Solid‐State [4+4] Cycloaddition and Cycloreversion with Use of Unpaired Hydrogen‐Bond Donors to Achieve Solvatomorphism and Stabilization

The crystal structure of a commercially available anthracene derivative, anthracene‐9‐thiocarboxamide, is reported here for the first time, and we demonstrate that the compound undergoes a [4+4] cycloaddition in the solid state to afford facile synthesis of the cycloadduct (CA). The cycloaddition is also reversible in the solid state using heat or mechanical force. Due to the presence of unpaired, strong hydrogen‐bond donor atoms on the CA, significant solvatomorphism is achieved, and components of the solvatomorphs self‐assemble into four different classes of supramolecular structures. The CA readily crystallizes with a variety of structurally‐diverse solvents including those containing oxygen‐, nitrogen‐, or pi‐acceptors. Some of the solvents the CA crystallized with include thiophene, benzene, and the three xylene isomers; thus, we employed the CA in industrially‐relevant solvent separation. However, in competition studies, the CA did not exhibit selectivity. Lastly, we demonstrate that the CA crystallizes with vinyl‐containing monomers and is currently the only compound that crystallizes with both widely used monomers 4‐vinylpyridine and styrene. Solid‐state complexation of the CA with the monomers affords over a 50 °C increase in the monomer’s thermal stabilities. We expect the strategy of designing molecules with unused donors can be applied to achieve separations or volatile liquid stabilization.