Intermolecular Interactions in Li⁺‐glyme and Li⁺‐glyme–TFSA⁻Complexes: Relationship with Physicochemical Properties of [Li(glyme)][TFSA] Ionic Liquids

The stabilization energies (ΔE_form) calculated for the formation of the Li⁺complexes with mono‐, di‐ tri‐ and tetra‐glyme (G1, G2, G3 and G4) at the MP2/6‐311G** level were −61.0, −79.5, −95.6 and −107.7 kcal mol⁻¹, respectively. The electrostatic and induction interactions are the major sources of the attraction in the complexes. Although the ΔE_formincreases by the increase of the number of the O⋅⋅⋅Li contact, the ΔE_formper oxygen atom decreases. The negative charge on the oxygen atom that has contact with the Li⁺weakens the attractive electrostatic and induction interactions of other oxygen atoms with the Li⁺. The binding energies calculated for the [Li(glyme)]⁺complexes with TFSA⁻anion (glyme=G1, G2, G3, and G4) were −106.5, −93.7, −82.8, and −70.0 kcal mol⁻¹, respectively. The binding energies for the complexes are significantly smaller than that for the Li⁺with the TFSA⁻anion. The binding energy decreases by the increase of the glyme chain length. The weak attraction between the [Li(glyme)]⁺complex (glyme=G3 and G4) and TFSA⁻anion is one of the causes of the fast diffusion of the [Li(glyme)]⁺complex in the mixture of the glyme and the Li salt in spite of the large size of the [Li(glyme)]⁺complex. The HOMO energy level of glyme in the [Li(glyme)]⁺complex is significantly lower than that of isolated glyme, which shows that the interaction of the Li⁺with the oxygen atoms of glyme increases the oxidative stability of the glyme.