Piperazinediium dioxamate

The title compound, C4H12N2 2+·2C2H2NO3 −, contains a network of doubly protanated piperazinium cations (lying about centres of inversion) and dioxamate anions. The piperazinium dication adopts a typical chair conformation. The crystal structure is stabilized by cation–to–anion N—H⋯O and anion–to–anion N—H⋯O hydrogen bonds.

, contains a network of doubly protanated piperazinium cations (lying about centres of inversion) and dioxamate anions. The piperazinium dication adopts a typical chair conformation. The crystal structure is stabilized by cation-to-anion N-HÁ Á ÁO and anion-to-anion N-HÁ Á ÁO hydrogen bonds.
SM and ASP thank Dr Babu Vargheese, SAIF, IIT, Madras, India, for his help with the data collection.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: LX2097).

Comment
Piperazines are among the most important building blocks in today's drug discovery. The piperazine nucleus is capable of binding to multiple receptors with high affinity and therefore piperazine has been classified as a privileged structure (Dinsmore et al., 2002). They are found in biologically active compounds across a number of different therapeutic areas (Berkheij et al., 2005) such as antifungal, antibacterial, antimalarial, antipsychotic, antidepressant and antitumour activity against colon, prostate, breast, lung and leukemia tumors (Humle & Cherrier, 1999). Also Piperazine derivatives are widely used as buffers (Good et al., 1966), and can act as complexing reagents with metal ions (Bharathi et al., 2006). Encouraged by the above information, we report the crystal structure of the title compound, piperazinium bis (dioxamate) (I) (Fig. 1).
In the crystal structure of (I), the piperazinium dication lies on a centre of inversion and adopts a typical chair conformation. The bond lengths in (I) are normal and comparable with the corresponding values observed in the related structure (Wilkinson & Harrison, 2007). The dihedral angle between the piperazinium dication and oxamate anion is 9.54 (3)°.
The crystal structure (Fig. 2) is stabilized by cation-to-anion N-H···O hydrogen bonds between the N-H atoms of the piperazinium ring and the O atoms of the oxamate (Fig. 2 and Table 1; symmetry code as in Fig. 2). The crystal packing is further stabilized by anion-to-anion N-H···O hydrogen bonds between the N-H atoms and the O atoms from the neighbouring oxamate anions ( Fig. 2 and Table 1; symmetry code as in Fig. 2). Thus, the symmetry-related molecules are cross linked by these hydrogen bonds to generate a three-dimensional network.

Experimental
Piperazinium bis(dioxamate) was prepared by adding aqueous solution (15ml) of piperazine (0.194g; 0.001mol) to the solution (15ml) of oxamic acid (0.089g; 0.001mol). The resulting clear solution was concentrated over water-bath to half the volume and kept for crystallization at room temperature. The transparent single crystals suitable for x-ray diffraction obtained after two days were filtered off, washed with ethanol and air dried.

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 > 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.