Noncovalent interactions such as hydrogen bonding and pi-stacking are powerful linkers for the formation of highly structured assemblies and enhance bulk properties in materials. Amongst those arising in the literature are approaches exploiting halogen bonding (XB). XB is a type of sigma-hole interaction in which a positive electrostatic potential area on a halogen atom (i.e., XB donor) coordinates with an electron rich region on another atom of the same or different molecule (i.e., XB acceptor). Most common XB donors are typically iodine-containing molecules while XB acceptors are usually Lewis bases containing non-bonding electrons (i.e., nitrogen, sulfur and oxygen). Whereas numerous research has focused on the development of new generations of XB donors, less attention has been shown towards the investigation of XB acceptors. Herein, a series of six pyrimidine-based XB acceptors were designed and synthesized. A total of twelve co-crystals were formed via vapor diffusion method and analyzed using thermal and spectroscopic tools. IR spectroscopy and melting point measurements were utilized as indicators for the formation of the co-crystals. Moreover, NMR spectroscopy was also employed to detect the presence of XB interactions and examine their relative strength via the chemical shifts of the associated bonds within the acceptors. The presence of XB and other noncovalent interactions were then confirmed via X-ray crystallography. Computational analysis compared the relative electron density on the nitrogen atoms in XB acceptors and revealed relative energy of all the interactions within each assembly. The incorporation of these novel aromatic moieties induce intermolecular overlap of pi-orbitals in the solid state. Results indicate that the synergy between XB and pi-pi stacking could be further employed for the design of supramolecular assemblies for material applications.

Tuning the properties of pyrimidine for halogen bond driven supramolecular assembly

255th National Meeting (2018)

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