Insight into Local Structure and Molecular Dynamics in Organic Solid-State Ionic Conductors

Elucidating the rate and geometry of molecular dynamics is particularly important for unravelling ion-conduction mechanisms in electrochemical materials. The local molecular motions in the plastic crystal 1-ethyl-1-methylpyrrolidinium tetrafluoroborate ([C(2)mpyr][BF4]) are studied by a combination of quantum chemical calculations and advanced solid-state nuclear magnetic resonance spectroscopy. For the first time, a restricted puckering motion with a small fluctuation angle of 25 degrees in the pyrrolidinium ring has been observed, even in the low-temperature phase (-45 degrees C). This local molecular motion is deemed to be particularly important for the material to maintain its plasticity, and hence, its ion mobility at low temperatures.