2-Aminoterephthalic acid–4,4′-bipyridine (1/1)

The asymmetric unit of the title compound, C10H8N2·C8H7NO4, contains two half-molecules, which constitute a 1:1 co-crystal. The 2-aminoterephthalic acid molecule is situated on an inversion center being disordered between two orientations in a 1:1 ratio. In the 4,4′-bipyridine molecule, which is situated on a twofold rotational axis, the two pyridine rings form a dihedral angle of 37.5 (1)°. In the crystal, molecules are held together via intermolecular N—H⋯O and O—H⋯N hydrogen bonds. The crystal packing exhibits π–π interactions between the aromatic rings with a centroid–centroid distance of 3.722 (3) Å.

The asymmetric unit of the title compound, C 10 H 8 N 2 Á-C 8 H 7 NO 4 , contains two half-molecules, which constitute a 1:1 co-crystal. The 2-aminoterephthalic acid molecule is situated on an inversion center being disordered between two orientations in a 1:1 ratio. In the 4,4 0 -bipyridine molecule, which is situated on a twofold rotational axis, the two pyridine rings form a dihedral angle of 37.5 (1) . In the crystal, molecules are held together via intermolecular N-HÁ Á ÁO and O-HÁ Á ÁN hydrogen bonds. The crystal packing exhibitsinteractions between the aromatic rings with a centroidcentroid distance of 3.722 (3) Å .

Comment
Bipyridine is a well known molecule often used as a linker in polymeric coordination compounds. 2-Aminoterephthalic acid is also sometimes used as a linker in polymeric compounds (Ma et al., 2005;Bauer et al., 2008). The title compound (I) is a 1:1 cocrystal of the aforementioned linkers. Herewith we present its crystal structure.
In (I) (Fig. 1), the 2-aminoterephthalic acid molecule is situated on an inversion center, therefore, it is disordered (namely, the amino group is disordered between two positions). The carboxyl groups are twisted from the benzene ring plane at 11.4 (1)°. The 4,4'-bipyridine molecule is situated on a twofold rotational axis, and two pyridine rings form a dihedral angle of 37.5 (1)°.
In the crystal structure, the molecules are held together via intermolecular N-H···O and O-H···N hydrogen bonds. The crystal packing exhibits π-π interactions between the aromatic rings with the centroid-to-centroid distance of 3.722 (3) Å.
Experimental 2-Diaminoterephthalic acid(10 mmol) and 4,4'-bipyridine(10 mmol) were dissolved to methanol (10 ml) and then hydrochloric acid(5 ml) was added. A few minutes later, an methanol solution (10 ml) of tin tetrachloride (5 mmol) was added with stirring. The reaction mixture was stirred for 4 h. The solution was held at room temperature for about two weeks, whereupon yellow crystals of the title compound, which were beyond expectations, were obtained.

Figures
Fig . 1. The structure of the title compound, showing 30% probability displacement ellipsoids and the atom-numbering scheme. (symmetry code A: x + 3/2, -y + 3/2, -z and B: -x + 1, y, -z + 3/2). For the disordered molecule of 2-aminoterephthalic acid, only one orientation is shown. 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ.