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57Octametilferrocenio tetrafluoroborato etiquetado con Fe. Estructuras cristalinas de rayos X de isómeros
Herwig Schottenberger1, Klaus Wurst, Ulrich J Griesser
1Faculty of Chemistry and Pharmacy, University of Innsbruck, 6020 Innsbruck, Austria. herwig.schottenberger@uibk.ac.at
Journal of the American Chemical Society
|May 5, 2005
Resumen
El tetrafluoroborato de octametilferrocenio (OMFc (((+)) BF (((4) ((-)) exhibe un polimorfismo conformacional debido a una pequeña diferencia de energía en la red. A diferencia de OMFc neutro, OMFc ((+) BF ((4)) no muestra un aumento repentino en el movimiento del átomo de metal, lo que indica una dinámica distinta.
Área de la Ciencia:
- Química organometálica Química orgánica de los metales.
- Química del estado sólido.
- La cristalografía es una técnica de cristalografía.
Sus antecedentes:
- El tetrafluoroborato de octametilferrocenio (OMFc(+) BF(4)(-)) es un compuesto organometálico con aplicaciones potenciales en la ciencia de los materiales.
- Comprender sus propiedades de estado sólido, incluidos el polimorfismo y la dinámica, es crucial para su utilización tecnológica.
Objetivo del estudio:
- Para investigar el polimorfismo conformacional de OMFc (((+) BF (((4) ((-).
- Para estudiar la dinámica dependiente de la temperatura del átomo de hierro en OMFc (((+) BF (((4) ((-).
- Para caracterizar los procesos de relajación de espín y las transiciones sólido-sólido en OMFc (((+) BF (((4) ((-).
Principales métodos:
- Determinación de la estructura de rayos X de cristales simples.
- Espectroscopia de Moessbauer dependiente de la temperatura de OMFc (57) Fe-etiquetado con el (57) Fe.
Principales resultados:
- Se identificaron dos formas cristalinas distintas de OMFc (((+) BF (((4)), que difieren en los ángulos de torsión del ligando (180° y 108°), atribuidos a una pequeña diferencia de energía de red (3,2 kJ mol ((-1)).
- La espectroscopia de Moessbauer no reveló ningún aumento anómalo en el movimiento de los átomos de metal hasta 370 K, a diferencia del neutro OMFc.
- Los espectros de relajación indicaron una relajación de espín mejor descrita por un proceso de Orbach, con una temperatura de celosía de Moessbauer de 89 K.
- Una transición sólido-sólido reversible a una mesofase cristalina plástica se produjo a 400 K.
Conclusiones:
- OMFc(+)BF(4)(-) exhibe un polimorfismo conformacional impulsado por variaciones sutiles de energía de la red.
- La dinámica del centro de hierro en OMFc (((+) BF (((4))) difiere significativamente de su contraparte neutral, con distintos mecanismos de relajación de espín.
- El compuesto sufre una transición de fase reversible a una mesofase cristalina plástica a temperaturas elevadas.
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