Portal de Periódicos da CAPES

Thermal effect on C–H stretching vibrations of the imidazolium ring in ionic liquids

2007; Royal Society of Chemistry; Volume: 9; Issue: 36 Linguagem: Inglês

10.1039/b706497g

1463-9084

A. Yokozeki, Daniel J. Kasprzak, Mark B. Shiflett,

Inorganic and Organometallic Chemistry

We have studied temperature dependent IR spectra of the C–H stretching modes of the imidazolium ring in [bmim][PF6], [bmim][Tf2N], [emim][Tf2N], [hmim][Tf2N], and [bmim][BF4]. Temperatures in this study are from 278 to 348 K at an interval of 10 K. Spectra of the C–H stretching modes have been deconvoluted using our previous computer program of the Voigt-lineshape function. Frequency shifts, Lorentzian spectral widths, and band absorbance were examined as a function of temperature. In order to interpret the observed behaviors, we have developed a simple mechanical model as well as a chemical equilibrium model. The model analyses suggest that enthalpy changes for the cluster and/or ion-pair breaking reactions in the liquid state are several kJ mol−1 endothermic, and the degree of dissociations of ion pairs or hydrogen bonded clusters is in the range from 0.3 to 0.9 with different magnitudes for the five ionic liquids.