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A dynamic thermal ATR-FTIR/chemometric approach to the analysis of polymorphic interconversions. Cimetidine as a model drug. J Pharm Biomed Anal 2014; 92:90-7. [DOI: 10.1016/j.jpba.2013.12.036] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2013] [Revised: 12/21/2013] [Accepted: 12/27/2013] [Indexed: 11/20/2022]
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Arakcheeva A, Pattison P, Bauer-Brandl A, Birkedal H, Chapuis G. Cimetidine, C10H16N6S, form C: crystal structure and modelling of polytypes using the superspace approach. J Appl Crystallogr 2013. [DOI: 10.1107/s0021889812048133] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
The H2 antagonist cimetidine forms many polymorphs, several of which have resisted structural analysis thus far. Using single-crystal X-ray measurements obtained from synchrotron radiation, the crystal structure of cimetidine form C has been solved. This layered structure crystallizes in space groupC2/cwith an unusually large lattice parameter,a= 82.904 Å. The thickness of each layerLis equal toa′ =a/6 = 13.82 Å, anda= 6a′ originates from a sixfoldLLLL′L′L′ sequence withLandL′ differing by 0.5b. This packing is reminiscent of polytypic stacking in metals. A (3 + 1)-dimensional superspace model is derived and used to explain and predict many polytypic modifications. This model is characterized by (i) the (3 + 1)-dimensional symmetry groupX2/c(α0γ)00, whereX= 0\textstyle{1 \over 2}0\textstyle{1 \over 2}; (ii) the lattice parametera′ and modulation vectorq= 1/n(a′*); (iii) the atomic positions of a single molecule of cimetidine form C; (iv) the primary variable, 1/n. The model reproduces the previously solved structure, the 6M polytype, and generates the related polytypesnM with lattice parameteranM =na′ forn= 1, 2, 3, 4 and 5. A comparison of powder X-ray diffraction patterns available for cimetidine form C with those simulated for thenM polytypes suggests that the powder samples published previously probably contain a mixture of various polytypes.
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