2,5-Dihydroxyterephthalic acid dihydrate

The title compound, C₈H₆O₆·2H ₂O, was obtained by accident within a project on the synthesis of metal-organic coordination polymers by the reaction of LiOH with 2,5-dihydroxy-terephthalic acid under solvothermal conditions. The asymmetric unit consists of half a 2,5-dihydroxy-terephthalic acid mol-ecule located on a centre of inversion and one solvent water mol-ecule that occupies a general position. The 2,5-dihydroxy-terephthalic acid mol-ecules are connected to the water mol-ecules via O - H⋯O hydrogen bonding to form a layer in the ab plane.