High-temperature, high-pressure hydrothermal synthesis and characterization of a salt-inclusion mixed-valence uranium(V,VI) silicate: [Na9F2][(U(V)O2)(U(VI)O2)2(Si2O7)2].

A salt-inclusion mixed-valence uranium(V,VI) silicate, [Na9F2][(U(V)O2)(U(VI)O2)2(Si2O7)2], was synthesized under hydrothermal conditions at 585 °C and 160 MPa and structurally characterized by powder and single-crystal X-ray diffraction (XRD). The valence states of uranium were established by U 4f X-ray photoelectron spectroscopy (XPS). The structure contains two-dimensional (2D) sheets of uranyl disilicate with the composition [UO2Si2O7], which are connected by U(1)(V)O6 tetragonal bipyramids to form thick layers. The Na(+) cations are located at sites in the intralayer and interlayer regions. In addition to Na(+) cations, the interlayer region also contains F(-) anions such that infinite chains with the formula FNa1/1Na4/2 are formed. The same type of chain was observed in K2SnO3. The title compound is not only the first example of salt-inclusion metal silicate synthesized under high-temperature, high-pressure hydrothermal conditions, as well as the first salt-inclusion mixed-valence uranium silicate, but it is also the first mixed-valence uranium(V,VI) silicate in the literature. Crystal data: [Na9F2][(U(V)O2)(U(VI)O2)2(Si2O7)2], triclinic, P1 (No. 2), a = 5.789(1) Å, b = 7.423(2) Å, c = 12.092(2) Å, α = 90.75(3)°, ß = 96.09(3)°, γ = 90.90(3)°, V = 516.5(2) Å(3), Z = 1, R1 = 0.0241, and wR2 = 0.0612.

A new ß-CdTeO3 polymorph with a structure related to α-CdTeO3.

A new ß-CdTeO3 polymorph was obtained by hydrothermal synthesis and its structure was solved ab initio from powder X-ray diffraction data. It appears that the structure of ß-CdTeO3 (Pnma, Z = 16, a = 7.45850(3) Å, b = 14.52185(6) Å, c = 11.04584(5) Å) is closely related to that of α-CdTeO3 (P21/c, Z = 8, a = 7.790(1) Å, b = 11.253(2) Å, c = 7.418(1) Å, ß = 113.5(1)°) previously reported. The 3D framework of ß-CdTeO3 is built of both [CdO6] distorted octahedra and [CdO7] mono-capped trigonal prisms and three different tellurium polyhedra: trigonal pyramids [TeIVO3E] and trigonal bipyramids [TeIVO4E] and [TeIVO3+1E] (E denotes the lone pair of TeIV). The electronic structure calculations based on density functional theory methods show that at the ground state α-CdTeO3 is slightly more stable than ß-CdTeO3 with an energy difference of 4.64 kJ mol-1. The band structures confirm the results of optical UV-Vis spectroscopy measurements: both polymorphs are wide bandgap semiconductors with Eg = 3.55 eV for ß-CdTeO3 and Eg = 3.91 eV for α-CdTeO3. The DOS calculations for both polymorphs enable one to understand that the presence of the [TeIVO4E] polyhedra in ß-CdTeO3 (absent in α-CdTeO3) lowers its bandgap. Above 540 °C ß-CdTeO3 transforms into α-CdTeO3 in a first order phase transition.

Ammonium Iron(II,III) Phosphate: Hydrothermal Synthesis and Characterization of NH4Fe2(PO4)2.

The mixed-valence iron phosphate NH4Fe2(PO4)2, which was synthesized by the high-temperature, high-pressure hydrothermal method, crystallizes in the monoclinic space group C2/c with a = 20.0066(1) Å, b = 14.8319(2) Å, c = 9.9899(1) Å, ß = 119.278(1)°, and Z = 16. Its compact structure consists of chains of edge-sharing FeIIO6 octahedra and chains of corner-sharing FeIIIO6 octahedra and PO4 tetrahedra. These chains are connected to each other and delimit tunnels in the [221], [22̄1], and [001] directions, in which NH4+ cations are located. Mössbauer spectroscopy confirms the presence of FeII and FeIII. The title compound is the first example of a mixed-valence ammonium iron phosphate.

Remarkable thermal stability of Eu(4-phosphonobenzoate): structure investigations and luminescence properties.

A new 3D rare-earth hybrid material Eu(p-O(3)PC(6)H(4)COO) has been synthesised by a hydrothermal route from Eu(NO(3))(3) x 5 H(2)O and the rigid precursor, 4-phosphonobenzoic acid. The structure of Eu(p-O(3)PC(6)H(4)COO) has been solved by X-ray diffraction on a powder sample and is described as an inorganic network in which both carboxylic and phosphonic acid groups are linked to Eu ions forming a three-dimensional architecture. Thermal analysis performed on this compound has underlined its remarkable stability up to 510 degrees C and an optical study has been conducted to examine its luminescence properties that have been related to the structure of the material. The structural and luminescence properties have also been compared with the related material Eu phenylphosphonate.

The route to fullernoid oxides.

Tetrahedral oxides, like silicates and aluminates, have attracted great interest due to their potential for numerous applications in various fields ranging from catalysis, ion exchange and molecular sieves, to thermo- and photoluminescence. In spite of their tetrahedral character, no effort has been made to date for establishing structural relationships between these tetrahedral oxides with different forms of carbon, for example, fullerenes. Here, we report for the first time an oxide that exhibits a three-dimensional framework of AlO4 tetrahedra forming huge 'Al84' spheres, similar to those of the D2d isomer of the C84 fullerenes. These Al84 spheres, displayed in a face-centred-cubic lattice, are easily identified by high-resolution electron microscopy. We also show that this Sr33Bi24+delta Al48O141+3 delta/2 aluminate exhibits an onion-skin-like subnanostructure of its Bi/Sr/O species located inside the Al84 spheres. The role of the original pseudo-spheric anion [Bi16O52-n empty square box n]-with n vacancies (empty square box)-in the stabilization of such a structure is discussed. This structure seems to be promising for the generation of a large family of fullerene-type (fullerenoid) oxides with various properties.