Probing halogen bonds with solid-state NMR spectroscopy: observation and interpretation of J(77Se,31P) coupling in halogen-bonded PSe⋯I motifs

Abstract

Halogen bonds constitute an important and topical class of non-covalent interaction. We report a combined X-ray diffraction, multinuclear (⁷⁷Se, ³¹P, ¹³C) solid-state magnetic resonance, and computational study of a series of crystalline triphenylphosphine selenide–iodoperfluorobenzene complexes which feature PSe⋯I–C halogen bonds. Selenium-77 chemical shifts increase due to halogen bonding with iodine and correlate with the PSe distance, which in turn correlates with the strength of the halogen bond. J(⁷⁷Se,³¹P) 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(⁷⁷Se,³¹P), 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.