Structure of LiBF4 Solvate Complexes in Ethylene Carbonate, Based on High-Resolution NMR and Quantum-Chemical Data

Abstract

The ion solvation of LiBF4 in ethylene carbonate is studied via high resolution NMR, conductometry, and quantum-chemical simulation. 7Li, 11B, 19F, 13C, and 17O NMR spectra are acquired for LiBF4 solutions in ethylene carbonate, and their conductivity is measured in the concentration range of 0.07–1.77 mol kg–1 at 40°C. Molecular models of solvate complexes of a Li+BF 4 − ion pair containing n ethylene carbonate molecules are constructed. The calculated 11B chemical shifts are virtually independent of n, which can provide a relationship between 11B experimental shifts and degree of dissociation (α). The α value is estimated from a theoretical change in chemical shift of −0.414 ppm when a BF 4 − ion transitions from a free state to an associated one of the contact ion pair. The α values are in reasonable agreement with the degree of dissociation for LiBF4 in propylene carbonate, found from the Walden product of the equivalent electrical conductivity of a solution by its viscosity.