2-Amino-5-(4-carboxylatophenyl)pyridinium monohydrate

The title compound, C12H10N2O2·H2O, crystallizes as a zwitterion in which the pyridine N atom is protonated and the carboxy –OH group is deprotonated. The benzene and pyridinium rings are inclined with a dihedral angle of 6.63 (5)° between them. In the crystal, intermolecular O—H⋯O and N—H⋯O hydrogen-bonding interactions link adjacent molecules into a two-dimensional double layered supramolecular network.

The title compound, C 12 H 10 N 2 O 2 ÁH 2 O, crystallizes as a zwitterion in which the pyridine N atom is protonated and the carboxy -OH group is deprotonated. The benzene and pyridinium rings are inclined with a dihedral angle of 6.63 (5) between them. In the crystal, intermolecular O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen-bonding interactions link adjacent molecules into a two-dimensional double layered supramolecular network.

Related literature
For the use of pyridinecarboxylate acid in coordination chemistry and for related structures, see: Jia et al. (2007); Zhang et al. (2011).  Table 1 Hydrogen-bond geometry (Å , ).
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: JJ2150).  (Jia et al., 2007;Zhang et al., 2011). We attempted to synthesize a Zn II complex with the ligand in hydrothermal synthesis conditions. However the title compound was obtained, its structure is reported here.

Experimental
A mixture of 4-(6-aminopyridin-3-yl)benzoic acid (0.0214 g, 0.1 mmol), Zn(CH 3 COO) 2 .2H 2 O (0.0219 g, 0.1 mmol) and water (8 ml) was stired vigorously for 30 min and then sealed in a Teflon-lined stainless-steel autoclave. The autoclave was heated and maintained at 393 K for 2 days, and then cooled to room temperature at 5 K h -1 to obtain colorless prism crystals suitable for X-ray analysis.

Refinement
The H atoms bonded to C and N atoms were positioned geometrically (C-H = 0.93 Å, N-H = 0.86 Å) and allowed to ride on their parent atoms, with U iso (H) value equal to 1.2U eq (C or N). The H atoms bonded to water O atoms were located in a difference Fourier map and refined with O-H distance restraint of 0.85±0.02 Å, U iso (H) = 1.5U eq (O).

Figure 2
The two-dimensional supramolecular network formed by N-H···O and O-H···O (dashed lines) hydrogen-bonding interactions.

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.  (4) 176 (5) Symmetry codes: (i) x−1/2, −y+1/2, z+1/2; (ii) −x+1, −y+1, −z; (iii) x−1/2, −y+3/2, z+1/2.