Crystal structure, supra-molecular and Hirshfeld surface analysis of piperazine-1,4-diium bis-(2,5-di-bromo-benzoate)

The title salt, C₄H₁₂N₂ ²⁺·2C₇H₃Br₂O₂ ^-, crystallizes in the monoclinic space group P2₁/c with Z = 4. The asymmetric unit comprises one-half of a piperazine-1,4-diium dication, located about an inversion center, and one 2,5-di-bromo-benzoate anion. In the dication, both nitro-gen atoms of the piperazine ring are protonated, while the 2,5-di-bromo-benzoic acid is deprotonated at the carboxyl group. The proton is transferred from the acid to the piperazine mol-ecule, resulting in the formation of the ionic salt. Charge neutrality is achieved by the presence of one dication for every two monobasic 2,5-di-bromo-benzoate anions. The piperazine ring adopts a chair conformation. The cations and anions are linked via N-H⋯O and N-H⋯Br hydrogen bonds, in which the carboxyl-ate O atoms and Br atoms act as acceptors. These inter-actions (N-H⋯O/Br), together with additional C-H⋯Br contacts, contribute to the cohesion of the crystal structure. The resulting supra-molecular architecture is analyzed in detail. Hirshfeld surface (HS) analysis, supported by two-dimensional fingerprint plots, indicates that H⋯O/O⋯H (47.5%) and H⋯Br/Br⋯H (34.0%) contacts are the major contributors for the cation, whereas H⋯Br/Br⋯H (31.6%) and H⋯O/O⋯H (21.4%) inter-actions dominate for the anion.