Pyridine-2,3-diamine

The molecule of the title pyridine derivative, C5H7N3, shows approximately non-crystallographic C s symmetry. Intracyclic angles cover the range 117.50 (14)–123.03 (15)°. In the crystal, N—H⋯N hydrogen bonds connect molecules into a three-dimensional network. The closest intercentroid distance between two π-systems occurs with the c-axis repeat at 3.9064 (12) Å.


Related literature
For the crystal structure of the dihydrochloride of the title compound, see: Hemamalini & Fun (2010). For the crystal structures of Zn complexes of the title compound, see: de Cires-Mejias et al. (2004). For graph-set analysis of hydrogen bonds, see: Etter et al. (1990); Bernstein et al. (1995).

Experimental
Crystal data

Comment
Chelate ligands have found widespread use in coordination chemistry due to the enhanced thermodynamic stability of resultant coordination compounds in relation to coordination compounds exclusively applying comparable monodentate ligands. Combining identical donor atoms in different states of hybridization, a molecular set-up to accomodate 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. For the title compound, two zinc-supported polymers have been reported whose crystal structure analysis shows the absence of chelate-type building motifs (de Cires-Mejias et al., 2004). At the beginning of a more comprehensive study to elucidate the formation of coordination polymers exclusively featuring nitrogen-containing ligands, we determined the structure of the title compound to enable comparative studies of metrical parameters in envisioned coordination compounds.
Information about the molecular and crystal structure of the dihydrochloride of the title compound is apparent in the literature (Hemamalini & Fun, 2010).
Intracyclic angles cover a range of 117.50 (14)-123.03 (15) ° with the smallest angle found on the carbon atom bearing the amino group in meta position to the intracyclic nitrogen atom and the biggest angle found on the carbon atom bearing a hydrogen atom in ortho position to the intracyclic nitrogen atom. Apart from the hydrogen atoms of the amino groups which point to opposite sides of the plane defined the aromatic system, all atoms are essentially residing in one common plane (r.m.s. deviation of all fitted non-hydrogen atoms = 0.0152 Å). The amino groups are not planar, the least-squares planes defined by the NH 2 groups subtend angles of 40.2 (2) ° and 79.5 (2) ° with the least-squares plane defined by the atoms of the heterocycle (Fig. 1).
The crystal structure of the title compound is marked by a hydrogen bonding system involving all hydrogen atoms of both amino groups as donors and the intracyclic as well as the exocyclic nitrogen atoms as acceptors. The intracyclic nitrogen atom serves as a twofold acceptor for one of the hydrogen atoms of each of the two different amino groups.
The remaining hydrogen atom on each amino group gives rise to a cooperative chain of hydrogen bonds, respectively. The latter ones are antidromic. In terms of graph-set analysis (Etter et al., 1990;Bernstein et al., 1995), the descriptor for this hydrogen bonding system on the unitary level is C 1 1 (2)C 1 1 (2)C 1 1 (4)C 1 1 (5). In total, the molecules are connected to a three-dimensional network (Fig. 2). The closest intercentroid distance between two aromatic systems follows the c-axis repeat at 3.9064 (12) Å.
The packing of the title compound 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.