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, C18H17FO4, 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)degrees compared to 20.8 (6)degrees 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)degrees,respectively, in contast to 10.7 (3) and 12.36 degrees 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)degrees] or anticlinical [+ac = 104.0 (4)degrees] position, compared to a +sc [53.0 (4)degrees] or -ac [-132.4 (7)degrees] position. While no classical hydrogen bonds are present, weak intermolecular C-H center dot center dot center dot pi-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 beta 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.