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, β = 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

High-Temperature, High-Pressure Hydrothermal Synthesis and Characterization of a Salt-Inclusion Mixed-Valence Uranium(V,VI) Silicate: [Na₉F₂][(U^VO₂)(U^VIO₂)₂(Si₂O₇)₂]

A salt-inclusion mixed-valence uranium­(V,VI) silicate, [Na₉F₂]­[(U^VO₂)­(U^VIO₂)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)^VO₆ 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 FNa_1/1Na_4/2 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^VO₂)­(U^VIO₂)₂(Si₂O₇)₂], triclinic, <i>P</i>1̅ (No. 2), <i>a</i> = 5.789(1) Å, <i>b</i> = 7.423(2) Å, <i>c</i> = 12.092(2) Å, α = 90.75(3)°, β = 96.09(3)°, γ = 90.90(3)°, <i>V</i> = 516.5(2) ų, <i>Z</i> = 1, <i>R</i>₁ = 0.0241, and <i>wR</i>₂ = 0.0612

High-Temperature, High-Pressure Hydrothermal Synthesis and Characterization of a Salt-Inclusion Mixed-Valence Uranium(V,VI) Silicate: [Na₉F₂][(U^VO₂)(U^VIO₂)₂(Si₂O₇)₂]

A salt-inclusion mixed-valence uranium­(V,VI) silicate, [Na₉F₂]­[(U^VO₂)­(U^VIO₂)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)^VO₆ 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 FNa_1/1Na_4/2 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^VO₂)­(U^VIO₂)₂(Si₂O₇)₂], triclinic, <i>P</i>1̅ (No. 2), <i>a</i> = 5.789(1) Å, <i>b</i> = 7.423(2) Å, <i>c</i> = 12.092(2) Å, α = 90.75(3)°, β = 96.09(3)°, γ = 90.90(3)°, <i>V</i> = 516.5(2) ų, <i>Z</i> = 1, <i>R</i>₁ = 0.0241, and <i>wR</i>₂ = 0.0612

High-Temperature, High-Pressure Hydrothermal Synthesis and Characterization of a Salt-Inclusion Mixed-Valence Uranium(V,VI) Silicate: [Na₉F₂][(U^VO₂)(U^VIO₂)₂(Si₂O₇)₂]

A salt-inclusion mixed-valence uranium­(V,VI) silicate, [Na₉F₂]­[(U^VO₂)­(U^VIO₂)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)^VO₆ 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 FNa_1/1Na_4/2 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^VO₂)­(U^VIO₂)₂(Si₂O₇)₂], triclinic, <i>P</i>1̅ (No. 2), <i>a</i> = 5.789(1) Å, <i>b</i> = 7.423(2) Å, <i>c</i> = 12.092(2) Å, α = 90.75(3)°, β = 96.09(3)°, γ = 90.90(3)°, <i>V</i> = 516.5(2) ų, <i>Z</i> = 1, <i>R</i>₁ = 0.0241, and <i>wR</i>₂ = 0.0612

High Pressure Transformation of La₄Cu₃MoO₁₂ to a Layered Perovskite

High Pressure Transformation of La4Cu3MoO12 to a Layered Perovskit

La₄Cu₃MoO₁₂: A Novel Cuprate with Unusual Magnetism

La4Cu3MoO12 is a new (ABO3)n=4 cuprate with mixed B-cations in a ratio of 1:3. When synthesized at ambient pressure, the structure is not perovskite as expected but rather a homeotype of YAlO3, a rare-earth hexagonal phase. While the P63/mmc and Pmnm space groups can be used to model average structures which appear in quenched samples; powder, electron, and neutron diffraction data all confirm that a slow-cooled sample crystallizes in the monoclinic space group, P1121/m. The copper and molybdenum are coordinated by oxygen in corner-sharing trigonal bipyramids that are sandwiched between layers of lanthanum cations. In the B-cation layer, the copper cations order into a kagomé-like lattice of triangular clusters. The magnetism has been measured from 2 to 800 K and is highly influenced by the geometric arrangement of the CuII cations. An antiferromagnetic transition occurs at 5 K, but the sample does not reach a purely paramagnetic state until 460 K