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  • 1
    ISSN: 1572-8854
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The crystal structure of tris(N,N-di-n-butyldiselenocarbamato)nickel(IV) bromide, Ni(Se2CN-(C4H9)2)3Br, has been determined by three-dimensional X-ray methods. The Laue symmetry is 6/mmm, but the structure could be solved only in space groupP¯31c. The crystals were, therefore, regarded as being microtwinned on (001). The unit cell dimensions area =b = 14·69(3) andc = 10·91(3) Å. From integrated Weissenberg photographs, 307 non-zero symmetry-independent reflexions were measured photometrically. The structural parameters were refined by least-squares methods to a conventionalR factor of 0·10. The quadrivalent nickel atom is octahedrally coordinated by six selenium atoms. The Ni-Se distance is 2·391(5) Å; the Se-Se distance within one diselenocarbamate ligand is 3·00(1) Å; Se-Se distances between different ligands are 3·51(1), 3·52(1) and 3·55(1) Å.
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  • 2
    ISSN: 1572-8854
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Analysis of X-ray counter data for the dihydrogen hexafluorosilicate monohydrates ofp-bromoaniline, BrC6H4NH2.1/2H2SiF6.H2O, andp-toluidine, CH3C6H4NH2.1/2H2SiF6.H2O, has shown that the two compounds are isostructural and that the orthorhombic crystals belong to the space groupPbca, witha = 7·80,b = 24·45,c = 9·48 Å anda = 7·89,b = 23·87,c = 9·53 Å, respectively, there being eight molecules in each unitcell. Structure analysis was initiated by the heavy atom method, and subsequent difference syntheses, carried out on thep-bromoaniline compound, then on thep-toluidine analogue, revealed the entire structure apart from the hydrogen atoms. From a difference synthesis on data for thep-toluidine compound refined by full-matrix least-squares procedures, the hydrogen atom sites were located, a reliability index,R = 0·052, being attained. The structures are sheet-like with bi-polar grouping of amino groups on either side of sheets of SiF 6 2− groups and are cross-linked by ionic forces and hydrogen bonds. The SiF 6 2− ion is octahedral, with an average Si-F distance of 1·69 ± 0·02 Å.
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  • 3
    ISSN: 1572-8854
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The crystal and molecular structure ofcis-dicarbonyltetraphosphinechromium(O), [(CO)2(PH3)4Cr] has been determined by X-ray diffraction methods. The compound crystallizes in the monoclinic system: space groupC2/c,a = 6·968(6),b = 11·98(1),c = 12·87(1) Å, β = 99·80(8) °,V= 1059(3) Å3,Z=4,D m = 1·534(5),D x = 1·531(5) gcm−3, diffraction symmetry 2/m. The structure was solved by conventional methods, and refined by least-squares techniques to an agreement factorR = 0·078. The chromium atoms lie on rotation diads, and thus the molecules must have at least the symmetry 2(C 2); they were found to have, within the limits of accuracy, the even higher symmetrymm2 (C 2v ). There are two distinct independent Cr-P distances in the molecule, the Cr-P bonds where phosphorus istrans to carbonyl [2·338(4) Å] being significantly longer than those where phosphorus istrans to phosphine [2·282(4) Å]. This difference may be attributed to a difference in the back-bonding capabilities of the two types of ligands.
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  • 4
    ISSN: 1572-8854
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The crystal and molecular structure of (2,2′-bipyridine) pyridine tricarbonyl molybdenum (III), [(C10H8N2)(C5H5N)(CO)3Mo], has been determined from three-dimensional data collected photographically. The space group isPnam; the unit cell has the dimensionsa = 14·755 ±1,b = 8·344 ± 1,c = 13·733 ± 1 Å (at 20 °C) and contains four molecules. The structure has been refined to a residual (R) of 0·073 using least-squares methods on 1394 independent non-zero reflexions. The molecule has been found to be octahedral in arrangement, with bipyridine and pyridine forming one triangle and the three carbonyl groups forming the opposite triangle of the octahedron. The best fit plane through the pyridine and lower carbonyl groups make an angle of 78 ° with the equatorial plane. There is evidence of significant distortion from the ideal octahedral angles of 90 °. Within the molecule, no interatomic distance or bond angle departs significantly from accepted values.
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  • 5
    ISSN: 1572-8854
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
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  • 6
    ISSN: 1572-8854
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The crystal structure of Dy(thd)3H2O has been solved by three-dimensional X-ray methods at room temperature. The space group isP¯1 and the cell dimensions area = 14·21(1),b = 14·88(2),c = 11·60(2) Å, α = 99·76(3), β = 109·91(1), γ = 114·08(1) °.Z = 2,D m = l·24 andD x = 1·238 gcm−3, respectively. Full-matrix least-squares refinement of atomic and individual isotropic thermal parameters, using 3015 intensities obtained by counter methods, terminated with a conventionalR of 0·058. The oxygen polyhedron around dysprosium has pure seven-coordination geometry, the seventh ligand being the water molecule. The water is hydrogen bonded to two oxygen atoms of a centre of symmetry related formula unit so that two formula units are in fact held together by hydrogen bonds in a dimer.
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  • 7
    ISSN: 1572-8854
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The crystal and molecular structure of diiodo-N,N,N′,N′-tetramethylthiuramdisulphidemercury(II), HgI2(S2CN(CH3)2)2, has been determined by a three-dimensional X-ray analysis. The compound crystallizes in the monoclinic space groupP21/c with the unit cell dimensionsa = 7·957 ± 4,b = 22·639 ± 7,c = 9·956 ± 6 Å and β = 112·14 ± 5 °;Z = 4. Intensities were obtained with an automatic diffractometer. The structural parameters were refined by least-squares methods to a conventionalR factor of 0·044 for 1294 non-zero observed reflexions. The mercury is in distorted tetrahedral coordination with two iodine and two sulphur atoms. The Hg-I distances are 2.654 ± 2 and 2·661 ± 2 Å; the Hg-S distances are 2·651 ± 7 and 2·882 ± 7 Å. The thiuramdisulphide ligand consists of two planar units S2CNC2, nearly perpendicular to each other. Bond distances of the ligand are compared with distances in tetraalkylthiuram disulphide molecules and agree with infrared observations.
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  • 8
    Electronic Resource
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    Springer
    Journal of chemical crystallography 1 (1971), S. 103-104 
    ISSN: 1572-8854
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
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  • 9
    ISSN: 1572-8854
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Irradiation of uracil in ice produces a small quantity of thecis-anti cyclobutyl type photodimer. The molecule contains a pseudo two-fold axis and a cyclobutyl ring which is puckered, with dihedral angles near 150°. Torsion angles about the C(5)-C(6′) and C(5′)-C(6) bonds are 21°. Each uracil residue has seven atoms which are coplanar to within 0-07 Å, while C(6) and C(6′) are 0·38 Å and 0·35 Å out of the planes of their respective residues. Each molecule participates in eight NH...O bonds which range from 2·83 to 2·97 Å. The material crystallizes in the triclinic space group P¯1 with unit cell parametersa = 8·594 Å,b = 7·478 Å,c = 6·915 Å, α = 96·9 °, β = 95·4 ° and γ = 85·5 °. The structure was solved by means of the symbolic addition procedure for phase determination.
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  • 10
    ISSN: 1572-8854
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract This is the first reported structure analysis of a cyclobutyl type photodimer obtained from the irradiation of thymine, uracil or its derivatives which contains water in the crystal lattice. Thecis-syn 6-methyluracil photodimer. H2O gives anomalous nmr and ir spectral data which may correlate with the crystal structure. The material crystallizes in space groupP21/a with unit cell parametersa = 15·58 Å,b = 11·33 Å,c = 7·28 Å and β = 107·2 °. Channels are formed in the crystal lattice which contain the H2O molecules. Each H2O molecule participates in hydrogen bonding to three different dimer molecules. The puckered cyclobutyl ring is significantly flatter than in the anhydrouscis-syn uracil photodimer and differences in the configurations of the uracil residues occur. The structure was solved by means of the symbolic addition procedure.
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