2-Amino-4-methylpyridinium 3-hydroxybenzoate

In the title salt, C6H9N2 +·C7H5O3 −, the anion is essentially planar, with a dihedral angle of 2.72 (17)° between the benzene ring and the carboxylate group. In the crystal, the anions are connected by O—H⋯O hydrogen bonds, forming a 41 helical chain along the c axis. The protonated 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 with an R 2 2(8) ring motif. The ion pairs are further connected via another N—H⋯O hydrogen bond, resulting in a three-dimensional network.

In the title salt, C 6 H 9 N 2 + ÁC 7 H 5 O 3 À , the anion is essentially planar, with a dihedral angle of 2.72 (17) between the benzene ring and the carboxylate group. In the crystal, the anions are connected by O-HÁ Á ÁO hydrogen bonds, forming a 4 1 helical chain along the c axis. The protonated 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 with an R 2 2 (8) ring motif. The ion pairs are further connected via another N-HÁ Á ÁO hydrogen bond, resulting in a three-dimensional network.

Related literature
For the role of hydrogen bonding in crystal engineering, see: Goswami & Ghosh (1997); Goswami et al. (1998); Lehn (1992). For related structures, see: Kvick & Noordik (1977). For hydrogen-bond motifs, see: Bernstein et al. (1995). For bond-length data, see: Allen et al. (1987). For the stability of the temperature controller used in the data collection, see: Cosier & Glazer (1986 Table 1 Hydrogen-bond geometry (Å , ). Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009 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). In order to study some hydrogen bonding interactions, the synthesis and structure of the title salt, (I), is presented here.
The bond lengths and angles are normal (Allen et al., 1987).

Experimental
Hot methanol solution (20 ml) of 2-amino-4-methylpyridine (54 mg, Aldrich) and 3-hydroxybenzoic acid (35 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 (I) appeared after a few days. and were refined using a riding model, with U iso (H) = 1.2U eq (C) or 1.5U eq (methyl C). A rotating-group model was used for the methyl group. One outlier (0 2 0) was omitted in the final refinement.

Figure 1
The molecular structure of the title compound with atom labels with 50% probability displacement ellipsoids.  (Cosier & Glazer, 1986) operating at 100.0 (1) K. 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.