Six 1-halo­benzoyl-4-(2-meth­­oxy­phen­yl)piperazines having Z′ values of one, two or four; disorder, pseudosymmetry, twinning and supra­molecular assembly in one, two or three dimensions

Six 1-halobenzoyl-4-(2-meth­oxy­phen­yl)piperazines have been prepared using carbodi­imide-mediated coupling reactions between halo­benzoic acids and N-(2-meth­oxy­phen­yl)piperazine. The mol­ecules of 1-(4-fluoro­benzo­yl)-4-(2-meth­oxy­phen­yl)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-Chloro­benzo­yl)-4-(2-meth­oxy­phen­yl)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-bromo­benzo­yl)-4-(2-meth­oxy­phen­yl)piperazine, C18H19BrN2O2 (III), which also crystallizes in space group Pca21 but with Z′ = 2, the bromo­benzoyl unit in one of the mol­ecules 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 mol­ecules of 1-(4-iodo­benzo­yl)-4-(2-meth­oxy­phen­yl)piperazine, C18H19IN2O2 (IV), into simple chains but in the isomeric 3-iodo­benzoyl 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 mol­ecules of 1-(2-fluoro­benzo­yl)-4-(2-meth­oxy­phen­yl)piperazine, C18H19FN2O2 (VI), into simple chains. Comparisons are made with the structures of some related compounds.