198 Topics in Current Chemistry Editorial Board: A. de Meijere KN ...

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186 M.R. Caira schematically in Fig. 9. We obtained crystals of a second polymorph of sulphamerazine [110] by recrystallization from methanol and established the space group as Pn2 1a, Z=8. This form contains the same hydrogen bonded motif as shown in Fig. 9, but it is pseudo-centrosymmetric. The two polymorphs are distinguishable from IR spectra, the form containing the centrosymmetric dimer (with only one unique N-H◊◊◊N hydrogen bond) yielding only one IR peak (3453 cm –1 ) assignable ton asNH whereas that containing the pseudo-centrosymmetric dimer (with two distinct N-H◊◊◊N hydrogen bonds) displayed a doublet (3493, 3478 cm –1 ). We recently reported FT-IR spectral data for seven crystalline forms of the androgen dehydroepiandrosterone [111], showing that differences in both fine structure and in the locations and intensities of major absorption bands can be used to distinguish them. X-ray crystal structures of three forms were determined [112], Form I (a polymorph), Form S1 (a 4 : 1 hydrate) and Form S4 (a methanol half-solvate). Form I (space group P2 1, Z=4) contains infinite chains of steroid molecules linked head-to-tail (shown schematically in Fig. 10) by two crystallographically distinct intermolecular O-H◊◊◊O=C hydrogen bonds, consistent with two observed O-H stretching bands (3501, 3458 cm –1 ). Doublets for the O-H absorption bands observed also in both Forms S1 and S4 can be correlated with distinct O-H ◊◊◊O hydrogen bonds observed by X-ray analysis, and specifically, with unusual “flip-flop” hydrogen bonding in Form S4. In this study, attempts to determine the thermodynamic relationships between the various polymorphic forms were based partly on the application of Burger’s IR rule [107] which relates IR band positions to relative stabilities. The use of IR-spectra to distinguish polymorphs from pseudopolymorphs of the same parent compound, or to distinguish pseudopolymorphs containing different solvents, is relatively straightforward, since solvent molecules which are commonly incorporated in pseudopolymorphic crystals (e.g. water, ketones, alcohols) will exhibit their own characteristic absorption bands. IR spectroscopy was used to distinguish polymorphs of the antidiabetic drug glibenclamide from its solvates with pentanol and toluene [113]. Pseudopolymorphs of the Fig. 9. Schematic representation of the hydrogen bonded dimer occurring in two polymorphs of sulphamerazine
Crystalline Polymorphism of Organic Compounds 187 compound gossypol (a toxic constituent of cotton-seed) obtained from three different solvents showed characteristic differences in their IR spectra in the 3500 cm –1 region [114]. Pseudopolymorphs of a host containing the same guest in different molar ratios are also known.An alicyclic diol of the helical tubuland family [115] forms two crystallographically distinct lattice inclusion complexes with 1,2-dichlorobenzene having host-guest ratios of 4:1 and 3:1 [116]. These were readily distinguished from their IR spectra in the fingerprint region. The spectral techniques available for the characterization of polymorphs and solvates have been reviewed [27] and the merits of FT-IR spectroscopy for the acquisition of high-quality spectra have been stressed. The review also lists drug substances whose polymorphism has been investigated by IR-spectroscopy. Another recent review on the use of the IR method to investigate polymorphism is based on spectra for a derivative of sulphadoxine as a model compound [21]. Dynamic aspects of polymorphism are also amenable to study by IR spectroscopy. The effect of hydrogen bonding on the lattice dynamics, polymorphism, mesomorphism and phase tranformations of long-chain carboxylic acids as gauged from IR spectra has recently been reported [117]. A relatively new trend is the application of near-IR spectroscopy for compound identification and quantitation in many industrial environments including chemical processing and food science. The advantages of near-IR over conventional IR spectroscopy for the investigation of polymorphs have been described [118]. A fast, sensitive pattern recognition method for identifying a polymorph and determining its quality using near-IR spectra has been developed [119]. Pattern recognition methods involve training a computer to recognize spectra of acceptable samples of a material and to reject unacceptable ones by multivariate statistical analyses. This study showed that the method described can discriminate between the desired polymorph and other crystalline forms, the statistical results indicating that levels as low as 2% of an adulterating polymorph may be reliably detected. The authors maintain that the near-IR method, which can be automated, provides a reliability comparable to that of XRD for polymorphic identification but is likely to be less costly to implement. There is a growing interest in the use of Raman spectroscopy for studying polymorphism and pseudopolymorphism [27]. The Raman technique has recently been used to distinguish two triclinic polymorphs of terephthalic acid [120] and, in combination with IR spectroscopy, to study the conformational polymorphism of 1-bromopentane [121]. Fig. 10. Head-to-tail hydrogen bonding in Form I of dehydroepiandrosterone. A and B are crystallographically distinct and distances are in Å
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198 Topics in Current Chemistry Edi
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Design of Organic Solids Volume Edi
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Volume Editors Prof. Dr. Edwin Webe
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VIII preface tion at an amazing lev
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Contents of Volume 196 Carbon Rich
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2 J.P. Glusker 5 Interactions of Pl
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4 J.P. Glusker Perturbations to the
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6 J.P. Glusker 2.1 Sources of Cryst
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8 J.P. Glusker other induced, will
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10 J.P. Glusker The forces here hav
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12 J.P. Glusker lographic structure
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14 J.P. Glusker a c Fig. 6 a - c. D
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16 J.P. Glusker hydrogen bond H◊
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18 J.P. Glusker Fig. 9. Citric acid
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20 J.P. Glusker peptide plane and a
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22 J.P. Glusker 4.5 F◊◊◊H Int
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24 J.P. Glusker rine-containing com
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26 J.P. Glusker Fig. 17. The packin
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28 J.P. Glusker bind to a metal ion
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30 J.P. Glusker As for carboxylate
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32 J.P. Glusker Fig. 24. The magnes
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34 J.P. Glusker structures of magne
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36 J.P. Glusker b a Fig. 28 a, b. A
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38 J.P. Glusker Fig. 30. Complexati
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40 J.P. Glusker 7.1 Descriptions of
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42 J.P. Glusker Fig. 34. Glycine cr
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44 J.P. Glusker bonding capabilitie
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46 J.P. Glusker 2. Non-intercalativ
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48 J.P. Glusker d Fig. 37 d. The ch
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50 J.P. Glusker Fig. 39. Hydrogen-b
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52 J.P. Glusker 72, 104], but other
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54 J.P. Glusker 23. Cody V, Murray-
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56 J.P. Glusker: Directional Aspect
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58 A. Nangia · G.R. Desiraju 7 Sup
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60 A. Nangia · G.R. Desiraju elect
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62 A. Nangia · G.R. Desiraju 14 15
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64 A. Nangia · G.R. Desiraju [23]
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66 A. Nangia · G.R. Desiraju struc
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68 A. Nangia · G.R. Desiraju Fig.
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70 A. Nangia · G.R. Desiraju -NH 2
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74 A. Nangia · G.R. Desiraju and r
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76 A. Nangia · G.R. Desiraju bonds
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86 A. Nangia · G.R. Desiraju PYRAZ
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88 A. Nangia · G.R. Desiraju napht
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92 A. Nangia · G.R. Desiraju all a
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94 A. Nangia · G.R. Desiraju 42. J
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132 Y. Aoyama 4 Catalysis . . . . .
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