2,2′-(p-Phenylene)bis(4,5-dihydro-1H-imidazol-3-ium) bis(3-nitrobenzoate)

In the title compound, C12H16N4 +·2C7H4NO4 −, the complete 2,2′-(p-phenylene)bis(4,5-dihydro-1H-imidazol-3-ium) (bib) dication is generated by crystallographic inversion symmetry. The bib cations reside on crystallographic inversion centers, which coincide with the centroids of the respective benzene rings. In the cation, the imidazole ring adopts an envelop conformation with the flap atom displaced by 0.082 (3) Å from the plane through the other ring atoms. In the crystal, the cations and anions are linked through intermolecular N—H⋯O hydrogen bonds, forming chains running along the a axis. C—H⋯O interactions also occur. Weak π–π contacts between the imidazole rings of bib and between the benzene rings of NB [centroid–centroid distances = 3.501 (1) and 3.281 (2) Å, respectively] may further stabilize the structure.

In the title compound, C 12 H 16 N 4 + Á2C 7 H 4 NO 4 À , the complete 2,2 0 -(p-phenylene)bis(4,5-dihydro-1H-imidazol-3-ium) (bib) dication is generated by crystallographic inversion symmetry. The bib cations reside on crystallographic inversion centers, which coincide with the centroids of the respective benzene rings. In the cation, the imidazole ring adopts an envelop conformation with the flap atom displaced by 0.082 (3) Å from the plane through the other ring atoms. In the crystal, the cations and anions are linked through intermolecular N-HÁ Á ÁO hydrogen bonds, forming chains running along the a axis. C-HÁ Á ÁO interactions also occur. Weakcontacts between the imidazole rings of bib and between the benzene rings of NB [centroid-centroid distances = 3.501 (1) and 3.281 (2) Å , respectively] may further stabilize the structure.

Comment
Attention has been recently focused on the use of supramolecular interactions, such as hydrogen bonding and π-π interactions, in the controlled assembly of supramolecular architectures (Jeffrey, 1997). Hydrogen bonds often play a dominant role in crystal engineering because of their combine strength with directionality. We have reported several complexes having an imidazole entity, and have concluded that hydrogen bonding involving this group influences the geometry around the metal atom and the crystallization mechanism (Ren, Ye, He et al., 2004;Ren, Ye, Zhu et al., 2004;Ren, et al., 2007;Ren, et al., 2009). As a further contribution to this field, we describe herein the synthesis and crystal structure of the title compound.
The asymmetric unit of the title compound ( In the crystal structure, the bib and NB ligands are joined together through hydrogen bonds between the carboxy oxygen in NB and nitrogen atom in bib to give a macrocycle N1-H1···O1 and N2-H2···O2 with the hydrogen bond geometry given in Table 1, and a face-to-face intracyclic π-π interaction at 3.50 (1) /A. Each bib group also features another macrocycles, resulting in 1-D chains running along the a axis. As illustracted in Fig. 2, the adjacent NB ligands are furthermore linked in the antiparallel alignment with offset along the bc plane by π-π contacts (3.28 (1)/A) in a 3-D structure (Fig. 2). Weak intermolecular C-H···O contacts contribute to the stability of the layered structure (Table 1).

Experimental
All the reagents and solvents employed were commercially available and used as received without further purification.

Refinement
Anisotropic thermal parameters were applied to all nonhydrogen atoms. The organic hydrogen atoms attached to C atoms and N atom were fixed geometrically and treated as riding with C-H = 0.93 Å (aromatic) or 0.97 Å (methylene) and N-H = 0.86 Å with U iso (H) = 1.2 U eq (C or N). Rigid bond restraint instruction DELU was applied to improve the anisotropic displacement parameters involving N3 and C12. Fig. 1. The structure of the title complex 1,4-bis(4,5-dihydro-H,4H-imidazol-2-yl)benzene bis(3-nitrobenzoate) showing 30° probability displacement ellipsoids.  Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.