Structures and phase transitions in (MoO2)2P2O7.

We report structural investigations into (MoO2)2P2O7 using a combination of X-ray, neutron and electron diffraction, and solid-state NMR supported by first principles quantum chemical calculations. These reveal a series of phase transitions on cooling at temperatures of 377 and 325 K. The high temperature γ-phase has connectivity consistent with that proposed by Kierkegaard at room temperature (but with improved bond length distribution), and contains 13 unique atoms in space group Pnma with lattice parameters a = 12.6577(1) A, b = 6.3095(1) A, c = 10.4161(1) A, and volume 831.87(1) A3 from synchrotron data at 423 K. The low temperature α-structure was indexed from electron diffraction data and contains 60 unique atoms in space group P21/c with cell parameters a = 17.8161(3) A, b = 10.3672(1) A, c = 17.8089(3) A, β = 90.2009(2)°, and volume 3289.34(7) A3 at 250 K. First principles calculations of 31P chemical shift and J couplings were used to establish correlation between local structure and observed NMR...