Chalcogen-Bonded Cocrystals of Substituted Pyridine N‑Oxides and Chalcogenodiazoles: An X‑ray Diffraction and Solid-State NMR Investigation

• Published in: Crystal growth & design 2020-12, Vol.20 (12), p.7910-7920
• Main Authors: Xu, Yijue, Kumar, Vijith, Bradshaw, Maressa J. Z, Bryce, David L
• Format: Article
• Language: English
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/acs.cgd.0c01173

We introduce methyl, methoxy, and phenyl substituents at the para-, meta-, and ortho- positions of pyridine N-oxide to investigate the effect of chemical substitution on the resulting nine chalcogen-bonded structures formed upon cocrystallization with 3,4-dicyano-1,2,5-selenodiazole and 3,4-dicyano-1,2,5-telluradiazole. Single-crystal X-ray diffraction studies reveal the presence of double chalcogen bonding interactions in the cocrystals and demonstrate the impact of the substitution on the geometric features of the chalcogen bonds. 77Se and 125Te solid-state NMR spectroscopy is employed to measure selenium and tellurium chemical shift tensors of the products, and various trends are described. The smallest component of the 77Se chemical shift tensor (δ33) provides the strongest correlation with the chalcogen bond distance. Solution NMR provides qualitative evidence for the persistence of the chalcogen bonds in solution. Finally, 1 J(77Se,14N) coupling constants in 3,4-dicyano-1,2,5-selenodiazole and its chalcogen-bonded cocrystals are measured after accounting for residual dipolar coupling between 77Se and 14N; however, changes in 1 J(77Se,14N) attributable to chalcogen bonding upon cocrystallization are comparable to the experimental uncertainties. This systematic study of chalcogen-bonded cocrystals demonstrates the potential utility of the substitution effect for applications of chalcogen bonds in crystal engineering and demonstrates the value of solid-state NMR in characterizing such systems.