The tailoring of crystal structures via the self-assembly of organic coordination compounds by N⋯I non-covalent halogen bonds: co-crystals of sterically hindered N-heterocycles and 1,4-diiodo-tetrafluorobenzene

Abstract

The N-containing heteroaromatics 2,3,5,6-tetramethylpyrazine (tmpyr), 2,2′-bipyridine (2,2′-bpy), 2,4′-bipyridine (2,4′-bpy) and o-phenanthroline (phen) were each cocrystallized with 1,4-diiodo-tetrafluoro-benzene (TFDIB). The effect of the sterically constrained aza cycles on supramolecular assembly and the crystal structure determining interactions is discussed. The N⋯I non-covalent halogen bonds are the main directing interactions responsible for the observed structures. Nevertheless, steric hindrance of the donor sites increases the impact of weaker intermolecular interactions such as CH⋯F bonding and π–π interactions provoking changes in the coordination behaviour of the donor modules. In spite of steric constraints, the co-crystals tmpyr·TFDIB (1) and 2,2′-bpy·TFDIB (2) exhibit polymeric structures consisting of infinite one-dimensional chains of alternating electron donors (D) and acceptors (A). In contrast, the structures of the cocrystals 2,4′-bpy·TFDIB (3) and phen·TFDIB (4) reveal a packing of termolecular [A₁D₂] complexes. It follows that the structure type of such halogen bonded supramolecular assemblies can be tuned by choosing the appropriate precursors.