(E)-2-Chloro-N′-(4-hydroxybenzylidene)benzohydrazide

The title hydrazone molecule, C14H11ClN2O2, has a trans conformation with respect to the methylidene unit. The dihedral angle between the two benzene rings is 37.6 (3)°. In the crystal, the presence of O—H⋯O, O—H⋯N and N—H⋯O hydrogen bonds leads to the formation of a three-dimensional network. The title compound crystallized in the chiral orthorhombic space group P212121 and was refined as an inversion twin [Flack parameter = −0.20 (18)].

The molecule of the title compound ( Fig. 1) exists in a trans conformation with respect to the methylidene unit. The dihedral angle between the (C1-C6) and (C9-C1) benzene rings is 37.6 (3)°.
In the crystal, O-H···O, O-H···N, and N-H···O hydrogen bonds leads to the formation of a three-dimensional network (Table 1, Fig. 2).

Experimental
A mixture of 4-hydroxybenzaldehyde (0.122 g, 1 mmol) and 2-chlorobenzohydrazide (0.171 g, 1 mmol) in 30 ml of methanol containing few drops of acetic acid was refluxed for about 1 h. On cooling to room temperature, a solid precipitate was formed. The solid was filtered and then recrystallized from methanol. Colourless crystals, suitable for Xray diffraction analysis, were obtained by slow evaporation of a solution of the title compound in methanol.

Refinement
H atom H1 was located in a difference Fourier map and was freely refined. The remaining H-atoms were positioned geometrically and refined using a riding model: O-H = 0.82 Å, C-H = 0.93 Å, with U iso (H) = 1.5U eq (O) and = 1.2U eq (C).

Figure 2
A view along the a axis of the crystal packing of the title compound. The various hydrogen bonds are indicated by dashed lines (see Table 1 for details; C-bound H-atoms have been omitted for clarity).. 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.