Anion-Additive Interactions Studied by Ab Initio Calculations and Raman Spectroscopy.
Journal article, 2009
The ability of the caLi x (6)pyrrole (C6P) additive to form complexes with several anions is addressed. Ab initio calculations and Raman spectroscopy are used in combination to evaluate the coordination preferences of C6P in the gas phase and to probe the existence of C6P-anion complexes in solution. Favorable reaction energies are calculated for the formation of 1:1 coordination complexes from the isolated species, with the following anion preference: BF 4 - AsF 6 - > ClO 4 - ≈CF 3 SO 3 - > PF 6 - > I - . In connection with available macroscopic data, the calculated results support the assumption of anion coordination by C6P as a mechanism for lithium transference number enhancement. Upon anion coordination to the additive, calculated vibrational spectra show large differences in the N-H stretching region (∼3400 cm -1 ). However, at lower wavenumbers ( < 3300 cm -1 ) no significant differences are predicted. The latter is in agreement with experimental Raman data for the three examined samples: C6P, C6P-AsF 6 -, and C6P- I - . © 2009 The Electrochemical Society.