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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 ∼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...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...Br/I and Br/I...H contacts could be basically classified as type‐I interactions. [ABSTRACT FROM AUTHOR]

Single crystals of isomeric 1,2,3‐tribromobenzene (123TBB), 1,2,4‐tribromobenzene (124TBB) and 1,3,5‐tribromobenzene (135TBB) have been grown from different solvents and their structures determined by X‐ray diffraction at 100, 200 and 270 K. The melting‐point differences of ca 40 K between 135TBB, 123TBB and 124TBB have been correlated with the molecular symmetry and packing preferences in the crystal, as well as with the main types of intermolecular halogen interactions, i.e. Br...Br, Br...C (Br...π) and Br...H. The relationship between symmetry and melting point in Carnelley's rule has been extended to the accessibility of terminal atoms for the formation of intermolecular interactions, their occurrences and distribution, and the close packing. The electrostatic potential mapped on molecular surfaces demonstrates that in more symmetric molecules the more evenly distributed substituents are more accessible and form more optimum intermolecular interactions. [ABSTRACT FROM AUTHOR]

Trends in the melting points of analogous halogenated benzene isomers are rationalized in terms of molecular symmetry, crystal structure and interactions. [ABSTRACT FROM AUTHOR]

High‐nitrogen‐content compounds 6‐azido‐1,2,4‐triazolo[4,3‐b]pyridazine (C5H3N7) and its 3‐methyl derivative (C6H5N7) have been in situ crystallized in a diamond‐anvil cell and their structures determined by single‐crystal X‐ray diffraction. Under ambient and high‐pressure conditions the crystallizations yield the same phases: the C5H3N7 anhydrate and C6H5N7 hydrated clathrate. In both the structures there are clearly distinguished regions of short CH...N and N...N intermolecular contacts, the latter involving exclusively the azide groups. High pressure initially increases the contents of water in the channel pores of the clathrate. [ABSTRACT FROM AUTHOR]