Abstract
Zeolitic imidazolate frameworks (ZIFs) are composed of metal atoms connected with imidazole-like linkers, and these frameworks have potential for applications in molecular sieving, gas sequestration, and catalysis. In addition, these materials form true polymorphs with the same chemical composition but different topologies. In this paper, we present the results of low temperature heat capacity and inelastic neutron scattering studies of the sodalite (SOD) and diamondoid (dia) topologies of the popular zinc 2-methylimidazolate framework, Zn(MeIm)2. Molar heat capacities from 1.8 K to 300 K are presented, along with theoretical fits and the values of Cp,m°, Δ0TSm°, Δ0THm°, and Φm° calculated from those fits. The Gibbs energy of the transformation from SOD to dia is −(4.6 ± 2.2) kJ, and this transformation is primarily enthalpically driven. The results of this study are compared with previous measurements on the zinc 2-ethylimidazolate framework, Zn(EtIm)2. Inelastic neutron scattering measurements confirm the presence of low energy modes and suggest that the higher heat capacity of SOD at low temperatures is due to the dynamics of the methyl groups on the methylimidazolate linkers.
Original language | English |
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Pages (from-to) | 160-169 |
Number of pages | 10 |
Journal | Journal of Chemical Thermodynamics |
Volume | 136 |
DOIs | |
State | Published - Sep 2019 |
Funding
The heat capacity work was financially supported by a grant from the U.S. Department of Energy under grant DE-SC0016446 . Data analysis based on recent measurements of enthalpies of transformation was supported by the U.S. Department of Energy under grant DE-SC0016573 . The INS work was financially supported by a grant from the U.S. Department of Energy under grant DE-SC0016448 . TF and ADK acknowledge the support of NSERC Strategic Grant (Grant no. NSERC STPGP 463405-14 ), the NSERC E.W.R. Steacie Memorial Fellowship (TF), and FRQNT Post-doctoral Bursary (ADK). The neutron-scattering research at the Spallation Neutron Source, Oak Ridge National Laboratory, was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. The heat capacity work was financially supported by a grant from the U.S. Department of Energy under grant DE-SC0016446. Data analysis based on recent measurements of enthalpies of transformation was supported by the U.S. Department of Energy under grant DE-SC0016573. The INS work was financially supported by a grant from the U.S. Department of Energy under grant DE-SC0016448. TF and ADK acknowledge the support of NSERC Strategic Grant (Grant no. NSERC STPGP 463405-14), the NSERC E.W.R. Steacie Memorial Fellowship (TF), and FRQNT Post-doctoral Bursary (ADK). The neutron-scattering research at the Spallation Neutron Source, Oak Ridge National Laboratory, was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.
Funders | Funder number |
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Office of Basic Energy Sciences | |
Scientific User Facilities Division | |
U.S. Department of Energy | DE-SC0016573, DE-SC0016448, DE-SC0016446 |
Oak Ridge National Laboratory | |
Natural Sciences and Engineering Research Council of Canada | NSERC STPGP 463405-14 |
Fonds de Recherche du Québec - Nature et Technologies |
Keywords
- Heat capacity
- Inelastic neutron scattering
- MOFs
- ZIF-8
- Zeolitic imidazolate frameworks