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

The title compound, C18H18Cl4N2O2, crystallizes as monoclinic and orthorhombic polymorphs from CHCl3-CH3OH 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 center dot center dot center dot N hydrogen bond. In the monoclinic polymorph (space group P2(1)/ c), the molecules are linked by intermolecular C-H center dot center dot center dot Cl hydrogen bonds into a ribbon sheet built from R-8(8)(34) rings. In the orthorhombic polymorph (space group Pbcn), the molecules are linked by intermolecular C-H center dot center dot center dot O hydrogen bonds into a ribbon sheet of R-6(6)(34) rings. The sheets in the orthorhombic polymorph are crosslinked into a three-dimensional framework by pi-pi stacking interactions.