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1998 (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    Martin Jäger1, Paul Schuler1, HartmutB. Stegmann, Antal RockenbauerbRequires cookie*
 Title    Molecular Recognition Analyzed by Observing Intramolecular Interconversion with E PR Spectroscopy  
 Abstract    Molecular recognition between Rebek's cleft R and 4-(2-benzimidazolyl)-aminomethyl-2,6-di-rm-butyl-phenol (Bi) is investigated by means of EPR spectroscopy. Their specific inter-molecular interactions are distinguished from non-specific interactions represented by mere protonation on addition of benzoic acid. Both interactions are related to intramolecular in­ terconversions at the CQ-atom of Bi*, where a two-jump mechanism is found for free and protonated Bi* and a two-site exchange for the complexed ligand. While NMR spectroscopy indicates the existence of 1:1 and 1:2 receptor-substrate complexes, the faster time scale of EPR spectroscopy allows to identify one 1 : 2 as well as three 1 : 1 associates and to elucidate their formation conditions. Based upon the corresponding hf parameters, binding modes and sites are proposed for the key-in-the-lock system. 
  Reference    Z. Naturforsch. 53b, 1511—1519 (1998); received July 22 1998 
  Published    1998 
  Keywords    Rock-Key-Equilibria, Spin Labeling, Molecular Dynamics 
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 TEI-XML for    default:Reihe_B/53/ZNB-1998-53b-1511.pdf 
 Identifier    ZNB-1998-53b-1511 
 Volume    53