scholarly journals Combining precession electron diffraction data with X-ray powder diffraction data to facilitate structure solution

2008 ◽  
Vol 41 (6) ◽  
pp. 1115-1121 ◽  
Author(s):  
Dan Xie ◽  
Christian Baerlocher ◽  
Lynne B. McCusker
Keyword(s):  
Electron Diffraction ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Electron Diffraction Data ◽  
Powder Diffraction Data ◽  
Powder Charge ◽  
X Ray ◽  
Structure Solution ◽  
Precession Electron Diffraction ◽  
Using Data

Information derived from precession electron diffraction (PED) patterns can be used to advantage in combination with high-resolution X-ray powder diffraction data to solve crystal structures that resist solution from X-ray data alone. PED data have been exploited in two different ways for this purpose: (1) to identify weak reflections and (2) to estimate the phases of the reflections in the projection. The former is used to improve the partitioning of the reflection intensities within an overlap group and the latter to provide some starting phases for structure determination. The information was incorporated into a powder charge-flipping algorithm for structure solution. The approaches were first developed using data for the moderately complex zeolite ZSM-5, and then tested on TNU-9, one of the two most complex zeolites known. In both cases, including PED data from just a few projections facilitated structure solution significantly.

Using phases retrieved from two-dimensional projections to facilitate structure solution from X-ray powder diffraction data

2011 ◽  
Vol 44 (5) ◽  
pp. 1023-1032 ◽  
Author(s):  
Dan Xie ◽  
Christian Baerlocher ◽  
Lynne B. McCusker
Keyword(s):  
Electron Microscopy ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Two Dimensional ◽  
Powder Diffraction Data ◽  
Phase Information ◽  
Powder Charge ◽  
X Ray ◽  
Structure Solution ◽  
Using Data

A single-crystal charge-flipping algorithm has been applied to two-dimensional projections derived from X-ray powder diffraction data to retrieve structure-factor phases. These phases proved to be as reliable as those obtained from high-resolution transmission electron microscopy (HRTEM) images or from precession electron diffraction data. In particular, the stronger reflections tend to be correctly phased. The two-dimensional electron-density `images' obtained in this way show the same features as the corresponding HRTEM images, but with higher resolution. Application of the powder charge-flipping algorithm to the full three-dimensional powder diffraction data in conjunction with phases derived from several such (arbitrarily selected) projections was found to have a significant and beneficial effect on the structure solution. The approach was first developed using data collected on the complex zeolite TNU-9, and was then tested further using data for IM-5 and SSZ-74, two similarly complex zeolites. All three of these structures were originally solved by combining X-ray powder diffraction and electron microscopy data, because X-ray diffraction data alone were not sufficient. In all three cases, the phase information derived from two-dimensional subsets of the X-ray powder diffraction data resulted in a significant improvement in the electron-density maps generated by the powder charge-flipping algorithm. The inclusion of this phase information allowed all three structures to be determined from the X-ray data alone. This two-dimensional X-ray powder diffraction approach appears to offer a remarkably simple and powerful method for solving the structures of complex polycrystalline materials.

scholarly journals Crystal structure solution of an elusive polymorph of Dibenzylsquaramide

2013 ◽  
Vol 28 (S2) ◽  
pp. S470-S480 ◽  
Author(s):  
Anna Portell ◽  
Xavier Alcobé ◽  
Latévi M. Lawson Daku ◽  
Radovan Černý ◽  
Rafel Prohens
Keyword(s):  
Crystal Structure ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Structural Features ◽  
Powder Diffraction Data ◽  
Asymmetric Unit ◽  
X Ray ◽  
The Third ◽  
Group Assignment ◽  
Structure Solution

The crystal structure of the third polymorph of dibenzylsquaramide (Portell, A. et al., 2009), (fig. 1) has been determined from laboratory X-ray powder diffraction data by means of direct space methods using the computing program FOX. (Favre-Nicolin and Černý, 2002) The structure resolution has not been straightforward due to several difficulties on the indexing process and in the space group assignment. The asymmetric unit contains two different conformers, which has implied an additional difficulty during the Rietveld (Rietveld, 1969) refinement. All these issues together with particular structural features of disquaramides are discussed.

scholarly journals Analysis of Sr3-xCa1+xMn2CoO9 combining electron, X-ray and neutron diffraction

2014 ◽  
Vol 70 (a1) ◽  
pp. C929-C929
Author(s):  
Philippe Boullay ◽  
Olivier Pérez ◽  
Bernard Raveau ◽  
Seikh Motin ◽  
Caignaert Vincent
Keyword(s):  
Electron Diffraction ◽  
Neutron Diffraction ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Structural Model ◽  
X Ray ◽  
Cell Parameters ◽  
Precession Electron Diffraction ◽  
Different Temperatures ◽  
Scattering Lengths

The AxBX3 hexagonal perovskite-type compounds exhibit interesting magnetic properties such as complex magnetism or random spin chain magnetism[1,2]. Their structures are built up from infinite [BO3] chains consisting of alternating octahedral and trigonal prismatic units, separated by A infinite chains. Sr3-xCa1+xMn2CoO9 are belonging to this family of materials. X-ray powder diffraction patterns are collected for different Sr3-xCa1+xMn2CoO9 samples with different x values. Pattern matching analysis with the SG P-3 and the following cell parameters a=b=9.490(1)Å c=3xc'=3x2.57=7.732(1)Å reveals problematic groups of reflections; these reflections are shifted from one pattern to another one and, moreover, have positions preventing their indexation. Owing to the lack of spatial resolution and peaks overlapping in the powder data, the understanding of the present problem is quite impossible. Electron Diffraction Tomography (EDT) combined with Precession Electron Diffraction (PED) has been used for exploring the reciprocal space of the Sr3-xCa1+xMn2CoO9, x=0 sample. The slight deviations observed from the rational 1/3 c'* value is in agreement with the existence of aperiodicities. The structure of this family of materials has been then described using the super space formalism as a composite structure. The structural model is determined from the PED data integrated with PETS[2]; the first and second sublattices are referring to (Mn,Co)O3 and (Ca,Sr) structural parts respectively. This model is confirmed by the refinement of the X-ray powder diffraction data. Powder neutron diffraction data were then collected at PSI for different temperatures and different Sr3-xCa1+xMn2CoO9 samples. Using the previously refined model, a Co/Mn ordering is revealed thanks to the neutron scattering lengths of these two elements (see fig1). Finally, the treatment of the antiferromagnetic behavior observed bellow 25K is performed in the 4d approach using Jana2006[3].

Structure solution and refinement of tetracaine hydrochloride from X-ray powder diffraction data

2002 ◽  
Vol 26 (4) ◽  
pp. 469-472 ◽  
Author(s):  
Harriott Nowell ◽  
J. Paul Attfield ◽  
Jason C. Cole ◽  
Philip J. Cox ◽  
Kenneth Shankland ◽  
...  
Keyword(s):  
Powder Diffraction ◽  
Diffraction Data ◽  
Powder Diffraction Data ◽  
X Ray ◽  
Structure Solution

scholarly journals Solving molecular crystal structures from laboratory X-ray powder diffraction data withDASH: the state of the art and challenges

2005 ◽  
Vol 38 (2) ◽  
pp. 249-259 ◽  
Author(s):  
Alastair J. Florence ◽  
Norman Shankland ◽  
Kenneth Shankland ◽  
William I. F. David ◽  
Elna Pidcock ◽  
...  
Keyword(s):  
Global Optimization ◽  
Crystal Structures ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Degrees Of Freedom ◽  
Search Space ◽  
Powder Diffraction Data ◽  
Multi Centre Study ◽  
X Ray ◽  
Structure Solution

The crystal structures of 35 molecular compounds have been redetermined from laboratory monochromatic capillary transmission X-ray powder diffraction data using the simulated-annealing approach embodied within theDASHstructure solution package. The compounds represent industrially relevant areas (pharmaceuticals; metal coordination compounds; nonlinear optical materials; dyes) in which the research groups in this multi-centre study are active. The molecules were specifically selected to form a series within which the degree of structural complexity (i.e. degrees of freedom in the global optimization) increased systematically, the degrees of freedom increasing with increasing number of optimizable torsion angles in the structural model and with the inclusion of positional disorder or multiple fragments (counterions; crystallization solvent;Z′ > 1). At the lower end of the complexity scale, the structure was solved with excellent reproducibility and high accuracy. At the opposite end of the scale, the more complex search space offered a significant challenge to the global optimization procedure and it was demonstrated that the inclusion of modal torsional constraints, derived from the Cambridge Structural Database, offered significant benefits in terms of increasing the frequency of successful structure solution by restricting the magnitude of the search space in the global optimization.

Brianyoungite, a new mineral related to hydrozincite, from the north of England orefield

1993 ◽  
Vol 57 (389) ◽  
pp. 665-670 ◽  
Author(s):  
A. Livingstone ◽  
P. E. Champness
Keyword(s):  
Thermogravimetric Analysis ◽  
Electron Diffraction ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Empirical Formula ◽  
New Mineral ◽  
Powder Diffraction Data ◽  
X Ray ◽  
Cell Parameters ◽  
The North

AbstractBrianyoungite, which is chemically and structurally related to hydrozincite, occurs as white rosettes (<100 μm) with gypsum on rubbly limestone within the oxidised zone at Brownley Hill Mine, Nenthead, Cumbria. The mineral contains (wt.%) 71.47 ZnO, 9.90 CO2, 6.62 SO3 and 10.70 H2O+. Based on 29 oxygen atoms, the empirical formula is Zn11.73[(CO3)3.00,(SO4)1.10]4.10(OH)15.88 or ideally Zn3(CO3,SO4)(OH)4. Brianyoungite is either orthorhombic or monoclinic with β very close to 90° Cell parameters determined by electron diffraction and refined from X-ray powder diffraction data are a = 15.724, b = 6.256 and c = 5.427 Å. Density is > 3.93, < 4.09 g/cm3 (meas.) and 4.11 g/cm3 (calc.); Z = 4. Thermogravimetric analysis, IR and XRD powder data (23 lines) are presented.

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