Structures and Phase Transitions in (MoO<sub>2</sub>)<sub>2</sub>P<sub>2</sub>O<sub>7</sub> Sarah E. Lister Anne Soleilhavoup Ray L. Withers Paul Hodgkinson John S. O. Evans 10.1021/ic902166j.s002 https://acs.figshare.com/articles/dataset/Structures_and_Phase_Transitions_in_MoO_sub_2_sub_sub_2_sub_P_sub_2_sub_O_sub_7_sub_/2788834 We report structural investigations into (MoO<sub>2</sub>)<sub>2</sub>P<sub>2</sub>O<sub>7</sub> 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 <i>Pnma</i> with lattice parameters <i>a</i> = 12.6577(1) Å, <i>b</i> = 6.3095(1) Å, <i>c</i> = 10.4161(1) Å, and volume 831.87(1) Å<sup>3</sup> 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 <i>P</i>2<sub>1</sub><i>/c</i> with cell parameters <i>a</i> = 17.8161(3) Å, <i>b</i> = 10.3672(1) Å, <i>c</i> = 17.8089(3) Å, β = 90.2009(2)°, and volume 3289.34(7) Å<sup>3</sup> at 250 K. First principles calculations of <sup>31</sup>P chemical shift and <i>J</i> couplings were used to establish correlation between local structure and observed NMR parameters, and 1D and 2D <sup>31</sup>P solid-state NMR used to validate the proposed crystal structures. The intermediate β-phase is believed to adopt an incommensurately modulated structure; <sup>31</sup>P NMR suggests a smooth structural evolution in this region. 2010-03-01 00:00:00 MoO cell parameters electron diffraction data 2 D 31 P First principles calculations NMR parameters space group Pnma electron diffraction principles quantum chemical calculations Phase Transitions 31 P NMR Å3 phase transitions volume 1 D 31 P chemical shift synchrotron data 250 K crystal structures J couplings lattice parameters 423 K room temperature 325 K