catena-Poly[[[diaqua(1,3-benzimidazole-κN 3)manganese(II)]-μ-benzene-1,3-dicarboxylato-κ3 O 1,O 1′:O 3] dihydrate]

In the polymeric title complex, {[Mn(C8H4O4)(C7H6N2)(H2O)2]·2H2O}n, the MnII cation is coordinated by two benzenedicarboxylate anions, one benzimidazole ligand and two water molecules in a distorted MnNO5 octahedral geometry. In the crystal, each benzenedicarboxylate anion bridges adjacent MnII cations through the terminal carboxylate groups, forming a polymeric complex chain along the a axis. One Mn—Ocarboxylate bond is much longer than the others. In the crystal, π–π stacking is observed between nearly parallel [dihedral angle = 4.32 (6)°] benzimidazole aromatic ring systems of adjacent molecules, the centroid–centroid distance between the imidazole and benzene rings being 3.5421 (11) Å. Extensive intermolecular O—H⋯O and N—H⋯O hydrogen bonding is present in the crystal structure. The two lattice water molecules are located on twofold rotation axes.

In the polymeric title complex, {[Mn(C 8 H 4 O 4 )(C 7 H 6 N 2 )-(H 2 O) 2 ]Á2H 2 O} n , the Mn II cation is coordinated by two benzenedicarboxylate anions, one benzimidazole ligand and two water molecules in a distorted MnNO 5 octahedral geometry. In the crystal, each benzenedicarboxylate anion bridges adjacent Mn II cations through the terminal carboxylate groups, forming a polymeric complex chain along the a axis. One Mn-O carboxylate bond is much longer than the others. In the crystal,stacking is observed between nearly parallel [dihedral angle = 4.32 (6) ] benzimidazole aromatic ring systems of adjacent molecules, the centroid-centroid distance between the imidazole and benzene rings being 3.5421 (11) Å . Extensive intermolecular O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonding is present in the crystal structure. The two lattice water molecules are located on twofold rotation axes.

Related literature
For background tostacking, see: Deisenhofer & Michel (1989). For a related structure, see: Hu et al. (2006). For a longer Mn-O bond length in complex with a seven-coordinate Mn II atom, see: Liu et al. (2005).
A fragment of the title polymeric Mn II complex, together with lattice water molecules, is shown in Fig. 1. The Mn II ion is surrounded by two bdc anions, one bzim and two coordination water molecules in a distorted octahedral geometry.
Each bdc anion bridges two Mn II ions to form the one dimensional polymeric chain running along the a axis. The Mn-O4 distance of 2.6075 (16) Å is much longer than the Mn-O3 bond distance (Table 1) but is comparable to 2.5356 (16) Å found in a seven-coordination Mn II complex (Liu et al. 2005).
In the asymmetric unit two lattice water molecules locate on twofold rotation axes and are hydrogen bonded to the carboxyl groups of the complex, while the other lattice water molecule locates on a general position and links with bzim ligand of the complex via N-H···O hydrogen bonding (Table 2). Lattice water molecules are linked together via O-H···O hydrogen bonding and filled in the cavity formed by the polymeric complex chains (Fig. 3).

Experimental
An ethanol solution (5 ml) of benzimidazole (0.236 g, 2 mmol) was mixed with an aqueous solution (5 ml) of manganese(II) acetate tetrahydrate (0.490 g, 2 mmol) at room temperature. The solution was refluxed for 30 min. Then an aqueous solution (8 ml) containing 1,3-benzenedicarboxylic acid (0.332 g, 2 mmol) and NaOH (0.160 g, 4 mmol) was added dropwise into the above solution. The mixture was refluxed for a further 2 h. After cooling to room temperature the solution was filtered.
Single crystals of the title compound were obtained from the filtrate after 2 week.

Refinement
Water H atoms were located in a difference Fourier map and refined as riding in their as-found relative positions, U iso (H) = 1.5U eq (O). Other H atoms were placed in calculated positions with N-H = 0.86 and C-H = 0.93 Å, and refined in riding mode with U iso (H) = 1.2U eq (N,C). Fig. 1. A fragment of the polymeric structure of (I) with 40% probability displacement ellipsoids (arbitrary spheres for H atoms) [symmetry code: