Isostructurality, Polymorphism and Mechanical Properties of Some Hexahalogenated Benzenes: The Nature of Halogen⋅⋅⋅Halogen Interactions

摘要: The nature of intermolecular interactions between halogen atoms, X···X (X=C1, Br, I), continues to be topical interest because these may used as design elements in crystal engineering. Hexahalogenated benzenes (C 6 Cl 6-n Br n , C I ) crystallise two main packing modes, which take the monoclinic space group P2 1/n and triclinic P1. former, is isostructural more common. For molecules that lack inversion symmetry, adoption this structure would necessarily lead crystallographic disorder. In planar form Cl...Cl contacts also π···π stacking interactions. When crystals are compressed mechanically along their needle length, is, [010], a bending deformation takes place, stronger direction. Further compression propagates consecutively snakelike motion through crystal, similar what has been suggested for dislocations. related weakness Cl···Cl compared with less common restricted have symmetrical (1,3,5- 2,4,6-) substitution pattern. This type characterised by specific, polarisation-induced result threefold-symmetrical X 3 synthons, especially when X=I; leads layered pseudohexagonal successive layers stacked so bumps one layer fit into hollows next space-filling manner. shear on application mechanical stress only plane deformation. shearing arises from sliding against another. Nonspecificity weak interlayer here demonstrated twinned compounds. One compounds studied (1,3,5-tribromo-2,4,6-triiodobenzene) dimorphic, adopting both structures, reasons polymorphism suggested. To summarise, chemical geometrical models need considered hexahalogenated benzenes. nonspecific, whereas some anisotropic, chemically specific crystal-structure directing.