Crystal structure of 3-benzoyl-2-[(5-bromo-2-hydroxy-3-methoxybenzylidene)amino]-4,5,6,7-tetrahydrobenzo[b]thiophene

In the title compound, the planes of the benzene and phenyl rings are inclined to the thiophene ring by 35.2 (4) and 57.7 (3)°, respectively, while the planes of the two aryl rings are almost normal to one another, making a dihedral angle of 86.4 (6)°. In the crystal, molecules are linked by C—H⋯O hydrogen bonds, forming chains propagating along the a-axis direction.


Chemical context
2-Aminothiophene derivatives have been used in a number of applications in pesticides, dyes and pharmaceuticals. Reviews on the synthesis and properties of these compounds have been reported (Sabnis et al. 1999;Puterová et al. 2010). Schiff base compounds are an important class of compounds both synthetically and biologically. These compounds show biological activities including antibacterial, antifungal, anticancer and herbicidal activities (Desai et al., 2001;Karia & Parsania, 1999;Samadhiya & Halve, 2001;Singh & Dash, 1988). Furthermore, Schiff bases are utilized as starting materials in the synthesis of compounds of industrial (Aydogan et al., 2001) and biological interest, such as -lactams (Taggi et al., 2002). The crystal and molecular structures of two 2-aminothiophenes have been reported by our group (Kubicki et al., 2012). In a continuation of our work on Schiff base derivatives of 2-aminothiophenes, we report herein on the synthesis and crystal structure of the title Schiff base compound. ISSN 2056-9890

Supramolecular features
In the crystal, molecules are linked via C-HÁ Á ÁO hydrogen bonds, observed between the benzene and phenyl rings of adjacent molecules, forming chains parallel to the [100] direction ( Fig. 2 Kaur et al., 2014e]. Two of the compounds, (II) and (IV), crystallize in the monoclinic space group P2 1 , while the others, including the title compound, crystallize in centrosymmetric monoclinic space groups.
A comparison of the structural properties of the title compound to these five closely related molecules reveals the following: (a) The cyclohexene ring is disordered in compounds (II), (III), and (V), and has a slightly distorted half-chair conformation in (I), (III), (IV), and (V), and a distorted chair conformation in (II); (b) The dihedral angle between the mean planes of the thiophene and phenyl rings is 70.4 (5) in (I), ca. 63.6 in (II), 65.7 (3) in (III), 63.0 (4) and 58.8 (9) for the two independent molecules in (IV) and 66.1 (2) in (V). The same dihedral angle in the title compound is 57.7 (3) ; Table 1 Hydrogen-bond geometry (Å , ). Symmetry code: (i) x þ 1; y; z.

Figure 1
A view of the molecular structure of the title compound, showing the atom labelling. Displacement ellipsoids are drawn at the 30% probability level. The intramolecular hydrogen bond is shown as a dashed line (see Table 1 for details).

Figure 2
A view along the b axis of the crystal packing of the title compound.
Dashed lines indicate weak C-HÁ Á ÁO hydrogen bonds (see Table 1 for details; H atoms not involved in hydrogen bonding have been omitted for clarity).
(c) The dihedral angle between the mean planes of the thiophene and benzene rings is 12.1 (9) in (I), 30.9 (8) in (II), 8.3 (4) in (III), 8.3 (5) and 6.7 (5) for the two independent molecules in (IV) and 9.2 (2) in (V). In the title compound this dihedral angle is 35.2 (4) , similar to the situation in compound (III); (d) In (I), (II), (III) and (V) the benzilidene and phenyl rings are inclined to one another by 81.0 (6), ca. 84.6, 73.8 (4) and 74.8 (8) , respectively, compared to 86.4 (6) in the title compound; (e) There is an O-HÁ Á ÁN intramolecular hydrogen bond in (I), as in the title compound; (f) In the crystals of (I) and (III), C-HÁ Á ÁO hydrogen bonds link molecules into chains along [100], as in the crystal of the title compound. In the crystal of (II), an array of C-HÁ Á ÁO hydrogen bonds along [001] and [101] forms sheets parallel to (011). In the crystal of (IV), N-HÁ Á ÁO hydrogen bonds link the molecules, forming chains along [101]. There are alsostacking interactions present, involving the thiophene and pyrrole rings of the two independent molecules, with an inter-centroid distance of 3.468 (2) Å . In the crystal of (V), molecules are linked by pairs of C-HÁ Á ÁO hydrogen bonds, forming inversion dimers.

Synthesis and crystallization
To a solution of (2-amino-4,5,6,7-tetrahydro-benzo[b]thiophen-3-yl)-phenylmethanone (200 mg, 0.79 mmol) in 10 ml of methanol an equimolar amount of 5-bromo-2-hydroxy-3methoxybenzaldehyde (183 mg, 0.79 mmol) was added with constant stirring. The mixture was refluxed for 6 h. A yellowish brown precipitate was obtained. Completion of the reaction was confirmed by thin layer chromatography. The precipitate obtained was filtered and dried at room temperature overnight. The solid was then recrystallized using a 1:1 solution of acetonitrile and dichloromethane, giving colourless block-like crystals.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. It was apparent from an early stage in the refinement that the saturated portion of the tetrahydrobenzothiophene unit exhibited conformational disorder over two sets of atomic sites having unequal occupancies. For the minor conformer, involving atoms C44-C47 (cf. Fig. 1), the bonded distances and the one-angle non-bonded distances were restrained to be the same as the corresponding distances in the major conformer, involving atoms C4-C7, subject to uncertainties of 0.005 and 0.01 Å , respectively. The atomic coordinates of atoms C4 and C44 were constrained to be identical, as were those of atoms C7 and C47. In addition, the anisotropic displacement parameters for pairs of partialoccupancy atoms occupying essentially the same physical space were constrained to be identical. The ratio of the occupancies of the disordered components refined to 0.753 (6):0.247 (6).