Syntheses and crystal structures of four 4-(4-nitro­phen­yl)piperazinium salts with hydrogen succinate, 4-amino­benzoate, 2-(4-chloro­phen­yl)acetate and 2,3,4,5,6-penta­fluoro­benzoate anions

The syntheses and crystal structures are presented for four organic salts of the 4-(4-nitro­phen­yl)piperazinium cation, namely, 4-(4-nitro­phen­yl)piperazinium hydrogen succinate, C(10)H(14)N(3)O(2) (+)·C(4)H(5)O(4) (−) (I), 4-(4-nitro­phen­yl)piperazinium 4-amino­benzoate monohydrate, C(10)H(14)N(3)O(2) (+)·C(7)H(6)NO(2) (−)·H(2)O (II), 4-(4-nitro­phen­yl)piperazinium 2-(4-chloro­phen­yl)acetate, C(10)H(14)N(3)O(2) (+)·C(8)H(6)ClO(2) (−) (III) and 4-(4-nitro­phen­yl)piperazinium 2,3,4,5,6-penta­fluoro­benzoate, C(10)H(14)N(3)O(2) (+)·C(7)F(5)O(2) (−) (IV). The salts form from mixtures of N-(4-nitro­phen­yl)piperazine and the corresponding acid [succinic acid (I), 4-amino­benzoic acid (II), 2-(4-chloro­phen­yl)acetic acid (III) and 2,3,4,5,6-penta­fluoro­benzoic acid (IV)] in mixed solvents of methanol and ethyl acetate. Salts I, III, and IV are anhydrous, whereas II is a monohydrate. In each structure, the overall conformation of the cation is determined by the disposition of the exocyclic N—C bond of the piperazine ring (either axial or equatorial) and twists about the N—C bond between the piperazine ring and its attached 4-nitro­phenyl ring. The packing motifs in each structure are quite different, though all are dominated by strong N—H⋯O hydrogen bonds, which are augmented in I and II by O—H⋯O hydrogen bonds, and in III by a π–π stacking inter­action between inversion-related 4-nitro­phenyl groups.