Solid octaaqua(kappa(2)O-perchlorato)thorium(IV) perchlorate hydrate, [Th(H(2)O)(8)(ClO(4))](ClO(4))(3).H(2)O, 1, and aquaoxonium hexaaquatris(kappaO-trifluoromethanesulfonato)thorium(IV) trisaquahexakis(kappaO-trifluoromethanesulfonato)thorinate(IV), H(5)O(2)[Th(H(2)O)(6)(OSO(2)CF(3))(3)][Th(H(2)O)(3)(OSO(2)CF(3))(6)], 2, were crystallized from concentrated perchloric and trifluoromethanesulfonic acid solutions, respectively. 1 adopts a severely distorted tricapped trigonal prismatic configuration with an additional oxygen from the perchlorate ion at a longer distance. 2 consists of individual hexaaquatris(kappaO-trifluoromethanesulfonato)thorium(IV) and trisaquahexakis(kappaO-trifluoromethanesulfonato)thorinate(IV) ions and an aquaoxonium ion bridging these two ions through hydrogen bonding. The hydrated thorium(IV) ion is nine-coordinated in aqueous solution as determined by extended X-ray absorption fine structure (EXAFS) and large angle X-ray scattering (LAXS). The LAXS studies also showed a second hydration sphere of about 18 water molecules, and traces of a 3rd hydration sphere. Structural studies in aqueous solution of the hydrolysis products of thorium(IV) have identified three different types of hydrolysis species: a mu(2)O-hydroxo dimer, [Th(2)(OH)(2)(H(2)O)(12)](6+), a mu(2)O-hydroxo tetramer, [Th(4)(OH)(8)(H(2)O)(16)](8+), and a mu(3)O-oxo hexamer, [Th(6)O(8)(H(2)O)(n)](8+). Detailed structures of these three hydrolysis species are given. A compilation of reported solid state structures of actinoid(IV) compounds with oxygen donor ligands show a strong correlation between the An-O bond distance and the coordination number. The earlier reported U-O bond distance in the hydrated uranium(IV) ion in aqueous solution, confirmed in this study, is related to nine-coordination. The hydrated tri- and tetravalent actinoid ions in aqueous solution all seem to be nine-coordinated. The trivalent ions show a significant difference in bond distance to prismatic and capping water molecules in assumed tricapped trigonal prismatic configuration, while the tetravalent ions seem to form more regular structures, probably because of higher polarization.

The structures of the polynuclear hydrolysis complexes of chromium(III) formed in acidic and alkaline aqueous solution have been determined by means of extended X-ray absorption fine structure and large angle X-ray scattering. Chromium(III) is present as mononuclear hydrated ions below pH 3-4, with the upper limit depending on concentration, ionic strength, and temperature. Chromium(III) hydrolyzes in aqueous solution above this pH in concentrated aged solutions to mainly cationic tetrameric complexes containing both single and double hydroxo bridges between the chromium(III) ions. Above pH 5, the solubility of chromium(III) decreases sharply to form solid hydrated chromium(III) hydroxide. The solubility of chromium(III) increases sharply at elevated pH, and fairly concentrated solutions can be prepared in concentrated aqueous solutions of sodium hydroxide. According to the literature, mononuclear tetrahydroxochromate(III) complexes, Cr(OH)(4)(-), are formed in alkaline aqueous solution. However, this study shows polymeric chains of six-coordinated chromium(III) ions connected through double hydroxo bridges and with two terminal hydroxo groups giving an overall composition of (Cr(OH)(4))(n)(n-). This polymer is stable for a long time in solution at pH = 15. However, at pH < 15, this polymer precipitates slowly with time, over months, to an amorphous phase with a structure around chromium similar to that in alpha-chromium(III) oxide hydroxide.

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The structures of the dimethyl sulfoxide (dmso) and N,N′‐dimethylpropyleneurea (dmpu) solvated thorium(IV) ions have been studied in solution by extended X‐ray absorption fine structure (EXAFS), and the structure of the solid oxonium bis[nonakis(κO‐dimethyl sulfoxide)]thorium(IV) trifluoromethanesulfonate dihydrate, (H3O)[Th((CH3)2SO)9]2(CF3SO3)9·2H2O (1) has been determined by single‐crystal X‐ray diffraction and EXAFS. Compound 1 was crystallized by evaporating a saturated dmso solution. It consists of two individual nonakis(κO‐dimethyl sulfoxide)thorium(IV) units, both of which have a tricapped trigonal prismatic configuration, as also found in nonakis(dimethyl sulfoxide)thorium(IV) perchlorate previously reported. Mean Th–O bond lengths of 2.47 and 2.43 Å are found for the two structural units, respectively, for which the differences may be explained by differences in occupancy and temperature factors. The EXAFS data of 1 revealed mean Th–O and S–O bond lengths of 2.449(3) and 1.525(3) Å, respectively, and a Th–O–S bond angle of 135.2(5)° to give a Th···S distance of 3.665(7) Å. In dmso solution, the mean Th–O and S–O bond lengths are 2.447(3) and 1.534(3) Å, respectively, the Th–O–S bond angle is 133.5(5)°, and there is a Th···S distance of 3.672(7) Å. The Th–O bond‐length distribution is somewhat asymmetric in both samples with Rmax values of 2.424 and 2.422 Å for 1 and solution, respectively. In dmpu solution, the Th–O and C–O bond lengths are 2.404(5) and 1.264(2) Å, respectively, and there is a Th–O–C angle of 157.1(5)° to give a Th···C distance of 3.594(7) Å. The observed Th–O bond length indicates strongly that thorium(IV) is eight‐coordinate in dmpu.

The two dimethyl sulfoxide solvated rhodium(III) compounds, [Rh(dmso-κO)(5)(dmso-κS)](CF(3)SO(3))(3) (1 & 1* at 298 K and 100 K, respectively) and [Rh(dmso-κO)(3)(dmso-κS)(2)Cl](CF(3)SO(3))(2) (2), crystallize with orthorhombic unit cells in the space group Pna2(1) (No. 33), Z = 4. In the [Rh(dmso)(6)](3+) complex with slightly distorted octahedral coordination geometry, the Rh-O bond distance is significantly longer with O trans to S, 2.143(6) Å (1) and 2.100(6) Å (1*), than the mean Rh-O bond distance with O trans to O, 2.019 Å (1) and 2.043 Å (1*). In the [RhCl(dmso)(5)](3+) complex, the mean Rh-O bond distance with O trans to S, 2.083 Å, is slightly longer than that for O trans to Cl, 2.067(4) Å, which is consistent with the trans influence DMSO-κS > Cl > DMSO-κO of the opposite ligands. Raman and IR absorption spectra were recorded and analyzed and a complete assignment of the vibrational bands was achieved with support by force field calculations. An increase in the Rh-O stretching vibrational frequency corresponded to a decreasing trans-influence from the opposite ligand. The Rh-O force constants obtained were correlated with the Rh-O bond lengths, also including previously obtained values for other M(dmso)(6)(3+) complexes with trivalent metal ions. An almost linear correlation was obtained for the MO stretching force constants vs. the reciprocal square of the MO bond lengths. The results show that the metal ion-oxygen bonding of dimethyl sulfoxide ligands is electrostatically dominated in those complexes and that the stretching force constants provide a useful measure of the relative trans-influence of the opposite ligands in hexa-coordinated Rh(III)-complexes.

The aqua ions of palladium(II) and platinum(II) undergo extremely slow hydrolysis in strongly acidic aqueous solution, resulting in polynuclear complexes. The size and structures of these species have been determined by EXAFS and small angle X-ray scattering, SAXS. For palladium(II), the EXAFS data show that the Pd-O and Pd⋯Pd distances are identical to those of crystalline palladium(II) oxide, but the intensities of the Pd⋯Pd distances in the Fourier transform at 3.04 and 3.42 Å are significantly lower compared to those of crystalline PdO. Furthermore, no Pd⋯Pd distances beyond 4 Å are observed. These observations strongly indicate that the polynuclear palladium(II) complexes are oxido-and hydroxido-bridged species with the same core structure as solid palladium(II) oxide. Based on the number of Pd⋯Pd distances, as derived from the EXAFS data, their size can be estimated to be approximately two unit cells, or ca. show Pt-O and Pt⋯Pt distances identical to those of amorphous platinum(II) oxide, precipitating from the solution studied. The Pt⋯Pt distances are somewhat different from those reported for crystalline platinum(II) oxide. The polynuclear platinum(II) complexes have a similar structure to the palladium ones, but they are somewhat larger, with an estimated diameter of 1.5-3.0 nm. It has not been possible to precipitate any of these species by ultracentrifugation. They are detectable by SAXS, indicating diameters between 0.7 and 2 nm, in excellent agreement with the EXAFS observations. The number of oxido-relative to hydroxido bridges will increase with increasing size of the complex. The charge of the complexes will remain about the same, +4, at growth, with approximate formulas [Pd 10 O 4 (OH) 8 for complexes with a size of 2 and 3 unit cells of the corresponding solid metal oxide, respectively. Their high ionic charge in acidic aqueous solution will result in a stabilizing hydration shell.

The recently described solid solution (Co,Ni,Mn)3Sb4O6F6 has proved stable and efficient as a catalyst for electrocatalytic water oxidation. The end component Co3Sb4O6F6 was found to be most efficient, maintaining a current density of j = 10 mA cm(-2) at an overpotential of 443 mV with good capability. At this current density, O2 and H2 were produced in the ratio 1 : 2 without loss of faradaic current against a Pt-cathode. A morphological change in the crystallite surface was observed after 0.5 h, however, even after 64.5 h, the overall shape and size of the small crystallites were unaffected and the electrolyte contained only 0.02 at% Co. It was also possible to conclude from in situ EXAFS measurements that the coordination around Co did not change. The oxofluorides express both hydrophilic and hydrophobic surface sites, incorporate a flexible metalloid element and offer the possibility of a mechanism that differs from other inorganic catalytic pathways previously described.

The speciation in the mixed Th(IV)-Fe(III) system has been studied in aqueous solution in the pH range of 2.0-4.8. In the individual systems iron(III) and thorium(IV) hydrolyze easily and hydrolysis products precipitate at approximately pH ≥ 2.0 and 4.0, respectively, at the metal concentrations used in this study, 0.02-0.05 mol dm(-3). In the mixed Th(IV)-Fe(III) system precipitation of ferrihydrite takes place after months of storage at low pH values, 2.0 (six-line ferrihydrite) and 2.3 (two-line ferrihydrite), as identified by X-ray powder diffraction. In the pH range 2.9-4.5 no precipitation was observed after 24 months. Two thorium(IV)-iron(III) solutions with pH = 2.9, C(Th) = 0.02 and 0.05 mol dm(-3) and C(Fe) = 0.02 mol dm(-3), were studied by extended X-ray absorption fine structure, EXAFS, using the Fe K and Th L(3) edges, and a third solution with pH = 2.9 and C(Th) = C(Fe) = 0.40 mol dm(-3) by large angle X-ray scattering, LAXS, to determine the structure of the predominating species. A heteronuclear hydrolysis complex with the composition [Th(2)Fe(2)(μ(2)-OH)(8)(H(2)O)(12)](6+) is proposed to form in solution, with Th···Th, Th···Fe and Fe···Fe distances of 3.94(2) and 3.96(2), 3.41(3) and 3.43(2), 3.04(2) and 3.02(4) Å, as determined by EXAFS and LAXS, respectively.