Mixed dicationic and monocationic benzidine species in the proton‐transfer compound of benzidine with 3,5‐dinitro­salicylic acid

The crystal structure of the proton‐transfer compound of 1,1′‐biphenyl‐4,4′‐diamine (benzidine) with 3,5‐dinitro­salicylic acid, viz. 1,1′‐biphenyl‐4,4′‐diaminium bis­(4′‐amino‐1,1′‐bi­phenyl‐4‐aminium) tetra­kis(2‐carb­oxy‐4,6‐dinitro­phenol­ate) ethanol disolvate, C₁₂H₁₄N₂²⁺·2C₁₂H₁₃N₂⁺·4C₇H₃N₂O₇⁻·2C₂H₆O, shows the presence of both diprotonated and monoprotonated benzidine cations. The diprotonated species lie across crystallographic inversion centres in the unit cell, while the monoprotonated species occupy general sites. All amine H atoms participate in hydrogen bonding with carboxyl, phenolate and nitro O‐atom acceptors of the salicylate anions, which also participate in hydrogen bonding with the disordered ethanol solvent mol­ecules. Significant inter‐ring anion–anion and anion–monocation π–π inter­actions are also present, giving a three‐dimensional framework structure.