Search results for "Diffraction"

QTAIM View of Metal-Metal Bonding in Di- and Trinuclear Disulfido Carbonyl Clusters

2012

The experimental and theoretical charge densities in the sulfido-bridged cluster compounds Fe2(μ-S2)(CO)6 (1), Fe3(μ3-S)2(CO)9 (2), Mn2(μ-S2)(μ-CO)(CO)6 (3), and Fe2(μ-S2)(CO)5(PPh3) (4) have been studied using the quantum theory of atoms in molecules (QTAIM) methodology. High-resolution X-ray diffraction data have been measured for compounds 2–4 at 100 K. The topological analyses show that only in compounds 1 and 4 is there any evidence for metal–metal bonding in terms of the presence of a bond path. For compound 1, the topology of the Fe2S2 cage is highly dependent on the Fe–Fe separation, and the deformation along this vector is an extremely soft mode. The experimentally observed topolog…

The influence of the cation on the conformation of the anion μ-hydridobis[pentacarbonylchromium(0)]: crystal and molecular structure of [(phenH)2Cl][…

1999

Abstract The crystal and molecular structures of [(phenH)2Cl][Cr2(CO)10(μ-H)] (1) and [K(phen)2][Cr2(CO)10(μ-H)] (2) have been determined by single crystal X-ray diffraction. The availability of the potassium cation for the carbonyl oxygens coordination influences the conformation of the anion in 2 as demonstrated by the comparison with the non-coordinating [(phenH)2Cl] cation in 1 and with literature data.

Powder X-Ray Diffraction Investigation of Xylazine Hydrochloride Solid Phase Transformation Kinetics

2013

The kinetics of the solid-state phase transformation of xylazine hydrochloride form X to A has been investigated using powder X-ray diffraction and differential thermal analysis. Three different kinetic models have been used to describe transition kinetics: the Avrami–Erofeev equation, the Cardew equation, and the methodology for simulation of solid-state phase transition kinetics by the combination of nucleation and nuclei growth processes. The latter has been recently developed and has been tested in this paper for the case of a real solid-state transition. The relative humidity, mechanical pressure, temperature, and sample-preparation effect on phase-transition kinetics have been investi…

Columnar supramolecular architecture of crystals of 2-(4-Iodophenyl)-1,10-phenanthroline derived from values of intermolecular interaction energy

2011

Using results of X-ray diffraction study supramolecular architecture of crystals of 2-(4-iodophenyl)-1,10-phenanthroline has been analyzed on the basis of quantum-chemical calculations of intermolecular interactions energy. It is demonstrated that these crystals have three levels of organization. Molecules form stacked dimers with the highest binding energy (first level). These dimers represent basic unit of infinite columns stabilized by stacking interactions between dimers (second level). The energy of intermolecular interactions between neighbouring stacked columns is very close. This does not allow to figure out any layers in the crystal. Therefore crystals of this compound have columna…

Behaviour of the non-linear optical material KTiOPO4in the temperature range 293-973 K studied by x-ray diffractometry at high resolution: alkaline d…

1999

The crystal structure of potassium titanyl phosphate, KTiOPO4 (space group Pna21), has been refined at room temperature, at 673 K, and at 973 K, by using accurate single-crystal x-ray diffraction techniques at high resolution (dmin = 0.35 A). The data show a large amount of anharmonic motion of the potassium ions, increasing with temperature. To describe this motion, two models are developed: a normal refinement including potassium anharmonic thermal displacement parameters, which describes the average motion of the alkaline sites, and another model in which the potassium sites are split within the harmonic approximation and the displacements of the potassium ions versus temperature are des…

ATR-FTIR and XRD quantification of solid mixtures using the asymptotic constant ratio (ACR) methods. Application to geological samples of sodium and …

2019

Two asymptotic constant ratio methods applied to the quantification of individual components of solid samples using attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray diffraction (XRD) are described. The methods involve the measurement of the peak current/peak areas of selected signals (diffraction peaks in XRD and absorption bands in ATR-FTIR) relative to the signal of standard added in constant proportion to the sample and the sample enriched with the analyte following the usual standard additions methodology. The proposed method compensates the absorption effects appearing in XRD and the presence of overlapping absorption bands of interferents by me…

Polarized Fourier transform infrared microscopy as a tool for structural analysis of adsorbates in molecular sieves

1992

Using FTIR microscopy with polarized IR radiation on silicalite I single crystals fully loaded with p-xylene, the existence of an ordered adsorbate could be proven for the first time by IR spectroscopy. By analyzing the polarized absorption bands the orientation of the p-xylene molecules relative to the host structure could be determined. The results agree well with structural data obtained from X-ray diffraction experiments. These first results suggest that polarized IR microscopy could develop into a powerful tool for the analysis of adsorbate structures, assisting in complete structure resolution by diffraction techniques

Vibrational Properties of InSe under Pressure: Experiment and Theory

1996

The pressure dependence of the phonon modes in the layered semiconductor γ-InSe has been investigated experimentally and theoretically for pressures up to 11 GPa. The mode Gruneisen parameters of all Raman-active zone-center phonons have been determined by Raman scattering under pressure. In addition, features corresponding to second and third-order scattering processes are apparent in the Raman spectra under resonance conditions, from which information about zone-edge modes can be obtained. For the assignment of the observed Raman features to vibrational modes we have calculated the phonon dispersion curves using a rigid-ion model including couplings to first-nearest neighbors and long-ran…

1985

Nonlinear optical self diffraction effects for a light beam in a liquid crystalline polymer in its isotropic fluid state was observed. This effect is characterized by the absence of a threshold intensity, a diffraction pattern that does not depend on the polarization of the reading beam relative to that of the writing beam and which cannot be disturbed by transversally applied static electrical fields. This effect is attributed to a thermally induced spatial refractive index modulation. The time constants of the response are of the order of ms.

Water Sorption on Mesoporous Aluminosilicate MCM-41

1995

Characterization of the interaction of water with the highly ordered mesoporous solid MCM-41 (pore diameter ∼2.5 nm) is undertaken with the aid of several techniques (adsorption gravimetry, X-ray diffraction, Fourier transform infrared spectroscopy, and controlled rate-evolved gas analysis). The relatively complex water-MCM-41 interactions are characterized by a type V isotherm indicating an initial repulsive character followed by a capillary condensation step of the adsorbate. This highlights both hydrophobic and hydrophilic properties of this potential model mesoporous adsorbent.