Anharmonic potential derived from EXAFS of hexaaqua transition metal complexes

Abstract

EXAFS (extended X-ray absorption fine structure) experiments were performed at several different temperatures for a series of 3d transition metal ions (Cr³⁺, Fe³⁺, Fe²⁺, Ni²⁺, Co²⁺ and Zn²⁺) in aqueous solutions. Anharmonic EXAFS analyses, which include up to third order cumulant, were carried out to study the metal–oxygen bonding potential. According to the model in which the dissociation process is dominant for the ligand water exchange reaction, the dissociation energy has been evaluated by combining experimental results of temperature dependence of a harmonic Debye–Waller factor and an anharmonic third order cumulant for hydrated metal complexes. The dissociation energies deduced from the EXAFS experiments were found to correlate well with those having been theoretically predicted, and with the experimental water-exchange rate constants.