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Rotación de C60 en estado sólido: dinámica de una parte superior esférica facetada
Science (New York, N.Y.)
|March 6, 1992
Resumen
El sólido C ((60) exhibe una rápida reorientación molecular, más rápido que en solución. Una transición de fase por debajo de 260 K revela una dinámica más lenta, con ambas fases mostrando comportamiento de Arrhenius.
Área de la Ciencia:
- Física del estado sólido física del estado sólido.
- Ciencia de los materiales ciencia de los materiales.
- Espectroscopia de resonancia magnética nuclear por resonancia magnética.
Sus antecedentes:
- Los fullerenos, particularmente el C60, son de interés debido a sus propiedades electrónicas y estructurales únicas.
- La comprensión de la dinámica molecular en el sólido C60) es crucial para las aplicaciones y la ciencia fundamental.
- Estudios anteriores sugirieron un comportamiento de rotación complejo en el sólido C60.
Objetivo del estudio:
- Para investigar la dinámica de rotación del sólido C60) utilizando técnicas avanzadas de RMN.
- Para cuantificar los tiempos de correlación de reorientación molecular (tau) y las constantes de difusión (D).
- Explorar las transiciones de fase y su impacto en el movimiento molecular.
Principales métodos:
- Se empleó la espectroscopia de resonancia magnética nuclear de carbono-13 ((13) C NMR).
- Se midió la tasa de relajación debido a la anisotropía de desplazamiento químico (1/9T1 ((CSA) ((1)).
- Se analizó la dependencia del campo magnético de T(1) para determinar tau y D.
Principales resultados:
- A 283 K, el tau se determinó como 9,1 picosegundos, lo que implica que D = 1,8 x 10 s-1).
- Los tiempos de reorientación son significativamente más rápidos que la rotación libre y más rápidos que en solución.
- Se observó una fase distinta de baja temperatura (por debajo de 260 K) con tiempos de reorientación más largos, lo que indica una transición de fase.
- Ambas fases exhibieron un comportamiento de Arrhenius con energías de activación distintas (1.4 y 4.2 kcal/mol).
Conclusiones:
- El sólido C60) sufre una rápida reorientación molecular, comparable al movimiento de un líquido.
- Una transición de fase de orientación se produce por debajo de 260 K, alterando la dinámica de rotación.
- La dinámica observada y el comportamiento de transición de fase son paralelos a los del adamantano, lo que sugiere principios subyacentes comunes.
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