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Volume 136, 2007
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An examination of polymorphic stability and molecular conformational flexibility as a function of crystal size associated with the nucleation and growth of benzophenone

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Abstract

The polymorphic behaviour of the aromatic ketone, benzophenone, which is a conformationally flexible molecule and forms crystal structures dominated by van der Waals intermolecular interactions, is examined. Crystallization of this material from the undercooled molten state yields the two known polymorphic forms, i.e. the stable α-form and the metastable β-form. The relative, energetic stabilities are examined using both crystal lattice and molecular conformational modelling techniques. Examination of nano-sized faceted molecular clusters of these forms, with cluster sizes ranging from 3 to 100 molecules, reveals that at very small cluster size (<5 molecules) the relative energetic stability of clusters representative for the two forms become very similar, indicating that for high melting undercooling (i.e. small critical cluster size for nucleation) crystallization of the metastable β-phase becomes more likely. Detailed analysis of the variation in molecular conformations within the simulated molecular clusters reveals more disordered three-dimensional structures at small compared to larger cluster sizes. The conformational disorder was found to be higher for the metastable β-form. This observation, together with the lower stability of clusters for this form is indicative of the difficulty in achieving crystallization of the metastable β-form from the melt, which requires a considerable undercooling.

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Publication details

The article was received on 20 Nov 2006, accepted on 29 Jan 2007 and first published on 08 May 2007


Article type: Paper
DOI: 10.1039/B616757H
Faraday Discuss., 2007,136, 91-106

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    An examination of polymorphic stability and molecular conformational flexibility as a function of crystal size associated with the nucleation and growth of benzophenone

    R. B. Hammond, K. Pencheva and K. J. Roberts, Faraday Discuss., 2007, 136, 91
    DOI: 10.1039/B616757H

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