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  • International Union of Crystallography (IUCr)  (39)
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  • 1
    Electronic Resource
    Electronic Resource
    Lattice energy calculations for (C6H5)5M0.5C6H12, M = P, As and Sb: towards an understanding of crystal packing in the pentaphenyl group V compounds (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 898-902 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Semi-empirical calculations of the energy due to intermolecular interactions have been made for crystals of (C6H5)5M. ½C6H12, M= P, As, and Sb. This energy has been calculated as a pairwise sum over nonbonded atoms; energy minimizations have been performed with respect to the unit-cell parameters and molecular positions and orientations. Two sets of potential functions including repulsive and van der Waals terms have been employed; one of the sets also contains r-1 (Coulombic) contributions to the energy. The experimentally determined structures of the arsenic and antimony compounds have been well reproduced, as has the disorder observed for the solvent molecule in the former; it is suggested that this disorder is also present in the latter crystal. A comparison of the energies calculated for these solvates with those computed previously for unsolvated species predicts the stability of (C6H5)5P.½C6H12, for which no crystallographic data have been previously reported. Crystals of this compound have now been identified. These comparisons also show the relative lattice energies of the three possible crystal structures seen in this system (Cc, P{\bar 1}, and the P{\bar 1} cyclohexane solvate considered here) to be the same for all three molecules, suggesting that the molecular packing is not greatly affected by a change in the central group V atom.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739477002204
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  • 2
    Electronic Resource
    Electronic Resource
    The role of crystal packing forces in the structure of pentaphenylantimony (1976)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 32 (1976), S. 38-42 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Pentaphenylantimony, (C6H5)5Sb, possesses square-pyramidal, rather than the expected trigonal-bipyramidal geometry in the solid state; an attempt has been made to determine whether the observed conformation results from crystal packing forces. A semi-empirical strain-energy minimization procedure has been used in which the energy is taken as a sum of bond and angle deformation terms and of repulsive and van der Waals interactions between non-bonded atoms. The phenyl rings were treated as rigid bodies having D6h symmetry. Calculations of intramolecular and lattice energies were made for (C6H5)5Sb as observed in the crystal and for a hypothetical trigonal-bipyramidal molecule and crystal structure derived from data on (C6H5)5P and (C6H5)5As. Comparisons show that intermolecular forces favor the square-pyramidal crystal structure by 4.6 kJ/mole but that intramolecular interactions favor trigonal-bipyramidal molecular geometry by 30.5 kJ/mole. We suggest that the failure to predict the experimentally observed structure may result from the neglect of Coulombic interactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739476000065
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  • 3
    Electronic Resource
    Electronic Resource
    The role of Coulombic interactions in explaining the anomalous structure of pentaphenylantimony (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 193-197 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The observation of anomalous square-pyramidal geometry for pentaphenylantimony, (C6H5)5Sb, has long been rationalized as a packing effect. The analogous P and As molecules are trigonal-bipyramidal in the solid state as expected. In this work calculations have been made of the energies resulting from intra- and intermolecular nonbonded interactions in both observed and hypothetical crystal structures of square-pyramidal and trigonal-bipyramidal pentaphenylantimony, pentaphenylarsenic, and pentaphenylphosphorus in order to determine if the solid state does indeed stabilize a non-equilibrium molecular geometry of (C6H5)5Sb, and if so, how much energy is involved. The energies have been taken as pairwise sums over nonbonded atoms; the atom-atom potential functions used include repulsive, van der Waals, and Coulombic terms. Results of these calculations have been compared with work in which the potential functions did not include such 1/r terms. Both observed and hypothetical structures of all three molecules lie in true minima of the energy surface with respect to variations in cell constants and molecular position and orientation whether or not electrostatic terms are included. However, only the potential functions with Coulombic terms predict the crystallization of pentaphenylantimony as a square pyramid. The lattice-energy stabilization is then calculated to be about 15 kJ mol-1
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739477000394
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  • 4
    Electronic Resource
    Electronic Resource
    A steroid derivative that crystallizes with three molecules in the asymmetric unit (1994)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 50 (1994), S. 434-438 
    Details
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108270193009230
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  • 5
    Electronic Resource
    Electronic Resource
    Planarity of nitro-substituted phenothiazines (1996)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 52 (1996), S. 713-719 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The structures of three nitro-substituted phenothiazines [1,3,4-trifluoro-2-nitrophenothiazine, 10-(4-chlorobutyl)-1,3,4-trifluoro-2-nitrophenothiazine and 10-(4-chlorobutyl)-3-nitrophenothiazine] have been determined. The first of these red compounds forms infinite stacks in the solid state, in which donor and acceptor regions of the approximately planar molecules alternate. The molecules of the other two compounds, which have folded, or `butterfly', conformations in the solid state, do not form stacks, presumably because the bulky chlorobutyl substituents cannot be accommodated. The very dark color of solid 3-nitrophenothiazine suggests the presence of extended molecular stacks, but crystals suitable for a structure determination could not be obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768196000201
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  • 6
    Electronic Resource
    Electronic Resource
    (S,S)-trans-2,3-Tetralindiol (1998)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 54 (1998), S. 1486-1488 
    Details
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S010827019800537X
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  • 7
    Electronic Resource
    Electronic Resource
    2:1 Adducts of Halotris(p-tolyl)tin(IV) with 1,9-Bis(4-oxopent-2-en-2-ylamino)-3,7-dithianonane (1998)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 54 (1998), S. 1618-1622 
    Details
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108270198006209
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  • 8
    Electronic Resource
    Electronic Resource
    Retention of -4 Symmetry in Compounds Containing MAr4 Molecules and Ions (1997)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 53 (1997), S. 780-786 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A search of the Cambridge Structural Database shows that MAr4 molecules usually retain the low-energy \overline 4 conformation in the crystal. MAr^{q}_{4} ions also usually occupy sites if the counterion can conform to \overline 4 (or higher) symmetry. The ability of the aryl groups to fit well around an empty \overline 4 site is crucial to the symmetry retention. Molecules (and ions) in the tetragonal structures pack in columns that parallel the c axis; the columnar cross sections are approximately square. Aryl groups in adjacent columns can interleave to form a sort of herringbone arrangement. The tetragonal packing of columns is sufficiently favorable that it sometimes occurs even if the molecules must be disordered. The columnar motif is also found in some lower-symmetry structures of MAr4 molecules and MAr^{q}_{4} ions; these structures may be pseudosymmetric.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768197005089
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  • 9
    Electronic Resource
    Electronic Resource
    Temperature Dependence of the Rigid-Body Motion of Anthraquinone (1998)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 54 (1998), S. 308-315 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Anthraquinone has been studied at five temperatures between 296 and 162 K. The unsatisfactory agreement factors obtained in earlier studies probably resulted from the use of data collected from twinned crystals; needle-like crystals with approximately equidimensional cross sections are usually contact twins related by reflection across (102¯). The temperature dependence of the T and L tensors is normal. The out-of-plane displacement parameters of the O atom indicate a large-amplitude internal vibration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768197013414
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  • 10
    Electronic Resource
    Electronic Resource
    4-Bromobiphenyl; an ordered crystal with a structure similar to that of biphenyl (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 968-971 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567740880005043
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