2-Aminopyridin-3-ol

The molecule of the title pyridine derivative, C5H6N2O, shows approximate C s symmetry. Intracyclic angles cover the range 118.34 (10)–123.11 (10)°. In the crystal, O—H⋯N, N—H⋯O and N—H⋯N hydrogen bonds connect the molecules into double layers perpendicular to the a axis. The shortest centroid–centroid distance between two π-systems is 3.8887 (7) Å.

The molecule of the title pyridine derivative, C 5 H 6 N 2 O, shows approximate C s symmetry. Intracyclic angles cover the range 118.34 (10)-123.11 (10) . In the crystal, O-HÁ Á ÁN, N-HÁ Á ÁO and N-HÁ Á ÁN hydrogen bonds connect the molecules into double layers perpendicular to the a axis. The shortest centroid-centroid distance between two -systems is 3.8887 (7) Å .

Comment
Chelate ligands have found widespread use in coordination chemistry due to the enhanced thermodynamic stability of resultant metal complexes in relation to coordination compounds exclusively applying comparable monodentate ligands (Gade, 1998). Combining different donor atoms, a molecular set-up to accommodate a large variety of metal centers of variable Lewis acidity is at hand. In this aspect, the title compound seemed interesting due to its use as strictly neutral or -depending on the pH value -as anionic or cationic ligand. Furthermore, thanks to the presence of three possible donor atoms, the title compound might serve as a building block in the formation of metal-organic framework structures. At the beginning of a more comprehensive study to elucidate the formation of coordination polymers featuring mixed N,O ligands, we determined the structure of the title compound to enable comparative studies of metrical parameters in envisioned reaction products.
Information about the molecular and crystal structure of 2,3-diaminopyridine is apparent in the literature (Betz et al., 2011).
Intracyclic angles range from 118.34 (10) ° to 123.11 (10) ° with the smallest angle found on the carbon atom bearing the hydroxyl group and the largest angle found on the unsubstituted carbon atom in ortho position to the intracyclic N atom.
The molecule is essentially planar (r.m.s. of all fitted non-hydrogen atoms = 0.0092 Å). The amino group is not planar, the least-squares planes defined by the atoms of the heterocycle on the one hand and the atoms of the NH 2 group on the other hand group enclose an angle of 30.73(1.69) ° (Fig. 1).
The crystal structure of the title compound is marked by hydrogen bonds (Fig. 2). While the hydroxyl group forms a hydrogen bond to the intracyclic N atom (and its O atom acts as acceptor for one of the NH 2 supported hydrogen bonds), there is also a cooperative hydrogen bonding system of the NH 2 ···NH 2 -type. In terms of graph-set analysis (Etter et al., 1990;Bernstein et al., 1995), the descriptor for these interactions on the unitary level is C 1 1 (2)C 1 1 (5)C 1 1 (5). In total, the molecules are connected to double layers perpendicular to the crystallographic a axis. The shortest intercentroid distance between two π-systems was measured at 3.8887 (7) Å.
The packing of the title compound in the crystal is shown in Figure 3.

Experimental
The compound was obtained commercially (Aldrich). Crystals suitable for the X-ray diffraction study were taken directly from the provided compound.