Insights into the Temperature-Dependent “Breathing” of a Flexible Fluorinated Metal–Organic Framework

Authors

  • Dr. Carlos A. Fernandez,

    Corresponding author
    1. Pacific Northwest National Laboratory, 902 N Battelle Blvd., Richland, WA, 99352 (USA), Fax: (+1) 509-375-2186
    • Pacific Northwest National Laboratory, 902 N Battelle Blvd., Richland, WA, 99352 (USA), Fax: (+1) 509-375-2186
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  • Dr. Praveen K. Thallapally,

    Corresponding author
    1. Pacific Northwest National Laboratory, 902 N Battelle Blvd., Richland, WA, 99352 (USA), Fax: (+1) 509-375-2186
    • Pacific Northwest National Laboratory, 902 N Battelle Blvd., Richland, WA, 99352 (USA), Fax: (+1) 509-375-2186
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  • Dr. B. Peter McGrail

    Corresponding author
    1. Pacific Northwest National Laboratory, 902 N Battelle Blvd., Richland, WA, 99352 (USA), Fax: (+1) 509-375-2186
    • Pacific Northwest National Laboratory, 902 N Battelle Blvd., Richland, WA, 99352 (USA), Fax: (+1) 509-375-2186
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Abstract

The framework expansion and contraction upon carbon dioxide uptake was studied in a partially fluorinated metal–organic framework, FMOF-2. The results show framework expansion and contraction (breathing) as a function of pressure and temperature. Even at temperatures as low as −30 °C, two phase transitions seem to take place with a pressure step (corresponding to the second transition) that is greatly dependent on temperature. This behavior is described by the model proposed by Coudert and co-workers showing that the material seems to undergo two phase transitions that are temperature-dependent. The isosteric heats of adsorption at high pressures show a minimum that is concurrent with the region of CO2 loadings where the second pressure step occurs. It was deduced that these lower enthalpy values are a consequence of the energy cost related to the expansion or reopening of the framework. Lastly, the large and reversible breathing behavior may be a product of the combination of the high elasticity of zinc (II) coordination and the apparent high flexibility of the V-shaped organic building block.

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