1-(2-Ammonioethyl)piperazin-1,4-diium dihydrogenophosphate monohydrogenophosphate

The structure of the title compound, C6H18N3·HPO4·H2PO4, is characterized by two kinds of inorganic chains running along the a-axis direction. The first one is composed of HPO4 2− anions, while the second one is built up by H2PO4 − anions. Both types of chains are held together by O—H⋯O hydrogen bonds. The organic cations are attached to these chains through N—H⋯O and C—H⋯O hydrogen bonds. The piperazin-1,4-diium ring adopts a chair conformation.

The structure of the title compound, C 6 H 18 N 3 ÁHPO 4 ÁH 2 PO 4 , is characterized by two kinds of inorganic chains running along the a-axis direction. The first one is composed of HPO 4 2À anions, while the second one is built up by H 2 PO 4 À anions. Both types of chains are held together by O-HÁ Á ÁO hydrogen bonds. The organic cations are attached to these chains through N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds. The piperazin-1,4-diium ring adopts a chair conformation.
Data collection: KappaCCD Server Software (Nonius, 1997); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN; program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEPIII (Burnett & Johnson, 1996); software used to prepare material for publication: SHELXL97 and WinGX (Farrugia, 1999). During the systematic investigation of interaction between monophosphoric acid with organic molecules, numerous structures of monophosphates with organic cations have been described. Hydrogen bonds take part to the stability and the cohesion of the corresponding compounds. We report in this work the chemical preparation and the structural investigation of a new hydrogenomonophosphate C 6 H 18 N 3 HO 4 PH 2 O 4 P. The main feature of the atomic arrangement is the existence of two kinds of infinite chains, located at y = 1/4 and y = 3/4, and crossing the unit cell parallel to the adirection. The first one is composed of HPO 4 2groups. The second one is formed by H 2 PO 4anions and characterized by the association between the neighboring chains via strong O-H···O hydrogen bonds with an R 2 2 (8) graph set motif (Bernstein et al., 1995) centered at (1/2, 1/2, 0) (Fig. 2). The ammonioethylpiperazinediium cations are anchored onto successive chains through N-H···O and C-H···O hydrogen bonds (Fig. 3). The piperazinediium ring adopts a chair conformation and all the measured main features are similar to intramolecular bond distances and angles usually reported for such ring in hydrogenmonophosphate of organic cations (Jensen et al., 2007). With regards to the geometrical features of the monophosphate anions, we remark the existence of two types of P-O distances. The shorter ones, varying between 1.488 (1) and 1.522 (1) Å, correspond to the oxygen atoms double bonded to the phosphorous atom, while the largest ones, varying between 1.556 (2) and 1.586 (1) Å, are associated with the P-OH single bond. This is in agreement with the literature data for monohydrogenophosphate anion in similar arrangements (e.g. Chtioui & Jouini, 2006;Kaabi et al., 2004).

Experimental
Crystals of the title compound were prepared at room temperature by slow addition of a solution of orthophosphoric acid (4 mmol in 30 ml of water) to an alcoholic solution of N-aminoethylpiperazine (2 mmol in 30 ml of ethanol). The acid was added until the alcoholic solution becomes turbid. After filtration, the solution was allowed to slowly evaporate at room temperature over several days leading to formation of transparent prismatic crystals with suitable dimensions for single-crystal structural analysis (yield 50%). The crystals are stable for months under normal conditions of temperature and humidity.

Refinement
The structure was refined using full-matrix least squares with anisotropic non-H atoms. All hydrogen atoms were located in the Difference Fourier map and refined isotropically.

Figure 1
A view of the title compound, showing 50% probability displacement ellipsoids and arbitrary spheres for the H atoms.  Projection along the c-axis of the inorganic chains in the structure of the title compound. PO 4 is given in the tetrahedral representation. Hydrogen bonds are shown as broken lines.

Figure 3
The packing diagram of the compound viewed down the b-axis. PO 4 is given in the tetrahedral representation. Hydrogen bonds are shown as broken lines.

1-(2-Ammonioethyl)piperazin-1,4-diium dihydrogenophosphate monohydrogenophosphate
Crystal data 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.