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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 96 (1997), S. 141-145 
    ISSN: 1432-2234
    Keywords: Key words: Nitrogenase ; Nitrogen fixation ; FeMo enzymes ; Oxidation reduction of FeMo cofactor ; INDO
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. Reduced and oxidized forms of the FeMo- cofactor of Azotobacter vinelandii nitrogenase are examined theoretically within the intermediate neglect of differential overlap model. The results obtained favor one of the experimentally suggested modes of contraction of the metal system which results in an expansion of the central cavity of the cofactor. The bond index analysis indicates marked changes in the Mo coordination upon electron addition which may contribute to an opening of the Mo atom as a possible binding site at the advanced stages of the reduction process. In this work we also compare the 39- and 41-electron [MoFe7] core as possible native resting states, both compatible with known spin and Mössbauer spectroscopies.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2234
    Keywords: INDO method for lanthanides ; Lanthanide halides ; Ce(NO3)6 2−
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract An intermediate neglect of differential overlap method of use for examining the electronic structure of lanthanide complexes is developed. It is characterized by a basis set obtained from relativistic Dirac-Fock atomic calculations, the inclusion of all one-center two-electron integrals, and a parameter set based on molecular geometry. Lanthanide halides MX2, MX3 and MX4 are studied here, as well as initial results for the twelve coordinate Ce(NO3)6 −2 ion. Geometries obtained are in excellent agreement with experimental values when available. Many MX3 complexes are found to be pyramidal, and EuCl2 and YbCl2 are calculated to be bent even at the SCF level. Models invoking London type forces are therefore not required. Ionization potentials are calculated for the trihalides (δSCF) and are in reasonable agreement with experiment. Contrary to conclusion of others, f-orbital participation, although small, is required — at least in this model — to obtain the spread of metal to halide bond distance observed in these complexes. However f-orbital participation does not seem to be significant even in the twelve coordinate Ce(NO3)6 −2 complex: rather the large coordination number seems to be a consequence of the relatively large size of the lanthanide ion.
    Type of Medium: Electronic Resource
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