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Polimorfas inducidas por dipolos del ácido trans-2-hidroxicicloheptanecarboxílico con prácticamente la misma unidad
Alajos Kálmán1, László Fábián, Gyula Argay
1Institute of Chemistry, Chemical Research Center, Hungarian Academy of Sciences, P.O. Box 17, Budapest 114, H-1525, Hungary. akalman@chemres.hu
Journal of the American Chemical Society
|January 8, 2003
Resumen
Los polimorfos del ácido trans-2-hidroxicicloheptanecarboxílico exhiben sutiles diferencias estructurales, lo que lleva a un único apilamiento de cristales y arreglos dipolo. Los cristales puros de la forma I no pueden aislarse debido a la interpenetración con la forma II.
Área de la Ciencia:
- La cristalografía es una técnica de cristalografía.
- Química del estado sólido.
Sus antecedentes:
- El polimorfismo en las moléculas orgánicas presenta desafíos en la ciencia de los materiales.
- Comprender el empaque de cristales es crucial para predecir las propiedades de los materiales.
Objetivo del estudio:
- Para investigar las diferencias estructurales entre los polimorfos del ácido trans-2-hidroxicicloheptanocarboxílico.
- Para dilucidar la relación entre la estructura cristalina y el comportamiento del dipolo.
Principales métodos:
- Cristalografía de rayos X para determinar las estructuras cristalinas.
- Análisis de grupos espaciales y parámetros de celosía.
- Investigación de las redes de enlaces de hidrógeno y los arreglos moleculares.
Principales resultados:
- Parámetros de red idénticos para ambos polimorfos, imitando el isomorfismo.
- Distintos grupos espaciales (Pn21 para el formulario II, Pn21a para el formulario I) dictan el empaque de cristales.
- La Forma II exhibe el apilamiento de capas antiparalelas, cancelando los dipolos de células unitarias.
- La forma I muestra el apilamiento de capas paralelas, con dominios antiparalelas que anulan los dipolos.
- Intercrecimiento de la forma II dentro de la forma I observado en los límites del dominio.
Conclusiones:
- La forma pura I del ácido trans-2-hidroxicicloheptanecarboxílico no puede ser aislada debido a la co-cristalización con la forma II.
- La proporción de la forma II dentro de la forma I puede variar entre cristales, lo que afecta las propiedades macroscópicas.
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