Journal of Physical Chemistry B, Vol.113, No.7, 2066-2070, 2009
Structural Analysis of [ChCl](m)[ZnCl2](n) Ionic Liquid by X-ray Absorption Fine Structure Spectroscopy
The components and structures of ionic liquid ChCl-ZnCl2 in different ChCl:ZnCl2 ratios were investigated using XAFS (X-ray absorption fine structure) technique. The average coordination number and distance of Zn species at different x(ZnCl2) (mole fraction of ZnCl2 when synthesizing) were calculated. It is shown that x(ZnCl2) has a regular influence on the coordination number of Zn species, due to the change of anion forms and structures in the ChCl-ZnCl2 ionic liquid. The possible forms and structures of Zn species in the ionic liquids were analyzed according to the coordination number. XAFS and DSC (differential scanning calorimetry) analysis imply that besides ZnCl3-and Zn2Cl5- anions, the Cl-Zn-Cl ion pair is a main species in the ionic liquid at higher x(ZnCl2). This newly discovered Zn species has substantial influence on the properties of the ionic liquid. From the analysis of the coordination numbers and coordination distance, a new mechanism of interactions between Ch(+) cation and Cl-Zn-Cl ion pairs or Cl- is proposed.