Predictability of Chalcogen-Bond-Driven Crystal Engineering: An X-ray Diffraction and Selenium-77 Solid-State NMR Investigation of Benzylic Selenocyanate Cocrystals.

We describe a series of new chalcogen-bonded cocrystals featuring 1,2-bis(selenocyanatomethyl)benzene (DSN) and 1,2,4,5-tetrakis(selenocyanatomethyl)-benzene (TSN) as the donor moieties and a variety of Lewis bases such as onium halides, N-oxides, and pyridine-containing heterocycles as the acceptors. Single-crystal X-ray diffraction demonstrates that, in every case, the selenocyanates consistently interact with the acceptor molecules through strong and directional Se···X chalcogen-bonds (ChBs) (X = halides, oxygen, and nitrogen). 77Se solid-state nuclear magnetic resonance spectroscopy was applied to measure selenium chemical shift tensor magnitudes and to explore potential correlations between these tensor elements and the local ChB geometry. In every case, the isotropic 77Se chemical shift decreases, and the chemical shift tensor span increases upon cocrystallization of DSN with the various ChB acceptors. This work contributes to a growing body of knowledge concerning the predictability and robustness of chalcogen bonds in crystal engineering as well as the NMR response to the establishment of chalcogen bonds. In particular, among the systems studied here, highly linear chalcogen bonds are formed exclusively at the stronger σ-hole of each and every selenium atom regardless of the size, charge, or denticity of the electron donor moiety.