Abstract
The structural determination of the ionic liquid, caesium bis-[(tri-fluoro-meth-yl)sulfon-yl]imide or poly[[μ4-bis-[(tri-fluoro-meth-yl)sulfon-yl]imido]caesium(I)], Cs[N(SO2CF3)2] or Cs[Tf2N], reveals a second polymorph that also crystallizes in a layer structure possessing monoclinic P21/c symmetry at 120 K instead of C2/c for the known polymorph [Xue et al. (2002 ▸). Solid State Sci.4, 1535-1545]. The caesium ions in the cationic layers are coordinated by the sulfonyl groups of the bis-triflimide mol-ecules from anion layers while the tri-fluoro-methyl groups are oriented in the opposite direction, forming a non-polar surface separating the layers. The layer direction is (100).