⁷Li NMR Studies on Complexation Reactions of Lithium Ion with Cryptand C211 in Ionic Liquids: Comparison with Corresponding Reactions in Nonaqueous Solvents

Abstract

(7)Li NMR spectra of DEME-TFSA [DEME=N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium; TFSA=bis(trifluoromethanesulfonyl)amide], EMI-TFSA (EMI=1-ethyl-3-methylimidazolium), MPP-TFSA (MPP = N-methyl-N-propylpyridinium), DEME-PFSA [PFSA=bis(pentafluoroethanesulfonyl)amide], and DEME-HFSA [HFSA=bis(heptafluoropropanesulfonyl)amide] ionic liquid (IL) solutions containing LiX (X=TFSA, PFSA, or HFSA) and C211 (4,7,13,18-tetraoxa-1,10-diazabicyclo[8.5.5]eicosane) were measured at various temperatures. As a result, it was found that the uncomplexed Li(I) species existing as [Li(X)(2)](-) in the present ILs exchange with the complexed Li(I) ([Li·C211](+)) and that the exchange reactions proceed through the bimolecular mechanism, [Li·C211](+) + [*Li(X)(2)](-)=[*Li·C211](+) + [Li(X)(2)](-). Kinetic parameters [k(s)/(kg m(-1) s(-1)) at 25 °C, ΔH(++)/(kJ mol(-1)), ΔS(++)/(J K(-1) mol(-1))] are as follows: 5.57×10(-2), 69.8 ± 0.4, and -34.9 ± 1.0 for the DEME-TFSA system; 5.77×10(-2), 70.6 ± 0.2, and -31.9 ± 0.6 for the EMI-TFSA system, 6.13×10(-2), 69.0 ± 0.3, and -36.7 ± 0.7 for the MPP-TFSA system; 1.35 × 10(-1), 65.2 ± 0.5, and -43.1 ± 1.4 for the DEME-PFSA system; 1.14×10(-1), 64.4 ± 0.3, and -47.1 ± 0.6 for the DEME-HFSA system. To compare these kinetic data with those in conventional nonaqueous solvents, the exchange reactions of Li(I) between [Li·C211](+) and solvated Li(I) in N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) were also examined. These Li(I) exchange reactions were found to be independent of the concentrations of the solvated Li(I) and hence proposed to proceed through the dissociative mechanism. Kinetic parameters [k(s)/s(-1) at 25 °C, ΔH(++)/(kJ mol(-1)), ΔS(++)/(J K(-1) mol(-1))] are as follows: 1.10 × 10(-2), 68.9 ± 0.2, and -51.3 ± 0.4 for the DMF system; 1.13×10(-2), 76.3 ± 0.3, and -26.3 ± 0.8 for the DMSO system. The differences in reactivities between ILs and nonaqueous solvents were proposed to be attributed to those in the chemical forms of the uncomplexed Li(I) species, i.e., the negatively charged species ([Li(X)(2)](-)) in ILs, and the positively charged ones ([Li(solvent)(n)](+)) in nonaqueous solvents.

Coordination of 1,10-Phenanthroline and 2,2′-Bipyridine to Li+ in Different Ionic Liquids. How Innocent Are Ionic Liquids?

“…Especially the application of sensitive catalytically active metal complexes can therefore be influenced or controlled by interactions with the anionic component of an IL. , Most recently, Shirai and Ikeda reported on the macrocyclic complexation of Li + by the cryptand C211 in ILs as solvents. Compared to the results obtained for nonaqueous solvents, line broadening experiments on the appropriate 7 Li NMR signals revealed a mechanistic changeover that could be attributed to the influence of the IL anions …”

Dynamics of Liquid 1-Ethyl-3-Methylimidazolium Acetate Measured with Implanted-Ion 8Li β-NMR

“…Relatively little is known about Li + as a solute in EMIM-Ac, compared to other imidazolium-based RTILs, which have been explored as electrolytes for lithium-ion batteries. , Their properties should be qualitatively comparable, but the details certainly differ as both anion size and shape play a role in diffusivity . Shown to compare favorably with implanted-ion β-NMR, conventional NMR can provide a comparison to some closely related RTILs: EMIM-TFSA and EMIM-FSA [FSA = bis­(fluorosulfonyl)­amide].…”

“…The inset of Figure 4 shows that motional narrowing causes the resonance linewidths to scale as η/T in the liquid state above T g , a situation also observed in DEME-TFSA [DEME = N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium; and TFSA = bis(tri uoromethane-sulfonyl) amide] with solute 7 Li NMR. 56 That this relationship holds for 8 Li is surprising; our β-NMR signal is due to the dynamics of a population of implanted local probes, for which solvent self-diffusion and probe tracer diffusion are not differentiated, whereas the viscosity is a bulk property. If 8 Li + is diffusing, it implies that the diffusion is controlled by the solvent dynamics.…”

Macrocyclic coordination chemistry

“…The exchange reaction of lithium between an oxaazacryptand and different ionic liquids was studied using 7 Li NMR. 97 9.2 N/S, O/S and N/S/O mixed donor macrocycles Bis-NS 2 cyclononane chelator L 62 forms a 1 : 1 complex with nickel(II) to give an octahedral coordination geometry (N 2 S 4 ) which can be chemically oxidised to a formal Ni(III) complex. 98 EPR studies and calculations confirm that the species has a SOMO that is 40-50% nickel 3d z 2 with significant ligand character.…”