[Li(MoO2)2O(AsO4)].

Single crystals of the molybdenum arsenate Li(MoO2)2O(AsO4) [lithium bis(dioxomolybdenum) arsenate oxide] have been prepared by solid-state reaction. The framework of Li(MoO2)2O(AsO4) consists of corner-shared Mo2AsO12 structural units, which form layers parallel to the ab plane. The Mo2AsO12 units result from the association of corner-shared AsO4 tetrahedra and Mo2O9 dimers. The Li+ ions are located between layers in a square-based-pyramidal environment. This structure is compared with those containing M2O9 dimers (M = Mo, Fe or V). The As, Li and one of the O atoms lie at sites with mm symmetry, while the Mo atom and two of the O atoms lie at sites with m symmetry.