Solid‐State Assembly by Chelating Chalcogen Bonding in Quinodimethane Tetraesters Fused with a Chalcogenadiazole

In contrast to p‐quinodimethane tetraesters, which undergo facile polymerization due to their diradical character, newly synthesized 1 and 2 consisting of a chalcogenadiazole fused to a p‐naphthoquinodimethane tetraester are thermodynamically stable due to butterfly‐shaped deformation. Such a folded molecular structure is also favorable for chalcogen bond (ChB) formation through intermolecular close contacts between a chalcogen atom (E: Se or S) and the oxygen atoms of ester groups in a crystal. The less‐explored chelating‐ChB through a C=O⋅⋅⋅E⋅⋅⋅O=C contact [Se⋅⋅⋅O: 2.94–3.37 Å] is the key supramolecular synthon for the formation of a one‐dimensional rod‐like assembly in a crystal, which is commonly observed in selenadiazole‐tetraesters (1) with OMe, OEt, and OiPr groups. The formation of inclusion cavities between the rods shows that 1 could serve as solid‐state host molecules for clathrate formation, as found in a hexane‐solvated crystal. In contrast, thiadiazole‐tetraesters (2) are less suitable for the formation of a rod‐like assembly since the ChB involving S is less effective, and thus is overwhelmed by weak hydrogen bonds through C−H⋅⋅⋅O contacts. p‐Quinodimethane tetraesters are labile and transformed into linear polymers by C−C bond formation even in the solid state whereas ring‐annulation prohibits polymerization by inducing butterfly‐shaped deformation to reduce the diradical character. It is not the covalent bond but the chalcogen bond that induces formation of one‐dimensional rod‐like assembly in the crystal of the title molecules, for which the chelating contact of C=O⋅⋅⋅Se⋅⋅⋅O=C is the key supramolecular synthon.