Evolution of intermolecular contacts with temperature and pressure in bromoethane and iodoethane - a comparative study

At ambient conditions two liquids, bromoethane, C2H5Br (MBE, m.p. 154.6 K) and iodoethane, C2H5I (MIE, m.p. 162.1 K), have been crystallized under both isobaric and isochoric conditions using in situ low-temperature and high-pressure techniques. The single-crystal X-ray diffraction studies, supported by the isothermal compressibility and isobaric differential scanning calorimetry measurements, allowed the monitoring and analysis at low temperature and high pressure of the effects of externally induced changes in MBE and MIE. The monoclinic MBE and MIE crystals are found to be isostructural. They are stable, in the investigated regimes, i.e. down to 100 K/0.1 MPa and up to similar to 295 K/3.7 GPa, without undergoing any symmetry or phase change. Both the contraction and compression is mainly noted for the intermolecular separation distances. The Hirshfeld surface analysis of intermolecular contacts clearly shows the nature of occurrence and hierarchy of interactions pointing out the role played by Br/I center dot center dot center dot Br/I contacts, in particular at ambient temperature and high-pressure conditions. The preferences for the formation of intermolecular contacts in MIE are more pronounced and do not require such extreme conditions as in the case of MBE. It is notable that the Br/I center dot center dot center dot Br/I and Br/I center dot center dot center dot H contacts could be basically classified as type-I interactions.