4,4′-{[1,2-Phenylenebis(methylene)]bis(oxy)}dibenzoic acid dimethylformamide disolvate

In the title solvate, C22H18O6·2C3H7NO, the complete dicarboxylic acid molecule is generated by a crystallographic twofold axis, which bisects the central benzene ring and one N,N-dimethylformamide solvent molecule. The dihedral angle between the central and pendant benzene rings is 54.53 (5)° while that between the pendant rings is 45.44 (5)°. In the crystal, the acid molecules are linked to the solvent molecules via O—H⋯O and weak C—H⋯O hydrogen bonds. Further weak C—H⋯O interactions link adjacent acid molecules into a three-dimensional network.

In the title solvate, C 22 H 18 O 6 Á2C 3 H 7 NO, the complete dicarboxylic acid molecule is generated by a crystallographic twofold axis, which bisects the central benzene ring and one N,N-dimethylformamide solvent molecule. The dihedral angle between the central and pendant benzene rings is 54. 53 (5) while that between the pendant rings is 45.44 (5) . In the crystal, the acid molecules are linked to the solvent molecules via O-HÁ Á ÁO and weak C-HÁ Á ÁO hydrogen bonds. Further weak C-HÁ Á ÁO interactions link adjacent acid molecules into a three-dimensional network.
Data collection: RAPID-AUTO (Rigaku, 1998); cell refinement: RAPID-AUTO; data reduction: CrystalClear (Rigaku/MSC, 2002); program(s) used to solve structure: SHELXS97 (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). In the past few years, multicarboxylic acids and their derivatives have attracted increasing attention as an important class of ligands used for the synthesis of porous metal organic framework compounds (Eddaoudi et al. 2002;Eubank et al. 2011;Zhang et al. 2012). The acid molecule in the title compound, as a conformationally flexible V-shaped long bicarboxylate ligand, has been already used to synthesize entangled frameworks having both polyrotaxane and polycatenane characteristics that also achieve different topological structures in the entangled system (Cao et al. 2009a;Hu et al. 2013). Although there are crystal structure reports in the literature regarding the title multicarboxylic acid, no crystallographic study has been already performed on the ligand itself.
In the crystal, the acid molecule are linked to the solvent molecules by a strong O-HO and a weak C-HO hydrogen bond [ Table 1 (entries 1 and 4) and Fig. 1]. Besides, weak intermolecular C-H···O interactions link the adjacent acid molecules into a three-dimensional network [Table 1 (entries 2 and 3) and Fig 2].

Experimental
The ligand 4,4′-(1,2-phenylenebis(methylene))bis(oxy)dibenzoic acid was synthesized according to the literature method (Cao et al. 2009a;Rajakumar et al. 2009). A mixture of 4,4′-(1,2-phenylenebis(methylene))bis(oxy)dibenzoic acid (37.8 mg, 0.1 mmol) and DMF (4 ml) was placed in a Teflon-lined stainless steel vessel (15 ml) and heated at 368 k for 48 h and then cooled to room temperature at a rate of 5 K h-1. The resulting colorless solution slowly evaporated in air for over two weeks and colorless block crystals of the title compound suitable for X-ray diffraction were obtained.

Refinement
The positions of the hydroxyl hydrogen H1A could be obtained from the difference electron-density map, and the other H   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 O1 0.40156 (