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121.
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123.
Kuznetsov V. V. Kutepov S. A. Makhova N. N. Lyssenko K. A. Dmitriev D. E. 《Russian Chemical Bulletin》2003,52(3):665-673
A new method was developed for the synthesis of 6-substituted 1,5-diazabicyclo[3.1.0]hexanes and 7-substituted 1,6-diazabicyclo[4.1.0]heptanes by condensation of N-monohalotrimethylene- and N-monohalotetramethylenediamines with carbonyl compounds in the presence of bases. X-ray diffraction studies and quantum-chemical B3LYP/6-31G* calculations demonstrated that the conformations of the resulting bicyclic systems are stabilized by stereoelectronic interactions. As a result, a boat conformation prevails in 1,5-diazabicyclo[3.1.0]hexanes, whereas the energies of chair, half-chair, and boat conformations of 1,6-diazabicyclo[4.1.0]heptanes are equalized. 相似文献
124.
Kerry J. Adams Thomas D. McGrath Georgina M. Rosair Andrew S. Weller Alan J. Welch 《Journal of organometallic chemistry》1998,550(1-2)
Analysis of the structures of 8,8-(PPh3)2-8,7-nido-RhSB9H10 and 9,9-(PPh3)2-9,7,8-nido-RhC2B8H11 by RMS misfit calculations has confirmed that these rhodaheteroboranes possess nido 11-vertex cluster geometries in apparent contravention of Wade's rules. However, examination of the molecular structures of both species shows that the {RhP2} planes are inclined by ca. 66° with respect to the metal-bonded SB3 or CB3 faces, and that two weak ortho-CHRh agostic interactions occupy the vacant co-ordination position thereby created. As a consequence of these agostic bonds the Rh atom, and hence the overall cluster, is provided with an additional electron pair, meaning that their nido structures are now fully consistent with Wade's rules. The chelated diphosphine compound 8,8-(dppe)-8,7-nido-RhSB9H10 is similar to the PPh3 compound in showing the same agostic bonding. Attempts to prepare a bis-P(OMe)3 analogue result in ligand scavenging and the formation of 8,8,8-{P(OMe)3}3-8,7-nido-RhSB9H10. Similarly, reaction between Cs[6-arachno-SB9H12] and RhCl(dmpe)CO does not result in CO loss but in formation of 8,8-(dmpe)-8-(CO)-8,7-nido-RhSB9H10, shown to exist as a mixture of two of three possible rotamers. Deprotonation of 8,8-(PPh3)2-8,7-nido-RhSB9H10 and 8,8-(dppe)-8,7-nido-RhSB9H10 with MeLi yields the anions [1,1-(PPh3)2-1,2-closo-RhSB9H9]− and [1,1-dppe-1,2-closo-RhSB9H9]−, respectively, with octadecahedral cage structures. It is argued that anion formation causes the agostic bonding to be `switched-off' and results in the cluster adopting the closo architecture predicted by Wade's rules. This structural change is fully reversible on reprotonation, and if reprotonation of [1,1-(dppe)-1,2-closo-RhSB9H9]− is carried out in MeCN, the product 8,8-(dppe)-8-(MeCN)-8,7-nido-RhSB9H10 forms. Interestingly, 8,8-(dppe)-8-(MeCN)-8,7-nido-RhSB9H10 reconverts to 8,8-(dppe)-8,7-nido-RhSB9H10 on standing in CDCl3, suggesting that the agostic bonding is sufficiently strong to displace co-ordinated MeCN. All new compounds are fully characterised by multinuclear NMR spectroscopy and, in many cases, by single crystal X-ray diffraction. 相似文献
125.
N. Bouad 《Journal of solid state chemistry》2004,177(1):221-226
We report in this paper a study of the mechanical alloying (MA) process for the Pb0.65Sn0.35Te alloy. MA has been carried out in a high-energy planetary ball mill. The mechanism of formation has been studied from systematic analyses of mechanically alloyed powders using X-ray diffraction, differential scanning calorimetry and scanning electron microscopy. As it was already observed for the MA of PbTe, this synthesis is associated with an exothermic reaction between the elemental powders. The required time to reach an homogeneous phase Pb0..65Sn0.35Te is 31 h. 相似文献
126.
A. M. Shestopalov A. P. Yakubov D. V. Tsyganov Yu. M. Emel'yanova V. N. Nesterov 《Chemistry of Heterocyclic Compounds》2002,38(10):1180-1189
Substituted 6-aminopyrano[2,3-c]pyrazoles were synthesized by the two-component condensation of arylidenemalononitriles and substituted 5-pyrazolones or three-component condensation of aromatic aldehydes, malononitrile, and substituted 5-pyrazolones. It was established by X-ray crystallographic analysis that pyranopyrazoles exist in the 2H and not the 1H tautomeric form. 相似文献
127.
Cu-12.7(wt)%Al合金从900℃高温淬至365℃~500℃温度范围等温不同时间(30秒至15分钟)的试样中形成了大量树枝状的γ_2相沉淀粒子。应用配有X线能谱仪(XEDS)和电子能量损失谱仪(EELS)的分析电子显微镜(JEOL JEM-2000FX型)对上还试样研究,结果表明:这些γ_2相粒子具有富铝的“核心”,长大到粒子线度大于约800nm后以不稳定方式生长成“花朵”状。生长过程中伴随着溶质元素Al由基体向γ_2相内的富集。而且在γ_2相粒子内部呈现出Spinodal分解组织的形貌特征,表明γ_2粒子内形成了化学成分调幅。EELS分析表明试样含氧。 相似文献
128.
G. Ortega Zarzosa S. A. Palomares Sánchez J. R. Martánez Facundo Ruiz M. G. Sánchez-Loredo 《Journal of Sol-Gel Science and Technology》2005,35(1):5-11
Composites containing Pd aggregates dispersed in amorphous silica are of interest from both a fundamental and applied point of view because of their attractive catalytic properties. The silica powders added with palladium, prepared by the sol-gel method, were studied using X-ray diffraction, and IR- and UV-Vis-spectrophotometry. Silica xerogel samples were prepared using a ethanol/H2O/TEOS molar ratio of 4:11.6:1 and loaded with sodium tetrachloropalladate. The silica xerogel microstructure of the powders was studied as a function of annealing temperature. Attention was paid to the evolution of the glass matrix as well as the palladium aggregates in the SiO2 matrix. We found in our samples partial crystallization of the glass matrix in form of quartz and cristobalite phases with palladium oxide and metallic palladium phase at 1000∘C. The Rietveld refinement method was used in order to determine the percentage of the phase contents. 相似文献
129.
Vora A. Riga A. Dollimore D Alexander K. 《Journal of Thermal Analysis and Calorimetry》2004,75(3):709-717
This study attempts to identify the degradative process which folic acid undergoes in the solid-state under thermal stress.
In order to facilitate the process, the various pieces of the chemical structure, namely, p-amino benzoic acid, pterin and glutamic acid as both its d- and l-isomers were investigated as separate entities. These structured solid-state pieces were then compared to the composite solid
state folic acid degradative curves in order to identify the peaks seen and provide direction for the interpolation of the
degradative mechanism. It was observed that none of the structural pieces could be superimposed as assumed earlier and hence
an attempt was made to identify the decomposition products using various analytical techniques such as infrared spectroscopy,
mass spectroscopy and X-ray diffraction which suggested that the glutamic acid fragment is lost first as evidenced by acid
loss and amide enhancement in the IR spectra. The vitamin was ultimately degrading to carbon fragments and that further identification
was not necessary.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
130.
对稀土金属间Laves相赝二元化合物进行X射线衍射分析。其(440)峰出现劈裂,由(440)峰劈裂的程度可以确定内禀磁致伸缩的大小。本文采用X射线衍射的方法对Pr0.15TbxDy0.85-xFe2系列粉末样品的(440)峰步进扫描,并对扫描结果进行拟合,对拟合得到的两组双线峰之间的间距计算得到内禀磁致伸缩λ111,拟合曲线与实验点符合很好,结果表明Pr0.15TbxDy0.85-xFe2的内禀磁致伸缩随Tb含量的增加而增加,并且用0.15的Pr替代Dy后,在x=0.3时,Pr0.15TbxDy0.85-xFe2的内禀磁致伸缩λ111比Tb0.27Dy0.73Fe2的内禀磁致伸缩λ1ll大。 相似文献