4,4′-Bipyridine–2-methoxybenzoic acid (1/2)

The asymmetric unit of the title compound, C10H8N2·2C8H8O3, contains two 2-methoxybenzoic acid molecules and one 4,4′-bipyridine molecule. The 4,4′-bipyridine molecule is disordered over two positions in a 1:1 ratio. In the crystal, the 2-methoxybenzoic acid and 4,4′-bipyridine molecules are connected by intermolecular O—H⋯N hydrogen bonds. The dihedral angle between the carboxy group and its attached ring is 26.823 (2)°.

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: DS2171).

Xiao-Yan Qian and Feng-Zhi Liu Comment
Bipyridine is a well known molecule often used as a linker in polymeric coordination complexes. 2-Methoxybenzoic acid is also sometimes used as a common ligand in coordination polymers (Vollano et al., 1984;Smith et al., 1986;Li, 2005;Andrews et al., 2006;Ren et al., 2006;Zhao et al., 2008;Sharma et al., 2009.). The title compound, (I), is a 1:2 cocrystal of the aforementioned linkers. Herewith we present its crystal structure. The asymmetric unit of the title compound ( Fig.   1) contains two 2-methoxybenzoic acid molecules and one 4,4′-bipyridine molecule. The dihedral angle of carboxy group to its ring is 26.823 (2)°. The 4,4′-bipyridine molecule is disordered over two positions in a 1:1 ratio. In the crystal structure, the 2-methoxybenzoic acid and 4,4′-bipyridine are held together by intermolecular O-H···N hydrogen bonds.

Experimental
An ethanol solution (20 ml) of 2-methoxybenzoic acid (0.1 mmol) and 4,4′-bipyridine (0.1 mmol) was heated at 333 K for 2 h. Then the mixture was cooled to room temperature. After two weeks colorless crystals were obtained that were suitable for X-ray diffraction study.

Refinement
Four C atoms of bipyridyl group are disordered over two sites. The occupancy factors refined to 0.761 (2) and 0.239 (2).

Figure 2
The O-H···N hydrogen bonds of (I

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 Occ. (