10.1021/ic902166j.s002 Sarah E. Lister Sarah E. Lister Anne Soleilhavoup Anne Soleilhavoup Ray L. Withers Ray L. Withers Paul Hodgkinson Paul Hodgkinson John S. O. Evans John S. O. Evans Structures and Phase Transitions in (MoO<sub>2</sub>)<sub>2</sub>P<sub>2</sub>O<sub>7</sub> American Chemical Society 2010 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 2010-03-01 00:00:00 Dataset 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.