Benzimidazolium 3,5-dicarboxybenzoate trihydrate

Cocrystallization of benzimidazole with benzene 1,3,5-tricarboxylic acid in slightly basic medium afforded the title compound, C7H7N2 +·C9H5O6 −·3H2O, in which one of the imidazole N atom is protonated and one carboxylic group of aromatic acid is deprotonated. In the crystal structure, intermolecular N—H⋯O hydrogen-bonding connects the two organic components into dimers, which are further linked into a three-dimensional network by O—H⋯O and N—H⋯O interactions between the water molecules and the dimers.

Cocrystallization of benzimidazole with benzene 1,3,5-tricarboxylic acid in slightly basic medium afforded the title compound, C 7 H 7 N 2 + ÁC 9 H 5 O 6 À Á3H 2 O, in which one of the imidazole N atom is protonated and one carboxylic group of aromatic acid is deprotonated. In the crystal structure, intermolecular N-HÁ Á ÁO hydrogen-bonding connects the two organic components into dimers, which are further linked into a three-dimensional network by O-HÁ Á ÁO and N-HÁ Á ÁO interactions between the water molecules and the dimers.

Experimental
Data collection: APEX2 (Bruker, 2003); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008) and DIAMOND (Brandenburg & Berndt, 1999); software used to prepare material for publication: SHELXL97. lecular recognition (Oxtoby et al., 2005), and pharmaceutical chemistry (Remenar et al., 2003). Obviously, the conguated organic components with rich carboxylate or amino groups have became good blocks for the construction of self-assembly systems, since hydrogen-bonding and π··· π interactions are the main driven forces of the assembly process. In this context benzimidazole (bim) and its derivatives have been used as promising building blocks for the construction of supramolecular aggregates. As a continuation of this work bim and 1,3,5-benzenetricarboxylic acid (H 3 btc) were reacted in slightly basic medium and the product were identified by single crystal X-ray diffraction.
The asymmetric unit of the title compound comprises one Hbim + cation, one monodeprotonated H 2 btcanion and three water molecules all of the located in general positions (Fig. 1). The two carboxyl groups are located within the plane of the aromatic ring, whereas the deprotonated carboxylate group is slightly twisted out of the ring plane. The dihedral angle between the aromatic and the benzimidazole rings amount to 6.84 (5) o .
In the crystal structure, the Hbim + cations and H 2 btcanions are connected into dimers by N-H···O hydrogen-bonding between the N-H H atoms and the carboxylate group (Table 1). These dimers are further connected by O-H···O and N-H···O hydrogen bonding between the water molecules, the carboxyl and carboxylate groups as well as the N-H H atoms into a three-dimensional hydrogen bonded network ( Figure 2 and Table 1). In this interactions the water molecules act as hydrogen bond donor and acceptor.

Refinement
The C-H, N-H and hydroxy H atoms were located in difference maps, but were placed in calculated positions (O-H allowed to rotate but not to tip) and treated as riding, with C -H = 0.93, O -H = 0.82 and N -H = 0.86 Å. The water H atoms were located in difference map and were refined using restraints. All H were refined isotropic with [U iso (H) = 1.2 U eq (C, N) or 1.5 U eq (O)]. Fig. 1. The molecular structure of the title compound with labeling and displacement ellipsoids drawn at the 30% probability level.