02.03.2013 Views

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 ...

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

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

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!