Polymorphs of p-nitrophenol as studied by variable-temperature X-ray diffraction and calorimetry: comparison with m-nitrophenol.

Crystal structures of two polymorphic forms of p-nitrophenol have been determined at several temperatures between 120 and 375 K. The thermal expansion tensor has been determined for both polymorphs. The rigid-body mean-square amplitudes of molecular translations and librations and the amplitudes of the internal torsions of the nitro group have been calculated at different temperatures.

Atomic thermal motions studied by variable-temperature X-ray diffraction and related to non-linear optical properties of crystalline meta-dinitrobenzene.

The meta-dinitrobenzene crystal structure has been determined at five temperatures in the 100-300 K temperature range. The thermal expansion coefficients have been calculated from the temperature variation of the lattice parameters. Rigid-body motion analysis with allowance for large-amplitude internal motions provided the T, L and S tensors' values at the temperatures studied and was used to characterize the torsional motion of two nitro groups in the molecule.