共查询到20条相似文献,搜索用时 62 毫秒
1.
Manfred Martin Richard Dronskowski Jürgen Janek Klaus-Dieter Becker Daniel Roehrens Jochen Brendt Marck W. Lumey Lakshmi Nagarajan Ilia Valov Alexander Börger 《Progress in Solid State Chemistry》2009,37(2-3):132-152
Within the ternary system Ga–O–N we performed experimental and theoretical investigations on the thermodynamics, structure and kinetics of new stable and metastable compounds.We studied the ammonolysis of β-Ga2O3 at elevated temperatures by means of ex situ X-ray diffraction, ex situ neutron diffraction, and in situ X-ray absorption spectroscopy (XAS). From total diffraction pattern refinement with the Rietveld method we analyzed the anionic occupancy factors and the lattice parameters of β-Ga2O3 during the reaction. Within the detection limits of these methods, we can rule out the existence of a crystalline oxynitride phase that is not derived from wurtzite-type GaN. The nitrogen solubility in β-Ga2O3 was found to be below the detection limit of about 2–3 at.% in the anionic sublattice. The kinetics of the ammonolysis of β-Ga2O3 to α-GaN and of the oxidation of α-GaN to β-Ga2O3 was studied by means of in situ X-ray absorption spectroscopy. In both cases the reaction kinetics could be described well by fitting linear combinations of β-Ga2O3 and α-GaN spectra only, excluding that other crystalline or amorphous phases appear during these reactions. The kinetics of the ammonolysis can be described well by an extended Johnson–Mehl–Avrami–Kolmogorow model with nucleation and growth of GaN nuclei, while the oxidation kinetics can be modeled by a shrinking core model where Ga2O3 grows as a layer. Investigations by means of TEM and SEM support the assumptions in both models.To investigate the structure and energetics of spinel-type gallium oxynitrides (γ-galons) we performed first-principles calculations using density-functional theory. In addition to the ideal cubic γ-Ga3O3N we studied gallium deficient γ-galons within the Constant-Anion-Model.In highly non-stoichiometric, amorphous gallium oxide of approximate composition GaO1.2 we found at a temperature around 670 K an insulator–metal transition, with a conductivity jump of seven orders of magnitude. We demonstrate through experimental studies and density-functional theory calculations that the conductivity jump takes place at a critical gallium concentration and is induced by crystallization of stoichiometric β-Ga2O3 within the metastable oxide matrix. By doping with nitrogen the critical temperature and the conductivity in the highly conducting state can be tuned. 相似文献
2.
This paper describes the first assessment of intermolecular weak N–H…F and N–H…Cl hydrogen bonding in stabilising hetero- and homodimers in solution. Aromatic amide and urea monomers have been designed and synthesised. The association constants of the heterodimers formed by two complementary monomers and the homodimers formed by self-complementary monomers have been determined by using 1H titration and dilution experiments. The results show that both N–H…F and N–H…Cl hydrogen bonds are able to stabilise the corresponding dimers to a measurable extent, even though the stability of the dimers is generally low. 相似文献
3.
《Physics and Chemistry of Liquids》2012,50(2):117-126
Complex formation of 1?:?1 mixtures of naphthols, viz. (α-naphthol and β-naphthol) with triethylamine in benzene have been studied at a frequency of 2?MHz in the concentration range of 0.010–0.090 and at varying temperatures of 30, 40 and 50°C. Using the measured ultrasonic velocity, the thermoacoustical parameters such as adiabatic compressibility, intermolecular free length, molar sound velocity, molar compressibility and acoustic impedance have been calculated. The ultrasonic velocity shows a maxima and adiabatic compressibility shows a corresponding minima as a function of concentration for these mixtures. These, in turn, are used to study the solute–solute interaction and the possibility of complex formation between unlike molecules of naphthols and triethylamine through intermolecular hydrogen bonding. The hydrogen bond is formed between hydrogen atom of naphthols and nitrogen atom of triethylamine molecule. The result obtained using infrared spectroscopy for both the systems also supports the existence of complex formation through intermolecular hydrogen bonding. 相似文献
4.
Debbie J. Beard Sumer A. Barakat Nathanael B. Lockhart Chandler R. Pace Charles U. Pittman Jr. Burnette W. Hamil Svein Saebo 《Structural chemistry》2012,23(2):351-357
A systematic computational study of four-membered cyclic ketene –O,O–, –O,S–, –O,N–, –S,N– and –N,N-acetals as well as their protonated analogs have been performed at the second order M?ller Plesset level with a polarized
triple zeta basis set. The main purpose of this study was to make predictions about the nucleophilicity of these systems and
the variations in nucleophilicity with the hetero atoms. Our calculations suggest that all six target molecules are good nucleophiles,
and that the N,N analog is the strongest and the S,S analog the weakest nucleophile. Our results include molecular geometries, bond lengths, proton affinities, vibrational frequencies,
and calculated charges. 相似文献
5.
《Journal of Coordination Chemistry》2012,65(20):3635-3647
Reactions of anhydrous copper(II) chloride with NaX (1 : 1 or 1 : 2) and AgX (1 : 2) containing appropriate N,N,N′,N′-tetraalkylpyridine-2,6-dicarboxamides(O-daap) in CH3CN yield monosubstituted five-coordinate [Cu(L1)Cl(CF3SO3)] (1), [Cu(L2)Cl(ClO4)] (2), [Cu(L3)Cl(ClO4)] (3), and six-coordinate [Cu(L2)(CF3SO3)2] · H2O (4) (X = ?OClO3 and–OSO2CF3; L1 = N,N,N′,N′-tetraethylpyridine-2,6-dicarboxamides; L2 = N,N,N′,N′-tetraisopropylpyridine-2,6-dicarboxamides; L3 = N,N,N′,N′-tetraisobutylpyridine-2,6-dicarboxamides). The structures of these complexes have been determined by X-ray crystallography. The Cu2+ in 1–3 adopts distorted square-pyramidal geometry, while 4 exhibits octahedral structure. Steric factors in conjunction with lattice effects and the nature of the anions are responsible for the variety in coordination spheres. These compounds undergo extensive intermolecular H-bonding to give to 2-D sheets extending along various planes. 相似文献
6.
《中国科学:化学(英文版)》2017,(11)
Amide, as a ubiquitous functional group, is essential in various aspects of chemistry and biology. Although the history of studying amide is rich and fruitful, the synthetic application of amide is very limited due to the inertness of amide C–N bond. Recently,significant advances have been achieved towards the nickel-mediated C–N activation of amides. This approach allows a facile generation of acyl-nickel intermediates, and a number of unique transformations have been designed and realized based on the amide C–N bond activation. Focused on the catalytic transformation, this review summarizes and categorizes the recent advances on the synthetic applications of Ni-mediated C–N bond activation of amides. 相似文献
7.
Maria Brandl Klaus Lindauer Michael Meyer Jürgen Sühnel 《Theoretical chemistry accounts》1999,101(1-3):103-113
Small molecule studies indicate that C–H...X interactions (X: O,N) constitute weak H-bonds. We have performed a comprehensive
analysis of their occurrence and geometry in RNA structures. Here, we report on statistical properties of the total set of
interactions identified and discuss selected motifs. The distance/angle distribution of all interactions exhibits an excluded
region where the allowed C–H...X angle range increases with an increasing H...X distance. The preferred short C–H...X interactions
in RNA are backbone-backbone contacts between neighbour nucleotides. Distance/angle distributions generated for various interaction
types can be used for error recognition and modelling. The axial C2′(H)...O4′ and C5′(H)...O2′ interactions connect two backbone
segments and form a seven-membered ring that is specific for RNA. An AA base pair with one standard H-bond and one C–H...N
interaction has been identified in various structures. Despite the occurrence of short C–H...X contacts their free energy
contribution to RNA stability remains to be assessed.
Received: 17 May 1998 / Accepted: 4 August 1998 / Published online: 2 November 1998 相似文献
8.
The monomer/dimer equilibrium has been studied for a series of alkyl and aryl substituted and functionalized iminochlorophosphane
species of the type R–N=P–Cl. In agreement with experiment, theoretical data always favor the dimer when the group R is small,
while bulky groups such as Mes* destabilize the dimer by a considerable steric repulsion. This effect is superimposed by electronic
effects. Para-substitution in the aryl systems either favors the monomer (energy gain ca. 15–30 kJ/mol) when a π-electron donating group such as p-NMe2 is used or favors the dimer when a π-electron withdrawing group such as p-NO2 is used (energy gain ca. 1–13 kJ/mol). 相似文献
9.
Kyle W. Knouse Laura E. Ator Lauren E. Beausoleil Zachary J. Hauseman Rebecca L. Casaubon Gregory R. Ott 《Tetrahedron letters》2017,58(3):202-205
Improved and expanded one-pot, two-component syntheses of bicyclic heterocycles containing a 3-N-acyl-3-amino-1,2-pyrazole motif from N′-hydroxy-carboxyamidines and acylbenzotriazoles have been developed. Importantly, this sequence obviates the need for hydrazine or N-aminating reagents to synthesize the key nitrogen–nitrogen (N–N) bond of these heterocycles, which is formed via Boulton-Katritzky rearrangement. A diverse array of pharmaceutically relevant N–N containing heterocycles has been prepared with this methodology using readily available reagents without the need for special equipment or conditions. 相似文献
10.
The reaction of 1,1-diaminoferrocene 1 with 1,3-dichloro-1,1,3,3-tetramethyl-1,3-disiloxane in the presence of triethylamine gave the new 1,5,3,2,4-diazaoxadisila[5]ferrocenophane, which was characterized in the solid state by X-ray structural analysis, 13C and 29Si MAS NMR spectroscopy, and in solution by [1H], [13C], [15N], and [29Si]NMR spectroscopy. The ideal ferrocene geometry is slightly distorted, and the cycle containing the heteroelements N, Si, and O is nonplanar. In solution, NMR spectra indicate dynamic processes which may involve both the cyclopentadienyl rings and ring inversion. 相似文献
11.
Zhong Linlin Wang Jiayu Xu Jie Wang Xiaohua Rong Mingzhe 《Plasma Chemistry and Plasma Processing》2019,39(6):1379-1396
Plasma Chemistry and Plasma Processing - C4F7N is one of the most promising candidate to replace SF6 as arc quenching medium. Some buffer gases (N2 and CO2) are usually mixed with C4F7N to reduce... 相似文献
12.
Dong Tang Xiao-Long Li Xin Guo Ping Wu Ji-Hui Li Kai Wang Huan-Wang Jing Bao-Hua Chen 《Tetrahedron》2014
An efficient and facile approach to synthesize imidazoles from amidines and arylketone via oxidative coupling of sp3 C–H bond and N–H bond is reported. This strategy exhibits high performance in terms of regioselectivity with moderate to high yields by using easily available materials, and provides an alternative method to synthesize multi-substituted imidazole skeletons. 相似文献
13.
Ines García-Lodeiro A. Fernández-Jiménez M. Teresa Blanco Angel Palomo 《Journal of Sol-Gel Science and Technology》2008,45(1):63-72
The study explored the compatibility between the main product of Portland cement hydration and the main product of the alkali
activation of fly ash: C–S–H and N–A–S–H gels, respectively. Both gels were synthesized with laboratory reagents at different
pH values. Blends of the two were synthesized as well, using the sol–gel procedure. All the gels were characterized with Fourier
transform IR spectroscopy (FTIR). The gels synthesized with this procedure were shown to precipitate together with a silica-rich
gel. In addition, the pH level was found to play a determinant role in both C–S–H and N–A–S–H gel synthesis. The C–S–H gel
is the major phase formed at pH > 11 and N–A–S–H gel for pH > 12. The results relating to the joint synthesis of the two (C–S–H
and N–A–S–H) gels were not conclusive. Technique used for the characterization failed to differentiate between them in the
blended material.
相似文献
Ines García-LodeiroEmail: |
14.
《Comptes Rendus de l''Academie des Sciences Series IIB Mechanics Physics Astronomy》2000,3(5):345-351
Bombardment of a silicon target in a high vacuum with a molecular beam (mixture of high energy H2+N2, obtained by charge exchange) and a thermal beam of O2 produces on the target a variety of compounds. The target is then bombarded by the same molecular beams which produce, extracted by an electrostatic field at an energy of about 10 keV, molecular ions due to the compounds thus formed. These ions are analysed (electromagnet) to give a primary spectrum of ions according to their mass, which are individually selected and dissociated in a collision cell (same H2+N2 mixture). Mass analysis of the dissociation fragments leads to the identification of silicon clusters (Si)n and of Si–O–N–H derivatives, the fragmentations of which permit a definitive determination of their molecular complexity. Dissociation spectra have thus been obtained for some of the most intense peaks of the primary spectrum, on the one hand, and on the other hand for some peaks of lower intensity but of special interest to us (see below). The composition of the fragments is confirmed by the study of the satellite ions derived from the natural 28, 29 and 30 isotopes of silicon, and by the use of deuterium instead of hydrogen. None of the Si–O–N–H derivatives obtained was apparently known earlier. It is shown that some of these molecules (those ‘of special interest to us’) may be identical with sila-analogues of standard amino acids and of nucleic bases: the fact that their fragmentations are identical with those of the corresponding carbon analogues speaks in favour of a structural identity. However, one cannot yet distinguish between the various possible isomeric arrangements, as none of them has been independently prepared, which excludes a direct comparison with reference samples, and as these isomers might give identical fragments; we hope to be able to resolve this ambiguity later. Anyhow, the substances formed are the most complex molecular silicon derivatives so far produced: e.g. Si2O2NH5, Si3O2NH7, Si4O3NH9, Si4O2N2H4, Si4ON3H5, Si5O3N2H10, Si5O2NH11, corresponding to sila-glycine, sila-alanine, sila-threonine, sila-uracile, sila-cytosine, sila-valine, sila-glutamine, – or isomers. Similar results have been obtained using a silicon dioxide target and high energy molecular beams of hydrogen and of nitrogen, without thermal oxygen, or with a carborundum target. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SASmolecular impact / silicon derivatives / amino-acid silicon analogues 相似文献
15.
16.
Tian Yongmei Huang Jichun Gao Yuan Cao Dianxue Wang Guiling 《Journal of Solid State Electrochemistry》2012,16(5):1901-1906
Fe–N–C catalysts were prepared through metal-assisted polymerization method. Effects of carbon treatment, Fe loading, nitrogen
source, and calcination temperature on the catalytic performance of the Fe–N–C for H2O2 electroreduction were measured by voltammetry and chronoamperometry. The Fe–N–C catalyst shows optimal performance when prepared
with pretreated active carbon, 0.2 wt.% Fe, paranitroaniline (4-NA) and one-time calcination. The Fe–N–C catalyst displayed
good performance and stability for electroreduction of H2O2 in alkaline solution. An Al–H2O2 semi-fuel cell was set up with Fe–N–C catalyst as cathode and Al as anode. The cell exhibits an open-circuit voltage of 1.3 V
and its power density reached 51.4 mW cm−2 at 65 mA cm−2. 相似文献
17.
DABCO (1,4-diazabicyclo[2.2.2]octane) based Cu(I) metal organic framework (here after represented as Cu(I)-MOF) catalyzed Sonogashira cross-coupling reaction of iodobenzene and phenylacetylene was conducted smoothly to afford diphenylacetylene in excellent yield under N2 atmosphere. For comparative study, piperidine based Cu(I) clusters were also investigated. Among these catalysts, Cu(I)-MOF exhibited higher activity with good selectivity for the C–C cross-coupled product. Cu(I) catalysts investigated in this study exhibited similar activity in the C–C homo-coupling reaction of phenylacetylene in O2 atmosphere. Application of these catalysts was extended in the C–N coupling reactions between phenylboronic acid and aromatic/aliphatic/heterocyclic amines. Cu(I)-MOF can be readily recovered from the reaction mixture and reused for several cycles without loss in the catalytic activity. 相似文献
18.
<正>1 X-ray crystallography Suitable single crystal of 2 was sealed in a thin-walled glass capillary, and data collection was performed at 293(2) K on a Bruker SMART diffractometer with graphite-monochromated Mo Kα radiation(λ = 0.71073 ). Suitable single crystals of 3and 4 were mounted under nitrogen atmosphere on a glass fiber, and data collection was performed at 133(2) K on a Bruker APEX2 diffractometer with graphite-monochromated Mo Kα radiation(λ = 0.71073 ). The SMART program package was used to determine the unit cell parameters. The absorption correction was applied using SADABS. The structures were solved 相似文献
19.
P. Rutkowski L. Stobierski G. Górny 《Journal of Thermal Analysis and Calorimetry》2014,116(1):321-328
This study concerns new Si3N4–graphene composites manufactured using the hot-pressing method. Because of future applications of silicon nitride for cutting tools or specific parts of various devices having contact with high temperatures there is a need to find a ceramic composite material with good mechanical and especially thermal properties. Excellent thermal properties in the major directions are characteristic of graphene. In this study, the graphene phase is added to the silicon nitride phase in a quantity of up to 10 mass%, and the materials are sintered under uniaxial pressure. The mixture of AlN and Y2O3 is added as sintering activator to the composite matrix. The studies focus on thermal stability of produced composites in argon and air conditions up to the temperature of 1,000 °C. The research also concerns the influence of applied uniaxial pressure during the sintering process on the orientation of graphene nanoparticles in the Si3N4 matrix. The study also presents research on anisotropy of thermal diffusivity and following thermal conductivity of ceramic matrix composites versus the increasing graphene quantity. Most of the presented results have not been published in the literature yet. 相似文献
20.
Shashi Singh Shahla Parveen Divya Shukla Maimoona Yasmin Manisha Gupta J. P. Shukla 《Journal of solution chemistry》2011,40(5):889-899
Experimental values of the density and ultrasonic velocity have been measured for binary mixtures of butylamine with 1-butanol
and with tert-butanol at temperatures of 293.15, 303.15 and 313.15 K over the entire mole fraction range. From these data, the excess molar
volumes, deviations in isentropic compressibility, excess internal pressures, and excess molar enthalpies have been calculated.
All of the excess functions were fitted to Redlich-Kister polynomial relations to estimate the adjustable parameters along
with the standard deviations of the fits. The variations of these excess functions with mole fraction of butylamine have been
examined. The changes in these parameters with composition suggest that the interaction between butylamine and 1-butanol is
strong, whereas its interaction with tert-butanol is weak. Further, the partial molar volumes and partial molar compressibilities at infinite dilution have also been
evaluated since these parameters provide better insight for studying intermolecular interactions. 相似文献