XAS Study of Vitamin B₁₂ Derivatives and Related Compounds

Abstract
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 [1] and multiple scattering models [2]. In these 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 )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.