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(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

Low-Temperature Phase Transitions of the Ionic Liquid 1-Ethyl-3-methylimidazolium Dicyanamide

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Bernardino, Kalil [1] ; Lima, Thamires A. [1] ; Ribeiro, Mauro C. C. [1]
Total Authors: 3
[1] Univ Sao Paulo, Lab Espect Mol, Dept Quim Fundamental, Inst Quim, BR-05508000 Sao Paulo, SP - Brazil
Total Affiliations: 1
Document type: Journal article
Source: Journal of Physical Chemistry B; v. 123, n. 44, p. 9418-9427, NOV 7 2019.
Web of Science Citations: 0

Several calorimetric measurements have shown that 1-ethyl-3-methylimidazolium dicyanamide, {[}C(2)C(1)im]{[}N(CN)(2)], is a glass-forming liquid, even though it is a low-viscous liquid at room temperature. Here, we found slow crystallization during cooling of {[}C(2)C(1)im]{[}N(CN)(2)] along Raman spectroscopy measurements. The low-frequency range of the Raman spectrum shows that the same crystalline phase is obtained at 210 K either by cooling or by reheating the glass (cold-crystallization). Another crystalline phase is formed at ca. 260 K just prior the melting at 270 K. X-ray diffraction and calorimetric measurements confirm that there are two crystalline phases of {[}C(2)C(1)im]{[}N(CN)(2)]. The Raman spectra indicate that polymorphism is related to {[}C(2)C(1)im](+) with the ethyl chain on the plane of the imidazolium ring (the low-temperature crystal) or nonplanar (the high-temperature crystal). The structural reason for the glass-forming ability of {[}C(2)C(1)im]{[}N(CN)(2)], despite the relatively simple molecular structures of the ions, was pursued by quantum chemistry calculations and molecular dynamics (MD) simulations. Density functional theory calculations were performed for ionic pairs in order to draw free-energy surfaces of the anion around the cation. The MD simulations using a polarizable model provided maps of occurrence of anions around cations. Both the quantum and classical calculations suggest that the delocalization of preferred positions of the anion around the cation, which adopts different conformations of the ethyl chain, is on the origin of the crystallization being hampered during cooling and the resulting glass-forming ability of {[}C(2)C(1)im]{[}N(CN)(2)]. (AU)

FAPESP's process: 16/21070-5 - Vibrational spectroscopy with spatial resolution
Grantee:Mauro Carlos Costa Ribeiro
Support type: Research Projects - Thematic Grants
FAPESP's process: 17/12063-8 - Non-equilibrium molecular dynamics of ionic liquids
Grantee:Kalil Bernardino
Support type: Scholarships in Brazil - Post-Doctorate
FAPESP's process: 14/15049-8 - A Raman spectroscopy study of the glass transition of ionic liquids under high pressure.
Grantee:Thamires Andrade Lima
Support type: Scholarships in Brazil - Post-Doctorate
FAPESP's process: 19/04785-9 - Molecular dynamics study of the effect of flexibility over the melting point of ionic liquids
Grantee:Kalil Bernardino
Support type: Scholarships abroad - Research Internship - Post-doctor