Abstract
We report on the preparation and study of a series of thiocyanate and selenocyanate compounds exhibiting halogen bonding between iodine and nitrogen, sulfur, or selenium. The novel compounds (Me4NSeCN)(p-C6F4I2)(2) (1), (Me4NSeCN)(o-C6F4I2)(2) (2), and (Me4NSCN)(p-C6F4I2)(2) (4) were synthesized. Their crystal structures and local halogen bonding interactions, along with those of related additional thiocyanate and selenocyanate compounds (e.g., KSCN, Me4NSCN, Me4NSeCN, etc.) were investigated by single-crystal X-ray diffraction and multinuclear (C-13/N-15/Se-77) solid-state magnetic resonance spectroscopy. Compounds 1 and 2 exhibit trifurcated I center dot center dot center dot SeCN- close contacts with characteristic bonding angles near 90 degrees. X-ray and C-13/N-15 solid-state NMR evidence indicates that the thiocyanate moieties in 4 exhibit 2-fold disorder. The utility of C-13/N-14 dipolar coupling and residual dipolar coupling data is discussed. N-14 solid-state :NMR spectroscopy is found to be impractical in the compounds of interest due to fast T-2 relaxation. C-13 chemical shifts of the thiocyanates are observed to increase slightly in complexes exhibiting halogen bonding relative to reference compounds with only simple counterions, while N-15 chemical shifts decrease sligihtly under the same conditions. The opposite trends are noted for the selenocyanates. More substantial changes are observed in both the Se-77 isotropic chemical shift and in the geudounique principal component of the Se-77 chemical shift tensor when Comparing simple selenocyanates with those where the Se-77 is engaged in halogen bonding interactions with iodine. These results are interpreted in the context of Ramsey's theory to show that the iodine-selenium interactions axe reflected in the Se-77 solid-state NMR parameters, thereby providing an example of the utility of NMR methods in characterizing halogen bonding interactions in the solid state.