EXAFS INVESTIGATION OF THE 2ND HYDRATION SHELL OF METAL-CATIONS IN DILUTE AQUEOUS-SOLUTIONS

EXAFS spectra of aqueous dilute solutions (0.1 M) containing Cr3+, Rh3 +, Ga3+, and Zn2+ ions are presented. From the EXAFS fit parameters it is deduced that always the first hydration shell is formed by six wat er molecules with M-O distances between 1.95 and 2.06 Angstrom. A seco nd hydration shell is also observed in all cases, although the amplitu de of this contribution increases with the stability of aquocomplexes. This can be quantified by the correlation between the Debye-Waller fa ctors for the first and second hydration shells, and the first-shell w ater release constants of the hydrated cations.