A monoclinic polymorph of 5-[(1H-benzimidazol-1-yl)meth­yl]benzene-1,3-dicarb­oxy­lic acid

Crystals of the title compound, C₁₆H₁₂N₂O₄, were obtained accidentally by the hydro­thermal reaction of 5-[(1H-benzo[d]imidazol-1-yl)meth­yl]isophthalic acid with manganese chloride tetra­hydrate in the presence of KOH as alkaline reagent for the deprotonation. A triclinic polymorph of this structure has been reported previously from a similar reaction [Cheng (2011). Acta Cryst. E67, o3299]. The benzimidazole ring system is almost planar, with a maximum deviation from the mean plane of 0.020 (4) Å. The benzimidazole unit and benzene ring are inclined at a dihedral angle of 68.17 (4)°, reflecting the axial rotation of the flexible benzimidazolyl arm. In the crystal, pairs of O—H...O hydrogen bonds link adjacent mol­ecules into inversion dimers. O—H...N contacts connect these dimers into zigzag chains along [010].