Researchers from the Department of Chemistry Nikola Bedeković, Vladimir Stilinović and Dominik Cinčić, in collaboration with Tomislav Piteša and Mihael Eraković from the Ruđer Bošković Institute have published the study Anticooperativity of Multiple Halogen Bonds and Its Effect on Stoichiometry of Cocrystals of Perfluorinated Iodobenzenes in the ACS journal Crystal Growth & Design (IF = 4.076).
One of the most fascinating aspects of the study of intermolecular interactions is the effect one interaction can have on other interactions present in the same supramolecular structure. This effect can be manifested through strengthening (cooperativity) or weakening (anticooperativity) of the interactions involved. The paper presents a study of anticooperativity between multiple halogen bonds formed by a di- or tritopic donor with nitrogen bases, and the effect of the anticooperativity on the stoichiometries of dicomponent solids (co-crystals) obtained by combining given donors and acceptors. The study was based on ‘classical’ ditopic (1,3-diiodotetrafluorobenzene and i 1,4-diodotetrafluorobenzene) and tritopic (1,3,5-triiodotrifluorobenzene) halogen bond donors, and has included preparation of 18 novel co-crystals, a detailed database survey of the structures of previously known co-crystals of the same donors, as well as quantum-chemical computations of the effect binding an acceptor molecule will have on the molecular electrostatic potential of the donor, and energies of subsequent halogen bonds. The calculations have shown that binding of a single acceptor molecule on one of the iodine atoms of the halogen bond donor reduces the electrostatic potential on the remaining iodine atoms and dramatically decreases their potential for forming further halogen bonds, which explains both the high occurrence of crystal structures where the donors do not achieve their maximal topicity and the observed differences in halogen bond lengths. Despite the fact that this effect increases with the basicity of the acceptor, when the increase of halogen bond energy due to the basicity of the acceptor compensates its decrease due to the reduction of the acidity of the donor, it enables strong bases to form co-crystals in which a potentially polytopic XB donor achieves its maximal topicity.
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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