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

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 P=Se⋯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. (⁷⁷Se, ³¹P) coupling constants increase in magnitude as the halogen bond weakens. This observation is understood 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 (⁷⁷Se, ³¹P), with the selenium-phosphorus bonding orbital being the second largest contributor. This work suggests that couplings measured 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. [ABSTRACT FROM AUTHOR]