2-Amino-5-methylpyridinium 6-oxo-1,6-dihydropyridine-2-carboxylate

The anion of the title salt, C6H9N2 +·C6H4NO3 −, undergoes an enol-to-keto tautomerism during the crystallization. In the crystal structure, the cation and anion are held together by a relatively short N—H⋯O hydrogen bond, and the two anions are further connected to each other by a pair of N—H⋯O hydrogen bonds with an R 2 2(8) ring motif, thus forming a centrosymmetric 2 + 2 aggregate. The aggregates are further linked through weak N—H⋯O and C—H⋯O hydrogen bonds, resulting a three-dimensional network.

The anion of the title salt, C 6 H 9 N 2 + ÁC 6 H 4 NO 3 À , undergoes an enol-to-keto tautomerism during the crystallization. In the crystal structure, the cation and anion are held together by a relatively short N-HÁ Á ÁO hydrogen bond, and the two anions are further connected to each other by a pair of N-HÁ Á ÁO hydrogen bonds with an R 2 2 (8) ring motif, thus forming a centrosymmetric 2 + 2 aggregate. The aggregates are further linked through weak N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds, resulting a three-dimensional network.
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). interesting characteristics: firstly, it was characterized by a similar enol-keto tautomerism due to the labile hydrogen atom of -OH group in α-position migrating easily to the basic pyridine N atom; secondly, the multiple coordination sites such as the carbonyl oxygen, the amide nitrogen and carboxylate oxygen atoms are able to coordinate with various metal ions (Sun et al., 2004;Soares-Santos et al., 2003). In order to study some interesting hydrogen bonding interactions of this compound, the synthesis and structure of the title salt is presented here.
These motifs are further self-organized through N-H···O hydrogen bonds to generate an array of four hydrogen bonds, resulting in the rings with R 2 2 (8), sandwiched by two R 2 2 (7). One of the O atoms of the carboxylate group acts as an acceptors of bifurcated N2-H1N2···O3 i and N3-H2N3···O3 i hydrogen bonds (symmetry code in Table 1) with the protonated pyridine and amine N atoms of the cation, forming an R 2 1 (6) ring motif. The crystal structure are further stabilized by strong N3-H1N3···O2 ii and weak C3-H3A···O1 iii and C9-H9A···O1 iv hydrogen bonds (symmetry codes in Table 1), resulting a three-dimensional network.

Experimental
Hot methanol solutions (20 ml) of 2-amino5-methylpyridine (54 mg, Aldrich) and 6-Hydroxypicolinic acid (69 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 the methyl group. In the final refinement, four outliers were omitted (-1 3 2, -4 6 5,-1 1 1 and -4 6 4).

Figure 1
The molecular structure of the title compound with atom labels with 50% probability displacement ellipsoids.

Figure 2
The crystal packing of the title compound, viewed down the c axis. 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.