Six 1-aroyl-4-(4-methoxyphenyl)piperazines: similar molecular structures but different patterns of supramolecular assembly

Six new 1-aroyl-4-(4-meth­oxy­phen­yl)piperazines have been prepared, using coupling reactions between benzoic acids and N-(4-meth­oxy­phen­yl)piperazine. There are no significant hydrogen bonds in the structure of 1-benzoyl-4-(4-meth­oxy­phen­yl)piperazine, C₁₈H₂₀N₂O₂, (I). The mol­ecules of 1-(2-fluoro­benzo­yl)-4-(4-meth­oxy­phen­yl)piperazine, C₁₈H₁₉FN₂O₂, (II), are linked by two C—H⋯O hydrogen bonds to form chains of rings, which are linked into sheets by an aromatic π–π stacking inter­action. 1-(2-Chloro­benzo­yl)-4-(4-meth­oxy­phen­yl)piperazine, C₁₈H₁₉ClN₂O₂, (III), 1-(2-bromo­benzo­yl)-4-(4-meth­oxy­phen­yl)piperazine, C₁₈H₁₉BrN₂O₂, (IV), and 1-(2-iodo­benzo­yl)-4-(4-meth­oxyphen­yl)piperazine, C₁₈H₁₉IN₂O₂, (V), are isomorphous, but in (III) the aroyl ring is disordered over two sets of atomic sites having occupancies of 0.942 (2) and 0.058 (2). In each of (III)–(V), a combination of two C—H⋯π(arene) hydrogen bonds links the mol­ecules into sheets. A single O—H⋯O hydrogen bond links the mol­ecules of 1-(2-hy­droxy­benzo­yl)-4-(4-meth­oxy­phen­yl)piperazine, C₁₈H₂₀N₂O₃, (VI), into simple chains. Comparisons are made with the structures of some related compounds.