Six 1-halobenzoyl-4-(2-meth-oxy-phen-yl)piperazines having Z' values of one, two or four; disorder, pseudosymmetry, twinning and supra-molecular assembly in one, two or three dimensions.

Six 1-halobenzoyl-4-(2-meth-oxy-phen-yl)piperazines have been prepared using carbodi-imide-mediated coupling reactions between halo-benzoic acids and N-(2-meth-oxy-phen-yl)piperazine. The mol-ecules of 1-(4-fluoro-benzo-yl)-4-(2-meth-oxy-phen-yl)piperazine, C18H19FN2O2 (I), are linked into a chain of rings by a combination of C-H⋯O and C-H⋯π(arene) hydrogen bonds. 1-(4-Chloro-benzo-yl)-4-(2-meth-oxy-phen-yl)piperazine, C18H19ClN2O2 (II), crystallizes in the space group Pca21 with Z' = 4 and it exhibits both pseudosymmetry and inversion twinning: a combination of six C-H⋯O and two C-H⋯π(arene) hydrogen bonds generate a three-dimensional assembly. In 1-(4-bromo-benzo-yl)-4-(2-meth-oxy-phen-yl)piperazine, C18H19BrN2O2 (III), which also crystallizes in space group Pca21 but with Z' = 2, the bromo-benzoyl unit in one of the mol-ecules is disordered. Pseudosymmetry and inversion twinning are again present, and a combination of three C-H⋯O and one C-H⋯π(arene) hydrogen bonds generate a two-dimensional assembly. A single C-H⋯O hydrogen bond links the mol-ecules of 1-(4-iodo-benzo-yl)-4-(2-meth-oxy-phen-yl)piperazine, C18H19IN2O2 (IV), into simple chains but in the isomeric 3-iodo-benzoyl analogue (V), which crystallizes in space group P212121 with Z' = 2, a two-dimensional assembly is generated by a combination of four C-H⋯O and two C-H⋯π(arene) hydrogen bonds; pseudosymmetry and inversion twinning are again present. A single C-H⋯O hydrogen bond links the mol-ecules of 1-(2-fluoro-benzo-yl)-4-(2-meth-oxy-phen-yl)piperazine, C18H19FN2O2 (VI), into simple chains. Comparisons are made with the structures of some related compounds.