1. Multinuclear Solid-State Magnetic Resonance and X-ray Diffraction Study of Some Thiocyanate and Selenocyanate Complexes Exhibiting Halogen Bonding
   Viger-Gravel, J.; Korobkov, I.; Bryce, D. L.
   Cryst. Growth Des. 2011, 11, 4984-4995

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 (¹³C/¹⁵N/⁷⁷Se) solid-state magnetic resonance spectroscopy. Compounds 1 and 2 exhibit trifurcated I···SeCN^– close contacts with characteristic bonding angles near 90°. X-ray and ¹³C/¹⁵N solid-state NMR evidence indicates that the thiocyanate moieties in 4 exhibit 2-fold disorder. The utility of ¹³C/¹⁴N dipolar coupling and residual dipolar coupling data is discussed. ¹⁴N solid-state NMR spectroscopy is found to be impractical in the compounds of interest due to fast T₂ relaxation. ¹³C chemical shifts of the thiocyanates are observed to increase slightly in complexes exhibiting halogen bonding relative to reference compounds with only simple counterions, while ¹⁵N chemical shifts decrease slightly under the same conditions. The opposite trends are noted for the selenocyanates. More substantial changes are observed in both the ⁷⁷Se isotropic chemical shift and in the pseudounique principal component of the ⁷⁷Se chemical shift tensor when comparing simple selenocyanates with those where the ⁷⁷Se 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 are reflected in the ⁷⁷Se solid-state NMR parameters, thereby providing an example of the utility of NMR methods in characterizing halogen bonding interactions in the solid state.

DOI : 10.1021/cg200889y