4-Nitrophenylhydrazinium picrate monohydrate

In the crystal structure of the title compound, C6H8N3O2 +·C6H2N3O7 −·H2O, N—H⋯O and O—H⋯O hydrogen bonds link the components into a two-dimensional network parallel to (010). In addition, there are pairs of weak inversion-related C—H⋯O hydrogen bonds within the two-dimensional network. The three nitro groups are twisted by 1.6 (3), 7.8 (3) and 12.1 (3)° from the ring plane in the anion, while in the cation, the nitro group makes a dihedral angle of 4.6 (2)° with the ring.


Comment
Cocrystal strategy has been often used due to its application in the fields of drug chemistry, physical material chemistry and biological crystallography. Picric acid, as a strong organic acid, is very frequently adopted to facilitate the crystallization of some difficult-crystallized organic bases (Herbstein & Kaftory, 1976;Dubost et al., 1981;Harrison et al., 2007;Peng et al., 2011;Zeng et al., 2011;Dey et al., 2011). In this report, we report the 1:1 cocrystallized complex of 4-nitrophenylhydrazine and picric acid in 95% methanol solution.
In the title compound (I), the asymmetric unit consists of a 4-nitrophenyldrazinium cation, a picrate anion and a solvent water molecule (Fig.1). During the preparation of (I) the picric acid proton has been transferred to the terminal hydrazine atom N1. In the picrate molecule, the phenolate (O3-C7) bond distance is 1.245 (3) Å shows an indication of delocalization between the precursor single C-O bond and the benzene ring with three electron-withdrawing nitro groups. As a result, the neighbouring C7-C8 and C7-C12 bond lengths of 1.459 (3) Å and 1.452 (3) Å are longer by ca 0.08 Å than the mean distance of the other four C-C bonds. The C8-C7-C12 angle is about 10° smaller than the mean value (121.4°) of the other five benzene inner angles. The three nitro groups N4/O4/O5, N5/O6/O7 and N6/O8/O9 are twisted by 1.6 (3)°, 7.8 (3)° and 12.1 (3)° from the picrate benzene ring plane, respectively.
In the crystal, N-H···O and O-H···O hydrogen bonds link the components of the structure into a two-dimensional network parallel to (010) (Fig. 2). In addition, there are pairs of weak inversion related C-H···O hydrogen bonds within the two-dimensional network.

Experimental
All the reagents and solvents were used as obtained without further purification. 1:1 molar amount of 4-nitrophenylhydrazine (0.2 mmol, 30.6 mg) and picric acid (0.2 mmol, 45.8 g) were dissolved in 95% methanol (20.0 ml). The mixture was stirred for half an hour at ambient temperature and then filtered. The resulting yellow solution was kept in air for one week. Yellow needles of (I) suitable for single-crystal X-ray diffraction analysis were grown by slow evaporation of the solution at the bottom of the vessel. The crystals were filtered and dried in air. Yield: 60.2 mg, 75% (based on picric acid or 4-nitrophenylhydrazine).   Part of the crystal structure of (I) showing the formation of a two-dimensional network parallel to (010). Hydrogen bonds are shown as dashed lines. For the sake of clarity, H atoms not involved in the motif have been omitted.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > 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.