The Structure of the Hydrated Gallium(III), Indium(III), and Chromium(III) Ions in Aqueous Solution. A Large Angle X-ray Scattering and EXAFS Study

Abstract

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.

Oligomerization of chromium(iii) and its impact on the oxidation of chromium(iii) by hydrogen peroxide in alkaline solutions

“…There have been arguments in the literature 18,19 as to whether the MS within the first coordination shell or the SS from more distant shell(s) is of greater importance in interpreting the EXAFS data. However, since there are no Cr-Cr interactions in the monomer and the minor peak at 3.4 Å still shows in the Fourier Transform of its EXAFS, it is reasonable to assume that, in these systems, the MS within the first Cr-O shell is more important than the SS from a more distant Cr-Cr shell.…”

“…The structures of hydrated chromium(III) ions in acidic solutions 18,19 and chromium(III) sorbed on bentonite 20 and oxide-water interface 21 have been elucidated. However, this technique has not been used to directly study the chromium(III) speciation in alkaline solutions.…”

Dimethyl sulfoxide solvates of the aluminium(iii), gallium(iii) and indium(iii) ions. A crystallographic, EXAFS and vibrational spectroscopic studyElectronic supplementary information (ESI) available: normalized X-ray absorption edges, calculated separate contributions of the different scattering paths to the EXAFS oscillations for the dimethyl sulfoxide solvated gallium(iii) and indium(iii) ions in the solid state and solution; correlation between compression ratio (s/h) and bond lengths in [M(dmso)6]3+ c

“…Scandium() probably coordinates † Electronic supplementary information (ESI) available: normalized Xray absorption edges, calculated separate contributions of the different scattering paths to the EXAFS oscillations for the dimethyl sulfoxide solvated gallium() and indium() ions in the solid state and solution; correlation between compression ratio (s/h) and bond lengths in [M(dmso) 6 ] 3ϩ complexes; correlation between metal-oxygen (M-O) force constants and bond lengths in [M(dmso) 6 ] 3ϩ complexes. See http:// www.rsc.org/suppdata/dt/b2/b212140a/ seven water molecules in a monocapped trigonal prism, 8 yttrium() eight in a square antiprism, 9 and lanthanum() nine waters in a tricapped trigonal prism.…”

“…The conformation of the (CH 3 ) 2 SO ligand in the [M(dmso) 6 ] 3ϩ complexes, reflected by the 3.0Њ larger M-O-S angle for the aluminium solvate (cf. Table 2), also affects the cell volume.…”

The structure of hyperalkaline aqueous solutions containing high concentrations of gallium – a solution X-ray diffraction and computational study

“…2,35,36 In alkaline Ga(III)-bearing solutions, 2,37 r Ga−O was found to be 1.80−1.83 Å. In crystalline solid Ga(III) compounds, for the tetrahedrally O-coordinated Ga(III), [38][39][40][41] r Ga-O = 1.82 ± 0.04 Å (e.g., in alkali-gallosilicates 1.83 Å, in Ga-bearing zeolites 1.78−1.85 Å and in β-Ga 2 O 3 , 1.83−1.86 Å).…”