Multicomponent Hydrogen-Bonding Salts Constructed from Tris(2-benzimidazylmethyl)amine and Various Carboxylic Acids: Role of Benzimidazolium-Carboxylate Supramolecular Heterosynthons on Network Assembly
2010-07-07T00:00:00Z (GMT) by
A survey of the Cambridge Structural Database (CSD) indicates that 79% of complexes that contain both imidazole and carboxyl groups generate imidazolium-carboxylate supramolecular heterosynthons rather than carboxyl or imidazole supramolecular homosynthons. In the absence of other competing factors, the occurrence of such heterosynthons is increased to 100%. This observation is further supported by the crystal structures of seven new complexes that contain tris(2-benzimidazylmethyl)amine (TBMA) and a variety of carboxylic acids, including benzoic acid (HBA), p-methoxybenzoic acid (HPMBA), phthalic acid (H2PA), terephthalic acid (H2TPA), isophthalic acid (H2PIA), trimesic acid (H3TMA), and pyromellitic acid (H4PMA). In all seven complexes, (H2TBMA)·(BA)2·DMF (1), (HTBMA)·(PMBA)·(TBMA)·(HPMBA)2·2DMF·H2O (2), (HTBMA)·(H2TBMA)·(HPA)·(PA)·3DMF·H2O (3), (HTBMA)2·(TPA)·2DMF (4), (HTBMA)2·(PIA)·2DMF (5), (H2TBMA)·(HTMA)·0.5DMF·H2O (6), and (HTBMA)2·(H2PMA)·2DMF·H2O (7), proton transfer occurs from acid to aromatic nitrogen of benzimidazole (partial proton transfer for 3, 6, and 7). Analysis of the H-bonding synthons and their effect on crystal packing is also presented in the context of crystal engineering and host−guest chemistry. In the structure of 1, discrete acid/base hexamers are formed via synthons III, V, and VI, while in 2−5, self-recognition via synthons IV, V, and VI results in one-dimensional (1-D) chains, and these structures are extended to high-dimensional architectures (two-dimensional (2-D) structures in 3 and three-dimensional (3-D) structures in 2, 4, and 5) via additional C−H···O, C−H···π and π···π interactions. Interestingly, salts 6 and 7 display the 3-D supramolecular networks via synthons III, IV, V, and VI, which have 1-D channels that are occupied by DMF guests.