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 aqueou s dilute and concentrate solutions. The existence of a symmetric polyhedron of water molecules around yttrium(III) cations at 2.35 Angstrom, as well a s the absence of contact Y-Br ion pairs, in all of the investigated solutio ns was deduced from the EXAFS analysis. The existence of a multiple electro n transition of nonnegligible intensity within the EXAFS region of the spec tra has been proven. This transition induces an overestimation in the coord ination numbers derived from the EXAFS analysis so that we have extended ou r study to the XANES part of the spectra. We have performed detailed comput ations of the XANES spectra by using a one-electron full-multiple-scatterin g code. This analysis shows unambiguously that the eight water molecules su rround yttrium(III) cations at 2.35 Angstrom forming a symmetric square ant iprism.