On the polymorphism of aspirin: Crystalline aspirin as intergrowths of two "polymorphic" domains

Angewandte Chemie - International Edition

Volumn 46, Issue 4, 2007, Pages 618-622

  Bond, Andrew D ^a   Boese, Roland ^b   Desiraju, Gautam R ^c  

^a UNIVERSITY OF SOUTHERN DENMARK   (Denmark)

^b UNIVERSITY OF DUISBURG ESSEN   (Germany)

^c UNIVERSITY OF HYDERABAD   (India)

Author keywords

Aspirin; Polymorphism; Polytypism; Stacking fault; X ray crystallography

Indexed keywords

CRYSTAL GROWTH; CRYSTALLIZATION; STACKING FAULTS; X RAY CRYSTALLOGRAPHY;

ASPIRIN; POLYMORPHISM; POLYTYPISM;

DRUG PRODUCTS;

ACETYLSALICYLIC ACID;

ARTICLE; CHEMICAL STRUCTURE; CHEMISTRY; CRYSTALLIZATION; HYDROGEN BOND; X RAY CRYSTALLOGRAPHY;

ASPIRIN; CRYSTALLIZATION; CRYSTALLOGRAPHY, X-RAY; HYDROGEN BONDING; MOLECULAR STRUCTURE;

EID: 33846505562     PISSN: 14337851     EISSN: None     Source Type: Journal    
DOI: 10.1002/anie.200603373     Document Type: Article

References (38)

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7. -1 lower in energy than the established crystal structure, and in our opinion this value is so small that the order of energies might just as easily have been reversed.
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9. int = 0.029), 1149 observed reflections, R1(I>2σ(I)) = 0.041, wR2(all data) = 0.116, S = 1.02. CCDC-617840 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.ca-m.ac.uk/ data_request/cif.
10. Compared to the powder X-ray diffraction pattern of pure form I, the principal features that reveal the presence of form II domains are peaks at 2θ ≈ 20.9 and 26.0° (at 295 K, see the Supporting Information).
11. int = 0.059), 2586 observed reflections, R1(I>2σ(I)) = 0.042, wR2(all data) = 0.119, S = 1.04. CCDC-618012 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif
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20. In crystallographic parlance, the Bragg reflections with even l are referred to as "family reflections" and are common to both the form I and form II structures. The family reflections alone define a "superposition structure", which in the case of aspirin comprises two O-H⋯O dimers overlaid in a unit cell with c dimension half that of the true c dimension. The distribution of the intensities along the odd l rows contains the information to decompose the superposition structure into chemically reasonable arrangements, that is, the information regarding the particular sequence of the O-H⋯O layers. See Ref. [12].
21. Neglecting any diffuse scattering is clearly a simplification. However, the procedures that we describe have the advantage that they are standard (that is, they are based only on procedures used for routine crystallographic analyses), require no specialist knowledge, and can be applied in any crystallographic laboratory.
22. The term "form II data set" refers to the list of intensities (the hkl file) that is obtained when the diffraction data are indexed on the basis of the form II unit cell and integrated using standard procedures. The additional Bragg reflections that could be described on the basis of the form I unit cell and any diffuse features are ignored. The term "form I data set" refers to the opposite situation.
23. In particular, there may be problems associated with assessment of the background intensity in the presence of diffuse streaks in the vicinity of the Bragg reflections.
24. 2 data. The Figure provides an immediate approximate guide, based on standard refinement procedures. Application of the batch refinement procedure will provide an improved estimate.
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26. Since interlayer arrangements A and B are structurally and energetically so finely balanced, disorder is thermodynamically inherent in the aspirin system. All aspirin crystals should contain some of arrangements A and B at real temperatures. They are detectable by X-ray diffraction only when their number becomes significant.
27. In general, for any system of hydrogen bonds (O-H⋯O or C-H⋯O) wherein the dimer and catemer alternatives are well matched, there is a consensus that the catemer is kinetically favored since it is a higher dimensional pattern than the dimer. See: D. Das, G. R. Desiraju, Chem. Asian J. 2006, 1, 231.
28. PZ have reported that "form II" transforms into form I at 100 K. Our assessment of the stability of the form II domains is based on re-collection of single-crystal data for 1b after the crystal had stood in air for two months.
29. Co-crystal: a) G. R. Desiraju, CrystEngComm 2003, 5, 466;
30. b) J. D. Dunitz, CrystEngComm 2003, 5, 468.
31. Pseudopolymorph: c) K. R. Seddon, Cryst. Growth Des. 2004, 4, 1088;
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34. f) A. Nangia, Cryst. Growth Des. 2006, 6, 1.
35. However, one of us has argued (in Ref. [23d]) that difficulties in the use of the word "pseudopolymorph" might have arisen because the definition of the term "polymorph" is too rigid with respect to identity of chemical composition among substances that are deemed to qualify for the polymorph epithet.
36. To some extent, this situation parallels that of isomorphous crystalline solvates, for which patents have been granted for ranges of solvent content. However, while variable solvent content is a common occurrence, it is not clear how common the aspirin situation will be.
37. A. R. Verma, P. Krishna, Polymorphism and Polytypism in Crystals, Wiley, New York, 1966.
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