Inclusion of [H3PW12O40] and [H4SiW12O40] into a silica gel matrix via "sol-gel" methodology

Indexación: Web of Science; Scopus.Here we report the inclusion of two Keggin Polyoxometalates (POMs), [H3PW12O40] and [H4SiW12O40], into silica gels by integrating them during the preparation of the SiO2 matrix via "sol-gel" methods. Aerogels were produced by supercritical drying of the wet gels impregnated with the POMs, and lyogels were obtained by means of a lyophilization process. These materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transformed infrared (FT-IR) spectroscopy and thermoanalytical techniques (TGA-DSC). We found that a large fraction of POMs are lost during the aging time, and solvent exchange for lyophilization. However the thermal stability of the bare matrix is modified by the inclusion of POMs. Some aggregates with a high content of POMs were found via SEM-EDX.http://ref.scielo.org/3fg9t

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Evidence for Quantization of Mechanical Rotation of Magnetic Nanoparticles

We report evidence of the quantization of the rotational motion of solid particles containing thousands of atoms. A system of CoFe 2 O 4 nanoparticles confined inside polymeric cavities has been studied. The particles have been characterized by the x-ray diffraction, transmission electron microscopy, plasma mass spectroscopy, ferromagnetic resonance (FMR), and magnetization measurements. Magnetic and FMR data confirm the presence of particles that are free to rotate inside the cavities. Equidistant, temperature-independent jumps in the dependence of the microwave absorption on the magnetic field have been detected. This observation is in accordance with the expectation that orbital motion splits the low-field absorption line into multiple lines

Bis(1,3-dibenzyl­imidazolium) μ-oxido-bis­[trichloridoferrate(III)]

In the title compound (C17H17N2)2[Fe2Cl6O], obtained from the solid-state reaction of FeCl2 and N,N′-dibenzyl­imidazolium chloride, the complex anion has approximate D 3d symmetry with crystallographically imposed inversion symmetry coincident with the bridging μ-O atom. The stereochemistry about each FeCl3O centre is distorted tetra­hedral [Fe—Cl = 2.2176 (5)–2.2427 (5) Å and Fe—O = 1.7545 (2) Å]. The Cl atoms are involved in weak anion–cation C—H⋯Cl inter­actions, giving a network structure

Preliminary results of the small animal rotational positron emisson tomography scanner

[Abstract] AMI Annual Conference 2004, March 27-31, Orlando, FloridaThis contribution reports preliminary results of a high-resolution small animal positron emission tomography (PET) based on pairs of opposed scintillation rotating detectors working in time coincidencePublicad

Quadratic transverse anisotropy term due to dislocations in Mn12-Ac directly obtained by EPR spectroscopy

High-Sensitivity Electron Paramagnetic Resonance experiments have been carried out in fresh and stressed Mn12-Acetate single crystals for frequencies ranging from 40 GHz up to 110 GHz. The high number of crystal dislocations formed in the stressing process introduces a E(S_x^2-S_y^2) transverse anisotropy term in the spin hamiltonian. From the behaviour of the resonant absorptions on the applied transverse magnetic field we have obtained an average value for E = 22 mK, corresponding to a concentration of dislocations per unit cell of c = 10^-3.Comment: 13 pages and 4 figure