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. Frequencies of the translational and librational modes and of the torsional modes of the nitro groups have been compared with the wave numbers at the maximum of bands in the low-frequency Raman and IR spectra. Ab initio calculations were performed in order to assess the contribution from large-amplitude internal motions to the static first-order hyperpolarizability of the m-dinitrobenzene molecule.

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. Differential scanning calorimetry was used to find the temperature and enthalpy of the polymorphic transformation. The results were compared with those recently obtained for m-nitrophenol polymorphs. Some conclusions concerning the polymorphism of p- and m-nitrophenols are presented.

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The crystal structure of 1‐chloro‐2‐nitro­benzene, C6H4ClNO2, is made up of mol­ecules which are linked by N—O⋯Cl halogen bonds. These mol­ecular chains are involved in aromatic π–π stacking; the inter­molecular O⋯Cl distance is 3.09 Å. Such short halogen bonds are not common. A rigid‐body analysis including the non‐rigidly attached rigid group provides the mean‐square amplitudes of the mol­ecular translations and librations, and of the inter­nal torsional vibrations of the nitro group. The results reveal the driving role of the torsional vibrations of the nitro group in the phase transition to the liquid phase.

Molecular crystals with globular molecules have interesting properties and form systems amenable to theoretical modelling with some degree of realism. The hardest behaviour to incorporate in a model is the large amplitude librations of the molecules. This study introduces a method of calculating the effect of large angle librational behaviour on the X-ray scattering produced by such molecules. The technique could be extended to other molecular solids. We have applied the method to illustrate the scattering from SF6, adamantane (C10H16) and Buckminsterfullerene (C60), using librational amplitudes derived from molecular dynamic simulation and other sources. The results illustrate nicely how increasing angles of libration smear out the molecular specific features of the scattering. Adding in the effect of vibrational smearing through the influence of the Debye-Waller term enables one to see how realistic scattering contours in reciprocal space are built-up from the sum total of the processes contributing to the scattering.