Complex superstructures of Mo2P4O15.

We report structural studies on Mo(2)P(4)O(15) 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) A, b = 19.5324(5) A, c = 25.0854(6) A, beta = 100.015(1) degrees, and V = 11635.0(5) A(3) at 120 K, containing 441 unique atoms in space group Pn, a remarkably high number for a material with such a simple composition. Mo(2)P(4)O(15) undergoes a structural phase transition at approximately 520 K to a high-temperature phase in space group P1, with lattice parameters a = 17.947(3) A, b = 19.864(3) A, c = 21.899(3) A, alpha = 72.421(3) degrees, beta = 78.174(4) degrees, gamma = 68.315(4) degrees, and V = 6877.2(19) A(3) at 573 K. The high-temperature structure, with 253 unique atoms, retains much of the low-temperature complexity.