Spectral and Structural Investigation on Weak Interactions of Bipyridine/Pentafluorophenol and Bipyridine/Pentafluorobenzoic Acid Co-Crystals

Pentafluoro phenol (PFP) and pentafluorobenzoic acid (PFBA) as ligands were combined with 4,4'-bipyridine (BP) to obtain two kinds of co-crystals, BP/PFP and BP/PFBA, respectively. Raman and infrared spectra of two co-crystals and their precursors were obtained. The relevant peaks were analyzed, with the help of the calculated spectra throughdensity functional theory (DFT). Infrared spectra show rich hydrogen bonds existed in these two co-crystals. Raman characterization indicates that hydrogen bonding in the BP/PFBA co-crystal is stronger than that in the BP/PFP. In addition, combined with infrared, Raman and crystal structure data, it is found that hydrogen bond and pi-pi interaction coexist in the BP/PFP co-crystal. The difference of weak interaction results in the difference of crystal structure. This study displays significance for further under standing of the structure and properties of co-crystals, which is helpful for the design of novel co-crystals.