The Crystal Structure of the 2:1 Complex of Pyromellitic Dianhydride with trans-4-Methylstilbene

Abstract

Abstract The 2: 1 complex of pyromellitic dianhydride with trans-4-methylstilbene crystallizes in the Cc space group with four pyromellitic dianhydride molecules and two trans-4-methylstilbene molecules in a unit cell with dimensions of a=12.780, b=7.446, c=15.050 Å, and β=91.09°. In addition to the clearly-defined Laue spots, diffuse streaks elongated perpendicular to the molecular layers were observed with a half period of the b* axis of the reciprocal lattice. The structure was solved from a three-dimensional |E|2 Patterson synthesis and was refined by a block-diagonal least-squares method to the final R value of 0.13 for the visually-estimated 703 reflections. Refinement was difficult, however, because of the large correlation between parameters caused by the disorder. The crystal is built up of molecular layers stacked parallel to the (10\bar2) plane and is disordered in the stacking arrangement of the molecular layers. The pyromellitic dianhydride molecule and one of the benzene rings of the trans-4-methylstilbene molecule are alternately stacked plane-to-plane in infinite columns along [10\bar2]. The ethylene group of the trans-4-methylstilbene molecule joins the two columns. The molecular arrangement of the component molecules resembles those observed in the anthracene, pyrene, and perylene complexes with pyromellitic dianhydride and presents a striking contrast to that of the trans-stilbene complex. The interplanar distances range from 3.25 to 3.56 Å, smaller than that of the trans-stilbene complex.