Intermolecular interactions in Li+-glyme and Li+-glyme-TFSA- complexes: relationship with physicochemical properties of [Li(glyme)][TFSA] ionic liquids

Abstract

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.