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···I halogen bond is driving the co-crystal synthesis in each case, whereas the N–H···N/N···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

Establishing a Hierarchy of Halogen Bonding by Engineering Crystals without Disorder

It has been shown, using a foundation of new structural data, that the relative strength and capability of iodo- and bromo-based molecules to act as halogen-bond donors in a competitive supramolecular arena accurately reflect a ranking of halogen-bond donors based upon electrostatic molecular potentials. Furthermore, to obtain the critical structural information, a protocol (comprising a lowering of molecular symmetry and the addition of strong and directional hydrogen bonds) for engineering crystals without positional disorder was successfully developed