Orientational disorder of monomethyl-quinacridone investigated by Rietveld refinement, structure refinement to the pair distribution function and lattice-energy minimizations

Abstract

The crystal structure of the organic pigment 2-monomethyl-quinacridone (Pigment Red 192, C 21 H 14 N 2 O 2 ) was solved from X-ray powder diffraction data. The resulting average structure is described in space group P1, Z = 1 with the molecule on the inversion centre. The molecules are arranged in chains. The molecules, which have no inversion symmetry, show orientational head-to-tail disorder. In the average structure, the methyl group is disordered and found on both ends of the molecule with an occupancy of 0.5 each. The disorder and the local structure were investigated using various ordered structural models. All models were analysed by three approaches: Rietveld refinement, structure refinement to the pair distribution function (PDF) and lattice-energy minimization. All refinements converged well. The Rietveld refinement provided the average structure and gave no indication of a long-range ordering. The refinement to the PDF turned out to be very sensitive to small structural details, giving insight into the local structure. The lattice-energy minimizations revealed a significantly preferred local ordering of neighbouring molecules along the [0 1 11] direction. In conclusion, all methods indicate a statistical orientational disorder with a preferred parallel orientation of molecules in one direction. Additionally, electron diffraction revealed twinning and faint diffuse scattering. research papers Acta Cryst. (2020). B76, 353-365 Carina Schlesinger et al. Orientational disorder of monomethyl-quinacridone 365

Structural Analysis of Molecular Materials Using the Pair Distribution Function

“…In such cases, insights can be gained by comparison with related crystalline forms such as for p -terphenyl and cyclohexane . Head-to-tail disorder of molecules was studied for the case of 2-monomethyl-quinacridone (Pigment Red 192) . A preferred local orientational ordering of molecules was observed along one diagonal direction, in agreement with theoretical calculations.…”

“…488 Head-to-tail disorder of molecules was studied for the case of 2-monomethyl-quinacridone (Pigment Red 192). 489 A preferred local orientational ordering of molecules was observed along one diagonal direction, in agreement with theoretical calculations.…”

3Delectron diffraction for structure determination of small‐molecule nanocrystals: A possible breakthrough for the pharmaceutical industry

“…In the case of the organic pigment 2-monomethyl-quinacridone, the faint diffuse scattering streaks were instead connected with the presence of two twinned domains. The domains share one common axis and the diffuse scattering is always associated with the smaller and weakly scattering one (Schlesinger et al, 2020).…”

Kristallstrukturbestimmung organischer Verbindungen mittels Röntgenbeugungsmethoden : Vergleich, Grenzen und Kombination

“…Fehlordnung durch Anpassung an die PDF bestimmt werden konnte. [CS07] Große Erfolge konnten bei der Methodenentwicklung der PDF-Analyse erzielt werden. Die Raumgruppe.…”