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Cocrystals help break the "rules" of isostructurality: solid solutions and polymorphism in the malic/tartaric acid system

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posted on 2018-03-05, 12:44 authored by Aurora J. Cruz-Cabeza, Monica Lestari, Matteo LusiMatteo Lusi
Crystalline solid solutions have the potential to afford tunable materials for pharmaceutical and technological applications. Unfortunately, these poorly understood phases are difficult to obtain and, hence, to study. In fact, commonly accepted empirical rules prescribe that only molecules of similar size and electron distribution are mutually soluble in the solid state. Here, despite the evident structural and electronic differences, the enantiomers of malic acid and tartaric acid are crystallized together in a variable stoichiometric ratio to produce both cocrystals and solid solutions. In some cases, physical mixtures are observed. The composition and polymorphism of the crystalline products are explained by DFT-d molecular substitution calculations for the cocrystallized molecules in different (known) structures. At the same time, from a crystal engineering perspective, the behavior of this complex system is rationalized thanks to the existence of intermediate cocrystal forms that merge the structural features of the pure molecular components.Crystalline solid solutions have the potential to afford tunable materials for pharmaceutical and technological applications. Unfortunately, these poorly understood phases are difficult to obtain and, hence, to study. In fact, commonly accepted empirical rules prescribe that only molecules of similar size and electron distribution are mutually soluble in the solid state. Here, despite the evident structural and electronic differences, the enantiomers of malic acid and tartaric acid are crystallized together in a variable stoichiometric ratio to produce both cocrystals and solid solutions. In some cases, physical mixtures are observed. The composition and polymorphism of the crystalline products are explained by DFT-d molecular substitution calculations for the cocrystallized molecules in different (known) structures. At the same time, from a crystal engineering perspective, the behavior of this complex system is rationalized thanks to the existence of intermediate cocrystal forms that merge the structural features of the pure molecular components.

Funding

Stellar Physics and Stellar Evolution

National Science Foundation

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History

Publication

Crystal Growth and Design;18 (2), pp. 855-863

Publisher

American Chemical Society

Note

peer-reviewed

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SFI

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© 2017 ACS This document is the Accepted Manuscript version of a Published Work that appeared in final form in Crystal Growth and Design copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/acs.cgd.7b01321

Language

English

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