Syntheses and crystal structures of four 4-(4-nitro-phenyl)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, C₁₀H₁₄N₃O₂⁺․C₄H₅O₄⁻ (I), 4-(4-nitrophenyl)piperazinium 4-aminobenzoate monohydrate, C₁₀H₁₄N₃O₂⁺․C₇H₆NO₂⁻․H₂O (II), 4-(4-nitro-phenyl)piperazinium 2-(4-chlorophenyl)acetate, C₁₀H₁₄N₃O₂⁺․C₈H₆ClO₂⁻ (III) and 4-(4-nitrophenyl)piperazinium 2,3,4,5,6-pentafluorobenzoate, C₁₀H₁₄N₃O₂⁺․C₇F₅O₂⁻ (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.