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

The stabilization energies (Eform) 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 kcalmol-1, respectively. The electrostatic and induction interactions are the major sources of the attraction in the complexes. Although the Eform increases by the increase of the number of the OLi contact, the Eform per 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 kcalmol-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.