The Pseudo Symmetric Crystal Structure of 1,4-Diazabicyclo[2·2·2]octane-1,4-diium bis(5-hydroxy-2,4-dinitrophenolate)

Reaction of 4,6-dinitroresorcinol (1) and the nitrogen base 1,4-diazabicyclo[2·2·2]octane (2) affords the 1:2 salt and proton-transfer compound 1,4-diazabicyclo[2·2·2]octane-1,4-diium bis(5-hydroxy-2,4-dinitrophenolate) (3). Compound 3 crystallizes in the triclinic crystal system (space group P-1) with a = 8.3242(5) Å, b = 11.9915(7) Å, c = 12.4595(7) Å, α = 116.282(2)°, β = 100.576(3)°, γ = 101.051(2)°, 1042.30(11) ų and Z = 2. The dication 2- \({\text{H}}_{2}^{2+}\) ${\text{H}}_2^{2+}$ forms charge assisted donating bifurcated N⁺−H⋅⋅⋅O⁻ hydrogen bonds to the phenolate moieties of two monoanions of 1. The latter exhibit an intramolecular O−H⋅⋅⋅O hydrogen bond between the hydroxy group and the nitro group in ortho position. The crystal structure of 3 features pseudo B-centering of the lattice, which relates the two crystallographically distinct monoanions of 1 by a pseudo translation. The possible B-centring is broken by the ethylene groups of 2-H₂²⁺, which are related in neighbouring molecules by centres of symmetry.