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) Å 3 and Z = 2. The dication 2 - 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 -H 2 2+ , which are related in neighbouring molecules by centres of symmetry. Graphical Abstract The 1:2 proton-transfer compound 1,4-diazabicyclo[2.2.2]octane-1,4-diium bis(5-hydroxy-2,4-dinitrophenolate) features pseudo B -centering of the lattice.