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

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 C²₂(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 threedimensional 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). [ABSTRACT FROM AUTHOR]