(E)-N′-(5-Bromo-2-hydroxybenzylidene)-2-(4-isobutylphenyl)propanohydrazide

The title compound, C20H23BrN2O2, containing an ibuprofen core, crystallizes with three independent molecules of similar conformation in the asymmetric unit. In these three molecules, the two benzene rings make dihedral angles of 82.7 (2), 71.2 (2) and 78.0 (3)° with respect to each other. The atoms of the isobutyl groups in two of the molecules are disordered over two positions, with site-occupancy ratios of 0.516 (8):0.484 (8) and 0.580 (8):0.420 (8). In the crystal, molecules are linked by N—H⋯O, C—H⋯O and O—H⋯N hydrogen bonds. Furthermore, C—H⋯π interactions are also observed.

Cg2, Cg3, Cg4 and Cg6 are the centroids of the C31-C36, C41-C46, C51-C56 and C11-C16 benzene rings, respectively. As shown in Fig. 1, the asymmetric unit of (I) contains three independent molecules of similar conformation and the same orientations. Their bond lengths and bond angles are in normal range and are similar to each other and those reported for related structures (Mohamed et al., 2012;Amir & Kumar, 2005;Goh et al., 2010;Fun et al., 2009a,b;Wu et al., 2010). In these three molecules A (with Br21), B (with Br41) and C (with Br1), the dihedral angles between the two benzene rings are 82.7 (2), 71.2 (2) and 78.0 (3)°, respectively.
The crystal packing is stabilized by C-H···O, N-H···O and O-H···N hydrogen bonds (Table 1, Fig. 2), forming a three dimensional network. In addition, C-H···π interactions (Table 1) help to stabilize the crystal structure.

Experimental
A mixture of 220 mg (1 mmol) 2-(4-isobutylphenyl)propane hydrazide and 201 mg (1 mmol) 5-bromo-2-hydroxybenzaldehyde was grinded in a mortar with a pestle before being well mixed with three drops of acetic acid. The powder mixture was transferred and homogeneously spread in a Petri dish, and then irradiated with microwaves (at 600 W) for a total of 2 min at intervals of 30 s. The resulting product was collected and crystallized from ethanol to obtain prismatic crystals in 92% yield with a m.p. of 434-436 K.

Refinement
In the asymmetric unit, the atoms (C38, C39 and C40 for molecule A, and C58, C59 and C60 for molecule B) of the isobutyl groups of two of the three molecules are disordered over two positions, with site-occupancy ratios of   View of the molecular packing and the hydrogen bonding along the a axis. The minor disorder components and hydrogen atoms not involved in hydrogen bonding have been omitted for clarity.

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses 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 observed criterion of F 2 > σ(F 2 ) is used only for calculating -R-factor-obs 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.