Piperazine-1,4-diium diacetate

In the title salt, C4H12N2 2+·2C2H3O2 −, the piperazine-1,4-diium cation has 2/m symmetry with the NH2 unit located on a mirror plane and the acetate anion has m symmetry with all non-H atoms and one H atom located on a mirror plane. The piperazine ring adopts a chair conformation. In the crystal, the cations are linked with the anions via N—H⋯O hydrogen bonding into chains parallel to the c axis.

In the title salt, C 4 H 12 N 2 2+ Á2C 2 H 3 O 2 À , the piperazine-1,4diium cation has 2/m symmetry with the NH 2 unit located on a mirror plane and the acetate anion has m symmetry with all non-H atoms and one H atom located on a mirror plane. The piperazine ring adopts a chair conformation. In the crystal, the cations are linked with the anions via N-HÁ Á ÁO hydrogen bonding into chains parallel to the c axis.

Comment
The amino derivatives have found wide range of applications in material science, such as solid crystalline materials with special optical and dielectric behaviors (Fu et al. 2009). With the purpose of obtaining solid crystalline materials of amino compounds, various amines have been studied and a series of new salts with this organic molecules have elaborated (Blagden et al. 2008;Vishweshwar, et al. 2006). The synthesis of organic salts often relies on the acid-amide H-bonds interactions.
Herein, we report the crystal structure of the title compound, piperazine-1,4-diium acetate.
The asymmetric unit is composed of a quarter piperazine-1,4-diium cation and half acetate anion (Fig.1). The amine N1 atom was protonated. And the carboxyl group was deprotonated to keep the charge balance. The whole anion and N1 atom were located on the ac plane. The geometric parameters of the title compound are in the normal range.
In the crystal structure, all the amino H atoms and hydroxy H atom are involved in intermolecular N-H···O hydrogen bonds interactions with the carboxyl O atoms. These hydrogen bonds link the ionic units into a one-dimentional chain parallel to the c-axis (Table 1 and Fig.2).

Experimental
A mixture of piperazine (2.0 mmol) and acetic acid (2.0 mL) in 20 mL distilled water was refluxed for 5 h, then cooled and filtrated. The filtrate was evaporated slowly in the air. Colorless block crystals suitable for X-ray analysis were obtained after one week.

Refinement
All H atoms attached to C atoms were fixed geometrically and treated as riding with C-H = 0.97 Å (methylene) and C-H = 0.96 Å (methyl) with U iso (H) = 1.2U eq (methylene) and U iso (H) = 1.5U eq (methyl). H atoms bonded to N atoms were located in difference Fourier map and restrained with the H-N1 = 0.90 (2)Å. In the last stage of refinement they were treated as riding on the N atom with U iso (H) = 1.5U eq (N). Fig. 1. Molecular view of the title compound with the atomic numbering scheme. Displacement ellipsoids are drawn at the 30% probability level.

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 supplementary materials sup-3 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 > 2sigma(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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )