2-[(1-Oxidopyridin-4-yl)sulfanyl]benzoic acid

In the title compound, C12H9NO3S, the dihedral angle between the pyridine and benzene rings is 83.93 (7)°. In the crystal, pairs of O—H⋯O hydrogen bonds link the molecules, forming inversion dimers with graph-set notation R 2 2(22). These dimers are in turn linked by weak C—H⋯O hydrogen bonds along [100], forming R 2 2(8) rings.

In the title compound, C 12 H 9 NO 3 S, the dihedral angle between the pyridine and benzene rings is 83.93 (7) . In the crystal, pairs of O-HÁ Á ÁO hydrogen bonds link the molecules, forming inversion dimers with graph-set notation R 2 2 (22). These dimers are in turn linked by weak C-HÁ Á ÁO hydrogen bonds along [100], forming R 2 2 (8) rings.

Comment
In a previous study in our research group, it was possible to obtain the 2-amino-3-(N-oxipiridin-4-ilsulfanil)-propionic acid dihydrate (NPNOCys) by a novel synthesis (Moreno-Fuquen et al., 2010). We then tried to form other organic sulfur compounds by this same synthetic route. In this study nitropyridine N-oxide and 2-mercaptobenzoic acid were combined following the same synthetic route. The crystal structure determination of the title compound (I) was carried out in order to examine its structural characteristics and supramolecular behavior. The molecular structure of the title compound is shown in Fig. 1. Bond lengths (Allen et al., 1987) are in the normal values. The benzene and pyridine rings bridged by the sulfur atom are tilted with respect to each other forming a dihedral angle of 83.93 (7)°. The C-S bond length which links the sulfur to the oxipiridinic ring is similar to the distance in the NPNOCys compound [C-S = 1.7533 (12) Å]. The crystal packing is stabilized by O-H···O hydrogen bonds and weak C-H···O intermolecular interactions, forming R 2 2 (22) and R 2 2 (8) fused-rings along [100] (see Fig. 2; Etter, 1990). The O1 atom of the carboxyl group at (x,y,z) acts as hydrogen-bond donors to O3 atom of the N-oxide group at (-x + 1,-y + 1,-z + 2) and the C11 atom at (x,y,z) acts as hydrogen-bond donors to the O3 atom at (-x + 2,-y + 1,-z + 2) (see Table 1; Nardelli, 1995).

Experimental
The reagents and solvents for the synthesis were obtained from the Sigma-Aldrich Chemical Co., and they were used without additional purification. To form this compound, equimolar amounts of 4-nitropyridine N-oxide (0.835 g. 5.96 mmol) and thiosalicylic acid were taken. They were completely dissolved in a hot mixture of acetonitrile -methanol (20%) to give a saturated solution. The solution was allowed to slowly evaporating at room temperature. Crystals of good quality and suitable for single-crystal X-ray diffraction were grown from this mixture. The mechanism of the reaction is similar to that reported in other work published before (Moreno-Fuquen et al., 2010).

Refinement
All H-atoms were placed in calculated positions [C-H= 0.93 Å for aromatic and O-H = 0.82 Å for carboxyl] and they were refined with U iso (H) 1.2 or 1.5 times U eq of the parent atom, respectively.

Figure 2
Part of the crystal structure of (I), showing the formation of chains of molecules running along [100]. Symmetry code: (i) -x + 2,-y -1,-z; (ii) -x + 1,-y -1,-z. Hydrogen bonds are shown as dashed lines. 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.