Taking the guesswork out of ionic liquids

What is it about the structures of ionic liquids (ILs) that make them so promising as alternatives to conventional solvent systems? In an attempt to figure this out, Robin Rogers and his colleagues at the University of Alabama, US, have looked at the crystal structures of two ILs with bis(trifluoromethane-sulfonyl)imide (TFSI) as the anion. Somewhat surprisingly, they found that with 1,3-dimethylimidazolium as the cation, in the solid state, the TFSI ion had a cis geometry, which is a first for this kind of salt.

As well as uncovering new information about IL structures, the skill it takes to crystallise samples of the ILs is in itself impressive. And for the future? Rogers says that his structural work is an ’attempt to understand ILs at a fundamental molecular level and utilise that understanding to design "ideal" ILs for a given application’, adding that ’without a method to model or predict physical properties of the ILs we are reduced to trial and error or at best educated guessing’.

Katharine Sanderson