Abstract
Halogen bonds constitute an important and topical class of non-covalent interaction. We report a combined X-ray diffraction, multinuclear (Se-77, P-31, C-13) solid-state magnetic resonance, and computational study of a series of crystalline triphenylphosphine selenide-iodoperfluorobenzene complexes which feature P=Se center dot center dot center dot I-C halogen bonds. Selenium-77 chemical shifts increase due to halogen bonding with iodine and correlate with the P=Se distance, which in turn correlates with the strength of the halogen bond. J(Se-77, P-31) coupling constants increase in magnitude as the halogen bond weakens. This observation is understood via a natural localized molecular orbital (NLMO) DFT approach which shows that contributions from the selenium lone pair orbital tend to dominate both the magnitude and trends in J(Se-77, P-31), with the selenium-phosphorus bonding orbital being the second largest contributor. This work suggests that J couplings measured via NMR spectroscopy may play an important role in the characterization of halogen bonds, in clear analogy with their role in the characterization of hydrogen bonds.