Structure of LiBF 4 Solvate Complexes in Ethylene Carbonate, Based on High-Resolution NMR and Quantum-Chemical Data

The ion solvation of LiBF 4 in ethylene carbonate is studied via high resolution NMR, conductometry, and quantum-chemical simulation. 7 Li, 11 B, 19 F, 13 C, and 17 O NMR spectra are acquired for LiBF 4 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 11 B chemical shifts are virtually independent of n , which can provide a relationship between 11 B 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 LiBF 4 in propylene carbonate, found from the Walden product of the equivalent electrical conductivity of a solution by its viscosity.