Crystal structure and computational study of 2,4-dichloro-N-[(E)-(5-nitrothiophen-2-yl)methylidene]aniline

The title compound, C11H6Cl2N2O2S, is a Schiff base that incorporates an N-bound 2,4-dichlorophenyl and a C-bound 5-nitrothiophene ring. The crystal structure features C—H⋯O hydrogen bonds and π–π stacking interactions. Geometric parameters from quantum-chemical calculations are in good agreement with experimental X-ray diffraction results.


Chemical context
Schiff bases, which contain C N double bonds, are well known starting materials for the synthesis of many drugs (Aydog an et al., 2001) and often possess very important biological activities, such as anti-inflammatory and analgesic properties (Sondhi et al., 2006). In addition, nitrothiophene and its derivatives also exhibit many biological activities, including antibacterial and antifungal (Kalluraya et al., 1994;Kalluraya & Shetty, 1997) properties. We report the synthesis, structural analysis and theoretical calculations of the title compound, C 11 H 6 Cl 2 N 2 O 2 S (I), which is a new Schiff base that includes a nitrothiophene group.

Structural commentary
The title compound (Fig. 1) is nearly planar, the maximum deviation from the mean plane of 0.233 (4) Å is for atom N2. Schiff bases that are derived from salicylaldehyde show thermochromism and photochromism properties that are dependent upon planarity or non-planarity of the molecules (Cohen et al., 1964;Hadjoudis et al., 1987). Since the dihedral angle ISSN 2056-9890 between the benzene and thiophene rings is 9.7 (2) , the title compound may exhibit thermochromic features. The slight twist of the molecule is caused by a steric repulsion of atoms H5 and H7. The C7 N2 double-bond distance is 1.267 (6)Å , which is comparable to those of reported structures (Ö zdemir Tarı & Işık, 2012;Ceylan et al., 2012). The C8-C7-N2-C6 torsion angle is 178.5 (5) .

Theoretical Calculations
Quantum-chemical calculations were performed to compare with the experimental analysis. Ab initio Hartree-Fock (HF) and density functional DFT(B3LYP) methods were used with the standard basis set of 6-31+G(d) (Becke, 1993;Lee et al., 1988;Schlegel, 1982;Peng et al., 1996) using the Gaussian 03 software package (Frisch et al., 2004;Dennington et al., 2007) to obtain the optimized molecular structure. The computational results are consistent with experimental crystallographic data. The C7 N2 bond length was calculated to be 1.25 and 1.28 Å using HF and DFT(B3LYP) methods, respectively. The torsion angle C8-C7-N2-C6 was calculated to be À177.98 and À176.09 by HF and DFT(B3LYP) methods, respectively.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All H atoms were positioned geometrically with C-H = 0.93 Å and refined with using a riding model with U iso (H) = 1.2U eq (C).

Figure 2
A partial packing view of (I). Dashed lines indicate the C-HÁ Á ÁO hydrogen-bonding interactions A view of (I), with the atom-numbering scheme and 50% probability displacement ellipsoids.  (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012).

2,4-Dichloro-N-[(E)-(5-nitrothiophen-2-yl)methylidene]aniline
Crystal data C 11 H 6 Cl 2 N 2 O 2 S M r = 301.14 Monoclinic, P2 1 /c a = 7.5731 (9)  Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.