- G. R. Goward, K. Saalwächter, I. Fischbach, and H. W. Spiess.
Reorientation Phenomena in Imidazole Methyl Sulfonate as Probed
by Advanced Solid-State NMR.
Solid-State NMR 24, 150-162 (2003).
Evidence for reorientation of imidazolium rings in imidazole methylsulfonate is
demonstrated using solid-state NMR. This material is a model system for exciting
new proton-conducting materials based on imidazole. Two advanced NMR methods,
and 1H-15N REPT
(recoupled polarization transfer) with dipolar sideband pattern analysis, and
analysis of the coalescence of 13C lineshapes
are used to characterize the ring reorientation. The process is found to occur
at temperatures well below the melting point of the salt, between 240K-380K, and
is described by a single activation energy, of 53±5 kJ/mol. This material is
considered as a model system for quantifying the ring reorientation process,
which is often proposed to be the rate limiting step in proton transport in
imidazole-based proton conducting materials.