Despite the supramolecular interactions such as halogen bonding are frequently termed "noncovalent" interactions, they have been predicted using computational methods to possess a significant covalent component. In this article, we adopt a unique strategy that combines experimental solid-state NMR and relativistic DFT approaches to explore the electronic nature of previously postulated supramolecular covalency [Bora et al., Chem. Eur. J., 2017, 23, 7315]. Our approach involves analysis of hyperfine interactions and hyperfine shifts in NMR spectra of halogen-bonded cocrystals containing a paramagnetic transition-metal complex. We demonstrate that hyperfine interaction pertaining to the paramagnetic transition-metal center and being observed at the probed nucleus of the cocrystalized (halogen-bonded) molecule is governed by the Fermi-contact mechanism. This contact mechanism originates in "through-bond" spin transmission and, therefore, unequivocally reports on the electron sharing between the halogen-bonded molecules, i.e., halogen-bond covalency.

This article is Open Access

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