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La brecha entre los singlet y los triplet en los triplet biradicals del estado fundamental se modula mediante efectos
David A Shultz1, Scot H Bodnar, Hyoyoung Lee
1Department of Chemistry, North Carolina State University, Raleigh 27695-8204, USA. david_shultz@ncsu.edu
Journal of the American Chemical Society
|August 22, 2002
Resumen
Se sintetizaron tres nuevos complejos ferromagnéticos de bis ((semiquinona) acoplados al espín. El análisis estructural reveló conformaciones consistentes de ligandos, con efectos de sustitución que influyen principalmente en el parámetro de acoplamiento de intercambio observado (J).
Área de la Ciencia:
- Química Inorgánica La Química Inorgánica es la química inorgánica.
- Ciencia de los materiales Ciencia de los materiales.
- Química cuántica es la química cuántica.
Sus antecedentes:
- Los complejos de bis (semiquinona) son de interés por sus propiedades magnéticas únicas.
- El acoplamiento de intercambio intramolecular es crucial para lograr los comportamientos magnéticos deseados.
- El ajuste de las propiedades electrónicas y estéricas de los sustituyentes puede modular las interacciones magnéticas.
Objetivo del estudio:
- Para sintetizar y caracterizar los nuevos complejos S = 1 bis ((semiquinona).
- Para investigar la influencia de los meta-sustitutos en el acoplamiento de intercambio intramolecular ferromagnético.
- Para correlacionar las conformaciones estructurales con los parámetros de intercambio magnético.
Principales métodos:
- Síntesis de tres complejos distintos de bis (semiquinona) con meta-sustitutos variados (NMe (2), t-Bu, NO (2)).
- Cristalografía de rayos X para la determinación estructural detallada de los complejos.
- Mediciones de susceptibilidad magnética para determinar el parámetro de acoplamiento de intercambio (J).
Principales resultados:
- Los tres complejos exhiben estados de espín S = 1 con acoplamiento ferromagnético.
- La cristalografía de rayos X confirmó conformaciones de ligandos casi idénticas en todos los complejos (torsión media del anillo de semiquinona de 32 ° ± 2 °).
- El parámetro de acoplamiento de intercambio (J) varió de +31.0 cm−1 (NO(2) a +59.3 cm−1 (t-Bu), lo que indica una modulación dependiente del sustituyente.
Conclusiones:
- Las variaciones observadas en el acoplamiento de intercambio ferromagnético se atribuyen principalmente a efectos de sustitución electrónica, no a cambios conformacionales.
- Este estudio proporciona información sobre el diseño racional de imanes moleculares con propiedades magnéticas sintonizables.
- La teoría de Hückel y el trabajo computacional apoyan los hallazgos experimentales sobre los efectos de sustitución.
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