A Research Paper Published in Crystal Growth & Design

The work was focused on studying the halogen bond donor potential of two novel halogen bond donors, peripherally perhalogenated imines. Imines were prepared by a condensation reaction between 2,3,5,6-tetrafluoro-4-iodoaniline with either salicylaldehyde or ortho-vanillin, and were cocrystallized with ditopic nitrogen-containing bases: 4,4′-bipyridine, 1,2-bis(4-pyridyl)ethane and 1,4-diazabicyclo[2.2.2]octane. Six new cocrystals exhibiting 2:1 stoichiometric ratio of donor and acceptor were prepared mechanochemically and by crystallization from reactant solutions, and were afterwards characterized by powder and single crystal X-ray diffraction, by thermogravimetric analysis and differential scanning calorimetry. Structural analysis has confirmed the donor potential of the studied imines and revealed that all six cocrystals exhibit molecular trimers containing two imine molecules and one acceptor molecule interconnected by I···N halogen bonds. Solid-state thermochromic studies revealed that both imines and their cocrystals show reversible thermochromic behavior. Comparison of crystals tructures determined at 293 K and 170 K showed that the color change is not accompanied by significant changes in molecular structure and crystal packing. The results presented in this paper demonstrate that the prepared peripherally perhalogenated imines can be reliably used as halogen bond donors for the synthesis of cocrystals, and that this design of halogen bond donors may offer a new route to halogen-bonded cocrystals which exhibit photochromic and thermochromic properties.

The research was performed as a part of the research project New building blocks for the supramolecular design of complex multi-component molecular crystals based on halogen bonds (HaloBond IP-2019-04-1868) funded by the Croatian Science Foundation.