4-Acetylpyridine–fumaric acid (2/1)

In the crystal structure of the title cocrystal, 2C7H7NO·C4H4O4, the complete fumaric acid molecule is generated by a crystallographic inversion centre. The two components of the cocrystal are linked by an O—H⋯N hydrogen bond.

In the crystal structure of the title cocrystal, 2C 7 H 7 NOÁ-C 4 H 4 O 4 , the complete fumaric acid molecule is generated by a crystallographic inversion centre. The two components of the cocrystal are linked by an O-HÁ Á ÁN hydrogen bond.

Comment
The fumaric acid and acetylpyridine have been widely used in the biological and medicine fileds (Thomas et al. 2007;Fidler et al. 2003). In the medicine composition the carboxyl group of the fumaric acid is usually deprotonated while the pyridine derivatives are protonated. But some crystal structure determinations showed the neutral pyridine derivatives and fumaric acid in the crystal structures, i.e. the pyridine derivatives are not protonated while the fumaric acid is also not deprotonated in these crystal structures (Bowes et al. 2003;Aakeroy et al., 2002Aakeroy et al., , 2006Aakeroy et al., , 2007Haynes et al. 2006;Bu et al. 2007). Herein we report the crystal structure of the new compound containing pyridine derivative and fumaric acid components.
The crystal structure of the title compond consists of fumaric acid and 4-acetylpyridine molecules (Fig. 1). The planar fumaric acid molecule is centrosymmetric with the mid-point of the C═C double bond located at an inversion center. The C8-O2 bond distance of 1.204 (3) Å is much shorter than the C8-O3 bond distance of 1.297 (3) Å, it suggests that the carboxyl group is not deprotonated in the crystal structure (Liu et al. 2003).
The acetylpyridine molecule is not protonated in the crystal structure, which contrasts with that found in the crystal structure of the 4-acetylpyridinium chloride (Kochel, 2005). The geometry data of the acetylpyridine is consistent with those found in metal complexes of acetylpyridine (Steffen & Palenik, 1977;Pang et al., 1994). The planar acetylpyridine molecule is twisted to the fumaric acid with a dihedral angle of 25.97 (11)° in the crystal structure.
The intermolecular classic O-H···N hydrogen bonding and weak C-H···O hydrogen bonding help to stabilize the crystal structure (Table 1).

Experimental
Reagents and solvent were used as purchased without further purification. 4-Acetylpyridine (2 mmol) and fumaric acid (1 mmol) were dissolved in water-ethanol (6 ml, 1:5) at room temperature. The single crystals were obtained from the solution after 3 d.

Refinement
The carboxyl H atom was located in a difference Fourier map and refined isotropically. Methyl H atoms were placed in calculated positions with C-H = 0.96 Å and the torsion angle was refined to fit the electron density, U iso (H) = 1.5U eq (C).
Other H atoms were placed in calculated positions with C-H = 0.93 Å and refined in riding mode with U iso (H) = 1.2U eq (C). Geometric parameters (Å, °)