Crystal structures and magnetic properties of 6H-perovskite-type oxides Ba3MIr2O9 (M=Mg, Ca, Sc, Ti, Zn, Sr, Zr, Cd and In)

Crystal structures and magnetic properties of quaternary oxides Ba₃MIr₂O₉ (M=Mg, Ca, Sc, Ti, Zn, Sr, Zr, Cd and In) were investigated. Rietveld analyses of their X-ray diffraction data indicate that they adopt the 6H-perovskite-type structure with space group P6₃/mmc or, in the case of M=Ca, Sr and Cd, a monoclinically distorted structure with space group C2/c. The Ir valence configurations are (M=Mg, Ca, Zn, Sr and Cd), (M=Sc and In) and (M=Ti and Zr). Magnetic susceptibility and specific heat measurements were carried out. In the , the Ir⁵⁺ ions have a non-magnetic ground state and the magnetic behavior for these compounds is explained by the Kotani's theory. For , the effective magnetic moment of these compounds is significantly small, although the Ir⁴⁺ ions have magnetic moment, which indicates the existence of the strong antiferromagnetic interaction between Ir⁴⁺ ions in the Ir⁴⁺₂O₉ face-shared bioctahedra. In the case of , a specific heat anomaly was found at about 10 K (M=Sc) and 1.6 K (M=In), which suggests the magnetic ordering of the magnetic moments of Ir⁴⁺ in the (Ir⁴⁺Ir⁵⁺)O₉ bioctahedra.     

Crystal structures of two new oxysulfides La5Ti2MS5O7 (M=Cu, Ag): evidence of anionic segregation

Two new compounds, La₅Ti₂MS₅O₇ (M=Cu, Ag) were synthesized and their structures solved from single crystal X-ray data. Both compounds are isotypic. They crystallize in the orthorhombic system (space group Pnma, Z=4) with lattice constants a=19.423(1) Å, b=3.9793(2) Å, c=18.1191(9) Å for La₅Ti₂CuS₅O₇, and a=19.593(2) Å, b=3.9963(1) Å, and c=18.2973(15) Å for La₅Ti₂AgS₅O₇. The structure of these compounds is built from fragments of the rock-salt, perovskite and fluorite types and a clear anionic segregation of the anions appears in the structure. La₅Ti₂CuS₅O₇ and La₅Ti₂AgS₅O₇ exhibit an orange-yellow color and measurement of their optical band gap gave 2.02 and 2.17 eV, respectively.     

Double (n=2) and triple (n=3) [M4Bi2n−2O2n] polycationic ribbons in the new Bi∼3Cd∼3.72M∼1.28O5(PO4)3 oxyphosphate (M=Co, Cu, Zn)

The crystal structure of the new Bi_∼3Cd_∼3.72Co_∼1.28O₅(PO₄)₃ has been refined from single crystal XRD data, R₁=5.37%, space group Abmm, a=11.5322(28) Å, b=5.4760(13) Å, c=23.2446(56) Å, Z=4. Compared to Bi_∼1.2M_∼1.2O_1.5(PO₄) and Bi_∼6.2Cu_∼6.2O₈(PO₄)₅, this compound is an additional example of disordered Bi³⁺/M²⁺ oxyphosphate and is well described from the arrangement of double [Bi₄Cd₄O₆]⁸⁺ (=D) and triple [Bi₂Cd_3.44Co_0.56O₄]⁶⁺ (=T) polycationic ribbons formed of edge-sharing O(Bi,M)₄ tetrahedra surrounded by PO₄ groups. According to the nomenclature defined in this work, the sequence is TT/DtDt, where t stands for the tunnels created by PO₄ between two subsequent double ribbons and occupied by Co²⁺. The HREM study allows a clear visualization of the announced sequence by comparison with the refined crystal structure. The Bi³⁺/M²⁺ statistic disorder at the edges of T and D entities is responsible for the PO₄ multi-configuration disorder around a central P atom. Infrared spectroscopy and neutron diffraction of similar compounds (without the highly absorbing Cadmium) even suggests the long range ordering loss for phosphates. Therefore, electron diffraction shows the existence of a modulation vector q^*=1/2a^*+(1/3+ε)b^* which pictures cationic ordering in the (001) plane, at the crystallite scale. This ordering is largely lost at the single crystal scale. The existence of mixed Bi³⁺/M²⁺ positions also enables a partial filling of the tunnels by Co²⁺ and yields a composition range checked by solid state reaction. The title compound can be prepared as a single phase and also the M=Zn²⁺ term can be obtained in a biphasic mixture. For M=Cu²⁺, a monoclinic distortion has been evidenced from XRD and HREM patterns but surprisingly, the orthorhombic ideal form can also be obtained in similar conditions.     

Synthesis and crystal structure of Ln2MGe4O12, Ln=rare-earth element or Y; M=Ca, Mn, Zn

The crystal structure of the promising optical materials Ln₂M²⁺Ge₄O₁₂, where Ln=rare-earth element or Y; M=Ca, Mn, Zn and their solid solutions has been studied in detail. The tendency of rare-earth elements to occupy six- or eight-coordinated sites upon iso- and heterovalent substitution has been studied for the Y_2−xEr_xCaGe₄O₁₂ (x=0-2), Y_2−2xCe_xCa_1+xGe₄O₁₂ (x=0-1), Y₂Ca_1−xMn_xGe₄O₁₂ (x=0-1) and Y_2−xPr_xMnGe₄O₁₂ (x=0-0.5) solid solutions. A complex heterovalent state of Eu and Mn in Eu₂MnGe₄O₁₂ has been found.     

Crystal structures and chemistry of double perovskites Ba2M(II)M′(VI)O6 (M=Ca, Sr, M′=Te, W, U)

Structures of the double perovskites Ba₂M(II)M ′(VI)O₆ (M=Ca, Sr, M′=Te, W, U) at room temperature have been investigated by the Rietveld method using X-ray and neutron powder diffraction data. For double perovskites with M=Sr, the observed space groups are I2/m (M′ =W) and (M′=Te), respectively. In the case of M=Ca, the space groups are either monoclinic P2₁/n (M′=U) or cubic (M′=W and Te). The tetragonal and orthorhombic symmetry reported earlier for Ba₂SrTeO₆ and Ba₂CaUO₆, respectively, were not observed. In addition, non-ambient X-ray diffraction data were collected and analyzed for Ba₂SrWO₆ and Ba₂CaWO₆ in the temperature range between 80 and 723 K. It was found that the rhombohedral structure exists in Ba₂SrWO₆ above room temperature between the monoclinic and the cubic structure, whereas the cubic Ba₂CaWO₆ undergoes a structural phase transition at low temperature to the tetragonal I4/m structure.     

Physical and optical properties of the quaternary sulfides SrCu2MS4 and EuCu2MS4 (M=Ge and Sn)

Four quaternary sulfides SrCu₂MS₄ and EuCu₂MS₄ (M=Ge and Sn) were prepared from a thoroughly ground mixture of EuS or SrS, Cu, or Sn, and S in stoichiometric proportions. Electrical conductivity measurements on pressed pellets showed that all the phases are semiconductors. The optical band gaps were assessed at 2.8 eV for SrCu₂GeS₄, 2.1 eV for SrCu₂SnS₄, 2.2 eV for EuCu₂SnS₄, and 1.6 eV for EuCu₂GeS₄. Both Sr-based compounds present a temperature-independent paramagnetism, of about +135×10⁻⁶ and +92×10⁻⁶ emu/mol, for SrCu₂SnS₄ and SrCu₂GeS₄, respectively. In the case of the europium compounds, they follow a Curie-Weiss dependence above 1.8 K (EuCu₂GeS₄) and above 4 K (for EuCu₂SnS₄), with values of the magnetic effective moment μ_eff and the Curie-Weiss temperature Θ, equal to 6.27 μ_B and −2.8 K for EuCu₂GeS₄, and 6.81 μ_B and +0.7 K, for EuCu₂SnS₄. The experimental magnetic moments confirm that the europium ion is in divalent state, similar to Sr in the related compounds.     

Crystal structures of the ionic conductors Bi46M8O89 (M=P, V) related to the fluorite-type structure

The crystal structures of the two oxides Bi₄₆M₈O₈₉ (M=P, V) have been solved from single crystals X-ray data at room temperature. Bi₄₆P₈O₈₉ crystallizes in the monoclinic symmetry (space group C2/m) with the cell parameters , , and β=112.14(3)°. The symmetry of Bi₄₆V₈O₈₉ is also monoclinic but the space group is P2₁/c with the unit-cell parameters: , , and β=107.27(3)°. Both structures derive from an oxygen deficient fluorite-type structure where the Bi and M cations (M=P, V) are ordered in the framework. The structures are characterised by isolated MO₄ tetrahedra (M=P, V) which contradicts the previous results. The difference between the two structures is only due to a different order of the M atoms (M=P, V) in the fluorite-type superstructure. It will be shown that some oxygen sites are partially occupied in both structures which can explain the ion conduction properties of these phases. A structural building principle will be proposed that can explain the large domain of solid solution related to the fluorite-type observed in both systems.     

Crystal chemistry of MSeO3 and MTeO3 (M = Mg,Mn, Co,Ni, Cu,and Zn)

New selenites and tellurites MgSeO₃, MnSeO₃, CoSeO₃, NiSeO₃, CuSeO₃, MnTeO₃, CoTeO₃, and NiTeO₃ were synthesized under high pressures and temperatures. All the compounds are isomorphous and their crystal system is orthorhombic. Structure analyses were carried out for all the selenites and CoTeO₃. The structure is described as a salt of M²⁺ and SeO₃^2? or TeO₃^2? ions or as a distorted perovskite. In these compounds an Se or Te atom is closely linked to three oxygen atoms to form a flattened trigonal pyramid. The features of this coordination are discussed. At low temperature, magnetic order appears in all the compounds containing iron group ions, among which CuSeO₃ is a ferromagnet with the Curie temperature of 26°K.     

Crystal structures of lazulite-type oxidephosphates TiTi3O3(PO4)3 and M4Ti27O24(PO4)24 (M=Ti, Cr, Fe)

Single crystals of the oxidephosphates Ti^IIITi^IV₃O₃(PO₄)₃ (black), Cr^III₄Ti^IV₂₇O₂₄(PO₄)₂₄ (red-brown, transparent), and Fe^III₄Ti^IV₂₇O₂₄(PO₄)₂₄ (brown) with edge-lengths up to 0.3 mm were grown by chemical vapour transport. The crystal structures of these orthorhombic members (space group F2dd ) of the lazulite/lipscombite structure family were refined from single-crystal data [Ti^IIITi^IV₃O₃(PO₄)₃: Z=24, a=7.3261(9) Å, b=22.166(5) Å, c=39.239(8) Å, R₁=0.029, wR₂=0.084, 6055 independent reflections, 301 variables; Cr^III₄Ti^IV₂₇O₂₄(PO₄)₂₄: Z=1, a=7.419(3) Å, b=21.640(5) Å, c=13.057(4) Å, R₁=0.037, wR₂=0.097, 1524 independent reflections, 111 variables; Fe^III₄Ti^IV₂₇O₂₄(PO₄)₂₄: Z=1, a=7.4001(9) Å, b=21.7503(2) Å, c=12.775(3) Å, R₁=0.049, wR₂=0.140, 1240 independent reflections, 112 variables). For Ti^IIITi^IVO₃(PO₄)₃ a well-ordered structure built from dimers [Ti^III,IV₂O₉] and [Ti^IV,IV₂O₉] and phosphate tetrahedra is found. The metal sites in the crystal structures of Cr₄Ti₂₇O₂₄(PO₄)₂₄ and Fe₄Ti₂₇O₂₄(PO₄)₂₄, consisting of dimers [M^IIITi^IVO₉] and [Ti^IV,IV₂O₉], monomeric [Ti^IVO₆] octahedra, and phosphate tetrahedra, are heavily disordered. Site disorder, leading to partial occupancy of all octahedral voids of the parent lipscombite/lazulite structure, as well as splitting of the metal positions is observed. According to Guinier photographs Ti^III₄Ti^IV₂₇O₂₄(PO₄)₂₄ (a=7.418(2) Å, b=21.933(6) Å, c=12.948(7) Å) is isotypic to the oxidephosphates M^III₄Ti^IV₂₇O₂₄(PO₄)₂₄ (M^III: Cr, Fe). The UV/vis spectrum of Cr₄Ti₂₇O₂₄(PO₄)₂₄ reveals a rather small ligand-field splitting Δ_o=14,370 cm⁻¹ and a very low nephelauxetic ratio β=0.72 for the chromophores [Cr^IIIO₆] within the dimers [Cr^IIITi^IVO₉].     

Crystal structure and properties of the new vanadyl(IV)phosphates Na2MVO(PO4)2, M=Ca and Sr

Two new complex vanadyl(IV)phosphates Na₂MVO(PO₄)₂ (M=Ca, Sr) were synthesized in evacuated quartz ampoules and investigated by means of X-ray diffraction, electron microscopy, DTA, ESR and magnetic susceptibility measurements. The crystal structure of Na₂SrVO(PO₄)₂ was solved ab initio from X-ray powder diffraction data. Both compounds are isostructural: a=10.5233(3) Å, b=6.5578(2) Å, c=10.0536(3) Å and a=10.6476(3) Å, b=6.6224(2) Å, c=10.2537(3) Å for Ca and Sr, respectively; S.G. Pnma, Z=4. The compounds have a three-dimensional structure consisting of V⁴⁺O₆ octahedra connected by PO₄ tetrahedra via five of the six vertexes forming a framework with cross-like channels. The strontium and sodium atoms are located in the channels in an ordered manner. Electron diffraction as well as high-resolution electron microscopy confirmed the structure solution. The new vanadylphosphates are Curie-Weiss paramagnets in a wide temperature range down to 2 K with θ=12 and 5 K for Ca and Sr phases, respectively.     

Reactivity of metal oxides: Thermal and photochemical dissolution of MO and MFe2O4 (M=Ni, Co, Zn)

Dissolution rates of NiO, CoO, ZnO, α-Fe₂O₃ and the corresponding ferrites in 0.1 mol dm⁻³ oxalic acid at pH 3.5 were measured at 70 °C. The dissolution of simple oxides proceeds through the formation of surface metal oxalate complexes, followed by the transfer of surface complexes (rate-determining step). At constant pH, oxalate concentration and temperature, the trend in the first-order rate constant for the transfer of the surface complexes (k_Me; Me=Ni, Co, Zn, Fe) parallels that of water exchange in the dissolved metal ions (k_−w). Thus, the most important factor determining the rates of dissolution of metal oxides is the lability of Me-O bonds, which is in turn defined by the electronic structure of the metal ion and its charge/radius ratio. UV (384 nm) irradiation does not increase significantly the dissolution rates of NiO, CoO and ZnO, whereas hematite is highly sensitive to UV light. For ferrites, the reactivity order is ZnFe₂O₄>CoFe₂O₄?NiFe₂O₄. Dissolution is congruent, with rates intermediate between those of the constituent oxides, Fe₂O₃ and MO (M=Co, Ni, Zn), reflecting the behavior of very thin leached layers with little Zn and Co, but appreciable amounts of Ni. The more robust Ni²⁺ labilizes less the corresponding ferrite. The correlation between log k_M and log k_−w is somewhat blurred and displaced to lower k_M values. Fe(II), either photogenerated or added as salt, enhances the rate of Fe(III) phase transfer. A simple reaction mechanism is used to interpret the data.     

Crystal Structures and Magnetic Properties of 6H-Perovskites Ba3MRu2O9 (M=Y, In, La, Sm, Eu, and Lu)

Magnetic properties of quaternary oxides Ba₃MRu₂O₉ (M=Y, In, La, Sm, Eu, and Lu) are reported. Rietveld analyses of the X-ray diffraction data indicate that they adopt the 6H-perovskite structure and have the valence state of Ba₃M³⁺ Ru^4.5+₂O₉. All compounds are nonmetallic at least over the temperature range of 100-400 K. The magnetic susceptibilities show a broad maximum at 135-370 K except for the La compound, which shows a plateau around 22 K. In addition, another magnetic anomaly is observed at 4.5-12.5 K by the magnetic susceptibility and specific heat measurements for any compound. It is considered that this magnetic behavior is ascribed to the antiferromagnetic coupling between two Ru ions in a Ru₂O₉ dimer and to the magnetic interaction between the Ru₂O₉ dimers.     

A simple solvothermal synthesis of MFe2O4 (M=Mn, Co and Ni) nanoparticles

Nanoparticles of MFe₂O₄ (M=Mn, Co and Ni), with diameters ranging from 5 to 10 nm, have been obtained through a solvothermal method. In this synthesis, an alcohol (benzyl alcohol or hexanol) is used as both a solvent and a ligand; it is not necessary, therefore, to add a surfactant, simplifying the preparation of the dispersed particles. We have studied the influence of the synthetic conditions (temperature, time of synthesis and nature of solvent) on the quality of the obtained ferrites and on their particle size. In this last aspect, we have to highlight that the solvent plays an important role on the particle size, obtaining the smallest diameters when hexanol was used as a solvent. In addition, the magnetic properties of the obtained compounds have been studied at room temperature (RT). These compounds show a superparamagnetic behaviour, as was expected for single domain nanoparticles, and good magnetization values. The maxima magnetization values of the MFe₂O₄ samples are quite high for such small nanoparticles; this is closely related to the high crystallinity of the particles obtained by the solvothermal method.     

Crystal structure and magnetic properties of Sr4Mn2NiO9

The crystal structure of Sr₄Mn₂NiO₉ has been refined on single crystal. This phase belongs to the series A_1+x(A^′_xB_1–x)O₃ (x=1/3) related to the 2H-hexagonal perovskite. The structure contains transition metals in chains of oxide polyhedra (trigonal prisms and octahedra); neighboring chains are separated from each other by the Sr atoms. The sequence of the face sharing polyhedra along the chains is two octahedra + one trigonal prism. Mn occupies the octahedra and Ni is disordered in the trigonal prism with ≈80% in the pseudo square faces of the prism and ≈20% at the centre. This result has been confirmed by XANES experiments at Mn K and Ni K edges, respectively. Sr₄Mn₂NiO₉ is antiferromagnetic with a Néel temperature at T=3 K. The Curie constant measured at high temperature is in good agreement with ≈80% of the Ni²⁺ ions in the spin state configuration S=0.     

Electronic band structures and photovoltaic properties of MWO4 (M=Zn, Mg, Ca, Sr) compounds

Divalent metal tungstates, MWO₄, with wolframite (M=Zn and Mg) and scheelite (M=Ca and Sr) structures were prepared using a conventional solid state reaction method. Their electronic band structures were investigated by a combination of electronic band structure calculations and electrochemical measurements. From these investigations, it was found that the band structures (i.e. band positions and band gaps) of the divalent metal tungstates were significantly influenced by their crystal structural environments, such as the W-O bond length. Their photovoltaic properties were evaluated by applying to the working electrodes for dye-sensitized solar cells. The dye-sensitized solar cells employing the wolframite-structured metal tungstates (ZnWO₄ and MgWO₄) exhibited better performance than those using the scheelite-structured metal tungstates (CaWO₄ and SrWO₄), which was attributed to their enhanced electron transfer resulting from their appropriate band positions.     

Three-dimensional five-connected coordination polymer [M2(C3H2O4)2(H2O)2(μ2-hmt)]n with 46 topologies (M=Zn, Cu; hmt=hexamethylenetetramine)

Two novel three-dimensional five-connected coordination polymers [M₂(C₃H₂O₄)₂(H₂O)₂(μ₂-hmt)]_n with 4⁴6⁶ topologies (M=Zn, Cu; hmt=hexamethylenetetramine) were synthesized and characterized by elemental analysis, crystal structure, IR, thermal gravimetric analyses. Both [Zn₂(C₃H₂O₄)₂(H₂O)₂(μ₂-hmt)]_n and [Cu₂(C₃H₂O₄)₂(H₂O)₂(μ₂-hmt)]_n all crystallize in the orthorhombic system, space group Imm2, and with Z=2. Metal ions have all octahedral geometry coordinated by four oxygen atoms from three malonates, one oxygen atom from a water molecule and one nitrogen atom of hmt ligand. Each malonate binds a metal ion with its two oxygen atoms in a chelating mode and connects to adjacent two metal ions with another two oxygen atoms to form an infinite wavy layer. The layers are bridged by μ₂-hmt molecules to form a three-dimensional framework with channels. The magnetic susceptibility data show there is a weak antiferromagnetic exchange interaction in the complex [Cu₂(C₃H₂O₄)₂(H₂O)₂(μ₂-hmt)]_n.     

Studies of microstructure and ruthenium valence in the ruthenocuprates Pb2RuSr2Cu2O8Cl and (Ru, M)Sr2GdCu2O8 (M=Sn, Nb)

Ruthenocuprate microstructures and Ru valences have been studied. Electron microscopy reveals short-range order of the RuO₆ octahedra rotations into a √2a×√2a×c supercell in Pb₂RuSr₂Cu₂O₈Cl. However, reanalysis of neutron diffraction data gives no significant difference between the populations of the rotation states, showing that the coherence length is very short (<100 Å). The Ru valence estimated from the XANES spectrum of Pb₂RuSr₂Cu₂O₈Cl is ∼5, in keeping with the physical properties of this material which show that there is essentially no Ru-Cu charge transfer. The Ru valence in doped Ru_1−xM_xSr₂GdCu₂O₈ (M=Sn, Nb) is ∼4.8 in all samples, verifying a previous rigid band analysis of the charge distribution in these materials.     

Rare-earth-rich tellurides: Gd4NiTe2 and Er5M2Te2 (M=Co, Ni)

Three new rare earth metal-rich compounds, Gd₄NiTe₂, and Er₅M₂Te₂ (M=Ni, Co), were synthesized in direct reactions using R, R₃M, and R₂Te₃ (R=Gd, Er; M=Co, Ni) and single-crystal structures were determined. Gd₄NiTe₂ is orthorhombic and crystallizes in space group Pnma with four formula units per cell. Lattice parameters at 110(2) K are a=15.548(9), b=4.113(2), . Er₅Ni₂Te₂ and Er₅Co₂Te₂ are isostructural and crystallize in the orthorhombic space group Cmcm with two formula units per cell. Lattice parameters at 110(2) K are a=3.934(1), b=14.811(4), , and a=3.898(1), b=14.920(3), , respectively. Metal-metal bonding correlations were analyzed using the empirical Pauling bond order concept.     

Synthesis and crystal structure of new uranyl tungstates M2(UO2)(W2O8) (M=Na, K), M2(UO2)2(WO5)O (M=K, Rb), and Na10(UO2)8(W5O20)O8

The solid-state reactions of UO₃ and WO₃ with M₂CO₃ (M=Na, K, Rb) at 650°C for 5 days result, accordingly the starting stoichiometry, in the formation of M₂(UO₂)(W₂O₈) (M=Na (1), K (2)), M₂(UO₂)₂(WO₅)O (M=K (3), Rb (4)), and Na₁₀(UO₂)₈(W₅O₂₀)O₈ (5). The crystal structures of compounds 2, 3, 4, and 5 have been determined by single-crystal X-ray diffraction using Mo(Kα) radiation and a charge-coupled device detector. The crystal structures were solved by direct methods and Fourier difference techniques, and refined by a least-squares method on the basis of F² for all unique reflections. For (1), unit-cell parameters were determined from powder X-ray diffraction data. Crystallographic data: 1, monoclinic, a=12.736(4) Å, b=7.531(3) Å, c=8.493(3) Å, β=93.96(2)°, ρ_cal=6.62(2) g/cm³, ρ_mes=6.64(1) g/cm³, Z=4; 2, orthorhombic, space group Pmcn, a=7.5884(16) Å, b=8.6157(18) Å, c=13.946(3) Å, ρ_cal=6.15(2) g/cm³, ρ_mes=6.22(1) g/cm³, Z=8, R1=0.029 for 80 parameters with 1069 independent reflections; 3, monoclinic, space group P2₁/n, a=8.083(4) Å, b=28.724(5) Å, c=9.012(4) Å, β=102.14(1)°, ρ_cal=5.83(2) g/cm³, ρ_mes=5.90(2) g/cm³, Z=8, R1=0.037 for 171 parameters with 1471 reflections; 4, monoclinic, space group P2₁/n, a=8.234(1) Å, b=28.740(3) Å, c=9.378(1) Å, β=104.59(1)°, ρ_cal=6.13(2) g/cm³,  g/cm³, Z=8, R1=0.037 for 171 parameters with 1452 reflections; 5, monoclinic, space group C2/c, a=24.359(5) Å, b=23.506(5) Å, c=6.8068(14) Å, β=94.85(3)°, ρ_cal=6.42(2) g/cm³,  g/cm³, Z=8, R1=0.036 for 306 parameters with 5190 independent reflections. The crystal structure of 2 contains linear one-dimensional chains formed from edge-sharing UO₇ pentagonal bipyramids connected by two octahedra wide (W₂O₈) ribbons formed from two edge-sharing WO₆ octahedra connected together by corners. This arrangement leads to [UW₂O₁₀]²⁻ corrugated layers parallel to (001). Owing to the unit-cell parameters, compound 1 probably contains similar sheets parallel to (100). Compounds 3 and 4 are isostructural and the structure consists of bi-dimensional networks built from the edge- and corner-sharing UO₇ pentagonal bipyramids. This arrangement creates square sites occupied by W atoms, a fifth oxygen atom completes the coordination of W atoms to form WO₅ distorted square pyramids. The interspaces between the resulting [U₂WO₁₀]²⁻ layers parallel to plane are occupied by K or Rb atoms. The crystal structure of compound 5 is particularly original. It is based upon layers formed from UO₇ pentagonal bipyramids and two edge-shared octahedra units, W₂O₁₀, by the sharing of edges and corners. Two successive layers stacked along the [100] direction are pillared by WO₄ tetrahedra resulting in sheets of double layers. The sheets are separated by Na⁺ ions. The other Na⁺ ions occupy the rectangular tunnels created within the sheets. In fact complex anions W₅O₂₀¹⁰⁻ are built by the sharing of the four corners of a WO₄ tetrahedron with two W₂O₁₀ dimmers, so, the formula of compound 5 can be written Na₁₀(UO₂)₈(W₅O₂₀)O₈.