Experimental Evidence for Non‐Fermi‐Contact J Coupling Across Chalcogen Bonds in Ionic Salt Cocrystal Polymorphs

A pair of novel polymorphic ionic cocrystals of 3,4‐dicyanotelluradiazole and tetraphenylphosphonium bromide are synthesized and are characterized by single‐crystal XRD. Strong and directional non‐covalent chalcogen bonds (ChB) between Te and Br are analyzed via solid‐state NMR to reveal large and anisotropic J(125Te,79/81Br) coupling tensors, providing unequivocal evidence for non‐Fermi contact contributions across ChBs. Along with large 79/81Br quadrupolar couplings for the Br− anions, these data provide new tools to characterize chalcogen bonds and to differentiate between ChB polymorphs. Experimental evidence for non‐Fermi‐contact contributions to J couplings across chalcogen bonds is presented for a pair of newly discovered ionic cocrystal polymorphs. Large and anisotropic J(125Te, 79/81Br) coupling and 79/81Br quadrupolar coupling tensor magnitudes measured via 125Te and 79/81Br solid‐state nuclear magnetic resonance (NMR) spectroscopy provide new experimental insight into the nature of the chalcogen bond.