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931.
Synthesis, structure and magnetic properties of the S=1/2, one-dimensional antiferromagnet, Y5Re2O12
Lisheng Chi 《Journal of solid state chemistry》2003,172(2):451-457
Single crystals of Y5Re2O12 have been grown, and the crystal structure has been determined by X-ray diffraction. This compound crystallizes in space group C2/m with cell dimensions of a=12.4081(10) Å b=5.6604(5)Å, c=7.4951(6) Å, β=107.837(3)°, Z=2. The final refinement led to R1=0.0238, WR2=0.0459 for 1053 observed reflections with F>4σ(F0). Edge-sharing ReO6 octahedra form infinite linear [ReO2O4/2]n chains along the b direction with alternating short and long Re-Re distances. Three crystallographically independent yttrium atoms surround O2 to form OY4 tetrahedra, which share edges and corners in the ab plane to form a two-dimensional Y5O4 network which separates the [ReO2O4/2]n magnetic chains. This compound is therefore isostructural with the series Ln5Re2O12Ln=Gd-Lu, which have been known since 1969. The average Re oxidation state is +4.5 in the chains and a reasonable, if qualitative MO scheme results in one unpaired electron per Re dimer. Consistent with this, magnetic susceptibility data can be fitted to the one-dimensional antiferromagnetic Heisenberg model with S=1/2 and parameters Jintra/k=−89(1)K, g=2.15(4) and χ(TIP)=5(1)×10−4 emu/mol. There is no sign of long-range magnetic order down to 2 K. These results are contrasted with those for the isostructural Y5Mo2O12. 相似文献
932.
Labeling experiments using several deuterated lipids were pursued to study the biosynthesis of macrocyclic isoprenoidal lipids of thermophilic methanogenic archaea, Methanothermobacter thermautotrophicus. The isopropylidene terminal of geranylgeranyl group of monomeric precursor appeared to be important for the CC bond formation at the hydrophobic end in the macrocyclic lipids. A mechanism involving a radical trigger at the allylic methyl group is proposed for this CC bond formation. 相似文献
933.
The reductions of several substituted acetophenones using supercritical 2-propanol were carried out to estimate the Hammett's reaction constant (ρ=0.33). Also, the reduction of acetophenone using supercritical deuteriated 2-propanol was carried out to determine the rate-determining step. The kinetic isotope effects were observed in the reduction using 2-deuterio-2-propanol (kH/kD=1.6) and O-deuterio-2-propanol (kH/kD=2.0). These findings suggest that the reaction proceeds via a cyclic transition state between acetophenone and 2-propanol similar to that of the Meerwein-Ponndorf-Verley reduction. 相似文献
934.
935.
相转移催化合成对甲氧基肉桂酸-2-乙基己酯的研究 总被引:5,自引:1,他引:5
对甲氧基肉桂酸 2 乙基己酯是一种有效的UVB防晒剂[1 ,2 ] ,一般采用Claisen Schmidt缩合反应制得[3] ,但由于催化剂KOH处于水相 ,对反应物不能充分起到催化作用导致产率较低[4] 。我们利用乙二醇 (PEG)为相转移催化剂合成立体专一的反式对甲氧基肉桂酸 2 乙基己酯 ,产率提高到 72 .5 %。合成路线如下 :1 实验部分1 .1 仪器与试剂BIO RAPFT45 0红外光谱仪 ,用液膜法测试 ;Brurer AM 30 0超导核磁共振仪 (溶剂DC Cl3) ;MAT/44S ,GC MS型色质联用谱仪 ;试剂均为分析纯 ,上海化学试剂… 相似文献
936.
Bitao Su Ke Wang Jie Bai Hongmei Mu Yongchun Tong Shixiong Min Shixiong She Ziqiang Lei 《Frontiers of Chemistry in China》2007,2(4):364-368
Fe3+-doped TiO2 composite nanoparticles with different doping amounts were successfully synthesized using sol-gel method and characterized
by X-ray diffraction (XRD), transmission electron microscopy (TEM) and ultravioletvisible spectroscopy (UV-Vis) diffuse reflectance
spectra (DRS). The photocatalytic degradation of methylene blue was used as a model reaction to evaluate the photocatalytic
activity of Fe3+/TiO2 nanoparticles under visible light irradiation. The influence of doping amount of Fe3+ (ω: 0.00%–3.00%) on photocatalytic activities of TiO2 was investigated. Results show that the size of Fe3+/TiO2 particles decreases with the increase of the amount of Fe3+ and their absorption spectra are broaden and absorption intensities are also increased. Doping Fe3+ can control the conversion of TiO2 from anatase to rutile. The doping amount of Fe3+ remarkably affects the activity of the catalyst, and the optimum efficiency occurs at about the doping amount of 0.3%. The
appropriate doping of Fe3+ can markedly increase the catalytic activity of TiO2 under visible light irradiation.
__________
Translated from Journal of Northwest Normal University (Natural Science), 2006, 42(6): 55–56 [译自: 西北师范大学学报(自然科学版)] 相似文献
937.
Radoslav D. Mii Radmila P. Marinkovi-Neduin Zoltán Schay István Nagy Jelena S. Kiurski Ern E. Kiss 《Reaction Kinetics and Catalysis Letters》2007,91(1):85-92
Investigations of a commercial NiMo/Al2O3 hydrodesulfurization (HDS) catalyst are directed towards optimization of the activation procedure of HDS catalyst concerning
active phase formation and thermal stability. Structural and textural data obtained with XRD, IR-FTIR, XPS and LTNA reveal
that the optimal temperature for the formation of active species on the catalyst surface and an appropriate pore structure
is 300°C. 相似文献
938.
钇对金属陶瓷力学性能和组织的影响 总被引:6,自引:0,他引:6
研究了添加钇对Ti(C,N)基金属瓷力学性能和组织的影响。结果表明,加入适量的钇能提高Ti(C,N)基金属陶瓷的抗变强度和硬度,其原因是由于钇与杂质硫起反应在化合物,净化了陶瓷相-金属相,陶瓷相-陶瓷相界面提高子界面结合强度 相似文献
939.
940.
A Minor New Flavone from Scutellaria baicalensis Georgi 总被引:1,自引:0,他引:1
A new flavone,6,2′-dihydroxy-5,7,8,6′-tetramethoxyflavone,was isolated from the roots of Scutellaria baicalensis. Its structure was established on the basis of spectral evidences. 相似文献