Pyrrolidinium imides: A new family of molten salts and conductive plastic crystal phases

A new family of molten salts is reported, based on the N-alkyl, N-alkyl pyr rolidinium cation and the bis-(trifluoromethane sulfonyl)imide anion. Some of the members of the family are molten at room temperature, while the smal ler and more symmetrical members have melting points around 100 degrees C. Of the room-temperature molten salt examples, the methyl butyl derivative e xhibits the highest conductivity; at 2 x 10(-3) S/cm this is the highest mo lten salt conductivity observed to date at room temperature among the ammon ium salts. This highly conductive behavior is rationalized in terms of the role of cation planarity. The salts also exhibit multiple crystalline phase behavior below their melting points and exhibit significant conductivity i n at least their higher temperature crystal phase. For example, the methyl propyl derivative (mp = 12 degrees C) shows ion conductivity of 1 x 10(-6) S/cm at 0 degrees C in its higher temperature crystalline phase.