N′-(2-Hydroxybenzylidene)-2-(hydroxyimino)propanohydrazide

The molecule of the title compound, C10H11N3O3, adopts an all-trans conformation and is approxomately planar, the largest deviation from the least-squares plane through all non-H atoms being 0.261 (1) Å. An intramolecular O—H⋯N hydrogen bond occurs. In the crystal, the molecules are packed into layers lying parallel to the ab plane by π-stacking interactions between the benzene ring of one molecule and the C—N bond of the oxime group of another molecule; the shortest intermolecular C⋯C separation within the layer is 3.412 (1) Å. The layers are connected by O—H⋯O and N—H⋯O hydrogen bonds.

The molecule of the title compound, C 10 H 11 N 3 O 3 , adopts an all-trans conformation and is approxomately planar, the largest deviation from the least-squares plane through all non-H atoms being 0.261 (1) Å . An intramolecular O-HÁ Á ÁN hydrogen bond occurs. In the crystal, the molecules are packed into layers lying parallel to the ab plane by -stacking interactions between the benzene ring of one molecule and the C-N bond of the oxime group of another molecule; the shortest intermolecular CÁ Á ÁC separation within the layer is 3.412 (1) Å . The layers are connected by O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds.
In the structure 1 the N'-(2-hydroxybenzylidene)-2-(hydroxyimino)propanehydrazide molecules are connected by extensive system of hydrogen bonds. The bond lengths N-O and C-N in the oxime group are 1.3838 (9) and 1.2854 (9) Å respectively, which is typical for protonated moieties of this type (Świątek-Kozłowska et al., 2000;Mokhir et al., 2002;Sachse et al., 2008). The oxime group is in a trans position with respect to the amide group, in accordance with the structures of 2-hydroxyiminopropanamide and other amide derivatives of 2-hydroxyiminopropanoic acid (Onindo et al., 1995;Duda et al., 1997;Sliva et al., 1997). There are three hydrogen bonds in structure of 1 ( Table 2). The O1-H1···N1 is an intramolecular hydrogen bond, where the phenolic oxygen atom acts as donor and the azomethine nitrogen atom acts as receptor. The O3-H3···O2 and N2-H2···O1 hydrogen bonds are intermolecular, the oximic oxygen and the hydrazone nitrogen atoms act as donors and the hydrazone oxygen and the phenolic oxygen atoms act as acceptors.
In the crystal packing, molecules of 1 form layers parallel to ab plane. The molecules in the layer are connected by π-stacking between the benzene ring of one molecule and C-N bond of the oxime group of another molecule. The distance between two planes formed by neighboring molecules is 3.3493 (7) Å. The layers are connected by extensive system of hydrogen bonds.

Experimental
A mixture of 2-(hydroxyimino)propanehydrazide synthesized according to (Fritsky et al., 1998) (0.117 g, 0.1 mmol) and salicylic aldehyde (0.122 g, 0.1 mmol) in 10 ml of methanol was heated to reflux for 2 h. On cooling to room temperature, a solid precipitate was formed. The solid was filtered and then recrystallized from methanol. Yellowish needle crystals of 1 were obtained by slow evaporation of the methanolic solution. Yield: 2 g (90%).
supplementary materials sup-2 Refinement All hydrogen atoms were positioned geometrically and constrained to ride on their parent atoms, with C-H = 0.95-0.98 Å, N-H = 0.88 Å, O-H = 0.84 Å, and U iso = 1.2-1.5 U eq (parent atom). The highest peak is located 0.64 Å from atom N3 and the deepest hole is located 0.30 Å from atom H3. Fig. 1. The molecular structure of the title compound, with displacement ellipsoids shown at the 50% probability level and atom labelling.

Special details
Geometry. All s.u.'s (except the s.u.'s in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The 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 Rfactors(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.