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Title: Heat capacity and thermodynamic functions of crystalline forms of the metal-organic framework zinc 2-methylimidazolate, Zn(MeIm) 2

Abstract

Zeolitic imidazolate frameworks (ZIFs) are comprised of metal atoms connected with imidazole-like linkers, and these frameworks have potential for applications in molecular sieving, gas sequestration, and catalysis. Furthermore, these materials form true polymorphs with the same chemical composition but different topologies. In this work, 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 C p,m°, Δ 0 TS m°, Δ 0 TH m°, and Φ m° 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.

Authors:
 [1];  [1];  [1];  [2];  [2];  [3];  [4]; ORCiD logo [5];  [1]
  1. Brigham Young Univ., Provo, UT (United States)
  2. McGill Univ., Montreal, QC (Canada)
  3. Univ. of California, Davis, CA (United States)
  4. Virginia Polytechnic Inst. and State Univ. (Virginia Tech), Blacksburg, VA (United States)
  5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Scientific User Facilities Division
OSTI Identifier:
1523724
Alternate Identifier(s):
OSTI ID: 1542541
Grant/Contract Number:  
AC05-00OR22725; SC0016446; SC0016573; SC0016448
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Chemical Thermodynamics
Additional Journal Information:
Journal Volume: 136; Journal Issue: C; Journal ID: ISSN 0021-9614
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
ZIF-8; MOFs; Zeolitic imidazolate frameworks; Heat capacity; Inelastic neutron scattering

Citation Formats

Rosen, Peter F., Calvin, Jason J., Dickson, Matthew S., Katsenis, Athanassios D., Friščić, Tomislav, Navrotsky, Alexandra, Ross, Nancy L., Kolesnikov, Alexander I., and Woodfield, Brian F. Heat capacity and thermodynamic functions of crystalline forms of the metal-organic framework zinc 2-methylimidazolate, Zn(MeIm)2. United States: N. p., 2019. Web. doi:10.1016/j.jct.2019.05.008.
Rosen, Peter F., Calvin, Jason J., Dickson, Matthew S., Katsenis, Athanassios D., Friščić, Tomislav, Navrotsky, Alexandra, Ross, Nancy L., Kolesnikov, Alexander I., & Woodfield, Brian F. Heat capacity and thermodynamic functions of crystalline forms of the metal-organic framework zinc 2-methylimidazolate, Zn(MeIm)2. United States. doi:10.1016/j.jct.2019.05.008.
Rosen, Peter F., Calvin, Jason J., Dickson, Matthew S., Katsenis, Athanassios D., Friščić, Tomislav, Navrotsky, Alexandra, Ross, Nancy L., Kolesnikov, Alexander I., and Woodfield, Brian F. Mon . "Heat capacity and thermodynamic functions of crystalline forms of the metal-organic framework zinc 2-methylimidazolate, Zn(MeIm)2". United States. doi:10.1016/j.jct.2019.05.008.
@article{osti_1523724,
title = {Heat capacity and thermodynamic functions of crystalline forms of the metal-organic framework zinc 2-methylimidazolate, Zn(MeIm)2},
author = {Rosen, Peter F. and Calvin, Jason J. and Dickson, Matthew S. and Katsenis, Athanassios D. and Friščić, Tomislav and Navrotsky, Alexandra and Ross, Nancy L. and Kolesnikov, Alexander I. and Woodfield, Brian F.},
abstractNote = {Zeolitic imidazolate frameworks (ZIFs) are comprised of metal atoms connected with imidazole-like linkers, and these frameworks have potential for applications in molecular sieving, gas sequestration, and catalysis. Furthermore, these materials form true polymorphs with the same chemical composition but different topologies. In this work, 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.},
doi = {10.1016/j.jct.2019.05.008},
journal = {Journal of Chemical Thermodynamics},
number = C,
volume = 136,
place = {United States},
year = {2019},
month = {5}
}

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This content will become publicly available on May 13, 2020
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