engleski

Topicity of 1,3,5-triiodo-2,4,6-trifluorobenzene vs. basicity of pyridine derivatives as halogen bond acceptors

Perfluorinated halogenobenzenes are a group of halogen bond donors that includes a wide range of compounds with different number of donor atoms, what ultimately allows to synthesize halogen bonded cocrystals with various stoichiometries and crystal packing motifs.1 It was previously reported that formation of a three halogen bonds in cocrystals of tritopic donor 1, 3, 5-triiodo-2, 4, 6-trifluorobenzene (135tftib) is quite rare and in competition with specific local interactions, which contribute to a more favorable crystal packing of molecules in crystal structures.2, 3, 4 Besides, according to the available data, it is expected that the basicity of the acceptor also has a significant impact on the formation of a larger number of halogen bonds and their strength.3 In order to investigate this hypothesis, we have prepared 10 binary solids of 135tftib and monotopic pyridine derivatives of different basicity. Furthermore, the binding energies of one, two and three bonded acceptor molecules with 135tftib have been calculated for the four chosen acceptors, as well as the molecular electrostatic potentials (MEP) on donor atoms which do not participate in halogen bonding. It has been shown that the most basic acceptors bind most strongly to the donor molecule, but they also cause a large depletion of the MEP value on free donor atoms. However, most of the strong bases form cocrystals of 1:3 stoictiometric ratio. In contrast, the binding energies of weak bases to 135tftib are quite small, they cause minor change in MEP value on free donor atoms and their cocrystals are mostly of stoichiometry 1:1. Binding energies of moderately strong bases are between those of strong and weak bases, but they form cocrystals with both 1:1 and 1:2 stoichiometry.

halogen bonding

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