Generation of Square-Shaped Cyclic Dimers vs Zigzag Hydrogen-Bonding Networks and Pseudoconformational Polymorphism of Tethered Benzoic Acids

Two approaches to create hydrogen-bonding (H-bonding) cyclic dimers of tethered benzoic acids in a crystalline state were examined. The cyclic dimers of the methoxy derivative 1 were generated by inclusion of aromatic guest molecules: benzene or benzonitrile. Depending on the size of the guests, the conformation of the pentylene linker of 1 took either the all-trans or 1,2- and 4,5-gauche conformation to adjust the size of the cavity for the guest. The tethered benzoic acids 2 possessing benzyloxy groups as pendants generated a poly(pseudo)rotaxane-like structure in which pendants were included in the cavity of the cyclic dimer itself. In contrast, 1 afforded a zigzag H-bonding network by recrystallization from methanol or ethanol. Incorporation of methanol in the zigzag network was observed when 1 was recrystallized from methanol.