4,4′-Dichloro-2,2′-(piperazine-1,4-diyldimethylene)diphenol

In the titile compound, C18H20Cl2N2O2, the piperazine ring adopts a chair conformation. The molecule has a non-crystallographic inversion centre in the middle of the piperazine ring at approximate position (3/4, 1/8, 3/8). There are intramolecular O—H⋯N hydrogen bonds forming S(6) ring motifs. Intermolecular C—H⋯O hydrogen bonds generate antiparallel C(5) chain motifs propagating along the b axis, forming sheets parallel to the bc plane with a first-level graph-set S(6)C(5)R 6 6(26).

The molecular structure of the title compound ( In the crystal structure of (I), there are two intermolecular C-H···O hydrogen bonds (Table 1). Atom C7 in the molecule at (x, y, z) acts as hydrogen bond donor to atom O2 in the molecule at (x, 1/2 -y, z -1/2), so forming a C(5) (Bernstein et al., 1995) chain running parallel to the [010] direction and generated by the c-glide plane at y = 1/4. In addition, atom C12 in the molecule at (x, y, z) acts as hydrogen bond donor to atom O1 atom in the molecule at (3/2 -x, -y, 1/2 + z), so forming a C(5) chain running parallel to the [010] direction and generated by the 2 1 screw axis along (3/4, 0, z). The molecules are linked by the combination of the two S(6) rings and the two antiparalle C(5) chains into a sheet parallel to b,c-plane with a first level graph set S(6)C(5)R 6 6 (26) (Fig. 2).

Experimental
A mixture of 4-chlorophenol (25.0 g, 194 mmol), piperazine (8.34 g, 97.2 mmol) and paraformaldehyde (5.82 g, 194 mmol) in methanol (80 ml) was refluxed for 6 h. The mixture was cooled to room temperature, then the solvent was evaporated under vacuum. The product was recrystallized from CHCl 3 -MeOH to give prismatic crystals of (I) [

Refinement
The H atoms of the hydroxyl groups were found from a difference Fourier map. The other H atoms were placed at idealized positions with C-H = 0.95 Å. All the H atoms were refined as a riding model with U iso (H) = 1.2 U eq (C).  Fig. 1. The molecular structure of (I) with the atom-labelling scheme and displacement ellipsoids are drawn at the 50% probability level. H atoms are represented by circles of arbitrary size.

Special details
Geometry. The molecule adopts a non-crystallographic inversion centre in the middle of the piperazine ring at an approximate position (3/4, 1/8, 3/8).
Refinement. Refinement was performed using reflections with F 2 > 2.0 σ(F 2 ). The weighted R-factor (wR) and goodness of fit (S) are based on F 2 . R-factor (gt) are based on F. The threshold expression of F 2 > 2.0 σ(F 2 ) is used only for calculating R-factor (gt).