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  • Artikel  (51.986)
  • Artikel: DFG Deutsche Nationallizenzen  (51.986)
  • International Union of Crystallography (IUCr)  (51.986)
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  • 1
    Digitale Medien
    Digitale Medien
    X-ray topographic dislocation contrast visible in reflections orthogonal to the Burgers vectors of axial screw dislocations in hexagonal silicon carbide (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 20-26 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: Contrast is associated with micropipes in X-ray topographs of SiC crystals obtained with prismatic reflections, representing an apparent violation of the g·b = 0 invisibility criterion. This is explained as a population of basal-plane dislocations with Burgers vectors of the set b = {\textstyle{1 \over 3}}〈11{\bar{2}}0〉 that occur in a high density within a few micrometers of the micropipes, below the resolution of X-ray topography. These basal-plane dislocations could be observed under an electron microscope. The presence of the surfaces of the micropipes influences the dislocation images in the topographs taken with prismatic reflections, often resulting in a band of light contrast along the axes of the micropipes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889800017027
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  • 2
    Digitale Medien
    Digitale Medien
    Automated matching of high- and low-resolution structural models (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 33-41 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: A method is presented for automated best-matching alignment of three-dimensional models represented by ensembles of points. A normalized spatial discrepancy (NSD) is introduced as a proximity measure between three-dimensional objects. Starting from an inertia-axes alignment, the algorithm minimizes the NSD; the final value of the NSD provides a quantitative estimate of similarity between the objects. The method is implemented in a computer program. Simulations have been performed to test its performance on model structures with specified numbers of points ranging from a few to a few thousand. The method can be used for comparative analysis of structural models obtained by different methods, e.g. of high-resolution crystallographic atomic structures and low-resolution models from solution scattering or electron microscopy.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889800014126
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  • 3
    Digitale Medien
    Digitale Medien
    Alternative algorithm for the correction of preferred orientation in Rietveld analysis (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 16-19 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: Texture effects caused by preferred orientation can be corrected in Rietveld analysis by an alternative algorithm presented in this contribution. This algorithm is equivalent to models using symmetrized linear combinations of spherical harmonic functions, but it is unique to all Laue classes and to all orders. Positive definiteness of the polar-axis density is achieved by the exponential method. The outlined algorithm was tested during Rietveld refinement of selected polycrystal samples. The algorithm was proven to be numerically robust and satisfactorily described deviations from the ideal intensity ratios of the Bragg reflections caused by the texture of the samples.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S002188980001623X
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  • 4
    Digitale Medien
    Digitale Medien
    A modified Pinkerton-type helium gas-flow system for high-accuracy data collection at the X3 SUNY synchrotron beamline at NSLS (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 76-79 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: As the combination of high-intensity synchrotron sources and area detectors allows collection of large data sets in a much shorter time span than previously possible, the use of open helium gas-flow systems is much facilitated. A flow system installed at the SUNY X3 synchrotron beamline at the National Synchrotron Light Source has been used for collection of a number of large data sets at a temperature of ∼16 K. Instability problems encountered when using a helium cryostat for three-dimensional data collection are eliminated. Details of the equipment, its temperature calibration and a typical result are described.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889800014291
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  • 5
    Digitale Medien
    Digitale Medien
    Optimization of the energy constant of the methionine Sδ—Cε bond for X-PLOR refinement of protein structure (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 80-81 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: The bond energy constant of methionine Sδ—Cε, 170.066 kcal mol−1 Å−2, is given as a default value in X-ray protein structure refinement with X-PLOR [Brünger (1992). X-PLOR Version 3.1. A system for X-ray Crystallography and NMR. New York University Press]. When the atomic parameters of 3564 amino acid residues of bovine heart cytochrome c oxidase were refined at 2.0 Å resolution by using X-PLOR with default restraining parameters, 36 bond lengths deviated by over 0.06 Å from their ideal values. Out of the 36 bonds, 25 were methionine Sδ—Cε bonds. Refinement with an energy parameter of 500.0 kcal mol−1 Å−2 for the methionine Sδ—Cε bond resulted in convergence of the Sδ—Cε bond lengths to within 0.06 Å from their ideal values and reduced the crystallographic R and free-R factors by 0.6 and 0.3%, respectively. Consequently, a strong bond energy constant for Sδ—Cε of 500.0 kcal mol−1 Å−2 is recommended instead of the default value of 170.066 kcal mol−1 Å−2.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889800019944
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  • 6
    Digitale Medien
    Digitale Medien
    Notes for Authors (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 89-94 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889800016368
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  • 7
    Digitale Medien
    Digitale Medien
    Determination of the crystallized fractions of a largely amorphous multiphase material by the Rietveld method (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 114-118 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: The Rietveld method has proved to be a very effective means to characterize and quantify the crystalline phases and the amorphous phase in glass ceramic materials using X-ray powder diffraction data. The technique was applied to a borosilicate glass of the type used for high-level nuclear-waste containment, in order to measure the proportions of the crystallized phases after heat treatment and, thus, to qualify the thermal stability of the glass. Six crystalline phases were analysed in this way in an almost entirely (〉95 wt%) amorphous material after adding a known proportion of an internal standard (TiO2). The quantitative analyses were corrected to allow for microabsorption effects resulting from grain-size and absorption-contrast effects. In addition to the quantitative data, unit-cell parameters and site-occupancy refinements revealed solid-solution and substitution phenomena in the crystal.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889800017908
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  • 8
    Digitale Medien
    Digitale Medien
    On planarity and similarity restraints (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 480-483 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: Planarity and similarity restraints are described using a unified framework for the computation layout. In both cases, the gradient and Hessian of the restraint residual with respect to atomic coordinates are derived. All computed quantities (residual, gradient, Hessian, normal and distance to the plane for planarity restraints, rotation and translation in the case of similarity) can be obtained directly, without iterative procedure.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889801008470
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  • 9
    Digitale Medien
    Digitale Medien
    Monte Carlo simulation of a reactor-based neutron strain scanning diffractometer (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 613-624 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: A Monte Carlo code for the simulation of neutron strain scanning experiments on a reactor-based two-axis diffractometer is described. In order to validate this code, several experiments have been performed. A comparison is made between experimental and simulated results for instrumental resolution, primary beam divergence and wavelength distribution in the incident neutron beam. Finally, the application of the simulation results to the analysis of a real neutron strain scanning experiment is outlined.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889801009190
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  • 10
    Digitale Medien
    Digitale Medien
    A monolithic monochromator–collimator for high-resolution X-ray diffraction (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 608-612 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: The possibility of finding, for a given X-ray wavelength, the conditions for obtaining multiple coplanar reflections in a single block of crystal is investigated. It is found that by introducing a small relative tilt between two parts of the crystal, the conditions for a high-resolution X-ray monochromator for conventional and synchrotron X-ray sources can be obtained. The design of a new high-resolution monochromator–collimator based on a single crystal, which takes advantage of the existence for almost any wavelength of n and m planes in the single crystal that lie near the Bragg condition, is presented. A weak link between the two reflecting surfaces is used to align the crystal planes and to obtain efficient reflections in the dispersive configuration. DuMond diagrams are used to evaluate the total diffracted intensity and the resolution of such a monochromator. The experimental results obtained from prototypes made of single crystals of silicon and germanium are in good agreement with theoretical predictions. This new type of monochromator offers the advantages of a compact design and simple alignment.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889801010913
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  • 11
    Digitale Medien
    Digitale Medien
    Sagittal focusing of high-energy synchrotron X-rays with asymmetric Laue crystals. II. Experimental studies (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 646-653 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: The use of bent asymmetric Laue crystals to focus synchrotron X-rays sagittally from 15 to 50 keV is described. A four-bar bender, bending a rectangular planar crystal, produced the necessary sagittal and meridional bending for this unique application. Adjustments of the tilt angle and height of the bent crystal resulted in first- and second-order corrections, respectively, to the dependence of the angle of diffraction on the horizontal position on the crystal. After these corrections, the remaining variation of the diffraction angle was of the order of 10 µrad. The theoretical sagittal focal length was verified. A prototype of a double-crystal sagittally focusing monochromator was constructed and tested, using two identical Laue crystals. A horizontal divergence of 3 mrad was focused to a horizontal dimension of about 0.4 mm. The X-ray flux density at the focus was a few hundred times larger than that of unfocused X-rays.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889801010627
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  • 12
    Digitale Medien
    Digitale Medien
    Micro X-ray diffraction on capillary powder samples: a novel and effective technique for overcoming preferred orientation (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 663-665 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: In past years, both experimental and analytical approaches have been developed for eliminating preferred orientation effects on powder X-ray diffraction patterns. The state of the art does not allow one to face the problem without difficult sample treatments, mechanical randomization, pole-figure study or pattern fitting based on the Rietveld approach. These methods are time consuming or need the knowledge of all the structural parameters, and, moreover, must be managed by specialized operators. Besides, none of the above techniques can be applied to powder samples of drugs loaded into polymeric carriers, the diffraction patterns of which present a structured amorphous halo from which the crystalline drug peaks rise up. In this paper, it is shown that micro X-ray diffraction on capillary powder samples, combined with a two-dimensional detector, is a promising solution to preferred orientation problems, since it provides easy and rapid preparation of randomly oriented powder samples, fast measurements (acquisition times of a few minutes) and correct powder diffraction patterns.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889801012237
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  • 13
    Digitale Medien
    Digitale Medien
    Robust Rietveld refinement in the presence of impurity phases (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 691-698 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: A modified least-squares analysis is presented that allows reliable structural parameters to be extracted from a powder diffraction pattern even in the presence of a substantial unmodelled impurity contribution. The algorithm is developed within the context of Bayesian probability theory. Experimental points that fall above those calculated, and are thus more probably from impurity peaks, are systematically down-weighted. This approach is illustrated with a two-phase example.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889801011396
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  • 14
    Digitale Medien
    Digitale Medien
    A new method for analysing peak broadening caused by compositional fluctuation in X-ray diffraction measurements (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 681-690 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: A new method for analysing X-ray peak broadening caused by compositional fluctuation is proposed. The method is applicable to epitaxial layers with diamond or zinc-blende structure on (001) substrates. In the new method, a rescaling procedure with a difference variable ΔA is applied to measured X-ray profiles and the dependence of the profiles on various reflection indices hkl is analysed. The theoretical formula reveals that X-ray peak profiles become independent of hkl after the rescaling. A new criterion is proposed; an experimental examination based on the criterion makes it possible simply to judge whether or not X-ray peak broadening is caused by compositional fluctuation. The method is verified experimentally and demonstrated by applying it to an InGaAs multilayer sample having artificial compositional fluctuation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889801011347
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  • 15
    Digitale Medien
    Digitale Medien
    The precision of diffraction peak location (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 737-743 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: Much of crystallography is concerned with the accurate location of the centre of diffraction peak profiles. Simple analytical expressions are derived for estimating the precision of diffraction peak location that can be achieved for Gaussian diffraction peaks with a flat background, in terms of the standard deviation, integrated intensity and peak height (H) to background (B) ratio. Two formulations are derived using standard methods: one for the case of very low background, the other for significant backgrounds. It is found that in cases of significant background, peak position is less well determined by a factor of [1+2(21/2)B/H]1/2 compared with the case of no background. The applicability of the expression has been demonstrated by Monte Carlo simulation of Gaussian profiles and by the analysis of real data collected at a large number of neutron and synchrotron sources, largely as part of the VAMAS TWA20 project. While the solution is presented for Gaussian peak shapes, it is believed to be approximately correct for a wide range of other common diffraction peak shapes (Lorentzian, Voigtian etc.). The method is applied to the assessment of the variation in optimal measuring time as a function of the depth of the gauge volume for residual strain scanning measurements.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S002188980101411X
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  • 16
    Digitale Medien
    Digitale Medien
    High-pressure structures of α- and δ-ZrMo2O8 (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 20-26 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: In situ high-pressure synchrotron X-ray powder diffraction studies of trigonal α-ZrMo2O8, zirconium molybdate, have been performed from ambient conditions to 1.9 GPa, over the α–δ phase transition at 1.06–1.11 GPa. The monoclinic structure of δ-ZrMo2O8, stable between 1.1 and 2.5 GPa at 298 K, has been solved by direct methods and refined using the Rietveld method. Significant distortions of the ZrO6 and MoO4 polyhedral elements are observed for δ-ZrMo2O8, as compared to the ambient conditions of the α-phase, while the packing of anions becomes more symmetric at high pressure.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768100013215
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  • 17
    Digitale Medien
    Digitale Medien
    Structures of three cis-β1 and three cis-β2 isomers of [Co(trien)(aminoacidato)]2+ complexes (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 45-53 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The crystal structures and absolute configurations of three cis-β1 and three cis-β2 isomers of [Co(trien)(L-aminoacidato)]2+, namely β1-Λ(SSS)(λλδ)/(λδδ)-[Co(trien)(L-isoleucinato)](ClO4)2, L-isoleucinato(triethylenetetramine)cobalt(III) diperchlorate (1), β1-Λ(SRS)(λδλ)-[Co(trien)(L-valinato)](ClO4)2, L-valinato(triethylenetetramine)cobalt(III) diperchlorate (2), β1-Δ(RSS)(δλδ)-[Co(trien)(L-pyroglutamato)]ClO4, L-pyroglutamato(triethylenetetramine)cobalt(III) perchlorate (3), β2-Δ(RRS)(δδλ)-[Co(trien)(L-isoleucinato)]I2·H2O, L-isoleucinato(triethylenetetramine)cobalt(III) diiodide monohydrate (4), β2-Δ(RRS)(δδλ)-[Co(trien)(L-isoleucinato)](ClO4)2·2H2O, L-isoleucinato(triethylenetetramine)cobalt(III) diperchlorate dihydrate (5), and β2-Λ(SSS)(δλλ)[Co(trien)(L-leucinato)](ClO4)2·2H2O, L-leucinato(triethylenetetramine)cobalt(III) diperchlorate dihydrate (6), have been determined. Both β1 and β2 isomers form inter-cation hydrogen-bonding interactions through double or triple hydrogen bonds which link the cations into helices. However, the motifs of the interactions are different in β1 and β2 isomers, resulting in different packing structures. A localized hydrophobic area is observed in the packing structure of (1), a unique feature amongst these six structures. This work describes the first synthesis of the β1 isomer by direct reaction between amino acids and cis-α-[Co(trien)Cl2]Cl in mildly basic solution.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768100013896
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  • 18
    Digitale Medien
    Digitale Medien
    Anisotropic thermal expansion of potassium dinitramide: a variable-temperature crystallographic study (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 113-118 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The structure of potassium dinitramide (KDN), KN3O4, has been refined in the temperature range 85–298 K from single-crystal X-ray diffraction data. The unit-cell axial lengths and the cell volume decrease linearly on cooling with the b axis being the most sensitive to the change of temperature. The β cell angle increases with decreasing temperature. The thermal expansion of KDN is significantly anisotropic, expanding along the b axis [010] more than three times the amount parallel to any other crystallographic direction. Other eigenvectors of the thermal expansion tensor lie approximately parallel to the diagonals of the ac plane. A rigid-body analysis of the dinitramide ion using the TLS formalism was performed and shows that the thermal motion of the anion is well represented by the rigid-body model. The eigenvalues of the libration tensor show significant anisotropy, whereas the translation tensor is close to isotropic. The variation of all descriptions of the thermal motion with respect to temperature indicates an anharmonic contribution to the mean field potential. The direction of greatest unit-cell expansion coincides with the largest components of the displacement tensor of the potassium ions and the direction of the largest atomic amplitudes due to the libration of the dinitramide anions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768100018887
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  • 19
    Digitale Medien
    Digitale Medien
    Synthons and design in metal phosphates and oxalates with open architectures (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1-12 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: We briefly describe the structures of open-framework metal phosphates with different dimensionalities, such as the one-dimensional linear-chain and ladder structures, two-dimensional layer structures and three-dimensional structures with channels. We demonstrate the role of the zero-dimensional four-membered ring monomer and of the one-dimensional ladder structure as the starting building units or synthons involved in the formation of the complex architectures. Thus, we show how the one-dimensional ladder structure transforms to two- and three-dimensional structures under mild conditions. The two-dimensional layer structures also transform to three-dimensional structures, while the zero-dimensional monomer transforms to layered and three-dimensional structures under ordinary reaction conditions. These transformations provide an insight into the possible pathways involved in the building up of the complex structures of metal phosphates. The isolation of amine phosphates during the hydrothermal synthesis of metal phosphates and also the facile reactions between amine phosphates and metal ions to yield a variety of open-framework materials have thrown light on the mechanism of formation and design of these structures. The existence of a hierarchy of open-framework metal oxalates and their ready formation by employing amine oxalates as intermediates provides additional support to the observations made earlier with regard to the phosphates.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768100017638
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  • 20
    Digitale Medien
    Digitale Medien
    Synthesis and structure of, and bonding in some derivatives of 2,6,9,10-tetraoxatricyclo[3.3.1.13,8]decane (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 63-71 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: Five derivatives of 2,6,9,10-tetraoxatricyclo[3.3.1.13,8]decane were synthesized and their molecular structures in the solid state were determined by means of X-ray diffraction analysis. In addition, the structures of all the molecules were optimized at different levels of computational quantum chemistry (HF/6-31G*, B3LYP/6-31G*). Experimentally determined bond lengths were compared with their calculated counterparts, and striking differences between the Hartree–Fock (HF) results and the experimental data could be traced back to the lack of correlation energy in the geometry optimizations. Two of the compounds under consideration are diastereomers and their relative stability was not only calculated with a conventional ab initio method (ZPE+MP2/6-31G*//HF/6-31G*), but also within the framework of density functional theory (B3LYP/6-31G*). In some of the calculations the influence of the solvent was included in single point calculations by means of an electrostatic model. Moreover, combining experimental as well as computational results, the exclusive axial orientation of a Cl atom in one of the compounds could be explained by an interplay of kinetic and energetic effects.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768100013331
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  • 21
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    Digitale Medien
    Automatic detection of molecular symmetry in the Cambridge Structural Database (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 88-94 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: A method for the detection of approximate molecular symmetry in crystal structures has been developed. The point-group symmetry is assigned to each molecule and the relevant symmetry elements can be visualized, superimposed on the molecule. The method has been validated against reference structures with exact symmetry subjected to small random perturbation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S010876810001380X
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  • 22
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    Digitale Medien
    Notes for Authors (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 107-111 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768100016335
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  • 23
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    Digitale Medien
    Ferroelectric–paraelectric phase transitions with no group–supergroup relation between the space groups of both phases? (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 599-601 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The structures of Sr3(FeF6)2, β-NbO2, TlBO2 and CrOF3, previously reported as possible ferroelectrics with no group–supergroup relation between the ferroelectric and the paraelectric symmetries, have been carefully studied. We could not confirm any structural pseudosymmetry with respect to a space group which is not a supergroup of their room-temperature polar space group. In all cases, pseudosymmetry was indeed detected, but only for non-polar supergroups of the actual space groups of the structures. In this sense, the four compounds are possible ferroelectrics, but fulfilling the usual group–supergroup relation between the phase symmetries.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768101006164
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  • 24
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    Digitale Medien
    Determination of the structure of 2(benzene-1,3,5-tricarboxylic acid)·1.5(pyrene)·2(methanol) and comparison with that of 2(benzene-1,3,5-tricarboxylic acid)·pyrene·2(ethanol) (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 692-696 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The structure of the title methanol complex (P\bar 1, Z = 2) has been determined and compared with that of the title ethanol complex (C2/c, Z = 8) using published data. Both complexes have layer structures, the (essentially planar) layers being constructed from rings of six TMA molecules, hydrogen bonded through four `carboxyl dimers' and two `interrupted dimers', where methanol (ethanol) is included in the R^4_4(12) (graph set) ring. The packing of the layers differs in the two complexes, leading to different three-dimensional structures. In the methanol complex, one pyrene molecule is located within the layer and the other, at a centre of symmetry, between the layers in one type of interlayer space, while the methyls of methanol protrude into the other type of interlayer space. In the ethanol complex, the superpositioning of the layers is such that two types of stack are formed; one of these is mixed, containing pyrene and one of the independent TMA molecules in alternating sequence, while the other stack contains only the second type of TMA. Spectroscopic study is needed to establish whether the partial mixed stack arrangement in the crystalline ethanol complex implies donor–acceptor interaction.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768101010527
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  • 25
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    Digitale Medien
    Crystal structure determination. By Werner Massa. (English translation by R. O. Gould.) Heidelberg: Springer-Verlag. Pp. xi + 206. Price (soft cover) DM 69.00. ISBN 3-540-65970-6. (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 440-440 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768101007935
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  • 26
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    Digitale Medien
    Structure refinement of the layered composite crystal Sc2B1.1C3.2 in a five-dimensional formalism (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 449-457 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The crystal structure of a layered compound Sc2B1.1C3.2, scandium boride carbide (Mr = 140.43), has been re-refined as a commensurate composite crystal using 1795 single-crystal X-ray diffraction intensities with I 〉 2\sigma(I) collected by Shi, Leithe-Jasper, Bourgeois, Bando & Tanaka [(1999), J. Solid State Chem. 148, 442–449]. The crystal is composed of two layered subsystem structures, i.e. Sc—C—Sc sandwiches and graphite-like layers of the composition B1/3C2/3. The structure refinement was performed in a five-dimensional formalism based on the trigonal superspace group P\bar{3}m1(p00)(0p0)0m0. The unit cell and other crystal data are a = b = 3.387 (1), c = 6.703 (2) Å, V = 66.59 (1) Å3, \boldsigma_{1} = (9/7 0 0), \boldsigma_{2} = (0 9/7 0), Z = 1, Dx = 3.501 Mg m−1. Two different three-dimensional sections through the superspace were analyzed, corresponding to two different superstructure models, one with P\bar{3}m1 and the other with P\bar{3}m1. A random distribution of B and C was assumed in the graphite-like layer and 41 structural parameters were introduced. RF/wRF} were 0.0533/0.0482 and 0.0524/0.0476, respectively, for the first and second models. Although the difference between these RF or wRF values was too fine to exclude one of the models definitely, the advantages of using a superspace group were obvious. It not only brought about better convergence of refinement cycles by virtue of fewer parameters, but also gave an insight into the problem of symmetry of the superstructure.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768101006607
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  • 27
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    Digitale Medien
    Structures of copper(II) and manganese(II) di(hydrogen malonate) dihydrate; effects of intensity profile truncation and background modelling on structure models (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 497-506 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The crystal structures of the title compounds were determined with net intensities I derived via the background–peak–background procedure. Least-squares optimizations reveal differences between the low-order (0 〈 s 〈 0.7 Å−1) and high-order (0.7 〈 s 〈 1.0 Å−1) structure models. The scale factors indicate discrepancies of up to 10% between the low-order and high-order reflection intensities. This observation is compound independent. It reflects the scan-angle-induced truncation error, because the applied scan angle (0.8 + 2.0 tan θ)° underestimates the wavelength dispersion in the monochromated X-ray beam. The observed crystal structures show pseudo-I-centred sublattices for three of its non-H atoms in the asymmetric unit. Our selection of observed intensities (I 〉 3σ) stresses that pseudo-symmetry. Model refinements on individual data sets with (h + k + l) = 2n and (h + k + l) = 2n + 1 illustrate the lack of model robustness caused by that pseudo-symmetry. To obtain a better balanced data set and thus a more robust structure we decided to exploit background modelling. We described the background intensities B(\displaystyle\mathrel{\mathop H^{\rightharpoonup}}) with an 11th degree polynomial in θ. This function predicts the local background b at each position \displaystyle\mathrel{\mathop H^{\rightharpoonup}} and defines the counting statistical distribution P(B), in which b serves as average and variance. The observation R defines P(R). This leads to P(I) = P(R)/P(B) and thus I = R − b and σ2(I) = I so that the error σ(I) is background independent. Within this framework we reanalysed the structure of the copper(II) derivative. Background modelling resulted in a structure model with an improved internal consistency. At the same time the unweighted R value based on all observations decreased from 10.6 to 8.4%. A redetermination of the structure at 120 K concluded the analysis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768101004050
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  • 28
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    Digitale Medien
    Perchlorophenalenyl radical, C13Cl9: a modulated structure with nine threefold-symmetric molecules in the asymmetric unit (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 680-691 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The odd-alternant perchlorophenalenyl radical, C13Cl9, forms molecular stacks centered on crystallographic threefold rotation axes, but the spacing within the stacks (3.78 Å) is too large to allow good overlap of the orbitals in which the spin density is localized. The radical is ruffled because of the intramolecular repulsions between α Cl atoms (the Cl...Cl peri interactions); the average displacement of an α Cl atom from the molecular plane is ∼0.7 Å. The deviations from molecular planarity do not, however, determine the spacing within the stacks, which is determined instead by interactions between stacks. The modulations found in the P3c1 superstructure are a response to the short interstack contacts that would occur in the average pseudocell structure (R\bar 3m, c′ = c/6). The primary modulation is a pattern of enantiomeric alternation; a secondary modulation involves small rotations of the molecules around their threefold axes. The number (9) of independent molecules in the true cell is exceptionally large because of the conflict between the preference within the molecular stacks for threefold rotational symmetry and the preference in directions perpendicular to the stack axes for twofold alternation of enantiomers. The structural complexity reduces the precision of the distances and angles determined, but the average values found are in excellent agreement with those calculated by density functional theory.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768101011193
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  • 29
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    Digitale Medien
    Structure of Nd10W22O81 from high-resolution electron microscopy and X-ray powder diffraction (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 13-19 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The crystal structure of Nd10W22O81, neodymium tungstate, has been determined using a combination of high-resolution transmission electron microscopy and X-ray powder diffraction methods. The unit-cell dimensions determined from X-ray data are a  =  3.8613 (1), b  =  35.9431 (1), c  =  21.8900 (1) Å, V = 3038.05 Å3, Z  =  2, space group Pbcm. The structure is built up of pentagonal columns (PCs) connected to ReO3-type fragments consisting of three octahedra, thus forming W9O32 units. These units form `pillars' along a. These `pillars' are joined by pairs of tilted octahedra (W2O11 groups) to form corrugated layers perpendicular to b. The Nd atoms are located in the space between these layers and form the only link between them. Interstitial O atoms are located between two of the Nd atoms. The formula Nd10W22O81 can thus be alternatively given as Nd5W11O39 + x (x ∼ 1.5), where x represents the interstitial O atoms. Nd10W22O81 is a new type of PC structure.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768100013203
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  • 30
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    Digitale Medien
    X-ray investigations of sulfur-containing fungicides. II. Intramolecular forces governing the conformation of four novel α-phenylazo- and α-phenylhydrazono-β-ketosulfones (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 54-62 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The crystal and molecular structures of four novel β-ketosulfones, phenyl benzoyl(phenylhydrazono)methyl sulfone (I), phenyl benzoyl(4-nitrophenylhydrazono)methyl sulfone (II), (benzoyl)(phenyl)(phenylazo)methyl phenyl sulfone (III) and (benzoyl)(phenyl)(3-chlorophenylazo)methyl 4-tolyl sulfone (IV), have been investigated using X-ray analysis and density functional theory supplemented by ab initio Hartree–Fock calculations. The conformations of (I) and (II) are stabilized by strong intramolecular resonance-assisted hydrogen bonds formed between the sulfonyl and the α-hydrazono moieties. The following increase of a positive charge on the S atoms is compensated via π-conjugation and stereoelectronic back-donation from the nearby β-carbonyl group. Compounds (III) and (IV) adopt a strongly distorted propeller shape with pivotal tetrahedral C1 atoms. Distortion mostly follows from the approximate coplanarity of the α-azophenyl and α-phenyl moieties opposite each other. The main stereoelectronic interactions involve the donation of electron density from the α-azo N2 towards the sulfonyl S and the β-carbonyl C2 atoms.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768100013197
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  • 31
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    Digitale Medien
    Structural studies on C-amidated amino acids and peptides: structures of hydrochloride salts of C-amidated Ile, Val, Thr, Ser, Met, Trp, Gln and Arg, and comparison with their C-unamidated counterparts (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 72-81 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: To elucidate the structural features of amino acids caused by the C-terminal α-amidation, the crystal structures of HCl salts of C-terminal amidated Ile, Val, Thr, Ser, Met, Trp, Gln and Arg were analysed and compared with those of their C-terminal free acids. The bonding parameter of the amide group was little affected by the different chemical properties of the side chains. As for the molecular packing patterns, some structural differences were observed by the C-amidation. The Cα—H...O hydrogen bonds and carbonyl–carbonyl interactions were more strengthened by the salt formation with HCl in C-amides than C-acids. Furthermore, there is a clear difference between the interaction patterns with Cl ions. In most C-amide crystals, Cl ions are bifurcately hydrogen-bonded to two neighbouring amide NH2 groups and the parallel layers of the C-amides and Cl ions are alternatively formed. In the case of the carboxyl OH in C-acid crystals, however, the direct hydrogen bond with the Cl ion is not always observed and is largely dependent on the crystal packing environment. This suggests the superior hydrogen-bonding ability of NH...Cl− compared with OH...Cl−. The difference in hydrogen-bonding ability between the amide and carboxyl groups is considered, based on the spatial dispositions of the hydrogen-bonding polar atoms/groups.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768100013975
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  • 32
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    Digitale Medien
    Kinetic behaviour investigations and crystal structure of nitric acid dihydrate (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 27-35 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: X-ray powder diffraction experiments are performed to prove the possible crystallization of nitric acid dihydrate (HNO3·2H2O, further denoted NAD) and to determine the best thermal conditions for growing a single crystal. It is shown that the kinetic behaviour of NAD strongly depends on the preliminary thermal treatment. One good single crystal obtained by an in situ adapted Bridgman method procedure enabled determination of the crystal structure. The intensities of diffracted lines with h odd are all very weak. The H atom of nitric acid is delocalized to one water molecule leading to an association of equimolar nitrate (NO3−) and an H5O2+ ionic group. The asymmetric unit contains two such molecules. These two molecules are related by a pseudo a/2 translation (with a 0.3 Å mean atomic distance difference), except for one H atom of the water molecules (0.86 Å) because of their different orientations in the two molecules. The two molecules, linked by very strong hydrogen bonds, are arranged in layers. Two layers which are linked by weaker hydrogen bonds are approximately oriented along the c axis. The structure may be described by translations of this set of two layers along the c axis without hydrogen bonds leading to a two-dimensional hydrogen-bond network. The structures of the monohydrate (NAM) and trihydrate (NAT) are re-determined for comparisons. These structures may be described by one- and three-dimensional hydrogen-bond networks, respectively.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768100014506
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  • 33
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    Digitale Medien
    Modern crystallography. Vol. 2. Structure of Crystals. (Third edition). Edited by B. K. Vainshtein, V. M. Fridkin and V. L. Indenbom. Heidelberg: Springer-Verlag, 2000. Pp. xx + 520. Price DM 198. ISBN 3-540-67474-8. (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 112-112 
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    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768100019881
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  • 34
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    Digitale Medien
    Synchrotron X-ray analysis of the electron density in CoF2 and ZnF2 (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 128-135 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: Accurate structure factors for small crystals of the rutile-type structures CoF2, cobalt difluoride, and ZnF2, zinc difluoride, have been measured with focused λ = 0.8400 (2) Å synchrotron X-radiation at room temperature. Phenomenological structural trends across the full series of rutile-type transition metal difluorides are analysed, showing the importance of the metal atom in the degree of distortion of the metal–F6 octahedra in these structures. Multipole models reveal strong asphericities in the electron density surrounding the transition metals, which are consistent with expectations from crystal field theory and the structural trends in these compounds. Transition metal 3d-orbital populations were computed from the multipole refinement parameters, showing significant repopulation of orbitals compared with the free atom, particularly for CoF2.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768100017353
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  • 35
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    Digitale Medien
    Synchrotron X-ray study of Er3Al5O12 and Yb3Al5O12 garnets (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 136-141 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: Structure factors for Er3Al5O12 and Yb3Al5O12 garnets were measured using focused synchrotron X-radiation, with λ = 0.7500 (2) and 0.7000 (2) Å, respectively. The difference electron density maps for Er3Al5O12 and Yb3Al5O12 were similar, as expected. This was attributed to the 4f electrons being shielded, which reduces their effectiveness in chemical bonding and the relative position of the rare-earth atoms in the periodic table. The symmetry of the difference electron density around the rare-earth atoms was found to reflect that of the cation geometry, emphasizing the importance of second nearest-neighbor interactions. This is consistent with the view that oxide-type structures may be regarded as a packed array of cations with anions in the interstices.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768100019923
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  • 36
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    Digitale Medien
    Salts of 3,5-dinitrobenzoic acid with organic diamines: hydrogen-bonded supramolecular structures in one, two and three dimensions (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 201-212 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The trigonally trisubstituted carboxylic acid 3,5-dinitrobenzoic acid, (O2N)2C6H3COOH, forms 2:1 salts with a range of organic diamines L, with the general composition [LH2]2+·[{(O2N)2C6H3COO}−]2. When L is a bis-tertiary amine the hard N—H...O hydrogen bonds generate finite three-component aggregates, anion...cation...anion, and these aggregates are further linked by soft C—H...O hydrogen bonds to form one-dimensional molecular ladders when L is N,N,N′,N′′-tetramethyl-1,2-diaminoethane and chains of rings when L is 4,4′-dipyridylethane or 4,4′-dipyridylethene; two-dimensional sheets are formed when L is 1,4-diazabicyclo[2.2.2]octane and a three-dimensional framework is formed when L is N,N′-dimethylpiperazine. When L is the bis-secondary amine piperazine, the hard N—H...O and soft C—H...O hydrogen bonds each generate continuous motifs in the form of distinct chains of rings, the combination of which generates sheets, while when L is the bis-primary amine 1,2-diaminoethane the hard N—H...O hydrogen bonds alone generate a three-dimensional framework.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S010876810001853X
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  • 37
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    Digitale Medien
    Structural basis for the phase transitions of Cs2HgCl4 (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 231-236 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The a0 × b0 × 2c0 twofold superstructure of dicaesium mercury tetrachloride, Cs2HgCl4, at T = 120 K has been determined by single-crystal X-ray diffraction using synchrotron radiation. Lattice parameters were found as a = 9.7105 (2), b = 7.4691 (1), c = 26.8992 (4) Å, and β = 90.368 (1)° with the supercell space group P21/c. Refinements on 1828 observed unique reflections converged to R = 0.053 (wR = 0.057) using anisotropic temperature factors for all atoms. This phase is the stable phase of Cs2HgCl4 below 163 K. A quantitative comparison is made of the distortions of the 2c0 superstructure with the undistorted phase that is stable at room temperature, and with the 3c0 and 5a0 superstructures that are stable at temperatures between 163 K and room temperature. The principal difference between the 2c0 superstructure and all other phases of Cs2HgCl4 is that the Cs cations are displaced away from the centers of their coordination polyhedra in the 2c0 superstructure. The structural basis for the driving force of the series of phase transitions in this compound is found in the variations of the environments of Cs atoms and in the variations of the distortions of the HgCl4 tetrahedra.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768100020322
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  • 38
    Digitale Medien
    Digitale Medien
    Commensurate structure of Ca2CoSi2O7, a new twinned orthorhombic structure (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 271-277 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The crystal structure of the commensurate phase of Ca2CoSi2O7, dicalcium cobalt disilicate, has been derived from the modulated structure described in (3 + 2)-dimensional space. The structure is orthorhombic P21212; a = 23.510 (4), b = 23.510 (4), c = 5.025 (1) Å (at 170 K), Z = 18. Since the crystal is twinned and the apparent diffraction symmetry is 4/mmm, the parameters were refined by a newly developed least-squares program for the refinement of twinned crystals. The structure is essentially similar to the known structure of the melilite group, but with regular arrangement of the bundles along [001] formed with four arrays of the sixfold coordinated Ca polyhedra and an array of CoO4 tetrahedra. The distribution of the bundles found in the present structure is different from that reported by Riester et al. [(2000), Z. Kristallogr. 215, 102–109].
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S010876810100101X
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  • 39
    Digitale Medien
    Digitale Medien
    Hydrogen-bonded hexagonal and pseudo-hexagonal grid motifs in supramolecular cobalt(II) and nickel(II) cupferronato complexes incorporating neutral N-donors with intermolecular NH2 connectors and solvent molecules (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 303-310 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The cobalt(II) and nickel(II) cupferronato (N-nitroso-N-phenylhydroxylaminato) mixed-ligand complexes of 2-aminopyridine (2-NH2py) [Co(PhN2O2)2(2-NH2py)2] (1), [Ni(PhN2O2)2(2-NH2py)2] (2) and 2,6-diamino-4-phenyl-1,3,5-triazine (dpt) [Co(PhN2O2)2(dpt)2]·[Co(PhN2O2)2(EtOH)2] (3) have been synthesized and characterized by X-ray diffraction analysis. The cobalt (1) and nickel (2) complexes are isostructural. The crystal lattice of (3) contains different neutral cobalt(II) complexes [Co(PhN2O2)2(dpt)2] (3a) and [Co(PhN2O2)2(EtOH)2] (3b). Molecules of (1)–(3) contain octahedral metal centres with all-cis-(1) and -(2) and all-trans-(3) disposal of the ligands. Intramolecular N—H...O hydrogen bonding between the NH2 groups and the O atom of the cupferronato anion can be observed in (1)–(3). Intermolecular N—H...O and N—H...N interactions between symmetry-related molecules of (1) and (2) led to hexameric aggregates which connect through common edges into a two-dimensional supramolecular network of hexagonal-grid type. In complex (3) the self-complementary dpt units of the (3a) molecules are maintained by intermolecular N—H...N hydrogen bonds, generating infinite chains. These (3a) chains are crosslinked by the (3b) subunits via N—H...O and O—H...N hydrogen bonds, thus completing the parallel two-dimensional supramolecular network consisting of pseudo-hexagonal-grid sheets. In each crystal structure the two-dimensional supramolecular networks are controlled by both hydrogen bonds and π...π stacking interactions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768101004426
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  • 40
    Digitale Medien
    Digitale Medien
    Hydrated salts of 3,5-dihydroxybenzoic acid with organic diamines: hydrogen-bonded supramolecular structures in two and three dimensions (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 329-338 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The trigonally trisubstituted acid 3,5-dihydroxybenzoic acid forms hydrated salt-type adducts with organic diamines. In 1,4-diazabicyclo[2.2.2]octane–3,5-dihydroxybenzoic acid–water (1/1/1) (1), where Z′ = 2 in P21/c, the constitution is [HN(CH2CH2)3N]+·[(HO)2C6H3COO]−·H2O: the anions and the water molecules are linked by six O—H...O hydrogen bonds to form two-dimensional sheets and each cation is linked to a single sheet by one O—H...N and one N—H...O hydrogen bond. Piperazine–3,5-dihydroxybenzoic acid–water (1/2/4) (2) and 1,2-diaminoethane–3,5-dihydroxybenzoic acid–water (1/2/2) (3) are also both salts with constitutions [H2N(CH2CH2)2NH2]2+·2[(HO)2C6H3COO]−·4H2O and [H3NCH2CH2NH3]2+·2[(HO)2C6H3COO]−·2H2O, respectively. Both (2) and (3) have supramolecular structures which are three-dimensional: in (2) the anions and the water molecules are linked by six O—H...O hydrogen bonds to form a three-dimensional framework enclosing large centrosymmetric voids, which contain the cations that are linked to the framework by two N—H...O hydrogen bonds; in (3) the construction of the three-dimensional framework requires the participation of cations, anions and water molecules, which are linked together by four O—H...O and three N—H...O hydrogen bonds.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768100019832
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  • 41
    Digitale Medien
    Digitale Medien
    Experimental electron density of urea–phosphoric acid (1/1) at 100 K (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 353-358 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The deformation electron density of the urea–phosphoric acid adduct has been studied from 100 K X-ray and neutron diffraction experiments. Data were interpreted according to the Hirshfeld model. The long hydrogen bonds show characteristics of electrostatic interaction. Deformation density maps on the short hydrogen bond shows hydrogen more strongly bonded to urea than to phosphoric acid, and peak maxima at almost midway between the two O—H bonds.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768101004359
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  • 42
    Digitale Medien
    Digitale Medien
    Structure of β-trimyristin and β-tristearin from high-resolution X-ray powder diffraction data (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 372-377 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The crystal structures of β-1,2,3-tritetradecanoylglycerol (β-trimyristin or β-MMM) and β-1,2,3-trioctadecanoylglycerol (β-tristearin or β-SSS) have been determined from high-resolution synchrotron X-ray powder diffraction data. Grid search and Rietveld refinement have been used to determine and refine the structure, respectively. Both substances crystallize in space group P\bar 1 with Z = 2. The unit-cell parameters for β-MMM are a = 12.0626 (6), b = 41.714 (1), c = 5.4588 (3) Å, α = 73.388 (4), β = 100.408 (5) and γ = 118.274 (4)°. For β-SSS the unit-cell parameters are a = 12.0053 (7), b = 51.902 (2), c = 5.4450 (3) Å, α = 73.752 (5), β = 100.256 (6) and γ = 117.691 (5)°. Soft-distance restraints have been applied to the molecules during refinement. For β-MMM the final Rp value obtained is 0.053 and for β-SSS the final Rp value is 0.041.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768100019121
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  • 43
    Digitale Medien
    Digitale Medien
    X-ray and neutron structure of 1,8-(3,6,9-trioxaundecane-1,11-diyldioxy)-9,10-dihydro-10,10-dimethylanthracene-9-ol (P326); some pitfalls of automatic data collection (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 339-345 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The structure of the crown ether 1,8-(3,6,9-trioxaundecane-1,11-diyldioxy)-9,10-dihydro-10,10-dimethylanthracene-9-ol, C24H30O6·H2O (1), code name P326, the parent compound for a series of derivatives, has been determined by both X-ray diffraction at room temperature and neutron diffraction at very low temperature. The unit cells are very similar at both temperatures and in both cases the crystals exhibit P21 symmetry with Z = 4 (two molecules, A and B, respectively, per asymmetric unit) and pseudosymmetry P21/c. The higher symmetry is broken mainly by the two independent water molecules in the unit cell, some reflections which would be absent in P21/c having strong intensities in both the X-ray and neutron data. In both molecules A and B hydrogen bonds involving the water molecule stabilize the macrocyclic ring structure, one involving the macrocyclic O(9) as a donor. Close contacts between the water and macrocyclic O atoms in each molecule also suggest the presence of two bifurcated hydrogen bonds, involving water HW2 to both O(16) and O(18), and water HW1 to both O(18) and O(20), respectively, with considerable variation in the geometry being present. Both molecules A and B exhibit very close pseudosymmetry across a plane perpendicular to the molecular plane and through atoms C(9) and O(18), and in addition are predominantly planar structures. The X-ray analysis failed to reveal one H atom per water molecule, each being subsequently included after location and refinement in the neutron analysis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768100015184
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  • 44
    Digitale Medien
    Digitale Medien
    Migration of the proton in the strong O—H...O hydrogen bond in urea–phosphoric acid (1/1) (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 435-439 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The structure of urea–phosphoric acid is reported at a large number of temperatures in the range 150–335 K from neutron diffraction data collected using a novel multiple single-crystal data collection method. The work focuses on the behaviour of the H atom involved in the short strong O—H...O hydrogen bond in this material. The position of this atom is shown to vary significantly, by around 0.035  Å, as a function of temperature, becoming effectively centred at the highest temperatures studied. This result, only accessible due to the accurate determination of H-atom parameters by neutron diffraction, has implications for the potential governing the hydrogen bond.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768100018875
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  • 45
    Digitale Medien
    Digitale Medien
    Topochemically controlled solid-state methyl rearrangement in thiocyanurates (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 428-434 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: 4,6-Dimethoxy-3-methyl-1,3,5-triazine-2(3H)-thione crystallizes in two polymorphic forms, needles and plates. In the needle-shaped crystals (9a) the molecules occupy the crystallographic mirror plane, thus the layers are stacked along the b axis. The molecules of the other polymorph [plate-shape crystals, (9b)] are packed in a herringbone packing mode. Upon heating, (9b) undergoes a phase transition to form (9a). At 378 K the needles undergo O → S topochemically controlled methyl transfer in the solid state to produce 1-methyl-4-methoxy-6-methylthio-1,3,5-triazine-2(1H)-one in 75% yield. The enthalpy of the rearrangement is estimated to be −39.1 kJ mol−1. 1-Methyl-6-methoxy-4-methylthio-1,3,5-triazine-2(1H)-thione crystallizes in space group P21 with two crystallographically independent molecules in the asymmetric unit. Compound (9b) undergoes O → S methyl transfer in the solid state at 373 K. The rearrangement is topochemically assisted and the product, 1-methyl-2,4-bismethylthio-1,3,5-triazine-6(1H)-one, is obtained in quantitative yield. The enthalpy of the rearrangement is estimated to be −58.8 kJ mol−1. The crystal structures of the compounds as well as their DSC thermographs are described and discussed. Energy calculation by ab initio methods shows that the driving force for the reactions is the difference between the molecular energies of the pre-rearranged compounds and their products, 54.2 and 59.3 kJ mol−1 in the two cases, respectively.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768101005171
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  • 46
    Digitale Medien
    Digitale Medien
    Parametrization of perovskite structures: an ab initio study (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 491-496 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: An overview of the pressure, temperature and chemical composition dependence of the lattice distortion in orthorhombic ABO3 perovskite structures is presented. Within the framework of the so-called global parametrization method (GPM) [Thomas (1998). Acta Cryst. B54, 585–599] an improved description for the position of the A cation in terms of the AO_{12} and BO_6 polyhedral volume ratio is proposed. The relationship is derived from an extensive ab initio study based on the density functional theory. The applicability of the improved GPM in combination with ab initio total energy calculations in the prediction of changes in the structural distortion under increasing hydrostatic pressure is investigated. Test calculations are performed for the geophysically important magnesium silicate perovskite and the results are compared with the available theoretical and experimental data.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S010876810100893X
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  • 47
    Digitale Medien
    Digitale Medien
    Hexagonal Frank–Kasper phases interpreted as modulated crystals (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 466-470 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The structures of the hexagonal Frank–Kasper phases F and K, which have been described in terms of the aggregation of clusters, are interpreted as modulated crystal structures. They are basically composed of two close-packed layers with ordered atomic vacancies rotated by 90° to each other about their normal.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768101006267
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  • 48
    Digitale Medien
    Digitale Medien
    Solid-state structures of group 1 and group 2 metal 1,5-naphthalenedisulfonates: systematic investigation of lamellar three-dimensional networks constructed by metal arenedisulfonate (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 520-530 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: Seven Group 1 and Group 2 1,5-naphthalenedisulfonates (1,5-nds) have been synthesized and structurally characterized by single-crystal X-ray diffraction, IR spectroscopy and thermal gravimetric analysis. For Group 1 metal complexes, with M = Li+ (1), Na+ (2) and K+ (3), all crystallize in the same space group (P21/c) with the same composition, [M2(1,5-nds)(H2O)2]. They adopt similar three-dimensional packing arrangements with the metal–sulfonate inorganic layers pillared by naphthalene rings. However, the coordination behavior of three metal cations toward the SO_3^- group and water molecule are different, resulting in different architectures for the inorganic portion. For Group 2 complexes with M = Mg2+ (4), Ca2+ (5), Sr2+ (6) and Ba2+ (7), Mg2+ shows no direct coordination by the SO_3^- group while Ca2+ is coordinated by four SO_3^- groups and a two-dimensional network is formed. Complexes (6) and (7) are isostructural, adopting the same three-dimensional, inorganic–organic pillared framework as seen for (1)–(3). The coordination behavior of the metal cations in these structures neatly illustrates the increase in coordination strength with decreasing charge/radius ratio for Group 1 and Group 2 metal cations with large organic anions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S010876810100862X
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  • 49
    Digitale Medien
    Digitale Medien
    Structure determination of the [Fe(teec)6](BF4)2 metal complex from laboratory and synchrotron X-ray powder diffraction data with grid-search techniques (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 531-538 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The structure of the coordination compound [Fe(teec)6](BF4)2, hexa[1-(2-chloroethyl)tetrazole]iron(II) di(borotetrafluoride), has been determined using the grid-search techniques of the program suite MRIA. A Guinier-camera data set was used to determine the unit cell, the space group and to position the initial model. A high-resolution synchrotron powder data set was used to position a more detailed model using torsion-angle variation and to refine the structure leading to Rp = 0.0689, Rw = 0.0805 and GoF = 1.38. The crystal structure at room temperature shows the existence of two symmetry-equivalent iron(II) ions in the high-spin state.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S010876810100828X
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  • 50
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    Digitale Medien
    Structural complexity of a polar perhydrotriphenylene inclusion compound brought to light by synchrotron radiation (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 579-590 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The complex diffraction pattern of the heavily disordered co-crystals of perhydrotriphenylene and 1-(4-nitrophenyl)piperazine (5C18H30·C10H13N3O2) has been investigated with synchrotron radiation and an area detector. Five (almost) complete, three-dimensional data sets have been obtained from the tips and the centre of a needle-like crystal at room temperature and 120 K. They revealed a rich variety of features including one,- two- and three-dimensional diffuse scattering, as well as incommensurate satellites. At the centre and one tip of the crystal the symmetry appears to be orthorhombic, whereas at the other tip the symmetry of the satellites and of some of the diffuse scattering is clearly monoclinic, indicating that the crystal is not homogeneous. Most of the scattering could be assigned to R/S occupational disorder of the chiral host molecules, to positional disorder of the guest molecules or to local distortions of the average structure. Assignments are based on the disorder deduced from the average structure and the molecular form factors of host and guest molecules which show characteristic patterns in reciprocal space. Two smaller, orthorhombic twin fragments and an additional phase with hexagonal symmetry have also been found.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768101005468
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  • 51
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    Digitale Medien
    Nucleic acids: structures, properties and functions. By Victor A. Bloomfield, Donald M. Crothers and Ignacio Tinoco Jr. Pp. xii + 794. Sausalito: University Science Books, 2000. Price US$79.20. ISBN 0-935702-49-0. (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 602-602 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768101011880
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  • 52
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    Digitale Medien
    Charge distribution as a tool to investigate structural details. II. Extension to hydrogen bonds, distorted and hetero-ligand polyhedra (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 652-664 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: It is shown that one of the main reasons for most failures of the methods for calculating distance-dependent bond strengths is related to the distortion of the coordination polyhedra. The charge distribution (CD) method which depends on only one universal empirical parameter (contraction parameter) is modified to include: (i) an iterative calculation of the effective coordination number (ECoN), to deal with structures containing very distorted coordination polyhedra; (ii) a specific contraction parameter to treat structures containing any type of hydrogen bond; (iii) scale factors for coordination subshells, to treat structures with hetero-ligand polyhedra. The contraction parameter for the hydrogen bonds was obtained from 119 well refined structures based on neutron diffraction data. Examples of the application of the iterative charge distribution (CD-IT) are presented to show the efficiency of the new method in dealing with distorted (including hydrogen bonding) and hetero-ligand polyhedra. In particular, analysis of a series of 74 structures with pentacoordinated cations shows that deviations from overall trends are related to structure instability. The possible failure of the method with polyionic structures and `dynamic' structures is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768101009879
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  • 53
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    Digitale Medien
    Self-association and stereochemistry study of 2-methylthio-, 2-dimethylaminocyclohexanone oximes and the parent cyclohexanone oxime (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 705-713 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: X-ray diffraction analyses of 2-substituted cyclohexanone oximes C5H9(X)C=NOH [X = SMe (1), NMe2 (2)] and of the parent compound [X = H (3)] showed that their cyclohexyl rings are in a slightly distorted chair conformation. These compounds assume in the solid state the (E) configuration bearing the 2-substituents in the axial conformation. Compounds (1) and (2) exist as dimeric and polymeric hydrogen-bond associates, respectively. Low-temperature X-ray analysis of the cyclohexanone oxime (3) showed that the molecules are associated forming two independent trimers. The dimer in (1) and the trimer in (3) are built up via [O—H...N=C] hydrogen bonds, while the polymer of (2) is via the [OH...NMe2] hydrogen bond. The comparative IR νOH and νC=N analysis of the title compounds, in the solid state and in CCl4 solution, fully supports the nature of the associates for (1)–(3) obtained by X-ray diffraction. The IR azomethyne frequency shift analysis (ΔνC=N) also suggests the occurrence of the πC=N/σ*C—X orbital interaction which stabilizes the axial conformations of (1) and (2).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768101009624
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  • 54
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    Digitale Medien
    Studies of molecular structure parameters of 20-piperidin-2-yl-5α-pregnan-3β,20-diol and its N-methyl derivative: two inhibitors of Δ24(25) sterol methyl transferase and Δ24(24′) sterol methyl reductase of Trypanosoma cruzi (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 714-721 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: Molecular structural parameters of two potential drugs against Trypanosoma cruzi epimastigotes, 20-piperidin-2-yl-5α-pregnan-3β,20-diol (1) and 20-N-methylpiperidin-2-yl-5α-pregnan-3β, 20-diol (2) were studied using a combination of a stereoselective synthetic route, spectroscopic characterization and single-crystal X-ray analysis. Both compounds were synthesized with an R configuration at C20. This chirality is a consequence of the stereoselectivity observed during the formation of the intermediate 20-pyridin-2-yl-5α-pregnan-3β,20R-diol (4). NMR data indicated that the six-membered aza ring of (2) is conformationally more restrained, in CDCl3 solution, than (1). X-ray studies showed that maximum deviations among structural molecular parameters of (1) and (2) correspond to torsion angles along the C20—C22 bonds, leading to a different relative orientation of the N atom; a critical structural parameter for the binding properties of aza-sterols to Δ24(25) sterol methyl transferase. Cremer–Pople parameters of the five-membered rings of (1) and (2) lie in the observed range for a family of tetracyclic fused ring systems retrieved from the CSD. The φ2 parameter of (1) lies just on the mean of the family, while φ2 of (2) deviates significantly towards the lower limit.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768101013234
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  • 55
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    Digitale Medien
    Systematic generation of all nonequivalent closest-packed stacking sequences of length N using group theory (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 766-771 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: An algorithm has been developed that generates all of the nonequivalent closest-packed stacking sequences of length N. There are 2N + 2(−1)N different labels for closest-packed stacking sequences of length N using the standard A, B, C notation. These labels are generated using an ordered binary tree. As different labels can describe identical structures, we have derived a generalized symmetry group, Q ∼ DN × S3, to sort these into crystallographic equivalence classes. This problem is shown to be a constrained version of the classic three-colored necklace problem.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S010876810101552X
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  • 56
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    Digitale Medien
    Use of software to search for higher symmetry: space group C2 (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 800-805 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: From a search of the October 2000 release of the Cambridge Structural Database we find coordinate data for approximately 1500 entries under space group No. 5: C2 or, occasionally, A2, I2 or B112. Software designed to detect cases of missed higher symmetry identified 144 entries for detailed inspection. Of these, 50 should, we believe, be revised to space groups of higher symmetry. The most common revision is to space group C2/m, which entails adding a center of inversion and usually results in important changes in bond lengths and angles.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768101014331
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  • 57
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    Digitale Medien
    Hydrogen-bond network in cyclodecaamylose hydrate at 20 K; neutron diffraction study of novel structural motifs band-flip and kink in α-(1→4)-D-glucoside oligosaccharides (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 833-841 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: A single-crystal neutron diffraction study of cyclodecaamylose (CA10) was carried out at 20 K. CA10 crystallizes with 27.18 water molecules [(C6H10O5)10·27.18H2O] in space group C2 with unit-cell constants a = 29.31 (5), b = 9.976 (10), c = 19.34 (2) Å, β = 121.07 (2)°. The asymmetric unit contains a half molecule of CA10 and 13.59 water molecules, the other half being related by a crystallographic twofold rotation axis. All H atoms except two water H atoms could be located from difference neutron-density maps; structure refinement converged at R = 0.635. Two of the five CH2—O6 groups and one of the 15 O2, O3 hydroxyl groups of CA10 are twofold orientationally disordered. A total of 13.59 water molecules in the asymmetric unit are distributed over 23 positions; 20 of which are in the CA10 cavity, and the other three occupy intermolecular interstices. Of the 123 symmetry-independent hydrogen bonds, 25 (= 20%) are three-centered and 7 (= 6%) are four-centered. Water molecules and O—H groups of CA10 form an extended network with cooperative O—H...O—H...O—H hydrogen bonds. They are arranged in 11 polygons with three, four, five, six and eight O—H bonds and in homodromic, antidromic and heterodromic arrangements. Nine polygons are located within the cavity and the others are outside.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768101014288
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  • 58
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    Digitale Medien
    Associations of squaric acid and its anions as multiform building blocks of hydrogen-bonded molecular crystals (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 859-865 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: Squaric acid, H2C4O4 (H2SQ), is a completely flat diprotic acid that can crystallize as such, as well as in three different anionic forms, i.e. H2SQ·HSQ−, HSQ− and SQ2−. Its interest for crystal engineering studies arises from three notable factors: (i) its ability of donating and accepting hydrogen bonds strictly confined to the molecular plane; (ii) the remarkable strength of the O—H...O bonds it may form with itself which are either of resonance-assisted (RAHB) or negative-charge-assisted [(−)CAHB] types; (iii) the ease with which it may donate a proton to an aromatic base which, in turn, back-links to the anion by strong low-barrier N—H+...O1/2− charge-assisted hydrogen bonds. Analysis of all the structures so far known shows that, while H2SQ can only crystallize in an extended RAHB-linked planar arrangement and SQ2− tends to behave much as a monomeric dianion, the monoanion HSQ− displays a number of different supramolecular patterns that are classifiable as β-chains, α-chains, α-dimers and α-tetramers. Partial protonation of these motifs leads to H2SQ·HSQ− anions whose supramolecular patterns include ribbons of dimerized β-chains and chains of emiprotonated α-dimers. The topological similarities between the three-dimensional crystal chemistry of orthosilicic acid, H4SiO4, and the two-dimensional one of squaric acid, H2C4O4, are finally stressed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768101014963
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  • 59
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    Digitale Medien
    4-{[(1E)-(2-Hydroxyphenyl)methylidene]amino}-1,5-dimethyl-2-phenyl-2,3-dihydro-1H-pyrazol-3-one (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 117-119 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: In the title compound, C18H17N3O2, a strong intramolecular O—H...N hydrogen bond [N...O 2.607 (3), O—H 0.97 (3) and H...N 1.71 (3) Å, and O—H...N 153 (2)°] was observed, which leads to a unique phenol–imine tautomerism in the solid state. The C=N imine bond distance and the C—N—C bond angle [1.287 (2) Å and 121.7 (1)°, respectively] indicate the existence of this phenol–imine tautomer. In solution, the phenol–imine tautomer of the title free Schiff base ligand is dominant in both polar and non-polar solvents, as supported by 1H NMR and UV–visible spectroscopic data.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270100015535
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  • 60
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    Digitale Medien
    A cationic hydroxo-bridged dinuclear gallium complex (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 143-144 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The crystal structure of μ-hydroxo-bis{[N-isopropyl-2-(isopropylamino)troponimino-N,N′](methyl)gallium(II)} tetrakis(pentafluorophenyl)borate (troponimine is 2,4,6-cycloheptatrien-1-imine), [Ga2(C14H22N2)2(OH)]B(C6H5)4, is discussed. The two (iPr2-ATI)GaMe (ATI is aminotroponimime) units of the dinuclear cation are linked by a bridging hydroxo group and are both slightly twisted from planarity.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270100013962
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  • 61
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    Digitale Medien
    (η2-Allylammonium)aquabis(sulfamato-N)copper(I) (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 151-153 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The CuI atom in the title complex, [Cu(NH2SO3)2(C3H8N)(H2O)], is coordinated by the C=C bond of the allylammonium cation, two N atoms of the sulfamate anions and the O atom of the H2O molecule in the apical position. Thus, the central atom is in a distorted trigonal–pyramidal environment. Strong N—H...O and O—H...O contacts connect separate moieties of the complex into a three-dimensional framework. The title compound is representative of hitherto unknown copper(I)–sulfamate π-complexes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270100016218
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  • 62
    Digitale Medien
    Digitale Medien
    Sodium scandium arsenate, Na3Sc2(AsO4)3 (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 2-3 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: Nasicon-type trisodium discandium tris(arsenate), Na3Sc2(AsO4)3, contains a polyhedral network of vertex-sharing octahedral ScO6 and tetrahedral AsO4 units [dav(Sc—O) = 2.089 (2) Å and dav(As—O) = 1.672 (2) Å] encapsulating two types of Na+ species. The sodium site occupancies are similar to those of the equivalent species in β-Na3Sc2(PO4)3.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S010827010001372X
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  • 63
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    Digitale Medien
    Absolute configuration of N-[(–)-2-(7-methoxy-1,2,3,4-tetrahydro-1-naphthyl)ethyl]cyclopropylcarboxamide, a highly potent and selective melatonin analogue (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 100-101 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The title compound, C17H23NO2, a tetrahydronaphthalenic analogue of melatonin, crystallizes in the monoclinic space group P21 with one molecule in the asymmetric unit. The crystal structure has been determined by X-ray analysis at room temperature. The absolute configuration of this compound was determined unambiguously as R at the chiral naphthalene C-1 position.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270100014724
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  • 64
    Digitale Medien
    Digitale Medien
    4,4′-Bipyridine dihydrate at 130 K (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 111-112 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The 4,4′-bipyridine molecules in the title compound, C10H8N2·2H2O, are stacked in the direction of the crystallographic b axis. These stacks are connected via O—H...N and O—H...O hydrogen bonds to form sheets which lie parallel to (100). Chains of O—H...O hydrogen-bonded water molecules are located between the bipyridine stacks. Altogether, four crystallographically independent water molecules and two crystallographically independent bipyridine molecules are involved.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270100014888
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  • 65
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    Digitale Medien
    3,3-Diphenyl-6-(p-toluenesulfonyl)-6-aza-3-silabicyclo[3.1.0]hexane (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 120-122 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The title compound, C23H23NO2SSi, at 100 K adopts a boat conformation which brings the C—H bond of an axial phenyl substituent into proximity [C...N = 3.376 (1) Å] with the aziridine lone pair. The factors which favour this conformation for bicyclo[3.1.0]hexane systems are considered.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270100015638
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  • 66
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    Digitale Medien
    The double-layered hydroxide 3CaO·Al2O3·0.5CaBr2·0.5CaCl2·10H2O (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 137-138 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The title compound, calcium oxide–dialuminium trioxide–calcium dibromide–calcium dichloride hydrate (3/1/0.5/0.5/10), also formulated as Ca2Al(OH)6Br0.478Cl0.522·2H2O (dicalcium aluminium hydroxide hemibromide hemichloride dihydrate), is a double-layered hydroxide which belongs to the solid solution Ca2Al(OH)6BrxCl1−x·2H2O, where x can vary from 0 to 1. Chloride and bromide anions of the negatively charged interlayer [Br0.5Cl0.5·2H2O]− share statistically the same crystallographic site. Al3+ and Ca2+ cations are coordinated by six and seven O atoms, respectively. All water molecules are bonded to Ca2+ cations and assume the seventh coordination position. Anions in the interlayer are surrounded by ten H atoms. Br− and Cl− are therefore connected to the main layer by ten hydrogen bonds, six of 2.74 (2) Å and four of 2.52 (5) Å, where the donors are hydroxyl groups and water molecules, respectively. Like the chloride equivalent, the title compound is a 6R polytype with trigonal space group R\overline 3c and lattice parameters a = 5.7537 (4) Å and c = 48.108 (4) Å.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270100014025
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  • 67
    Digitale Medien
    Digitale Medien
    Tetrathioureamercury(II) tetrathiocyanatomanganate(II) (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 145-146 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: In the title complex, [Hg(CH4N2S)4][Mn(NCS)4], the Hg and Mn atoms sit at special positions with \overline 4 symmetry and are tetrahedrally coordinated to four thiourea (TU) S and four thiocyanate (SCN) N atoms, respectively. The structure consists of discrete cationic and anionic [Hg(TU)4]2+ and [Mn(SCN)4]2− complexes, and weak NTU—H...SSCN hydrogen-bond bridges exist between these complexes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270100015651
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  • 68
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    Digitale Medien
    Dichloro[N,N,N′,N′-tetrakis(2-pyridylmethyl)benzene-1,4-diamine]iron(II) (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 156-157 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: In the title complex, [FeCl2(C30H28N6)], the Fe atom is five-coordinated by two terminal chloride ligands and one end of the bis-tridentate ligand. The complexes display intermolecular C—H...π, π-stacking and C—H...X (X = N, Cl) interactions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S010827010001684X
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  • 69
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    Digitale Medien
    Tetrakis(μ-2,3-dimethoxybenzoato)bis[(2,2′-bipyridine)(2,3-dimethoxybenzoato)lanthanum(III)] (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1048-1050 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The title compound, tetrakis(μ-2,3-dimethoxybenzoato)-κ4O:O′;κ6O,O′:O′-bis[(2,2′-bipyridine-N,N′)(2,3-dimethoxybenzoato-O,O′)lanthanum(III)], [La2(2,3-DMOBA)6(2,2′-bpy)2], where 2,3-DMOBA is 2,3-dimethoxybenzoate (C9H9O4) and 2,2′-bpy is 2,2′-bipyridine (C10H8N2), is a dimer with a centre of inversion between the La atoms bridged by four carboxylate ligands. The central La atom is ennea-coordinated and has a distorted monocapped square-antiprism geometry.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101009337
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  • 70
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    Digitale Medien
    Bis(2,4,7-trimethylindenyl)cobalt(II) and rac-2,2′,4,4′,7,7′-hexamethyl-1,1′-biindene (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1056-1059 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The crystal and molecular structures of bis(η5-2,4,7-trimethylindenyl)cobalt(II), [Co(C12H13)2], (I), and rac-2,2′,4,4′,7,7′-hexamethyl-1,1′-biindene, C24H26, (II), are reported. In the crystal structure of (I), the Co atom lies on an inversion centre and the structure represents the first example of a bis(indenyl)cobalt complex exhibiting an eclipsed indenyl conformation. The (1R,1′R) and (1S,1′S) enantiomers of the three possible stereoisomers of (II), which form as by-products in the synthesis of (I), cocrystallize in the monoclinic space group P21/c. In the unit cell of (II), alternating (1R,1′R) and (1S,1′S) enantiomers pack in non-bonded rows along the a axis, with the planes of the indenyl groups parallel to each other and separated by 3.62 and 3.69 Å.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S010827010100974X
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  • 71
    Digitale Medien
    Digitale Medien
    (1S)-(Z)-2-Benzyloxy-N-(3-methyl-1-butylidene)-1-phenylethylamine N-oxide (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1079-1080 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The preparation and crystal structure of the title compound, C20H25NO2, are described. The N atom substituent of the nitrone function adopts a conformation which minimizes the 1,3-allylic strain.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101009477
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  • 72
    Digitale Medien
    Digitale Medien
    Two intermediates in the synthesis of decahydroisoquinolines with NMDA and AMPA receptor antagonist activity (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1089-1091 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: In 6-methyl-N-(4-nitrobenzoyl)-5,6-dihydropyridin-2(1H)-one, C13H12N2O4, (I), the piperidone ring is in a distorted half-chair conformation. In 8-methoxy-3-methyl-N-(4-nitrobenzoyl)-1,2,3,4,5,6,7,8-octahydroisoquinoline-1,6-dione, C18H20N2O6, (II), the heterocyclic ring is in a slightly distorted half-boat conformation, while the other six-membered ring is in a distorted chair conformation. Compound (II) presents a strong intramolecular C—H...O hydrogen bond. In both (I) and (II), the molecules interact through C—H...O interactions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101009702
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  • 73
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    Digitale Medien
    X-ray powder structure of a new two-dimensional nickel(II) coordination polymer with pyrazine-2,3,5,6-tetracarboxylic acid (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1144-1146 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The new nickel(II) coordination polymer poly[diaquanickel(II)-μ-(pyrazine-2,3,5,6-tetracarboxylato)-tetraaquanickel(II)], {[{Ni(C8N2O8)(H2O)2}Ni(H2O)4]}n, has been synthesized and characterized both spectroscopically and crystallographically, by X-ray powder diffraction analysis. In this two-dimensional coordination polymer, NiII ions are bridged by pyrazine-2,3,5,6-tetracarboxylic acid, coordinating in a bis-bidentate manner, so forming one-dimensional polymeric chains. The chains are linked by a second NiII ion, via an O atom of the coordinated carboxylate group, resulting in the formation of a two-dimensional layer-like polymer. The remaining coordination sites of the two independent octahedral NiII ions are occupied by water molecules. The layers are connected via hydrogen bonds involving all six coordinated water molecules.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S010827010101068X
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  • 74
    Digitale Medien
    Digitale Medien
    A potassium–18-crown-6 salt of a cyclic myo-inositol phosphate (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1147-1148 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The six-membered phosphorinane ring in (1,4,7,10,13,16-hexaoxacyclooctadecane)potassium 2-O-benzoyl-1,3,5-O-methylidyne-myo-inositol 4,6-cyclophosphate trihydrate, [K(C12H24O6)](C14H12O9P)·3H2O, has a boat rather than a chair conformation. The K+ ion is eight-coordinate and is connected to one of the phosphate O atoms, one of the O atoms of the myo-inositol residue and the six O atoms of the crown ether.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101011222
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  • 75
    Digitale Medien
    Digitale Medien
    4-Iodo-2-methyl-5-nitroaniline exhibits neither strong hydrogen bonding nor intermolecular I...nitro interactions (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1212-1214 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: In the title compound, C7H7IN2O2, the O atoms of the nitro group are disordered over two sets of sites and there is evidence that the intramolecular I...nitro interaction is repulsive. In the crystal structure, there are neither strong hydrogen bonds, nor intermolecular I...nitro interactions, nor aromatic π–π-stacking interactions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101013373
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  • 76
    Digitale Medien
    Digitale Medien
    The methanol hemisolvate of amiloride hydrochloride (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1217-1219 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: In the asymmetric unit of N-(3,5-diamino-6-chloropyrazin-2-ylcarbonyl)-N-(diaminomethylene)ammonium chloride methanol hemisolvate, C6H9ClN7O+·Cl−·0.5CH4O, there are two crystallographically different amiloride molecules. Crystallographically identical amiloride molecules are stacked one above the other, alternately rotated by 180°. These stacks are arranged parallel to each other, forming layer A. The least-squares plane of the non-H atoms of the other molecules lying in layer B is tilted against the corresponding plane of the molecules in layer A by an angle of 79.89 (3)°. The methanol molecules and Cl− anions are located between these layers, although the methanol molecules are closer to layer A.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101012550
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  • 77
    Digitale Medien
    Digitale Medien
    5-Nitro-2-nitromethyl-2H-1,2,3,4-tetrazole (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1101-1102 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The molecule of the title compound, C2H2N6O4, consists of three planar fragments, namely a tetrazole ring, a nitromethyl group and a nitro group. The nitro group and the tetrazole cycle are arranged in the same plane, but the planar nitromethyl group is located nearly orthogonal to this plane. The molecules are packed in the crystal via van der Waals interactions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101010125
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  • 78
    Digitale Medien
    Digitale Medien
    Ethyl 6-amino-2-methoxypyridine-3-carboxylate, interplay of molecular and supramolecular structure (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1103-1105 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The title compound, C9H12N2O3, crystallizes with two molecules in the asymmetric unit. There is extensive hydrogen bonding which results in the formation of a two-dimensional corrugated sheet. This supramolecular structure is determined by the formation of hydrogen-bonded chains resulting from the presence of a 6-amino group and an ethoxycarbonyl group as substituents on a pyridine ring in relative para positions which constitute a π-electron `push–pull' system.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101010228
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  • 79
    Digitale Medien
    Digitale Medien
    1,3,5-Triiodo-2,4,6-trimethylbenzene at 293 K (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1106-1108 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: In the structure of triiodomesitylene (1,3,5-triiodo-2,4,6-trimethylbenzene), C9H9I3, at 293 K, the benzene ring is found to be significantly distorted from ideal D6h symmetry; the average endocyclic angles facing the I atoms and the methyl groups are 123.8 (3) and 116.2 (3)°, respectively. The angle between the normal to the molecular plane and the normal to the (100) plane is 5.1°. No disorder was detected at 293 K. The thermal motion was investigated by a rigid-body motion tensor analysis. Intra- and intermolecular contacts are described and topological differences compared with the isomorphous compounds trichloromesitylene and tribromomesitylene are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101010113
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  • 80
    Digitale Medien
    Digitale Medien
    Polysulfonylamines. CXLV.N-Diethylcarbamoyl-o-benzenedisulfonimide, a urea with non-planar geometry at nitrogen and an amide single bondPart CXLIV: Moers, Blaschette & Jones (2001a). (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1109-1111 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The prominent features in the molecular structure of the title compound (alternative name: 2-diethylcarbamoyl-1,1,3,3-tetraoxo-1,3,2-benzodithiazole), C11H14N2O5S2, arise in the urea moiety S2N—C(O)—N′C2: the sum of the angles at N is 332.3 (1)°, the N—C(O)—N′C2 unit is planar, and distances N—C(O) = 1.494 (3) Å, N′—C(O) = 1.325 (2) Å and C—O = 1.215 (2) Å. The molecules are associated via five C—H...O hydrogen bonds to form layers parallel to the yz plane. This compound and its dimethyl homologue, which were synthesized by treating the silver salt of o-benzenedisulfonimide with carbamoyl chlorides, are prone to rapid hydrolysis at the weak N—C(O) bond. For both molecules, the rotational barrier about the partial N′—C(O) double bond is ca 50 kJ mol−1 at 250 K (from dynamic 1H NMR experiments).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101010605
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  • 81
    Digitale Medien
    Digitale Medien
    X-ray investigations of sulfur-containing fungicides. IV.Part III: Wolf (2001b).4′-{[Benzoyl(4-chlorophenylhydrazono)methyl]sulfonyl}acetanilide and 4′-{[benzoyl(4-methoxyphenylhydrazono)methyl]sulfonyl}acetanilide (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1112-1115 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The conformations of the two approximately isomorphous structures 4′-{[benzoyl(4-chlorophenylhydrazono)methyl]sulfonyl}acetanilide, C22H18ClN3O4S, and 4′-{[benzoyl(4-methoxyphenylhydrazono)methyl]sulfonyl}acetanilide, C23H21N3O5S, are stabilized by resonance-assisted intramolecular hydrogen bonds linking the hydrazone moieties and sulfonyl groups. The stronger bond is observed in the former compound. The difference in electronic properties between the Cl atom and the methoxy group is too small to significantly alter the non-bonding interactions of the sulfonyl and β-carbonyl groups.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101010642
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  • 82
    Digitale Medien
    Digitale Medien
    Methyl (SR)-10-chloro-1,2,3,4,5,6-hexahydro-6-hydroxy-8-methoxy-1-methyl-1,9-phenanthroline-6-carboxylate (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1116-1117 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: In the title compound, C16H19ClN2O4, the pyridine ring is nearly planar, the piperidine ring is non-planar and the cyclohexane ring adopts a screw-boat conformation. The carboxylate group makes a dihedral angle of 80.9 (2)° with the least-squares plane through the cyclohexane ring.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101010770
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  • 83
    Digitale Medien
    Digitale Medien
    1,4-Methano-11a-methyl-4,4a,11,11a-tetrahydro-1H-benzo[b]fluoren-11-one (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1118-1119 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The title compound, C19H16O, crystallizes with two molecules of opposite chirality in the asymmetric unit. In both molecules, the naphthalene and cyclopentanone moieties are individually planar. The two cyclopentane rings adopt envelope conformations, while the cyclohexane ring adopts a boat conformation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101010976
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  • 84
    Digitale Medien
    Digitale Medien
    Melaminium chloride hemihydrate (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1120-1122 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The crystals of a new melaminium salt, 2,4,6-triamino-1,3,5-triazin-1-ium chloride hemihydrate, C3H7N6+·Cl−·0.5H2O, are built up from single-protonated melaminium residues, chloride anions and water molecules. The protonated melaminium cations lie on a twofold axis, while the chloride anions and water molecule lie on the m plane. The melaminium residues are interconnected by N—H...N hydrogen bonds, forming chains parallel to the (001) plane. The chains of melaminium residues form a three-dimensional network through hydrogen-bond interactions with chloride anions and water molecules.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101011283
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  • 85
    Digitale Medien
    Digitale Medien
    Alkaline metal oxoantimonates(III), A3[SbO3] (A = K or Cs) (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1127-1128 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The two title trialkaline trioxoantimonates(III), tripotassium trioxoantimonate(III), K3[SbO3], (I), and tricaesium trioxoantimonate(III), Cs3[SbO3], (II), crystallize in the cubic Na3[AsS3] structure type in space group P213. The structures show discrete Ψ-tetrahedral [SbO3]3− anions with C3v point-group symmetry. The Sb—O distances are 1.923 (4) Å in (I) and 1.928 (2) Å in (II), and the O—Sb—O bond angles are 99.5 (2)° in (I) and 100.4 (1)° in (II).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101006230
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  • 86
    Digitale Medien
    Digitale Medien
    Cyclic lipoundecapeptide amphisin from Pseudomonas sp. strain DSS73 (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1123-1124 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The crystal structure of the lipoundecapeptide amphisin, presented here as the tetrahydrate, C66H114N12O20·4H2O, originating from non-ribosomal biosynthesis by Pseudomonas sp. strain DSS73, has been solved to a resolution of 0.65 Å. The primary structure of amphisin is β-hydroxydecanoyl-D-Leu-D-Asp-D-allo-Thr-D-Leu-D-Leu-D-Ser-L-Leu-D-Gln-L-Leu-L-Ile-L-Asp (Leu is leucine, Asp is aspartic acid, Thr is threonine, Ser is serine, Gln is glutamine and Ile is isoleucine). The peptide is a lactone, linking Thr4 Oγ to the C-terminal. The stereochemistry of the β-hydroxy acid is R. The peptide is a close analogue of the cyclic lipopeptides tensin and pholipeptin produced by Pseudomonas fluorescens. The structure of amphisin is mainly helical (310-helix), with the cyclic peptide wrapping around a hydrogen-bonded water molecule. This lipopeptide is amphiphilic and has biosurfactant and antifungal properties.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101010782
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  • 87
    Digitale Medien
    Digitale Medien
    A new crystalline phase of nitric acid dihydrate (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1129-1131 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The crystal structure of a new high-temperature phase of nitric acid dihydrate, HNO3·2H2O, has been determined at 225 K by single-crystal X-ray diffraction. The H atom of the nitric acid is delocalized to one water molecule, leading to an association of equimolar NO3− and H5O2+ ionic groups. The asymmetric unit contains two molecules of HNO3·2H2O. The two independent molecules are related by a pseudo-twofold c axis, by a translation of 0.54 (approximately ½) along b, with a mean atomic distance difference of 0.3 Å, except for one H atom of the water molecules (1.5 Å), because of their different orientations in the two molecules. The two independent molecules, linked by strong hydrogen bonds, are arranged in layers. These layers are linked by weaker hydrogen bonds oriented approximately along the c axis. A three-dimensional hydrogen-bond network is observed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101010101
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  • 88
    Digitale Medien
    Digitale Medien
    A comparison of 2,7-dihydro-2,2,7,7-tetramethyl-3,6-diphenyl-1,4,5-thiadiazepine and the corresponding 1,1-dioxide (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 431-432 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The structures of the highly substituted title heterocycles, C20H22N2S and C20H22N2O2S, have been determined at 123 (1) K. Both molecules possess exact C2 symmetry and the seven-membered rings have very similar twist-boat conformations. The magnitudes of the C—S—C bond angles, 107.13 (6) and 108.27 (7)°, respectively, are influenced significantly by the four substituent methyl groups on the seven-membered rings.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270100020564
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  • 89
    Digitale Medien
    Digitale Medien
    3-(1-Hydroxyethylidene)-1-phenylpyrrolidine-2,4-dione (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 433-434 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: Analysis of C12H11NO3 revealed a coplanar N-substituted phenyl group on a pyrrolidine ring with two keto moieties and a hydroxyethylidene functionality. The hydroxy group forms part of a hydrogen-bonding network characterized by a short intramolecular H...O distance of 1.81 (3) Å, and a longer intermolecular interaction with an H...O distance of 2.38 (3) Å. Both keto groups form additional intra- and intermolecular C—H...O contacts with H...O distances ranging from 2.26 to 2.41 Å.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270100020758
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  • 90
    Digitale Medien
    Digitale Medien
    Anti-inflammatory drugs. IX. Hydrated diethylammonium [2-(2,6-dichlorophenylamino)phenyl]acetate (HDEA·D·H2O)Part VIII: Castellari, Comelli & Ottani (1999). (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 437-438 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: In the solid-state structure of the title compound, C4H12N+·C14H10Cl2NO2−·H2O, the asymmetric unit contains one cation, one anion and a water molecule. A complex network of hydrogen bonds is present. A comparison is made with the structure of the anhydrous salt.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S010827010002076X
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  • 91
    Digitale Medien
    Digitale Medien
    Complexes of AgI with cationic ligands: bis[(pyridylmethyl)ammonio]silver(I) salts (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1162-1165 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: Bis[(2-pyridylmethyl)ammonio]silver(I) trinitrate, [Ag(C6H9N2)2](NO3)3, (I), and bis{bis[(4-pyridylmethyl)ammonio]silver(I)} hexakis(perchlorate) dihydrate, [Ag(C6H9N2)2]2(ClO4)6·2H2O, (II), are rare examples of complexes with cationic ligands. In (I), the Ag+ cation has a T-shaped [2+1] coordination involving the pyridine N atoms and a nitrate O atom, while in (II) there are three independent two-coordinate Ag complex cations (two with the Ag atoms on independent inversion centres) and disordered ClO4− ions. The crystal structures reveal the role of hydrogen bonding in stabilizing these complexes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101012380
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  • 92
    Digitale Medien
    Digitale Medien
    Diaquabis(ethylenediamine)copper(II) bis[tris(ethylenediamine)nickel(II)] tris(naphthalene-2,6-disulfonate) tetrahydrate (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1168-1170 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The title mixed-metal compound, [Cu(C2H8N2)2(H2O)2][Ni(C2H8N2)3]2(C10H6O6S2)3·4H2O, was obtained during investigations of the porous frameworks constructed by amino-coordinated metal complex cations and large organic anions. All three naphthalene-2,6-disulfonate anions and the [Cu(en)2(H2O)2]2+ cation are located on crystallographic inversion centers and assemble into an extended two-dimensional network through intermolecular hydrogen bonds, creating cavities in which the [Ni(en)3]2+ cations and water molecules are included.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101013324
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  • 93
    Digitale Medien
    Digitale Medien
    Short intramolecular S...O interactions in S-substituted 2-mercaptoacetophenones (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1174-1176 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The non-bonded S...O intramolecular interactions in the title compounds 2-(phenylthio)acetophenone {IUPAC: 2-[2-(phenylsulfanyl)phenyl]ethanone}, C14H12OS, and 2-(benzylthio)acetophenone {IUPAC: 2-[2-(benzylsulfanyl)phenyl]ethanone}, C15H14OS, are unusually short, indicating the contribution of heterocyclic oxathiole-type resonance structures to the overall bonding.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101008216
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  • 94
    Digitale Medien
    Digitale Medien
    Azole. 47.Teil 46: Bernard (2001). Über 3-Thiomorpholino- und 3-(4-Methylpiperazino)-5-nitroindazole (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1189-1191 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The structures of 5-nitro-3-thiomorpholino-1H-indazole, C11H12N4O2S, (IIa), and 3-(4-methylpiperazino)-5-nitro-1H-indazole–methanol–water (2/1/1), 2C12H15N5O2·CH3OH·H2O, (IIIa), are described. In the crystal lattice of (IIa), the molecules are linked into dimers by N—H...N hydrogen bonds. The asymmetric unit of (IIIa) contains two independent molecules of the indazole moiety, one molecule of methanol and one of water. The three components of (IIIa) are linked by hydrogen bonds to form double chains running along the x axis. π-Stacking involving the indazole moieties occurs in both compounds.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101011027
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  • 95
    Digitale Medien
    Digitale Medien
    Hydrogen bonding in the inner-salt zwitterion and in two different charged forms of 5,6-bis(2-pyridyl)pyrazine-2,3-dicarboxylic acid (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1184-1188 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: 5,6-Bis(2-pyridyl)pyrazine-2,3-dicarboxylic acid exists as an inner-salt zwitterion, 3-carboxy-5-(2-pyridinio)-6-(2-pyridyl)pyrazine-2-carboxylate, (Ia), C16H10N4O4. The adjacent pyridine and pyridinium rings are almost coplanar due to the presence of an intramolecular hydrogen bond involving the pyridine N atom and the NH H atom of the pyridinium group. In the crystal of (Ia), symmetry-related molecules are hydrogen bonded via the carboxylic acid OH group and one of the carboxylate O atoms to form a polymer, which exhibits a channel-type structure. In the HCl, HClO4 and HPF6 salts, 6-carboxy-5-carboxylatopyrazine-2,3-diyldi-2-pyridinium chloride 2.25-hydrate, (II), C16H11N4O4+·Cl−·2.25H2O, 6-carboxy-5-carboxylatopyrazine-2,3-diyldi-2-pyridinium perchlorate trihydrate, (IIIa), C16H11N4O4+·ClO4−·3H2O, and 6-carboxy-5-carboxylatopyrazine-2,3-diyldi-2-pyridinium hexafluorophosphate trihydrate, (IIIb), C16H11N4O4+·PF6−·3H2O, both pyridine rings are protonated. In the perchlorate form, and in the isomorphous hexafluorophosphate form, the molecule possesses C2 symmetry, with has a symmetrical intramolecular hydrogen bond involving the adjacent carboxylate and carboxylic acid substituents. In the crystals of the chloride and perchlorate (or hexafluorophosphate) salts, hydrogen-bonded polymers are formed which are three-dimensional and one-dimensional, respectively.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101010757
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  • 96
    Digitale Medien
    Digitale Medien
    Hexahydroxybenzene–2,2′-bipyridine (1/2) (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1194-1195 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: 2,2′-Bipyridine (2BPY) and hexahydroxybenzene (HHB) crystallize in a 2:1 ratio as a neutral molecular adduct, C6H6O6·2C10H8N2, in space group P\overline 1 with Z = 1 and with the HHB molecule lying on an inversion centre. HHB, of which this is the first single-crystal X-ray structure determination, forms O—H...O hydrogen-bonded chains parallel to the a axis, with O...O distances of 2.761 (1) and 2.782 (1) Å. O—H...N hydrogen bonds to the 2BPY molecules crosslink these chains, with O...N distances of 2.707 (1) and 2.735 (1) Å.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101011350
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  • 97
    Digitale Medien
    Digitale Medien
    Cinnamoyl shikoninCDRI Communication No. 6153. (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1199-1200 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The title compound, 1-(5,8-dihydro-1,4-dihydroxy-5,8-dioxo-2-naphthyl)-4-methylpent-3-en-1-yl cinnamate, C25H22O6, crystallizes in space group P21. The phenyl ring of the cinnamate is anti to the carbonyl group of the same moiety [C—C—C—C = −175.6 (2)°] and is nearly parallel to the naphthyl ring system. Two six-membered rings formed by intramolecular hydrogen bonds, with O—H...O distances of 2.587 (2) and 2.589 (2) Å, occur on either side of the fused ring system, creating a tetracyclic pyrene-shaped system. The phenyl ring forms an intermolecular stack with the benzoquinone ring, as a result of aromatic π–π interactions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101011842
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  • 98
    Digitale Medien
    Digitale Medien
    4-Nitro-2-(1H-tetrazol-1-yl)phenol (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1204-1206 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: There are two symmetry-independent molecules in the unit cell of the title compound, C7H5N5O3. The tetrazole and phenyl rings are essentially planar and are not coplanar in either molecule [dihedral angles 30.2 (1) and 7.0 (1)°]. In the structure, four molecules are connected by O—H...N bridges, forming four-membered molecular aggregates which are linked together by a complex three-dimensional hydrogen-bond network.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101012100
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  • 99
    Digitale Medien
    Digitale Medien
    Hydrogen bonding in C-methylated nitroanilines: a room-temperature monoclinic polymorph of 4-methyl-3-nitroaniline with Z′ = 2 (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1207-1208 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The title compound, C7H8N2O2, is monoclinic (space group P21/n) at 295 (2) K with Z′ = 2. The two types of molecule form independent C(7) chains, and the structure is related to that of the low-temperature triclinic polymorph, where Z′ = 4 in P\overline 1, by a simple displacive transformation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270101012185
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  • 100
    Digitale Medien
    Digitale Medien
    Design of peptides with α,β-dehydro residues: a dipeptide with a branched β-carbon dehydro residue at the (i+1) position, methyl N-(benzyloxycarbonyl)-α,β-didehydrovalyl-L-tryptophanate (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1220-1221 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The structure of the title peptide, C25H27N3O5, has been determined and its conformation analysed. Values of the standard peptide torsion angles are φ1 = −44.2 (3)°, ψ1 = 135.9 (2)°, φ2 = −141.6 (2)° and ψ2T = 168.0 (2)°. The crystal structure is stabilized by an intermolecular hydrogen bond, with an N...O distance of 2.919 (3) Å, which is formed between screw-axis-related NH and CO groups of dehydrovaline residues.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S010827010100840X
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