New mixed-valence antimony phosphates: α- and β-Sb IIISb V(P 2O 7) 2

Abstract

The compounds α- and β-Sb IIISb V(P 2O 7) 2 were obtained by heating at 923 K (α-type) or 773 K (β-type) a mixture of Sb 2O 5, nH 2O with an excess of NH 4H 2PO 4. α-Sb IIISb V(P 2O 7) 2 crystallizes in the monoclinic system, space group P2 1 c with a = 8.088(1) Å, b = 16.015(3) Å, c = 8.135(5) Å, β = 90.17(2)°, Z = 4. The β-type crystallizes in the orthorhombic system, space group Pna2 1, with a = 8.018(1) Å, b = 16.134(3) Å, c = 8.029(5) Å, Z = 4. Both crystal structures were determined from reflections collected on a Nonius CAD4 automatic diffractometer with Mo K α radiation. The final R index and weighted R w index are 0.041 and 0.050, respectively, for α- and 0.041 and 0.052, respectively, for β-Sb IIISb V(P 2O 7) 2. Both structures are built up from corner-shared Sb IIIO 6 or Sb VO 6 octahedra and P 2O 7 groups. Each P 2O 7 group shares its six vertices with six different SbO 6 octahedra and each octahedron is connected with six P 2O 7 groups thus leading to two different three-dimensional frameworks. Nevertheless, both structures are closely related to that of the zirconium diphosphate ZrP 2O 7.