Aza-stilbenes are a special group of compounds in the Schiff base family which can be synthesized by the reaction of aldehyde with aniline. Aza-stilbenes have been shown to possess potent biological properties such as antibacterial (Tamizh et al., 2012), antioxidant (Cheng et al., 2010; Lu et al., 2012), antifungal (da Silva et al., 2011) and antiproliferative (Fujita et al., 2012) activities. The interesting biological activities of aza-stilbenes have led us to synthesize the title compound (I) and study its antibacterial and antioxidant activities. Our antibacterial assay have shown that (I) possesses moderate to weak antibacterial activity against B. subtilis, S. aureus, P. aeruginosa, S. typhi and S.sonnei with the MIC values in the range of 37.5 to 150 µg/ml. In addition (I) also shows interesting antioxidant activity by DPPH assay with the IC₅₀ value of 0.080 ± 0.0004 µg/ml. We report here the crystal structure of the title compound.

There are two independent molecules, A and B in the asymmetric unit of the title compound, with similar conformations but some differences in bond angles (Fig. 1). The molecular structure exists in a trans configuration with respect to the methylidene C7═N1 double bond [1.2868 (13) and 1.2823 (19) Å for molecules A and B, respectively] and with the torsion angle C8—N1—C7—C1 = -175.58 (13)° for molecule A [177.48 (13)° for molecule B]. The molecule is twisted with the dihedral angle between the two substituted benzene rings being 80.52 (7)° in molecule A and 83.53 (7)° in molecule B. In both molecules, the three methoxy groups are co-planar with their bound benzene rings with the C14—O1—C2—C3 = -3.2 (2)°, C15—O2—C4—C3 = -6.7 (2)° and C16—O3—C6—C5 = -1.5 (2)° in molecule A, and the corresponding values are 5.07 (19), 1.86 (19) and -1.7 (2)° in molecule B. In each molecule, an intramolecular O—H···N hydrogen bond (Fig. 1 and Table 1) generates an S(5) ring motif (Bernstein et al., 1995). The bond distances are in normal ranges (Allen et al., 1987) and are comparable with the related structures (Kaewmanee et al., 2013; Sun et al., 2011).

In the crystal structure, the molecules are linked into dimers by O—H···N and O—H···O hydrogen bonds (Table 1) which form two R²₁(6) ring motifs and an R²₂(10) ring motif (Fig. 2). These dimers are further linked by C—H···O interactions (Table1) into chains along the b direction which arranged into sheets parallel to the ab plane (Fig. 3). There are π–π interactions with Cg1···Cg3 and Cg1···Cg3^iv distances of 3.6030 (9) and 3.9452 (9) Å, respectively (Fig. 2) [symmetry code: (iv) = -1 + x, y, z]; Cg1 and Cg3 are the centroids of C1A–C6A and C1B–C6B rings, respectively.]

The title compound (I) was prepared by mixing 1:1 molar ratio solutions of 2-aminophenol (2.5 mmol, 0.25 g) in toluene (20 ml) and 2,4,6-trimethoxybenzaldehyde (2.5 mmol, 0.50 g) in toluene (20 ml). The reaction mixture was refluxed for around 4 h, yielding white solids , which was collected by filtration, washed with cold ethanol and dried in air. Colorless block-shaped single crystals suitable for X-ray structure determination were recrystalized from methanol by slow evaporation of the solvent at room temperature after several days (m.p. 450–452 K).

Hydroxy H atom was located in a difference map and refined freely. The remaining H atoms were fixed geometrically and allowed to ride on their parent atoms, with d(C—H) = 0.95 Å for aromatic and CH, and 0.98 Å for CH₃ atoms. The U_iso(H) values were constrained to be 1.5U_eq of the carrier atom for water and methyl H atoms and 1.2U_eq for the remaining H atoms. A rotating group model was used for the methyl groups.

Symmetry codes: (i) x+1, y, z; (ii) x, y−1, z.