Cs[Tf(2)N]: a second polymorph with a layered structure

The structural determination of the ionic liquid, caesium bis­[(tri­fluoro­meth­yl)sulfon­yl]imide or poly[[μ(4)-bis­[(tri­fluoro­meth­yl)sulfon­yl]imido]caesium(I)], Cs[N(SO(2)CF(3))(2)] or Cs[Tf(2)N], reveals a second polymorph that also crystallizes in a layer structure possessing monoclinic P2(1)/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 bis­triflimide mol­ecules from anion layers while the tri­fluoro­methyl groups are oriented in the opposite direction, forming a non-polar surface separating the layers. The layer direction is (100).