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41.
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
42.
43.
Kulwinder K FloraTracey Keeling-Tucker Christopher W HogueJohn D Brennan 《Analytica chimica acta》2002,470(1):19-28
Sol-gel derived materials offer a unique advantage for the development of sensing and screening platforms in that they allow for the entrapment of multiple species within a confined space. In this work, we show that it is possible to entrap an intact protein-peptide interaction, consisting of bovine calmodulin (bCaM) and melittin, into a sol-gel derived silicate material. Fluorescence emission data demonstrate that the entrapped complex behaves similarly to the complex in solution, and can undergo reversible dissociation upon introduction of the denaturant guanidine hydrochloride. Screening of antagonists of the bCaM-melittin complex was accomplished based on induced dissociation of the entrapped complex, which was followed by measuring the loss of sensitization of Tb(III) luminescence originating from energy transfer from the Trp of melittin to Tb(III) bound in the loops of bCaM. This study shows that entrapped protein-peptide complexes can be used as targets for drug screening or for fluorescence-based biosensing. 相似文献
44.
Silica xerogels with different structures and morphology, synthesized using a sol-gel procedure, were used as a carrier of vanadium catalysts (VOCl3/AlEt2Cl) for ethylene polymerization. Two techniques of catalyst synthesis were applied: slurry impregnation and gas-phase adsorption and the relevant polymerization methods were then employed. The effect of the carrier structure and morphology on the vanadium loading in the catalysts, the catalyst’s activity and kinetic stability were investigated. 相似文献
45.
A. M. Churakov A. Yu. Tyurin E. L. Goncharova S. L. Ioffe Yu. A. Strelenko V. A. Tartakovsky 《Russian Chemical Bulletin》1995,44(5):890-896
The addition of 1-aryl-2-bromodiazene 1-oxides to olefins yields 1-aryl-2-(2-bromoalkyl)diazene 1-oxides (4). A radical mechanism of the reaction has been suggested. Compounds4 decompose to give bromohydrazones of formaldehyde and aldehydes. The structural factors that affect the rate of this process are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 917–923, May, 1995.The work was carried out in the Scientific Educational Center of the Institute of Organic Chemistry of the RAS with financial support of the Russian Foundation for Basic Research (Project No. 93-03-18461). 相似文献
46.
WO3 and WO3:P (5 mol% H3PO4) thin films were prepared using the sol-gel route and the electrochromic properties of the films were investigated using
in situ spectroelectrochemical methods. The measurements were performed in propylene carbonate solution with 0.1 M LiClO4 as electrolyte. During the cathodic polarization at –0.8 V a blue coloration is observed with a reversible variation between
14% and 84% of the transmittance at λ=633 nm. The kinetics for the bleaching process is faster for the WO3:P film than for the undoped WO3 film.
Electronic Publication 相似文献
47.
A hydrothermal cleavage-decomposition mechanism was used to synthesize single-crystal α-Mn2O3 nanorods at 160 °C for 16 h using KMnO4 as manganese source and CTAB as reducing regent. The as-synthesized products were characterized by powder X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy and infrared spectrum. The results indicate that the reaction temperature is a crucial factor for the formation of α-Mn2O3 nanorods. These nanorods exhibit single-crystal nature, and have an average diameter of 36 nm and lengths of up to 1 μm. Based on our experimental results, a hydrothermal cleavage-decomposition mechanism has been proposed on the formation of α-Mn2O3 nanorods. 相似文献
48.
Ion-imprinting concept and polysaccharide incorporated sol-gel process were applied to the preparation of a new silica-supported organic-inorganic hybrid sorbent for selective separation of Cd(II) from aqueous solution. In the prepared shell/core composite sorbent, covalently surface coating on the supporting silica gel was achieved by using a Cd(II)-imprinting sol-gel process starting from an inorganic precursor, γ-glycidoxypropyltrimethoxysiloxane (GPTMS), and a functional biopolymer, chitosan (CS). The sorbent was prepared through self-hydrolysis of GPTMS, self-condensation and co-condensation of silanol groups (Si-OH) from siloxane and silica gel surface, in combination with in situ covalent cross-linking of CS with partial amine shielded by Cd(II) complexation. Extraction of the imprinting molecules left a predetermined arrangement of ligands and tailored binding pockets for Cd(II). The prepared sorbent was characterized by using X-ray energy dispersion spectroscopy (EDX), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Batch experiments were conducted to study the sorption performance by removal of Cd(II) when present singly or in binary system, an aqueous Cd(II) and Zn(II) mixture. The ion-imprinted composite sorbent offered a fast kinetics for the sorption of Cd(II) and the maximum capacity was 1.14 mmol g−1. The uptake capacity of the imprinted sorbent and the selectivity coefficient were much higher than that of the non-imprinted sorbent. The imprinted sorbent exhibited high reusability. The prepared functional sorbent was shown to be promising for the preconcentration of cadmium in environmental and biological samples. 相似文献
49.
Marina Lulla Jelena Asari Jaan Aarik Kaupo Kukli Raul Rammula Unto Tapper Eero Kauppinen Väino Sammelselg 《Mikrochimica acta》2006,155(1-2):195-198
Quantitative electron probe microanalysis of highly insulating materials is a complicated problem, partially solved by coating
samples with grounded thin conductive layers or using novel scanning electron microscopy (SEM) techniques, such as low-voltage
and/or variable pressure SEM. In this work, some problems of quantitative X-ray microanalysis of thin HfO2 films, in particular the possibility to determine mass thickness correlated to the density of the layer material, are discussed.
For comparison, Al2O3, Ta2O5 and TiO2 films grown onto both semiconductive Si and insulating quartz substrates were also analysed. All the films studied were synthesized
by atomic layer deposition method. 相似文献
50.
In this article we study the effect of energetic heterogeneity of a crystalline surface on the adsorption of hydrogen ions (protons) from the liquid phase. In particular, we examine the influence of the shape of the adsorption energy distribution on the equilibrium isotherms of hydrogen ions. To that purpose, a few popular distribution functions, including rectangular, exponential, and asymmetric Gaussian are considered. Additionally, multimodal distribution functions, which may correspond to the adsorption on different crystal planes of the oxide, are also used. Lateral interactions between adsorbed charges are modeled using the potential function proposed by Borkovec et al., which accounts also for polarization of the liquid medium. The results presented here are obtained using both Monte Carlo (MC) simulations and theoretical calculations involving Mean Field Approximation (MFA). They indicate that increased energetic heterogeneity of the adsorbing surface may, in general, considerably change the behavior of the adsorption isotherms, regardless of the assumed distribution function. It is also shown that the predictions of the proposed theory are consistent with the data obtained from the MC simulations. 相似文献