198 Topics in Current Chemistry Editorial Board: A. de Meijere KN ...
198 Topics in Current Chemistry Editorial Board: A. de Meijere KN ...
198 Topics in Current Chemistry Editorial Board: A. de Meijere KN ...
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Crystall<strong>in</strong>e Polymorphism of Organic Compounds<br />
M<strong>in</strong>o R. Caira<br />
Department of <strong>Chemistry</strong>, University of Cape Town, Ron<strong>de</strong>bosch 7700, South Africa.<br />
E-mail: xraym<strong>in</strong>o@psipsy.uct.ac.za<br />
Crystal polymorphism is encountered <strong>in</strong> all areas of research <strong>in</strong>volv<strong>in</strong>g solid substances. Its<br />
occurrence <strong>in</strong>troduces complications dur<strong>in</strong>g manufactur<strong>in</strong>g processes and adds another<br />
dimension to the complexity of <strong>de</strong>sign<strong>in</strong>g materials with specific properties. Research on<br />
polymorphism is fraught with unique difficulties due to the subtlety of polymorphic transformations<br />
and the <strong>in</strong>advertent formation of pseudopolymorphs. In this report, a summary of<br />
thermodynamic, k<strong>in</strong>etic and structural consi<strong>de</strong>rations of polymorphism is presented. A wi<strong>de</strong><br />
variety of techniques appropriate to the study of organic crystall<strong>in</strong>e polymorphism and pseudopolymorphism<br />
is then surveyed, rang<strong>in</strong>g from simple crystal <strong>de</strong>nsity measurement to<br />
observation of polymorphic transformations us<strong>in</strong>g variable-temperature synchrotron X-ray<br />
diffraction methods. Application of newer methodology <strong>de</strong>scribed <strong>in</strong> this report is yield<strong>in</strong>g<br />
fresh <strong>in</strong>sights <strong>in</strong>to the nature of the crystallization process, hold<strong>in</strong>g promise for a <strong>de</strong>eper<br />
un<strong>de</strong>rstand<strong>in</strong>g of the phenomenon of polymorphism and its practical control.<br />
Keywords: Crystal polymorphism, Pseudopolymorphism, Crystallization.<br />
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164<br />
2 Crystal Polymorphism – Theoretical Pr<strong>in</strong>ciples<br />
and Practical Implications . . . . . . . . . . . . . . . . . . . . . . . . 165<br />
2.1 Background – The Role of Polymorphism<br />
<strong>in</strong> the Production ofMaterials . . . . . . . . . . . . . . . . . . . . . . 165<br />
2.2 Crystallization and Polymorphic Transformations –<br />
Thermodynamic and K<strong>in</strong>etic Consi<strong>de</strong>rations . . . . . . . . . . . . . 166<br />
2.3 Polymorphism – Structural Consi<strong>de</strong>rations . . . . . . . . . . . . . . 171<br />
3 Methodology for the Study of Crystal Polymorphism . . . . . . . . . 177<br />
3.1 Review of Preparative Methods . . . . . . . . . . . . . . . . . . . . . 177<br />
3.2 Review of Investigative Methods . . . . . . . . . . . . . . . . . . . . . 180<br />
3.3 Polymorphic Systems and Polymorphic Changes – Case Studies . . . <strong>198</strong><br />
4 Towards Control of Polymorphism . . . . . . . . . . . . . . . . . . . 199<br />
4.1 The Need for Polymorphic Control . . . . . . . . . . . . . . . . . . . 199<br />
4.2 <strong>Current</strong> Strategies and Prognosis for Crystal Eng<strong>in</strong>eer<strong>in</strong>g . . . . . . 200<br />
5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204<br />
<strong>Topics</strong> <strong>in</strong> <strong>Current</strong> <strong>Chemistry</strong>, Vol. <strong>198</strong><br />
© Spr<strong>in</strong>ger Verlag Berl<strong>in</strong> Hei<strong>de</strong>lberg 1998