Anatoly F. Selevich

Two isostructural manganese (III) diphosphates, acid α-MnHP2O7 and double MnLiP2O7: crystal structure determination from X-ray powder diffraction data

Summary Ab initio crystal structure determination of the α form of MnHP2O7 and Rietveld refinement of the MnLiP2O7 structure were performed using powder X-ray diffraction data. The final structures have been obtained using soft restraints on interatomic bond lengths and bond angles for the diphosphate group. The two compounds were found to be to a great extent isostructural. They crystallize in the monoclinic space group P21, Z = 2, a = 6.7547(6), b = 8.3160(7), c = 4.8769(5) Å, β = 113.1791(18)°, Rp = 0.0283, Rwp = 0.0390, RBragg = 0.0930, RF = 0.0869 for α-MnHP 22O7, and a = 7.0018(5), b = 8.1616(6), c = 4.7267(4)Å, β = 109.404(3)°, Rp = 0.0307, Rwp = 0.0423, RBragg = 0.0960, RF = 0.0861 for MnLiP2O7. In both compounds, diphosphate groups adopt nearly eclipsed configuration. Their structures present three-dimensional networks, which have tunnels including the lithium cations or hydrogen atoms. The behaviour of the crystalline forms of MnHP2O7 in H/Li exchange reactions is discussed, vs. their structural aspects.

The crystal structure of Y2P4O13 from X-ray powder diffraction data

Abstract The crystal structure of Y2P4O13 has been determined from X-ray powder diffraction data. Y2P4O13 crystallizes in the orthorhombic space group C2221 (No. 20) with a = 17.2817(7) Å, b = 6.9823(4) Å, c = 8.5391(3) Å, V = 1030.38(8) Å3, and Z = 4. The structure has been solved by direct methods using EXPO program and refined by FULLPROF package. The final RBragg value was 9.1%. The tetraphosphate anion has the point group 2 symmetry. The yttrium atom is seven-coordinated forming strongly distorted octahedron with one bifurcated vertex. There are infinite chains of oxygen-bridged ittrium atoms running parallel to the b axis and linked together by the tetraphosphate anions with formation of three-dimensional network.

The crystal structure of Na3HP2O7 ⋅ H2O from X-ray powder diffraction data

The crystal structure of Na3HP2O7 H2O has been determined from X-ray powder diffraction data. The structure is monoclinic, space group P21/n (No. 14), with unit cell dimensions a 1⁄4 10.4242(1) A, b 1⁄4 6.8707(1) A, c 1⁄4 10.0837(1) A, b 1⁄4 99.2258(7) , V 1⁄4 712.87(2) A3, Z 1⁄4 4, Dm 1⁄4 2.43 g/cm3 and Dx 1⁄4 2.41 g/cm3. The structure has been solved by direct methods using EXPO program and refined by FULLPROF package. The final RBragg value was 7.6%. Positions of hydrogen atoms were not defined. There are three sodium cations in the asymmetric unit. Two of them are five-coordinated and one cation has sixfold oxygen coordination. Each HP2O7 anion is hydrogen bonded to its two adjacent neighbours forming infinite chains parallel to the b axis. Water molecules are located in infinite channels extended along the b direction. The oxygen atom of the water molecule is connected with two sodium cations and hydrogen bonded with one oxygen atom of diphosphate group.

Crystal structure determination of In3(H3O)(H2PO4)6(HPO4)2 · 4H2O from X-ray powder diffraction

Abstract The crystal structure of indium hydrogen phosphate hydrate, In3(H3O)(H2PO4)6(HPO4)2 · 4H2O, has been determined from X-ray powder diffraction data by using direct methods (EXPO program), and refined by FULLPROF package to RBragg value of 5.6%. The structure is monoclinic, space group C2/c (No. 15), unit cell dimensions a = 17.0835(5), b = 9.6795(3), c = 17.8776(4) Å, β = 90.301(2)°, V = 2956.2(1) Å3, Z = 4, Dx = 2.73 g/cm3. Hydrogen atoms were placed on calculated positions. There are two unique indium atoms in the crystal structure. InO6 octahedra are connected together via the corners of PO4 tetrahedra to form layers parallel to the xy plane. The layers are linked together by water molecules, located in the interlayer space, through their hydrogen bonds. Within the layers there are hollows occupied by oxonium cations. The compound was found to be isostructural with salts of the composition M III3MI(H2PO4)6(HPO4)2 · 4H2O, where M III-trivalent metal, M I-monovalent metal, oxonium or ammonium.

X-ray powder diffraction investigation of the faulted crystal structure of MnH2P3O10 · 2H2O

Abstract The crystal structure of manganese(III) dihydrogen triphosphate dihydrate, MnH2P3O10 · 2H2O, has been studied by means of X-ray powder diffraction data using the Rietveld method. The compound crystallizes in the monoclinic space group P2/c, with unit cell dimensions a = 7.8286(2), b = 4.9503(2), c = 12.25415(18) Å, β = 95.7922(11)°, V = 472.47(2) Å3, Z = 2. It has a layered structure, with manganese-triphosphate polymeric layers, parallel to the bc plane, and water molecules located in the interlayer space. Powder pattern of the compound exhibits anisotropic peak broadening, which cannot be explained by crystallite size effects. The reflections with k = 2n remain narrow, whereas those with k = 2n + 1 and h ≠ 0 are widened substantially. These features have been assigned to stacking faults with a b/2 translation. Simulated diffraction patterns, calculated with the program DIFFaX by recursion method for different values of stacking faults probability, reproduced the experimental X-ray powder pattern. A phenomenological treatment of anisotropic peak broadening was used to complete the Rietveld refinement.

The restrained Rietveld refinement of modulated trivalent metal polyphosphates M(PO3)3

Abstract Room temperature X-ray powder diffraction data were used to investigate modulated crystal structures of two monoclinic polyphosphates of crystal form C, In(PO3)3 and Y(PO3)3, by the Rietveld refinement. The structures were refined with the program JANA2006 in the superspace groups Xc(0β0)0, β = 1/3, for commensurately modulated In(PO3)3, and Cc(0β0)0, β = 0.36564(7), for incommensurately modulated Y(PO3)3. The positional modulations were described with the first-order harmonic functions. The Rietveld refinement was performed with soft restraints on bond lengths and valence angles in PO4 tetrahedra, as well as on angles in MO6 octahedra. No initial information about modulation parameters was used. A good agreement of the observed and calculated intensities of main and satellite reflections was achieved for both compounds. Obtained modulated structures of In(PO3)3 and Y(PO3)3 are close to published single crystal data.

Crystal structure determination of Ga3(H3O)H8(PO4)6 · 6 H2O from X-ray powder diffraction data

Abstract The crystal structure of the gallium hydrogen phosphate hydrate, Ga3(H3O)H8(PO4)6 · 6 H2O, has been determined from X-ray powder diffraction data. The structure is trigonal, space group P31c (No. 159), with unit cell dimensions a = 9.0227(1) Å, c = 16.6389(3) Å, V = 1173.08(3) Å3, Z = 2, and Dx = 2.59 g/cm3. The structure was solved by direct methods using EXPO program and refined by FULLPROF package to RBragg value of 8.6%. Positions of hydrogen atoms were not defined. There are three unique gallium atoms in the crystal structure, having octahedral oxygen coordination. GaO6 octahedra are linked together via the corners of PO4 tetrahedra to form a three-dimensional network with channels running along the c axis. There are two types of water molecules in the crystal, which essentially differ in their atomic environment. Oxonium cations, lying on crystallographic threefold axis, are surrounded by oxygen atoms of the phosphate groups and water molecules.

The crystal structure of Er(HPO4)(NO3)·3 H2O: ab initio determination from X-ray powder diffraction data

Abstract The crystal structure of orthorhombic Er(HPO4)(NO3)·3 H2O has been determined from X-ray powder diffraction data. The unit cell dimensions are a = 10.1653(4) Å, b = 11.9178(5) Å, c = 6.8533(3) Å, V = 830.26(6), Z = 4. The space group is Pbcm (No. 57) or Pbc21 (No. 29). The structures were solved ab initio using EXPO program and refined by FULLPROF package. Because geometrical features of the two solutions are the same, the crystal structure has been described in the scope of the centrosymmetric Pbcm space group. Positions of the hydrogen atoms were not defined. The erbium atom is eight coordinated. It is surrounded by one nitrate anion, one water molecule and four phosphate groups. [ErO8] polyhedra are linked together through their edges forming infinite chains extended along the c axis. The chains are connected by phosphate groups to form layers palallel to the yz plane. Probable hydrogen bonds are discussed.

Ab initio structure determination of In2H2(P2O7)(P4O12) from X-ray powder diffraction data

Abstract The crystal structure of In2H2(P2O7)(P4O12) has been determined from X-ray powder diffraction data. The structure is orthorhombic, space group Pmmn (No. 59), with unit cell dimensions a = 12.9398(2) Å, b = 11.3725(3) Å, c = 5.0385(1) Å, V = 741.45(3) Å3, Z = 2, and Dx = 3.23 g/cm3. The structure has been solved by direct methods using EXPO program and refined by FULLPROF package. The final RBragg value was 4.6%. Positions of hydrogen atoms were not defined. Indium cation has sixfold oxygen coordination being surrounded by two diphosphate and four cyclotetraphosphate groups. Probable scheme of hydrogen bonding is discussed.