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, C(7)H(9)N(2)(+)center dot C(5)H(3)N(2)O(4)(-)center dot 0.5H(2)O (BenzamH(+)center dot Or(-)), (I), benzamidinium isoorotate (2,4-dioxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate) trihydrate, C(7)H(9)N(2)(+)center dot C(5)H(3)N(2)O(4)(-)center dot 3H(2)O (BenzamH(+)center dot Isor(-)), (II), benzamidinium diliturate (5-nitro-2,6-dioxo-1,2,3,6-tetrahydropyrimidin-4-olate) dihydrate, C(7)H(9)N(2)(+)center dot C(4)H(2)N(3)O(5)(-)center dot 2H(2)O (BenzamH(+)center dot Dil(-)), (III), and benzamidinium 5-nitrouracilate (5-nitro-2,4-dioxo-1,2,3,4-tetrahydropyrimidin-1-ide), C(7)H(9)N(2)(+)center dot C(4)H(2)N(3)O(4)(-) (BenzamH(+)center dot 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 center dot center dot center dot O(-) and N(+)-H center dot center dot center dot N(-) (+/-)-charge-assisted hydrogen bonds (CAHB).