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Mo K (mo + k)
Selected AbstractsComparative refinement of correct and incorrect structural models of tetrabutylammonium tetrabutylborate , pitfalls arising from poor-quality dataACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2010Vladimir Stilinovi This paper demonstrates how numerical parameters usually used to assess the quality of a crystal structure solution (R, wR and S) may be misleading when studying a model refined against poor-quality data. Weakly diffracting crystals of tetrabutylammonium tetrabutylborate, a low-density organic salt comprising isoelectronic cations and anions, were measured using Cu and Mo K, radiation. Along with the correct structural model, six erroneous structural models were constructed and refined against the same data. For both data sets it was found that models based on an incorrect unit-cell choice give lower values of R and wR than the correct one, thus apparently being in better agreement with measured data. Closer inspection of the measured data shows that this is in fact not the case. [source] Investigations of the bond-selective response in a piezoelectric Li2SO4·H2O crystal to an applied external electric fieldACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2009O. Schmidt Piezoelectric lithium sulfate monohydrate, Li2SO4·H2O, was analyzed with respect to the relationship between the static structural properties of the crystal and its response to an external electric field. The static electron density was determined via standard low-temperature X-ray data collection at 90,(5) K using an Enraf,Nonius CAD-4 diffractometer, Mo K, radiation and multipole model refinement. Then a synchrotron-radiation experiment using the D3 beamline at HASYLAB was conducted in order to investigate the structural deformations in Li2SO4·H2O caused by an applied external electric field. In particular, the shifts of Bragg-peak positions induced by the electric field were measured and the piezoelectric constants d211, d222, d233 and d213 of Li2SO4·H2O were obtained from the shifts. With the same experimental setup the variations of more than 100 Bragg intensities were measured under an applied electric field. The data were used to refine the corresponding displacements of individual atoms within the unit cell. The distortions of the cation,anion bond lengths in the LiO4, LiO3(H2O) and SO4 tetrahedra were evaluated and then analyzed in terms of the electron-density-related properties of the Li,O and S,O bonds. The two lithium structural units were found to be strongly deformed by the applied electric field, while the SO4 tetrahedron changed less. This is in agreement with the low bond strength of the Li,O bonds. [source] Systematic intensity errors caused by spectral truncation: origin and remedyACTA CRYSTALLOGRAPHICA SECTION A, Issue 6 2001A. T. H. Lenstra The wavelength dispersion of graphite(002)-monochromated X-ray beams has been determined for a Cu, a Mo and an Rh tube. The observed values for ,,, were 0.03, 0.14 and 0.16, respectively. The severe reduction in monochromaticity as a function of wavelength is determined by the absorption coefficient , of the monochromator. ,(monochromator) varies with ,3. For an Si monochromator with its much larger absorption coefficient, ,,, values of 0.03 were found, regardless of the X-ray tube. This value matches a beam divergence defined by the size of the focus and of the crystal. This holds as long as the monochromator acts as a mirror, i.e.,(monochromator) is large. In addition to monochromaticity, homogeneity of the X-ray beam is also an important factor. For this aspect the mosaicity of the monochromator is vital. In cases like Si, in which mosaicity is practically absent, the reflected X-ray beam shows an intensity distribution equal to the mass projection of the filament on the anode. Smearing by mosaicity generates a homogeneous beam. This makes a graphite monochromator attractive in spite of its poor performance as a monochromator for , < 1,Å. This choice means that scan-angle-induced spectral truncation errors are here to stay. These systematic intensity errors can be taken into account after measurement by a software correction based on the real beam spectrum and the applied measuring mode. A spectral modeling routine is proposed, which is applied on the graphite-monochromated Mo K, beam. Both elements in that spectrum, i.e. characteristic ,1 and ,2 emission lines and the Bremsstrahlung, were analyzed using the 6318 reflection of Al2O3 (s = 1.2,Å,1). The spectral information obtained was used to calculate the truncation errors for intensities measured in an ,2, scan mode. The results underline the correctness of previous work on the structure of NiSO4·6H2O [Rousseau, Maes & Lenstra (2000). Acta Cryst. A56, 300,307]. [source] X-ray study and structure simulation of amorphous tungsten oxideACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2002L. A. Lugovskaya In this work, X-ray studies of the amorphous oxide films obtained by thermal evaporation of WO3 powder in a vacuum and by anodic oxidation were carried out. X-ray diffraction patterns were obtained in the symmetric reflection geometry on a DRON-4 diffractometer (Mo K, radiation, LiF monochromator) in automatic mode. Molecular dynamics simulation of amorphous tungsten oxide atomic configurations has been carried out in the micro-canonical ensemble (NVE) for N,=,208 atoms and N,=,624 atoms, in a cubic cell, using pairwise Born,Mayer interaction potentials and periodic boundary conditions. One of the purposes of the present work is to analyze the influence of the parameters and the cutoff of the interaction potentials on the interatomic distances. The values obtained in the molecular dynamics simulation for the pair functions D(r) are compared with the experimental data for amorphous oxides in order to choose the most convenient aforesaid values. The values of the average interatomic distances and the coordination numbers obtained by both methods are also compared. The result shows that the tungsten subsystem can be well reproduced using the potential cutoff radius of about 4,Å, but the oxygen subsystem can be well reproduced when the cutoff of the potential for the W,O pairs is equal to 2.8,Å. The configuration built during the molecular dynamics experiment consists of distorted octahedra. These octahedra form chains, as in the WO3 phases of type ReO3, and hexagonal rings, of the same type as in the WO3(1/3)H2O phase, when we extract (1/3)O at every WO3 unit. The pair function D(r) and scattering intensity I(s) distribution curves calculated for simulation configurations show a satisfactory agreement with experiment. [source] An Unprecedented 2D 4f-3d-5d Multimetal-Isonicotinic Acid Complex: Synthesis, Structural Characterization and Magnetic PropertiesCHINESE JOURNAL OF CHEMISTRY, Issue 9 2008Wen-Tong CHEN Abstract A novel heterometallic metal-isonicotinic acid inorganic-organic hybrid complex [Zn0.5(H2O)]{(Hg2Cl5)- [Er(C6NO2H4)3(H2O)2]}(HgCl2)·0.5CH3OH·0.5H2O (1) has been successfully synthesized via a hydrothermal reaction and structurally characterized by single-crystal X-ray diffraction. Complex 1 crystallizes in the space group C2/c of the monoclinic system with eight formula units in a cell: a=34.165(4) Å, b=9.4692(8) Å, c=24.575(3) Å, , =115.090(5)°, V=7200(1) Å3, C18.50H21Cl7ErHg3N3O10Zn0.50, Mr=1495.25, Dc=2.759 g/cm3, T=293(2) K, µ(Mo K,) =15.954 mm,1, F(000) =5400 and R1/wR2=0.0561/0.0909 for 3157 observed reflections [I>2,(I)] and 6468 unique reflections. Complex 1 is characteristic of a novel 2D {(Hg2Cl5)[Er(C6NO2H4)3(H2O)2]} layered structure constructed from the [Er(C6NO2H4)3(H2O)2] chains interconnected by the Hg2Cl5, linkers. The 2D {(Hg2Cl5)[Er(C6NO2H4)3(H2O)2]} layers, mercury chloride and the lattice water molecules are held together via hydrogen bonds to form a three-dimensional framework with the methanol molecules and the hydrated zinc ions located in the cavities. The magnetic properties show that complex 1 exhibits antiferromagnetic-like interactions. [source] New Type of Polymeric Chain Constructed by Exo-bidentate Binaphthol DerivativeCHINESE JOURNAL OF CHEMISTRY, Issue 10 2005Ya-Qiong Gong Abstract The self-assembly of a racemic exo-bidentate ligand 2,2,-bis(4-pyridylmethyloxy)-1,1,-binaphthyl, namely Rac -L, with cadmium(II) salt gave rise to a new one-dimensional polymer, which has been characterized by single crystal X-ray diffraction analysis. The polymer crystallizes in a triclinic space group P -1 with unit cell parameters: a=0.6976(1) nm, b=1.30160(14) nm, c=1.71146(17) nm,,=105.141(3) °,,=94.263(5)°,,=100.405(4)°, V=1.4633(2) nm3, Z=2, C32H29CdCl2N2O4.5, M=696.88, Dc=1.584 g/cm3, F(000) =708, ,(Mo K,) =0.972 mm,1. The final R and wR are 0.0498 and 0.1282 for 5079 observed reflections with I,,(I). [source] Crystal structure, thermal analysis and theoretical calculation of a one-dimensional chain complex [zn(dafo)2(H2O)2](NO3)2CHINESE JOURNAL OF CHEMISTRY, Issue 8 2004Rong-Lan Zhang Abstract A novel one-dimensional chain complex [Zn(dafo)2(H2O)2](NO3)2 was obtained when we tried synthesizing a mixed ligand supramolecular compound of Zinc(II) with dafo and o -phthalic acid. Its structure was determined by single-crystal X-ray diffraction analysis. The crystal belongs to triclinic system, P -1 space group. The crystallographic data: a=0.6989(4) nm, b=0.8281(5) nm, c=1.0231(5) nm, ,=94.934(5)°, ,=91.366(7)°, ,=99.820(7)°, V=0.5809(5) nm3, Z= 1, F(000)=300, Mr=589.78, Dc=1.686 g/cm3, ,(Mo K,)=1.130 mm,1, R1=0.0521, wR2=0.1096. The analysis of the crystal structure indicates that the compound has a one-dimensional chain structure which is formed by hydrogen bonds. The constitutes of the title complex were proved by elemental analysis, IR spectra and thermal analysis. On the basis of the experimentation, the complex was calculated by DFT-B3LW/LANL2DZ in Gaussian-98w also. [source] Synthesis and Crystal Structure of a Two-dimensional Silver(I)-Iron(III) Heteronuclear Coordination Polymer: {[Ag,Fe2(SCN)12(H2O)2] [(inaH)2(H2O)2]}nCHINESE JOURNAL OF CHEMISTRY, Issue 1 2004Xiu-Ling Li Abstract The 2-D heteronuclear coordination polymer {[Ag4Fe2(SCN)12(H2O)2] (inaH)2(H2O)2}n (1) (inaH is the abbreviation of protonated isonicotinic acid) with chemical formula C24Ag4Fe2N14O8S12 has been synthesized and characterized by single crystal X-ray diffraction, elemental analysis and IR spectroscopy. The Ag2S2 rings connect two kinds of octahedral geometries of Fe(III) ions, [Fe(NCS)6]3, and Fe(H2O)2(NCS)4], units with bridging thiocyanate ions leading to 2-D [Ag4Fe2(SCN)12(H2O)22, anion framework. Four kinds of rings including the unprecedented thirty-two membered Ag4Fe4(SCN)8 rings share comers or edges in the 2-D anion layer structure. All thiocyanates coordinate to the metal ions according to the HSAB principle with N atoms binding to the Fe(III) ions and with S atoms binding to Ag(I) ions. Pronoated ina cations stabilize the layer structure as counter ions and hydrogen bonds were formed within the pronoated in a cations dimer and between the dimers and the lattice waters. Crystal data: Mr= 1560.44, triclinic, P1, a=0.76082(1) nm, b=0.9234 nm, c= 1.85611(4) nm, a= 103.0170(10)°, ,=93.7780(10)°, y=97.4080(10)°, V= 1.25385(3) nm3, Z=1, ,(Mo K,)=2.650 mm,1, Dc,=2.067 g · cm,3, F(000)=758, R1=0.0412. wR2=0.1003. [source] | ||||||||||