Thermochemistry of Zeolitic Imidazolate Frameworks of Varying Porosity

Abstract

The first thermochemical analysis by room-temperature aqueous solution calorimetry of a series of zeolite imidazolate frameworks (ZIFs) has been completed. The enthalpies of formation of the evacuated ZIFs-ZIF-zni, ZIF-1, ZIF-4, CoZIF-4, ZIF-7, and ZIF-8-along with as-synthesized ZIF-4 (ZIF-4·DMF) and ball-milling amorphized ZIF-4 (a(m)ZIF-4) were measured with respect to dense components: metal oxide (ZnO or CoO), the corresponding imidazole linker, and N,N dimethylformamide (DMF) in the case of ZIF-4·DMF. Enthalpies of formation of ZIFs from these components at 298 K are exothermic, but the ZIFs are metastable energetically with respect to hypothetical dense components in which zinc is bonded to nitrogen rather than oxygen. These enthalpic destabilizations increase with increasing porosity and span a narrow range from 13.0 to 27.1 kJ/mol, while the molar volumes extend from 135.9 to 248.8 cm(3)/mol; thus, almost doubling the molar volume results in only a modest energetic destabilization. The experimental results are supported by DFT calculations. The series of ZIFs studied tie in with previously studied MOF-5, creating a broader trend that mirrors a similar pattern by porous inorganic oxides, zeolites, zeotypes, and mesoporous silicas. These findings suggest that no immediate thermodynamic barrier precludes the further development of highly porous materials.

Exploring the interplay between ligand and topology in zeolitic imidazolate frameworks with computational chemistry

“…The hypothetical LTL ZIF -the least stable structure considered in this study -was found to be , 23 kJ/mol less stable than the zni analogue. ZIF-8 was found to be , 13 kJ/mol less stable than zni, which is very similar to 14 kJ/mol measured by Hugues et al [28] Downloaded by [Australian National University] at 17:18 09 January 2015 Molecular Simulation through calorimetry. Although dispersion corrections were not included at this stage, the calculations found that the variation in the total energy of the three SOD structures (ZIF-7, -8, -9) ranges from 12 to 17.5 kJ mol 21 indirectly reflecting the impact of the linkers on the stabilisation of a given topology.…”

New High- and Low-Temperature Phase Changes of ZIF-7: Elucidation and Prediction of the Thermodynamics of Transitions

“…25 They observed a trend where the enthalpy of formation is higher with increasing porosity of the ZIF. They obtained the enthalpy difference between the highly porous (e.g.…”

Molecular Mechanism of Swing Effect in Zeolitic Imidazolate Framework ZIF‐8: Continuous Deformation upon Adsorption

“…They also feature strengthstypical of the zeolitesfamily,int erms of thermal, mechanical and chemical stability.F inally,d ue to the large diversity of four-connected nets, over 100 different ZIF structures have been reported so far,w ith many more potential structures existing within as mallr ange of enthalpy of formation. [9][10][11] ZIFs present ag reat potentialf or applications such as gas capture (CO 2 in particular), [12] sensing, [13] encapsulationa nd controlled delivery, [14] and fluid separation. [15][16][17][18] ZIF-8, in particular, is commercially available, hasb een widely studied,a nd has excellent performance at lab scale for the separation of many strategic mixtures, including C 2 /C 3 hydrocarbons, CO 2 /CH 4 ,C O 2 /N 2 ,b iobutanol fermentation mixture, phenolic isomers, etc.…”