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Comportamiento crítico homólogo en los marcos moleculares Zn(CN) 2 y Cd(imidazolato) 2

Ines E Collings¹, Andrew B Cairns, Amber L Thompson

¹Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory, South Parks Road, Oxford, OX1 3QR, United Kingdom.

Journal of the American Chemical Society

|April 24, 2013

Resumen

Las distorsiones estructurales en el cianuro de zinc y el imidazolato de cadmio revelan ideas sobre la expansión térmica negativa. Estos hallazgos sugieren que la termodinámica del marco molecular depende de la eficiencia del embalaje y de las inestabilidades dinámicas.

Área de la Ciencia:

Ciencia de los materiales Ciencia de los materiales.
Química del estado sólido.
La cristalografía es una técnica de cristalografía.

Sus antecedentes:

Las estructuras moleculares como el cianuro de zinc (Zn) y el imidazolato de cadmio (Cd) exhiben comportamientos estructurales complejos.
Comprender su respuesta a estímulos externos es crucial para el diseño de materiales avanzados.

Objetivo del estudio:

Investigar las transiciones de fase estructural inducidas por la temperatura y la presión en Zn (CN) 2 y Cd (im) 2.
Para dilucidar los mecanismos atómicos detrás de la expansión térmica negativa en Zn(CN) 2.
Para explorar la relación entre la topología del marco, la eficiencia de embalaje y las propiedades termodinámicas.

Principales métodos:

Se emplearon mediciones de difracción de rayos X de cristal único y polvo.
Se realizaron estudios de temperatura variable y de presión variable.
Se realizó un análisis de desplazamientos atómicos y distorsiones estructurales.

Principales resultados:

Zn(CN) 2 sufre una transición de fase de desplazamiento de primer orden a una fase ortorrómbica a 1.52 GPa.
Los desplazamientos atómicos implican inclinaciones correlacionadas de los tetraedros centrados en Zn, lo que explica la expansión térmica negativa.
Cd(im) 2 exhibe respuestas mecánicas similares a los cambios de temperatura que se observan en Zn(CN) 2 bajo presión.

Conclusiones:

El estudio revela una transición de fase inducida por presión en Zn(CN) 2 relacionada con la expansión térmica negativa.
El comportamiento mecánico de Zn (CN) 2 y Cd (im) 2 sugiere principios de gobierno termodinámicos comunes.
La eficiencia de embalaje y la inestabilidad del marco dinámico son factores clave en la termodinámica de los marcos moleculares.

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