4,4′-(Anthracene-9,10-diyl)dibenzoic acid dimethylformamide disolvate

In the title compound, C28H18O4·2C3H7NO, the dihedral angle between the benzene rings and the anthracene system is 74.05 (12)°. A crystallographic inversion centre is located in the middle of the anthracene unit. The dimethylformamide solvent molecules are partially disordered over two positions of approximately equal occupancy [0.529 (6):0.471 (6)]. Intermolecular O—H⋯O hydrogen bonds with the major occupancy formamide O atom as acceptor result in the formation of 2:1 solvate–complex aggregates, which are alternately linked to shorter solvate units via weak intermolecular C—H⋯O contacts generated from the rotational disorder of the formamide O atom (minor occupancy component). Weak C—H⋯π interactions between the solvent molecules as the donor and the outer anthracene rings support these contacts in the crystal structure for both disorder components.

In the title compound, C 28 H 18 O 4 Á2C 3 H 7 NO, the dihedral angle between the benzene rings and the anthracene system is 74.05 (12) . A crystallographic inversion centre is located in the middle of the anthracene unit. The dimethylformamide solvent molecules are partially disordered over two positions of approximately equal occupancy [0.529 (6):0.471 (6)]. Intermolecular O-HÁ Á ÁO hydrogen bonds with the major occupancy formamide O atom as acceptor result in the formation of 2:1 solvate-complex aggregates, which are alternately linked to shorter solvate units via weak intermolecular C-HÁ Á ÁO contacts generated from the rotational disorder of the formamide O atom (minor occupancy component). Weak C-HÁ Á Á interactions between the solvent molecules as the donor and the outer anthracene rings support these contacts in the crystal structure for both disorder components.

Related literature
For the structure of 4-(2,5-dihexyloxyphenyl)benzoic acid and the syntheses of related compounds, see: Li et al. (2008). For palladium-catalysed Suzuki coupling reactions, see: Xu et al. (2006Xu et al. ( , 2008Li et al. (2006) Table 1 Hydrogen-bond geometry (Å , ).  In the title compound ( Fig.1), the dihedral angle between benzene rings and anthracene rings is 74.05 (12)°. A crystallographic inversion centre is in the middle of the anthracene unit, and an approximate two-fold pseudo rotation axis is running along the plane of the anthracene unit. The dimethylformamide solvent molecules are partially disordered over two positions, O3 and O3', of approximately equal occupancy, (0.529 (6) (Table 1) which are alternately linked via weak intermolecular C-H···O contacts generated from the rotational disorder of the formamide oxygen atom (0.471 (6) site occupancy). C-H···π interactions support these contacts in the crystal structure foming a one-dimensional supramolecular architecture ( Fig. 1 and Fig. 2).

Experimental
The title compound was obtained from the Suzuki coupling reaction of 9,10-dibromoanthracene and 4-carboxyphenylboronic acid as described in the literature (Li et al., 2008) and recrystallized from dimethylformamide at room temperature to give the desired crystals suitable for single-crystal X-ray diffraction.

Refinement
H atoms attached to C atoms of the title compound were placed in geometrically idealized positions and treated as riding with C-H distances constrained to 0.93 (aromatic CH), or 0.96 Å (methyl CH 3 ), and constrained to ride on their parent atoms, with U iso (H) = 1.2U eq (C) (1.5U eq for methyl H). The atom-site occupancies for the rotational disordered formamide oxygen atoms O3 and O3' refined to a ratio of 0.53/0.47.
Alert levels A and B for short intermolecular O1···O3' and H2D···H15' contacts with distances of2.50 Å and 2.01 Å may be explained by the difficulties to split the whole solvent molecule due to the pseudo two-fold rotation of the methyl groups around the N1-C15 axis. BUMP instruction or splitting of the whole solvent molecule resulted in unstable refinements.
Introduction of shift-limiting restraints (DAMP instruction) resulted in larger R-values without improving the geometries.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 Rfactors(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.