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121.
M. Sc. William P. Clark Dr. Simon Steinberg Prof. Dr. Richard Dronskowski Dr. Catherine McCammon Dr. Ilya Kupenko Dr. Maxim Bykov Prof. Dr. Leonid Dubrovinsky Dr. Lev G. Akselrud Priv.-Doz. Dr. Ulrich Schwarz Prof. Dr. Rainer Niewa 《Angewandte Chemie (International ed. in English)》2017,56(25):7302-7306
The combination of laser-heated diamond anvil cells and synchrotron Mössbauer source spectroscopy were used to investigate high-temperature high-pressure chemical reactions of iron and iron nitride Fe2N with nitrogen. At pressures between 10 and 45 GPa, significant magnetic hyperfine splitting indicated compound formation after annealing at 1300 K. Subsequent in situ X-ray diffraction reveals a new modification of FeN with NiAs-type crystal structure, as also rationalized by first-principles total-energy and chemical-bonding studies. 相似文献
122.
运用第一性原理赝势方法,对氮化硅新相(六方Pˉ6和Pˉ6′相)的电子结构、光学性质和相变过程进行分析,研究能带结构、介电函数谱、反射谱和能量损失函数的变化机理.研究发现,β→Pˉ6→δ相变是可行的,在室温下β→Pˉ6和Pˉ6→δ相变的临界压强分别为42.9和47.7 GPa;相界的斜率为正值表明Pˉ6→δ相变过程伴随着晶胞体积的塌缩;Pˉ6和Pˉ6′相分别属于直接带隙和间接带隙半导体,能隙宽度分别为4.98和4.01 eV;得到了两相的零频介电常数;反射谱表明,两相的强反射峰均位于真空紫外线区域,因此可以用作紫外光屏蔽或紫外探测材料;在可见光区域,两相表现为近似透明. 相似文献
123.
Eva Wirnhier Maria B. Mesch Prof. Dr. Jürgen Senker Prof. Dr. Wolfgang Schnick 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(6):2041-2049
Until recently, melam, [C3N3(NH2)2]2NH, has been regarded as a short‐lived intermediate in the condensation process of melamine that is only detectable under special reaction conditions owing to its high reactivity. A new synthetic approach has allowed a closer look at the formation and condensation behavior of melam by using elevated ammonia pressure in autoclaves. Whereas the thermal treatment of dicyandiamide at 450 °C and 0.2 MPa ammonia yielded melam in large amounts, prolonged treatment under these conditions (9 days) led to the formation of a melam–melem adduct, thus enabling the first insight into the condensation process of melam into melem. The hydrothermal treatment of melam at 300 °C (24 h) yields melam hydrate, [C3N3(NH2)2]2NH ? 2 H2O (space group P21/c; a=676.84(2), b=1220.28(4), c=1394.24(4) pm; β=98.372(2)°; V=1139.28(6)×106 pm3; Z=4), which crystallizes as a layered structure that is composed of almost‐planar melam molecules, thereby forming ellipsoidal rosette‐like motifs. The resulting voids are filled with four water molecules, thus forming a dense network of hydrogen bonds. 相似文献
124.
A first-principles study on the mechanical stability, elastic and thermodynamic properties of WN2 with P63/mmc and P-6m2 phases are reported using the pseudo potential plane wave method within the generalized gradient approximation. The calculated equilibrium parameters are in good agreement with the available theoretical data. A complete elastic tensor and crystal anisotropies of the ultra-incompressible WN2 are determined in the wide pressure range. By the elastic stability criteria, it is predicted that P63/mmc and P-6m2 phases in WN2 are not stable above 175.1 GPa and 170.1 GPa, respectively. Finally, by using the quasiharmonic Debye model, the isothermal and adiabatic bulk modulus, and the heat capacity of WN2 are also successfully obtained. 相似文献
125.
Yumeng Liu Dong Tian Akash N. Biswas Zhenhua Xie Sooyeon Hwang Ji Hoon Lee Hong Meng Jingguang G. Chen 《Angewandte Chemie (International ed. in English)》2020,59(28):11345-11348
The electrochemical carbon dioxide reduction reaction (CO2RR) to produce synthesis gas (syngas) with tunable CO/H2 ratios has been studied by supporting Pd catalysts on transition metal nitride (TMN) substrates. Combining experimental measurements and density functional theory (DFT) calculations, Pd‐modified niobium nitride (Pd/NbN) is found to generate much higher CO and H2 partial current densities and greater CO Faradaic efficiency than Pd‐modified vanadium nitride (Pd/VN) and commercial Pd/C catalysts. In‐situ X‐ray diffraction identifies the formation of PdH in Pd/NbN and Pd/C under CO2RR conditions, whereas the Pd in Pd/VN is not fully transformed into the active PdH phase. DFT calculations show that the stabilized *HOCO and weakened *CO intermediates on PdH/NbN are critical to achieving higher CO2RR activity. This work suggests that NbN is a promising substrate to modify Pd, resulting in an enhanced electrochemical conversion of CO2 to syngas with a potential reduction in precious metal loading. 相似文献
126.
Dr. Wai‐Lun Man Jianhui Xie Po‐Kam Lo Dr. William W. Y. Lam Dr. Shek‐Man Yiu Dr. Kai‐Chung Lau Prof. Tai‐Chu Lau 《Angewandte Chemie (International ed. in English)》2014,53(32):8463-8466
Exploring new reactivity of metal nitrides is of great interest because it can give insights to N2 fixation chemistry and provide new methods for nitrogenation of organic substrates. In this work, reaction of a (salen)ruthenium(VI) nitrido complex with various alkynes results in the formation of novel (salen)ruthenium(III) imine complexes. Kinetic and computational studies suggest that the reactions go through an initial ruthenium(IV) aziro intermediate, followed by addition of nucleophiles to give the (salen)ruthenium(III) imine complexes. These unprecedented reactions provide a new pathway for nitrogenation of alkynes based on a metal nitride. 相似文献
127.
Schaaf Peter Landry Felix Han Meng Carpene Ettore Lieb Klaus-Peter 《Hyperfine Interactions》2002,139(1-4):307-314
Nitriding is a common method for improving the hardness, mechanical properties, wear and corrosion resistance of metals. Laser nitriding of metals is an efficient process, where the irradiation of surfaces in air or nitrogen atmospheres with short laser pulses leads to a fast take-up of nitrogen into the irradiated surfaces. This process has been extensively investigated for pure iron, but usually, no tools or functional parts are made of pure iron. Mainly steel or cast iron is used as a base material. Therefore, when looking for technical applicability, also the influence of alloying elements on the laser nitriding process is of great interest. Besides the pure iron various carbon steels and an austenitic stainless steel were studied in laser nitriding experiments in order to investigate the influence of the material itself. Here, the process is investigated via Conversion Electron and X-ray Mössbauer Spectroscopy (CEMS and CXMS), Resonant Nuclear Reaction Analysis (RNRA), and X-Ray Diffraction (XRD). It appears that carbon steels are even better suited for the laser nitriding process than pure iron, and the laser nitriding also works efficiently for the stainless steel which is normally difficult to be nitrided. 相似文献
128.
Nucleophilic Reactivity of a Nitride‐Bridged Diuranium(IV) Complex: CO2 and CS2 Functionalization
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Marta Falcone Lucile Chatelain Dr. Marinella Mazzanti 《Angewandte Chemie (International ed. in English)》2016,55(12):4074-4078
Thermolysis of the nitride‐bridged diuranium(IV) complex Cs{(μ‐N)[U(OSi(OtBu)3)3]2} ( 1 ) showed that the bridging nitride behaves as a strong nucleophile, promoting N?C bond formation by siloxide ligand fragmentation to yield an imido‐bridged siloxide/silanediolate diuranium(IV) complex, Cs{(μ‐NtBu)(μ‐O2Si(OtBu)2)U2(OSi(OtBu)3)5}. Complex 1 displayed reactivity towards CS2 and CO2 at room temperature that is unprecedented in f‐element chemistry, affording diverse N‐functionalized products depending on the reaction stoichiometry. The reaction of 1 with two equivalents of CS2 yielded the thiocyanate/thiocarbonate complex Cs{(μ‐NCS)(μ‐CS3)[U(OSi(OtBu)3)3]2} via a putative NCS?/S2? intermediate. The reaction of 1 with one equivalent of CO2 resulted in deoxygenation and N?C bond formation, yielding the cyanate/oxo complex Cs{(μ‐NCO)(μ‐O)[U(OSi(OtBu)3)3]2}. Addition of excess CO2 to 1 led to the unprecedented dicarbamate product Cs{(μ‐NC2O4)[U(OSi(OtBu)3)3]2}. 相似文献
129.
130.