In this study we present X-ray Absorption Spectra of a series of Cobal
amins and related Cobalt complexes at the Cobalt K edge. This series c
ompletes the spectra already published by other groups in order to all
ow a systematic study of the structure-spectra relationships. The evol
ution 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 [1] and multiple scattering models [2]. In thes
e interpretations we have found some important contradictions with the
experimental spectra. We have performed a FEFF [3] calculation of the
XANES spectrum of Co(NH3)(6)(3+). It was then possible to analyse whi
ch experimental peaks can be assigned to specific scattering paths and
also which peaks are still impossible to interpret within theses simp
le models.