CsP 8W 8O 40: A diphosphate tungsten bronze with octagonal tunnels

Abstract

Reddish maroon crystals of a new bronze CsP 8W 8O 40 have been synthesized. They are orthorhombic, space group Pcmn, with a = 13.061(1), b = 12.319(1), and c = 5.2960(5) Å. The structure, solved by the heavy-atom method was refined to R = 0.022 ( R w = 0.025) for 1646 observed reflections. The framework can be described as 2 × 2 WO 6 octahedra wide ReO 3-type columns extending indefinitely along [001] and connected through P 2O 7 groups. These groups delimit octagonal tunnels running along [001] and built up from communicating cages limited by 17 oxygen atoms. Cs + ions are distributed at random, off-centered in the cages. The relationships between this original structure and those of P 8W 12 O 52, of the monophosphate tungsten bronzes with hexagonal tunnels A x (PO 2) 4(WO 3) 2 m and of the diphosphate tungsten bronzes A x (P 2O 4) 2(WO 3) 2 m are discussed. CsP 8W 8O 40 appears as the first potential unidimensional conductor which has been synthesized in the field of the phosphate tungsten bronzes.