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

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 pi-pi 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 [A(1)D(2)] complexes. It follows that the structure type of such halogen bonded supramolecular assemblies can be tuned by choosing the appropriate precursors.