7Li-NMR study of the stoichiometry, stability and exchange kinetics of Li+ ion with 12-Crown-4, 15-Crown-5 and cryptands C222, C221 and C211 in 50% ionic liquid–acetonitrile mixtures

7Li-NMR spectroscopy was used to study the complexation of Li+ ion with 12C4, 15C5, C222, C221, C211 in acetonitrile (AN) and its 50% (wt/wt) mixtures with two new room temperature ionic liquids, 1-ethyl-3-methylimidazolium hexafluorophosphate (EMim PF6) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMim BF4) at 298 K. Excluding the cases of Li+–C211 in all solvents and Li+–C221 in AN and 50% (wt/wt) AN–EMim PF6, in other cases, the exchange between free and 1:1 complexed Li+ was fast on the NMR time scale and only a single population average 7Li signal was observed. Formation constants of the resulting 1:1 complexes were evaluated by computer fitting of the chemical shift-mole ratio data and integration of two 7Li signals. All complexes in EMim PF6 were found to be more stable than those in EMim BF4. 7Li-NMR line-shape analysis was used to determine the kinetic parameters and the mechanism for the chemical exchange of Li+ between the free and 1:1 complex with C221 in 50% (wt/wt) AN–EMim PF6 mixtures solution. By comparing our study with the previous one, it is derived that, increasing the percentage of ion liquid in acetonitrile, changes the mechanism and decrease the exchange rate constant of Li+ ion between free and complex sites.

7Li-NMR spectroscopy was used to study the complexation reaction Li+ ion with 12-Crown-4, 15-Crown-5 and cryptand C222, C221, C211 in acetonitrile (AN) and its 50% (wt/wt) mixtures with two new room temperature ionic liquids. It was found that, stability of the resulting complexes strongly depended on the nature of ionic liquids used. All complexes in EMim PF6 were found to be more stable than those in EMim BF4. 7Li-NMR line-shape analysis was used to determine the kinetic parameters and the mechanism for the chemical exchange of Li+ between the free and 1:1 complex with C221 in 50% (wt/wt) AN–EMim PF6 mixtures solution.Figure optionsDownload as PowerPoint slideHighlights
► Effects of ionic liquids in complexation reaction of Li+-crown were studied.
► Complexation was studied in acetonitrile-ion liquid mixtures, using 7Li-NMR method.
► Addition of ionic liquid to acetonitrile decreased the stability of complexes.
► All complexes in EMim PF6 were found to be more stable than those in EMim BF4.