4-Amino-2-hydroxybenzohydrazide

The asymmetric unit of the title compound, C7H9N3O2, comprises two crystallographically independent molecules (A and B). In each molecule there is an intramolecular O—H⋯O hydrogen bond making an S(6) ring motif. In the crystal, a pair of N—H⋯N hydrogen bonds link the two molecules (A and B) into a dimer with an R 2 2(6) ring motif. The B molecules are linked via pairs of N—H⋯O hydrogen bonds, forming inversion dimers with an R 2 2(10) ring motif. The molecules are further linked via other N—H⋯O hydrogen bonds, forming undulating two-dimensional networks lying parallel to the bc plane. These networks are finally linked via N—H⋯O hydrogen bonds, forming a three-dimensional structure.

The asymmetric unit of the title compound, C 7 H 9 N 3 O 2 , comprises two crystallographically independent molecules (A and B). In each molecule there is an intramolecular O-HÁ Á ÁO hydrogen bond making an S(6) ring motif. In the crystal, a pair of N-HÁ Á ÁN hydrogen bonds link the two molecules (A and B) into a dimer with an R 2 2 (6) ring motif. The B molecules are linked via pairs of N-HÁ Á ÁO hydrogen bonds, forming inversion dimers with an R 2 2 (10) ring motif. The molecules are further linked via other N-HÁ Á ÁO hydrogen bonds, forming undulating two-dimensional networks lying parallel to the bc plane. These networks are finally linked via N-HÁ Á ÁO hydrogen bonds, forming a three-dimensional structure.
The asymmetric unit of the title compound, Fig. 1, comprises two crystallographically independent molecules (A and B). The bond lengths (Allen et al., 1987) and angles are within normal ranges. In each molecule an intramolecular O-H···O hydrogen bond (Table 1) make an S(6) ring motif (Bernstein et al., 1995).
In the crystal, there are number of N-H···N and N-H..O hydrogen bonds linking the molecules (Table 1). A pair of N-H···N hydrogen bonds link the two molecules (A and B) to form dimers with an R 2 2 (6) ring motif. The B molecules are linked via pairs of N-H···O hydrogen bonds to form inversion dimers with an R 2 2 (10) ring motif. The molecules are further linked through other N-H···O hydrogen bonds forming undulating two-dimensional networks lying parallel to the bc plane. These networks are finally linked via an N-H···O hydrogen bond to form a three-dimensional structure (Fig.   2).

Experimental
The title compound was synthesized by adding 1 mmol of methyl 4-amino-2-hydroxybenzoate to a solution of hydrazine hydrate (80%) (1 mmol) in methanol (30 ml). The mixture was refluxed with stirring for 30 min and after cooling to room temperature a white precipitate was filtered off and washed with diethylether and dried in air. Colourless needle-like crystals of the title compound, suitable for X-ray structure analysis, were recrystallized from ethanol by slow evaporation of the solvents at room temperature over several days.

Refinement
The N-bound H-atoms were located in a difference Fourier map and were constrained to ride on their parent N atoms with U iso (H) = 1.2U eq (N). The OH and C-bound H atoms were included in calculated positions and treated as riding atoms: O-H = 0.82 Å, C-H = 0.93 Å, with U iso (H) = k × U eq (O,C) where k = 1.5 for OH H atoms and = 1.2 for other H atoms.

4-Amino-2-hydroxybenzohydrazide
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.21 e Å −3 Δρ min = −0.21 e Å −3 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 > 2sigma(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.