Crystal structure of the chalcone (E)-3-(furan-2-yl)-1-phenylprop-2-en-1-one

The crystal packing of the compound is described by an intermolecular arrangement with the molecules as interlaced layers in a zigzag fashion, denoting interacting self-complementary dimers mainly by the localization of weak hydrogen bonds in a head-to-tail arrangement.

Many studies have shown that chalcone derivatives exhibit a wide range of pharmacological activities, such as potential cytotoxic, antimicrobial, antiviral, anti-inflammatory, antioxidant, anaesthetic, antimalarial, antileishmanial, antitubercular, antitumor and anticancer activities (Boeck et al., 2006;Chimenti et al., 2010;Elarfi & Al-Difar, 2012;Hamada & Sharshira, 2011;Hsieh et al., 2000;Kumar et al., 2003;Sharma et al., 2013). These versatile compounds and their furan derivatives are often used as intermediates in the syntheses of monoamine oxidase (MAO) inhibitors; moreover, the chalcones themselves have MAO inhibitory activity. Since the furan moiety represents a high -electron density that contributes to the interaction with the flavin nucleus of the cofactor in the inhibition of MAO, some furan-substituted chalcones, where an electron-rich heterocyclic oxygen replaces the benzene ring, have been synthesized to investigate their biological activity (Robinson et al., 2013;Shaikh et al., 2014;Sharma et al., 2013;Zheng et al., 2011). In view of the varied biological and pharmacological applications, we report ISSN 2056-9890 herein on the synthesis and the molecular and supramolecular structure of the title compound, synthesized by a conventional base-catalysed Claisen-Schmidt condensation reaction.

Structural commentary
The symmetry-independent molecule adopts an E conformation corresponding to an ,-unsaturated non-planar structure, which bridges the pair of aromatic groups (Fig. 1). The two main planar groups, the furanyl and the phenyl rings, form a dihedral angle of 24.07 (7) . In this context, the molecular structure can be considered, for descriptive purposes, as two fragments basically described by the furanyl acryloyl and the benzoyl moieties. The benzoyl group shows a non-planar structure and presents rotation when observing the C2-C1-C7-O2 torsion angle of 19.4 (2) , denoting a marked deviation from planarity at the C1-C7 bond, a single bond with rotational freedom. This deviation from planarity has also been reported previously in the crystal structure of an (E)-3-(4-hydroxyphenyl)-1-(4-methoxyphenyl)-prop-2-en-1-one derivative, when observing the analogous reported interplanar angle shown in the respectively 4-methoxybenzoyl moiety (Qiu et al., 2006). In the same manner, the furanyl acryloyl entity presents a quasi-planar structure indicated by the two small torsion angles O2-C7-C8-C9 [À5.4 (2) ] and C7-C8-C9-C10 [À176.31 (13) ], similar to the structure of the difuranyl chalcone derivative (E)-1,3-di(2-furyl)-2-propen-1one (Ocak Iskeleli et al., 2005b). On the other hand, the molecule interatomic linkage coincides with similar reported structures, specifically in the ,-unsaturated entity of the title crystal (Harrison et al., 2006;Ocak Iskeleli et al., 2005a,b). As a result, the interatomic distances are in agreement with the conjugative nature, which is additionally supported by other described types of different weak interactions (vide infra) and also define the characteristic quasi-planar structure of chalcone derivatives.

Supramolecular features
The crystal packing does not present geometrical parameters corresponding to classical hydrogen bonding (Gilli & Gilli, 2009;Steiner, 2002), neither intra-nor intermolecular. In the crystal, centrosymmetrically related molecules interact through a pair of weak hydrogen contacts (Table 1) with the C9 and C11 carbon atoms as donors and the O2 oxygen atom as a bifurcated acceptor, generating a ring with an R 1 2 (6) graph-set motif (Bernstein et al., 1995). The reciprocal interactions with the corresponding molecule positioned in a headto-tail mode generate the same ring motif and, as a consequence, an R 2 2 (10) ring is formed, describing a three-fused-ring system (Fig. 2). In addition, a weak hydrogen contact is present involving the C3 carbon atom as H-donor and the O2 oxygen atom acting, in this way, as a trifurcated acceptor. The propagation of this interaction generates a ribbon along the c-axis direction (Fig. 2). The supramolecular assembly is additionally supported by weak C-HÁ Á Á interactions, implicating the phenyl and furanyl systems (Fig. 3).

Synthesis and crystallization
To a solution of NaOH (2.18 g, 55 mmol) in H 2 O/EtOH (30 ml, 2:1 v/v) was added pure acetophenone (5. The molecular structure of the title compound, with displacement ellipsoids drawn at the 30% probability level. Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
A partial packing diagram of the title compound, showing the hydrogenbonded supramolecular assembly via C-HÁ Á ÁO interactions (blue dashed lines).
43 mmol), and stirring started; furfuraldehyde (4.6 g, 43 mmol) was then added at once. The reaction mixture was stirred for two hours and then kept in a refrigerator overnight.

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms attached to C atoms were placed in geometrically idealized positions and refined as riding on their parent atoms, with C-H = 0.95 Å and with U iso (H) = 1.2U eq (C).

Figure 3
A partial packing diagram of the title compound, showing the C-HÁ Á Á stacking interactions, depicted as blue and purple dotted lines for the C6-H6Á Á ÁCg1 and C13-H13Á Á ÁCg2 contacts, respectively. H atoms not involved in hydrogen-bonding interactions have been omitted for clarity.