bluuebunny/crossref_metadata_2025 huggingface dataset:
Aux/IAA Proteins Are Phosphorylated by Phytochrome in Vitro
Authors: Colón-Carmona Adán , Chen Donna L. , Yeh Kuo-Chen , Abel Steffen
Published: July 2002

Auxin/indole-3-acetic acid (Aux/IAA) genes encode short-lived transcription factors that are induced as a primary response to the plant growth hormone IAA or auxin. Gain-of-function mutations in Arabidopsis genes,SHY2/IAA3, AXR3/IAA17, andAXR2/IAA7 cause pleiotropic phenotypes consistent with enhanced auxin responses, possibly by increasing Aux/IAA protein stability. Semidominant mutations shy2-1D,shy2-2, axr3-1, and axr2-1induce ectopic light responses in dark-grown seedlings. Because genetic studies suggest that the shy2-1D andshy2-2 mutations bypass phytochrome requirement for certain aspects of photomorphogenesis, we tested whether SHY2/IAA3 and related Aux/IAA proteins interact directly with phytochrome and whether they are substrates for its protein kinase activity. Here we show that recombinant Aux/IAA proteins from Arabidopsis and pea (Pisum sativum) interact in vitro with recombinant phytochrome A from oat (Avena sativa). We further show that recombinant SHY2/IAA3, AXR3/IAA17, IAA1, IAA9, and Ps-IAA4 are phosphorylated by recombinant oat phytochrome A in vitro. Deletion analysis of Ps-IAA4 indicates that phytochrome A phosphorylation occurs on the N-terminal half of the protein. Metabolic labeling and immunoprecipitation studies with affinity-purified antibodies to IAA3 demonstrate increased in vivo steady-state levels of mutant IAA3 in shy2-2 plants and phosphorylation of the SHY2-2 protein in vivo. Phytochrome-dependent phosphorylation of Aux/IAA proteins is proposed to provide one molecular mechanism for integrating auxin and light signaling in plant development.
Calculation of diffraction line profiles from specimens with dislocations. A comparison of analytical models with computer simulations
Authors: Kamminga J.-D. , Delhez R.
Published: July 2002

A method is presented for the calculation of diffraction line profiles using Monte Carlo simulation. The method is used to calculate diffraction line profiles for specimens with some idealized distributions of dislocations. The results have been compared with analytical expressions available for these special dislocation distributions. This comparison has been used to validate some essential assumptions made in the derivation of the analytical expressions. In general, very good agreement has been found. Thus, the proposed method is shown to be a valuable tool for diffraction line profile analysis.
OVIONE: a new vector-search rotation-function program for macromolecular crystallography
Authors: Álvarez-Rúa Carmen , Borge Javier , García-Granda Santiago
Published: July 2002

A computer program (OVIONE) that uses a new vector-search rotation function for crystal-structure determination by the molecular-replacement method has been developed. Image-seeking functions have proved to be useful rotation functions in macromolecular crystallography, provided that some conditions on the statistical parameters of both the crystal and the model Patterson maps are fulfilled. An appropriate selection of the vectors involved in the calculation of the image-seeking functions is crucial for the success of the proposed procedure. This selection relies on certain parameters, a careful analysis of which has been performed in order to establish optimal ranges in which the discrimination of the rotation function is enhanced. Finally, the refinement of the highest peaks of the rotation function is carried out by making use of a simple and quick minimization algorithm.
On the resolution of neutron scattering instruments
Authors: Cussen Leo D.
Published: July 2002

Phase-space arguments are used to discuss the resolution of neutron scattering instruments. The usual practice in such studies is to assume that all beam elements have Gaussian profiles. Here, the assumption that all elements have rectangular profiles results in considerable clarification of the role of each instrument component. The discussion is limited to powder diffractometers and powder samples on three-axis spectrometers, but it is possible to use the results when considering more involved measurements. The choice of collimators and monochromator mosaic to optimize measurements is discussed. The assumption of rectangular elements is not entirely artificial, as it is now possible to build such components. Furthermore, the conclusions can be applied to instruments with Gaussian elements.
A citation analysis of the Cambridge Crystallographic Data Centre
Authors: Redman Jane , Willett Peter , Allen Frank H. , Taylor Robin
Published: July 2002

Citation analysis has been widely used to quantify the influence of research articles on the development of science. This paper reports a citation analysis of ten highly cited papers associated with the Cambridge Crystallographic Data Centre (CCDC), covering the variation of citation with time, the journals in which citations occur, and the types of organization and the geographic regions that use the Cambridge Structural Database. The ten most highly cited papers, comprising four database descriptions (CSD), two geometrical tabulations (TAB) and four basic research papers (RES), received a total of 8494 citations over the period 1981–1998, with more than half of these citations occurring in the literature published from 1995 onwards. The high citation rates of the database descriptions (3573 of 8494) indicate the value of crystallographic data. However, the large number of citations of the geometrical tables (3172) and the research papers (1767) indicate that this value resides not just in the raw data held in the Cambridge Structural Database, but also in the structural knowledge that can be derived from it. In the most recent years covered by the analysis (1995–1998), these ten CCDC publications have received more than 1000 citations per annum (CSD 507, TAB 398 and RES 153 citations per annum) and the detailed analysis shows that these papers, and the data that they discuss, are used not only by crystallographers but also by researchers across the entire range of the chemical sciences.
A new X-ray powder diffractometer working in the 87–1000 K range for phase-transition analyses
Authors: Sayetat F. , Prat A.
Published: July 2002

An X-ray powder diffractometer, operating in the 87–1000 K temperature range, is described. The experimental procedure and data analysis allow the measurement of small lattice distortions and very small parameter variations with good accuracy. The experiment setup is devoted to the detection of phase transitions, to the determination of thermal expansion curves and to the study of kinetic chemical reactionsin situ. The apparatus has been tested for angular sensitivity and resolution. The tests assess the overall performance of the instrument over the entire range of temperature. The cell parameter of the standard material cubic Na2Ca3Al2F14in the 90–600 K range is given as example. In a study of the thermal expansion of the cell parameter of cubic AgI in the 303–553 K range, a phase transition, of first-order character, is found between 398 and 453 K.
Extraction of domain structure information from small-angle scattering patterns of bulk materials
Authors: Stribeck Norbert
Published: July 2002

A method is presented that permits the extraction and visualization of topological domain structure information contained in small-angle scattering (SAS) patterns without complex pretreatment. Multi-dimensional noisy raw data can be processed. Such data are, for instance, accumulated in the field of materials research from short-exposure-timein situsmall-angle X-ray scattering (SAXS) experiments with synchrotron radiation. The result is a multi-dimensional intersect or chord distribution, which is defined as the Laplacian of the correlation function. Moreover, it is equivalent to the autocorrelation of the gradient of the electron density. The procedure is, in particular, adapted to the analysis of the nanoscale structure of samples with fibre symmetry, such as polymer fibres or strained elastomers. Multi-dimensional relations among morphological components become apparent in real space and help to elucidate the nature of the processes governing formation and change of structure on the nanometre scale. Utilizing digital signal processing tools, the algorithm is based on spatial frequency filtering of the raw data. The background to be subtracted from the small-angle scattering pattern is formed from its own low spatial frequencies. Noise may be removed by suppressing high spatial frequencies. In the frequency band between these low and high spatial frequencies, the domain structure information of the studied nanocomposite appears.
A multi-wavelength neutron monochromator system
Authors: Cooper M. J. , Forsyth J. B.
Published: July 2002

A neutron monochromator system is described which provides a choice of seven wavelengths in the range 0.88 to 2.63 Å and a facility for changing rapidly from one to another. Symmetrical transmission geometry is used for reflections in the [110] zone of a `squashed' germanium crystal and the wavelength is changed by a simple rotation of the crystal in its own plane. Experimental studies have confirmed the advantages which such a system can have for powder diffraction measurements when different experiments have different requirements in terms of the sinθ/λ range and the angular resolution.
LAZY PULVERIX, a computer program, for calculating X-ray and neutron diffraction powder patterns
Authors: Yvon K. , Jeitschko W. , Parthé E.
Published: July 2002

A computer program has been written with the aim of calculating powder patterns without the use of crystallographic tables. This has been achieved by deriving all symmetry information such as general equivalent positions from the Hermann-Mauguin space-group symbols, by calculating automatically the multiplicities of special positions and by storing the necessary constants, such as scattering factor tables, anomalous dispersion correction terms and X-ray wavelengths in the program. Owing to the very restricted amount of input data this program is especially suited for users with a limited knowledge of crystallography.
Determination of the correlation function directly from slit-smeared small-angle X-ray scattering curves
Authors: Gerber T. , Walter G. , Kranold R.
Published: July 2002

A simple technique has been developed for calculating the correlation function directly from small-angle X-ray scattering curves obtained with an `infinitely long' primary beam profile. The method is based on expanding the correlation function in a series of zero-order Bessel functions of the first kind, where the coefficients of the series are proportional to the intensities of the measured curve. The correlation function thus is represented by an analytical expression and can be calculated easily.
Two new SiC polytypes belonging to the [(44)
n
43]3 structure family
Authors: Kuo C. L. , Zhou J. , Ye H. Q. , Kuo K. H.
Published: July 2002

Using a modified Laue method as well as electron diffraction and lattice image methods, two new poly types of SiC, 93R and 261R, have been found which belong to a new structure family [(44)
n
43]3 based on 8H (44) stacking.
An auxiliary method of indexing electron diffraction patterns by means of gnomonic projections
Authors: Borges F. S.
Published: July 2002

A method is described which eliminates most – if not all – spurious solutions usually obtained when indexing an electron diffraction pattern from a substance having a structure with low symmetry. The proposed method is applicable when the diffraction pattern includes non-zero Laue zones, or when crystallographic planar features are recognized in the contrast images of the areas from which the diffraction patterns were taken. In the first situation, the tangential component of the stacking vector of reciprocal-lattice planes, normal to each beam direction calculated by the computer for a given diffraction pattern, is determined by means of gnomonic projections, and then compared with the one derived from the observed Laue zones. In the second situation, the trace orientation of a known planar feature observed is compared with those that can be drawn on the gnomonic projections. Alternatively, if a selected-area diffraction pattern has already been indexed, a presumed crystallographic orientation of a planar feature can be checked on a gnomonic projection.
An energy-dispersive spectrometer for the rapid measurement of X-ray absorption spectra using synchrotron radiation
Authors: Phizackerley R. P. , Rek Z. U. , Stephenson G. B. , Conradson S. D. , Hodgson K. O. , Matsushita T. , Oyanagi H.
Published: July 2002

The design and evaluation of an energy-dispersive spectrometer to measure X-ray absorption spectra rapidly using a synchrotron-radiation source is presented. The method employs a cylindrically bent triangular crystal to focus and disperse a quasi-parallel polychromatic X-ray beam onto the sample. The beam passing through the sample then diverges towards an X-ray detector where beam position can be correlated to energy. Both concentrated and dilute samples were measured on X-ray film and with an electronic linear photodiode array detector and the data analysed to determine the resolution obtained and the data quality. This method is shown to provide an efficient way to obtain high-quality EXAFS and absorption-edge data and should permit kinetic studies to be performed on small samples with good counting statistics. The method should find application in the fields of biophysics, chemistry and materials science.
X-ray diffraction studies on the arrangement of water molecules in a smectite. I.Homogeneous two-water-layer Na-beidellite
Authors: Brahim J. B. , Armagˇan N. , Besson G. , Tchoubar C.
Published: July 2002

A method of indirect analysis of X-ray diffraction patterns of homogeneous hydrated microcrystalline silicates is introduced. This method is applied to a sodium beidellite of Rupsroth, Bavaria, Germany, hydrated with two water layers to determine all its structural characteristics: namely, the average dimension and size distribution of coherent domains, stacking mode of the layers along the c* direction, levels and number per unit cell of water molecules. A critical analysis on the `concept of homogeneity' of hydrates and a discussion on the conditions of its application to lamellar microcrystalline silicates with a few numbers of layers are made.
Crystal data for nickel and cadmium α-L-alaninates
Authors: Démaret A. , Mercier D.
Published: July 2002

Powder data for bis(α-L-alaninato)nickel(lI) tetrahydrate (monoclinic), bis(α-L-alaninato)cadmium(II) trihydrate (hexagonal) and bis(α-L-alaninato)cadmium(II) (orthorhombic) are reported. Ni(C3H6NO2)2.4H2O: Mr
= 306.9, C2, Cm or C2/m, a = 20.34(1), b = 6.48(9), c = 9.73(7) Å, β = 93.0(3)°, V = 1283(28) Å3, Z = 4, Dm
= 1.54(3), Dx
= 1.56 Mg m−3, Cu Kα (λ = 1.5418 Å); Cd(C3H6NO2)2.3H2O: Mr
= 342.6, P3112, P3121, P3212 or P3221, a = 6.37 (1), c = 25.5(7) Å, V = 899(32) Å3, Z = 3, Dm
= 1.86(4), Dx
= 1.90 Mg m−3, Cu Kα; Cd(C3H6NO2)2: Mr
= 288.6, a = 5.45(2), b = 9.19(6), c = 18.08(4) Å, V = 907(11) Å3, Z = 4, Dm
= 2.00(5), Dx
= 2.11 Mg m−3, Cu Kα. The JCPDS Diffraction File Nos. are: 33-1991 for Ni(C3H6NO2)2.4H2O; 33-1992 for Cd(C3H6NO2)2.3H2O; 33-1993 for Cd(C3H6NO2)2.
The formation of macroscopic polytypic regions in ZnS crystals
Authors: Mardix S.
Published: July 2002

Vapor-phase ZnS crystals were grown under strict stabilization of temperature and pressure. Many crystals containing wide polytypic regions were found. Hollow tubes were observed, almost exclusively in the wide regions; the regions with no hollow tubes consist of a large number of very narrow faulted sub-regions. It is suggested that the creation of Shockley partials is associated with the strain in the vicinity of the growth screw dislocations. Those regions where the core of the dislocation is hollow are unstrained and the Shockley partials, moving in from neighboring regions, can climb unimpeded along the helicoidal basal planes, transforming them into the various observed polytypes.
Constructing rings of specified pucker
Authors: Millane R. P. , Nzewi E. U.
Published: July 2002

A method of constructing closed rings of specified pucker is described. A ring is constructed such that a set of puckering parameters as well as the ring bond lengths and bond angles are optimized towards desired values. A computer program is described which generates N-membered rings in this way and is illustrated with examples.
Interpretation of the diffuse scattering close to Bragg peaks by X-ray topography
Authors: Fewster P. F. , Andrew N. L.
Published: July 2002

Perturbations from crystal perfection will result in diffuse X-ray scattering, which can be imaged by topography to yield defect information without the swamping contribution of perfect-crystal scattering. This paper illustrates the importance of the probe shape for obtaining topographic images in this diffuse region not only to aid interpretation but to isolate the contributors to this scattering. The diffuse scattering in the vicinity of the Bragg peaks of GaAs, Si and Ge substrate crystals has been mapped to very high resolution and the diffuse scattering has been imaged by topography. It was found that the majority of the scattering emanates from surface damage and dislocations and not point defects or thermal diffuse scattering (TDS). These latter two components are found to be second-order effects in general and are only just discernable as a very weak background intensity in highly perfect crystals. This topography method is very sensitive to surface damage. This is because the associated diffuse scattering close to a Bragg peak can be used to form an image. Therefore, this relatively intense scattering provides a topograph within a few hours for assessing substrate-surface quality. The sensitivity of the method is illustrated with images of surface defects and dislocations in very perfect semiconductors. A procedure for measuring the diffuse scattering emanating from microdefects is also presented.
Synthesizing and fitting linear position-sensitive detector step-scanned line profiles
Authors: Cheary R. W. , Coelho A.
Published: July 2002

An X-ray powder diffractometer has been modified by the addition of a narrow-bandpass germanium pre-monochromator and a linear position-sensitive detector (LPSD) with its centre set at the normal θ–2θ focusing condition. Diffraction data are recorded using a step-scan procedure in which the patterns recorded at each step are summed to form the final pattern over a wide angular range. In this way, diffraction patterns covering 120 2θ can be recorded 100 times more rapidly than with conventional receiving-slit diffractometers for the same level of counting statistics. In this paper, an analysis has been carried out of the contribution of the instrumental parameters to the shapes of the X-ray diffraction lines obtained with either a stationary or a step-scanned LPSD. This is done by calculating theoretical profiles for defocusing, parallax error, thermal-noise broadening and LPSD pixel size and convoluting them with the Cu Kα emission spectrum and aberration profiles associated with a standard focusing powder diffractometer. Theoretical profiles for fitting to experimental step-scan data are synthesized by summing convoluted profiles across the detector window. The validity of this procedure is tested by fitting to experimental step-scan data from well characterized reference specimens of MgO and Y3Al5O12 (YAG). The extra broadening associated with the inclusion of a LPSD is refined in terms of the depth of the detector, the angular window of the LPSD and the angle of divergence of the incident beam. Good fits have been obtained to the reference profiles and the physical parameters of the diffractometer determined in this way agree well with directly measured values.
Aggregation in aluminium hydroxide solutions investigated by small-angle X-ray scattering
Authors: Kumru S. S. , Bale H. D.
Published: July 2002

Aluminium hydroxide particles, created by hydrolysis of aluminium nitrate solutions with sodium carbonate, aggregate rapidly to form mass fractal structures for which the fractal dimension varies from 1.7 to 2.1 depending on the OH/Al-ion ratio of the solution. This system has been studied by small-angle X-ray scattering (SAXS). The OH/Al ratios for the solutions were 1.5, 2.0 and 2.15. The maximum radius of gyration of the aggregates of about 50 Å is found in the solutions having the highest OH/Al ratio. SAXS measurements made at various stages of the aging process show that, in addition to fractal aggregation, there is a second process active in the solutions that leads to the break up of the fractal structure and formation of nonfractal particles, which are probably Al13 ions, [AlO4Al12(OH)24(OH2)12]7+. This process, which is strongly temperature dependent, is governed by an activation energy of approximately 162 kJ mol−1.
Small-Angle X-ray Scattering at the ESRF High-Brilliance Beamline
Authors: Bösecke P. , Diat O.
Published: July 2002

The high-brilliance beamline (BL4/ID2) at the European Synchrotron Radiation Facility (ESRF) in Grenoble has been constructed with the emphasis on time-resolved small-angle X-ray scattering and macromolecular crystallography. It has been open to users for two years. The beamline has opened up new areas in small-angle scattering research, facilitating (a) small-angle crystallography on structures with unit cells of several hundredths of nanometres, (b) overlap with the light scattering range for the study of optical systems, (c) high photon flux for time-resolved experiments and (d) a high spatial coherence allowing submicrometre imaging with X-rays. The set-up and the detector system of the small-angle scattering station are presented. A method for obtaining absolute scattering intensities is described. The parasitic background at the station is discussed in terms of absolute scattering intensities.
Synchrotron Small-Angle X-ray Scattering of Colloids and Photonic Colloidal Crystals
Authors: Megens M. , van Kats C. M. , Bösecke P. , Vos W. L.
Published: July 2002

Synchrotron small-angle X-ray scattering (SAXS) experiments have been performed at the ESRF on colloidal dispersions. The samples are optically multiply scattering and are aimed at so-called photonic applications. Scattering from dilute suspensions yields the particle form factor, which shows many oscillations. From these results, the radius, size distribution and information about the internal structure of the particles in situ can be determined, in contrast to most studies on colloids. Using the form factor, structure factors can be extracted from the diffraction patterns of the colloidal crystals. The structure factors clearly reveal sharp Bragg peaks. The crystal structure, lattice parameter and average orientations were determined as a function of height in sedimented samples. This provides important information for the interpretation of optical experiments.
White-beam topography of Rayleigh waves: a numerical study
Authors: Mocella V. , Epelboin Y.
Published: July 2002

This paper analyses the contrast of white-beam stroboscopic synchrotron topographs of Rayleigh waves induced by a piezoelectric transducer in an α-quartz crystal. The aim of the present investigation is to study the influence of the crystal thickness and of the vibration amplitude on the image contrast. A periodic optimal thickness is found that maximizes the film contrast.
Rietveld refinement guidelines
Authors: McCusker L. B. , Von Dreele R. B. , Cox D. E. , Louër D. , Scardi P.
Published: July 2002

A set of general guidelines for structure refinement using the Rietveld (whole-profile) method has been formulated by the International Union of Crystallography Commission on Powder Diffraction. The practical rather than the theoretical aspects of each step in a typical Rietveld refinement are discussed with a view to guiding newcomers in the field. The focus is on X-ray powder diffraction data collected on a laboratory instrument, but features specific to data from neutron (both constant-wavelength and time-of-flight) and synchrotron radiation sources are also addressed. The topics covered include (i) data collection, (ii) background contribution, (iii) peak-shape function, (iv) refinement of profile parameters, (v) Fourier analysis with powder diffraction data, (vi) refinement of structural parameters, (vii) use of geometric restraints, (viii) calculation of e.s.d.'s, (ix) interpretation ofRvalues and (x) some common problems and possible solutions.
Towards general diffractometry. II. Unrestricted normal-beam equatorial geometry
Authors: Dera Przemysław , Katrusiak Andrzej
Published: July 2002

A general normal-beam equatorial diffractometer, with no restrictions on the orientations of the goniometer axes, such as collinearity of the axes \boldphi and \boldtheta, or \boldomega and \boldtheta, is described. The geometries of this type of unrestricted equatorial normal-beam diffractometer can be unequivocally defined by four angular parameters. Analytical solutions of the goniometer equation and intergeometrical angle transformations, as well as a routine reflection-scan procedure, unaffected by the goniometer offsets, are presented, along with aplications of the unrestricted normal-beam equatorial diffractometer.
Correction of diffraction optics andP–V–Tdetermination using thermoelastic equations of state of multiple phases
Authors: Zhao Yusheng , Von Dreele Robert B. , Weidner Donald J.
Published: July 2002

This report discusses a new method to determine experimental pressure–volume–temperature (P–V–T) data and to correct misalignment of diffraction optics using thermoelastic equations of state of multiple phases. Analytical approaches as well as numerical approaches are presented for the technique. A number of phase combinations yield the best experimental result and the whole-pattern Rietveld and/or Le Bail refinement of diffraction patterns of multiple phases is a significant aspect of the technique. Specific examples indicate that the corrected pressure, temperature and diffraction optics are robust. Errors are estimated from the uncertainties of the measured cell dimensions. The error propagation for different experimental cases is discussed, along with the conditions and limitations of the method. This technique forP–V–Tdetermination and the correction of diffraction optics is crucial for experiments conducted under extreme conditions of high pressure, high temperature and dynamic reactions.
X-ray diffraction study of anisotropic thermal expansion in ZrMo2O8
Authors: Mittal R. , Chaplot S. L. , Lalla N. P. , Mishra R. K.
Published: July 2002

Temperature-dependent X-ray diffraction measurements are reported for ZrMo2O8in the trigonal phase from 80 to 925 K. The measurements reveal highly anisotropic thermal expansion coefficients with average values of −3.9 × 10−6and 52 × 10−6 K−1for theaandccell parameters, respectively.
Differential anomalous wide-angle X-ray scattering and X-ray absorption experiments to investigate the formation of glass ceramics in the CaO–SiO2–ZrO2system
Authors: Meneghini Carlo , Gualtieri Alessandro F. , Siligardi Cristina
Published: July 2002

The structure of a CaO–SiO2–ZrO2-based glass ceramic has been investigated by X-ray diffraction, X-ray absorption spectroscopy and differential anomalous scattering techniques as a function of the thermal treatment of the sample. The microstructure of the glass has been investigated at room temperature, before the recrystallization of the glass ceramic, and on two samples annealed at 1073 and 1273 K for 1 h to follow the early stages of nucleation of the quartz and wollastonite crystalline phases. Indications on the roles of Ca, Si and Zr during the devitrification process are given.
Monte Carlo calculation of A
3
B (111) ordering transition and surface X-ray intensities
Authors: Zhu X.-M. , Zabel H.
Published: July 2002

A Monte Carlo simulation of an ordering phase transition in the surface region of a f.c.c.-type A
3
B binary alloy is reported. The main emphasis of this simulation is the evaluation of short and long-range-order correlations near the surface which are used for calculating X-ray intensities under grazing-incident-angle conditions. These calculations suggest effective ways of conducting surface diffraction experiments on order-disorder phase transitions. The simulation results are also compared with available experimental data.
Metastable β-phase of benzophenone: independent structure determinations via X-ray powder diffraction and single crystal studies
Authors: Kutzke Hartmut , Klapper Helmut , Hammond Robert B. , Roberts Kevin J.
Published: July 2002

Benzophenone was the first organic molecular material to be identified as polymorphic. It is well known that benzophenone crystallizes in a stable orthorhombic α-form (m.p. 321 K) with space group P212121 and a = 10.28, b = 12.12, c = 7.99 Å, [Girdwood (1998). Ph.D. thesis. Strathclyde University, Glasgow, Scotland]. Here we report two separate structure determinations of the metastable β-form (m.p. 297–299 K). Crystalline material of the metastable polymorph was obtained from a melt supercooled to ∼243 K. The structure was determined from X-ray powder diffraction data by employing a novel, computational systematic search procedure to identify trial packing arrangements for subsequent refinement. Unit-cell and space-group information, determined from indexing the powder diffraction data, was used to define the search space. The structure was also determined from single-crystal diffraction data at room temperature and at 223 K. The metastable phase is monoclinic with space group C2/c and a = 16.22, b = 8.15, c = 16.33 Å, β = 112.91° (at 223 K). The structures derived from the individual techniques are qualitatively the same. They are compared both with each other and with the stable polymorph and other benzophenone derivatives.
On the inclusion of solvent molecules in the crystal structures of organic compounds
Authors: Görbitz Carl Henrik , Hersleth Hans-Petter
Published: July 2002

The Cambridge Structural Database has been searched for all crystal structures including organic solvent molecules (solvates) and solvent water molecules (hydrates). Well above 300 different solvent molecules were identified and the frequencies with which they occur in crystal structures, as a function of the year of publication, were established. The crystal structures are classified as `organic' and `metalloorganic'; it is shown that the relative prevalences of various cocrystallized solvents are different in the two groups. Several frequently used organic solvents are also common ligands for metal ions. Special interest has been focused on the existence of heterosolvates, i.e. crystal structures which include more than one type of solvent molecule. Up to five different types of solvent molecules were found in a single crystal structure. It is suggested that the use of solvent mixtures during crystallizations may prove to be a more useful and versatile approach for obtaining crystals of high-molecular-weight organic compounds than has hitherto been recognized.
Automated assignment of graph-set descriptors for crystallographically symmetric molecules
Authors: Motherwell W. D. Samuel , Shields Gregory P. , Allen Frank H.
Published: July 2002

Algorithms for the automatic assignment of graph-set notation for intermolecular networks have been extended to molecules having internal crystallographic symmetry, for patterns up to the second level. This provides a means of achieving systematic and consistent assignments for networks containing symmetric molecules. These methodologies have been implemented in the program RPLUTO. Examples are given of the application of the method to a number of molecules with hydrogen-bonded and other intermolecular networks, illustrating the diversity of the patterns that occur.
Analysis of LiKSO4 crystals in the temperature range from 573 to 943 K
Authors: Pinheiro Carlos Basílio , Pimenta Marcos Assunção , Chapuis Gervais , Speziali Nivaldo Lúcio
Published: July 2002

The structural phases observed in LiKSO_4 crystals due to thermotropic transitions have been studied for more than a century. Nowadays many different phases are referenced, but some of the results are still controversial. Structural studies by single-crystal X-ray diffraction from room temperature to 803 K are presented here. Phase II (708 \lt T \lt 943 K) is extensively discussed on the basis of ordered and disordered models, using harmonic and anharmonic atomic displacements, and considering a twinned crystal composed of three orthorhombic domains. Analyses of the same phase at different temperatures determine the best structure model.
Single crystal structure and molecular dynamics analysis of a myo-inositol derivative
Authors: Dillen Jan , Bredenkamp Martin W. , Prinsloo Mare-Loe
Published: July 2002

The crystal structure of 5-O-tert-butyldimethylsilyl-3,4-O-carbonyl-1,2-O-cyclohexylidene-2-oxo-3-oxa-4-bornanylcarbonyl-D-myo-inositol has been studied by single-crystal X-ray diffraction at both room temperature and 173 K. At room temperature, the tert-butyldimethylsilyl group exhibits dynamical disorder. A molecular dynamics simulation was used to model the disorder and this indicates that the group librates between two stable conformations in the crystal. Approximate relative energies of the different forms and energy barriers for the transition were obtained by empirical force field methods. Calculations of the thermal motion of the atoms are in good qualitative, but fair to poor quantitative agreement with the X-ray data.
Correction of the space group of [Ni(bipy)2(ONO2)2]·2(pyrene)
Authors: Herbstein Frank H.
Published: July 2002

The crystal structure of [Ni(bipy)2(ONO2)2]·2(pyrene), poly[[[bis(nitrato-O)nickel(II)]bis(μ-4,4′-bipyridyl-N,N′] bis(pyrene)], was originally reported in space group Pn [Biradha et al. (1999). Chem. Commun. pp. 1327–1328]. Reasons are given for changing the space group to P21/n. Consequently, incorrect descriptions of the title compound in the literature must be altered. In particular, the structure is not polar. It is further contended that description in terms of `complementary, interpenetrating covalent and noncovalent two-dimensional networks' is misleading as the `noncovalent network' (of pyrenes) has geometrical but not physical significance. The title compound is a typical host–guest inclusion complex.
La1.16Mo8O16: a hollandite-related compound with an incommensurate modulated structure
Authors: Leligny H. , Labbé P. , Ledésert M. , Raveau B. , Valdez C. , McCarroll W. H.
Published: July 2002

The hollandite-related structure La1.16Mo8O16, Mr
= 1184.66, tetragonal, P^{I4}_{\kern3pt 1}, a = 9.983 (1), c = 2.8890 (5) Å, V = 287.9 Å3, Z = 1, Dx
= 6.83 g cm−3, \lambda(Mo Kα) = 0.71069 Å, μ = 126 cm−1, F(0000) = 530, room temperature, R = 0.041 for 1145 unique reflections with I\geq3σ(I). At room temperature the compound exhibits a one-dimensional incommensurate modulated structure with a modulation wavevector q* = 0.608 (1)c*. Both a displacive modulation wave, acting on La, Mo and O atoms, and a modulation wave governing the occupancy probability of La sites inside the tunnels are involved in the crystal. Within the superspace group P^{I4}_{\kern3pt 1}, the final R values of main reflections (477) and first- and second-order satellite reflections (523 and 145) are 0.030, 0.050 and 0.133 respectively. The more spectacular modulation features are the occurrence of La—La pairs in the tunnels and the formation of Mo3 triangular clusters in the double chains of edge-sharing octahedra. Contrary to previous descriptions based upon rigid tunnels in structures of the hollandite type, the tunnels in the crystal studied are distorted in a periodic way along [001] (λ = 4.75 Å), giving rise to alternate contractions and expansions. The distortion of the double octahedral chains is considerable and probably created via the La—O(1) bonds by insertion of La atoms inside two adjacent tunnels.
Determination of the centroid or `the best centre' of a coordination polyhedron
Authors: Balić Žunić T. , Makovicky E.
Published: July 2002

The geometric parameters related to the point in the coordination polyhedron having the minimum variation of distances to the vertices (`the centroid of the coordination polyhedron') are proposed as a measure of polyhedral irregularity or deformation. The numerical method for the determination of the centroid coordinates is described. Knowing these coordinates, the radius of the sphere circumscribed to the coordination polyhedron, the degree of sphericity of coordination, the principal axes of the ellipsoid fitted to the polyhedron and the displacement of the central atom from the centroid are calculated. These quantities are measures for various aspects of irregularity in the coordination polyhedron. The centroid calculation has been applied to the family of ABS
2-type sulfides with cations in slightly to highly deformed octahedral coordinations.
Single-crystal structure analysis and energy minimizations of a MFI-type zeolite at low p-dichlorobenzene sorbate loading
Authors: van Koningsveld H. , Jansen J. C. , Man A. J. M. de
Published: July 2002

The crystal structure of a low-loaded adsorption complex of H-ZSM-5 with p-dichlorobenzene has been studied by single-crystal X-ray diffraction. The controversy in the literature, concerning the preferred location of the p-dichlorobenzene molecule, is explained by different interpretations of the difference electron-density map representing the electron density of the absorbed molecule. The crystal studied contains 2.56 (2) p-dichlorobenzene molecules per unit cell. The absorbed molecules prefer the position at the intersection of channels. Energy calculations, using the Biosym Catalysis and Sorption Software, strongly support this interpretation. In nearly all calculations the orientation of the relaxed molecule is close to the orientation found from the X-ray analysis. A second rotational position at the intersection, suggested from calculations in a fully relaxed structure, resembles the location of the p-xylene molecule at the intersection of channels in the high-loaded H-ZSM-5/8p-xylene complex. The unit cell of Si11.96Al0.04O24.0.32C6H4Cl2(+ 0.04H+), Mr
= 767.42, is orthorhombic, Pnma, with a = 20.009 (3), b = 19.909 (4), c = 13.366 (2) Å, V = 5324 (2) Å3, Z = 8,
Dx

= 1.922 Mg m−3 and μ(Mo Kα) = 0.734 mm−1. The final R(wR) is 0.044 (0.048), w = 1/σ
2(F), for 5306 observed reflections with I> 2.0σ(I) measured at 293 K.
Isotope effect on anharmonic thermal atomic vibration and κ refinement of 12C and 3C diamond
Authors: Yamanaka T. , Morimoto S.
Published: July 2002

Isotope dependence of diamond structure of the mixed crystals of 13C
x

12C(1−x), which were grown under high pressure, has been examined by diffraction study using synchrotron radiation. The lattice constant is expressed by: \eqalign{a(\AA) = 3.56712 (5) - [9.01 (5) \times 10^{-4}X]\cr + [3.65 (4) \times 10^{-4}X^{2}],} where X = [13C]/([12C] + [13C]). Anharmonic thermal vibration of natural (X = 0.020) and 13C diamond (X = 0.985) was clarified by applying the Gram–Charlier series expansion to the temperature factors. The anharmonicity of natural diamond was larger than that of 13C diamond. The isotope effect on the localized electron density has also been elucidated by application of the κ refinement. 13C diamond has a larger κ parameter, 0.993 (1), than natural diamond, 0.931 (7), which proves that the valence electron of natural diamond is more widely distributed than that of 13C diamond.
Structure of Mg6SO2(OH)14 determined by micro single-crystal X-ray diffraction
Authors: Hamada E. , Ishizawa N. , Marumo F. , Ohsumi K. , Shimizugawa Y. , Reizen K. , Matsunami T.
Published: July 2002

The structure of hexamagnesium sulfonyl tetradecahydroxide, Mg6SO2(OH)14, has been determined with an extremely small single-crystal (ca 0.5 × 100 × 2.5 μm) using synchrotron radiation [1.00 (1) Å]. The crystal is orthorhombic with space group Ccmm (No. 63), a = 15.895 (1), b = 3.105 (1), c = 13.367 (1) Å, V = 659.64 (3) Å3 and Z = 2. The final R and wR values are 0.073 and 0.083 for 105 crystallographically independent reflections. The structure consists of MO6 octahedra and SO4 tetrahedra. The MgO6 octahedra share their edges to form zigzag sheets parallel to (100). The SO4 tetrahedron shares two of the O atoms with the MgO6 octahedra at the turning of the sheet and is statistically located with a probability of 0.5. Fine streaks observed perpendicular to the b* axis on diffraction photographs indicate that the SO4 tetrahedra are distributed at random along the a and c axes, but alternately along the b axis. All the H atoms are considered to exist in the form of OH groups.
The hydrogen-bond C–H donor and π-acceptor characteristics of three-membered rings
Authors: Allen F. H. , Lommerse J. P. M. , Hoy V. J. , Howard J. A. K. , Desiraju G. R.
Published: July 2002

Crystallographic results, retrieved from the Cambridge Structural Database, show that the C--H protons of cyclopropane, aziridine and oxirane form C—H...O (particularly C—H...O—C) hydrogen bonds. The frequency of formation and geometrical characteristics of these bonds indicate a bond-strength ordering: Csp
1—H...O > C(ring)—H...O ≃ Csp
2—H...O > Csp
3—H...O, which is in excellent agreement with the well known ethylenic properties of C(ring)—H and with residual δ+ charges calculated for these systems. There is some evidence to suggest that C=C—H in cyclopropene, known to be a highly acidic H, forms stronger hydrogen bonds than C—H in saturated three-membered rings. Crystallographic data have also been used to provide geometrical evidence for the formation of O,N—H...π(ring) bonding to three-membered rings, proposed on the basis of spectroscopic data [Joris, Schleyer & Gleiter (1968). J. Am. Chem. Soc.
90, 327–336]. The two modes of H...π(ring) binding suggested there, viz. `edge-on' approach of H to a ring C—C bond and `face-on' approach towards the ring centroid, are found to be dominant in crystallographic observations of this novel hydrogen bond.
Synchrotron X-ray Studies of LiNbO3 and LiTaO3
Authors: Hsu R. , Maslen E. N. , du Boulay D. , Ishizawa N.
Published: July 2002

The structural geometry, vibrations and deformation density Δρ for lithium niobate, LiNbO3, and lithium tantalate, LiTaO3, are derived from synchrotron radiation diffraction measurements. Electron density is transferred from the Nb (Ta) atom towards the large O3 triangle near the Li atom. Spontaneous polarizations of 0.43 (LiNbO3) and 0.33 cm−2 (LiTaO3), calculated with Hirshfeld charges, agree qualitatively with experimental values of 0.71 and 0.50 −2, respectively. Both strong Li...Nb (Ta) interactions in the structure are markedly shorter than all Li...Li, Nb...Nb or Ta...Ta vectors, as expected if the Li and Nb (Ta) cations carry charges of opposite sign. The Li atom's negative charge plays a pivotal role in the polarization responsible for ferroelectricity. LiNbO3, space group R3c, rhombohedral, M

r
= 147.8, a = 5.493 (2) Å, α = 55.89 (3)°, V = 106.02 (4) Å3, Z = 2, D

x
= 4.629 Mg m−3, F(000) = 136, μ(0.7 Å) = 5.01 mm−l, y
min = 0.27, T = 293 K, R = 0.015, wR = 0.015, S = 3.276 (84) for 773 unique reflections. LiTaO3, R3c, rhombohedral, M

r
= 235.9, a = 5.471 (2) Å, α = 56.16 (3)°, V = 105.51 (4) Å3, Z = 2, D

x
= 7.412 Mg m−3, F(000) = 200, μ(0.7 Å) = 50.03 mm−1, y
min = 0.32, T = 293 K, R = 0.016, wR = 0.022, S = 1.372(35) for 773 unique reflections.
Structure of Na3NdSi6O15.2H2O – a Layered Silicate with Paths for Possible Fast-Ion Conduction
Authors: Haile S. M. , Wuensch B. J. , Laudise R. A. , Maier J.
Published: July 2002

Hydrothermal investigations of the high silica region of the Na2O–Nd2O3–SiO2 system, carried out in the search for new fast-ion conductors (FIC's), yielded the compound Na3NdSi6O15·2H2O (sodium neodymium silicate). Single-crystal X-ray methods provided lattice constants of a = 7.385 (2), b = 30.831 (7) and c = 7.1168 (13) Å, space group Cmm
2, and 22 atoms in the asymmetric unit. With four formula units per unit cell, the calculated density is 2.68 g cm−3. Refinement was carried out with 1113 independent structure factors to a weighted residual wR(F) of 2.63% [8.09% for wR(F
2)] using anisotropic temperature factors for all atoms. The structure, based on corrugated Si6O15 layers containing four-, five-, six- and eight- membered rings, is related to that of a model previously reported for a compound assigned the composition NaNdSi6O13(OH)2·nH2O. Our structure differs in the placement of sodium ions and water molecules, and contains no hydroxyl groups. We believe that both studies examined the same phase.
Hydrogen-Bonding Schemes of Galactonic Acid Hydrazide and its Hemihydrate
Authors: André C. , Luger P. , Fuhrhop J.-H. , Hahn F.
Published: July 2002

The crystal structure of L-galactonic acid hemihydrate was determined using data obtained from an imaging plate detector (Stoe IPDS), whereas a conventional scintillation counter was used for the elucidation of the crystal structure of anhydrous D-galactonic acid. The H atom of the terminal hydroxyl group of the water-free sugar participates only in an intramolecular hydrogen bond with the preterminal O atom. This hydrogen bond is part of an antidromic hydrogen-bonding cycle. The hydrogen-bonding scheme of the hemihydrate is very intricate due to the occurrence of two independent molecules and the incorporated water, whose coordination shell can be described by a distorted tetrahedron. One of the hydrogen-bond chains observed in the structure of the hemihydrate is infinite, forming a spiral running in the a direction. The crystal packing of both compounds displays a herringbone arrangement. However, the tilt angle between molecules in different herringbone halves is by far smaller in the structure of the hydrated sugar than in the water-free compound (~ 60 versus 96°).
Rutile Superstructure of Sb0.9V1.1O4
Authors: Landa-Cánovas A. R. , Hansen S. , Ståhl K.
Published: July 2002

The structure of Sb0.9V1.1O4, antimony vanadium oxide, has been studied by powder X-ray diffraction, electron diffraction and high-resolution electron microscopy (HREM). The X-ray powder diffraction pattern showed only basic rutile reflections [a

r
= 4.6085 (1), c

r
= 3.0867 (1) Å] and the basic rutile structure was refined using the Rietveld method. A rutile superstructure was revealed when the sample was studied by electron diffraction. The electron diffraction patterns were indexed on the unit cell a = 21/2
a

r
, b = 21/2
b

r
, c = 2c

r
. Its space group, I41
md, was determined by means of convergent-beam electron diffraction (CBED). A structural model based on alternating cation ordering along c in the chains of edge-sharing octahedra is proposed and its electron diffraction patterns and HREM image are calculated and matched with the experimental ones.
The Deformation of Di-μμ-halide Dinuclear Five-Coordinate Copper(II) Complexes in the Crystalline State
Authors: Bukowska-Strzyżewska M. , Maniukiewicz W. , Sieroń L.
Published: July 2002

The coordination geometries of 154 dinuclear di-\mu-chloro, di-\mu-bromo and di-\mu-fluoro five-coordinate (4 + 1) copper(II) complexes have been analyzed by the structural correlation method. Two reference CuII polyhedra have been established: (i) a trigonal bipyramid (TBP) in which the equatorial bond lengths are equal, but with the symmetry at the metal often deformed from D
3h
to C
2, and (ii) an elongated square pyramid (SQP), with either a pyramidally or tetrahedrally distorted base, in which the trans valence angles are equal. Six different paths for the SQP⇌TBP deformation of the CuII coordination have been established from three criteria: (a) the location of the bridging ligands (axial and equatorial or equatorial and equatorial in TBP); (b) the nature of the deformation of the SQP base plane (pyramidal or tetrahedral); (c) whether a bridging or nonbridging bond is elongated in a SQP. The causes of the angular distortions from C
2 symmetry along the apical bond of a SQP, typical for the TBP⇌SQP Berry path, are analyzed. A progressive reduction of the tetragonal elongation of the Cu—D apical (SQP) bond length along the SQP⇌TBP transformation path and trigonal equalization of the three equatorial Cu—D (TBP) bonds are observed. The dependence of the average Cu—Cu′ distance and Cu—X—Cu′ angles on the deformation path are also established.