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  • 76.60.Es  (3)
  • crystal structure  (2)
  • 33.20.K  (1)
  • ATOMIC AND MOLECULAR PHYSICS
  • Biochemistry and Biotechnology
  • Crystal structure
  • General Chemistry
  • 1990-1994  (6)
Collection
Keywords
Publisher
Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    Redetermination of the cobaltocene crystal structure at 100 K and 297 K: Comparison with ferrocene and nickelocene (1993)
    Springer
    Structural chemistry 4 (1993), S. 91-101 
    Details
    ISSN: 1572-9001
    Keywords: Cobaltocene ; molecular geometry ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The molecular and crystal structures of the monoclinic modification of cobaltocene Cp2Co (P21/n, Z=2) was determined at 100 K and 297 K with new sets of X-ray diffraction data (MoKα radiation, 3995 and 6534 reflections, refinement toR = 0.026 and 0.030 using 1061 and 1299 independent observable reflections, respectively). At 297 K the structure is disordered (similar to the isomorphous ferrocene and nickelocene) with two distinct orientations of the ring, differing in occupancy factors (80% and 20%) and by a rotation angle in the ring plane of approximately 34°. Just as for nickelocene but in contrast to ferrocene, no sharp phase transition was found on cooling Cp2Co to 100 K, but an essential ordering of the Cp-ring position was detected with a decrease of the contribution of the second minor orientation to nearly 10%. On the basis of a careful analysis of the molecular geometry, crystal packing, and anisotropic atomic displacement parameters, a dynamic temperature-dependent nature of the disorder in Cp2Co is assumed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00677370
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  • 2
    Electronic Resource
    Electronic Resource
    The electronic quantum size effect observed by195Pt NMR in the metal cluster compound Pt309Phen 36 * O30 (1993)
    Springer
    The European physical journal 26 (1993), S. 21-23 
    Details
    ISSN: 1434-6079
    Keywords: 74.30.Gn ; 74.70.Vy ; 76.60.Es
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract 195Pt NMR on the organic ligand stabilized metal cluster compound Pt309Phen 36 * O30 reveals two separate peaks in the lineshape. Ligand-bonded platinum atoms at the surface of the core are thought to be responsible for the peak that does not show any Knight shift. The corresponding spin-lattice relaxation timeT 1 is of the order of seconds. The second peak is Knight shifted and is attributed to the other Pt atoms, for which metallic behavior is inferred from the temperature dependence ofT 1. The Korringa relation holds down to 65 K. Below 65 K the relaxation of the magnetization becomes increasingly non-exponential with decreasing temperature. The relaxation process can be successfully modelled under the assumption of a Poisson distribution of the energy levels around the Fermi energy (the electronic quantum size effect).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01425605
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  • 3
    Electronic Resource
    Electronic Resource
    Solid state magic angle spinning13C and31P NMR of organic ligand stabilized high nuclearity metal clusters (1993)
    Springer
    The European physical journal 26 (1993), S. 24-26 
    Details
    ISSN: 1434-6079
    Keywords: 74.30.Gn ; 74.70.Vy ; 76.60.Es
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract 13C and31P solid state NMR measurements on the organic ligands in ligated Au55, Ni8, Pt309, Cu36 and Cu70 clusters are reported. The ligands behave like diamagnetic organic molecules, giving rise to relatively narrow lines with excellent cross-polarization efficiency. The resonance lines of the nuclei directly bound to the metal core are systematically broadened in the conducting compounds. No pronounced Knight shifts or evidence of metallic-like relaxation were observed. These results support a model for the electrical conduction involving tunneling between metal cores with the ligands playing the role of a tunneling barrier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01425606
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  • 4
    Electronic Resource
    Electronic Resource
    Optical plasmon losses in stabilized Au55 clusters (1991)
    Springer
    The European physical journal 20 (1991), S. 297-300 
    Details
    ISSN: 1434-6079
    Keywords: 33.20.K ; 36.40 ; 42.20 ; 78.40 ; 82.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Au55 cluster compounds are investigated by optical spectroscopy and TEM. The optical spectra appear to be rather structureless, neither showing a collective excitation resonance nor exhibiting distinct absorption bands known from lower nuclearity clusters. We discuss changes of the electronic properties compared to larger Au clusters affecting both, 6sp electrons and5d-6sp interband transitions, the cluster-ligand-interaction being considered as a charge transfer process. We additionally report on a low temperature instability of the cluster compound, which results in changed optical extinction spectra. A characteristic absorption feature at λ=400 nm is attributed to small, ligand-free Au cluster fragments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01543995
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  • 5
    Electronic Resource
    Electronic Resource
    NMR in metal cluster compounds compared to glasses (1991)
    Springer
    The European physical journal 20 (1991), S. 333-335 
    Details
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 76.60.Es
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The field and temperature dependence of the31P nuclear spin lattice relaxation rate in the metal cluster compound Ru55(P(t-Bu)3)12Cl20 follows a power law: 1/T 1 ∝T n B −m , withn=1.5±0.1 at 3.25 T andn=1.3±0.1 at 6.45 T;m ⋍ 1.4. Such dependences have so far only been observed in inorganic glasses and been attributed to two level systems. The correspondence suggests that the relaxation rate is due to interaction of theP-nuclear moment with electronic spins of stochastically moving charge carriers, which are thought to be responsible for the electrical conductivity through hopping between neigboring cluster molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01544004
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  • 6
    Electronic Resource
    Electronic Resource
    Phasenübergang von DecamethylmanganocenProfessor Kurt Dehnicke zum 60. Geburtstage gewidmet (1991)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 595 (1991), S. 27-34 
    Details
    ISSN: 0044-2313
    Keywords: Decamethylmanganocene ; phase transition ; crystal structure ; DSC thermogram ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Phase Transition of DecamethylmanganoceneDecamethylmanganocene (Cp2*Mn) has been investigated X-ray structural analytically at 240, 225, and 125 K, to study a reversible phase transition between 255 and 238 K (DSC thermogram). At 240 K the same space group C2/c is observed as at room temperature [9], whereas after the phase transition at 225 and 125 K the space group Cmca is found. In both phases the Cp* rings are staggered and slightly slipped, but less at 225 and 125 K compared with 240 K.The phase transition is to be traced back to a change of the molecule packing in the crystal lattice: With decreasing temperature the molecules cannot be packed closer in the monoclinic phase (C2/c), because the intermolecular H … H distances already remained under the sum of the van der Waals radii. In the orthorhombic phase (Cmca) (elongation of the a-axis and contraction of the b-axis) the repulsion along the b-axis is avoided.
    Notes: Decamethylmanganocen (Cp2*Mn) wurde bei 240, 225 und 125 K röntgenstrukturanalytisch untersucht, um einen zwischen 240 und 225 K stattfindenden reversiblen Phasenübergang (DSC-Thermogramm) zu untersuchen. Bei 240 K wird dieselbe Raumgruppe C2/c beobachtet wie bei Raumtemperatur [9], während nach dem Phasenübergang bei 225 und 125 K die Raumgruppe Cmca gefunden wird. In beiden Phasen sind die Cp*-Ringe gestaffelt und leicht gegeneinander verschoben angeordnet, jedoch bei 225 und 125 K weniger als bei 240 K. Der Phasenübergang ist auf eine Packungsänderung der Moleküle im Kristallgitter zurückzuführen: Mit abnehmender Temperatur können die Moleküle in der monoklinen Phase (C2/c) sich nicht mehr dichter packen, da die intermolekularen H … H-Abstände bereits die Summe der van der Waals-Radien unterschritten haben. In der orthorhombischen Phase (Cmca) (Verlängerung der a-Achse und Kontraktion der b-Achse) wird die Repulsion entlang der b-Achse vermieden.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19915950105
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