Supramolecular assemblies of multifunctional diimidazole and dicarboxylic acids via various hydrogen bonds and X•••π (X = π, CH) interactions

Multifunctional diimidazole, 2,6-bis[(imidazol-1-yl)methyl]-4-methylphenol (BIP), was crystallized with different dicarboxylic acids, such as oxalic acid (OA), isophthalic acid (IPA), and terephthalic acid (TPA), affording crystals of (BIP2+)center dot(OA(2-)) (1), (BIP)center dot(IPA) (2), (BIP)center dot(TPA) (3), and (BIP)center dot(TPA)(0.5) (4). X-ray single-crystal diffraction studies reveal that all four organic crystals contain strong classical hydrogen bonds (such as O-H center dot center dot center dot N, O-H center dot center dot center dot O, etc.), which are usually observed in organic cocrystals of carboxylic acids with heterocyclic bases. Besides, weak C-H center dot center dot center dot O hydrogen bonds and X center dot center dot center dot pi (X = pi, CH) interactions contribute to the formation of three-dimensional (3-D) networks for these crystals. Interesting annulus with internal dimensions of cavity (about 8.5 angstrom x 9.5 angstrom) are demonstrated in crystal 1, and these annuluses are connected through O-H center dot center dot center dot O hydrogen bonds to form a 2-D porous layer. Because of the coexistence of O-H center dot center dot center dot N and O-H center dot center dot center dot O hydrogen bonds between BIP and aromatic carboxylic acids, compounds 2 and 3 exhibit double-chain structures. Interestingly, while the molar ratio of BIP to TPA is 2:1 in crystal 4, an unusual single-double-chain structure is generated, which is obviously different from the double-chain structure of 3.