Hydration of the yttrium(III) ion in aqueous solution.: An X-ray diffraction and XAFS structural study

The yttrium(III) ion is found by means of extended X-ray absorption fine-structure spectroscopy (EXAFS) and large angle X-ray scattering (LAXS) to be hydrated by eight water molecules in aqueous solution. The EXAFS data show a slightly asymmetric distribution of the Y-O bond distances with the centroid of the distribution at 2.368(5) Angstrom. The width of the distribution implies a positional disorder of about 0.1 Angstrom on top of the thermally induced variation in the Y-O bond distances, The aqueous solutions and the solid compound [Y(OH2)(8)]Cl-3.(15-crown-5), in which eight water oxygen atoms from a distorted bicapped trigonal prism around the hydrated yttrium(III) ion, show very similar neat-edge and EXAFS spectra. For aqueous solutions the LAXS data give a mean Y-O bond distance of 2.365(5) Angstrom and show the presence of a second hydration sphere consisting of approximately 16 oxygen atoms at a mean Y ... O distance of 4.40(4) Angstrom.