Crystal structure of Pigment Red 254 from X-ray powder diffraction data.

The crystal structure of Pigment Red 254 [P.R. 254, CHClNO; systematic name: 3,6-bis-(4-chloro-phen-yl)-2,5-di-hydro-pyrrolo-[3,4-]pyrrole-1,4-dione] was solved from laboratory X-ray powder diffraction data using the simulated annealing method followed by Rietveld refinement because the very low solubility of the pigment in all solvents impedes the growth of single crystals suitable for X-ray analysis. The mol-ecule lies across an inversion center. The dihedral angle between the benzene ring and the pyrrole ring in the unique part of the mol-ecule is 11.1 (2)°. In the crystal, mol-ecules are linked N-H⋯O hydrogen bonds, forming chains along [110] incorporating (8) rings.