1,4-Diazoniabicyclo[2.2.2]octane bis(2,4,6-trinitrophenolate)

In the title compound, C6H14N2 2+·2C6H2N3O7 −, the cation possesses crystallographically imposed twofold rotation symmetry. In the crystal structure, the cation and anions are linked into a trimeric aggregate by intermolecular N—H⋯O hydrogen bonds. The trimeric units are further connected by π–π interactions [centroid–centroid distances = 3.507 (2)–3.660 (3) Å], forming layers parallel to the bc plane.

In the title compound, C 6 H 14 N 2 2+ Á2C 6 H 2 N 3 O 7 À , the cation possesses crystallographically imposed twofold rotation symmetry. In the crystal structure, the cation and anions are linked into a trimeric aggregate by intermolecular N-HÁ Á ÁO hydrogen bonds. The trimeric units are further connected by interactions [centroid-centroid distances = 3.507 (2)-3.660 (3) Å ], forming layers parallel to the bc plane.   Table 1 Hydrogen-bond geometry (Å , ). The author is grateful to the starter fund of Southeast University for financial support to buy the X-ray diffractometer.

Comment
The co-crystals of 1,4-diazabicyclo[2.2.2]octane (DABCO) and phenols are typically characterized by the presence of N-H···O or O-H···N hydrogen-bonded adducts (Kumai et al. (2007);Horiuchi et al., 2005). Many of this type of cocrystals have been designed by employing crystal-engineering strategies, and their structures have been studied extensively (Dabros et al., 2007;Jin et al., 2004;Glidewell et al., 1999). As a continuation of a study of phase transitions in hydrogen-bonded co-crystalline compounds between phenols and tertiary amines as N-H···O-type systems (Chen et al., 2009), the crystal structure of the 1:2 co-crystal of DABCO and 2,4,6-trinitrophenol obtained by a single-crystal X-ray analysis is reported herein. The compound shows no dielectric irregularity in the temperature range of 93-373K.
The cation has crystallographically imposed twofold rotation symmetry. The two protonated N atoms in the cation are almost equivalent with very close C-N bond lengths [1.4930 (19) to 1.4952 (18) Å] and C-N-C angles [109.79 (11)° to 110.72 (11)°]. Within the benzene ring of the 2,4,6-trinitrophenol anion, the C-C-C bond angles of the three nitro-connected C atoms are in the range 121.92 (13)-126.76 (13)°, and are a little larger than the remaining three C-C-C bond angles. In the crystal structure (Fig. 2), cation and anions are linked into a trimeric aggregate by intermolecular N-H···O hydrogen bonds (Table 1). The trimeric units are further connected by π-π interactions (centroid-to-centroid distance = 3.507 (2)-3.660 (3) Å) to form layers parallel to the bc plane.
Experimental 1,4-Diazabicyclo[2.2.2]octane (DABCO) (2.5 mmol) was dissolved in ethanol (10 ml).The clear solution obtained was added to a solution of 2,4,6-trinitrophenol(5 mmol) in ethanol (20 ml). The formed precipitate was then filtered and the obtained yellow solid was redissolved in DMF (15 ml). Yellow co-crystals of the title compound suitable for X-ray diffraction analysis were obtained by slow evaporation of the mixture at room temperature after 7 days.

Refinement
All the H atoms were calculated geometrically and were allowed to ride, with C-H = 0.95-0.99 Å, N-H = 0.93 Å, and with U iso (H) = 1.2U eq (C, N). Fig. 1. The molecular structure of the title compound, with the atomic numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. Atoms labelled with suffix A are generated by the symmetry operation (-x, y, 0.5-z).

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.