Crystal structure of 1,3,4-triphenyl-pyrrole-2,5-dione.

withdrawing groups and an electron-donating group. The electron-withdrawing groups are further conjugated with a double bond in the ring. The light-absorption characteristics of the molecule are expected to be modified by changing the substituents attached to the molecule. This indicates that the molecule can be one of the basic components in designing functional dyes. It is therefore of particular interest to investigate the effects of various bulky substituents on the structure of the 1H-pyrrole-2,5-dione moiety. An X-ray analysis of the title compound (Fig. 1) has been undertaken in order to understand the effect caused by phenyl rings attached to the ring. A yellow prismatic crystal with dimensions of 0.4 × 0.4 × 0.4 mm was obtained from an acetone solution at 293(1)K, and was used for diffraction experiments. The crystal and experimental data are given in Table 1. The structure was solved by direct methods and refined by full-matrix least-squares methods with anisotropic temperature factors for the non-H atoms. All H atoms were found from different Fourier maps and were refined with isotropic temperature factors. The atomic parameters for non-hydrogen atoms are listed in Table 2. Selected bond distances and angles are listed in Table 3. An ORTEP III3 drawing of the title compound together with the atomic and ring numberings is shown in Fig. 2. The bond distances and angles within the phenyl rings are within the expected ranges. The molecule as a whole adopts a non-planar propeller structure, as shown in Fig. 2. The dihedral angles between the least-squares plane of ring I and those of rings II, III and IV are 41.0(1), 32.2(1), and 44.7(1) ̊, respectively. The pyrroline ring is essentially planar. The bond lengths and angles are similar to those in polycitrin A4 in which one phenetyl and two phenyl groups are bonded at the 1, 3, and 4 positions of 1H-pyrrole-2,5-dione. The bulky substituents of the phenyl groups at the 1, 3 and 4 positions make the C3–C4 1471 ANALYTICAL SCIENCES DECEMBER 2001, VOL. 17 2001 © The Japan Society for Analytical Chemistry