Supramolecular association in proton‐transfer adducts containing benzamidinium cations. I. Four molecular salts with uracil derivatives

Four organic salts, namely benzamidinidium orotate (2,6‐dioxo‐1,2,3,6‐tetrahydropyrimidine‐4‐carboxylate) hemihydrate, C₇H₉N₂⁺·C₅H₃N₂O₄^?·0.5H₂O (BenzamH⁺·Or^?), (I), benzamidinium isoorotate (2,4‐dioxo‐1,2,3,4‐tetrahydropyrimidine‐5‐carboxylate) trihydrate, C₇H₉N₂⁺·C₅H₃N₂O₄^?·3H₂O (BenzamH⁺·Isor^?), (II), benzamidinium diliturate (5‐nitro‐2,6‐dioxo‐1,2,3,6‐tetrahydropyrimidin‐4‐olate) dihydrate, C₇H₉N₂⁺·C₄H₂N₃O₅^?·2H₂O (BenzamH⁺·Dil^?), (III), and benzamidinium 5‐nitrouracilate (5‐nitro‐2,4‐dioxo‐1,2,3,4‐tetrahydropyrimidin‐1‐ide), C₇H₉N₂⁺·C₄H₂N₃O₄^? (BenzamH⁺·Nit^?), (IV), have been synthesized by a reaction between benzamidine (benzenecarboximidamide or Benzam) and the appropriate carboxylic acid. Proton transfer occurs to the benzamidine imino N atom. In all four acid–base adducts, the asymmetric unit consists of one tautomeric aminooxo anion (Or^?, Isor^?, Dil^? and Nit^?) and one monoprotonated benzamidinium cation (BenzamH⁺), plus one‐half (which lies across a twofold axis), three and two solvent water molecules in (I), (II) and (III), respectively. Due to the presence of protonated benzamidine, these acid–base complexes form supramolecular synthons characterized by N⁺—H...O^? and N⁺—H...N^? (±)‐charge‐assisted hydrogen bonds (CAHB).