N-methyl-N-alkylpyrrolidinium tetrafluoroborate salts : ionic solvents and solid electrolytes

A series of <i>N</i>-methyl-<i>N</i>-alkylpyrrolidinium tetrafluoroborate salts were synthesised. The spectroscopic, physical and electrochemical characteristics of this family of salts have been investigated with respect to potential usage as ionic solvents and electrolytes. The lowest melting point among the family is 64°C for the <i>N</i>-methyl-<i>N</i>-propylpyrrolidinium tetrafluoroborate (P₁₃BF₄). This is sufficiently low to enable this salt to be useful as an ionic liquid in chemical synthesis involving reactions above 70°C. Most of the compounds exhibit one or more solid–solid transitions below the melting point, this behaviour is thought to indicate the existence of plastic crystal phases.<br />