Assembling Extended Structures with Flavonoids

Three flavonoids, 3-hydroxyflavone (1), 3,3′,4′,5,7-pentahydroxyflavone (2), and 4′,5′,7-trihydroxyflavanone (3), were mixed with diazobicyclooctane (DABCO, 4) in varying ratios. Single crystals from these solutions were analyzed by X-ray diffraction studies revealing extended structures exhibiting intermolecular hydrogen bonding. Four different structural motifs emerged: an undulating chain with π-π stacking in [1]2[4]; an helix in [1][4]; three-centered hydrogen bonding incorporating HDABCO+ and π-π stacking in [3][4]; and a three-dimensional hydrogen-bonded network in [2]2[4]3. Both the solvent and the number of hydroxyl substituents play a role in extended structure formation.