2022 Volume 53 Pages 97-117
Fitting thermodynamic models to ultraviolet-visible absorption spectra yielded the distribution of the cobaltous aqua and chloro complexes and their molar attenuation coefficients. The X-ray absorption near edge structures and the extended X-ray absorption fine structures spectra of the individual species were assessed dividing a series of spectra by the distribution obtained through the fitting analysis. Then, the structure analysis was conducted using the decomposed EXAFS spectra of the individual species. However, the most possible complex structure for each species could not be fixed. The most possible structures were determined by comparing the single point energies between the observed structures and the optimum structures calculated using ab-initio technique. It was confirmed that there were three complexes of [CoII(H2O)6]2+, [CoIICl2(H2O)4]0, and [CoIICl4]2- and their stability constants were determined. The analysis procedure conducted in the present work consisted of ultraviolet-visible/X-ray absorption spectra, fitting analysis of thermodynamic models, and ab-initio calculation. The distribution and the structures of the cobaltous aqua and chloro complexes were determined with the benefit of the mutual compensation for the disadvantages of the other analyses.
