Layer and tunnel structures in new molybdenophosphates: Cs₂Mo₄P₆O₂₆ and M₄Mo₈P₁₂O₅₂ (M = Cs, Rb, K, Tl)

Crystals of Cs₂Mo₄P₆O₂₆ and Cs₄Mo₈P₁₂O₅₂ were both discovered in the same reaction product obtained from heating a stoichiometric mixture of Cs₂MoO₄, MoO₃, MoO₂, and P₂O₅ in an evacuated quartz tube at 800°C. For Cs₂Mo₄P₆O₂₆, monoclinic, P2 c, a = 7.479(3), b = 8.461(5), c = 9.018(2) Å, β = 101.99(3)°, V = 558.2(7) ų, Z = 1, and R = 0.045, R_w = 0.053 for 936 independent reflections. For Cs₄Mo₈P₁₂O₅₂, monoclinic, P2₁, a = 6.398(1), b = 19.497(6), c = 9.835(2) Å, β = 107.06(3)°, V = 1173(1) ų, Z = 1, and R = 0.046, R_w = 0.058 for 1398 independent reflections. Cs₂Mo₄P₆O₂₆ consists of layers of molybdenum phosphorus oxide with the cesium atoms between the layers. Each layer is built up from corner-sharing MoO₆ octahedra, PO₄ tetrahedra, and pyrophosphate groups, P₂O₇. Cs₄Mo₈P₁₂O₅₂ is composed of the same building units arranged in a different way to give rise to tunnels where the cesium cations reside. The rubidium, potassium, and thallium analogs of Cs₄Mo₈P₁₂O₅₂ were also prepared. The Cs₂Mo₄P₆O₂₆ structure is closely related to that of K₄Mo₈P₁₂O₅₂ (A. Leclaire, J. C. Monier, and B. Raveau, J. Solid State Chem. 48, 147 (1983)).