Syntheses, crystal structures and Hirshfeld surface analysis of three salts of 1-(4-nitrophenyl)piperazine

Abstract

The structures and Hirshfeld surface analysis of three salts of 1-(4-nitrophenyl)piperazine are discussed. In 4-(4-nitrophenyl)piperazin-1-ium salicylate (C10H14N3O2+·C7H5O3−), there are strong hydrogen bonds between cation and anion and the 4-nitrophenyl substituent occupies an equatorial position in the piperazinium ring. The cation and anion are linked together by supramolecular interactions [graph-set notation of hydrogen bonding C_{2}^{2}(6) propagating in the a-axis direction]. Additionally, there is π–π stacking involving the salicylate anion and the piperazinium cation in adjacent asymmetric units as well as a C—H...π interaction between a hydrogen atom on the piperazine ring and the phenyl ring within the salicyclate anion. In bis[4-(4-nitrophenyl)piperazin-1-ium] bis(4-fluorobenzoate) trihydrate (2C10H14N3O2+·2C7H4FO2−·3H2O), there are two cations, two anions, and three water molecules of solvation in the asymmetric unit, all linked by hydrogen bonds [graph-set notation of hydrogen bonding R22(20) between adjacent cations and R33(9) between a cation and its adjacent anion]. In the anion, the 4-nitrophenyl ring occupies an axial substitution position in the piperazinium ring, which is relatively rare. Within the asymmetric unit, the phenyl groups in the cations show an offset π–π interaction. Additionally, there is a C—H...π interaction between a hydrogen atom on the phenyl ring within a cation and the phenyl ring within an anion. In 4-(4-nitrophenyl)piperazin-1-ium 3,5-dinitrobenzoate (C10H14N3O2+·C7H4N2O6−), there is a strong N—H...O hydrogen bond linking the cation and anion and the 4-nitrophenyl ring occupies an axial substitution position in the piperazinium ring, as seen in the previous structure. In the crystal, the cation and the anion form a complex three-dimensional hydrogen-bonded array involving R22(8), R44(12) and R44(20) rings propogating in the a-axis direction. The nitrophenyl group is disordered with occupancies of 0.806 (10) and 0.194 (10).

Keywords

• crystal structure
• piperazinium salt
• hirshfeld surface analysis
• salicylate
• graph-set notation
• axial and equatorial substitution patterns in piperazinium rings