Crystal structures of 4-(pyrimidin-2-yl)piperazin-1-ium chloride and 4-(pyrimidin-2-yl)piperazin-1-ium nitrate

The title salts, C8H13N4 +·Cl−, (I), and C8H13N4 +·NO3 −, (II), contain linked pyridinium–piperazine heterocycles. In the crystal of (I), weak N—H⋯Cl interactions lead to zigzag chains along [100] while in the crystal of (II), bifurcated N—H⋯(O,O) hydrogen bonds and weak C—H⋯O interactions collectively link the components into infinite chains along [100].

The title salts, C 8 H 13 N 4 + ÁCl À , (I), and C 8 H 13 N 4 + ÁNO 3 À , (II), contain linked pyridinium-piperazine heterocycles. In both salts, the piperazine ring adopts a chair conformation with protonation at the N atom not linked to the other ring. In the crystal of (I), weak N-HÁ Á ÁCl interactions are observed, leading to zigzag chains along [100]. In the crystal of (II), both H atoms on the NH 2 + group form bifurcated N-HÁ Á Á(O,O) hydrogen bonds. Weak C-HÁ Á ÁO interactions are also observed. These bonds collectively link the components into infinite chains along [100].

Structural commentary
The structure of (I) and its atom numbering are shown in Fig. 1. It consists of a pyrimidylpiperazine cation joined by the C1/N3 atoms of each unit and a chloride anion. The C1-N3 bond is 1.373 (3) Å long, which compares favorably with similar ionic structures containing this cation [1.369 (3) (Yamuna et al., 2014a), and 1.36 (6) and 1.37 (1) Å (Ding et al., 2014)]. The N3/C5/C6/N4/C7/C8 piperazine unit adopts a slightly distorted chair conformation with protonation at the N4 nitrogen atom. The structure of (II) and its atom numbering are shown in Fig. 2. Similarly, it consists of a pyrimidylpiperazine cation joined by the C1/N3 atoms of each unit and a nitrate anion. The C1-N3 bond is 1.369 (3) Å , also in the range of the related structures described above. The N3/ C5/C6/N4/C7/C8 piperazine unit also adopts a slightly distorted chair conformation with protonation at the N4 atom.

Supramolecular features
In the crystal of (I), N4-H4AÁ Á ÁCl1 and N4-H4BÁ Á ÁCl1 interactions are observed between pyrimidylpiperazine cations and chloride anions, forming zigzag chains along [100] ( Fig. 3 and Table 1). In the crystal of (II), both of the H atoms on the N4 atom of the pyrimidylpiperazine cation are bifurcated, forming N-HÁ Á Á(O,O) hydrogen bonds ( Fig. 4 and Table 2). Additional C-HÁ Á ÁO interactions between the pyrimidyl unit and the nitrate anion are present which, in concert with the N-HÁ Á ÁO hydrogen bonds between the piperazine group and nitrate anions, form infinite chains along [100]. ORTEP drawing of C 8 H 13 N 4 + ÁCl À , (I), showing 30% probability displacement ellipsoids.

Figure 3
Molecular packing for C 8 H 13 N 4 + ÁCl À , (I), viewed along the b axis. Dashed lines indicate N-HÁ Á ÁCl interactions forming zigzag chains along the a axis (see Table 1 for details). H atoms not involved in hydrogen bonding have been omitted for clarity.

Synthesis and crystallization
For the preparation of title salt (I), a mixture of 1-(pyrimidin-2-yl)piperazine (0.2 g) and concentrated hydrochloric acid (5 ml) was stirred well over a magnetic stirrer at room temperature for 10 min and then warmed at 313 K for another 10 min. A white precipitate was obtained, which was dried in   Symmetry code: (i) x þ 1 2 ; Ày þ 3 2 ; Àz þ 1. Table 2 Hydrogen-bond geometry (Å , ) for (II). the open air overnight and then dissolved in hot dimethyl sulfoxide solvent. After few days, colourless blocks were obtained on slow evaporation (m.p. above 563 K). For the preparation of title salt (II), a mixture of 1-(pyrimidin-2-yl)piperazine, from Sigma-Aldrich (0.2 g), and concentrated nitric acid (5 ml) was stirred well over a magnetic stirrer at room temperature for 10 min. A white precipitate was obtained immediately, which was dried in the open air overnight and then dissolved in water. After a few days, colourless blocks were obtained on slow evaporation (m.p. 463-470 K).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. In both (I) and (II), all of the H atoms were placed in their calculated positions and then refined using a riding model with C-H bond lengths of 0.93 (CH) or 0.97 Å (CH 2 ) and N-H bond lengths of 0.97 Å . Isotropic displacement parameters for these atoms were set at 1.2U eq (CH,CH 2 ,NH). program(s) used to refine structure: SHELXL2012 (Sheldrick, 2008); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Cl1 0.08383 (9) 0.49612 (9) Hydrogen-bond geometry (Å, º)  Extinction correction: SHELXL2012 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0099 (14) 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.