Diaquabis(2,2′-bi-1H-imidazole)manganese(II) benzene-1,4-dicarboxylate

The asymmetric unit of the title compound, [Mn(C6H6N4)2(H2O)2](C8H4O4), contains one-half each of the centrosymmetric cation and anion. The MnII atom is coordinated by four N atoms [Mn—N = 2.2168 (14) and 2.2407 (14) Å] from two 2,2′-biimidazole ligands and two water molecules [Mn—O = 2.2521 (14) Å] in a distorted octahedral geometry. Intermolecular N—H⋯O and O—H⋯O hydrogen bonds consolidate the crystal packing, which also exhibits π–π interactions between five-membered rings, with a centroid–centroid distance of 3.409 (2) Å.

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: CV5293).  (Ramirez et al., 2002). One of the best strategies to construct such materials relies on the use of both the building block approach and the additional hydrogen bonding of the coordinated ligands to their linking capability (Baca et al., 2003). The 2,2′-biimidazole (H 2 biim) possesses these properties -coordination to metal centre and acting as a donor in hydrogen bonding interaction (Fortin & Beauchamp, 2001;Sang et al., 2002;Atencio et al., 2004;Wang et al., 2007).
The structure of the title complex consists of [Mn(H 2 biim) 2 (H 2 O) 2 ] 2+ cations and terephthalate dianions (Fig. 1). The coordination geometry of the manganese(II) centre can be described as a distorted octahedron including four nitrogen atoms from two chelating H 2 biim ligands and two oxygen atoms from aqua ligands. The crystal packing is stabilized by the hydrogen bonds N-H···O and O-H···O (Table 1).

Experimental
All reagents were of AR grade from commercial sources and used without further purification. Biimidazole was prepared following the known procedure (Ramirez et al., 2002). Mn(CH 3 COO) 2 (0.3 mmol), H 2 biim (0.3 mmol) and terephthalic acid (0.3 mmol) in the molar ratio of 1:1:1 were added directly as a solid in 10 ml deionized water respectively, after the mixture was stirred at room temperature for 30 min, the pH value was adjusted to 7.0 by aqueous KOH solution. Then the mixture was placed in a 25 ml Teflon-lined stainless steel vessel and heated at 160°C for 6 days under autogenous pressure. Afterwards, the vessel was cooled to room temperature at a rate of 10°C per hour. Light yellow sheet-like crystals of title complex were obtained and collected by filtration and washed with water (yield 40%).

Refinement
The O-bound H atoms were located in difference Fourier maps and were refined with restraints O-H=0.84 (3) Å and U iso (H) fixed to 0.08 Å 2 . The rest H atoms were geometrically positioned [C-H = 0.93 Å; N-H = 0.86 Å], and treated as riding, with U iso (H) = 1.2U eq of the parent atom.

Computing details
Data collection: SMART (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008  Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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 R-factors(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.