Avoiding "Synthon Crossover" in Crystal Engineering with Halogen Bonds and Hydrogen Bonds

A combination of halogen bonds and hydrogen bonds has been used for effective assembly of three co-crystals containing desired one-dimensional architectures where the interactions within each assembly can be modulated using tunable electrostatics. The central tecton in these structures, 2-aminopyrazine, can interact with suitable hydrogen-bond donors and halogen-bond donors simultaneously without any "synthon crossover". When different 2-aminopyrazine-based molecules are co-crystallized with 1,4-diiodo-tetrafluorobenzene (DITFB), a N center dot center dot center dot I halogen bond is driving the co-crystal synthesis in each case, whereas the N-H center dot center dot center dot N/N center dot center dot center dot H-N homosynthon is responsible for creating infinite chains of alternating pyrazine and DITFB molecules in the three crystal structures. The importance of electrostatic and geometric complementarity for refining strategies for supramolecular synthesis is emphasized.