2-Amino-4-methylpyridinium trifluoroacetate: a monoclinic polymorph

The title salt, C6H9N2 +·C2F3O2 −, is a monoclinic polymorph of a previously reported structure [Hemamalini & Fun (2010). Acta Cryst. E66, o781–o782]. In the crystal structure, the cations and anions are linked by two different types of N—H⋯O hydrogen bonds, forming cation–anion pairs. These pairs are hydrogen bonded to neighbouring pairs via another N—H⋯O hydrogen bonds involving an H atom of the NH2 group and one of the O atoms of the COO− group into a chain extended along the b axis.

The title salt, C 6 H 9 N 2 + ÁC 2 F 3 O 2 À , is a monoclinic polymorph of a previously reported structure [Hemamalini & Fun (2010). Acta Cryst. E66, o781-o782]. In the crystal structure, the cations and anions are linked by two different types of N-HÁ Á ÁO hydrogen bonds, forming cation-anion pairs. These pairs are hydrogen bonded to neighbouring pairs via another N-HÁ Á ÁO hydrogen bonds involving an H atom of the NH 2 group and one of the O atoms of the COO À group into a chain extended along the b axis.

Support of this investigation by Ferdowsi University of Mashhad is gratefully acknowledged.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: NG2740).

Comment
In the previous works, the structure determinations of 2-aminopyridinium trifluoroacetate and the triclinic polymorph of 2-amino-4-methylpyridinium trifluoroacetate (Hemamalini & Fun, 2010a,b) have been investigated; we report here on the crystal structure of title compound, 4-methyl-2-aminopyridinium trifluoroacetate (Fig. 1). The cation and anion are linked by two different types of N-H···O hydrogen bonds, forming the cation-anion pair. The pairs are hydrogen bonded to neighbouring pairs via another N-H···O hydrogen bonds between the hydrogen of NH 2 moiety and one of the oxygen atom of COOgroup into chain extended along the b axis ( Fig. 2).

Experimental
The title compound was obtained accidently from the reaction between 2,2,2-trifluoroacetamide, phosphorus pentachloride and formic acid and then the treatment of 2-amino-4-methylpyridine and triethylamine. The crystal was obtained from chloroform and n-heptane at room temperature.

Refinement
The H atoms of the NH2 group were located from the difference Fourier synthesis and refined isotropically, no restraints were used. Finally, the geometrical and thermal parameters obtained for these H-atoms, as well as parameters of the hydrogen bonds for these H-atoms included, were rather realistic. The H(C) atom positions were calculated and refined in isotropic approximation in riding model with the Uiso(H) parameters equal to 1.2 Ueq(Ci) for the aromatic C atoms, for methyl groups equal to 1.5 Ueq(Cii), where U(Ci) and U(Cii) are respectively the equivalent thermal parameters of the carbon atoms to which corresponding H atoms are bonded.

Special details
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 > σ(F 2 ) is used only for calculating Rfactors(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.