A second polymorph of (2E)-1-(4-fluoro­phen­yl)-3-(3,4,5-trimethoxy­phen­yl)prop-2-en-1-one

The crystal structure of the title compound, C(18)H(17)FO(4), reported here is a polymorph of the structure first reported by Patil et al. [Mol. Cryst. Liq. Cryst. Sci. Technol. Sect. A (2007), 461, 123–130]. It is a chalcone analog and consists of substituted phenyl rings bonded at the opposite ends of a propenone group, the biologically active region. The dihedral angle between the mean planes of the aromatic rings within the 4-fluoro­phenyl and trimethoxy­phenyl groups is 28.7 (1)° compared to 20.8 (6)° in the published structure. The angles between the mean plane of the prop-2-ene-1-one group and the mean plane of aromatic rings within the 4-fluoro­phenyl and trimethoxy­phenyl groups are 30.3 (4) and 7.4 (7)°, respectively, in contast to 10.7 (3) and 12.36° for the polymorph. While the two 3-meth­oxy groups are in the plane of the trimeth­oxy-substituted ring, the 4-meth­oxy group is in a synclinical [−sc = −78.1 (2)°] or anti­clinical [+ac = 104.0 (4)°] position, compared to a +sc [53.0 (4)°] or −ac [−132.4 (7)°] position. While no classical hydrogen bonds are present, weak inter­molecular C—H⋯π-ring inter­actions are observed which contribute to the stability of the crystal packing. The two polymorphs crystallize in the same space group, P2(1)/c, but have different cell parameters for the a, b and c axes and the β angle. A comparison of the mol­ecular geometries of both polymorphs to a geometry optimized density functional theory (DFT) calculation at the B3-LYP/6–311+G(d,p) level for each structure provides additional support to these observations.