Crystal-structure determination of the fluorescent bisazomethine pigment C36H26N4O4 from X-ray powder data

The compound C36H26N4O4, a derivative of Pigment Yellow 101, is one of the few organic pigments that show fluorescence in the solid state. Since single crystals could not be grown, the structure was determined from powder data. The X-ray powder pattern could be indexed with an orthorhombic unit cell. The space group remained ambiguous. The crystal structure was solved by lattice energy minimisation in different space groups using the program CRYSCA. Subsequently, the structure was refined by the Rietveld method using restraints. The compound crystallises in a herringbone pattern in Pbcn with a = 30.117(1) Å, b = 9.723(2) Å, c = 9.511(3) Å, Z = 4 with the molecule on an inversion centre. The insolubility and the solid-state fluorescence can be explained from the crystal structure.