Temperature-dependent structural changes of [Bmim]FeCl4 magnetic ionic liquid characterized by an in-situ X-ray absorption fine structure

The temperature-dependent structural changes in 1-butyl-3-methylimidazolium tetrafluoride ([Bmim]FeCl4) magnetic ionic liquid (MIL) were investigated by using in-situ X-ray absorption fine structure (XAFS) combined with Raman spectroscopy and DFT calculations. XAFS results revealed that the coordination number and bond length of Fe-Cl in the anion of [Bmim]FeCl4 MIL decreased with increments in temperature. These results directly reflected the dissociation of tetrahedral structure [FeCl4](-), and the formation of bridge-chain [Fe2Cl5](+), and [FeCl2](+) species in the anion of [Bmim]FeCl4 MIL. These behaviors indicated that [FeCl4](-) dissociation was endothermic, and was promoted by increased temperature. The results obtained through XAFS were in agreement with those obtained through Raman spectroscopy and DFT calculations. (C) 2019 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.