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(form) increases by the increase of the number of the O⋅⋅⋅Li contact, the ΔE(form) 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 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.