Hydrothermal synthesis and structures of the novel niobium phosphates [NbOF(PO4)](N2C5H7) and [(Nb0.9V1.1)O2(PO4)2(H2PO4)](N2C2H10)

Two new niobium phosphates were synthesized and their crystal structures determined from single-crystal X-ray data. [NbOF(PO₄)](N₂C₅H₇) (1) (monoclinic, space group P2₁/c, a=11.442(1), b=9.1983(7), c=9.1696(8) Å, β=109.94(1)°) has a layered structure and is the first example of a negatively charged NbOF(PO₄) layer analogous to the MO(H₂O)PO₄ (M=V, Nb) layers. The layer charge is compensated by interlayer 4-aminopyridnium cations that adopt an unusual arrangement as a consequence of H-bonding and π-π interactions. The interlayer aminopyridnium cations can be exchanged with alkylammonium ions which form bilayers inclined at ∼65° to the NbOF(PO₄) layer. [(Nb_0.9V_1.1)O₂(PO₄)₂(H₂PO₄)] (N₂C₂H₁₀) (2) (orthorhombic, space group Pbca, a=15.821(2),b=9.0295(9),c=18.301(2) Å) has a disordered three-dimensional structure based on NbO(PO₄) layers cross-linked by phosphate tetrahedra, and has a similar structure to the known vanadium analog [V₂O₂(PO₄)₂(H₂PO₄)] (N₂C₂H₁₀).     

Etude des equilibres solide-liquide des systems MIPO3Sm(PO3)3 (MI = Li,Na, Ag)

The M^IPO₃Sm(PO₃)₃(M^I = Li, Na, Ag) systems were studied. Differential thermal analysis and X-ray diffraction were used to investigate the liquidus and solidus relations. Three compounds LiSm(PO₃)₄, NaSm(PO₃)₄, and AgSm(PO₃)₄ were obtained which melt incongruently at 1248, 1143, and 1078 K, respectively. These compounds are isomorphous with their homologs LiLn(PO₃)₄, NaLn(PO₃)₄, AgLn(PO₃)₄ (Ln = Ce, La, Nd). They belong to the monoclinic system. The LiSm(PO₃)₄ unit cell parameters refined by least squares method are a = 16.43(3) Å, b = 7.16(1) Å, c = 9.65(3) Å, β = 125,9°(1), with the space group $\text{C2}\text{c}$ and Z = 4. NaSm(PO₃)₄ and AgSm(PO₃)₄ are isotypic; they cristallize in the $\text{P2}{}_1\text{c}$ space group, Z = 4; their unit cell parameters are, respectively, a = 12.18(1) Å, b = 13.05(1) Å, c = 7.25(5) Å, β = 126,53°(4), $\text{a = 12.25(1)}\text{A}\text{?}$, b = 13.06(1) Å, c = 7.201(9) Å, β = 126,57°(7). The ir spectra of the last two compounds indicate that these phosphates are chain phosphates.     

Phase equilibrium relations in the binary systems LiPO3CeP3O9 and NaPO3CeP3O9

The LiPO₃CeP₃O₉ and NaPO₃CeP₃O₉ systems have been investigated for the first time by DTA, X-ray diffraction, and infrared spectroscopy. Each system forms a single 1:1 compound. LiCe(PO₃)₄ melts in a peritectic reaction at 980°C. NaCe(PO₃)₄ melts incongruently, too, at 865°C. These compounds have a monoclinic unit cell with the parameters: a = 16.415(6), b = 7,042(6), c = 9.772(7)Å; β = 126.03(5)°; Z = 4; space group $\text{C}{}_2\text{c}$ for LiCe (PO₃)₄; and a = 9.981(4), b = 13.129(6), c = 7.226(5) Å, β = 89.93(4)°, Z = 4, space group $\text{P2}{}_1\text{n}$ for NaCe(PO₃)₄. It is established that both compounds are mixed polyphosphates with chain structure of the type |M^I_IM^III_II (PO₃)₄|_∞M^I_I: alkali metal, M^III_II: rare earth.     

Crystal structures and phase transitions of SrZr(PO4)2-BaZr(PO4)2 solid solutions

A complete series of solid solutions was prepared in the SrZr(PO₄)₂-BaZr(PO₄)₂ system and examined by conventional X-ray powder diffraction (XRPD). The crystals of Sr_xBa_1−xZr(PO₄)₂ with x?0.1 were isomorphous with yavapaiite (KFe(SO₄)₂, space group C2/m). The solid solution with 0.2?x?0.7 has been composed of a new phase, showing a superstructure along the a-axis (c-axis of the yavapaiite substructure). The crystals with 0.8?x?0.9 were composed of both the new phase and the triclinic phase, the latter being isostructural with SrZr(PO₄)₂ (x=1). The crystal structure of the new phase has been determined using direct methods, and it has been further refined by the Rietveld method. The crystal of Sr_0.7Ba_0.3Zr(PO₄)₂ (x=0.7) is monoclinic (space group P2/c, Z=4 and D_x/Mg m⁻³=3.73) with a=1.53370(8) nm, b=0.52991(3) nm, c=0.84132(4) nm, β=92.278(1)° and V=0.68321(6) nm³. Final reliability indices are R_wp=7.32%, R_p=5.60% and R_B=3.22%. The powder specimen was also examined by high-temperature XRPD and differential thermal analysis (DTA) to reveal the occurrence of two phase transitions during heating; the space group changed from P2/c to C2/m at ∼400 K, followed by the monoclinic-to-hexagonal (or trigonal) transition at 1060 K. The P2/c-to-C2/m transition has been, for the first time, described in the yavapaiite-type compounds.     

Rare earth substituted fluoride-phosphate apatites

Compositions with the general formula Ln_xM_10?2xNa_x(PO₄)₆F₂ (Ln = La, Pi, Nd, Sm, Eu, Dy, Er, Lu, andY;M = Ca, Sr, and Ba) have been prepared and studied by X-ray diffraction methods. The hexagonal apatite like structure was indicated by the powder patterns of all the compounds (with Ba compounds only when Ln = La through Sm). Single crystal precession data reveal that the crystal lattice of all the compositions in the Ca and Sr system have space group P6₃/m, the Ln₂Ba₆Na₂(PO₄)₆F₂ compounds crystallize in space group P6 and the Ln₃Ba₄Na₃(PO₄)₆F₂ compounds in the trigonal space group P3. Order and disorder mechanisms of the substitution and its dependence on size and polarization effects are discussed.     

New Gallium Phosphate Frameworks Containing 1,4-Diaminobutane and 1,5-Diaminopentane: [NH3(CH2)xNH3][Ga4(PO4)4(HPO4)] and [NH3(CH2)xNH3][Ga(PO4)(HPO4)] (x=4 and 5)

Two new gallium phosphates, [NH₃(CH₂)₄NH₃][Ga₄(PO₄)₄ (HPO₄)] (I) and [NH₃(CH₂)₄NH₃][Ga(PO₄)(HPO₄)] (II), have been synthesized under solvothermal conditions in the presence of 1,4-diaminobutane and their structures determined using room-temperature single-crystal X-ray diffraction data. Compound (I) (M_r=844.90, triclinic, space group P-1, a=9.3619(3), b=10.1158(3) and c=12.6456(5) Å, α=98.485(1), β=107.018(2) and γ=105.424(1)°; V=1070.39 ų, Z=2, R=3.68% and R_w=4.40% for 2918 observed data [I>3(σ(I))]) consists of GaO₄ and PO₄ tetrahedra and GaO₅ trigonal bipyramids linked to generate an open three-dimensional framework containing 4-, 6-, 8-, and 12-membered rings of alternating Ga- and P-based polyhedra. 1,4-Diaminobutane dications are located in channels bounded by the 12-membered rings in the two-dimensional pore network and are held to the framework by hydrogen bonding. Compound (II) (M_r=350.84, monoclinic, space group P2₁/c, a=4.8922(1), b=18.3638(6) and c=13.7468(5) Å, β=94.581(1)°; V=1227.76 ų, Z=4, R=2.95% and R_w=3.37% for 2050 observed data [I>3(σ(I))]) contains chains of edge-sharing 4-membered rings of alternating GaO₄ and PO₄ tetrahedra constituting a backbone from which hang ‘pendant’ PO₃(OH) groups. Hydrogen bonding between the GaPO framework and the diamine dications holds the structure together. A previously reported phase, [NH₃(CH₂)₄NH₃][Ga₄(PO₄)₄(HPO₄)] (V), structurally related but distinct from its stoichiometric equivalent, (I), has been prepared as a pure phase by this method. Two further materials, [NH₃(CH₂)₅NH₃][Ga₄(PO₄)₄(HPO₄)] (III) (tricli- nic, lattice parameters from PXD: a=9.3565(4), b=5.0156(2) and c=12.7065(4) Å, α=96.612(3), β=102.747(4) and γ=105.277(3)°) and [NH₃(CH₂)₅NH₃][Ga(PO₄)(HPO₄)] (IV) (M_r=364.86, monoclinic, space group P2₁/n, a=4.9239(2), b=13.2843(4) and c=19.5339(7) Å, β=96.858(1)°; V=1268.58 ų, Z=4, R=3.74% and R_w=4.44% for 2224 observed room-temperature data [I>3(σ(I))]), were also prepared under similar conditions in the presence of 1,5-diaminopentane. (III) and (IV) are structurally related to, yet distinct from (I) and (II) respectively.     

Crystal structure of K3PCr4O16: A second example of a quaternary phosphorus

K₃PCr₄O₁₆ is monoclinic (Cc) with the following unit cell dimensions: a = 9.512(6), b = 11.74(2), c = 14.74(2) Å, β = 106.13(5)°, and Z = 4. The crystal structure has been solved, with a final R value 0.055. The main feature of this atomic arrangement is the geometrical configuration of the PCr₄O₁₆ anion: a central PO₄ tetrahedron sharing its four corners with CrO₄ tetrahedra. This phosphochromic anion provides the second example of a quaternary phosphorus in a finite anion.     

Koordinationsverhältnisse in Cyclopentadienylverbindungen: I. Die Struktur einer monomeren Ln(CpR)3-Verbindung Tris(methylcyclopentadienyl)ytterbium

Tris(methylcyclopentadienyl)ytterbium(III), Yb(mecp)₃, has been isolated from the reaction of YbCl₃ with Na(MeCP) in THF. The compounds crystallizes in the monoclinic space group Cc with unit cell dimensions a 807.5(2), b 1393.5(3), c 2639.0(5) pm, β 94.55(2)°, and D_calc. 1.841 g cm⁻¹ for Z = 8. There are two molecules in the asymmetric unit cell forming double layers. The ring centroids describe a distorted trigonal geometry around the ytterbium atom.     

Etude de phosphates condenses diagramme d’equilibre du systeme AgPO3−Pr(PO3)3 Données sur AgPr(PO3)4

The AgPO₃?Pr(PO₃)₃ system has been studied for the first time by differential thermal analysis, X-ray diffraction and IR spectroscopy. The system shows one compound AgPr(PO₃)₄ which melts in a peritectic decomposition at 1069 K. An eutectic appears at 761 K. AgPr(PO₃)₄ belongs to the monoclinic system with space group P2_t/c,Z=4. The parameters of the unit cell are:a=12.000(9),b=13.177(4),c=7.046(5) Å and β=123^o,81(6),Z=4. Its IR absorption spectrum is typical of chain phosphates.     

The chemistry of the phosphates of barium and tetravalent cations in the 1:1 stoichiometry

The chemistry of phosphates of barium and tetravalent cations [BaM^IV(PO₄)₂] is reviewed. Such phosphates crystallise in the C2/m space group for M^IV=Ti, Zr, Hf, Ge, Sn, and Mo, and in the P2₁/n space group for BaTh(PO₄)₂. The existence of BaM^IV(PO₄)₂ in which M^IV=Pb, Ce, and U is further evaluated. Several aspects, such as phase transitions in the compounds with yavapaiite structure, solid solutions of BaM^IV(PO₄)₂ compounds and practical applications are briefly discussed.     

Cristallisation de LiFe5O8 dans un verre 0,9 Li2B2O4O,1 LiFe5O8: C. Chaumont and J.C. Bernier,Départment Science des Matériaux,Ecole Nationale Supérieure de Chimie de Strasbourg, 1, rue Blaise Pascal,B.P. 296/R8, 67008 Strasbourg Cédex,France

The LiPO₃-La(P₃O₉) system was studied by microdifferential thermal analysis. The only new compound observed in the system was LiLa(PO₃)₄, melting incongruently at 960°C. A eutectic appears at 640°C, for the mixture containing 5 mole% LaP₃O₉. Crystallographic data and powder diagrams of the new compound are given. The LiLa(PO₃)₄ is an LiNd(PO₃)₄ isotype. It crystallises in the monoclinic system C2/c with a unit cell a = 16.53 (3), b = 7.08 (3), c = 9.88 (2) Å, β = 126.42 (5), and Z = 4.     

Template Synthesis and Structure of a Three-Dimensional Bimetallic Phosphate

Introducing cobalt into the Zn-P-O-amine system and using oxalates as starting materials, an amine-containing open-framework zinc cobalt phosphate, [C₂N₂H₁₀][Co_4.2Zn_1.8 (PO₄)₄(HPO₄)]·H₂O (1), has been hydrothermally synthesized. It crystallizes in monoclinic space group C2/c (No. 15) with cell parameters a=19.214(8) Å, b=5.0152(17) Å, c=21.175(8) Å, β=103.06(3)°, V=1987.7(13) ų, Z=4, D_cal=3.078 g cm⁻³. The structure contains two sets of M-O-M linkage: M-O-M dimer and unusual infinite helical -M-O-M- chain. Connecting the dimers by phosphates leads to three-membered ring chains. The linking of the helical chains by PO₄ groups results in a sheet structure. Using the three-membered ring chains as pillars, stacking of the sheets gives rise to a three-dimensional tunnel structure.     

New defect vanadium dioxide phases

Two new monoclinic V₂O₄ phases were prepared at high pressure from the regular monoclinic (M₁) form of V₂O₄. The unit cell dimensions for the unmodified monoclinic (M₂) phase are: a = 9.083, b = 5.763, c = 4.532 Å, and β = 91.30°. The space group $\text{C 2}\text{m}$ is consistent with the crystallographic data. The new vanadium dioxide exhibited a structural transition and an abrupt, reversible change in resistivity (approx. 4 orders of magnitude) at 66°C similar to that observed in M₁-type V₂O₄. This new form of V₂O₄ is believed to be stabilized by chemical and structural defects. Controlled substitution of V⁵⁺ for V⁴⁺ in the structure led to yet another monoclinic (M₃) phase. This phase is closely related to the M₂ phase. The M₃ unit cell dimensions are: a = 4.506, b = 2.899, c = 4.617 Å, and β = 91.79°, having the space group $\text{P 2}\text{m}$. The substitution of V³⁺ yielded only monoclinic (M₁) derivatives. The modified products have varied semiconductor to metal transition temperatures which depend on the type and amount of substitution and defect structure.     

Coordination of the new weakly coordinating anions Al(OCH(CF3)2)4−, Al(OC(CH3)(CF3)2)4−, and Al(OC(Ph)(CF3)2)4− to the monovalent metal ions Li+ and Tl+

The structures of Li⁺ or Tl⁺ salts of three new fluoroalkoxide-containing aluminate anions were determined by X-ray crystallography. For LiAl(OC(Ph)(CF₃)₂)₄, monoclinic, C2/c, a=42.297(6), b=10.641(1), c=19.132(2) Å, β=114.808(9)°, Z=8, T=−100°C, R=0.052; for TlAl(OC(CH₃)(CF₃)₂)₄, monoclinic, P2₁/c, a=12.650(3), b=9.970(2), c=21.237(4) Å, β=94.00(3)°, Z=4, T=−100°C, R=0.073; for TlAl(OCH(CF₃)₂)₄, monoclinic, P2₁/n, a=14.261(1), b=9.8024(9), c=16.911(2) Å, β=93.467(8), Z=4, T=−130°C, R=0.053. The monatomic, monovalent cations interact with their respective anions by means of M–O and M–F bonds. The Tl⁺ cations in TlAl(OCH(CF₃)₂)₄ and TlAl(OC(CH₃)(CF₃)₂)₄ interact with three different aluminate anions. The Li⁺ cation in LiAl(OC(Ph)(CF₃)₂)₄ interacts with only one aluminate anion, forming a rare trigonal–prismatic LiO₂F₄ coordination unit.     

Synthesis and characterization of a new layered gallium phosphate [Co(en)3][Ga3(H2PO4)6(HPO4)3] templated by cobalt complex

A new layered gallium phosphate [Co(en)₃][Ga₃(H₂PO₄)₆(HPO₄)₃], denoted as GaPO-CJ14, has been synthesized solvothermally by using a racemic mix of chiral metal complex Co(en)₃Cl₃ as a template. Its structure was determined by single-crystal X-ray diffraction analysis and further characterized by X-ray powder diffraction, ICP, and TG analyses. The compound crystallizes in the monoclinic space group P2₁/m (No. 11) with a=9.2103(3), b=22.0936(8), c=9.5458(4) Å, β=108.278(2)°, Z=2, R₁=0.0497 and wR₂=0.1122 for all data. The inorganic layer is built up by alternation of Ga-centered octahedra (GaO₆) and P-centered tetrahedra (PO₃(OH), PO₂(OH)₂ , PO₂(O)(OH) and PO(O)(OH)₂) forming a 4.12-net. The sheet structure is featured by a series of structural units composed of two centrosymmetrically related [3.3.3] propellane-like chiral motifs. The metal complex cations locate in the interlayer region and interact with the host network through H-bonds.     

Open-Framework Cobalt (II) Phosphates with Sodalite-Related Architectures

Three new framework cobalt (II) phosphates have been synthesized hydrothermally in the presence of piperazine as a structure-directing agent. Crystal data: compound I, [C₄N₂H₁₂][Co(HPO₄)₂], monoclinic space group=P2₁/n 001(no. 14), a=8.5521(10) Å, b=13.5791(15) Å, c=10.0405(11) Å, β=96.855(2)°, V=1157.7(2) ų, Z=4, M=339.04, D_c= 1.945 g m−3, MoKα, λ=0.71073 Å, R₁(F₀)=0.053; compound II, [C₄N₂H₁₁][Co₂(PO₄)(H₂PO₄)₂], monoclinic space group=C2/c (no. 15), a=13.444(5) Å, b=12.874(5) Å, c=8.224(2) Å, β=94.64(2)°, V=1418.8 (2)A 3, Z=8, M=494.96, D_c=2.317 g cm−3, MoKα, λ=0.71073 Å ,R₁(F₀)=0.047; compound III, [C₄N₂H₁₂]₂[Co₄(HPO₄)₆], monoclinic space group=P2₁/c (no. 14) a=12.8780(13) Å, b=26.671(3) Å, c=8.2592(8) Å, β=96.931(2)°, V=2816.0(5) Å3, Z=4, M=987.90, D_c=2.330gcm-3, MoKα, λ=0.71073 Å, R₁(F₀)=0.048. The structure of I consists of one-dimensional chains built up of corner-shared four rings (Co₂P₂) which are key structural units that form the sodalite cage. Compounds II and III have interrupted sodalite-type structures resulting from the removal of Co²⁺ atoms from sites related by two-fold axes passing through the four rings of the normal sodalite cage structure. The modes of the interruptions in II and III differ in relation to the structure of a regular sodalite cage.     

Syntheses and crystal structures of new vanadium(IV) oxyphosphates M(VO)2(PO4)2 with M = Co,Ni

We have extended our research interest on titanium oxyphosphates (M^II(TiO)₂(PO₄)₂, with M^II = Mg, Fe, Co, Ni, Cu, Zn) to vanadium oxyphosphates M^II(V^IVO)₂(PO₄)₂ (M^II = Co, Ni). For each compound two phases, named α and β according to synthesis conditions, have been stabilized at room temperature, then characterized. The four crystal structures M(VO)₂(PO₄)₂ (α and β for M = Co, Ni) have been determined in monoclinic P2₁/c space group using X-ray single crystals diffraction data. Structure of the α phase is derived from the Li(TiO)(PO₄) (orthorhombic Pnma) and LiNi_0.50(TiO)₂(PO₄)₂ (monoclinic P2₁/c) types, with cell parameters: a = 6.310(1) Å, b = 7.273(1) Å, c = 7.432(1) Å, β = 90.43(1)° for M = Co, and a = 6.297(2) Å, b = 7.230(2) Å, c = 7.421(2) Å, β = 90.36(2)° for M = Ni. Structure of the β phase is derived from the Ni(TiO)₂(PO₄)₂-type (monoclinic P2₁/c) with cell parameters: a = 7.2742(2) Å, b = 7.2802(2) Å, c = 7.4550(2) Å, β = 120.171(2)° for M = Co, and a = 7.2691(2) Å, b = 7.2366(2) Å, c = 7.4453(2) Å, β = 120.231(2)° for M = Ni. All these structures consist of a three dimensional (3D) framework built up of infinite chains of tilted corner-sharing [VO₆] octahedra, cross-linked by corner-sharing [PO₄] tetrahedra. The M²⁺ ion (M = Co, Ni) is located in a triangular based antiprism which shares faces with two [VO₆] octahedra. Structural filiation is discussed based on a common structural unit, a sheet where divalent cations M²⁺ (M = Co, Ni) are inserted. A thermal study of the α ? β transition is also presented.     

(Pentaphenyl)aluminacyclopentadiene as a complexing ligand. The molecular structure of (pentaphenyl)aluminacyclopentadiene and its complex with 1,5-cyclooctadienenickel

The molecular conformations of a (pentaphenyl)aluminacyclopentadiene ligand (I) and its complex with 1,5-cycloactadienenickel (II) have been determined from single crystal X-ray data collected at room temperature with counter methods. The free ligand crystallizes in the monoclinic space group Cc with 4 molecules in a unit cell of dimensions a 10.5598(5), b 22.7089(12), c 13.3417(4) Å, β 98.064(3)°; its (COD)Ni complex Crystallizes in the monoclinic space group P2₁/n with 4 molecules in a unit cell of the dimensions a 11.9948(8), b 16.9758 (13), c 18.7721(14) Å. β 97.958(3)°. Both structures have been refined anisotropically to R values of 0.0577 and 0.0493, respectively. Upon complexation of I to the nickel atom the planarity of the ring system is distorted, with the aluminum being bent away from the nickel. A direct metal—metal interaction in II (NiAl: 2.748(1) Å) cannot be ruled out.     

Synthesis and characterization of a novel layered zinc phosphate

The syntheses and crystal structures of a novel layered zinc phosphate and its high temperature variant are described. Both structures were solved from powder diffraction data using both synchrotron and conventional X-ray radiation. The as-synthesized material (UiO-27-as) with composition [C₆H₁₇N₃]²⁺[Zn₃(HPO₄)(PO₄)₂]²⁻·H₂O crystallizes in the space group P2₁/c with a=12.67072(15), b=8.24293(8), c=18.48425(19) Å, β=109.1346(7)° and V=1823.904(35) ų. The zinc phosphate layers are built from corner sharing hexameric secondary building units. In the interlamellar space there are organic cations and water molecules. A high temperature variant exists around 200°C (UiO-27-200). This compound [C₆H₁₇N₃]²⁺[HZn₃(PO₄)₃]²⁻ crystallizes in the monoclinic space group P2₁/c with a=12.29010(23), b=8.39995(13), c=18.49914(30) Å, β=114.2504(11)° and V=1741.261(51) ų. The transformation to UiO-27-200 involves removal of the interlamellar water molecules. The atomic arrangement within the zinc phosphate layers is maintained; however, the layers are brought closer which leads to inter-layer hydrogen bonding interactions.     

Synthesis and crystal structure of mixed metal(III) tungstenyl(VI) ortho-pyrophosphates

The series of isotypic anhydrous ortho-pyrophosphates M^III(W^VIO₂)₂(P₂O₇)(PO₄) (M: Sc, V, Cr, Fe, Mo, Ru, Rh, In, Ir) was obtained via vapor phase moderated solid state reactions in sealed ampoules. The crystal structure of the phosphates M^III(W^VIO₂)₂(P₂O₇)(PO₄) (M: V, Ru, Rh) was solved from single crystal X-ray data (C2/c, Z = 16). Fairly regular MO₆ and distorted WO₆ octahedra share vertices with PO₄ and P₂O₇ units to form a 3D network. For the ortho-pyrophosphates with M: V³⁺, Cr³⁺, and Fe³⁺ the oxidation state of M is confirmed by magnetic measurements. ³¹P-MAS-NMR spectra of the diamagnetic phosphates M^III(W^VIO₂)₂(P₂O₇)(PO₄) (M: Sc, In, Ir) show surprisingly different isotropic chemical shifts for the seven phosphorus sites. V^III(W^VIO₂)₂(P₂O₇)(PO₄) occurs as equilibrium phase in the quasi-binary system (V_1–xW_x)OPO₄ at x = 0.67 and exhibits a small homogeneity range 0.60 ≤ x ≤ 0.67. The scandium compound shows a fully inverted occupancy of the M sites according to the formulation W(Sc_1/2W_1/2O₂)₂(P₂O₇)(PO₄).