1H-1,2,4-Triazol-4-ium 4-nitrobenzenesulfonate monohydrate

In the 4-nitrobenzene sulfonate anion of the title compound, C2H4N3 +·C6H4NO5S−·H2O, the nitro group is slightly twisted from the plane of the benzene ring [dihedral angle = 2.8 (3)°]. In the crystal, the three components are linked via N—H⋯O, O—H⋯N, O—H⋯O and C—H⋯O hydrogen bonds, forming a two-dimensional network parallel to the bc plane. A short intermolecular O⋯N contact of 2.872 (3) Å is also observed between the nitro and sulfonate groups.

In the 4-nitrobenzene sulfonate anion of the title compound, C 2 H 4 N 3 + ÁC 6 H 4 NO 5 S À ÁH 2 O, the nitro group is slightly twisted from the plane of the benzene ring [dihedral angle = 2.8 (3) ]. In the crystal, the three components are linked via N-HÁ Á ÁO, O-HÁ Á ÁN, O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds, forming a two-dimensional network parallel to the bc plane. A short intermolecular OÁ Á ÁN contact of 2.872 (3) Å is also observed between the nitro and sulfonate groups.

Comment
In recent years, there has been of great interest in the design and utilization of 1,2,4-triazole and its derivatives in coordination and biological chemistry for they represent the simple small molecular ligands. Aromatic sulfonates are used in monitoring the merging of lipids (Yachi et al., 1989) and in many other fields (Spungin et al., 1992;Jiang et al., 1990;Narayanan & Krakow, 1983). An X-ray study of the title compound was undertaken in order to determine its crystal and molecular structure owing to the biological importance of its analogues. The molecular structure of the title compound (I).
In the crystal structure, (Fig. 2), the ion pairs and water molecules are linked via intermolecular N-H···O, O-H···N, O-H···O and C-H···O hydrogen bonds (Table 1), forming two-dimensional networks parallel to (100). A short O···N contact of 2.87 Å is also observed.

Experimental
A methanol solution (20 ml) of 1-(p-Nitrobenzenesulfonayl)-1H-1,2,4-triazole (63.55 mg, Aldrich) was warmed over a heating magnetic stirrer for 15 minutes. The resulting solution was allowed to cool slowly at room temperature. Crystals of the title compound appeared from the mother liquor after a few days.

Refinement
Atoms H1NA and H1NB were located in a difference Fourier map and refined freely [N-H = 0.86 (3)

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The 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 > 2σ(F 2 ) is used only for calculating Rfactors(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.