K(0.78)Na(0.22)MoO(2)AsO(4)

The title compound, potassium sodium dioxidomolybden­um(VI) arsenate, K(0.78)Na(0.22)MoO(2)AsO(4), was synthesized by a solid-state reaction route. The structure is built up from corner-sharing MoO(6) octa­hedra and AsO(4) tetra­hedra, creating infinite [MoAsO(8)](∞) chains running along the b-axis direction. As, Mo and all but one O atom are on special positions (4c) with m symmetry and K (occupancy 0.78) is on a position (4a) of -1 in the tunnels. The possible motion of the alkali cations has been investigated by means of the bond-valance sum (BVS) model. The simulation shows that the Na(+) motion appears to be easier mainly along the b-axis direction. Structural relationships between the different compounds of the AMoO(2)AsO(4) (A = Ag, Li, Na, K, Rb) series and MXO(8) (M = V; X = P, As) chains are discussed.