Hydrated polymorphs of 2,3,4,5,6-pentachlorobenzoic acid: Crystallographical and computational analyses of disordered hydrogen-bonding networks

The title compound, 2,3,4,5,6-pentachlorobenzoic acid (PCBAH), was found to have two crystal poly-morphs, I and II. In this work, novel two hydrated polymorphs, polymorph III and IV, were reported. An asymmetric unit of the polymorph III is comprised of one PCBAH and a water molecule. They align alter-natively along the a axis, forming C 2 2 (6) hydrogen-bonding. The water molecule makes another hydrogen bond with a water molecule in an inversion symmetry to give two-legged ladder hydrogen-bonding net-work. In polymorph IV, there are two PCBAHs, 2,3,4,5,6-pentachlorobenzate (PCBA) and H3O+ in an asym-metric unit. H3O+ molecule makes hydrogen-bonding with two PCBA anions, forming C 2 2 (6) hydrogen-bonding along the 2 1 axis. Two PCBAH molecule make hydrogen bonds with both H3O+ and PCBA. In both hydrated polymorphs, hydrogen atoms of water molecules are disordered. The positions of hydro-gen atoms of the water molecules were determined with assistance of computational calculations under the crystalline environment.(c) 2022 Elsevier B.V. All rights reserved.