Monoclinic and orthorhombic polymorphs of 4,4',6,6'-tetrachloro-2,2'-(piperazine-1,4-diyldimethylene)diphenol.

The title compound, C(18)H(18)Cl(4)N(2)O(2), crystallizes as monoclinic and orthorhombic polymorphs from CHCl3-CH(3)OH solution. In both polymorphic forms, the molecule lies on a crystallographic centre of inversion (at the piperazine ring centroid) and exhibits an intramolecular O-H...N hydrogen bond. In the monoclinic polymorph (space group P2(1)/c), the molecules are linked by intermolecular C-H...Cl hydrogen bonds into a ribbon sheet built from R8(8)(34) rings. In the orthorhombic polymorph (space group Pbcn), the molecules are linked by intermolecular C-H...O hydrogen bonds into a ribbon sheet of R6(6)(34) rings. The sheets in the orthorhombic polymorph are crosslinked into a three-dimensional framework by pi-pi stacking interactions.