KxP2W2O16: A bronze with a tunnel structure built up from PO4 tetrahedra and WO6 octahedra

The structure of a $\text{K}{}_{\mathrm{x}}\text{P}{}_2\text{W}{}_4\text{O}{}_{16}\text{(x ? 0.4)}$ crystal was established by X-ray analysis. The solution in the cell of symmetry $\text{P2}{}_1\text{m}$, with a = 6.6702(5), b = 5.3228(8), c = 8.9091(8) Å, β = 100.546(7)°, Z = 1, has led to R = 0.033 and R_w = 0.036 for 2155 reflections with $\text{σ(I)}\text{I}\text{≤ 0.333}$. This structure can be described as two octahedra-wide ReO₃-type slabs connected through “planes” of PO₄ tetrahedra. A new structural family K_xP₂W_2nO_6n+4 can be foreseen which is closely related to the orthorhombic P₄W₈O₃₂ and the monoclinic Rb_xP₈W_8nO_24n+16 series.     

K1.4P4W14O50: An odd-m member (m = 7) of the monophosphate tungsten bronze series KxP4O8(WO3)2m

The crystal structure of K_xP₄W₁₄O₅₀ (x = 1.4) has been solved by three-dimensional single crystal X-ray analysis. The refinement in the cell of symmetry $\text{A2}\text{m}$, with a = 6.660(2) Å, b = 5.3483(3) Å, c = 27.06(5) Å, and β = 97.20(2)°, Z = 1, has led to R = 0.036 and R_w = 0.039 for 2436 reflections with $\text{σ(I)}\text{I}\text{≤ 0.333}$. This structure belongs to the structural family K_xP₄O₈(WO₃)_2m, called monophosphate tungsten bronzes (MPTB), which is characterized by ReO₃-type slabs of various widths connected through PO₄ single tetrahedra. This bronze corresponds to the member m = 7 of the series and its framework is built up alternately of strands of three and four WO₆ octahedra. The structural relationships with the P₄O₈(WO₃)_2m series, called M′PTB, are described and the possibility of intergrowth between these two structures is discussed.     

Bronzes with a tunnel structure KxP4O8(WO3)2m: The tenth member of the series—KP8W40O136

The crystal structure of KP₈W₄₀O₁₃₆, the tenth member of the series K_xP₄O₈(WO₃)_2m, has been resolved by three-dimensional single-crystal X-ray analysis. The space group is $\text{P2}{}_1\text{c}$ and the cell parameters are a = 19.589(3) Å, b = 7.5362(4) Å, c = 16.970(3) Å and β = 91.864(14)°. The framework is built up from ReO₃-type slabs connected through pyrophosphate groups. The structure is compared to those of the other members of the series: although the ReO₃-type slabs show a different type of tilting of the WO₆ octahedra, the dispersion of WO distances is always higher for the octahedra linked to one or two P₂O₇ groups and decreases in proportion as W is farther from these groups. The perovskite cages of the slabs are described and compared to those encountered in the structures of WO₃ and of the bronzes A_xWO₃.     

Formation of pentagonal tunnels bordered with P2O7 groups in diphosphate tungsten bronzes (P2O4)2(WO3)2m: A HREM investigation

During the investigation of the phosphate bronzes (PO₂)₄(WO₃)_2m [MPTB_P] and K_x(P₂O₄)₂WO₃)_2m [DPTB_H] crystals of a new type were observed. HREM images of these crystals showed twinned ReO₃-type slabs the junction of which was parallel to the (102)_ReO3 plane. The proposed model identified the twin boundary as built from P₂O₇ groups involving the formation of pentagonal tunnels. The structure of this new type of extended defects is quite original: it corresponds to a new structural type named “diphosphate tungsten bronzes with pentagonal tunnels” [DPTB_P], for which no regular member could be synthesized. Image calculations were performed to confirm the junction model. Apart from the disordered stacking of the ReO₃-type slabs, very few defects were observed and shear planes were only obtained in reduced samples. This new structural type takes its place in the large family of phosphate tungsten bronzes where all members (DPTB_H, MPTB_H, MPTB_P) are very closely related.     

Phase relations in the K2W2O7-K2WO4-KPO3-Bi2O3 system and structure of K6.5Bi2.5W4P6O34

The phase relations in the cross-section of the K₂W₂O₇-K₂WO₄-KPO₃ containing 15 mol% Bi₂O₃ were undertaken using flux method. Crystallization fields of K_6.5Bi_2.5W₄P₆O₃₄, K₂Bi(PO₄)(WO₄), Bi₂WO₆, KBi(WO₄)₂ and their cocrystallization areas were identified. Novel phase K_6.5Bi_2.5W₄P₆O₃₄ was characterized by single-crystal X-ray diffraction: sp. gr. P−1, a=9.4170(5), b=9.7166(4), c=17.6050(7) Å, α=90.052(5)°, β=103.880(5)° and γ=90.125(5)°. It has a layered structure, which contains {K₇Bi₅W₈P₁₂O₆₈}_∞ layers stacked parallel to ab plane and sheets composed by potassium atoms separating these layers. Sandwich-like {K₇Bi₅W₈P₁₂O₆₈}_∞ layers are assembled from [W₂P₂O₁₃]_∞ and [BiPO₄]_∞ building units, and are penetrated by tunnels with K/Bi atoms inside. FTIR-spectra of K₂Bi(PO₄)(WO₄) and K_6.5Bi_2.5W₄P₆O₃₄ were discussed on the basis of factor group theory.     

Synthesis and characterization of the novel Nb3O5F5 niobium oxyfluoride: the term n=3 of the NbnO2n−1Fn+2 series

The solid-state synthesis of the oxyfluoride Nb₃O₅F₅, its crystal structure determined from X-ray powder diffraction data as well as some physical characterizations, are reported. Nb₃O₅F₅ constitutes the term n=3 of the Nb_nO_2n−1F_n+2 series related to the Dion-Jacobson phases. It crystallizes, at room temperature, in the tetragonal system (space group I4/mmm (no. 139); Z=4; a=3.9135(1) Å, c=24.2111(2) Å, and V=370.80(3) Å³). The crystal structure appears to be an in-between of the three-dimensional network of NbO₂F and the two-dimensional packing of NbOF₃ (term n=1 of the Nb_nO_2n−1F_n+2 series). This layered structure consists of slabs made of three Nb(O,F)₆ corner-linked octahedra in thickness (n=3) shifted one from another by a ()/translation. Oxygen and fluorine atoms are randomly distributed over all the ligand sites.     

Novel perovskite-related barium tungstate Ba11W4O23

Ba₁₁W₄O₂₃ was synthesized at 1300 °C, followed by quenching with liquid nitrogen. The crystal structure, which was known to be cryolite-related but has remained unclear, was initially determined by single-crystal X-ray diffraction for the isostructural Ru-substituted compound Ba₁₁(W_3.1Ru_0.9)O_22.5, which was discovered during exploratory synthesis in the Ba-Ru-O system. The structure of Ba₁₁W₄O₂₃ was refined by a combined powder X-ray and neutron Rietveld method (Fd-3m, a=17.1823(1) Å, Z=8, R_p=3.09%, R_wp=4.25%, χ²=2.8, 23 °C). The structure is an example of A-site vacancy-ordered 4×4×4 superstructure of a simple perovskite ABO₃, and it may be written as (Ba_1.75□_0.25)BaWO_5.75□_0.25, emphasizing vacancies on both metal and anion sites. The local structure of one of two asymmetric tungsten ions is the WO₆ octahedron, typical of perovskite. The other tungsten, however, is surrounded by oxygen and anionic vacancies statistically distributed over three divided sites to form 18 partially occupied oxygen atoms (∼30% on average), represented as WO_18/3. The A-site cation-vacancies are ordered at the 8a (, , ) site in between adjoining WO_18/3 polyhedra which form 1-D arrangements along [110] and equivalent directions. In situ high-temperature XRD data have shown that the quenched Ba₁₁W₄O₂₃ at room temperature is isostructural to the high-temperature phase at 1100 °C.     

Low-temperature phases of the solid electrolyte Ag26I18W4O16

Single crystal X-ray diffraction photographs taken with a Buerger precession camera, at temperatures 250, 214, and 122 K, corroborate the existence of three low-temperature phases of Ag₂₆I₁₈W₄O₁₆. These phases are labeled α′, β, and γ in order of decreasing temperature. The α′ phase is monoclinic, space group P2₁, Z = 2; the β phase is triclinic, space group $\text{P}\text{1}$ or P1, Z = 2; and the γ phase is triclinic, space group P1, Z = 1. Lattice constants at the aforementioned temperatures are given. Twins in the β and γ phases are related by the albite and pericline laws, as are twins in the feldspars. The highest symmetry known to be attained by the (W₄O₁₆)^8? entity is 2(C₂), which, strictly, it must lose at the transition to the α′ phase.     

Intercalation behavior of n-alkylamines into an A-site defective layered perovskite H2W2O7

Intercalation behavior of n-alkylamines into a protonated form of an A-site defective layered perovskite H₂W₂O₇ has been investigated. Results from XRD indicate these materials are layered with the corresponding interlayer spacing governed by the n-alkylamine chain length, and a reversible intercalation and deintercalation property is observed among these intercalation compounds. The IR spectra of the intercalation compounds with n-alkylamines clearly show that n-alkyl chains possess an all-trans conformation, and H₂W₂O₇ accommodate n-alkylamines (C_nH_2n+1NH₂: n=3, 4, 7, 8, 12, 16) to form intercalation compounds via an acid-base mechanism. A linear relationship between the interlayer distance and the number of carbon atoms in n-alkyl chains is observed to show a bilayer arrangement of the n-alkyl chains with a tilt angle of ∼71.6°. Elemental analysis studies reveal that the amounts of intercalated n-alkylamines are about 2.0 mol per [W₂O₇]. Despite the surface geometry of H₂W₂O₇ is almost identical to those of layered perovskites H₂[A_n−1B_nO_3n+1], the amounts of intercalated n-alkylamines of them are different. A reasonable explanation is given through our research.     

Structural investigation of R2Mo4O15 (R=La, Nd, Sm), and polymorphs of the R2Mo4O15 (R=rare earth) family

Pyrolysis of rare earth (R) polyoxomolybdate, [R₂(H₂O)₁₂Mo₈O₂₇]·xH₂O (R=La, Nd and Sm), at 750°C for 2-8 h results in crystallization of R₂Mo₄O₁₅ compounds. β-La₂Mo₄O₁₅ crystallizes together with an α-form in monoclinic P2₁/a (No. 14), a=13.8893(5), b=13.0757(4), c=20.0927(8) Å, β=95.199(2)°, V=3634.1(2) Å³, Z=12, R₁(I>2σ(I))=0.048, R_w (all data)=0.116. The structure is built up with {LaO_n} (n=9, 10) and {MoO_n′} (n′=4-6) polyhedral units. The {LaO_n} units are polymerized into a linear {La₆O₃₉}_∞ chain, while the {MoO_n} are connected together to form {Mo₄O₁₅} and {Mo₇O₂₆} groups. The structure can be related to the α-form by partial rearrangement of O atoms and small shifts of La and Mo atoms. The R₂Mo₄O₁₅ (R=Nd and Sm) compounds are isomorphous with the previously reported R=Eu and Gd analogs, crystallizing in triclinic, (No. 2), a=9.4989(5) and 9.4076(7), b=11.0088(7) and 10.9583(8), c=11.5665(6) and 11.5234(8) Å, α=104.141(3) and 104.225(3), β=109.838(3) and 109.603(3), γ=108.912(3) and 108.999(3)°, V=987.3(1) and 970.5(1) Å³, Z=3, R₁(I>2σ(I))=0.028 and 0.030, R_w (all data)= 0.079 and 0.094, respectively. The crystal structure is composed of {RO₈} and {MoO_n′} (n′=4-6) polyhedral units. The molybdate units are condensed to give a corrugated {Mo₄O₁₇}_∞ chain. The square-antiprismatic {RO₈} units share their trigonal and square faces, forming {R₂O₁₃} and {R₂O₁₂} groups, respectively. A very short R?R distance (3.557(6) Å for R=Nd; 3.4956(6) Å for R=Sm) is achieved in the latter unusual {R₂O₁₂} group. A common cationic arrangement was found in all the structures in the R₂Mo₄O₁₅ family: a R-R pair with the shortest separation and surrounding 12 Mo atoms. The symmetry of the cationic arrangement was reduced with an increase of atomic number of R, viz. La>Ce, Pr>Nd-Gd≈Tb, Ho.     

A one-dimensional organic-inorganic hybrid based on the bimolecular {[Cu(en)2]2[Cu2Si2W22O78]} polyoxometalate

A one-dimensional coordination polymer [Cu(en)₂]₂[Cu(en)₂(H₂O)]₂{[Cu(en)₂]₂[Cu₂Si₂W₂₂O₇₈]}·4.5H₂O (en=ethylenediamine), which represents the first example of one-dimensional organic-inorganic hybrid based on the bimolecular Keggin polyoxometalates {[Cu(en)₂]₂[Cu₂Si₂W₂₂O₇₈]}⁸⁻ has been hydrothermally synthesized and characterized by elemental analyses, IR, TG and single crystal X-ray diffraction. Crystal data: C₂₄H₈₅Cu₈N₂₄O_84.5Si₂W₂₂, monoclinic, P2₁/c, a=18.8126(3), b=23.0896(4), c=26.0711(4) Å, β=96.3790(10)°, V=11254.5(3) Å³, T=293(2) K; Z=4, μ=23.983 mm⁻¹, R₁=0.0628, wR₂=0.1210 [I>2σ], R₁=0.0854, wR₂=0.1285 (all data ).     

The monophosphate tungsten bronzes with pentagonal tunnels (MPTBP, P4O8(WO3)2m: A high-resolution electron microscopy study

A series of monophosphate tungsten bronzes of composition P₄O₈(WO₃)_2m with pentagonal tunnels, MPTB_P, have been investigated by high resolution electron microscopy. Most of the micrographs of the integral m members exhibit an asymmetrical contrast which could not be explained qualitatively by the structural models derived from X-ray diffraction studies of some members of the series. Image calculations were thus performed on the m = 4 member (P₄W₈O₃₂), which showed that the unexpected symmetry does not result from a structural anomaly, but could be due to a titled electron beam. The observations revealed that ordered crystals can be obtained up to m = 16. The investigation of the nonintegral m compositions showed two sorts of intergrowths: disordered intergrowths of different m members belonging to the MPTB_P series and ordered intergrowths of the MPTB_P structure with a related phosphate tungsten bronze structure based upon hexagonal tunnels.     

The crystal structure of Na7Mg4.5(P2O7)4

The crystal structure of Na₇Mg_4.5(P₂O₇)₄ has been solved by direct methods from the three-dimensional X-ray data. The space group is $\text{P}\text{1}$. The crystal structure consists of Mg²⁺, Na⁺, and P₂O^4?₇ ions. One magnesium atom at symmetry center (0,0,0) and two sodium atoms at ±(?0.0421, ?0.0596, 0.2230) display occupation factors 0.5 each. A short interatomic distance between these Na⁺ and Mg²⁺ ions (1.80 ± 0.01 Å) excludes the occupation of both sites in the same unit cell. The crystal structure of Na₇Mg_4.5(P₂O₇)₄ consists of unit cells containing Na₈Mg₄(P₂O₇)₄ or Na₆Mg₅(P₂O₇)₄ with a statistical occurrence 1:1.Each Mg²⁺ ion is octahedrally coordinated by six O^2? ions at distances 1.979 – 2.270 Å. The coordination polyhedra around the Na⁺ ions are ill-defined. The bond angles POP in the P₂O^4?₇ groups are 126.6 and 133.6° (±0.3°). The final reliability factor R is 7.1%.     

The crystal structure of a complex cerium(III) molybdate containing a dimolybdate chain,Ce2(MoO4)2(Mo2O7)

Ce₂(MoO₄)₂(Mo₂O₇) crystallizes in the triclinic system with unit cell dimensions (from single-crystal data) a = 11.903(8), b = 7.509(5), c = 7.385(5) Å, α = 94.33(8), β = 97.41(8), γ = 88.56(7)°, and space group $\text{P}\text{1}\text{, z = 2}$. The structure was solved using Patterson (“P1 method”) and Fourier techniques. Of the 8065 unique reflections measured by counter techniques, 6314 with I ≥ 3σ(I) were used in the least-squares refinement of the model to a conventional R of 0.035 (R_w = 0.034). The structure of Ce₂(MoO₄)₂(Mo₂O₇) consists of dimolybdate chains of the K₂Mo₂O₇ and (NH₄)₂Mo₂O₇ type separated by isolated MoO₄ tetrahedra and cerium(III) polyhedra.     

Monophosphate tungsten bronzes with pentagonal tunnels (PO2)4(WO3)2m: Structure of two even-m members P4W12O44 (m = 6) and P4W16O56 (m = 8)

Crystals of P₄W₁₂O₄₄ and P₄W₁₆O₅₆ have been synthesized. They are orthorhombic, space group P2₁2₁2₁ with a = 5.2927(7), b = 6.5604(7), c = 23.549(3)Å for P₄W₁₂O₄₄ and a = 5.2943(5), b = 6.5534(4), c = 29.700(4)Å for P₄W₁₆O₅₆. Structures were solved by the heavy-atom method and refined to R = 0.033 (R_w = 0.044) with 2031 independent reflections for P₄W₁₂O₄₄ and R = 0.043 (R_w = 0.052) with 2272 independent reflections for P₄W₁₆O₅₆. The structures are related to that of P₄W₈O₃₂ and can be described by the association of zig-zag chains of octahedra and tetrahedra. The members of the series (PO₂)₄(WO₃)_2m differ from one another by the length of the links in the chains of polyhedra. Pentagonal tunnels and O₁₈ cages are formed at the junction between the ReO₃-type slabs and the slices of PO₄ tetrahedra. The surroundings of P and W have been studied and compared with those of other phosphate tungsten bronzes; the relation with the apparent oxidation state of tungsten is discussed.     

High n-value phases in the complex bismuth oxides with layered structure,Bi2CaNan−2NbnO3n+3

Complex bismuth oxides with layered structure are prepared with a series of compositions in the system Bi₂CaNb₂O₉-NaNbO₃. It is found by X-ray powder diffraction that each compound is composed of more than two phases, which are described by a formula Bi₂CaNa_n?2Nb_nO_3n+3, e.g., in the sample with the nominal composition Bi₂CaNb₂O₉ · 8NaNbO₃, the phases with n = 6 to 8 appear predominantly. These phases are closely intergrown to each other. Moreover, high-resolution electron microscopy reveals that microsyntactic intergrowth frequently occurs in the phases with n > 5. The occurrence of the latter intergrowth is explained in terms of the bond length obtained.     

Crystal structure of KSbP2O8

KSbP₂O₈ crystallizes in the rhombohedral system, space group $\text{R}\text{3}$, with a = 4.7623(4) Å, c = 25.409(4)Å, and Z = 3. The structure was determined from 487 reflexions collected on a NONIUS CAD4 automatic diffractometer with MoK^?α radiation. The final R index and weighted R_w index are 0.030 and 0.038, respectively. This structure is built up from layers of SbO₆ octahedra and PO₄ tetrahedra sharing corners. These (SbP₂O^?₈)_n layers are very similar to the (ZrP₂O^2?₈)_n layers in the well-known α-ZrP compound.     

Structure, crystal chemistry and thermal evolution of the δ-Bi2O3-related phase Bi9ReO17

The thermal evolution and structural properties of fluorite-related δ-Bi₂O₃-type Bi₉ReO₁₇ were studied with variable temperature neutron powder diffraction, synchrotron X-ray powder diffraction and electron diffraction. The thermodynamically stable room-temperature crystal structure is monoclinic P2₁/c, a=9.89917(5), b=19.70356(10), c=11.61597(6) Å, β=125.302(2)° (R_p=3.51%, wR_p=3.60%) and features clusters of ReO₄ tetrahedra embedded in a distorted Bi–O fluorite-like network. This phase is stable up to 725 °C whereupon it transforms to a disordered δ-Bi₂O₃-like phase, which was modeled with δ-Bi₂O₃ in cubic Fm3¯m with a=5.7809(1) Å (R_p=2.49%, wR_p=2.44%) at 750 °C. Quenching from above 725 °C leads to a different phase, the structure of which has not been solved but appears on the basis of spectroscopic evidence to contain both ReO₄ tetrahedra and ReO₆ octahedra.     

Etude structurale de la forme ordonnée de LiAl5O8

A single crystal of ordered LiAl₅O₈ has been prepared by image furnace melting and its structure has been determined; 400 X-ray reflections were collected on an automatic counter diffractometer (MoKα radiation). The structure is of the spinel type. The space group is P4₃32 (or P4₁32); the lattice parameter is a = 7.908(2), Å, Z = 4. The value of R is 0.022. The distribution of cations shows the absence of Li⁺ ions in tetrahedral cation sites and 1–3 imperfect ordering of Li⁺ and Al₃₊ in octahedral cation sites of spinel.     

A novel germanate, Cu2Fe2Ge4O13, with a four tetrahedra oligomer

The structure of Cu₂Fe₂Ge₄O₁₃, previously thought to be CuFeGe₂O₆, has been determined from single-crystal X-ray diffraction data to be monoclinic, P2₁/m, a=12.1050(6), b=8.5073(4), c=4.8736(2) Å, β=96.145(1)°, Z=2, with R1=0.0231 and wR2=0.0605. The unique structure has an oligomer of four germanate tetrahedra, cross-linked laterally by square-planar copper ions, joined end-to-end by a zigzag chain of edge-sharing iron oxide octahedra. Running along the a-direction the metal oxide chain consists of alternating Cu-Cu and Fe-Fe dimers. A hypothetical series of homologous structures (Cu_n−2Fe₂Ge_nO_3n+1 with n=3,4,…,∞) with different length germanate oligomers is proposed, where as n increases, the infinite chain of the CuGeO₃ is approached. In this context, Cu₂Fe₂Ge₄O₁₃ is viewed as being built from blocks of CuGeO₃ and the Fe oxide chains. This material has significance to the study of low-dimensional mixed-spin systems.