The structure of the hydrated gallium(III), indium(III), and chromium(III) ions has been determined in aqueous perchlorate and nitrate solutions by means of the large-angle X-ray scattering (LAXS) and extended X-ray absorption fine structure (EXAFS) techniques. The EXAFS studies have been performed over a wide concentration range, 0.005-1.0 mol.dm(-)(3) (2.6 mol.dm(-)(3) for chromium(III)), while the LAXS studies are restricted to concentrated solutions, ca. 1.5 mol.dm(-)(3). All three metal ions were found to coordinate six water molecules, each of which are hydrogen bonded to two water molecules in a second hydration sphere. The metal-oxygen bond distance in the first hydration sphere of the gallium(III), indium(III), and chromium(III) ions was determined by LAXS and EXAFS methods to be 1.959(6), 2.131(7), and 1.966(8) Å. The LAXS data gave mean second sphere M.O distances of 4.05(1), 4.13(1), and 4.08(2) Å for the gallium(III), indium(III), and chromium(III) ions, respectively. The perchlorate ion was found to be hydrogen bonded to 4.5(7) water molecules with the O.O distance 3.05(2) Å and Cl.O 3.68(3) Å. Analyses of the Ga, In, and Cr K-edge EXAFS data of the aqueous perchlorate and nitrate solutions showed no influence on the first shell M-O distance by a change of concentration or anion. The minor contribution from the second sphere M.O distance is obscured by multiple scattering within the tightly bonded first shell. EXAFS data for the alum salts CsM(SO(4))(2).12H(2)O, M = Ga or In, showed the M-O bond length of the hexahydrated gallium(III) and indium(III) ions to be 1.957(2) and 2.122(2) Å, respectively.

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) Å. The width of the distribution implies a positional disorder of about 0.1 Å on top of the thermally induced variation in the Y−O bond distances. The aqueous solutions and the solid compound [Y(OH2)8]Cl3·(15-crown-5), in which eight water oxygen atoms form a distorted bicapped trigonal prism around the hydrated yttrium(III) ion, show very similar near-edge and EXAFS spectra. For aqueous solutions the LAXS data give a mean Y−O bond distance of 2.365(5) Å 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) Å.

A new polymorph of ZrW2O8, structurally related to trigonal ZrMo2O8, has been prepared at low temperatures using nonhydrolytic sol−gel chemistry. Its identity was established by powder X-ray diffraction, energy dispersive X-ray analysis, and extended X-ray absorption fine structure (EXAFS). This material is denser than the previously reported cubic and orthorhombic forms of ZrW2O8 and decomposes into the binary oxides on prolonged heating at 700 °C. An EXAFS investigation of the crystallization of “ZrW2O8” gels, prepared by nonhydrolytic methods, suggests that the coordination environments of the cations in the heat-treated gels evolve toward those found in the new form of ZrW2O8 prior to the crystallization of this product.