Engineering crystals using sp3-C centred tetrel bonding interactions.

1,1,2,2-Tetracyanocyclopropane derivatives 1 and 2 were designed and synthesized to probe the utility of sp 3 -C centred tetrel bonding interactions in crystal engineering. The crystal packing of 1 and 2 and their 1,4-dioxane cocrystals is dominated by sp 3 -C(CN) 2 ∙∙∙O interactions with significant van der Waals overlap (≤ 0.266 A) and DFT calculations indicate interaction energies of up to -11.0 kcal·mol -1 . A cocrystal of 2 with 1,4-thioxane reveals that the cyclopropane synthon prefers O-binding over S-binding. Computational analyses revealed that the electropositive C 2 (CN) 4 pocket in 1 and 2 can be seen as a strongly directional 'tetrel-bond donor', similar to halogen bond or hydrogen bond donors. This disclosure is expected to have implications for the utility of such 'tetrel bond donors' in molecular disciplines such as crystal engineering, supramolecular chemistry, molecular recognition and medicinal chemistry.