4-[(E)-2-(Pyridin-2-yl)ethenyl]pyridine–terephthalic acid (2/1)

The title 2:1 co-crystal, 2C12H10N2·C8H6O4, crystallizes with one molecule of 4-[(E)-2-(pyridin-2-yl)ethenyl]pyridine (A) and one half-molecule of terephthalic acid (B) in the asymmetric unit. In the crystal, the components are linked through heterodimeric COOH⋯Npyridine synthons, forming linear aggregates of composition –A–B–A–B–. Further linkage through weak C—H⋯O and C—H⋯π interactions gives two-dimensional hydrogen-bonded undulating sheets propagating in the [100] and [010] directions. These layers are connected through additional weak C—H⋯O contacts, forming a three-dimensional structure.

In the crystal lattice, each terephthalic acid is linked to two bipyridine molecules through intermolecular O-H···N and C-H···O interactions giving the well known heterodimeric COOH···N pyridine synthon. The so formed linear aggregates are connected through additional weak C-H···O contacts to generate tapes parallel to the (1-41) series of planes, which through C-H···π contacts generate undulating two-dimensional supramolecular layers ( Fig. 2 and Table 1). In the third dimension, these layers are interconnected through additional weak C-H···O contacts. Interestingly, the 2-pyridine nitrogen atom is not involved in short intermolecular hydrogen bonding interactions.
Experimental 0.200 g (1.10 mmol) of 4-((E)-2-(pyridin-2-yl)ethenyl)pyridine and 0.180 g (1.10 mmol) of terephthalic acid were ground in a mortar for 20 min after adding 3 drops of CH 3 OH. The resulting powder was then dissolved in 10 ml of CH 3 OH and kept for crystallization by slow evaporation of the solvent at ambient conditions to give colourless block-like crystals, suitable for single-crystal X-ray diffraction analysis, after one week. Spectroscopic and TGA data for the title compound are available in the archived CIF.

Refinement
H atoms bonded to C atoms were positioned geometrically and constrained using the riding-model approximation [aryl C -H = 0.93 A and U iso (H) = 1.2U eq (C)]. The H atom bonded to O was initially located in a difference Fourier map, then the position was refined with the O-H distance restraint of 0.84 (1) Å with U iso (H) = 1.5U eq (O). One reflection that was located behind the beam stop has been omitted during the refinement (020).

Figure 1
The molecular structures of the components in the title compound, showing the atom numbering. Displacement ellipsoids are drawn at the 50% probability level. [symmetry code: (i) -x + 2, -y, -z + 1].

Figure 2
View of the two-dimensional supramolecular layer formed through O-H···N, C-H···O and C-H···π interactions (dashed lines; see Table 1 for details), in the crystal structure of the title compound. 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.