N-methyl-N-alkylpyrrolidinium bis(perfluoroethylsulfonyl)amide ([NPf 2]-) and tris(trifluoromethanesulfonyl)methide ([CTf 3]-) salts: Synthesis and characterization

Novel salts based the pyrrolidinium cation [C(n)mpyr](+) (where n denote the number of carbons in the straight alkyl chain) and either the [NPf(2)](-) or [CTf3](-) anions have been synthesized and characterized to determine their thermal behaviour, stability, and conductivity. [C(1)mpyr][NPf(2)], [C(2)mpyr][NPf(2)], and [C(1)mpyr][CTf3] exhibit behaviour indicative of a plastic crystal phase. Both [C(3)mpyr][NPf(2)] and [C(4)mpyr][NPf(2)] are RTILs, while all of the [CTf3](-) salts, have melting points above 60 degrees C. [C(3)mpyr][NPf(2)] exhibited the widest electrochemical window of 5.5V. The [NPf(2)](-) salt exhibited similar reductive limits to the [NTf2](-) anion, -3.2V versus Fc(+) Fc, while [CTf3](-) had lower reductive stability. The [CTf3](-) salts were more stable towards oxidation, +2.5V versus Fc(+) Fc, compared to the [NPf(2)](-) and [NTf2](-) salts.