A second polymorph of (2E)-1-(4-fluoro-phen-yl)-3-(3,4,5-trimethoxy-phen- yl)prop-2-en-1-one

Abstract

The crystal structure of the title compound, C18H 17FO4, 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-fluoro-phenyl and trimethoxy-phenyl 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-fluoro-phenyl and trimethoxy-phenyl 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-meth-oxy groups are in the plane of the trimeth-oxy-substituted ring, the 4-meth-oxy group is in a synclinical [-sc = -78.1 (2)°] or anti-clinical [+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 inter-molecular C - H⋯π-ring inter-actions are observed which contribute to the stability of the crystal packing. The two polymorphs crystallize in the same space group, P21/c, but have different cell parameters for the a, b and c axes and the Β angle. A comparison of the mol-ecular 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. © 2009 Jasinski et al.