Home About us Contact
|
Home About us Contact | ||
|
|
||
Diffraction Experiments (diffraction + experiment)
Kinds of Diffraction Experiments Selected AbstractsStructure of Fast Ion Conductors Li3xLa2/3-xTiO3 Deduced from Powder Neutron Diffraction Experiments.CHEMINFORM, Issue 28 2005A. Varez Abstract For Abstract see ChemInform Abstract in Full Text. [source] New Eremophilane Sesquiterpenes from the Roots of Ligularia fischeriHELVETICA CHIMICA ACTA, Issue 3 2009Meicai Deng Abstract New eremophilane sesquiterpenes, (3,,6,,8,,10,)-3-acetyl-6,8,10-trihydroxyeremophil-7(11)-eno-12,8-lactone (1), (3,,6,,8,,10,)-3-acetyl-8,10-dihydroxy-6-(2-methyl-1-oxobutoxy) eremophil-7(11)-eno-12,8-lactone (2), (3,,6,,10,)- and (3,,6,,10,)-3-acetyl-6,10-dihydroxyeremophila-7(11),8-dieno-12,8-lactone (3 and 4, resp.), and a dinoreremophilane derivative, (3aR,4R,5S,7aS)-2-acetyl-3a,4,5,6,7,7a-hexahydro-7a-hydroxy-1H -inden-5-yl acetate (5), were isolated from the roots of Ligularia fischeri. Their structures were elucidated by spectroscopic methods including 1D and 2D NMR spectra, and the structure of 1 was further confirmed by a single-crystal X-ray diffraction experiment. Among the isolated compounds, lactone 1 exhibited inhibitory activity towards PTP1B with an IC50 value of 1.34,,Min vivo. The other compounds were inactive. [source] The Bravais polar lattice as a didactic tool for diffraction beginnersJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5-2 2010Massimo Nespolo When undergraduate students discover crystallography for the first time, they are usually already familiar with the phenomenon of diffraction as the `bending' of waves around small obstacles. The special (periodic) nature of crystals acting as `diffraction gratings' that produce interference of diffracted waves is typically rationalized in terms of the reciprocal lattice of the crystal. The concept of the reciprocal lattice, however, remains somewhat abstract for beginners, until they perform a diffraction experiment. It can be made more easily understandable through an intermediate step, namely its ancestor, the Bravais polar lattice. By means of a short historical trip through pre-X-ray crystallography, a generalized introduction to the notion of the dual lattice is given, of which the reciprocal lattice is the most common but by no means the only example, and it is shown how the use of the Bravais polar lattice can ease the introduction of the reciprocal lattice. [source] Growth of large protein crystals by a large-scale hanging-drop methodJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2010Keisuke Kakinouchi A method for growing large protein crystals is described. In this method, a cut pipette tip is used to hang large-scale droplets (maximum volume 200,µl) consisting of protein and precipitating agents. A crystal grows at the vapor,liquid interface; thereafter the grown crystal can be retrieved by droplet,droplet contact both for repeated macroseeding and for mounting crystals in a capillary. Crystallization experiments with peroxiredoxin of Aeropyrum pernix K1 (thioredoxin peroxidase, ApTPx) and hen egg white lysozyme demonstrated that this large-scale hanging-drop method could produce a large-volume crystal very effectively. A neutron diffraction experiment confirmed that an ApTPx crystal (6.2,mm3) obtained by this method diffracted to beyond 3.5,Å resolution. [source] Dependence of small-angle neutron scattering contrast on the difference in thermal expansions of phases in two-phase alloysJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2009Pavel Strunz Theoretical expressions describing small-angle neutron scattering (SANS) contrast dependence on temperature in the region where no phase-composition changes occur were derived for two-phase Ni superalloys. The theory is based on the difference in thermal expansion of the two primary phases, , and ,,. The simulations show that the scattering contrast temperature evolution is significant enough to be considered in in situ SANS experiments with superalloys at elevated temperatures. The simulations performed show that the magnitude of the scattering contrast at room temperature is firmly connected with the particular shape of the scattering contrast temperature dependence. This fact can be used for determination of the scattering contrast without a knowledge of the compositions of the individual phases. The theoretical expressions derived for scattering contrast were proven experimentally on an Ni,Fe-base alloy, DT706. The evolution of lattice parameters of both the matrix and the precipitate phases was obtained from an in situ wide-angle neutron diffraction experiment. The theoretical scattering contrast dependence was then successfully fitted to the measured SANS integral intensity. [source] Nondestructive characterization of ferrofluids by wide-angle synchrotron light diffraction: crystalline structure and size distribution of colloidal nanoparticlesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2008Alexei Vorobiev The combination of magnetic and nonmagnetic interactions between the colloidal particles in ferrofluids results in various local inter-particle correlations that, in turn, change the macroscopic properties of the whole system. Therefore, characterization of the particle ensemble is a crucial point, allowing optimization of a ferrofluid for a particular application. Here it is shown how the crystal structure of the particles can be easily obtained in a fast synchrotron light diffraction experiment without any special treatment of the ferrofluid sample. Moreover, from the same diffraction patterns, such important parameters as particle mean size and dispersion are retrieved; these are compared with the corresponding parameters obtained from electron microscopy data. A particular problem of magnetite,maghemite transformation in nanoparticles stabilized by the surfactant shell is pointed out. [source] A heating stage up to 1173,K for X-ray diffraction studies in the whole orientation spaceJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2003R. Resel A multi-purpose heating attachment designed primarily for X-ray four-circle diffractometers but applicable also for classical powder diffraction is presented. When working in reflection geometry, the air-cooled heating stage allows diffraction studies to be performed on plate-like samples up to 1173,K in the whole orientation space. This paper gives a detailed description of the assembly and important technical specifications for the performance of experiments. The heating characteristics of the heating stage, the displacement of the sample from the goniometer centre as a result of thermal expansion and the influence of the protecting dome on the diffraction experiment are presented. The simple technical construction, the low weight, the small size and good heating performance make this equipment a general purpose heating attachment for X-ray diffraction experiments in reflection geometry. [source] Waveguide-enhanced scattering from thin biomolecular filmsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2002F. Pfeiffer An X-ray diffraction experiment on multilamellar membranes incorporated into an X-ray waveguide structure is reported. In the device, the lipid bilayers are confined to one side by the silicon substrate and to the other side by an evaporated thin metal cap layer. Shining a highly brilliant X-ray beam onto the system, resonantly enhanced, precisely defined and clearly distinguishable standing-wavefield distributions (modes) are excited. The in-plane structure of the acyl chain ordering is then studied by grazing incidence diffraction under simultaneously excited modes. A significant gain in signal-to-noise ratio as well as enhanced spatial resolution can be obtained with such a setup. [source] Performance of a confocal multilayer X-ray opticJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2002J. Kusz In recent years, several companies have developed the technique of arranging two multilayer mirrors in confocal optics for monochromatizing X-rays. In this study, a focusing device of Osmic Inc., with a source-to-focus distance of 1005,mm, has been used. The goal was to measure the homogeneity of the beam, the cross section at various distances from the focus and the efficiency of the optic when it is operated with vacuum and with air in the beam path. A small crystal sphere set at various distances is used to compare the intensities and the widths of reflections with those of a flat graphite monochromator. In a standard diffraction experiment (crystal size 0.25,mm), the gain factor with respect to graphite is roughly ten at a position where the beam plateau is 0.5,mm. The suppression of the Cu K, radiation and of higher harmonics of K, is very good. [source] A furnace for in situ X-ray diffraction studies of insertion processes in electrode materials at elevated temperaturesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2001T. Eriksson A furnace is described for in situ X-ray diffraction studies, in transmission mode, of structural changes in electrode materials for Li-ion (polymer) batteries in the ambient to 300°C temperature range. The method exploits the thin flat-cell geometry of the lithium-polymer battery concept. The flat sample is able to oscillate about a horizontal axis in its own plane in the X-ray beam, to provide better averaging during the diffraction experiment. The use of the device is demonstrated in a study of lithium intercalation in graphite (a commonly used anode material in lithium-ion batteries) during electrochemical cycling and storage at 70°C. [source] CCD-based X-ray area detector for time-resolved diffraction experimentsJOURNAL OF SYNCHROTRON RADIATION, Issue 6 2004Naoto Yagi A fast X-ray area detector for diffraction, scattering and imaging experiments at microsecond to millisecond time resolution has been developed. The key element of the detector is a fast (291,frames,s,1) framing camera with three CCDs. A prism forms identical images on the CCDs and the frame rate is increased three times by reading them alternately. In order to convert X-rays into visible light that is detectable with the CCDs, an X-ray image intensifier is used. The camera can also be used with a high-resolution X-ray detector. In both cases it was found to be important to use a phosphor with a short decay time to fully make use of the high-speed framing capability of the camera. Preliminary results of a fibre diffraction experiment on a skeletal muscle and coronary angiography are presented. [source] Intensified spin-dependent-transport and localized-spin freezing in magnetite sinter made from low size-dispersion hematite nanoparticles with low temperature calcinationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2006H. Kobori Abstract The spin-dependent-transport (SDT) has been studied for magnetite (Fe3O4) nano-particle sinter (MNPS) made from low size-dispersion hematite (,-Fe2O3) nanoparticles (LSDHN's) with low temperature calcination. Two kinds of LSDHN's are grown by the hydrothermal synthesis. The average sizes of them are 30 nm and 60 nm. The MNPS is produced by calcining the LSDHN's at 500 °C for 5 hours in the atmosphere of Ar(90%)/H2(10%) mixed gases. As compared with a bulk single crystal, the considerable intensification of negative-differential-magnetoresistance (ND-MR) has been observed for the MNPS. We have not observed abrupt change of the electrical resistivity in the vicinity of the temperature of the Verwey transition (which is the metal-insulator transition) appeared for a bulk single crystal. The ND-MR for 30 nm shows larger values than that of 60 nm on the temperature dependence. From the X-ray diffraction experiment, the MNPS is found to include crystalline magnetite regions. We consider that the MNPS is composed of large amorphous-like grain-boundaries and small crystalline grains. The electrical current is inferred to flow in grain-boundary regions. In grain-boundary regions, since the localized spins are relatively random distributed, the spin-polarized conduction electrons show the SDT. Below the Verwey temperature, we have observed the magnetization difference between zero-field cooling (ZFC) and field-cooling (FC). This phenomenon indicates that the localized spins in the amorphous-like grain-boundaries are frozen in some degree. Above the Verwey temperature, the magnetoresistance is well fitted by the square of the Langevin function. We consider that the localized spins in the amorphous-like grain-boundaries do not form perfectly random configuration and are somewhat ordered in a short range region. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Reversal magnetoresistance and unusual localized-spin freezing in magnetite sinter made from low size-dispersion hematite nano-particles with high temperature calcinationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2006H. Kobori Abstract The magneto-resistance and magnetization have been studied for magnetite (Fe3O4) sinter made from low size-dispersion hematite (,-Fe2O3) nanoparticles (LSDHN's) with high temperature calcination. Two kinds of LSDHN's were grown by the hydrothermal synthesis. The average particle sizes of them are 30 nm and 60 nm. The magnetite sinter was produced by calcining the LSDHN's at 800 °C for 5 hours in the atmosphere of Ar(90%)/H2(10%) mixed gases. We have observed an abrupt change of the electrical resistivity by one order of magnitude in the vicinity of the Verwey temperature (123 K) of a bulk single crystal. From the X-ray diffraction experiment, we have found that the magnetite sinter includes crystalline region. The magnetite sinter is considered to be composed of relatively narrow grain-boundary regions of amorphous-like magnetite and large grain regions of crystalline magnetite. It is regarded that the grain-boundary-conduction is dominant below the Verwey temperature and the inter-grain-conduction is dominant above the Verwey temperature. We have observed the positive differential magnetoresistance (PD-MR) in low temperature regions and the negative differential magnetoresistance (ND-MR) in high temperature regions. The ND-MR is an ordinary phenomenon for magnetite, but the PD-MR is a peculiar one. In addition, an unusual localized-spin-freezing phenomenon has been also observed. Below the Verwey temperature, the magnetization difference between zero-field-cooling and field-cooling has been observed. The magnetization difference shows a sudden change in the vicinity of the Verwey temperature. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] GABAergic phthalide dimers from Angelica sinensis (Oliv.) DielsPHYTOCHEMICAL ANALYSIS, Issue 6 2006Shixin Deng Abstract The methanol extract of Angelica sinensis (Oliv.) Diels roots (Dang Gui) has been shown to exhibit competitive binding to the GABAa receptor, suggesting the presence of GABAergic ligands. Chromatographic fractionation of the methanol extract led to the isolation of two GABAergic dimeric phthalides 1 and 2. Gelispirolide (1) was elucidated as a new phthalide dimer composed of a Z -ligustilide and a Z -butylidenephthalide unit on the basis of spectroscopic approaches including one- and two-dimensional NMR, HRESIMS and HRESIMS-MS. Compound 2 was identified as the known dimeric phthalide, riligustilide, by comparison of its spectroscopic data with literature values. Its dimeric linkage and stereochemistry were ascertained by a single crystal X-ray diffraction experiment. Both dimers 1 and 2 were found to be active in an in vitro GABAa receptor-binding assay with IC50 values of 29 and 24 µm, respectively. Copyright © 2006 John Wiley & Sons, Ltd. [source] X-ray diffraction by a crystal in a permanent external electric field: general considerationsACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2005Semen V. Gorfman The variations of X-ray diffraction intensities from a crystal in the presence of a permanent external electric field is modeled analytically using a first-order stationary perturbation theory. The change in a crystal, induced by an external electric field, is separated into two contributions. The first one is related to a pure polarization of an electron subsystem, while the second contribution can be reduced to the displacements of the rigid pseudoatoms from their equilibrium positions. It is shown that a change of the X-ray diffraction intensities mainly originates from the second contribution, while the influence of the pure polarization of a crystal electron subsystem is negligibly small. The quantities restored from an X-ray diffraction experiment in the presence of an external electric field were analyzed in detail in terms of a rigid pseudoatomic model of electron density and harmonic approximation for the atomic thermal motion. Explicit relationships are derived that link the properties of phonon spectra with E -field-induced variations of a structure factor, pseudoatomic displacements and piezoelectric strains. The displacements can be numerically estimated using a model of independent atomic motion if the Debye,Waller factors and pseudoatomic charges are known either from a previous single-crystal X-ray diffraction study or from density functional theory calculations. The above estimations can be used to develop an optimum strategy for a data collection that avoids the measurements of reflections insensitive to the electric-field-induced variations. [source] How to easily replace the independent atom model , the example of bergenin, a potential anti-HIV agent of traditional Asian medicineACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2009Birger Dittrich Bergenin, which has been isolated from a variety of tropical plants, has several pharmacological applications in traditional Asian medicine. Its electron-density distribution was obtained from a room-temperature low-resolution X-ray data set measured with point detection making use of multipole populations from the invariom library. Two refinement models were considered. In a first step, positional parameters and ADPs were refined with fixed library multipoles (model E1). This model was suitable to be input into a second refinement of multipoles (model E2), which converged smoothly although based on Cu,K, room-temperature data. Quantitative results of a topological analysis of the electron density from both models were compared with Hartree,Fock and density-functional calculations. With respect to the independent atom model (IAM) more information can be extracted from invariom modelling, including the electrostatic potential and hydrogen-bond energies, which are highly useful, especially for biologically active compounds. The reliability of the applied invariom formalism was assessed by a comparison of bond-topological properties of sucrose, for which high-resolution multipole and invariom densities were available. Since a conventional X-ray diffraction experiment using basic equipment was combined with the easy-to-use invariom formalism, the procedure described here for bergenin illustrates how it can be routinely applied in pharmacological research. [source] Disordered misfit [Ca2CoO3][CoO2]1.62 structure revisited via a new intrinsic modulationACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2008Hervé Muguerra The structure of the thermoelectric lamellar misfit cobalt oxide [Ca2CoO3][CoO2]1.62 was refined again using single-crystal X-ray diffraction data. A new commensurate intrinsic modulation was observed involving a modulation vector orthogonal to the misfit direction (,,0,,,). The five-dimensional superspace group is C2/m(1,0)(,0,)gm and the structure was solved using a commensurate approximation. A new model is given involving an occupation modulation of the split sites of the [CoO] layer. This [CoO] layer can be described by triple chains running along b. The residual disorder along b can then be explained by the assumption of a local ordering with two types of clusters: CoO2 and Co5O4. A powder neutron diffraction experiment confirmed the ordering evidenced by the single-crystal X-ray diffraction study, but was not sufficient by itself to deal with this double modulated scheme. The new intrinsic modulation is destroyed by partial metal substitutions in the [CoO] layer. The structural modifications of this layer directly influence the physical properties which are related to the electronic structure of the [CoO2] layers. [source] Extracting charge density distributions from diffraction data: a model study on ureaACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2000R. Y. De Vries The quality of the extraction of electron density distributions by means of a multipole refinement method is investigated. Structure factors of the urea crystal have been obtained from an electron density distribution (EDD) resulting from a density function calculation with the CRYSTAL95 package. To account for the thermal motion of the atoms, the stockholder-partioned densities of the atoms have been convoluted with thermal smearing functions, which were obtained from a neutron diffraction experiment. A POP multipole refinement yielded a good fit, R = 0.6%. This disagreement factor is based on magnitudes only. Comparison with the original structure factors gave a disagreement of 0.8% owing to differences in magnitude and phase. The fitted EDD still showed all the characteristics of the interaction density. After random errors corresponding to the experimental situation were added to the structure factors, the refinement was repeated. The fit was R = 1.1%. This time the resulting interaction density was heavily deformed. Repetition with another set of random errors from the same distribution yielded a widely different interaction density distribution. The conclusion is that interaction densities cannot be obtained from X-ray diffraction data on non-centrosymmetric crystals. [source] Multivariate phase combination improves automated crystallographic model buildingACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2010Pavol Skubák Density modification is a standard technique in macromolecular crystallography that can significantly improve an initial electron-density map. To obtain optimal results, the initial and density-modified map are combined. Current methods assume that these two maps are independent and propagate the initial map information and its accuracy indirectly through previously determined coefficients. A multivariate equation has been derived that no longer assumes independence between the initial and density-modified map, considers the observed diffraction data directly and refines the errors that can occur in a single-wavelength anomalous diffraction experiment. The equation has been implemented and tested on over 100 real data sets. The results are dramatic: the method provides significantly improved maps over the current state of the art and leads to many more structures being built automatically. [source] Cryoprotection properties of salts of organic acids: a case study for a tetragonal crystal of HEW lysozymeACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2010Grzegorz Bujacz Currently, the great majority of the data that are used for solving macromolecular structures by X-ray crystallography are collected at cryogenic temperatures. Selection of a suitable cryoprotectant, which ensures crystal stability at low temperatures, is critical for the success of a particular diffraction experiment. The effectiveness of salts of organic acids as potential cryoprotective agents is presented in the following work. Sodium formate, acetate, malonate and citrate were tested, as were sodium potassium tartrate and acetate in the form of potassium and ammonium salts. For each salt investigated, the minimal concentration that was required for successful cryoprotection was determined over the pH range 4.5,9.5. The cryoprotective ability of these organic salts depends upon the number of carboxylic groups; the lowest concentration required for cryoprotection was observed at neutral pH. Case-study experiments conducted using the tetragonal form of hen egg-white lysozyme (HEWL) confirmed that salts of organic acids can successfully act as cryoprotective agents of protein crystals grown from high concentrations of inorganic salts. When crystals are grown from solutions containing a sufficient concentration of organic acid salts no additional cryoprotection is needed as the crystals can safely be frozen directly from the crystallizing buffers. [source] Know your dose: RADDOSEACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2010Karthik S. Paithankar The program RADDOSE is widely used to compute the dose absorbed by a macromolecular crystal during an X-ray diffraction experiment. A number of factors affect the absorbed dose, including the incident X-ray flux density, the photon energy and the composition of the macromolecule and of the buffer in the crystal. An experimental dose limit for macromolecular crystallography (MX) of 30,MGy at 100,K has been reported, beyond which the biological information obtained may be compromised. Thus, for the planning of an optimized diffraction experiment the estimation of dose has become an additional tool. A number of approximations were made in the original version of RADDOSE. Recently, the code has been modified in order to take into account fluorescent X-ray escape from the crystal (version 2) and the inclusion of incoherent (Compton) scattering into the dose calculation is now reported (version 3). The Compton cross-section, although negligible at the energies currently commonly used in MX, should be considered in dose calculations for incident energies above 20,keV. Calculations using version 3 of RADDOSE reinforce previous studies that predict a reduction in the absorbed dose when data are collected at higher energies compared with data collected at 12.4,keV. Hence, a longer irradiation lifetime for the sample can be achieved at these higher energies but this is at the cost of lower diffraction intensities. The parameter `diffraction-dose efficiency', which is the diffracted intensity per absorbed dose, is revisited in an attempt to investigate the benefits and pitfalls of data collection using higher and lower energy radiation, particularly for thin crystals. [source] HKL -3000: the integration of data reduction and structure solution , from diffraction images to an initial model in minutesACTA CRYSTALLOGRAPHICA SECTION D, Issue 8 2006Marcin Cymborowski A new approach that integrates data collection, data reduction, phasing and model building significantly accelerates the process of structure determination and on average minimizes the number of data sets and synchrotron time required for structure solution. Initial testing of the HKL -3000 system (the beta version was named HKL -2000_ph) with more than 140 novel structure determinations has proven its high value for MAD/SAD experiments. The heuristics for choosing the best computational strategy at different data resolution limits of phasing signal and crystal diffraction are being optimized. The typical end result is an interpretable electron-density map with a partially built structure and, in some cases, an almost complete refined model. The current development is oriented towards very fast structure solution in order to provide feedback during the diffraction experiment. Work is also proceeding towards improving the quality of phasing calculation and model building. [source] Recursive direct phasing with reference-beam diffractionACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2003Qun Shen The reference-beam diffraction technique provides a practical way to measure a large number of triplet phases in a standard oscillating-crystal diffraction experiment for protein crystals. The triplet-phase data set from such reference-beam measurements contains a unique phase-ocurrence pattern that leads to a new recursive phasing algorithm for the individual structure-factor phases. Application of the new algorithm is demonstrated for tetragonal lysozyme using 7360 triplet phases measured in a reference-beam experiment with a median phase discrepancy of 45°. An electron-density map obtained using this phasing algorithm and the measured triplet phases shows good agreement with the known protein structure. [source] Electronic Properties of 3,3,-Dimethyl-5,5,-bis(1,2,4-triazine): Towards Design of Supramolecular Arrangements of N-Heterocyclic CuI ComplexesCHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2007Blandine Courcot Dr. Abstract A new efficient and safe synthesis of 3,3,-dimethyl-5,5,-bis-(1,2,4-triazine) is presented. The electron-density distribution and electrostatic properties (charge, electrostatic potential) of this molecule were analyzed. These properties were derived from a high-resolution single-crystal X-ray diffraction experiment at 100,K and compared to the results obtained from ab initio DFT quantum-mechanical calculations. Comparisons of its electrostatic potential features and integrated atomic charges (quantum theory of atoms in molecules, QTAIM) have been made with those of related molecules such as bipyrimidine ligands. Two methods were used to derive integrated charges: one is based on the conventional analytical procedure and the second uses a steepest-ascent numerical algorithm. Excellent agreement was obtained between these two methods. Charges and electrostatic potential were used as predictive indices of metal chelation and discussed in the light of complexation abilities of the title compound and related molecules. The crystal structure of a CuI complex of 3,3,-dimethyl-5,5,-bis(1,2,4-triazine) is reported here. In the solid state, this complex forms a three-dimensional multibranch network with open channels in which counterions and solvent molecules are located. This architecture involves both cis and trans isomers of the title compound. [source] Solid-State Structures and Properties of Europium and Samarium HydridesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2010Holger Kohlmann Abstract The structural chemistry of europium and samarium hydrides in the solid state is very rich, ranging from typical ionic hydrides following the hydride-fluoride analogy to complex transition metal hydrides and interstitial hydrides. While crystal structure, electrical, and magnetic properties suggest that europium is divalent in all hydrides investigated so far, samarium is easily transformed to a trivalent oxidation state in its hydrides and shows similarities to other lanthanide(III) hydrides. The problem of neutron absorption of europium and samarium, hampering crystal structure solution and limiting the available structural information, is discussed in detail, and practical solutions for neutron diffraction experiments are given. [source] A Novel Copper(I) Halide Framework Templated by Organic,Inorganic Hybrid Polyoxometalate Chains Formed In Situ: A New Route for the Design and Synthesis of Porous FrameworksEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2006Hua Jin Abstract A 1D organic,inorganic hybrid polyoxometalate chain has been used as a non-coordinating anionic template for the construction of a novel 3D copper halide 4,4,-bipy framework, namely [Cu3ICl(4,4,-bipy)4][CuII(1,10-phen)2Mo8O26]. X-ray diffraction experiments revealed that the title compound consists of chloride-bridged trinuclear CuI units linked by neutral organic 4,4,-bipy groups into a 3D framework with hexagon-like channels in which 1D organic,inorganic hybrid polyoxometalate chains reside. This is the first example of a 1D organic,inorganic hybrid polyoxometalate chain functioning as a novel anionic template for the construction of a 3D framework. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Consecutive Nucleation Events During Divetrification of Zr52.5Cu17.9Ni14.6Al10Ti5 Bulk Metallic Glass,ADVANCED ENGINEERING MATERIALS, Issue 11 2008L. Yang Differential scanning calorimetry revealed two exothermal peaks in Zr52.5Cu17.9Ni14.6 -Al10Ti5 bulk metallic glass during divetrification. Analysis of the calorimetry data as well as in-situ X-ray diffraction experiments show that the exothermal peaks correspond to two nucleation events, controlled by interface and long-range diffusion, respectively. [source] The ,-to-, Transition in BiFeO3: A Powder Neutron Diffraction StudyADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Donna C. Arnold Abstract High-temperature powder neutron diffraction experiments are conducted around the reported ,,, phase transition (,930,°C) in BiFeO3. The results demonstrate that while a small volume contraction is observed at the transition temperature, consistent with an insulator,metal transition, both the ,- and ,-phase of BiFeO3 exhibit orthorhombic symmetry; i.e., no further increase of symmetry occurs during this transition. The ,-orthorhombic phase is observed to persist up to a temperature of approximately 950,°C before complete decomposition into Bi2Fe4O9 (and liquid Bi2O3), which subsequently begins to decompose at approximately 960,°C. [source] Synthesis and structural studies of N -(p -toluenesulfonyl)-amino acid 3,5-di- tert -butyl-2-phenolamidesHETEROATOM CHEMISTRY, Issue 2 2004Margarita Tlahuextl This paper describes the synthesis and structural studies of N -(p -toluenesulfonyl)-amino acid 3,5-di- tert -butyl-2-phenolamides by 1H, 13C, and 15N. The presence of intra - and intermolecular hydrogen bonds were studied by variable temperature NMR spectroscopy. The molecular structure of two amides in the solid state was determined by X-ray diffraction experiments. The results show that tert -butyl substituents in the phenolic ring have important effects in the nature of hydrogen bonds and conformation of these amides. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:114,120, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10223 [source] DFT calculations of light-induced excited states and comparison with time-resolved crystallographic resultsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2005Philip Coppens Abstract DFT calculations of the ground and first excited states of several transition metal complexes have been performed to complement time-resolved diffraction experiments. The results from different functionals and relativistic treatments are tested against both diffraction and spectroscopic values. Calculations of the d8,d8 complex [Pt2(pyrophosphite)4]4, quantitatively reproduce metal,metal shortening on excitation to the triplet state and support bond formation between the two metal centers, as do calculations on [Rh2(1,3-diisocyanopropane)4]2+. Results on homoleptic and heteroleptic copper(I) 2,9-dimethyl,1,10-phenanthroline (dmp) complexes, which are investigated because of their potential for solar energy capture, confirm considerable molecular deformations on excitation. The distortion calculated for the isolated complex [Cu(dmp)(dmpe)]+ (dmpe=1,2-bis(dimethylphosphino)ethane) is significantly larger than observed in the crystal, indicating the constraining effect of the crystalline environment. The change in the net charge of the Cu atom upon photo-induced metal-to-ligand charge transfer is less than 0.2 e, showing the limitations of the formal Cu(I),Cu(II) designation. Electron density difference maps show a pronounced change in electronic structure of the Cu atom on excitation. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] | ||||||||||||||||||||||||||||||||||