Poly[bis(ethanol)(μ4-2,3,5,6-tetrafluorobenzene-1,4-dicarboxylato)cadmium]

In the title compound, [Cd(C8F4O4)(C2H5OH)2]n, the CdII cation sits on an inversion centre and is coordinated by six O atoms from four tetrafluorobenzene-1,4-dicarboxylate anions and two ethanol molecules in a distorted octahedral geometry. The anionic ligand is also located on an inversion centre, and connects four CdII cations, generating a two-dimensional polymeric layer parallel to the ab plane. Within the layer, the ethanol molecule links F and O atoms of the nearest anionic ligands via O—H⋯O and O—H⋯F hydrogen bonds. The ethyl group of the ethanol molecule is disordered over two positions with an occupancy ratio of 0.567 (10):0.433 (10).

In the title compound, [Cd(C 8 F 4 O 4 )(C 2 H 5 OH) 2 ] n , the Cd II cation sits on an inversion centre and is coordinated by six O atoms from four tetrafluorobenzene-1,4-dicarboxylate anions and two ethanol molecules in a distorted octahedral geometry. The anionic ligand is also located on an inversion centre, and connects four Cd II cations, generating a two-dimensional polymeric layer parallel to the ab plane. Within the layer, the ethanol molecule links F and O atoms of the nearest anionic ligands via O-HÁ Á ÁO and O-HÁ Á ÁF hydrogen bonds. The ethyl group of the ethanol molecule is disordered over two positions with an occupancy ratio of 0.567 (10):0.433 (10).

Comment
We reported previously a metal-organic framework (MOF) composed of iron ions and 2,3,5,6-tetrafluorobenzene-1,4-dicarboxylate (or tetrafluoroterephthalate) linkers (Yoon et al., 2007). The title compound in this work was obtained in the course of making a new MOF using cadmium ion with the same organic linker. However, unlike other MOFs prepared through solvothermal reactions in common amine solvent such as N,N-dimethylformamide, the title compound could be obtained as single crystals in hot ethanol.

Experimental
The title compound was obtained as colorless plate crystals by a solvothermal reaction between cadmium(II) nitrate tetrahydrate (25 mg) and tetrafluorobenzene-1,4-dicarboxylic acid (12 mg) in ethanol (8 ml)in a Teflon-lined vessel (23 ml) at 353 K and for 2 days.

Refinement
The ethyl group in ethanol is disordered over two sites with site occupancy factors, 0.56709 (C5 and C6) and 0.43291 (C5A and C6A), respectively. Hydrogen atoms of the ethanol molecule were placed at calculated positions with C-H = 0.99 Å (methylene), C-H = 0.98 Å (methyl) or O-H = 0.85 Å (alcohol) and allowed to ride, with U iso (H) = 1.5 U eq (C) for methyl H atoms and 1.2U eq (C,O) for the others.

Computing details
Data collection: SMART (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: publCIF (Westrip, 2010   The coordination environment of the title compound is shown with H-bonds (dotted lines).  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 > 2sigma(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.