Structure cristalline de type alluaudite K0.4Na3.6Co(MoO4)3.

A new triple molybdate, potassium sodium cobalt tris-(molybdate), K0.4Na3.6Co(MoO4)3, was synthesized using solid-state reactions. The Co(2+) 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 M 2O10 (M = Co/Na) dimers, which are linked by MoO4 tetra-hedra, forming infinite layers. The latter are connected firstly by insertion of one type of MoO4 tetra-hedra and secondly by sharing corners with the other type of MoO4 tetra-hedra. This results in an open three-dimensional framework with the cavities occupied by the Na(+) and K(+) cations. The structure is isotypic with Na3In2As3O12 and Na3In2P3O12. A comparison is made with structures such as K2Co2(MoO4)3 and β-NaFe2(MoO4)3 and their differences are discussed.