Structure determination of di-mu-hydroxo-bis[(2-(2-pyridyl)phenyl-kappa2N,C1)palladium(II)] by X-ray powder diffractometry

The title compound was synthesized in the form of a powder, and was studied by elemental analysis, IR spectroscopy, thermogravimetry and mass spectroscopy. Its crystal structure was then determined by X-ray powder diffractometry, using X-ray diffraction data collected in the reflection Bragg-Brentano geometry. The methodology followed in the present study to resolve the crystal structure consisted of peak indexing, then the use of the Monte-Carlo/parallel tempering search algorithm, and finally Rietveld refinement coupled with difference-Fourier synthesis. We found that the crystals are composed of monoclinic unit cells, with 1.5 molecules in the asymmetric unit and therefore six molecules per unit cell. In addition, we concluded that the complexes adopt a planar conformation, forming trimers created by groups of parallel molecules.

Structure determination of nitrato-κO-bis[2-(2-pyridyl-κN)amino-5,6-dihydro-4H-1,3-thiazine-κN]copper(II) nitrateviamolecular modelling coupled with X-ray powder diffractometry

The title copper(II) coordination compound, C18H22CuN8O6S2{[Cu(NO3)(PyTz)2]NO3}, was synthesized in the form of small crystals unsuitable for structure determination by single-crystal X-ray diffractometry. It was therefore characterized by molecular modelling coupled with X-ray powder diffractometry [monoclinic, space groupP21/n,a= 20.695 (7) Å,b= 8.054 (2) Å,c= 15.157 (4) Å, β = 112.09 (2)° andRwp= 0.129]. The procedure used to resolve the structure followed direct space methods with a `Monte Carlo/parallel tempering' search algorithm, where the starting configuration was obtained by means of molecular mechanics. A final refinement was performed with the Rietveld method. Bond distances, bond angles and torsion angles were compared with those of similar compounds deposited in the Cambridge Structural Database.

Chemical isomerism as a key to explore free-energy landscapes in disordered matter

The effects of a minor chemical modification on the microscopic structure of a material in its glass and crystal phases are investigated by the concurrent use of neutron diffraction and computer simulation. Significant changes in short-, intermediate-, and long-range order are found, resulting from the change in molecular structure. These differences are explainable by a shift in the balance between directional and excluded-volume interactions.

Deconvolution of X-ray diffraction profiles by using series expansion

The deconvolution of X-ray diffraction profiles is a basic step in order to obtain reliable results on the microstructure of crystalline powder (crystallite size, lattice microstrain,etc.). A procedure for unfolding the linear integral equationh=g finvolved in the kinematical theory of X-ray diffraction is proposed. This technique is based on the series expansion of the `pure' profile,f. The method has been tested with a simulated instrument-broadened profile overlaid with random noise by using Hermite polynomials and Fourier series, and applied to the deconvolution of the (111) peak of a sample of 9-YSZ. In both cases, the effects of the `ill-posed' nature of this deconvolution problem were minimized, especially when using the zero-order regularization combined with the series expansion.

A Gaussian–Hermite polynomials function for X-ray diffraction profile fitting

In recent years, several profile-shape functions have been successfully used in X-ray powder diffraction studies. Here, a new profile function for approximating the X-ray diffraction peaks is proposed. This model, based on a Gaussian function multiplied by a correction factor in the form of a series expansion in Hermite polynomials, can be employed in the cases where there are peak asymmetries. The function has been tested by using samples of α-Al2O3and 9-YSZ (yttria-stabilized zirconia), yielding generally satisfactory results.

The Use of the Pseudo-Voigt Function in the Variance Method of X-ray Line-Broadening Analysis

A modified application of the variance method, using the pseudo-Voigt function as a good approximation to the X-ray diffraction profiles, is proposed in order to obtain microstructural quantities such as the mean crystallite size and root-mean-square (r.m.s.) strain. Whereas the variance method in its original form is applicable only to well separated reflections, this technique can be employed in the cases where there is line-profile overlap. Determination of the mean crystallite size and r.m.s. strain for several crystallographic directions in a nanocrystalline cubic sample of 9-YSZ (yttria-stabilized zirconia) has been performed by means of this procedure.