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Keywords:

  • electrolytes;
  • ionic liquids;
  • NMR spectroscopy;
  • plastic crystals;
  • X-ray diffraction

Abstract

The carbamoylcyano(nitroso)methanide (ccnm) anion has been used for the synthesis of eight new salts, two of which are liquid at room temperature. The ionic liquid containing a large phosphonium cation displays the highest thermal stability, while the imidazolium salt is the most fluid and conductive. Analysis of the crystal structures of four of the new materials, containing pyrrolidinium and small phosphonium cations, reveals notably different anion stacking behaviour depending on the nature of the cation. The solid [ccnm] salts all display good ionic conductivities, above 1 mS cm−1 for the four different pyrrolidinium species. This, and their soft appearance, is hypothesized to be a result of the presence of both the syn and anti conformational isomers of the [ccnm] anion. Finally, solid-state NMR linewidth analysis and second moment calculations have been used to gain further insight into the disorder within one of the pyrrolidinium plastic crystals, revealing significant, quantifiable translational motion of some fraction of the material at temperatures over 0 °C.