A monoclinic polymorph of 5-[(1H-benzimidazol-1-yl)meth-yl]benzene-1,3-dicarb-oxy-lic acid.

Crystals of the title compound, C(16)H(12)N(2)O(4), were obtained accidentally by the hydro-thermal reaction of 5-[(1H-benzo[d]imidazol-1-yl)meth-yl]isophthalic acid with manganese chloride tetra-hydrate 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 mol-ecules into inversion dimers. O-H⋯N contacts connect these dimers into zigzag chains along [010].