 NO→OH C2H2N的反应机理．在B3LYP／6-31G(d)水平上优化了反应物、中间体、过滤态、产物的几何构型，通过频率分析确定了11个中间体和10个过渡态．所有的反应物、中间体、过渡态、产物都在CCSD／6-311 G(d，P)水平上进行了单点能较正．并讨论了反应的异构化过程．计算结果表明10是能量最低的中间体，比反应物的能量低308．479kJ／mol；过渡态1／3，2／5，3／4，4／8比反应物的能量高，其中3／4是能量最高的过渡态，比反应物的能量高91．894kJ／mol．通道(a)和(b)的理论放热值分别为111．059和96．619kJ／mol．