Crystal structures of six 4-(4-nitro­phenyl)­piperazin-1-ium salts

Six piperazinium salts, namely 4-(4-nitro­phenyl)­piperazin-1-ium 4-bromo­ben­zo­ate dihydrate, C(10)H(14)N(3)O(2) (+)·C(7)H(4)BrO(2) (−)·2H(2)O, (I), 4-(4-nitro­phenyl)­pi­per­a­zin-1-ium 4-iodo­benzoate dihydrate, C(10)H(14)N(3)O(2) (+)·C(7)H(4)IO(2) (−)·2H(2)O, (II), 4-(4-nitro­phenyl)­piperazin-1-ium 4-hy­droxy­benzoate monohydrate, C(10)H(14)N(3)O(2) (+)·C(7)H(5)O(3) (−)·H(2)O, (III), 4-(4-nitro­phenyl)­piperazin-1-ium 4-methyl­benzoate monohydrate, C(10)H(14)N(3)O(2) (+)·C(8)H(7)O(2) (−)·H(2)O, (IV), 4-(4-nitro­phenyl)­piperazin-1-ium 4-meth­oxy­benzoate hemihydrate, 2C(10)H(14)N(3)O(2) (+)·2C(8)H(7)O(3) (−)·H(2)O, (V), and 4-(4-nitro­phenyl)­piperazin-1-ium 4-eth­oxy­benzoate, 2C(10)H(14)N(3)O(2) (+)·2C(9)H(9)O(3) (−), (VI), have been synthesized and their crystal structures solved by single-crystal X-ray diffraction, revealing that all of them crystallize in the triclinic space group P [Image: see text] except for (V), which crystallizes in the monoclinic space group P2(1)/c and has a disordered nitro group. Compounds (I) and (II) are isostructural. The crystal packing of (I)–(V) is constructed from organic chains formed by a combination of hydrogen bonds of type N—H⋯O and/or O—H⋯O and other weak inter­actions of type C—H⋯O and/or C—H⋯π, forming sheets, whereas (VI) shows a cationic and anionic-based layer structure.