trans-2,5-Dimethylpiperazine-1,4-diium dinitrate

In the structure of the title salt, C6H16N2 2+·2NO3 −, the cations are connected to the anions through bifurcated N—H⋯(O,O) and weak C—H⋯O hydrogen bonds, generating corrugated layers parallel to the (100) plane. The organic cation is centrosymmetric and the diprotonated piperazine ring adopts a chair conformation, with the methyl groups occupying equatorial positions.

In the structure of the title salt, C 6 H 16 N 2 2+ Á2NO 3 À , the cations are connected to the anions through bifurcated N-HÁ Á Á(O,O) and weak C-HÁ Á ÁO hydrogen bonds, generating corrugated layers parallel to the (100) plane. The organic cation is centrosymmetric and the diprotonated piperazine ring adopts a chair conformation, with the methyl groups occupying equatorial positions.
Supporting information for this paper is available from the IUCr electronic archives (Reference: BG2529).

Comment
Piperazine and its derivatives are widely used due to their interesting biological and pharmacology proprieties (Conrado et al., 2008). In this work, we report the preparation and the structural investigation of a new organic nitrate, C 6 H 16 N 2 ·(NO 3 ) 2 (I). The asymmetric unit of (I) is composed of a half trans-2,5-dimeyhylpipeazine-1,4-dium cations and one nitrate anion ( Figure 1). In the structure, the cations are connected to the anions through bifurcated N-H···O(O) and weak C-H···O hydrogen bonds, generating a corrugated layers parallel to the (001) plane (Fig. 2).
Interatomic bond lengths and angles of the nitrate anions spread respectively within the ranges [1.2398 (13)-1.2706 (13) Å] and [118.65 (10)-121.73 (10)°]. These geometrical features have also been noticed in other crystal structures (Marouani et al., 2012;Kefi et al., 2013;Gatfaoui et al., 2013Gatfaoui et al., , 2014a. It is worth noting that the distance N1-O1 is significantly longer than the N1-O2 and N1-O3 distances because O1 is applied in three hydrogen bonds (table1) while O2 and O3 are applied in only one hydrogen bond. Inside such a structure, the complete organic entity is generated by inversion symmetry located at (0, 0, 0) and (0, 1/2, 1/2). So it is built up by only the half of the cation. Examination of the organic cations shows that the bond distances and angles show no significant difference from those obtained in other complex involving the same organic groups (Rother et al., 1997). The diprotonated piperazine ring adopts a chair conformation, with the methyl groups occupying an equatorial position, with puckering parameters: Q = 0.6083 Å, θ = 90 ° and φ = 166 ° (Cremer & Pople, 1975).
The established H-bonds of types N-H···O(O) and C-H···O involve oxygen atoms of the nitrate anions as acceptors, and protonated nitrogen atoms and methine groups of the trans-2,5-dimethylpiperazine-1,4-diium as donors.

Experimental
An aqueous solution containing 2 mmol of HNO 3 in 10 ml of water was added to 1 mmol of trans-2,5-dimethylpiperazine in 20 ml of water. The obtained solution was stirred for 1 h, filtered and then left to stand at room temperature. Colorless single crystals of the title compound were obtained after some days.

Refinement
All H atoms were located in a difference map. Nevertheless, they were geometrically placed and refined using a riding    Projection of (I) along the a axis. The H-atoms not involved in H-bonding are omitted. 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.