Interrogating the Interplay between Hydrogen and Halogen Bonding in Graphitic Carbon Nitride Building Blocks.

Two graphitic carbon nitride (g-C3N4) molecular building blocks designed for halogen bond driven assembly are evaluated through computational quantum chemistry. Unlike those typically reported in the literature, these g-C3N4-based acceptors each offer three unique sites for halogen bond formation, which when introduced to their donor counterparts, lead to 1:1, 2:1, and 3:1 donor-acceptor complexes. Although halogen bonding interactions are present in all donor-acceptor complexes considered in the work, intermolecular hydrogen bonding emerges in complexes in which an iodine-based donor is directly involved. The halogen bond complexes identified herein feature linear halogen bonds and supportive intermolecular hydrogen bonds that lead to nearly additive electronic binding energies of up to -9.7 (dimers), -18.6 (trimers), and -26.5 kcal mol-1 (tetramers). Select vibrational stretching frequencies (νC-X and νC≡C), and the perturbative shifts they incur upon halogen bond formation, are interrogated and compared to those observed in pyridine- and pyrimidine-based halogen-bonded complexes reported in the literature.