2-[3-(1 H -Benzimidazol-2-yl)prop-yl]-1 H -benzimidazol-3-ium 3,4,5-tri-hydroxy-benzoate-1,3-bis-(1 H -benzimidazol-2-yl)propane-ethyl acetate (2/1/2.94): co-crystallization between a salt, a neutral mol-ecule and a solvent.

The chemical formula of the title compound, 2C 17 H 17 N 4 + ·2C 7 H 5 O 5 - ·C 17 H 16 N 4 ·2.94C 4 H 8 O 2 , was established by X-ray diffraction of a single-crystal obtained by reacting 1,3-bis-(benzimidazol-2-yl)propane ( L ) and gallic acid (HGal) in ethyl acetate. The mol-ecular structure can be described as a salt (H L ) + (Gal) - co-crystallized with a mol-ecule L , with a stoichiometric relation of 2:1. Moreover, large voids in the crystal are filled with ethyl acetate, the amount of which was estimated by using a solvent mask during structure refinement, affording the chemical formula (H L + ·Gal - ) 2 · L ·(C 4 H 8 O 2 ) 2.94 . The arrangement of components in the crystal is driven by O-H⋯O, N-H⋯O and O-H⋯N hydrogen bonds rather than by π-π or C-H⋯π inter-actions. In the crystal, mol-ecules and ions shape the boundary of cylindrical tunnels parallel to [100] via R (rings) and D (discrete) supra-molecular motifs. These voids, which account for about 28% of the unit-cell volume, contain disordered solvent mol-ecules.