EXAFS DEBYE-WALLER FACTOR AND LIGAND-EXCHANGE REACTION OF HYDRATED METAL-COMPLEXES

The EXAFS (Extended X-Ray Absorption Fine Structure) spectra of hydrat ed transition metal complexes were measured to investigate the relatio n between the Debye-Waller factor in EXAFS, sigma(2), and their ligand exchange reaction rate constant, k(1), in aqueous solution. A good co rrelation between these two factors was obtained for various transitio n metal ions. The relation between sigma(2) and log k(1) is studied th eoretically using the Arrhenius theory. The introduction of an anharmo nic Morse function as the interaction potential was found to lead to a simple expression connecting sigma(2) and log k(1), which is in accor dance with the experimental results. It is also found that k(1) correl ates not only with sigma(2) but also a third order cumulant in EXAFS, C-3; the greater the k(1) value, the greater the increase in C-3 With temperature. The behavior of C-3 implies that the anharmonicity in the potential of the metal-oxygen interaction must be taken into consider ation for the study of the ligand exchange reaction.