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 23Na 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 31P 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 KamletTaft set of parameters, and compared to the donor numbers reported by other groups.