A New Vanadium–Molybdenum Mixed Bronze Family with a Tunnel Structure: The Phases Ax(Mo,V)8O21 (A=K+, Rb+, Cs+)

Abstract

The isostructural compounds of general formula Ax(Mo, V)8O21 (A=K+, Rb+, Cs+) have been synthesized by solid state reaction. They crystallize in the monoclinic system, space group I2/m, Z=2, within the case of K+: a=16.194(2) Å, b=13.716(1) Å, c=13.716(1) Å, and β=90.983(1)°. The three-dimensional network is built up by layers parallel to the (101) plane, constituted of two triple chains of MO6 octahedra (M=Mo, V) associated by edges along the [010] direction and sharing corners in the [101] direction, which are connected in the [001] direction via double chains of edge-sharing VO5 square pyramids. This leads to large tunnels where the alkali ions are located. This family provides a new example of a mixed vanadium–molybdenum bronze.