4-Aza-1-azoniabicyclo[2.2.2]octane eosinide

 The title compound, C₆H₁₃N₂⁺·C₂₀H₇Br₄O₅^-, is a molecular salt of singly protonated 1,4-diazabicyclo[2.2.2]octane and the eosinide monoanion. Contrary to a handful of previous crystal structures which contain eosin in its dianionic form, here, the carboxyl group of the anion has retained its H atom. The dihedral angle between the triple ring system and the pendant benzene ring in the anion is 86.0 (2)°. In the crystal structure, the components interact by way of a bifurcated N-H center dot center dot center dot (O,Br) hydrogen bond linking cation and anion, and an O-H center dot center dot center dot O hydrogen bond which links the anions into infinite chains propagating in [001].