A new lead Mo(IV) phosphate with a tunnel structure: Pb2Mo2O(PO4)2P2O7

A molybdenum (IV) phosphate containing lead, Pb₂Mo₂(PO₄)2P₂O₇, has been synthesized for the first time. It crystallizes in the space group C2/c with a=14.098(1) Å, b=14.187(2) Å, c=6.5592(4) Å and β=102.08(1)°. Its original tunnel structure, built up of Mo₂O₁₁ bioctahedra, P₂O₇ and PO₄ phosphate groups can be described from the assemblage of [Mo₄P₄O₂₄]_∞ ribbons interconnected through monophosphate groups. The stereoactivity of the 6s² lone pair of Pb²⁺, which is surrounded by nine oxygen atoms, is discussed.     

Synthesis and crystal structure of the novel Pb5Sb2MnO11 compound

The new Pb₅Sb₂MnO₁₁ compound was synthesized using a solid-state reaction in an evacuated sealed silica tube at 650°C. The crystal structure was determined ab initio using a combination of X-ray powder diffraction, electron diffraction and high-resolution electron microscopy (a=9.0660(8)Å, b=11.489(1)Å, c=10.9426(9)Å, S.G. Cmcm, R_I=0.045, R_P=0.059). The Pb₅Sb₂MnO₁₁ crystal structure represents a new structure type and it can be considered as quasi-one-dimensional, built up of chains running along the c-axis and consisting of alternating Mn⁺²O₇ capped trigonal prisms and Sb₂O₁₀ pairs of edge sharing Sb⁺⁵O₆ octahedra. The chains are joined together by Pb atoms located between the chains. The Pb⁺² cations have virtually identical coordination environments with a clear influence of the lone electron pair occupying one vertex of the PbO₅E octahedra. Electronic structure calculations and electron localization function distribution analysis were performed to define the nature of the structural peculiarities. Pb₅Sb₂MnO₁₁ exhibits paramagnetic behavior down to T=5 K with Weiss constant being nearly equal to zero that implies lack of cooperative magnetic interactions.     

Pb2VO(VO4)(V2O7)0.5, a Novel Lead Vanadium III Vanadate Possessing Trivalent Vanadium Rutile-Like Chains: Relationship with Related Compounds

The crystal structure of the new Pb₂V₃O_8.5 has been determined and refined with final R₁ and wR₂ values 0.045 and 0.128, respectively, from 1063 independent single crystal reflections. It crystallizes with the P2/c space group, a=7.687(2) Å, b=5.996(2) Å, c=17.337(4) Å, and β=112.636(4)°. The structure consists of one-dimensional rutile-type chains of edge-sharing V^IIIO₆ octahedra parallel to the b axis. Bidentate V^VO₄ tetrahedra share corners with the chains to form one-dimensional columns. They are interconnected by divanadate V^V₂O₇ to form infinite layers. In the presented work, the Pb₂V₃O_8.5 crystal structure is compared to several closely related materials including Ba₂V₃O₉ and the mineral Vauquelinite Pb₂CuCrO₄PO₄OH. Special attention is given to the existence along the rutile chains of V-V pairs due to strong V-O bonds with O₂ bridging edges.     

Conductivity and Structural Investigations in Lacunary Pb6Ca2Li2(PO4)6 Apatite

Prismatic crystals of Pb₆Li₂Ca₂(PO₄)₆ were obtained by solid-state reaction. They were characterized by IR spectroscopy and chemical analyses. The structure as determined by X-ray diffraction study on single crystal revealed that the compound is isostructural to the hexagonal phase Pb₈Na₂(PO₄)₆. Crystal data for Pb₆Li₂Ca₂(PO₄)₆: space group P63/m (No. 176), a=b=9.6790(15) Å, c=7.1130(7), Z=1, R=0.039. In the compound, lithium was found to preferentially occupy the site (I) and the structure is stabilized by interactions between electron lone pairs of lead (II) ions. Electrical conductivity measured in a wide range of temperature is governed by a hopping mechanism of Li ions in tunnels.     

A crystal structure of mixed-metal dianionic phosphate Cs3.70Mg0.60Ti2.78(TiO)3(P2O7)4(PO4)2

The single crystals of caesium magnesium titanium (IV) tri-oxo-tetrakis-diphosphate bis-monophosphate, Cs_3.70Mg_0.60Ti_2.78(TiO)₃(P₂O₇)₄(PO₄)₂, crystallize in sp. gr. P-1 (No. 2) with cell parameters a=6.3245(4), b=9.5470(4), c=15.1892(9) Å, α=72.760(4), β=85.689(5), γ=73.717(4), z=1. The titled compound possesses a three-dimensional tunnel structure built by the corner-sharing of distorted [TiO₆] octahedra, [Ti₂O₁₁] bioctahedra, [PO₄] monophosphate and [P₂O₇] pyrophosphate groups. The Cs⁺ cations are located in the tunnels. The partial substitution of Ti positions with Mg atoms is observed. The negative charge of the framework is balanced by Cs cations and Mg atoms leading to pronounced concurrency and orientation disorder in the [P₂O₇] groups, which coordinate both.     

Synthesis and characterizations of two anhydrous metal borophosphates: M2BP3O12 (M=Fe, In)

Two members of M^III₂BP₃O₁₂ borophosphates, namely Fe₂BP₃O₁₂ and In₂BP₃O₁₂, were synthesized by the solid-state method and characterized by the X-ray single crystal diffraction, the powder diffraction and the electron microscopy. They both crystallize in the hexagonal system, space group P6(3)/m (no. 176) and feature 3D architectures, build up of the M₂O₉ units and B(PO₄)₃ groups via sharing the corners; however, they are not isomorphic for the different crystallographically distinct atomic positions. Optical property measurements of both compounds and magnetic susceptibility measurements of Fe₂BP₃O₁₂ also have been performed. Moreover, in order to gain further insights into the relationship between physical properties and band structure of the M^III₂BP₃O₁₂ borophosphates, theoretical calculations based on density functional theory (DFT) were performed using the total-energy code CASTEP.     

Isomorphism and phase diagram of the Pb5(PO4)3Cl-Pb5(VO4)3Cl system

Compounds of composition Pb₅(P _x V_1−x O₄)₃Cl (0 ≤ x ≤ 1), which are synthetic analogues of minerals pyromorphite, vanadinite, and endlichite, were synthesized for the first time by high-temperature solid-phase reactions. X-ray diffraction and IR spectroscopy were used to determine the structure of the compounds and revealed complete miscibility in the solid phase of the Pb₅(PO₄)₃Cl-Pb₅(VO₄)₃Cl binary system. Adiabatic reaction calorimetry was used to determine standard enthalpies of mixing and formation and showed that the regular solutions model is applicable to the Pb₅(PO₄)₃Cl-Pb₅(VO₄)₃Cl system. Differential thermal analysis in tandem with high-temperature X-ray diffraction was used to study the phase diagram and characterize phase transitions.     

Synthesis, characterization, and structure determination of the orthorhombic U2(PO4)(P3O10)

β-UP₂O₇ has been synthesized under hydrothermal conditions (θ=500°C, P=200 MPa), using UO₂ and H₃PO₄. β-UP₂O₇ crystallizes in the orthorhombic space group Pn2₁a, with a=11.526 (2) Å, b=7.048 (2) Å, c=12.807 (2) Å and Z=4. Its structure has been determined through direct methods and difference Fourier synthesis and has been refined to R=0.0396. The structure is built on UO₈ polyhedral chains along the b-axis. PO₄³⁻ and P₃O₁₀⁵⁻ groups coexist in the structure and the latter groups form non-linear chains. Cohesion of the structure is made through the linkage of UO₈ chains by PO₄ and P₃O₁₀ groups leading to the formula U₂(PO₄)(P₃O₁₀) instead of β-UP₂O₇. Vibrational and optical spectra confirm the results obtained by X-ray diffraction. DTA-TGA measurements show that the transformation of U₂(PO₄)(P₃O₁₀) to the cubic α-UP₂O₇ occurs at θ=870°C.     

Solid solutions of Pb8M2(XO4)6 lead alkali apatites

The Pb₈Na_2?xK_x(PO₄)₆, Pb₈Na_2?xK_x(AsO₄)₆, Pb₈Na_2?xRb_x(PO₄)₆, and Pb₈K_2?xRb_x(PO₄)₆ systems were studied. The compounds crystallize at all compositions in the P6₃m hexagonal apatite structure and form true solid solutions. The change of the lattice parameters of the composition and of the c/a values and their relation to the ionic radii of the alkali ions are discussed.     

A Mixed-Valent Molybdenotungsten Monophosphate with a Tunnel Structure: Nax(Mo, W)2O3(PO4)2

A mixed-valent molybdenotungstophosphate, Na_x(Mo, W)₂O₃(PO₄)₂ (x 0.75) has been isolated for the first time. It crystallizes in the space group P 2₁/m with a = 7.200(1) Å, b = 6.369(1) Å, c = 9.123(1) Å, and β = 106.29(1)°. Its structure consists of M₂PO₁₃ units built up of two M O₆ octahedra (M = Mo, W) and one PO₄ tetrahedron sharing their apices as already observed in several molybdenum phosphates. These units share their apices with PO₄ tetrahedra forming [M₂P₂O₁₅]_∞ chains running along . The host lattice [(Mo, W)₂P₂O₁₁]_∞ can be described by the assemblage of such chains or by the assemblage of [MPO₈]_∞ chains running along , in which one PO₄ tetrahedron alternates with one MO₆ octahedron. The tridimensional framework [Mo, WP₂O₁₁]_∞ delimits tunnels running along , occupied by sodium with two kinds of coordination, 6 and 5. The distribution of the different species, in the octahedral sites according to the formulation Na_0.75(Mo^VI_0.42W^VI_0.58)_M1 (Mo^V_0.75W^VI_0.25)₂O₃(PO₄)₂, is discussed.     

Crystal growth and X-ray data of the lead phosphates Pb4P2O9 and Pb8P2O13

Single crystals of the title compounds have been grown by the Czochralski technique. Pb₄P₂O₉ crystallizes in the space group $\text{P2}{}_1\text{c}$ with the parameters a = 9.4812 Å, b = 7.1303 Å, c = 14.390 Å, β = 104.51° and Pb₈P₂O₁₃ in $\text{C2}\text{m}$ with a = 10.641 Å, b = 10.206Å c = 14.342 Å, β = 98.34°.     

Original close-packed structure and magnetic properties of the Pb4Mn9O20 manganite

The crystal structure of the Pb₄Mn₉O₂₀ compound (previously known as “Pb_0.43MnO_2.18”) was solved from powder X-ray diffraction, electron diffraction, and high resolution electron microscopy data (S.G. Pnma, a=13.8888(2) Å, b=11.2665(2) Å, c=9.9867(1) Å, R_I=0.016, R_P=0.047). The structure is based on a 6H (cch)₂ close packing of pure oxygen “h”-type (O₁₆) layers alternating with mixed “c”-type (Pb₄O₁₂) layers. The Mn atoms occupy octahedral interstices formed by the oxygen atoms of the close-packed layers. The MnO₆ octahedra share edges within the layers, whereas the octahedra in neighboring layers are linked through corner sharing. The relationship with the closely related Pb₃Mn₇O₁₅ structure is discussed. Magnetization measurements reveal a peculiar magnetic behavior with a phase transition at 52 K, a small net magnetization below the transition temperature, and a tendency towards spin freezing.     

Inorganic-organic hybrid materials: synthesis and crystal structure determination from powder diffraction data of Pb2(O3PCH2C6H4CH2PO3)

A new lead diphosphonate, Pb₂(O₃PCH₂C₆H₄CH₂PO₃) was hydrothermally synthesized from tetraethyl α,α′-p-xylenediphos-phonate and Pb(NO₃)₂. The structure was solved and refined using X-ray powder diffraction data. It crystallizes in the monoclinic space group P2₁/c, with a = 467.84(2), b = 2007.98(9), c = 639.10(2) pm, β = 101.020(3)°, V = 589.31(4) 10⁶ pm, Z=2, wR_p=0.034, R_p=0.027, R_F2=0.061, R_F=0.036. The structure is built from corner-linked [PbO₄] polyhedra, containing a lone pair of electrons. These polyhedra are connected to layers by phosphonate groups, RPO₃²⁻ and through the organic diphosphonic acid to a three-dimensional structure. Thermogravimetric as well as IR spectroscopic studies are also presented.     

Two mixed valent molybdenophosphates with a tunnel structure closely related to K0.17MoP2O7: Pb2(PbO)2Mo8(P2O7)8 and PbK2Mo8(P2O7)8

Two new mixed valent Mo(III)/Mo(IV) diphosphates containing lead Pb₂(PbO)₂Mo₈(P₂O₇)₈ and PbK₂Mo₈(P₂O₇)₈ have been synthesized. The [Mo₈P₁₆O₅₆]∞ frameworks of these phosphates are closely related to that of K_0.17MoP₂O₇: the MoO₆ octahedra and P₂O₇ groups form two sorts of large eight-sided tunnels. They are occupied in an ordered way by PbO chains and Pb²⁺ cations in Pb₂(PbO)₂Mo₈(P₂O₇)₈ and by K⁺ and Pb²⁺ cations in PbK₂Mo₈(P₂O₇)₈. It results in different symmetries of these two structures, which are tetragonal and monoclinic, respectively, showing the great flexibility of these mixed frameworks, susceptible to accommodate various species with different sizes.     

Hydrothermal synthesis and characterization of the first 1-D indiumphosphate chain In2(HPO4)2(H2PO4)2F2·C4N2H12, a precursor for high dimensional structures

The first one-dimensional (1-D) indiumphosphate chain, In₂(HPO₄)₂(H₂PO₄)₂F₂·C₄N₂H₁₂ (1), has been hydrothermally prepared using piperazine (PIP) as a template. The structure consists of infinite chains of trans,trans-corners-sharing InO₄F₂ octahedra with the adjacent octahedra being bridged by tetrahedral PO₃(OH) and PO₂(OH)₂ units, which are H-bonded with amine groups of the organic cations. Interestingly, this macroanionic chain InP₂O₈H₃F⁻ is similar to that found in the mineral tancoite-like chains and has potential to further set up higher-dimensional networks. On heating 1 in the presence of additional phosphoric acid at 180 °C under hydrothermal condition, compound 2, In₂(OH)(H₂O)(PO₄)₂·H₃O·H₂O, possessed a 3-D structure building from the repetition of a secondary building unit is obtained. When 1 is heated with additional PIP, an unknown phase, compound 3 is formed. Finally, on treatment with another amine, such as diethylenetriamine or 1,4-diaminobutane, at 180 °C, 1, as a precursor, can convert into a previously known 3-D framework structure with 16-membered ring compound 4. Compounds 1 and 2 are determined by single-crystal X-ray diffraction. Furthermore, 1 is characterized by X-ray powder diffraction, IR spectroscopy, inductively coupled plasma analysis, thermogravimetric analysis and differential thermal analysis.     

Crystal structure and cation transport properties of the layered monodiphosphates Rb6Bi4(PO4)2(P2O7)3

Single crystals of the new Bi(III) phosphates, Rb₆Bi₄(PO₄)₂(P₂O₇)₃, have been isolated and their structure has been determined by X-ray diffraction techniques. This compound crystallizes in the monoclinic space group P2₁/c with a=9.077(1)Å, b=9.268(2)Å, c=36.418(6)Å, β=95.75(1)° and Z=8. The crystal structure is made up of BiO₅ and BiO₆ polyhedra sharing the corners with PO₄ tetrahedra and P₂O₇ diphosphate groups. The structure can be described as infinite anionic layers with composition [Bi₄(PO₄)₂(P₂O₇)₃]_∞⁶⁻ parallel to the [301] plane, connected via P-O-Bi bridges to form a three-dimensional open framework. This framework delimits tunnels running along [100] and [010] directions, where the rubidium ions reside. This compound exhibits a rubidium ion conduction but with rather low conductivity value at 640 K.     

New perovskite-based manganite Pb2Mn2O5

A new perovskite based compound Pb₂Mn₂O₅ has been synthesized using a high pressure high temperature technique. The structure model of Pb₂Mn₂O₅ is proposed based on electron diffraction, high angle annular dark field scanning transmission electron microscopy and high resolution transmission electron microscopy. The compound crystallizes in an orthorhombic unit cell with parameters a=5.736(1) Å≈√2a_p, b=3.800(1) Å≈a_p, c=21.562(6) Å≈4√2a_p (a_p—the parameter of the perovskite subcell) and space group Pnma. The Pb₂Mn₂O₅ structure consists of quasi two-dimensional perovskite blocks separated by 1/2[110]_p(1?01)_p crystallographic shear planes. The blocks are connected to each other by chains of edge-sharing MnO₅ distorted tetragonal pyramids. The chains of MnO₅ pyramids and the MnO₆ octahedra of the perovskite blocks delimit six-sided tunnels accommodating double chains of Pb atoms. The tunnels and pyramidal chains adopt two mirror-related configurations (“left” L and “right” R) and layers consisting of chains and tunnels of the same configuration alternate in the structure according to an -L-R-L-R-sequence. The sequence is sometimes locally violated by the appearance of -L-L- or -R-R-fragments. A scheme is proposed with a Jahn-Teller distortion of the MnO₆ octahedra with two long and two short bonds lying in the a-c plane, along two perpendicular orientations within this plane, forming a d-type pattern.     

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.     

A novel Mo(V) diphosphate with an intersecting tunnel structure: Sr(MoO)2(P2O7)2

A novel Mo(V) diphosphate Sr(MoO)₂P₂O₇ has been synthesized. It crystallizes in the space group P2₁/n with a=7.925(1) Å, b=7.739(1) Å, c=9.485(1) Å and β=91.05(1)°. Its original framework consists of MoP₂O₁₁ units built up of one P₂O₇ group sharing two apices with one MoO₆ octahedron. The MoP₂O₁₁ units share corners, forming [MoP₂O₁₀]_∞ chains running along [101]. The assemblage of these chains forms the [Mo₂P₄O₁₆]_∞ intersecting tunnel framework. The Sr²⁺ cations are located at the tunnel intersection, showing a distorted cubic coordination. This structure is compared to those of Ba(MoO)₂P₂O₇ and LiMoOP₂O₇, which are also built up of MoP₂O₁₁ units forming [MoP₂O₁₀]_∞ chains, but with different configurations.     

Synthesis and structure investigation of the Pb3V(PO4)3 eulytite

Lead vanadium phosphate Pb₃V(PO₄)₃ was synthesized by solid state reaction and characterized by X-ray single crystal and powder diffraction, electron microscopy, and magnetic susceptibility measurements. The crystal structure model of Pb₃V(PO₄)₃ was refined using X-ray single crystal data (a=10.127(1)Å, S.G. Z=4). The compound has an eulytite-like structure and its average structure model may be presented as a three-dimensional network formed by strongly distorted mixed (Pb/V^III) metal-oxygen octahedra connected by edge sharing and forming corrugated chains. The octahedra are additionally linked by tetrahedral phosphate groups via corner sharing. Lead and vanadium atoms randomly occupy two close positions in the octahedra. The electron microscopy study revealed the presence of a rhombohedral superstructure with and indicating ordering in the structure. The same type of superstructure was found by us for two another lead-containing eulytite Pb₃Fe(PO₄)₃ where Fe⁺³ has an ionic radius close to that of V⁺³. Magnetic susceptibility measurements revealed Curie-Weiss behavior for the Pb₃V(PO₄)₃ compound.