(E)-1-(2-Thienyl)-3-(3,4,5-trimethoxyphenyl)prop-2-en-1-one

The molecule of the title heteroaryl chalcone, C16H16O4S, which consists of substituted thiophene and benzene rings bridged by the prop-2-en-1-one group, is slightly twisted. The dihedral angle between the thiophene and 3,4,5-trimethoxyphenyl rings is 12.18 (4)°. The three methoxy groups have two different conformations; two methoxy groups are coplanar [C—O—C—C torsion angles = −1.38 (12) and 0.47 (12)°] whereas the third is (-)-synclinal with the benzene ring. In the crystal structure, adjacent molecules are linked in a face-to-side manner into chains along the c axis by weak C—H⋯O(enone) interactions. These chains are stacked along the b axis by weak C—H⋯O(methoxy) interactions.

The molecule of the title heteroaryl chalcone, C 16 H 16 O 4 S, which consists of substituted thiophene and benzene rings bridged by the prop-2-en-1-one group, is slightly twisted. The dihedral angle between the thiophene and 3,4,5-trimethoxyphenyl rings is 12.18 (4) . The three methoxy groups have two different conformations; two methoxy groups are coplanar [C-O-C-C torsion angles = À1.38 (12) and 0.47 (12) ] whereas the third is (-)-synclinal with the benzene ring. In the crystal structure, adjacent molecules are linked in a face-toside manner into chains along the c axis by weak C-HÁ Á ÁO(enone) interactions. These chains are stacked along the b axis by weak C-HÁ Á ÁO(methoxy) interactions.

Comment
Chalcone or 1,3-diaryl-2-propen-1-one, originally isolated from natural sources, and its derivatives are known to display a variety of biological activities, demonstrating analgesic, anti-inflammatory, antibacterial and antimycotic properties (Dimmock et al., 1999;Go et al., 2005;Ni et al., 2004). Moreover synthetic chalcones have also been found to be non-linear optical (NLO) (Patil & Dharmaprakash, 2008) and electro-active fluorescent materials (Jung et al., 2008). We have previously reported the synthesis and crystal structures of chalcone derivatives (Chantrapromma et al., 2009;Suwunwong et al., 2009a, b). Our research into the NLO and biological properties of chalcone derivatives led us to synthesize the title heteroaryl chalcone (I). (I) crystallizes in the non-centrosymmetric orthorhombic space group Pna2 1 and should therefore exhibit second-order nonlinear optical properties.
In the crystal packing, the adjacent molecules are linked in a face-to-side manner into chains along the c axis through the enone unit by weak C1-H1A···O1 interactions (Fig. 2, Table 1). Weak C15-H15C···O3 interactions involving one of methoxy groups further stack these chains along the b axis (Fig. 3, Table 1).

Experimental
The title compound was synthesized by the condensation of 3,4,5-trimethoxybenzaldehyde (0.40 g, 2 mmol) with 2-acetylthiophene (0.35 ml, 2 mmol) in ethanol (30 ml) in the presence of 30% NaOH (aq) (5 ml). After stirring for 3 h in ice bath at 278 K, the resulting pale yellow solid was collected by filtration, washed with distilled water, dried in air and purified by repeated recrystallization from acetone (72% yield). Pale yellow block-shaped single crystals of the title compound suitable for x-ray structure determination were recrystalized from acetone/ethanol (1:1 v/v) by the slow evaporation of the solvent at room temperature after several days, Mp. 420-421 K.
supplementary materials sup-2 Refinement All H atoms were placed in calculated positions, with C-H = 0.93 Å, U iso = 1.2U eq (C) for aromatic and CH and C-H = 0.96 Å, U iso = 1.5U eq (C) for CH 3 atoms. A rotating group model was used for the methyl groups. The highest residual electron density peak is located at 0.22 Å from C3 and the deepest hole is located at 0.20 Å from S1. Fig. 1. The molecular structure of the title compound, showing 50% probability displacement ellipsoids and the atom-numbering scheme.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 120.0 (1) K. 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 Rfactors(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq S1 0.249987 (