Supplementary Figures Photographs of the sublimation apparatus Cold finger with thin layer of condensate Undistilled [C6mim][NTf2] Empty apparatus for comparison Supplementary Figure 13. A picture of the sublimation apparatus at the end of the distillation experiment with [C6mim][NTf2] in dry air at atmospheric pressure (left) and of a clean, empty sublimation apparatus for comparison (right). After 2 h at 250 C the liquid remaining in the flask was dark yellow and most of the cold finger was coated with a thin, barely visible film of condensate. Cold finger with distilled [C6mim][NTf2] Undistilled [C6mim][NTf2] Supplementary Figure 14. A picture of the sublimation apparatus at the end of the distillation experiment with [C6mim][NTf2] at ≤ 0.001 mbar. After an hour at 200 C, large beads of liquid had formed on the cold finger and on the lower wall of the flask; the liquid in the flask was still clear and colourless to the eye.