An unusually short inter-molecular N-H⋯N hydrogen bond in crystals of the hemi-hydro-chloride salt of 1-exo-acetamido-pyrrolizidine

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, C10H14N3O2 +·C4H5O4 - (I), 4-(4-nitro-phen-yl)piperazinium 4-amino-benzoate monohydrate, C10H14N3O2 +·C7H6NO2 -·H2O (II), 4-(4-nitro-phen-yl)piperazinium 2-(4-chloro-phen-yl)acetate, C10H14N3O2 +·C8H6ClO2 - (III) and 4-(4-nitro-phen-yl)piperazinium 2,3,4,5,6-penta-fluoro-benzoate, C10H14N3O2 +·C7F5O2 - (IV). The salts form from mixtures of N-(4-nitro-phen-yl)piperazine and the corresponding acid [succinic acid (I), 4-amino-benzoic acid (II), 2-(4-chloro-phen-yl)acetic acid (III) and 2,3,4,5,6-penta-fluoro-benzoic 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-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 I and II by O-H⋯O hydrogen bonds, and in III by a π-π stacking inter-action between inversion-related 4-nitro-phenyl groups.