X-ray absorption spectroscopy (XAS) study of the hydration structure of yttrium(III) cations in liquid and glassy states:: Eight or nine-fold coordination?

An extensive X-ray absorption spectroscopy study has been carried out on 0.005 to 2.0 molal YBr3. 6H(2)O aqueous solutions in liquid and glassy states to determine the solvation structure of the yttrium(III) cations in aqueous dilute and concentrate solutions. The existence of a symmetric polyhedron of water molecules around yttrium(III) cations at 2.35 Angstrom, as well as the absence of contact Y-Br ion pairs, in all of the investigated solutions was deduced from the EXAFS analysis. The existence of a multiple electron transition of nonnegligible intensity within the EXAFS region of the spectra has been proven. This transition induces an overestimation in the coordination numbers derived from the EXAFS analysis so that we have extended our study to the XANES part of the spectra. We have performed detailed computations of the XANES spectra by using a one-electron full-multiple-scattering code. This analysis shows unambiguously that the eight water molecules surround yttrium(III) cations at 2.35 Angstrom forming a symmetric square antiprism.