On the Colossal and Highly Anisotropic Thermal Expansion
Exhibited by Imidazolium Salts
I. de Pedro
A. García-Saiz
J. Dupont
P. Migowski
O. Vallcorba
J. Junquera
J. Rius
J. Rodríguez
Fernández
10.1021/acs.cgd.5b00633.s001
https://acs.figshare.com/articles/journal_contribution/On_the_Colossal_and_Highly_Anisotropic_Thermal_Expansion_Exhibited_by_Imidazolium_Salts/2113516
The imidazolium salts 1-ethyl-2,3-dimethylimidazolium
chloride,
Edimim[Cl], and bromide, Edimim[Br], exhibit negative and positive
thermal expansions, as determined by variable-temperature synchrotron
powder X-ray diffraction experiments. Both compounds crystallize in
the same monoclinic centrosymmetric space group, showing an anisotropic
H-bonding network and imidazolium–imidazolium π<sup>+</sup>–π<sup>+</sup> interactions, which have been corroborated
by density functional theory studies. The chloride derivative displays
a highly anisotropic thermal expansion with a colossal positive coefficient
along one direction. Replacement of Cl<sup>–</sup> by Br<sup>–</sup> in the same crystal structure produces an increase
of the colossal coefficient and induces a biaxial negative thermal
expansion. By studying the molecular vibration factors and the H-bonding
framework in their crystals as a function of temperature, it was possible
to rationalize at the molecular level the mechanism for the observed
anomalies in thermal expansion.
2015-11-04 00:00:00
coefficient
vibration factors
crystal structure
imidazolium
chloride
theory studies
centrosymmetric space group
anisotropic
Edimim