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+)·(OA2-)
(1), (BIP)·(IPA) (2), (BIP)·(TPA) (3), and (BIP)·(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···N, O−H···O, etc.), which are usually observed in organic cocrystals
of carboxylic acids with heterocyclic bases. Besides, weak C−H···O hydrogen bonds and X···π (X = π, 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 Å × 9.5 Å) are demonstrated in crystal 1, and these annuluses are connected through O−H···O hydrogen bonds to form
a 2-D porous layer. Because of the coexistence of O−H···N and O−H···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.