Raman and IR spectroscopy have been a useful tool in exploring ionic associations in systems composed of low lattice energy salts solvated by polyethers and polyamines for many years. In particular, interactions of the trifluoromethanesulfonate anion (Tf–) in polyethyleneoxide analogs have been well-correlated in several regions (i.e., δs(CF3), νs(SO3) and δs(SO3)). The antisymmetric CF3 stretch (νas(CF3)) in systems with LiTf concentrations ranging from 20:1 heteroatom:Li+ ratio to 5:1 heteroatom:Li+ ratio has been previously examined. However, at LiTf concentrations approaching the solubility limit, data became inconsistent across the δs(CF3), νs(SO3), δs(SO3), and νas(CF3) bands. These issues led to questions of priority of the bands in regard to accuracy. For example, in the 5:1 N:Li+ composed of LiTf in N,N’dimethylethylenediamine (DMEDA), the δs(CF3) band indicates an aggregated system while the νs(SO3) band suggests the presence of some amount of unassociated triflate anion. A similar trend was seen with LiTf in diglyme. These seemingly conflicting results at high concentrations may result from different bands preferentially sampling different populations. Upon further study, the limitations of these types of correlations and the factors making one band a better indicator of ionic association than another should be better understood.

Comparison of ionic association indicators: Lithium triflate in polyamine and polyether systems

2019 Spring National Meeting

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