Average structures of the disordered β-phase of Pigment Red 170: a single-crystal X-ray diffraction study

Single-crystal X-ray diffraction of the β-phase of Pigment Red 170 reveals lines of strong diffuse scattering indicating severe layer stacking disorder. An attempt to deduce an average structure resulted in two plausible solutions, thus challenging the concept of an average structure for this material.

Explanation of the stacking disorder in the β-phase of Pigment Red 170

Possible stacking sequences of this organic layer structure were derived by order–disorder theory. Lattice-energy minimizations revealed local structures and stacking probabilities, and explained the disorder and the diffuse scattering observed by X-ray single-crystal, powder and electron diffraction.

Structure determination from powder data without prior indexing, using a similarity measure based on cross-correlation functions

A method was developed and implemented for fitting a crystal structure to a powder pattern, even if the lattice parameters deviate strongly. The method is even successful for powder diagrams of very low quality. Applications include an automatic fit starting from predicted structures or isostructural compounds.