2-Amino-6-methylpyridinium 2,2,2-trichloroacetate

In the asymmetric unit of the title molecular salt, C6H9N2 +·C2Cl3O2 −, there are two independent 2-amino-6-methylpyridinium cations and two independent trichloroacetate anions. The pyridine N atom of the 2-amino-6-methylpyridine molecule is protonated and the geometries of these cations reveal amine–imine tautomerism. Both protonated 2-amino-6-methylpyridinium cations are essentially planar [maximum deviations = 0.026 (2) and 0.012 (2) Å]. In the crystal, 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, forming an R 2 2(8) ring motif. These motifs are connected via N—H⋯O and C—H⋯O hydrogen bonds to form slabs parallel to (101).

In the asymmetric unit of the title molecular salt, C 6 H 9 N 2 + Á-C 2 Cl 3 O 2 À , there are two independent 2-amino-6-methylpyridinium cations and two independent trichloroacetate anions. The pyridine N atom of the 2-amino-6-methylpyridine molecule is protonated and the geometries of these cations reveal amine-imine tautomerism. Both protonated 2-amino-6methylpyridinium cations are essentially planar [maximum deviations = 0.026 (2) and 0.012 (2) Å ]. In the crystal, 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, forming an R 2 2 (8) ring motif. These motifs are connected via N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds to form slabs parallel to (101).

Comment
2-Aminopyridine and its derivatives play an important role in heterocyclic chemistry (Katritzky et al., 1996). Pyridine heterocycles and their derivatives are present in many large molecules having photo-chemical, electro-chemical and catalytic applications. Some pyridine derivatives possess nonlinear optical (NLO) properties (Tomaru et al., 1991) and often possess antibacterial and antifungal activities (Akkurt et al., 2005). The use of pyridine derivatives as templating agents for the self-assembly of organic-inorganic supramolecular materials has been widely studied (Desiraju, 2001).
They are often involved in hydrogen bonding (Jeffrey, 1997). In order to further study the hydrogen bonding in these systems, the synthesis and structure of the title salt is presented herein.

Experimental
Crystals of the title compound were obtained by slow evaporation of a 1:1 mol. mixture of 2-Amino-6-methylpyridine and trichloroacetic acid in methanol at room temperature.

Refinement
N-bound H atoms were located in a difference Fourier map and refined with distance restraints: N-H = 0.89 (1) and 0.90 (1) Å for NH 2 and NH H atoms, respectively; N-H distances of the NH 2 groups were restrained to be equal. The Cbound H atoms were positioned geometrically and refined using a riding model: C-H = 0.93-0.96 Å with U iso (H) = 1.5U eq (C-methyl) and = 1.2U eq (C) for other H atoms. A rotating group model was used for the methyl group.

Figure 1
A view of the molecular structure of the two independent trichloroacetate anions and the two independent 2-amino-6methylpyridinium cations of the title salt. Displacement ellipsoids are drawn at the 30% probability level.  The crystal packing of the title compound, viewed normal to (101). The N-H···O and C-H···O hydrogen bonds are shown as dashed lines (see Table 1 for details; H atoms not involved in hydrogen bonding have been omitted for clarity).

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.