μ-2,5-Dihydroxyterephthalato-bis[triaqua(1,10-phenanthroline)zinc] dihydroxyterephthalate

In the title compound, [Zn2(C8H4O6)(C12H8N2)2(H2O)6](C8H4O6), the complete ions of both the binuclear dication and the dianion are generated by crystallographic inversion symmetry. The Zn atom is bonded to an N,N′-bidentate phenanthroline ligand, three water moleules and an O-monodenate 2,5-dihydroxyterephthalate dianion. In the resulting distorted octahedral ZnN2O4 coordination polyhedron, the water O atoms are in a mer orientation. Two intramolecular O—H⋯O hydrogen bonds occur in the bridging 2,5-dihydroxyterephthalate dianion within the complex cation and also in the free dianion. An intramolecular Ow—H⋯O (w = water) hydrogen bond also occurs within the dication. In the crystal, O—H⋯O hydrogen bonds link the component ions into a three-dimensional network.


Related literature
For a related structure, see: Sun et al. (2007). For background to the applications of coordination polymers, see: Perry et al. (2009).
Data collection: APEX2 (Bruker, 2002); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: SHELXTL. The design and synthesis of coordination compounds have attracted much interest in the fields of supramolecular chemistry and crystal engineering because of their intriguing structural diversities and potential applications (Sun et al., 2007;Perry IV, et al., 2009). To extend the previous work, we obtained the title compound, (I), by using Zn II , phenanthroline (phen) and 2,5-dihydroxyterephthalic acid (dhtp) as the starting materials.
The title compound, (I), is composed of a Zn II canion, a phen molecule, half a coordinated dhtp anion, half a free dhtp anion and three coordinated water molecules in the asymmetric unit as shown in Fig. 1. Zn II canion exhibits a distorted octahedral geometry, being coordinated by two N atoms of a phen molecule, one O atom from dhtp anion and three water O atoms. The Zn-O and Zn-N distances are normal. Zn II canions are connected by dhtp anion to form a [Zn 2 (phen) 2 (dhtp) (H 2 O) 6 ] II cation unit. In additon, the free dhtp anion as the counter-ion presents in the sturcture. By way of O-H···O hydrogen bonding between the cation units and counter-anions, a three-dimensional network is formed (Fig. 2). The detailed hydrogen-bonding parameters are summarized in Table 1.

Experimental
A mixture of Zn(CH 3 COO) 2 . 2H 2 O (0.2 mmol), phen (0.3 mmol) and dhtp (0.2 mmol) were dissolved in 15 ml water. The resulting solution was stirred for about 0.5 h at room temperature, sealed in a 25-ml Teflon-lined stainless steel autoclave and heated at 443 K for three days under autogenous pressure. Afterward, the reaction system was slowly cooled to room temperature and colourless blocks of the title compound were recovered.

Refinement
Carbon-bound H-atoms were positioned geometrically (C-H = 0.93 Å) and refined as riding, with U iso (H) fixed at 1.2U eq (C). Oxygen-bound for H3A and H6A atoms were positioned geometrically (O-H = 0.82 Å) and refined as riding, with U iso (H) fixed at 1.5U eq (O). In the case of coordinated water molecules, H atoms were clearly detected in a difference Fourier map, and refined freely. Final O-H bond length span the range 0.83-0.97 Å. Isotropic displacement parameters for H atoms were calculated as U iso (H) = 1.2U eq (C). program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figure 2
The packing diagram of the title compound. All H-atoms except for those involved in hydrogen bonds are omitted for clarity. (hydrogen bonds indicated by dashed lines).

µ-2,5-Dihydroxyterephthalato-bis[triaqua(1,10-phenanthroline)zinc] dihydroxyterephthalate
Crystal data  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.33 e Å −3 Δρ min = −0.29 e Å −3 Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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.