Bis(2-trifluoro-methyl-1H-benzimidazol-3-ium) naphthalene-1,5-disulfonate.

The asymmetric unit of the title compound, C(8)H(6)F(3)N(2) (+)·0.5C(10)H(6)O(6)S(2) (2-), consists of one 2-trifluoro-methyl-1H-benz-imidazol-3-ium cation and a half naphthalene-1,5-disulfate anion, which are linked by an N-H⋯O hydrogen bond. The anion sits across a centre of symmetry. The atoms of the benzimidazole ring are nearly coplanar (r.m.s. deviation of the fitted atoms = 0.0085 Å) and the triflouromethyl group lies out of this plane. In the crystal, the cations are linked to adjacent anions by N-H⋯O hydrogen bonds, forming a ladder structure parallel to the a axis in which the anions form the rungs. Adjacent ladders are linked by weak C-H⋯O inter-actions, forming sheets parallel to the ac plane.