Researchers from the Department of Chemistry Nea Baus Topić, Edi Topić and Dominik Cinčić, in collaboration with scientists Sibananda G. Dash and Mihails Arhangelskis from University of Warsaw have published the study Perhalogenated anilines as bifunctional donors of hydrogen and halogen bonds in cocrystals with ditopic nitrogen-containing acceptors in the ACS journal Crystal Growth & Design (IF = 3.8).
The work was focused on studying the experimental and theoretical capabilities of two perhalogenated anilines, 4-bromo-2,3,5,6-tetrafluoroaniline (btfa) and 2,3,5,6-tetrafluoro-4-iodoaniline (itfa), as hydrogen and halogen bond donors. A series of 11 cocrystals derived from the two anilines and selected ditopic nitrogen-containing acceptors (4,4′-bipyridine, 1,2-bis(4-pyridyl)ethane, and 1,4-diazabicyclo[2.2.2]octane) in 1:1 and 2:1 stoichiometries were prepared. Crystallographic analysis revealed bifunctional donor properties in both perhalogenated anilines. The dominant supramolecular interaction in four cocrystals of btfa is the N–H···Nacceptor hydrogen bond between btfa and acceptor molecules, while in the one remaining cocrystal, donor and acceptor molecules are connected via the N–H···Nacceptor hydrogen bond and the Br···Nacceptor halogen bond. In two cocrystals of itfa, the dominant supramolecular interaction is the I···Nacceptor halogen bond between itfa and acceptor molecules, while in the remaining four cocrystals, donor and acceptor molecules are additionally connected by the N–H···Nacceptor hydrogen bond. Periodic density-functional theory (DFT) calculations have been conducted to assess the formation energies of these cocrystals and the strengths of the established halogen and hydrogen bonds. Molecular DFT calculations on btfa and itfa indicate that the differences in electrostatic potential between the competing sites on the molecules are 261.6 and 157.0 kJ mol–1 e–1, respectively. Consistent with previous studies on HB/XB bifunctional donors, it is once more confirmed that a larger difference in electrostatic potentials at potential donor sites on the same molecule favors the formation of a singular preferred intermolecular interaction. The calculated energies of hydrogen and halogen bonds indicate that when present, hydrogen bonds are generally the stronger interactions in the cocrystals.
This research significantly contributes to our understanding of the hierarchy and competition between hydrogen and halogen bonds in cocrystals of perfluorinated donor molecules containing both an amino group and a halogen atom (Br or I). 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.
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