¹³C NMR Relaxation and ¹H Diffusion (DOSY) Studies of an Acidic Chloroaluminate Melt

Abstract

13C NMR relaxation studies of a 2:1 AlCl3:1-ethyl-3-methylimidazolium chloride (MEICl) melt between 26 and 57 °C provide rotational correlation times for MEI+ which are compared with viscosities and diffusion coefficients. Diffusion coefficients for MEICl in a 2:1 AlCl3−MEICl melt are determined using 1H diffusion ordered spectroscopy (DOSY) between 26 and 57 °C. All MEI+ diffusion coefficients (ring, methyl, and ethyl protons) are virtually identical at a given temperature. The MEI+ diffusion coefficients are viscosity dependent and correlate with conductivity and 13C NMR rotational correlation times, indicating that the transport properties of the 2:1 AlCl3−MEICl melt are determined by the molar quantities of salt and not by the properties of the individual ions. Microviscosity factors provide reasonable values for the radius of MEI+ from both viscosity and 13C NMR rotational correlation times. The "slip" model is used to describe the movement of MEI+ in the 2:1 AlCl3−MEICl melt where Al2Cl7- is the predominant anion. The ab initio structures of AlCl4- and Al2Cl7- have been calculated at the HF/6-31G(d) level.