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1.
The Raman spectra for (SiF2)x and GeF2 are reported. In the spectrum of (SiF2)x a band has been observed at 411 cm−1 and is most probably associated with SiSi bonding in the compound; this is the first direct evidence for such a bond. The high degree of similarity between the spectra of (SiF2)x and (CF2)x suggests that (SiF2)x is a zig-zag helical chain polymer similar to (CF2)x.  相似文献   

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4.
The MINDO/3 technique gives geometries for (CH4)+, (CCl4)+ and the intermediate ions (CHnCl4 ? n)+ (n = 1, 2, 3) which have symmetries in precise accord with the predictions of the Jahn—Teller effect. The ground state of (CH4)+ has D2d symmetry, with a C3v structure ca. 45.6 kJ mol?1 higher. (CCl4)+ has a C2v ground state, with a D2d structure ca. 144 kJ mol?1 higher: no bound state of C3v symmetry could be found. (CH3Cl)+ and (CHCl3)+ both have Cs symmetry, and (CH2Cl2)+ has C2v symmetry. The analogous fluoro ions are discussed briefly.  相似文献   

5.
The second osmotic virial coefficient (A2) and its entropic and enthalpic parts (A2,s and A2,H) have been determined, by means of light-scattering measurements, for solutions of polystyrene, polymethylmethacrylate and cellulose nitrate of different molecular weights in 19 solvents. A distinct qualitative correlation exists between A2 and A2,H and between A2,s and A2,H. The elimination of the “geometric” parameters of the polymer, by dividing these coefficients by suitably chosen reduction parameters, shows that the reduced coefficients obtained A20 and A2,s0 are predominantly functions of the reduced enthalpy coefficient A2,H0.  相似文献   

6.
New coordination polymers based on 3,3′,5,5′-tetramethyl-4,4′-bipyrazole (L) with the composition [M2(L)4A(NCS)2] (M2+ = Co2+, Zn2+, Cd2+; A2? = SiF 6 2? , SeO 4 2? ) have been synthesized and characterized by IR spectroscopy and X-ray diffraction. According to X-ray diffraction data, cobalt compounds crystallize in the orthorhombic system with the following unit cell parameters, [Co2(L)4SiF6(NCS)2] · 3CHCl3 · CH3OH: a = 20.568(4), b = 14.568(3), c = 22.929(5) Å, α = β = γ = 90°, V = 6870(2) Å3, space group Pbca (no. 61), R(I > 2σ(I)) = 0.0514; [Co2(L)4SeO4(NCS)2] · 2CHCl3 · 2CH3OH · H2O: a = 13.721(2), b = 21.539(3), c = 22.417(3) Å, α = β = γ = 90°, V = 6625(2) Å3, space group P212121 (no. 19), R(I > 2σ(I)) = 0.0452. The 3D structure of the coordination polymers is composed of wavelike two-dimensional coordination layers [ML2]n connected by bridging anions SiF 6 2? , or Se O 4 2? . The complexes have the same five-bonded topology but different symmetry.  相似文献   

7.
The kinetics of the solid-state mechanochemical synthesis of the nanosized product (TlCl) in the reaction 2NaCl + Tl2SO4 + zNa2SO4 = (z + 1)Na2SO4 + 2TlCl was studied experimentlaly. The method used was based on the dilution of the initial mixture of powdered reagents (2NaCl + Tl2SO4) with another exchange reaction product (Na2SO4) at the optimum theoretically estimated z value, z = z* = 11.25. Several special features of the development of this reaction were established. The parameters of the kinetic curve obtained for the mechanochemical synthesis of the desired product were compared with those of the kinetic curve determined theoretically for the model reaction KBr + TlCl + zKCl = (z + 1)KCl + TlBr with z = z 1 * = 13.5. This allowed us to experimentally estimate the mass transfer coefficient in a mechanochemical reactor by mobile milling bodies. This estimate was obtained for the first time. The dynamics of changes in the size of desired product nanoparticles depending on the time of mechanochemical activation in an AGO-2 ball planetary mill was studied.  相似文献   

8.
Anchored aluminoxanes are synthesized by the reaction of aluminum alkyls AlMe3 and Al(i-Bu)3 with water contained in the intracrystalline cavities of synthetic and natural zeolites (NaY (Si: Al = 5), HZSM-5 (Si: Al = 17 or 34), NH4ZSM-5 (Si: Al = 32), NaZSM-5 (Si: Al = 42), and clinoptilolite-containing tuff) and are used for the synthesis of heterogenized complexes of ansa-zirconocenes (rac-C2H4(Ind)2ZrCl2, rac-Me2Si(Ind)2ZrCl2, and rac-[1-(9-η5-Flu)-2-(5,6-cyclopenta-2-Me-1-η5-Ind)C2H4]ZrCl2) active in the polymerization of propylene. The nature of the zeolite support determines the content of zeolite water and affects the formation of anchored alkylaluminoxanes and the activity of immobilized catalysts. Among the studied catalytic systems supported on zeolites, NaY and NaZSM-5 are the most efficient for the polymerization of propylene. PP synthesized with the supported zirconocene catalysts has a higher molecular mass and a wider molecular-mass distribution than those in the case of the corresponding homogeneous catalyst. The index of isotacticity and the content of pentads mmmm in PP prepared with immobilized metallocenes with the C 2 symmetry, such as rac-C2H4(Ind)2ZrCl2 and rac-Me2Si(Ind)2ZrCl2, are likewise higher. The stereoselectivity of supported catalysts depends on the zeolite nature.  相似文献   

9.
《Solid State Sciences》2001,3(4):469-475
The structure of Li3Gd(BO3)2 has been solved by X-ray diffraction study on single crystal. This novel borate crystallizes in the monoclinic system with the P21/c space group (Z=4). The cell parameters are respectively equal to a=8.724(2), b=6.425(2), c=10.095(2) Å and β=116.85(2)°. Refinements of 110 parameters using 2924 independent reflections having I>2σ(I) converged to R1=0.028 (wR2=0.058). The structure of Li3Gd(BO3)2 is made up of double layers of eightfold coordinated Gd atoms parallel to the (bc) plane. They are linked by respectively three- and four-coordinated boron and lithium atoms. The structure is compared to that of the homologous sodium compounds, Na3Ln(BO3)2 (Ln: La, Nd), in which LnO8 polyhedra also form a bi-dimensional array.  相似文献   

10.
The chemistry of phosphates of barium and tetravalent cations [BaMIV(PO4)2] is reviewed. Such phosphates crystallise in the C2/m space group for MIV=Ti, Zr, Hf, Ge, Sn, and Mo, and in the P21/n space group for BaTh(PO4)2. The existence of BaMIV(PO4)2 in which MIV=Pb, Ce, and U is further evaluated. Several aspects, such as phase transitions in the compounds with yavapaiite structure, solid solutions of BaMIV(PO4)2 compounds and practical applications are briefly discussed.  相似文献   

11.
Single crystal and powder samples of the system TaS2?xSex have been prepared and studied. The range of solubility was found to extend from x = 0 to x = 2.0. X-Ray analysis has shown that mixed anion samples exhibit a series of hexagonal layered polymorphs similar to those found in TaS2 and TaSe2, with the a and c lattice parameters increasing monotonically from TaS2 to TaSe2. Electrical transport properties were measured on single crystals and found to be similar to the end compositions. Organic molecules such as pyridine and collidine were found to intercalate TaS2?xSex for x ≦ 1.4, and superconducting transition temperatures were measured for both intercalated and unintercalated samples. The highest Tc obtained was 4.1 K in the 4H(c) phase of the sample TaS1.6Se0.4.  相似文献   

12.
Phase relations in the ternary system Ce-Pt-Si have been established for the isothermal section at 800 °C based on X-ray powder diffraction, metallography, scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) techniques on about 120 alloys, which were prepared by various methods employing arc-melting under argon or powder reaction sintering. Nineteen ternary compounds were observed. Atom order in the crystal structures of τ18-Ce5(Pt,Si)4 (Pnma; a=0.77223(3) nm, b=1.53279(8) nm c=0.80054(5) nm), τ3-Ce2Pt7Si4 (Pnma; a=1.96335(8) nm, b=0.40361(4) nm, c=1.12240(6) nm) and τ10-CePtSi2 (Cmcm; a=0.42943(2) nm, b=1.67357(5) nm, c=0.42372(2) nm) was determined by direct methods from X-ray single-crystal CCD data and found to be isotypic with the Sm5Ge4-type, the Ce2Pt7Ge4-type and the CeNiSi2-type, respectively. Rietveld refinements established the atom arrangement in the structures of Pt3Si (Pt3Ge-type, C2/m, a=0.7724(2) nm, b=0.7767(2) nm, c=0.5390(2) nm, β=133.86(2)°), τ16-Ce3Pt5Si (Ce3Pd5Si-type, Imma, a=0.74025(8) nm, b=1.2951(2) nm, c=0.7508(1) nm) and τ17-Ce3PtSi3 (Ba3Al2Ge2-type, Immm, a=0.41065(5) nm, b=0.43221(5) nm, c=1.8375(3) nm). Phase equilibria in Ce-Pt-Si are characterised by the absence of cerium solubility in platinum silicides. Cerium silicides and cerium platinides, however, dissolve significant amounts of the third component, whereby random substitution of the almost equally sized atom species platinum and silicon is reflected in extended homogeneous regions at constant Ce content such as for τ13-Ce(PtxSi1−x)2, τ6-Ce2Pt3+xSi5−x or τ7-CePt2−xSi2+x.  相似文献   

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14.
With an objective to assess the chemical stabilities and their consequences in cell performance, the variations of oxygen content with lithium content (1−x) in chemically delithiated Li1−xCoO2, Li1−xNi0.85Co0.15O2, and Li1−xMn2O4 cathodes have been monitored with redox titrations. The Li1−xCoO2 system tends to lose oxygen from the lattice at deep lithium extraction, while the Li1−xNi0.85Co0.15O2 system does not lose oxygen at least for (1−x)>0.3. The chemical instability with a tendency to lose oxygen at deep lithium extraction could be the reason for the limited practical capacity of the Li1−xCoO2 system (140 mA h/g) compared to that realized with the Li1−xNi0.85Co0.15O2 system (180 mA h/g). The Li1−xMn2O4 spinel maintains an oxygen content of 4.0 without losing any oxygen for 0.15⩽(1−x)⩽1.  相似文献   

15.
In order to find such unknown molecules as MgC2 and AlC2 in interstellar space, accurate calculations to determine the equilibrium structures of these molecules were carried out. The ab initio MCSCF and MRSDCI methods were employed in the calculations. MgNC whose rotational constant has been observed was used to check the reliability of the computational scheme. The predicted geometrical structures of MgC2 and AlC2 were equilateral triangles and their rotational constants were Ae = 51.55, Be = 11.52 and Ce = 9.413 GHz for MgC2 and Ae = 50.76, Be = 12.00 and Ce = 9.705 GHz for AlC2.  相似文献   

16.
1-Hydroxy-2-chloromethyl-1,3-dioxolane (4) and 1-hydroxy-2-dichloromethyl-1, 3-dioxolane (5) have been detected as intermediates by1H NMR spectroscopy in the hydration of respectively 2-chloromethylene-1, 3-dioxolane and 2-dichloromethylene-1, 3-dioxolane in aqueous acetonitrile. The kinetics of the breakdown of (4) and (5) into ethylene glycol monochloroacetate and monodichloroacetate have been studied by uv spectroscopy and values ofkH+,kHO-, andkH2O evaluated. It was found that the introduction of chlorosubstituents into 2-hydroxy-2-methyl-1, 3-dioxolane caused a decrease inkH+ and increase inkH2O- and little change inkH2Ofor its breakdown. The mechanisms of these reactions are discussed. Present  相似文献   

17.
《Chemical physics letters》1987,134(5):433-437
Formaldehyde/oxygen/nitrogen mixtures were photolyzed with UV light in a gas flow system. The reaction mixtures were analyzed by pumping a small fraction of the flowing gas through a microprobe, trapping the condensable compounds on a cold finger (T = 96 K), and measuring the ESR spectrum of the solid. The ESR spectra consisted of partly overlapping components from HO2 and HOCH2OO radicals, the latter having g-tensor values g1 = 2.0025, g2 = 2.0090 and g3 = 2.0320. By simulating the experimental spectra with appropriate amplitude factors for their HO2 and HOCH2OO components, the concentration ratio [HO2]/[HOCH2OO] was determined. From these values and the H2CO concentrations, measured by UV absorption, equilibrium constants k1, k−1 for the reaction HO2+H2CO ⇌ HOCH2OO were calculated. The expression k1/k−1 = 2.4 × 10−26 exp(15.2 kcal mol−1/RT) cm3 was obtained from measurements in the temperature range 30–100° C.  相似文献   

18.
The concentration wave approach is applied to Ti and V oxides with noninteger variable valences. This approach enables both the composition and the structure of the homologous series of Magneli phases TinO2n−1 and VnO2n−1 to be predicted in the composition range between Ti2O3 and TiO2.  相似文献   

19.
The crystal structures of the carbides NdCoC2 (CeCoC2 type) and La2Ni5C3 (own type) were refined from single-crystal X-ray data to residuals of R = 0.033 (358 structure factors, 26 variable parameters) and R = 0.019 (265 F values, 22 variables). The CC distances of the C2 pairs are 140(2) pm and 135.9(8) pm respectively. The near-neighbour coordinations of these C2 pairs are discussed, together with those of related structures. The results of the hydrolyses with diluted hydrochloric acid of several ternary carbides are reported. The products range from methane, ethane and ethylene up to various isomers of hexane. There is little correlation between the CC bonding (C2 pairs with various bond lengths or isolated carbon atoms) and the amounts of the various hydrocarbons developed. La2Ni5C3 does not become superconducting down to 1.8 K. Comparative extended Hückel calculations for various real and hypothetical transition metal carbide polyanions [TC4n−]m and [TC2n−]m were carried out as a function of the number of valence electrons of the polyanions. High binding energies were found for the electron counts 30 and 34 per TC4 unit of the Er2FeC4 and Sc3CoC4 structures (polyanions [FeC46−]m and [CoC49−]m). Some possible distortions of the polyanion [TC23−]m of the CeNiC2-type structure were studied. It is found that the unpuckered form of this two-dimensionally infinite polyanion is most stable for electron counts of 19–21 per TC2 unit as is actually observed for all CeNiC2-type compounds, e.g. for DyTC2 (TFe, Co, Ni).  相似文献   

20.
The Ru-Ru single bond in [Ru2(CO)4(MeCN)6][BF4]2 remains intact in the reaction with 2-i-propyl-1,8-naphthyridine (iPrNP) and the isolated product is the cis-[Ru2(iPrNP)2(CO)4(OTf)2] (1) obtained via crystallization in the presence of [n-Bu4N][OTf]. The 2-t-butyl-1,8-naphthyridine (tBuNP), on the contrary, leads to the oxidative cleavage of the Ru-Ru single bond resulting in the trans-[Ru(tBuNP)2(MeCN)2][BF4]2[NC(Me)C(Me)N] (2). The anti-[NC(Me)C(Me)N]2− is the product of the two-electron reductive coupling of two acetonitrile molecules. The phenoxo appendage in 2-(2-hydroxyphenyl)-1,8-naphthyridine (hpNP) brings the identical effect of the scission of the Ru-Ru bond but the process is non-oxidative and the product obtained is the cis-[Ru(hpNP)2(CO)2][BF4] (3). The bis-(diphenylphosphino)methane (dppm) in dichloromethane oxidatively cleave the Ru-Ru bond leading to chloro bridged [Ru(μ-Cl)(dppm)(CO)(MeCN)]2[BF4]2 (4). All the complexes have been characterized by the spectroscopic and electrochemical measurements and their structures have been established by X-ray diffraction study.  相似文献   

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