Poly[chlorido[μ4-2,2′-(2-methyl-1H-benzimidazol-3-ium-1,3-diyl)diacetato]zinc]

The title compound, [Zn(C12H11N2O4)Cl]n, contains a centrosymmetric dimetal tetracarboxylate paddle-wheel moiety in which the ZnII atom is square-pyramidally coordinated by four carboxylate O atoms at the basal positions and one Cl− anion at the apical position. Each paddle-wheel unit is joined to four such neighbours through bridging dicarboxylate ligands, producing a two-dimensional undulating layer parallel to (-101). Adjacent sheets are stacked in a parallel fashion to form a three-dimensional supramolecular structure which is stabilized by interlayer π–π interactions between benzene rings, with a centroid–centroid distance of 3.722 Å. The range of Zn—O bond lengths is 2.0440 (17)–2.1256 (15) Å and the Zn—Cl bond length is 2.2622 (6) Å.


Experimental
Crystal data [Zn(C 12  Carboxylate-containing ligands have been intensively investigated to construct metal-organic frameworks with an intriguing variety of topologies and potential applications in gas sorption, separation and/or catalysis (Bourne et al., 2001;Chen et al., 2005;Kitagawa et al., 2004;Li et al., 2012;Xuan et al., 2012). Polycarboxylate ligands with suitable spacers are good choices for such architectures because the topological structures can be adjusted not only by carboxylate groups but also by the organic spacers. Here we use a flexible zwitterionic ligand, 1-acetoxy-2-methylbenzimidazole-3-acetate acid [HL], to prepare the title compound [Zn(L)Cl] n (I).
The motive consists of a centrosymmetric paddle-wheel dimetal tetracarboxylate moiety [Zn 2 (CO 2 ) 4 ] ( Fig. 1) in which each Zn II is square-pyramidally coordinated by four carboxylate oxygen atoms at the basal position and one Clanion at the apical position. Each paddle-wheel unit is bridged by four such neighbors through bridging dicarboxylate ligands, producing a two-dimensional undulate layer in which π-π interactions between phenyl rings of benzimidazole moieties (ring-centroid distance: 3.579 (2) Å) cooperate in the 2-D sheet formation (Fig. 2). Adjacent sheets are stacked in a parallel fashion to form a 3-D supramolecular structure stabilized by interlayer π-π interactions between phenyl rings with a ring-centroid distance of 3.722 (2) Å. The Zn-O span is 2.0440 (17)-2.1256 (15) Å and the Zn-Cl distance is 2.2622 (6) Å.

Experimental
After the pH of an ethanol/water mixture solution (10 ml with ratio of 4:1) containing ZnCl 2 .2H 2 O (0.0408 g, 0.3 mmol) and the HL ligand (0.0498 g,0.2 mmol) was adjusted to 7 by addition of triethylamine, the resulting solution was sealed in a Teflon-lined steel bomb (25 ml) and then heated at 140°C for 2 days. Colorless block crystals were collected. Yield:  ORTEP drawing (at 30% probability) of a paddle-wheel unit in the title compound (symmetry codes: A, -x, -y, -z; B, -0.5 + x, 1.5 -y, -0.5 + z; C, 0.5 -x, -0.5 + y, 1.5 -z). Hydrogen atoms are omitted for clarity.  The 2-D sheet structure parallel to the (-101) plane, hydrogen atoms are omitted for clarity.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq