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Crystal structure prediction of organic pigments: quinacridone as an example.

Panina N, Leusen FJ, Janssen FF, Verwer P, Meekes H, Vlieg E, Deroover G - J Appl Crystallogr (2007)

Bottom Line: After generation and energy minimization of the possible structures, their powder patterns were compared with the experimental ones.Three possible structures for the beta polymorph are proposed on the basis of X-ray powder patterns comparison.It is shown that the alpha structure in the Cambridge Structural Database is likely to be in error, and a new alpha structure is proposed.

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ABSTRACT
The structures of the alpha, beta and gamma polymorphs of quinacridone (Pigment Violet 19) were predicted using Polymorph Predictor software in combination with X-ray powder diffraction patterns of limited quality. After generation and energy minimization of the possible structures, their powder patterns were compared with the experimental ones. On this basis, candidate structures for the polymorphs were chosen from the list of all structures. Rietveld refinement was used to validate the choice of structures. The predicted structure of the gamma polymorph is in accordance with the experimental structure published previously. Three possible structures for the beta polymorph are proposed on the basis of X-ray powder patterns comparison. It is shown that the alpha structure in the Cambridge Structural Database is likely to be in error, and a new alpha structure is proposed. The present work demonstrates a method to obtain crystal structures of industrially important pigments when only a low-quality X-ray powder diffraction pattern is available.

No MeSH data available.


Powder patterns of structures 8, 9, 10, 11 and 12 of Table 1 ▶ compared with the experimental powder pattern of α-QA.
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fig11: Powder patterns of structures 8, 9, 10, 11 and 12 of Table 1 ▶ compared with the experimental powder pattern of α-QA.

Mentions: Several structures, with numbers 8–12 in Table 1 ▶, are predicted by the PP to have powder patterns similar to the experimental one (Fig. 11). Structures 8–11 are triclinic, space group . Each quinacridone molecule shares hydrogen bonds with two neighbours, forming ribbons similar to those in β-QA, along [100]. These are packed in such a manner that all molecules in the structure lie parallel to one another (Fig. 10 ▶ ▶). Structure 12 is monoclinic, space group , and it has a different packing motif. Crystallization of centrosymmetric molecules in a non-centrosymmetric space group is, however, very rare.


Crystal structure prediction of organic pigments: quinacridone as an example.

Panina N, Leusen FJ, Janssen FF, Verwer P, Meekes H, Vlieg E, Deroover G - J Appl Crystallogr (2007)

Powder patterns of structures 8, 9, 10, 11 and 12 of Table 1 ▶ compared with the experimental powder pattern of α-QA.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2483485&req=5

fig11: Powder patterns of structures 8, 9, 10, 11 and 12 of Table 1 ▶ compared with the experimental powder pattern of α-QA.
Mentions: Several structures, with numbers 8–12 in Table 1 ▶, are predicted by the PP to have powder patterns similar to the experimental one (Fig. 11). Structures 8–11 are triclinic, space group . Each quinacridone molecule shares hydrogen bonds with two neighbours, forming ribbons similar to those in β-QA, along [100]. These are packed in such a manner that all molecules in the structure lie parallel to one another (Fig. 10 ▶ ▶). Structure 12 is monoclinic, space group , and it has a different packing motif. Crystallization of centrosymmetric molecules in a non-centrosymmetric space group is, however, very rare.

Bottom Line: After generation and energy minimization of the possible structures, their powder patterns were compared with the experimental ones.Three possible structures for the beta polymorph are proposed on the basis of X-ray powder patterns comparison.It is shown that the alpha structure in the Cambridge Structural Database is likely to be in error, and a new alpha structure is proposed.

View Article: PubMed Central - HTML - PubMed

ABSTRACT
The structures of the alpha, beta and gamma polymorphs of quinacridone (Pigment Violet 19) were predicted using Polymorph Predictor software in combination with X-ray powder diffraction patterns of limited quality. After generation and energy minimization of the possible structures, their powder patterns were compared with the experimental ones. On this basis, candidate structures for the polymorphs were chosen from the list of all structures. Rietveld refinement was used to validate the choice of structures. The predicted structure of the gamma polymorph is in accordance with the experimental structure published previously. Three possible structures for the beta polymorph are proposed on the basis of X-ray powder patterns comparison. It is shown that the alpha structure in the Cambridge Structural Database is likely to be in error, and a new alpha structure is proposed. The present work demonstrates a method to obtain crystal structures of industrially important pigments when only a low-quality X-ray powder diffraction pattern is available.

No MeSH data available.