The Room-Temperature Superstructure of ZrP₂O₇ Is Orthorhombic: There Are No Unusual 180° P−O−P Bond Angles

The structure of room-temperature ZrP2O7 is shown to be orthorhombic by a combination of high-resolution synchrotron powder diffraction and single-crystal synchrotron diffraction data. Small nontwinned single crystals were obtained by synthesizing the compound using solvothermal methods at temperatures below the cubic to orthorhombic phase transition. The average P−O−P angle is 146°. DFT calculations (B3LYP/AUG-cc-pVDZ) on the isolated P2O74- anion yield a P−O−P angle of 153.42° and indicate that the barrier to inversion is of the order 3.6 kJ mol-1.