1,5-Bis(4-chlorophenyl)-3-(2-thienyl)pentane-1,5-dione

In the title molecule, C21H16Cl2O2S, the five-membered ring is rotationally disordered between two orientations in a 1:1 ratio. In the crystal structure, weak intermolecular C—H⋯O hydrogen bonds link molecules related by translation along the a axis into chains, which are further combined into layers parallel to the bc plane via C—H⋯π interactions. The crystal studied was a racemic twin with a 0.37 (19):0.63 (19) domain ratio.

In the title molecule, C 21 H 16 Cl 2 O 2 S, the five-membered ring is rotationally disordered between two orientations in a 1:1 ratio. In the crystal structure, weak intermolecular C-HÁ Á ÁO hydrogen bonds link molecules related by translation along the a axis into chains, which are further combined into layers parallel to the bc plane via C-HÁ Á Á interactions. The crystal studied was a racemic twin with a 0.37 (19):0.63 (19) domain ratio.

S1. Comment
In an earlier publication, the "Grindstone Chemistry" method for conducting exothermic reactions in the solvent-free mode has been described (Bose et al., 2004). We tested energy-saving procedures developed in our laboratory for the preparation of 1,5-diketones starting from the fragrant aldehydes and fragrant ketones in the presence of NaOH under solvent-free conditions. Using this method we obtained the title compound, (I).
In the crystal, the weak intermolecular C-H···O hydrogen bonds (Table 1) link the molecules related by translations along a axis into one-dimensional linear chains, which are further combined into layers parallel to a(b-c) plane via C-H···π interactions (Table 1).

S2. Experimental
4-Chloroacetophenone (6.25 mmol) and thiophene-2-carbaldehyde (3.125 mmol), NaOH (6.25 mmol) were aggregated with glass paddle in an open flask. The resulting mixture was washed with water for several times for removing NaOH, and recrystalized from ethanol, and afforded the title compound as a crystalline solid. Elemental analysis: calculated for C 21 H 16 Cl 2 O 2 S: C 62.54, H 4.00%; Found: C 62.58, H 4.03%.

S3. Refinement
All H atoms were positioned geometrically and refined using a riding model with C-H = 0.93-0.98 Å and U iso (H) = U eq (C). The five-membered ring was treated as disordered between two orientations with nearly equal occupancies refined to 0.501 (11) and 0.499 (11), respectively. The geometries and anisotropic displacement parameters of disordered atoms were refined with soft restraints using the SHELXL commands DFIX, FLAT and SIMU.  View of (I) showing the atomic labelling and displacement ellipsoids at the 30% level. Only one component of the disordered ring (S1,C1-C4) is shown. Hydrogen atoms are omitted for clarity.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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.