C-H hydrogen bond and halogen bond directed self-assembly of ethereal podands and C-X•••F-/HF2- halogen bonding in solution

A series of halogenated podands (P1-P8) have been synthesized from 1,3,5-tris(bromomethyl)mesitylene and halogen-substituted phenols to study the structure-directing roles of C-H hydrogen bonds and halogen bonds in the formation of self-assembled supramolecular frameworks. The ethereal podands are suitable for the study of C-H hydrogen bonds in the crystalline state due to the presence of three different types of C-H donors, such as methyl, methylene, and aromatic -CH groups, and three different types of acceptors such as ethereal oxygen, halogens, and aromatic rings. Single crystal X-ray structures of three halophenyl-functionalized podands (P2, P3 and P4) and a cyanophenyl-functionalized podand (P9) were determined at room temperature (298 K), and detailed Hirshfeld surface analysis of the crystal structures was performed to quantify the close contact contributions (in %) from different types of non-covalent interactions involved in the self-assembly of podands. The crystal structures of the halophenylfunctionalized podands (P2, P3, and P4) showed self-assembly primarily via intermolecular C-H center dot center dot center dot O, C-H center dot center dot center dot pi, and halogen bonding interactions. Hirshfeld surface analysis of the crystal structures revealed significantly higher contributions from H center dot center dot center dot C and H center dot center dot center dot X (X = halogen) close contacts in comparison to H center dot center dot center dot O and X center dot center dot center dot C close contacts in 2D-fingerprint plots. The self-assembly of the cyanophenylfunctionalized podand (P9) was largely governed by intermolecular C-H center dot center dot center dot O and C-H center dot center dot center dot N interactions. The podand crystals showed relatively high thermal stability in thermogravimetry analysis (250-290 degrees C), which can be attributed to the hydrogen and halogen bond assisted formation of 3D supramolecular frameworks. 19F-NMR spectra of tetraethylammonium fluoride in the presence of an equivalent amount of tris(2-halophenoxymethyl)mesitylene podand (P5 or P6) showed a downfield shift of the fluoride signal (Delta delta 3.2 ppm) indicating C-X center dot center dot center dot F- halogen bonding in solution. Further, F-19-NMR spectra of hydrogen bifluoride (HF2-) in the presence of P5 or P6 showed a large upfield shift of approximate to 21-22 ppm suggesting C-X center dot center dot center dot F-center dot center dot center dot H-F halogen bonding in solution.

Automated summary

A series of halogenated podands have been synthesized to study the roles of C-H hydrogen bonds and halogen bonds in the formation of self-assembled supramolecular frameworks. The crystal structures and Hirshfeld surface analysis reveal the contributions of different non-covalent interactions in the self-assembly of podands, and NMR spectra confirm the presence of halogen bonding in solution.