Syntheses and crystal structures of four 4-(4-nitro-phen-yl)piperazinium salts with hydrogen succinate, 4-amino-benzoate, 2-(4-chloro-phen-yl)acetate and 2,3,4,5,6-penta-fluoro-benzoate anions.

The syntheses and crystal structures are presented for four organic salts of the 4-(4-nitro-phen-yl)piperazinium cation, namely, 4-(4-nitro-phen-yl)piperazinium hydrogen succinate, CHNO ·CHO (), 4-(4-nitro-phen-yl)piperazinium 4-amino-benzoate monohydrate, CHNO ·CHNO ·HO (), 4-(4-nitro-phen-yl)piperazinium 2-(4-chloro-phen-yl)acetate, CHNO ·CHClO () and 4-(4-nitro-phen-yl)piperazinium 2,3,4,5,6-penta-fluoro-benzoate, CHNO ·CFO (). The salts form from mixtures of -(4-nitro-phen-yl)piperazine and the corresponding acid [succinic acid (), 4-amino-benzoic acid (), 2-(4-chloro-phen-yl)acetic acid () and 2,3,4,5,6-penta-fluoro-benzoic acid ()] in mixed solvents of methanol and ethyl acetate. Salts , , and are anhydrous, whereas 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-nitro-phenyl 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 and by O-H⋯O hydrogen bonds, and in by a π-π stacking inter-action between inversion-related 4-nitro-phenyl groups.