(E)-1-(2-Phenyldiazen-2-ium-1-yl)naphthalen-2-olate

In the title zwitterionic compound, C16H12N2O, the dihedral angle between the phenyl ring and the naphthalene ring system is 17.85 (8)°; an intramolecular N—H⋯O hydrogen bond occurs. In the crystal, π–π stacking is observed between naphthalene ring systems of adjacent molecules, the centroid–centroid distance being 3.6486 (11) Å.


Experimental
We report here in the crystal structure of the title compound, obtained through the diazotization of aniline followed by a coupling reaction with 2-naphthol.
The molecule of the title compound, with the atom numbering scheme, is shown in Fig. 1, crystallizes in the monoclinic space group P21/c.
The molecular structure of C 16 H 12 N 2 O is illustrated in Fig. 1. The molecule adopts an anti-configuration with the two aryl groups reside on the opposite side of azo-group. The dihedral angle between the benzene ring and naphthalene ring is 17.85 (8)°. An intramolecular N-H···O hydrogen bond is found (Table 1). It is more interesting, that hydrogen atom in the OH-group has transfer to N atom in the azo-group to form the structure of dipolar ion. Moreover, different Fourier map indicate hydrogen site location is closer to nitrogen atom of azo-group. In the crystal molecules are packed by the weak π-π interactions with the closest approach between centroids of aromatic rings is 3.6486 (11) Å.

Experimental
The compound was synthesized according to the literature procedure of other aromatic azo-compounds (Wang et al., 2003). Red prism of the compound were obtained by slow evaporation at room temperature from an aqueous solution containing water/THF (1/1, v/v).

Refinement
N-bound H atom was located in a differece Fourier map and refined with N-H distance constraint of 0.94 Å, other H atoms were placed in calculated positions and refined in riding mode. U iso (H) = 1.2U eq (N,C).

Figure 1
View of the molecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 50% probability level. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.18 e Å −3 Δρ min = −0.19 e Å −3 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 on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses 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 observed criterion of F 2 > 2sigma(F 2 ) is used only for calculating -R-factor-obs 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.  (9) 0.0639 (10) 0.0000 (7) 0.0040 (7) 0.0008 (6) N2 0.0613 (9) 0.0424 (9) 0.0534 (9) 0.0008 (7) 0.0040 (6) −0.0001 (6) O1 0.0601 (8) 0.0556 (9) 0.0902 (10) 0.0066 (7) 0.0019 (7) −0.0011 (7)