Poly[[[tetraaquacobalt(II)]-μ-bipyridine] terephthalate]

The CoII atom in the title complex, {[Co(C10H8N2)(H2O)4](C8H4O4)}n, is coordinated by two N atoms of two bipyridine ligands and four O atoms of four water molecules in an octahedral geometry. The one-dimensional [Co(C10H8N2)(H2O)4]2+ cation chain is further extended into a supramolecular network via O–H⋯O hydrogen-bond interactions. The Co atom lies on a twofold rotation axis; another twofold rotation axis passes through the carboxylate carbon atoms and the attached ring C atoms.

The Co II atom in the title complex, {[Co(C 10 H 8 N 2 )(H 2 O) 4 ]-(C 8 H 4 O 4 )} n , is coordinated by two N atoms of two bipyridine ligands and four O atoms of four water molecules in an octahedral geometry. The one-dimensional [Co(C 10 H 8 N 2 )(H 2 O) 4 ] 2+ cation chain is further extended into a supramolecular network via O-HÁ Á ÁO hydrogen-bond interactions. The Co atom lies on a twofold rotation axis; another twofold rotation axis passes through the carboxylate carbon atoms and the attached ring C atoms.

S1. Comment
Recently, research on organic-inorganic hybrid materials has attracted much attention owing to the wideness of potential applications in catalysis, materials chemistry and biochemistry (Hill, 1998;Banglin et al., 2001;Ferey, 2001). These compounds and many frameworks may be obtained by the assembly of lower dimensional coordination polymers via noncovalent intermolecular forces such as hydrogen-bonding interactions. However in the formation of supramolecular assembly, an important target is to establish the possible connections between units. Here, we report the crystal structure  (Table 1), thus forming a fishing-net layer structure (Fig. 2). A three-dimensional supramolecular network is obtained through O-H···O hydrogen-bonding interactions of the layers.

S2. Experimental
The title compound was obtained by a diffusion method. In one arm of U-tube was placed Na2(BDC) (42 mg, 0.2 mmol) in water/methanol (1:1; 10 ml) and in the other H 12 Cl 2 O 14 Cu (74 mg, 0.2 mmol) and bipy (31 mg, 0.2 mmol) in water/methanol (1:1; 10 ml). The purple platelike crystals were collected by filtration, washed with distilled water followed by methanol and dried under reduced pressure for 2 h.

S3. Refinement
The H-atoms were included in the riding-model approximation with C-H = 0.93 Å and O-H = 0.82 Å, and with U iso (H) = 1.2U eq (C-aromatic).  The structure of (I) showing 30% probability displacement ellipsoids and the atom-numbering scheme. The H atoms are omitted for clarity.

Figure 2
three-dimensional superamolecular structure of (I). Hydrogen bond interactions was shown.

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