Crystal structure of piperidinium 4-nitrophenolate

In the title salt, the piperidine ring of the cation adopts a chair conformation. In the crystal, N—H⋯O hydrogen bonds link adjacent anions and cations into infinite chains along [100]. The chains are linked by C—H⋯π interactions, forming sheets lying parallel to (001).

In the title molecular salt, C 5 H 12 N + ÁC 6 H 4 NO 3 À , the piperidine ring adopts a chair conformation and the cation is protonated at the N atom. In the anion, the nitro group is twisted at an angle of 10.30 (11) with respect to the attached benzene ring. In the crystal, N-HÁ Á ÁO hydrogen bonds link adjacent anions and cations into infinite chains propagating along [100]. The chains are linked by C-HÁ Á Á interactions, forming sheets lying parallel to (001).

Chemical context
Piperidine derivatives exhibit a broad-spectrum of biological activities such as anti-bacterial and anti-cancer (Parthiban et al., 2005). Nitro-aromatics are widely used either as materials or as intermediates in explosives, dyestuffs, pesticides and organic synthesis (Yan et al., 2006). We report herein on the synthesis and crystal structure of the title molecular salt, prepared by mixing piperidine with 4-nitrophenol.

Supramolecular features
In the crystal, adjacent cations and anions are linked by the N-HÁ Á ÁO hydrogen bonds, which generate infinite chains along [100] (see Table 1 and Fig. 2). The chains are linked by C-HÁ Á Á interactions, forming sheets lying parallel to the ab plane (Table 1).

Synthesis and crystallization
Piperidine (0.85 g) and 4-nitrophenol (1.39) in an equimolar (1:1) ratio were added to methanol as solvent and the mixture was stirred for 2 h, giving a clear solution. The solution was filtered into a beaker and sealed with parafilm and kept at room temperature for one week. Colourless crystals suitable for X-ray diffraction analysis were obtained after one week.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The N-bound and C-bound H atoms were positioned geometrically and refined using a riding model: N-H = 0.90, C-H = 0.93 and 0.97 Å for CH and CH 2 H atoms, respectively, and with U iso (H) = 1.2U eq (N,C).  Table 1 Hydrogen-bond geometry (Å , ).
Cg1 is the centroid of the C1-C6 ring.

Figure 2
The crystal packing of the title salt, viewed along the b axis. Hydrogen bonds are shown as dashed lines (see Table 1 for details; H atoms not involved in hydrogen bonding have been omitted for clarity).  program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 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. 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.