1,4-Bis(4,5-dihydro-1H-imidazol-2-yl)benzene-terephthalic acid-water (1/1/4).

The asymmetric unit of the title compound, C(12)H(14)N(4)·C(8)H(6)O(4)·4H(2)O, consists of one half of the 1,4-bis-(4,5-dihydro-1H-imidazol-2-yl)benzene (bib) mol-ecule, one half of the terephthalic acid (TA) mol-ecule and two water mol-ecules. Both the bib and the TA mol-ecules reside on crystallographic inversion centers, which coincide with the centroids of the respective benzene rings. The bib and the TA, together with the water mol-ecules, are linked through inter-molecular O-H⋯O, O-H⋯N and N-H⋯O hydrogen bonds, forming a three-dimensional network of stacked layers. Weak inter-molecular C-H⋯O contacts support the stability of the crystal structure.

The asymmetric unit of the title compound, C 12 H 14 N 4 Á-C 8 H 6 O 4 Á4H 2 O, consists of one half of the 1,4-bis(4,5dihydro-1H-imidazol-2-yl)benzene (bib) molecule, one half of the terephthalic acid (TA) molecule and two water molecules. Both the bib and the TA molecules reside on crystallographic inversion centers, which coincide with the centroids of the respective benzene rings. The bib and the TA, together with the water molecules, are linked through intermolecular O-HÁ Á ÁO, O-HÁ Á ÁN and N-HÁ Á ÁO hydrogen bonds, forming a three-dimensional network of stacked layers. Weak intermolecular C-HÁ Á ÁO contacts support the stability of the crystal structure.

Comment
Attention has recently focused on the use of supramolecular interactions such as hydrogen bonding and π-π interactions, in addition to coordinate bonds, 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 (Thaimattam, et al., 1998). On the other hand, supramolecular systems sustained by soft connections, such as hydrogen bonds, are comparatively more flexible and sensitive to the chemical environment. We described previously a number of such complexes, including the imidazole ligand, and have concluded that hydrogen bonding involving this group influences the geometry around the metal atom and the crystallization mechanism [Ren, et al. (2007 and literature cited therein); Shang et al. (2009)].
The crystal lattice contains two bib, two TA and eight lattice water molecules in the solid. The bib and TA in a trans, trans configuration are in a face-to-face orientation and the dihedral angle between acid TA and base bib components is 9.5°. And the bib and TA ligands are joined together by two water molecules through hydrogen bonds between the carboxy oxygen atom in TA and the nitrogen atom of -C=N-in bib to give a macrocycle O1W-H1WB···O2W, O2W-H2WB···O1, O1W-H1WA···O2, N2-H2C···O1W and O2-H2D···N1 with the hydrogen bond geometry given in Table 1, and a faceto-face intracyclic \<i>p-\<i>p interaction at 3.69 Å (Fig. 1). Each bib group also features another macrocycles, resulting in 1-D chains running along the a axis. As illustrated in Fig. 2, the adjacent TA ligands are furthermore linked in the antiparallel alignment with offset along the ab plane by hydrogen bonds between the water molecules and the oxygen of TA groups (O2W-H2WA···O1, O1W-H1WA···O2, O2W-H2WB···O1, and O1W-H1WB···O2W (see Table 1). These ab planes are packed and stabilized by the hydrogen bonds between the lattice water and oxygen atom of TA ligands (O2w-H2wa···O1 = 2.82 Å) into a 3-D structure. 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.
Syntheses of bib 1,4-Benzenedicarboxylic acid (2.31 g, 13.9 mmol), ethylenediamine (3.70 ml, 50 mmol), ethylenediamine dihydrochloride(6.64 g, 50 mmol) and toluene-p-sulfonic acid (0.208 g, 1.09 mmol) were added to the solvent of ethyleneglycol (20 ml), and the mixture solution was refluxed for 3 hr. About half of the ethylene glycol solvent was then slowly removed by distillation. The residue was dissolved in a mixture of water (40 ml) and concentrated HCl (11 M, 3 ml). The addition of 50% aqueous NaOH gave a yellow precipitate that was purified by recrystallization. The ligand bib was obtained in 83% based on 1,4-benzenedicarboxylic acid (ca 2.50 g).  (5 ml) of TA (0.034 g, 0.2 mmol) was added. The solution was allowed at room temperature in air for 48 hr by slow evaporation.

Refinement
All H 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) = 1.2U eq (C or N). The positions of H atoms for water molecules were calculated (Nardelli, 1999) and included in the subsequent refinement as riding with U iso (H) = 1.5U eq (O). Fig. 1. The molecular structure of the title molecule, with the atom-numbering scheme. Symmetry-related atoms shown labelled A and B. [symmetry codes A: (-x + 1, -y + 2, -z); B: (-x + 1, -y + 1, -z). 1,4-Bis(4,5-dihydro-1H-imidazol-2-yl)benzene-terephthalic acid-water (1/1/4)  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.