A new triple molybdate, potassium sodium cobalt tris(molybdate), K0.4Na3.6Co(MoO4)3, was synthesized using solid-state reactions. The Co2+and one Na+cation are located at the same general site, each with occupancy 0.5. Another site (site symmetry 2) is occupied by Na+and K+cations, with occupancies of 0.597 (7) and 0.402 (6), respectively. The other two Na+cations and one of the two Mo atoms lie on special positions (site symmetries -1, 2 and 2, respectively). The structure is characterized by
M2O10( M= Co/Na) dimers, which are linked by MoO4tetrahedra, forming infinite layers. The latter are connected firstly by insertion of one type of MoO4tetrahedra and secondly by sharing corners with the other type of MoO4tetrahedra. This results in an open three-dimensional framework with the cavities occupied by the Na+and K+cations. The structure is isotypic with Na3In2As3O12and Na3In2P3O12. A comparison is made with structures such as K2Co2(MoO4)3and β-NaFe2(MoO4)3and their differences are discussed.