Seven organic salts assembled from hydrogen-bonds of N–H⋯O, O–H⋯O, and C–H⋯O between acidic compounds and bis(benzimidazole)

• Seven organic acid–base salts have been prepared and structurally characterized.
• Hydrogen bond interactions of the bis(benzimidazole) and acidic compounds have been ascertained.
• All structures adopted hetero supramolecular synthons.
• Classical hydrogen bonds are the primary forces in the structures with OH⋯benzimidazole synthons.
• The secondary interactions also play important roles in the packing of the compounds.

Seven crystalline organic acid–base adducts derived from 1,4-bis(benzimidazol-2-yl)butane/1,2-bis(2-benzimidazolyl)-1,2-ethanediol and acidic components (picric acid, 2-hydroxy-5-(phenyldiazenyl)benzoic acid, 5-sulfosalicylic acid, oxalic acid, and 1,5-naphthalenedisulfonic acid) were prepared and characterized by the single crystal X-ray diffraction analysis, IR, mp, and elemental analysis. All of the seven compounds are organic salts involving proton transfer from the acidic components to the bis(benzimidazole). For the salt 3, although a competing carboxyl group is present, it has been observed that only the proton at the –SO3H group is deprotonized rather than the H at the COOH. While in the salt 7, both COOH and SO3H were ionized to exhibit a valence number of −2. For 4, the oxalic acid existed as unionized molecule, monoanion, and dianion simultaneously in one compound.All supramolecular architectures of the organic salts 1–7 involve extensive intermolecular N–H⋯O, O–H⋯O, and C–H⋯O hydrogen bonds as well as other noncovalent interactions. Since the potentially hydrogen bonding phenol group is present in the ortho position to the carboxyl group in 2, 3, and 7, it forms the more facile intramolecular O–H⋯O hydrogen bonding. The role of weak and strong noncovalent interactions in the crystal packing is ascertained. These weak interactions combined, all the complexes displayed 3D framework structure.