The effects of intermolecular interactions by a series of haloaromatic halogen bond donors on the normal modes and chemical shifts of the acceptor pyrimidine are investigated by Raman and NMR spectroscopies and electronic structure computations. Halogen-bond interactions with pyrimidine's nitrogen atoms shift normal modes to higher energy and upfield shift H and C NMR peaks in adjacent nuclei. This perturbation of vibrational normal modes is reminiscent of the effects of hydrogen bonded networks of water, methanol, or silver on pyrimidine. The unexpected observation of vibrational red shifts and downfield C NMR shifts in some complexes suggests that other intermolecular forces such as π interactions are competing with halogen bonding. Natural bond orbital analyses indicate a wide range of charge transfer is possible from pyrimidine to different haloaromatic donors and computed halogen bond binding energies can be larger than a typical hydrogen bond. These results emphasize the importance in strategic selection of substituents and electron withdrawing groups in developing supramolecular structures based on halogen bonding.

The use of a thiophene-based building block (Pyr-T) to achieve a supramolecular assembly driven by halogen bonding (XB) is described. X-ray crystallography, NMR, Raman spectroscopy, and computational chemistry afford evidence of strong XB and π–π stacking.

The Inside Cover picture highlights perturbations to vibrational energy levels and 13C NMR spectra of the acceptor pyrimidine upon complexation with halogen bond donors. Shifts and interaction energies increase with stronger electron withdrawing groups and more polarizable halogen atoms. More information can be found in the Full Paper by D. L. Watkins, G. S. Tschumper, N. I. Hammer, and co‐workers on page 1267 in Issue 10, 2017 (DOI: 10.1002/cphc.201700114).