共查询到20条相似文献,搜索用时 15 毫秒
1.
Olfa Labidi Florence Porcher Rose-Noëlle Vannier 《Journal of solid state chemistry》2008,181(9):2260-2267
Reinvestigation of PbBiOVO4 thermal behaviour revealed a phase transition. As shown by single-crystal X-ray diffraction and high-resolution neutron powder diffraction, α-PbBiOVO4 transforms to β-PbBiOVO4 at 550 °C. At 25 °C, α-PbBiOVO4 is triclinic, S.G. P-1, Z=2, with a=5.6088(3), b=7.1109(3), c=7.2978(3) Å, α=108.957(2), β=111.889(2), and γ=94.833(2)°. Above 550 °C, β-PbBiOVO4 is monoclinic, S.G. C2/m, Z=4, with a=13.61(1), b=5.64(1), c=7.18(1) Å, and β=113.75(1)°. Both structures are built upon (O2Bi2Pb2)∞ chains parallel to the [100] direction in the α polymorph and [001] in the β-polymorph. These chains are undulated in α and linear in β. In both structures, VO4 tetrahedra are organized in two sets of rows parallel to (O2Bi2Pb2)∞ chains, thus building layers of (OBiPb) sandwiched by two layers of VO4 oriented head to tail; VO4 displays different orientations in α- and β-PbBiOVO4. 相似文献
2.
Renée L. Beyer Hakan Kandemir Mohan Bhadbhade Ibrahim F. Sengul Chao-wei Leu Daniel Wenholz Naresh Kumar David StC. Black 《Tetrahedron letters》2018,59(51):4483-4486
Acylation reactions of 4,6-dimethoxyindoles with glyoxyloyl chlorides were achieved by the use of graphite powder in 1,2-dichloroethane at reflux. The products were monoketones as a result of decarbonylation, rather than the expected 1,2-diketones. Treatment of these monoketones with base led to their cyclisation and elimination of methanol to afford the novel dipyrrolo[2.3-a:1′,2′,3′-fg]acridin-12(1H)-ones. 相似文献
3.
Masatsugu Oishi Keiji Yashiro Junichiro Mizusaki 《Journal of solid state chemistry》2008,181(11):3177-3184
The defect chemical relationships in various B-site mixed LaCrO3-based ceramics were investigated by means of high-temperature gravimetry. The nonstoichiometric deviation, δ, in (La0.7Sr0.3)(Cr1−yTiy)O3−δ (y=0.1, 0.2 and 0.3) (LSCT), (La0.75Sr0.25)(Cr0.5Mn0.5)O3−δ (LSCM) and (La0.75Sr0.25)(Cr0.5Fe0.5)O3−δ (LSCF) were measured as a function of oxygen partial pressure, PO2, at temperatures between 973 and 1373 K.The effects of partial replacement of the donor on Cr-sites were examined in LSCT. In LSCM and LSCF, effects of the partial substitution of isovalent transition metals on Cr-sites are discussed. Oxygen nonstoichiometries of various B-site mixed LaCrO3-based ceramics were compared with those of A-site substituted perovskite-type oxides, (La1−xSrx)MO3−δ (where x=0-0.3, M=Cr, Mn and Fe). The partial substitution of the different elements on Cr-sites drastically changed the PO2 and temperature dependence of oxygen vacancy formation in LaCrO3-based ceramics. The defect equilibrium relationships of the localized electron well explained the oxygen vacancy formation in B-site mixed LaCrO3-based ceramics. Oxygen vacancy formation in (La0.7Sr0.3)(Cr1−yTiy)O3−δ (y=0.1 and 0.2) and (La0.7Sr0.3)(Cr0.7Ti0.3)O3−δ was explained by redox reaction of Cr and Ti ions, respectively. The defect equilibrium relationships of LSCM and LSCF were interpreted by redox reaction of Mn ions and Fe ions, respectively. No significant change in valence state of Cr3+ ions in LSCM and LSCF was confirmed under the experimental conditions. 相似文献
4.
H. El Shinawi J. Hadermann B. Santos F.J. Berry 《Journal of solid state chemistry》2010,183(6):1347-7122
The n=2 Ruddlesden-Popper phases LaSr2CoMnO7 and La1.2Sr1.8CoMnO7 have been synthesized by a sol-gel method. The O6-type phases LaSr2CoMnO6 and La1.2Sr1.8CoMnO6 were produced by reduction of the O7 phases under a hydrogen atmosphere. The materials crystallize in the tetragonal I4/mmm space group with no evidence of long-range cation order in the neutron and electron diffraction data. Oxygen vacancies in the reduced materials are located primarily at the common apex of the double perovskite layers giving rise to square pyramidal coordination around cobalt and manganese ions. The oxidation states Co3+/Mn4+ and Co2+/Mn3+ predominate in the as-prepared and reduced materials, respectively. The materials are spin glasses at low temperature and the dominant magnetic interactions change from ferro- to antiferromagnetic following reduction. 相似文献
5.
《Journal of Coordination Chemistry》2012,65(2):219-223
Abstract Reaction of titanocene prepared from Cp2TiCl2 and 2n-BuLi with β-diketones (β-diketone = 1-phenyl-1,3-butanedione, 1,3-diphenyl-1,3-propanedione, 3-methyl-2,4-pentanedione or 3-ethyl-2,4-pentanedione) afforded the titanocene(III) β-diketonate complex. The compounds [Ti(η5-Cp)2(1-phenyl-1,3-butanedionate)] and [Ti(η5?Cp)2(1,3-diphenyl-1,3-propanedionate)] have been characterized by X-ray crystallography. 相似文献
6.
In this work we address the optimization of mixed conductivity in fluorite compounds based on zirconia. Phase relations of the new systems YbO1.5-NbO2.5-ZrO2, and CaO-NbO2.5-ZrO2 are presented. The limit of the cubic defect fluorite phase in YbO1.5-NbO2.5-ZrO2 closely resembles that of the system YO1.5-NbO2.5-ZrO2, whilst in CaO-NbO2.5-ZrO2 is narrow extending to include composition Ca0.255Nb0.15Zr0.595O1.82 at 1500°C. The influence of dopant ion size, charge and composition on ionic conduction is assessed and parallels are drawn with the systems YO1.5-NbO2.5-ZrO2 and YO1.5-TiO2-ZrO2. Comparison of these results with published data on the Ti containing systems CaO-TiO2-ZrO2, GdO1.5-TiO2-ZrO2 shows that the highest mixed conducting compositions can only be offered in the system YO1.5-TiO2-ZrO2 out of all the systems here studied. 相似文献
7.
The M4+-containing K2NiF4-type phases La0.8Sr1.2Co0.5Fe0.5O4 and La0.8Sr1.2Co0.5Mn0.5O4 have been synthesized by a sol-gel procedure and characterized by X-ray powder diffraction, thermal analysis, neutron powder diffraction and Mössbauer spectroscopy. Oxide ion vacancies are created in these materials via reduction of M4+ to M3+ and of Co3+ to Co2+. The vacancies are confined to the equatorial planes of the K2NiF4-type structure. A partial reduction of Mn3+ to Mn2+ also occurs to achieve the oxygen stoichiometry in La0.8Sr1.2Co0.5Mn0.5O3.6. La0.8Sr1.2Co0.5Fe0.5O3.65 contains Co2+ and Fe3+ ions which interact antiferromagnetically and result in noncollinear magnetic order consistent with the tetragonal symmetry. Competing ferromagnetic and antiferromagnetic interactions in La0.8Sr1.2Co0.5Fe0.5O4, La0.8Sr1.2Co0.5Mn0.5O4 and La0.8Sr1.2Co0.5Mn0.5O3.6 induce spin glass properties in these phases. 相似文献
8.
Jan Hajduch 《Journal of fluorine chemistry》2008,129(2):112-118
Horner-Emmons fluoroolefination of an aryl aldehyde followed by introduction of a second fluorine via “FBr” addition provides an original approach to the preparation of 1-alkyl-2-aryl-1,2-difluoroethenes. The utility of this procedure is demonstrated by the preparation of (E and Z)-α,β-difluorourocanic acid. 相似文献
9.
本文利用单电子非相对论Hartree-Fock-Slater和完全相对论Dirac-Fock-Slater两种离散变分局域密度泛函方法(DV-Xα), 对MX~4(M=Ti,Zr,Hf;X=Cl,Br)的电子基态和相应于低能UV光谱的激发态进行了计算, 结果与实验符合得较好。用Mulliken布居分析方法研究了分子的共价性质, 发现除HfBr~4外,相对论效应对金属与配体之间的键级影响很小。 相似文献
10.
11.
Steffen Falgner 《Journal of organometallic chemistry》2010,695(24):2614-2617
An efficient, convenient, and reliable multi-step synthesis of rac-2′-(trimethylsilyl)isovaline (rac-3) that uses inexpensive reagents in all steps has been developed, starting from diethyl malonate (overall yield 28%). Compound rac-3 is the first α-ethylated α,α-dialkylated silicon-containing α-amino acid. 相似文献
12.
Preetam Singh 《Journal of solid state chemistry》2008,181(12):3248-3256
CeO2 and Ce1−xMxO2−δ (M=Zr, Ti, Pr, Y and Fe) nanocrystallites of 5-10 nm sizes have been synthesized by hydrothermal method using diethylenetriamine (DETA) and melamine as complexing agents. Compounds have been characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDX) and their structures have been refined by the Rietveld method. All the compounds crystallize in cubic fluorite structure. Even up to 50% Zr and Y, 40% Ti, 25% Pr and 15% Fe is substituted for Ce4+ in CeO2 by this method. Sizes of crystallites can be tuned by changing the complexing agent and reaction temperature. Nanocrystalline CeO2 and Ce1−xZrxO2 prepared here have higher or at least competitive oxygen storage capacity (OSC) than those reported in literature. Ce1−xFexO2−δ shows higher OSC and higher percentage of CO oxidation at lower temperature than Ce1−xZrxO2. 相似文献
13.
G. I. Zharkova I. A. Baidina S. A. Gromilov A. D. Vasiliev 《Journal of Structural Chemistry》2003,44(6):1046-1053
This paper describes a procedure for the synthesis of two new volatile complexes, C22H40N2NiO4 and C20H36N2NiO4, based on sterically hindered methoxy--iminoketones. The compounds were investigated by IR spectroscopy and DTA. Full crystal-chemical analysis has been carried out. The structures are molecular. The complexes have close geometrical characteristics; the distances are Ni–O 1.826 and Ni–N 1.842 ; the O–Ni–N chelate angle is 93.2°. The complexes have an intramolecular hydrogen bond N–H...O, estimated at 2.54 (2.08) . In both structures, the packing of complexes is similar to that in nickel(II) dipivalylmethanate. 相似文献
14.
Hua Fang Weizhu Chen Bihong Hong Yufen Zhao Meijuan Fang 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):2182-2193
This article describes the synthesis of α-hydroxyphosphonic acid esters using the Pudovik reaction. IR, 1H NMR, 13C NMR, 31P NMR, MS, and elemental analysis were employed to confirm their structures. X-ray structure analysis is reported for six compounds. The antibacterial activities of these compounds are also reported. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. 相似文献
15.
La4BaCu5−xMxO13+δ: M=Fe, Co, Ni, Zn were prepared by the solid-state route at 1000°C. Solid solution limits of x=1.0(1) [Fe], x=1.1(1) [Co], x=1.56(7) [Ni] and x=0.47(1) [Zn] were determined from XRD and EPMA results. Rietveld refinement of combined XRD/neutron powder diffraction data was carried out on undoped La4BaCu5O13+δ and x=1 for M=Fe, Co, Ni. For La4BaCu5O13+δ, which is an oxygen-deficient perovskite, the presence of square planar CuO4 groups, disordered over the Cu(2) sites with CuO5 square pyramids, is indicated, together with, for δ<0, either square planar CuO4 or square pyramidal CuO5 and octahedral CuO6 groups disordered over the Cu(1) sites. For M=Fe, Ni, there was preferential substitution onto the one-fold octahedral site; for M=Co, substitution took place on both the one-fold octahedral and four-fold square pyramidal sites. 相似文献
16.
Timothy R. Corkish Christian T. Haakansson Peter D. Watson Prof. Allan J. McKinley Dr. Duncan A. Wild 《Chemphyschem》2021,22(1):69-75
A combined experimental and theoretical approach has been used to investigate X−⋅⋅⋅CH2O (X=F, Cl, Br, I) complexes in the gas phase. Photoelectron spectroscopy, in tandem with time-of-flight mass spectrometry, has been used to determine electron binding energies for the Cl−⋅⋅⋅CH2O, Br−⋅⋅⋅CH2O, and I−⋅⋅⋅CH2O species. Additionally, high-level CCSD(T) calculations found a C2v minimum for these three anion complexes, with predicted electron detachment energies in excellent agreement with the experimental photoelectron spectra. F−⋅⋅⋅CH2O was also studied theoretically, with a Cs hydrogen-bonded complex found to be the global minimum. Calculations extended to neutral X⋅⋅⋅CH2O complexes, with the results of potential interest to atmospheric CH2O chemistry. 相似文献
17.
Clear evidence (in the form of structured diffuse scattering) is found for short range ordering of metal ions and associated induced structural relaxation in two members of the cubic BZN pyrochlore (Bi1.5−αZn0.5−β)(Zn0.5−γNb1.5−δ)O(7−1.5α−β−γ−2.5δ) solid solution. An average neutron powder diffraction structure refinement is carried out for one of these. Electron probe micro-analysis suggests that the primary mechanism for non-stoichiometry in cubic BZN is the removal of ZnO from the nominally fully occupied (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 end-member. A detailed bond valence sum analysis of a recently reported average crystal structure is used to suggest possible local cation ordering schemes along with the induced displacive relaxation that is likely to accompany such local cation ordering. The observed diffuse distribution is qualitatively interpreted via Monte Carlo modelling. 相似文献
18.
Yu. Stadnyk V.V. Romaka L.P. Romaka D. Fruchart 《Journal of solid state chemistry》2010,183(12):3023-3028
The n-TiNiSn ternary intermetallic semiconductor is doped by the V donor impurity and the crystalline structure of the obtained Ti1−xVxNiSn solid solutions (х=0-0.10) is determined by X-ray diffraction. Temperature and concentration dependences of the resistivity and thermopower are investigated in 80-380 K range. As main results, the TiNiSn conductivity type is revealed insensitive to V doping and the thermopower factor substantially increases versus V content. First principle calculations based on DFT using FPLO and KKR-CPA methods are performed as well. Experimental data and electronic structure calculations are compared and discussed in terms of thermopower improvements. 相似文献
19.
Three novel 3d–4f heterometal complexes [Ln(NiL)3(Btca)(NO3)] · xH2O (Ln = Sm(III) (I), Pr(III) (II), Eu(III) (III) (H2L = 2,3-dioxo-5,6,14,15-dibenzo-1,4,8,12-tetraazacyclo-pentadeca-7,13-dien, H2Btca = benzotriazole-5-carboxylic acid) were solvothermally synthesized and characterized by singlecrystal X-ray diffraction (CIF files CCDC nos. 1555557 (I), 1555555 (II), 1555556 (III)). They crystallized in the monoclinic space group P21/n for I (x = 1.5) and C2/c for (II) and (III) (x = 1), respectively. In these complexes, the central Ln(III) and external nickel ions are bridged by macrocyclic oxamide groups. The metal center of Ln(III) resides in a distorted bicapped square antiprism surrounding with six oxygen atoms of three oxamide groups, two oxygen atoms of Btca2– ion and two oxygen atoms of NO3-. Furthermore, there are C–H···O and/or C–H···N hydrogen bond interactions among nitrate, benzotriazole-5-carboxylate, macrocyclic oxamide and water to form three-dimensional superamolecular architecture. The fluorescence properties of the compounds I and II are also discussed. 相似文献
20.
Ibraev M. K. Turdybekov D. M. Fazylov S. D. Turdybekov K. M. Gazaliev A. M. Zhivotova T. S. 《Russian Journal of Organic Chemistry》2004,40(5):719-722
N-acryloylcitisine and N-(-morpholinopropionyl)cytisine were synthesized and spatial structures of compounds obtained were established by X-ray difraction analysis. 相似文献