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La transición de fase de cristal líquido induce el cruce de espín en un complejo polielectrolito anfífilo
Yves Bodenthin1, Guntram Schwarz, Zbigniew Tomkowicz
1University Siegen, FB7 Solid State Physics, D-57068 Siegen, Germany.
Journal of the American Chemical Society
|February 12, 2009
Resumen
Los polímeros supramoleculares del hierro y del níquel forman cristales líquidos. El calentamiento Fe-PAC induce un cruce de espín irreversible (SCO) con un cambio de color, mientras que Ni-PAC no muestra SCO. La disolución recupera el estado original.
Área de la Ciencia:
- Coordinación Química de la Coordinación
- Ciencia de los materiales Ciencia de los materiales.
- Química supramolecular de las moléculas.
Sus antecedentes:
- Los polielectrolitos de coordinación metalosupramolecular (MEPE) se forman por autoensamblaje de iones metálicos y ligandos.
- La incorporación de anfifiles como el fosfato de dihexadecilo (DHP) crea complejos polielectrolíticos anfifiles (PAC) con propiedades cristalinas líquidas.
Objetivo del estudio:
- Para investigar el comportamiento de cruce de espín (SCO) en los sistemas Fe-PAC y Ni-PAC.
- Comprender la relación entre los cambios estructurales, las propiedades térmicas y las transiciones magnéticas.
- Para comparar el comportamiento de la OCS en las PAC frente al MEPE.
Principales métodos:
- El autoensamblaje de los iones Fe (II) o Ni (II) con 6,6',6''-bis (II) -piridil) -2,2':4',4'':2'',2''-cuaterpiridina (btpy) para formar el MEPE.
- El ensamblaje secuencial con fosfato de dihexadecilo (DHP) para formar PACs.
- Análisis térmico (análisis termogravimétrico, calorimetría de barrido diferencial) y mediciones magnéticas.
Principales resultados:
- Fe-PAC exhibe un irreversible, casi completo (95%) espín-crossover de bajo espín a alto estado de espín al calentar, acompañado de un cambio de color.
- El SCO en Fe-PAC está relacionado con la fusión de la matriz anfifílica y los cambios estructurales asociados.
- El Fe-PAC no se vuelve a ensamblar al enfriarse, pero puede recuperarse por disolución; el Ni-PAC muestra cambios estructurales similares, pero no SCO.
Conclusiones:
- La matriz cristalina líquida en Fe-PAC es crucial para permitir una SCO completa e irreversible.
- Por el contrario, la arquitectura de estado sólido de Fe-MEPE restringe los cambios estructurales, lo que lleva a una SCO incompleta dependiente del historial de la muestra y el contenido de disolventes.
- Este estudio pone de relieve el papel de la matriz anfifílica en el control de las propiedades de SCO en materiales metalosupramoleculares.
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