On the Colossal and Highly Anisotropic Thermal Expansion Exhibited by Imidazolium Salts

Abstract: 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 p+–p+ 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– by Br– 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.

 Fuente: Cryst. Growth Des., 2015, 15 (11), pp 5207–5212

Editorial: American Chemical Society

 Fecha de publicación: 01/09/2015

Nº de páginas: 6

Tipo de publicación: Artículo de Revista

DOI: 10.1021/acs.cgd.5b00633

ISSN: 1528-7483,1528-7505

Proyecto español: MAT2011-27573-C04 ; FIS2012-37549-C05-04

Url de la publicación: https://doi.org/10.1021/acs.cgd.5b00633