(2E,7E)-2,7-Bis[(thiophen-2-yl)methylidene]cycloheptanone

The whole molecule of the title compound, C17H16OS2, is generated by two-fold rotational symmetry. The carbonyl C and O atoms of the cycloheptanone ring lie on the twofold rotation axis which bisects the opposite –CH2–CH2– bond of the ring. The molecule exists in an E,E conformation with respect to the C=C double bond. The cycloheptanone ring exhibits a twisted chair conformation and its mean plane makes a dihedral angle of 50.12 (19)° with the planes of the thiophene rings. The two S atoms are in an anti arrangement with respect the carbonyl O atom and the dihedral angle between the two thiophene ring planes is 69.38 (7)°. In the molecule, there are two intramolecular C—H⋯S hydrogen bond, forming S(6) ring motifs. In the crystal, inversion dimers are generated via pairs of C—H⋯O hydrogen bonds. These dimers are interconnected by another interaction of the same kind with a neighbouring molecule, forming a molecular chain along the c-axis direction.

The whole molecule of the title compound, C 17 H 16 OS 2 , is generated by two-fold rotational symmetry. The carbonyl C and O atoms of the cycloheptanone ring lie on the twofold rotation axis which bisects the opposite -CH 2 -CH 2 -bond of the ring. The molecule exists in an E,E conformation with respect to the C C double bond. The cycloheptanone ring exhibits a twisted chair conformation and its mean plane makes a dihedral angle of 50.12 (19) with the planes of the thiophene rings. The two S atoms are in an anti arrangement with respect the carbonyl O atom and the dihedral angle between the two thiophene ring planes is 69.38 (7) . In the molecule, there are two intramolecular C-HÁ Á ÁS hydrogen bond, forming S(6) ring motifs. In the crystal, inversion dimers are generated via pairs of C-HÁ Á ÁO hydrogen bonds. These dimers are interconnected by another interaction of the same kind with a neighbouring molecule, forming a molecular chain along the c-axis direction.

Experimental
Data collection: APEX2 (Bruker, 2004); cell refinement: APEX2 and SAINT (Bruker, 2004); data reduction: SAINT and XPREP (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and DIAMOND (Brandenburg, 2010); software used to prepare material for publication: SHELXL97 and publCIF (Westrip, 2010). Thiophenes are often a subject of considerable interest due to their numerous and interesting conducting properties as polymers and for their biological properties. The incorporation of rigid spacers into the thiophene backbone is anticipated to offer several distinct advantages. A polymer can be extended to afford a more planar conformation through diminished steric effects so that a maximum degree of delocalization of the π electrons is achieved (Kolodziejczyk et al., 2013).
Some thiophene derivatives were also evaluated for anti-cancer activity against PC-3 cell lines, for in vitro antioxidant potential and for β-glucuronidase and α-glucosidase inhibitory activities. Some also showed a potent DPPH radical scavenging antioxidant activity (Mishra et al., 2011).
The title compound (Scheme 1, Fig. 1) crystallizes in the orthorhombic space group Pbcn. It has an E configuration with respect to the C6=C7 bond on both sides of the cycloheptanone ring. The central moiety (cycloheptanone) exists in a twisted chair form making a dihedral angle of 50.12 (19)° with the thiophene ring. The C9-O1 (1.227 (5) Å) bond distance is very close to the reported bond lengths (1.222 (3) Å) of a keto group of a similar structure (Liang et al., 2007).
The two sulfur atoms are in an anti arrangement with respect to the carbonyl O atom and the dihedral angle between the two five-membered thiophene ring planes is 69.38 (7)°. There are no classical hydrogen bond interactions present in the structure. However, an intramolecular H bond interaction between one of the H atoms at C7 atom and the S1 atom forms a five membered ring with a D···A distance of 3.205 (3) Å (Fig. 2) within the molecule whereas two C-H···O intermolecular hydrogen bond interactions with a D···A distance of 3.282 (3) Å (Table 1) between H7A and O1 generate a centrosymmetric dimer (Layana et al., 2014) and also chain these centrosymmetric dimers into a 1-D chain along the c axis in the lattice (Fig. 3). In addition to this, there are two very weak π···π interactions found in the crystal between the thiophene rings with centroid-centroid distances of greater than 4 Å. Fig. 4 shows the packing of the title compound along c axis.

Experimental
The title compound was prepared by adapting a reported procedure (Alkskas et al., 2013). To a mixture of cycloheptanone (0.50 g, 4.4 mmol) and thiophene-2-carboxaldehyde (1.01 g, 8.7 mmol) in methanol (25 ml) taken up in a 100 ml flask, potassium hydroxide pellets (0.5 g, 8.7 mmol) were added and the reaction mixture was stirred at room temperature for 15 minutes whilst a yellow product separated out. The mixture was heated in a hot water bath at 60 °C for 6 h. until an appreciable amount of solid formed. The flask was then cooled in ice and the precipitate that separated out was collected by vacuum filtration. The crude product was washed several times with ice cold 1 ml portions of ethanol. Recrystallization from methanol gave diffraction quality crystals (yield 98%

Refinement
All H atoms on C were placed in calculated positions, guided by difference maps, with C-H bond distances of 0.93-0.97 Å. H atoms were assigned U iso (H) values of 1.2U eq (carrier).

Figure 1
ORTEP view of the compound, drawn with 50% probability displacement ellipsoids for the non-H atoms. Symmetry operator (i): (i) -x+2, y, -z+1/2.    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.