Crystal structure of N,N-diethylbenzene-1,4-diaminium dinitrate

In the structure of the title molecular salt, C10H18N2 2+·2NO3 −, the dinitrate salt of 4-(N,N-diethylamino)aniline, the two ethyl groups lie almost perpendicular to the plane of the benzene ring [the ring-to-ethyl C—C—N—C torsion angles are −59.5 (2) and 67.5 (3)°]. The aminium groups of the cation form inter-species N—H⋯O hydrogen bonds with the nitro O-atom acceptors of both anions, giving rise to chain substructures lying along c. The chains are linked via further N—H⋯O hydrogen bonds, forming two-dimensional networks lying parallel to (010). These sheets are linked by C—H⋯O hydrogen bonds, forming a three-dimensional structure.

In the title compound, Fig. 1, the two ethyl groups lie almost perpendicular to the plane of the benzene ring [C5-C4-N2-C7/C8 torsion angles are 67.5 (3) and -59.5 (2)°], respectively, which is similar to the conformation assumed by these groups in the structures of the analogous dications in all of the prevously mentioned complex structures.
In the crystal of the title salt, all the aminium groups of the cation form inter-species N-H···O hydrogen bonds with the nitro O-atoms of both anions (Table 1), which includes an asymmetric three-centre R 2 1 (4) association with the tertiary aminium group (N2) and O1 and O2 (Table 1). One-dimensional chains are formed along c (Fig. 2) and are further extended into a two-dimensional network lying parallel to (010). Weak C-H···O hydrogen-bonding associations are also present in an overall three-dimensional structure (Fig. 3), in which nitrate O-atoms O4 and O6 are not involved in any interactions.
After 10 d, single crystals suitable for X-ray diffraction were collected by filtration, washed with water and dried in air (yield 35%).

S3. Refinement
N-bound H atoms were located from a difference Fourier map and included in the refinement with restraints [N-H = 0.88 (2) Å] and allowed to ride with U iso (H) = 1.2U eq (N). Other H-atoms were placed in calculated positions [C-H = 0.93 Å (aromatic), 0.97 Å (methylene) and 0.96 Å (methyl)] and allowed to ride in the refinement, with U iso (H) = 1.2U eq (C) (aromatic and methylene) or 1.5U eq (C) (methyl).  The molecular structure of the title salt, with atom labelling. Displacement ellipsoids are drawn at the 30% probability level. Hydrogen bonds are shown as dashed lines (see Table 1 for details).

Figure 2
A partial extension of the cation-anion chain substructure in the title salt in the unit cell viewed along a. Non-associative H-atoms are omitted and formal hydrogen-bonding associations are shown as dashed lines (see Table 1 for details; for symmetry codes see Table 1).

Figure 3
The crystal packing of the title salt viewed along c, illustrating the three-dimensional structure. Hydrogen bonds are shown as dashed lines (see Table 1 for details).

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles 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 R-factors(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.