2-Hydroxypyridinium p-toluenesulfonate

In the title molecular salt, C5H6NO+·C7H7O3S−, the cations and anions are connected by N—H⋯O and O—H⋯O hydrogen bonds, forming [100] chains.


Yu Jin
Comment Several crystal structures of p-toluenesulfonate have been reported previously (Helvenston et al., 2006;Collier et al., 2006;Koshima et al., 2001). As an extension of this research, we report here the synthesis and the crystal structure of the title complex.
Until now, researchers have found that molecular motion can cause a rotation of the local structure to give rise to the formation of reversible structural phase transition from high-temperature disordered fashion to low temperature ordered fashion. Reversible structural phase transition is caused by many kinds of factors. Hydrogen-bonding interactions come to be the most common factor. Transition for hydrogen-bonding interactions from high-temperature disordered state to low temperature ordered state allows reversible structural phase transition. The compound reported here could have a tendency to hold such transition as a result of numerous hydrogen-bonding interactions in its crystal structure. The transition from the disordered arrangement to the ordered one gives rise to sharp change in the physical properties of these compounds. Only few compounds in which the components can be arranged in a disordered status at a relative high temperature and in an ordered one at a relative low temperature have been found until now (Zhang et al., 2008(Zhang et al., , 2009(Zhang et al., , 2010. As part of our search for simple ferroelectric compounds we have investigated the title compound and report its room temperature structure.
The asymmetric unit, containing one anion and one cation, is shown in Fig. 1 with the hydrogen bonds listed in Table 1.
The compound remains stable as a result of the existence of numerous hydrogen-bonding interactions formed in the crystal. These interactions tie the cations and anions together in a complex spatial geometry (Fig. 2).

Experimental
C 5 H 6 ON + .C 7 H 7 O 3 Swas formed from a mixture of C 5 H 5 ON (95.1 mg, 1.00 mmol), C 7 H 7 SO 3 H (172 mg, 1.00 mmol), and distilled water (5 mL), which was stirred a few minutes at room temperature, giving a clear transparent solution. After evaporation for a few days, block colourless crystals suitable for X-ray diffraction were obtained in about 71% yield and filtered and washed with distilled water.

Refinement
H atoms bound to C and N atoms were placed at idealized positions [C-H = 0.93-0.96 Å, N-H = 0.86 Å] and allowed to ride on their parent atoms with U iso = 1.5 U eq (C1) for the methyl group and U iso = 1.2 U eq (carrier atom) otherwise.
Hydroxyl H atom was found in a difference map and refined freely.

Figure 1
The structure of the title compound with displacement ellipsoids drawn at the 30% probability level.

Figure 2
Part of the crystal structure of the title compound viewed along the c axis. Intermolecular interactions are shown as dashed lines.