J. Phys. IV France 7 (1997) C2-623-C2-624
XAS Study of Vitamin B12 Derivatives and Related CompoundsA. Mimouni1, J. Moscovici1 and A. Michalowicz1, 2
1 Laboratoire de Physique des Milieux Désordonnés (LPMD), UFR des Sciences, Université Paris XII val de Marne, 61 avenue du General De Gaulle, 94010 Créteil cedex, France
2 Laboratoire pour l'Utilisation de Rayonnement Électromagnétique (LURE), Université Paris sud, Bât. 209D, 91405 Orsay cedex, France
In this study we present X- ray Absorption Spectra of a series of Cobalamins and related Cobalt complexes at the Cobalt K edge. This series completes the spectra already published by other groups in order to allow a systematic study of the structure-spectra relationships. The evolution of each peak and shoulder in the edge spectra of methyl, cyano, hydroxo cobalamins and dicyanocobinamid are compared to the "simplest" case of Co(III) hexaamin. These spectral features are confronted to the molecular orbital  and multiple scattering models . In these interpretations we have found some important contradictions with the experimental spectra. We have performed a FEFF  calculation of the XANES spectrum of Co(NH3 )63+ . It was then possible to analyse which experimental peaks can be assigned to specific scattering paths and also which peaks are still impossible to interpret within theses simple models.
© EDP Sciences 1997