Complex Superstructures of Mo₂P₄O₁₅

We report structural studies on Mo₂P₄O₁₅ over the temperature range 16−731 K, which show that it is considerably more complex than revealed by earlier work. Its low-temperature structure has lattice parameters a = 24.1134(6) Å, b = 19.5324(5) Å, c = 25.0854(6) Å, β = 100.015(1)°, and V = 11635.0(5) ų at 120 K, containing 441 unique atoms in space group Pn, a remarkably high number for a material with such a simple composition. Mo₂P₄O₁₅ undergoes a structural phase transition at ∼520 K to a high-temperature phase in space group P1̅, with lattice parameters a = 17.947(3) Å, b = 19.864(3) Å, c = 21.899(3) Å, α = 72.421(3)°, β = 78.174(4)°, γ = 68.315(4)°, and V = 6877.2(19) ų at 573 K. The high-temperature structure, with 253 unique atoms, retains much of the low-temperature complexity.