Many metal-organic frameworks (MOFs) of ultrahigh porosity (with molar volumes more than ten times greater than those of the corresponding dense phases) have been synthesized. However, the number of possible structures far exceeds those that have been made. It is logical to ask if there are energetic barriers to the stability of ultraporous MOFs or whether there is little thermodynamic penalty to their formation. Herein, we show that although the molar volumes of MOF-177 and UMCM-1 reach ultrahigh values, their energetic metastability is in the same range (of 7-36 kJ mol(-1)) as that seen previously for other porous materials. These findings suggest that there is little thermodynamic penalty for the synthesis of structures with varying porosity, and hence, ultraporous frameworks are energetically accessible. Therefore, innovative synthesis methods have the possibility to overcome the drawbacks of conventional approaches and greatly extend the number, porosity, and properties of new framework materials.
Keywords: calorimetry; energetics; metal-organic frameworks; molar volume; thermodynamics.
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