N′-(3-Bromo-5-chloro-2-hydroxybenzylidene)-2H-1,3-benzodioxole-5-carbohydrazide

The asymmetric unit of the title hydrazone compound, C15H10BrClN2O4, contains two independent molecules. The dihedral angles between the benzene rings are 38.7 (3)° in one molecule and 24.3 (3)° in the other. Both molecules exist in trans conformations with respect to the C=N double bonds of the central methylidene units. Intramolecular O—H⋯N contacts are observed in both molecules, forming S(6) rings. In the crystal, molecules are linked through N—H⋯O hydrogen bonds into chains along the a axis.

The asymmetric unit of the title hydrazone compound, C 15 H 10 BrClN 2 O 4 , contains two independent molecules. The dihedral angles between the benzene rings are 38.7 (3) in one molecule and 24.3 (3) in the other. Both molecules exist in trans conformations with respect to the C N double bonds of the central methylidene units. Intramolecular O-HÁ Á ÁN contacts are observed in both molecules, forming S(6) rings. In the crystal, molecules are linked through N-HÁ Á ÁO hydrogen bonds into chains along the a axis.

Experimental
The title compound was prepared by refluxing 3-bromo-5-chlorosalicylaldehyde (1.0 mol, 0.23 g) with [3,4]dioxolebenzohydrazide (1.0 mol, 0.18 g) in methanol (50 ml). Excess methanol was removed from the mixture by distillation. A colourless solid product was filtered, and washed three times with methanol. Colourless block-shaped crystals of the title compound were obtained from a methanol solution of the compound by slow evaporation in air.

Refinement
Atoms H2 and H4A were located in a difference Fourier map and refined isotropically, with the N-H distances restrained to 0.90 (1) Å. The remaining H atoms were placed in calculated positions (C-H = 0.93-0.97 Å, O-H = 0.82 Å) and refined as riding with U iso (H) = 1.2U eq (C) and 1.5 U eq (O). The structure contains solvent accessible voids of 78 Å 3 , which might accommodate a disordered methanol molecule. However, the effect of the presence of additional solvent was not investigated further.

Figure 1
The molecular structure of the title compound, showing 30% probability displacement ellipsoids for the non-hydrogen atoms. Intramolecular hydrogen bonds are shown as dashed lines.

Figure 2
The packing diagram of the title compound, viewed along the c axis. Hydrogen bonds are shown as dashed lines.  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.