Solid-state molecular folding and supramolecular structures of triptycene-derived secondary dicarboxamides

The synthesis and X-ray crystal structures of triptycene-derived secondary dicarboxamides 1 and 4-7 and reference compounds 2, 3, and 8 are reported. For comparison, molecular conformations of 1-8 in the gas phase and those of 1 and 3-6 in CD2Cl2 investigated by AM(1) modeling and H-1 NMR spectroscopy, respectively, are also included. The solid-state conformations of 1 and 5-8 are folded and compact, resulting from the cooperative effects of intramolecular amide-amide hydrogen bonding and edge-to-face arene-arene interactions between the triptycene and the N-acetylsulfanilyl groups. The sulfonyl ester groups are also essential in the folding of 1 and 5-8 and function as structural turn units. In contrast, the conformations of 2-4 are unfolded due to the lack of one of these three essentials. The extended triptycene ring systems in 6 and 7 provide an arene-arene contact mode that is different from that for 1 and 5. While AMI calculations suggest that the two possible arene-arene contact modes in 6 and 7 have similar conformational energies, the one observed in the solid state is also favored in solutions. To achieve a more regular shape for compact crystal packing, the bulky triptycene groups tend to pack in pairs. As a result, the intermolecular amide--amide hydrogen bonding is perturbed and modified with the participation of either the sulfonyl groups or the methanol solvent molecules, leading to various hydrogen-bonding motifs for these triptycene diamides.