Search

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]

The compression and thermal expansion of crystalline 1,2,4-trichlorobenzene, C6H3Cl3, 124TCB, investigated under isobaric and isothermal conditions, are in reverse relation, as for most of crystals, however, the isochoric strain along direction c is clearly different from those along a and b. Single crystals of 124TCB have been in situ grown under isochoric and isobaric conditions, at 270 K/0.1 MPa and 295 K/0.16 GPa, and also at 100 K/0.1 MPa and 295 K/0.64 GPa, when the unit-cell volume is similar. All crystallizations yielded the same phase, of monoclinic space group P21/n, with two symmetry-independent molecules (Z′ = 2). The structure is governed by Cl…Cl and Cl…H interactions and the molecules are all nearly parallel to the [001] direction. Systematic differences of these specific contacts afford rationalizing the isochoric strain of the crystal. The phase diagram of 124TCB has been outlined. [ABSTRACT FROM AUTHOR]