K. Jaouadi

Synthesis and crystal structure of a new form of potassium–bismuth polyphosphate KBi(PO3)4

Abstract Synthesis and complete structural characterization by X-ray diffraction, IR and Raman are given for a new form of potassium–bismuth polyphosphate. This compound is monoclinic P 2 1 / n with a structural type IV and with the following unit cell dimensions: a =10.443(4) A, b =8.989(2) A, c =10.757(4) A, β =105.76(2)°, V =971.8(5) A 3 , Z =4 and ρ cal =3.855 g/cm 3 . The structure was solved from 3390 independent reflections with R 1 =0.0420 and WR 2 =0.0910, refined with 164 parameters. The atomic arrangement can be described as a long chain polyphosphate organization. Two infinite (PO 3 ) n chains with a period of eight tetrahedra run along the [101] direction. Bismuth atoms have an eightfold coordination while potassium atoms have nine oxygen neighbours. Infrared and Raman spectra were investigated at room temperature in the frequency range, 250–1500 and 200–1600 cm −1 , respectively, showing some characteristic bands of infinite chain structure of PO 4 tetrahedra linked by a bridging oxygen.

X-ray single crystal, vibrational and phase transitions in the mixed Rb2(HSeO4)(H2PO4)

Ongoing studies of the RbHSeO4–RbH2PO4 system, aimed at developing novel proton conducting solids, resulted in the new compound Rb2(HSeO4)(H2PO4) (dirubidium hydrogenoselenate dihydrogenophosphate). Single-crystal X-ray diffraction (performed at room temperature) revealed Rb2(HSeO4)(H2PO4) to crystallize in space group P21/n with lattice parameters a = 7.514 (3) Å, b = 7.658 (2) Å, c = 7.696 (3) Å and β = 101.20 (3)°. The compound has a unit-cell volume of 434.4 (2) Å3 and two formula units per cell, giving a calculated density of 3.149. Six non-H atoms and three H atoms were located in the asymmetric unit, with SeO4 and PO4 groups randomly arranged on the single tetrahedral anions site. Refinement using all observed reflections yielded residuals of 0.0971 and 0.0438 based on F 2 and F values, respectively. Anisotropic temperature factors were employed for all six non-H atoms and isotropic temperature factors for the three H atoms. The structure contains zigzag chains of hydrogen bonded anion tetrahedra that extend in the [010] direction. Each tetrahedron is additionally linked to a tetrahedron neighbouring chain to give a planar structure with hydrogen-bonded sheets lying parallel to The rubidium atom is coordinated by nine oxygen atoms with Rb–O range from 2.868 (4) to 3.364 (5) Å. The infrared spectra of the new compound Rb2(HSeO4)(H2PO4) recorded at room temperature in the frequency range 4000–400 cm−1, confirm the presence of and groups in the same crystal. Differential scanning calorimetry traces show two phase transitions at 382 and 665 K in this material.

Synthesis, structural study and thermal behaviour of a new compound: trirubidium bis(hydrogen sulphate) dihydrogen arsenate Rb3(HSO4)2.5(H2AsO4)0.5

ABSTRACT Mixed crystals Rb3(HSO4)2.5(H2AsO4)0.5 have been prepared by slow evaporation from aqueous solution at room temperature. The crystals were characterized by X-ray single analysis, which revealed that Rb3(HSO4)2.5(H2AsO4)0.5 crystallizes in the space group P with lattice parameters: a = 7.471(3) Å; b = 7.636(1) Å; c = 12.193(2) Å; α = 71.91(1)°; β = 73.04(6)° and γ = 88.77(2)°. In this structure, the ordered S(1)O4 and the disordered S(3)/AsO4 tetrahedra are connected by O–H..O hydrogen bonds, to a zigzag chains running in the b-direction. These chains are, in turn, bonded to one another by disordered hydrogen bridges O–H..H–O, to give a planar structure, with hydrogen-bonded sheets, laying parallel to (1 0 0). Each disordered tetrahedron is linked to a tetrahedron neighbouring S(2)O4 by ordered hydrogen bonds. Broader peaks in IR spectrum of the title material support the assumption of disordered structure. Thermal analysis of the superprotonic transition in Rb3(HSO4)2.5(H2AsO4)0.5 showed that the transformation to the high-temperature phase occurs by one-step process at 404 K. Thermal decomposition of this compound takes place at much higher temperatures, with an onset of approximately 473 K.