Gutmann Donor and Acceptor Numbers for Ionic Liquids

We present for the first time Gutmann donor and acceptor numbers for a series of 36 different ionic liquids that include 26 distinct anions. The donor numbers were obtained by (23)Na NMR spectroscopy and show a strong dependence on the anionic component of the ionic liquid. The donor numbers measured vary from -12.3 kcal mol(-1) for the ionic liquid containing the weakest coordinative anion [emim][FAP] (1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate), which is a weaker donor than 1,2-dichloroethane, to 76.7 kcal mol(-1) found for the ionic liquid [emim][Br], which exhibits a coordinative strength in the range of tertiary amines. The acceptor numbers were measured by using (31)P NMR spectroscopy and also vary as a function of the anionic and cationic component of the ionic liquid. The data are presented and correlated with other solvent parameters like the Kamlet-Taft set of parameters, and compared to the donor numbers reported by other groups.