⁷Li nuclear magnetic spin–lattice relaxation investigation of lithium trifluoromethanesulfonate and its complex with poly(ethylene oxide)

Abstract

A 7Li NMR spin–lattice relaxation investigation over the temperature range 200–340 K is reported for a polycrystalline sample of LiCF3SO3 and a sample of poly(ethylene oxide)(PEO)–LiCF3SO3 with an O: Li molar ratio of 3.5:1. In both cases the 7Li magnetization recoveries were found to be single exponential and so the spin–lattice relaxation could be characterized by a single time constant, T1(7Li). The 7Li spin–lattice relaxation in polycrystalline LiCF3SO3 is shown to be dominated by a mechanism that involves the modulation of 7Li,19F magnetic dipolar interactions due to the reorientational motions of the CF3 groups about their threefold symmetry axes. The Arrhenius parameters derived for this motion are shown to be in good agreement with those determined in an earlier 19F spin–lattice relaxation study. The 7Li spin–lattice relaxation time measurements in the 3.5:1 PEO–LiCF3SO3 sample are taken to reflect the properties of the single crystalline complex, which is known to be present in PEO–LiCF3SO3 mixtures. The extent to which magnetic dipolar relaxation processes contribute to 7Li spin–lattice relaxation in this complex is discussed in some detail. It is demonstrated that modulation of 7Li, 1H magnetic dipolar interactions, due to backbone motions of the PEO chains, probably makes a significant contribution. There also appear to be strong links between the motional processes responsible for both 1H and 7Li spin–lattice relaxation.