Crystal structures of imidazolium bis(trifluoromethanesulfonyl)imide ?ionic liquid? salts: the first organic salt with a cis-TFSI anion conformationElectronic supplementary information (ESI) available: Fig. S1: Overlays of two cations and anions in the asymmetric unit of I. Fig. S2: Cation?anion hydrogen bonding in I. Fig. S3: Cation?anion hydrogen bonding in II. Fig. S4: DSC traces for II. See http://www.rsc.org/suppdata/dt/b4/b405901h/