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Powder Diffraction Experiments (powder + diffraction_experiment)

Distribution by Scientific Domains

Chemistry	100%

Selected Abstracts

Investigation of nanocrystalline CdS,glutathione particles by radial distribution function

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2003
V. I. Korsounski
Using high-energy synchrotron radiation, powder diffraction experiments were carried out on CdS nanocrystals stabilized with glutathione. The radial distribution function was calculated from the data and analysed. The nanoparticle core, of diameter estimated as 15,20,Å, consists of Cd and S atoms in the proportion 1:1. Inside the core, both Cd and S atoms coordinate each other approximately tetrahedrally. The surface S atoms are connected to just two or three Cd atoms of the core and belong to the glutathione molecules of the particle shell. These S atoms are also a part of the core structure and contribute about one half of the total number of S atoms per particle. First-neighbour Cd,S distances are 2.523,Å with a narrow distance distribution. No difference is observed between the lengths of Cd,S bonds involving the sulfur of the glutathione molecules and the sulfur atoms which are solely bound to Cd. The bond angle Cd,S,Cd at the surface bridging S atoms of glutathione is ca 99.5°, i.e. significantly smaller than an average one of 109.5° characteristic of the Cd and S atom packing inside the core. Beyond the range of the near interatomic distances, the influence of the surface and the defects cause a significant distinction of the particle core structure from those of zincblende and wurtzite, characteristic of bulk CdS. [source]

The crystallography beamline I711 at MAX,II

JOURNAL OF SYNCHROTRON RADIATION, Issue 4 2000
Y. Cerenius
A new X-ray crystallographic beamline is operational at the MAX,II synchrotron in Lund. The beamline has been in regular use since August 1998 and is used both for macro- and small molecule diffraction as well as powder diffraction experiments. The radiation source is a 1.8,T multipole wiggler. The beam is focused vertically by a bendable mirror and horizontally by an asymmetrically cut Si(111) monochromator. The wavelength range is 0.8,1.55,Å with a measured flux at 1,Å of more than 1011,photons,s,1 in 0.3,mm × 0.3,mm at the sample position. The station is currently equipped with a Mar345 imaging plate, a Bruker Smart 1000 area CCD detector and a Huber imaging-plate Guinier camera. An ADSC 210 area CCD detector is planned to be installed during 2000. [source]

The structure of short-lived excited states of molecular complexes by time-resolved X-ray diffraction

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2005
Philip Coppens
Experimental and computational methods for time-resolved (TR) diffraction now allow the determination of geometry changes on molecular excitation. The first results indicate significant changes in the interatomic distances and molecular shape on photo-excitation, but also a dependence of the induced changes on the molecular environment. Though the use of high-brightness synchrotron sources is essential, it limits the time resolution to the width of the synchrotron pulse which is currently 70,100,ps. The experiments discussed fall into two categories: (i) picosecond powder diffraction experiments on the molecular excitation to a singlet state, and (ii) microsecond experiments on the excited states of inorganic complexes. Both involve reversible processes for which a stroboscopic technique can be applied. [source]

Constitutional Self-Organization of Adenine,Uracil-Derived Hybrid Materials

CHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2007
Carole Arnal-Hérault Dr.
Abstract The alkoxysilane nucleobase adenine (A) and uracil (U) precursors described in this paper generate in solution a complex library of hydrogen-bonded aggregates, which can be expressed in the solid state as discrete higher oligomers. The different interconverting outputs that nucleobases may form by oligomerization define a dynamic polyfunctional diversity that may be "extracted selectively" in solid state by sol,gel transcription, under the intrinsic stability of the system. After the sol,gel process, unique constitutional preference for specific geometries in hybrid materials is consistent with a preferential arrangement of nucleobase systems, favoring the self-assembly by the Hoogsteen geometry. FTIR and NMR spectroscopy and X-ray powder diffraction experiments demonstrate the formation of self-organized hybrid supramolecular materials. Electron microscopy reveals the micrometric platelike morphology of the hybrid materials. The MA,U hybrid material is nanostructured in ordered circular domains of 5,nm in diameter of alternative light and dark rows with an one-dimensional periodicity of 3.5,Å. [source]

High-Spin- and Low-Spin-State Structures of [Fe(chloroethyltetrazole)6](ClO4)2 from Synchrotron Powder Diffraction Data

CHEMISTRY - A EUROPEAN JOURNAL, Issue 19 2006
Eva Dova Dr.
Abstract The spin-crossover complex [Fe(teec)6](ClO4)2 (teec = chloroethyltetrazole) exhibits a 50,% incomplete spin crossover in the temperature range 300,30 K. Time-resolved synchrotron powder diffraction experiments have been carried out to elucidate its structural behavior. We report crystal structure models of this material at 300 K (high spin) and 90 K (low spin), as solved from synchrotron powder diffraction data by using Genetic Algorithm and Parallel Tempering techniques and refined with Rietveld refinement. During short synchrotron powder diffraction experiments (five minutes duration) two distinguishable lattices were observed the quantities of which vary with temperature. The implication of this phenomenon, that is interpreted as a structural phase transition associated with the high-to-low spin crossover, and the structural characteristics of the high-spin and low-spin models are discussed in relation to other compounds showing a similar type of spin-crossover behavior. [source]