2-Amino-4-methylpyridinium hexa-2,4-dienoate dihydrate

In the title salt, C6H9N2 +·C6H7O2 −·2H2O, the non-H atoms of the 2-amino-4-methylpyridinium cation are coplanar, with a maximum deviation of 0.010 (1) Å. In the crystal structure, the pyridinium N atom and the 2-amino group of the cation are hydrogen bonded to the carboxylate O atoms of the anion via a pair of N—H⋯O hydrogen bonds, forming an R 2 2(8) ring motif. The sorbate anions and water molecules are linked through O—H⋯O hydrogen bonds, forming R 10 10(28) and R 6 4(12) ring motifs. The motifs form part of a three-dimensional framework.

In the title salt, C 6 H 9 N 2 + ÁC 6 H 7 O 2 À Á2H 2 O, the non-H atoms of the 2-amino-4-methylpyridinium cation are coplanar, with a maximum deviation of 0.010 (1) Å . In the crystal structure, the pyridinium N atom and the 2-amino group of the cation are hydrogen bonded to the carboxylate O atoms of the anion via a pair of N-HÁ Á ÁO hydrogen bonds, forming an R 2 2 (8) ring motif. The sorbate anions and water molecules are linked through O-HÁ Á ÁO hydrogen bonds, forming R 10 10 (28) and R 6 4 (12) ring motifs. The motifs form part of a threedimensional framework.

Comment
Hydrogen bonding plays a key role in molecular recognition (Goswami & Ghosh, 1997) and crystal engineering research (Goswami et al., 1998). The design of highly specific solid-state compounds is of considerable significance in organic chemistry due to important applications of these compounds in the development of new optical, magnetic and electronic systems (Lehn, 1992). Pyridinium derivatives often possess antibacterial and antifungal activities (Akkurt et al., 2005). They are often involved in hydrogen-bonding interactions (Jeffrey & Saenger, 1991;Jeffrey, 1997;Scheiner, 1997). In order to study some hydrogen bonding interactions, the synthesis and structure of the title salt, (I), is presented here.
The asymmetric unit of (I) contains one 2-amino-4-methylpyridinium cation, one sorbate anion and two water molecules ( Fig. 1). The non-H atoms of the 2-amino-4-methylpyridinium cation are coplanar, with a maximum deviation of 0.010 (1) Å for atom N1. The protonation of atom N1 has lead to a slight increase in the C1-N1-C5 angle to 121.96 (6)°. The bond lengths (Allen et al., 1987) and angles are within normal ranges.

Experimental
A hot methanol solution (20 ml) of 2-amino-4-methylpyridine (54 mg, Aldrich) and sorbic acid (56 mg, Merck) were mixed and warmed over a heating magnetic stirrer hotplate for a few minutes. The resulting solution was allowed to cool slowly at room temperature and crystals of the title compound appeared after a few days.

Refinement
Atoms H1N1, H1N2, H2N2, H1W2, H2W2, H1W1 and H2W1 were located in a difference Fourier map and were refined freely [N-H= 0.911 (18) Fig. 1. The asymmetric unit of the title compound. Displacement ellipsoids are drawn at the 50% probability level.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.