2-Amino-5-methylpyridinium trifluoroacetate

In the title salt, C6H9N2 +·C2F3O2 −, the F atoms of the anion are disordered over two sets of sites, with refined occupancies in a ratio of 0.505 (17):0.495 (17). In the crystal, cations and anions are linked via N—H⋯O hydrogen bonds, forming R 2 2(8) ring motifs. The ionic units are linked into a two-dimensional network parallel to (100) by N—H⋯O and weak C—H⋯O hydrogen bonds. The crystal structure is further stabilized by weak C—H⋯F hydrogen bonds, resulting in a three-dimensional network.

In the title salt, C 6 H 9 N 2 + ÁC 2 F 3 O 2 À , the F atoms of the anion are disordered over two sets of sites, with refined occupancies in a ratio of 0.505 (17):0.495 (17). In the crystal, cations and anions are linked via N-HÁ Á ÁO hydrogen bonds, forming R 2 2 (8) ring motifs. The ionic units are linked into a twodimensional network parallel to (100) by N-HÁ Á ÁO and weak C-HÁ Á ÁO hydrogen bonds. The crystal structure is further stabilized by weak C-HÁ Á ÁF hydrogen bonds, resulting in a three-dimensional network.
Trifluoroacetic acid is a very strong carboxylic acid, easily volatile, and used for protein purification. An example of a crystal structure of a trifluoroacetate salts has been reported (Rodrigues et al., 2001). In order to study potential hydrogen bonding interactions the crystal structure determination of the title compound (I) was carried out.

Experimental
To a hot methanol solution (20 ml) of 2-amino-5-methylpyridine (54 mg, Aldrich) was added a few drops of trifluoroacetic acid. The solution was 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.

Refinement
The F atoms of the anion are disordered over two sets of sites, with occupancies of 0.505 (17):0.495 (17). Atoms H1N1, H1N2 and H2N2 were located in a difference Fourier maps and refined freely. The remaining hydrogen atoms were positioned geometrically [C-H= 0.95-0.98 Å] and were refined using a riding model, with U iso (H)=1.2 U eq (C) or 1.5U eq (methyl C). A rotating group model was used for the methyl group.

Computing details
Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009  The molecular structure of the title compound, showing 50% probability displacement ellipsoids and the atom-numbering scheme. Both disorder components are shown. 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 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.