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1993 (1)
1984 (1)
1Author    E. Bill1, N. Blaes2, K. F. Fischer3, U. G. Onser2, K. H. Pauly3, R. Preston2, F. Seel4, R. Staab4, A.X T Rautw Ein1Requires cookie*
 Title    Crystal Structure and Mössbauer Spectroscopic Investigation of the Low Temperature Molecular Dynamics of Hexa(2-ethylimidazole)iron(II) Hydridotetracarbonylferrate(-II)  
 Abstract    The title compound 1 was synthesized as reaction product of pentacarbonyl iron with 2-ethyl-imidazole. A Zerewitinoff-determination shows that we are rather dealing with hydrido-tetracar-bonylferrate(-II) than with tetracarbonylferrate(-I) as supposed in a preceding paper. A new crystal structure analysis of 1 was performed. With respect to [HFe(CO)4]~ we found that three CO groups are ordered with normal tetrahedral angles, while the fourth CO group shows statisti­ cal distribution over three sites (disordered sites). The temperature parameters of the disordered CO sites are considerably more anisotropic than those of the ordered CO sites. Experimental Mössbauer spectra have been recorded between 4.2 K and 288.7 K. 1 exhibits a Mössbauer pattern with two subspectra, one for each of the cations and the anions. The cation subspectrum reflects normal ferrous high-spin behavior, while the anion subspectrum shows peculiar anomalies around 200 K. On the basis of our X-ray structure results molecular orbital calculations have been performed with the aim of deriving electric field gradient tensors for the various stochastic substates of [HFe(CO)4]~. These tensors were then used within the frame on an analytical lineshape formula. It turns out that the statistical distribution of the fourth CO group over three sites is associated with a jump behavior, similar to trapped diffusion, of the CO group among the three sites and not with static disorder. The Fe atom follows this jumb behavior, however, its triangular displacement body with jump distance d ~ 0.30 Ä is considerably smaller than that of the CO group. 
  Reference    Z. Naturforsch. 39b, 333 (1984); eingegangen am 15. A u gu st/10. Oktober 1983 
  Published    1984 
  Keywords    Hydridotetracarbonylferrate, Crystallography, Mössbauer Spectra, Temperature Factors, Molecular Dynamics 
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 TEI-XML for    default:Reihe_B/39/ZNB-1984-39b-0333.pdf 
 Identifier    ZNB-1984-39b-0333 
 Volume    39 
2Author    A. G. Tsarkov, V. G. TsirelsonRequires cookie*
 Title    The Identification of Phonon-Phonon Interactions in Anharmonic Crystals by X-Ray Diffraction Data  
 Abstract    The effect of anharmonic atomic vibrations on the elastic scattering of X-rays by a crystal is treated by time-independent perturbation theory. The complete expression for the anharmonic temperature factor (TF) in the high-temperature limit is presented for atoms in general positions. The phonon-phonon interactions in an anharmonic crystal may be identified with X-ray diffraction data by using various temperature and scattering vector q dependencies of different anharmonic contri-butions to the TF. The expression for the intensity of elastic scattering by an anharmonic crystal contains an additional factor -the anharmonic cross-term. This term has to be taken into account for obtaining the unbiased thermal parameters of fourth order in | q | from X-ray diffraction data. 
  Reference    Z. Naturforsch. 48a, 21—24 (1993); received November 8 1991 
  Published    1993 
  Keywords    Lattice vibrations, Anharmonicity, Phonon-phonon interactions, Temperature factor, X-ray diffraction 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0021.pdf 
 Identifier    ZNA-1993-48a-0021 
 Volume    48