Bis(3-hydroxypyridinium) fumarate

The crystal structure of the title compound, 2C5H6NO2 +·C4H2O4 2−, consists of 3-hydroxypyridinium cations and fumarate dianions. The dianion is located on an inversion center and the cation is linked to it by O—H⋯O and N—H⋯O hydrogen bonds. The cation is twisted with respect to the anion by 24.83 (5)°.

The crystal structure of the title compound, 2C 5 H 6 NO 2 + Á-C 4 H 2 O 4 2À , consists of 3-hydroxypyridinium cations and fumarate dianions. The dianion is located on an inversion center and the cation is linked to it by O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds. The cation is twisted with respect to the anion by 24.83 (5) .
The work was supported by the ZIJIN Project of Zhejiang University, China.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: NG2594).

S1. Comment
The hydropyridine derivatives and the fumaric acid have been extensively applied in biological and medicine fields (Zhang et al., 2004;Thomas et al., 2007;Fidler et al., 2003). Although the carboxyl group of the fumaric acid is usually deprotonated while the pyridine derivatives are protonated in the solution (Lezina et al., 1981), some crystal structures showed that they also exist as co-crystal of neutral molecules (Bowes et al. 2003;Aakeroy et al., 2002;Haynes et al. 2006;Xu et al. 2009). Herein we report the crystal structure of the title compound containing pyridine derivative and fumaric acid components.
The crystal structure of the title compond consists of fumarate anions and 3-hydroxypyridinium cations (Fig. 1). The planar fumarate anion is located in an inversion center. The C1-O1 bond distance of 1.2603 (15) Å is similar to C1-O2 bond distance of 1.2452 (15) Å, it agrees with those found in metal complexes of fumarate (Liu et al. 2003;Liu & Xu, 2004).
In the crystal structure the planar hydroxypyridinium cation is twisted respect to the planar fumarate with a dihedral angle of 24.83 (5)°, and links with the fumarate anions via N-H···O and O-H···O hydrogen bonding (Table 1 and Fig. 2).

S2. Experimental
Reagents and solvent were used as purchased without further purification. 3-Hydroxypyridine (2 mmol) and fumaric acid (1 mmol) were dissolved in ethanol (5 ml) at room temperature. The single crystals were obtained from the solution after one week.  The molecular structure of the title compound with 40% probability displacement (arbitrary spheres for H atoms).

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.