1H NMR Relaxation Studies of Proton-Conducting Imidazolium Salts of Dicarboxylic Acids

Abstract

The proton nuclear magnetic resonance spin–lattice relaxation time has been successfully used to evidence the reorientation of the imidazolium rings in carboxylic acid salts of imidazole: imidazolium oxalate, imidazolium adipate monohydrate and diimidazolium suberate. The process occurs in the temperature range between 325 K and the melting point of the salts (523, 379 and 360 K) and is described by a single activation energy of 20, 48 and 66 kJ/mol for imidazolium oxalate, imidazolium adipate monohydrate and diimidazolium suberate, respectively. The studied salts are considered as possible candidate materials for fuel-cell membranes.