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Compuestos de espín cruzado de hierro (III) con una amplia histeresis térmica aparente alrededor de la temperatura
1Special Research Laboratory for Optical Science, Kanagawa Academy of Science and Technology, East 412, 3-2-1 Sakado, Takatsu-ku, Kawasaki-shi, Kanagawa 213-0012, Japan.
Journal of the American Chemical Society
|November 22, 2001
Resumen
Los compuestos de cruce de espín [Fe ((qsal) ]2NCSe-MeOH y [Fe ((qsal) ]2NCSe-CH2Cl2 exhiben aparentemente anchos bucles de histeresis térmica inicialmente. Después de la pérdida de disolvente, muestran un distinto comportamiento de cruce de espín de dos pasos al calentarse y un paso al enfriarse.
Área de la Ciencia:
- Ciencia de los materiales Ciencia de los materiales.
- Química del estado sólido.
- El magnetismo es el magnetismo.
Sus antecedentes:
- Los compuestos de espín cruzado (SCO) son materiales moleculares que pueden cambiar entre estados de espín bajo y alto.
- Los complejos SCO son de interés para aplicaciones potenciales en sensores, dispositivos de memoria y pantallas.
- Comprender los factores que influyen en el comportamiento de la SCO, como la histeresis y la cooperatividad, es crucial para el diseño de materiales.
Objetivo del estudio:
- Para investigar las propiedades magnéticas y el comportamiento de cruce de espín de dos nuevos compuestos de hierro (II): [Fe (qsal) ]2NCSe-MeOH (1) y [Fe (qsal) ]2NCSe-CH2Cl2 (2).
- Caracterizar la histeresis térmica y la naturaleza de las transiciones de cruce de espín en estos complejos.
- Explorar el papel de las interacciones intermoleculares en los fenómenos observados de la SCO.
Principales métodos:
- Mediciones de las propiedades magnéticas (susceptibilidad dependiente de la temperatura).
- Análisis termogravimétrico (TGA) para determinar las temperaturas de pérdida de disolventes.
- Análisis de las temperaturas de transición de giro-cruce y anchos de histeresis.
- Modelado del comportamiento de la OCS utilizando un marco teórico previamente establecido.
Principales resultados:
- Los compuestos 1 y 2 mostraron inicialmente amplios bucles de histeresis térmica aparente (140 K y 180 K, respectivamente) debido a la pérdida de disolvente.
- Después de la eliminación del disolvente, ambos compuestos exhibieron un cruce de espín de dos pasos al calentarse (centrado en 215 K y 282 K) y un cruce de un paso al enfriarse (centrado en 212 K).
- Se observó un ancho de histeresis significativo de 70 K para el segundo paso en la transición de calentamiento, uno de los más amplios reportados para los complejos SCO, atribuido a las interacciones pi intermoleculares.
Conclusiones:
- Los anchos bucles de histeresis iniciales son artefactos de escape de moléculas de disolvente.
- Los compuestos demuestran un comportamiento complejo de cruce de espín con distintas transiciones de varios pasos.
- Las interacciones pi intermoleculares entre los anillos de quinolina y fenilo son clave para la cooperatividad observada y la amplia histeresis en el proceso SCO.
- El comportamiento experimental del SCO puede simularse con éxito utilizando un modelo teórico.
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