2-Amino-4-methylpyridinium 4-aminobenzoate

In the structure of the title salt, C6H9N2 +·C7H6NO2 −, the 4-aminobenzoate anions are linked to adjacent anions and 2-amino-4-methylpyridinium cations via N—H⋯O hydrogen bonds, forming a three-dimensional supramolecular structure. The crystal structure also shows a weak C—H⋯O hydrogen bond between adjacent anions. Within the 4-aminobenzoate anion, the carboxylate group is twisted by 14.0 (4)° with respect to the benzene ring.


Comment
The presence of the outside lone-pair electrons on the pyridine-N atom suggests that 2-amino-4-methyl-pyridine is an appropriate ligand for preparing metal complexes. However a search of the Cambridge Structure Database (November 2007 update;Allen, 2002) shows that in the most cases the 2-amino-4-methyl-pyridine presents as a counter cation but does not coordinate to the metal ion (Choudhury et al., 2007;Halvorson et al., 1987;Geiser et al., 1986;Geiser & Willett, 1984). This implies that the 2-amino-4-methyl-pyridine, as a weak base, is easy to be protonated in acid condition. The crystal structures of two inorganic salt of 2-amino-4-methyl-pyridine, 2-amino-4-methyl-pyridinium phosphate (Kaabi & Khedhiri, 2004) and 2-amino-4-methyl-pyridinium arsenate (Chtioui et al., 2006), have been reported previously. Recently we prepared the title organic salt of 2-amino-4-methyl-pyridine, and its crystal structure is reported here.
The smaller difference in C-O bond distances of the carboxyl group (Table 1) indicates the carboxyl group is deprotonated in the crystal. Within the anion the carboxyl group is twisted with respect to the benzene ring by a dihedral angle of 14.0 (4)°.
In the crystal, the aminobenzoate anions are linked with both of adjacent aminobenzoate anions and aminomethylpyridinium cations via N-H···O hydrogen bonding, to form the three dimensional supramolecular structure. The crystal structure also contains weak C-H···O hydrogen bonding between adjacent anions.
Experimental 2-Amino-4-methyl-pyridine (0.054 g, 0.5 mmol) and 4-amino-benzoic acid (0.069 g, 0.5 mmol) were dissolved in ethanol (5 ml) at room temperature. The solution was filtered and light brown single crystals were obtained from the filtration after 2 weeks.

Refinement
H atoms bonded to N atoms were located in a difference Fourier map and were refined as riding in as-found relative positions, with U iso (H) = 1.5U eq (N). Methyl H atoms were placed in calculated positions with C-H = 0.96 Å and the torsion angle was refined to fit the electron density, U iso (H) = 1.5U eq (C). Aromatic H atoms were placed in calculated positions with C-H = 0.93 Å, and refined in riding mode with U iso (H) = 1.2U eq (C). In the absence of significant anomalous scattering effects, Friedel pairs were merged.