1-[(E)-2-(2-Hydroxy-5-methylphenyl)diazen-2-ium-1-yl]naphthalen-2-olate

The title zwitterion, C17H14N2O2, crystallizes with two independent molecules in the asymmetric unit, both of which are approximately planar, the dihedral angles between the benzene ring and the naphthalene ring system being 4.39 (12)° in one molecule and 5.83 (12)° in the other, and show an E conformation with respect to the azo double bond. An intramolecular N—H⋯O hydrogen bond in each molecule helps to establish their near planar conformation. In the crystal, molecules are linked through O—H⋯O hydrogen bonds into infinite chains running along the a-axis direction. In addition, the chains are stacked along the b axis via π–π interactions between the benzene and the naphthalene rings of adjacent molecules, the centroid–centroid distances being 3.722 (3) and 3.823 (4) Å.

The title zwitterion, C 17 H 14 N 2 O 2 , crystallizes with two independent molecules in the asymmetric unit, both of which are approximately planar, the dihedral angles between the benzene ring and the naphthalene ring system being 4.39 (12) in one molecule and 5. 83 (12) in the other, and show an E conformation with respect to the azo double bond. An intramolecular N-HÁ Á ÁO hydrogen bond in each molecule helps to establish their near planar conformation. In the crystal, molecules are linked through O-HÁ Á ÁO hydrogen bonds into infinite chains running along the a-axis direction. In addition, the chains are stacked along the b axis viainteractions between the benzene and the naphthalene rings of adjacent molecules, the centroid-centroid distances being 3.722 (3) and 3.823 (4) Å .

Related literature
For general background to the use of azo compounds as dyes, pigments and advanced materials, see: Lee et al. (2004). For details of azo pigments, see: Herbst & Hunger (2004). For related structures of hydrazone derivatives, see: Olivieri et al. (1989); Oakes (2002). For bond-length data, see: Yazıcı et al.   Table 1 Hydrogen-bond geometry (Å , ). bond should have a length of 1.20-1.28 Å and the bond length of N-N single bonds, as in hydrazone tautomers, should be more than 1.4 Å. In the title compound, N-N bond lengths are 1.385 Å for N1-N2 and 1.305 Å for N5-N6, between the suggested N=N double bond and N-N single bond lengths.In the molecule, all bond lengths are in good agreement with those reported for other azo compounds (Yazıcı et al., 2010;Karadayı et al., 2006).
The molecular structure of the title compound is shown in Figure 1.There are two independent molecules in the asymmetric unit, each consists of a benzene ring linked to the first nitrogen atom of the N = N chromophore and two aromatic rings of the core 2-naphthol, with a trans configuration with respect to the azo double bond. The dihedral angles between the benzene ring and naphthalene ring system being 4.39 (12)° in one molecule and 5.83 (12)° in the other. Intramolecular N-H···O hydrogen bonds stabilize the planar geommetry in each of the independent molecules. In the crystal, the molecules are linked through O-H···O into infinite one-dimensional chains running along the a axis, Figure   2. In addition, the chains are stacked along the b axis via π-π interactions between the benzene and the naphthalene rings of adjacent molecules, the centroid-centroid distances being 3.722 (3) and 3.823 (4) Å.

Experimental
The title compound (E)-1-((2-hydroxy-5-methylphenyl)diazenyl)naphthalen-2-ol was prepared following the classical method of synthesis of other aromatic azo-compounds (Wang et al., 2003). Diazotization of 2-amino-4-methylphenol followed by a coupling reaction with 2-naphthol. This gives a red powder which was recrystallized from ethanol leading to crystals in the form of red prisms.

Refinement
All non-hydrogen atoms were refined with anisotropic atomic displacement parameters. All H atoms, attached to carbo(n atoms have been placed in geometrically idealized positions and refined as riding, with C-H = 0.93 (aromatic), 0.96 Å supplementary materials sup-2 . E69, o1322-o1323 (methyl), and U iso (H) = 1.2 U eq (C) or 1.5 U eq (methyl C). Hydroxyl H atoms were introduced in calculated positions and treated as riding on their parent atoms with O-H = 0.82 Å (hydroxyl) and U iso (H) = 1.5 U eq (O). The remaining H atoms of amino-group were located in a difference Fourier map and refined freely with N-H= 0.88 Å and U iso (H) = 1.2 U eq (N).

Figure 1
The molecular structure of (I), with 50% probability displacement ellipsoids for non-H atoms.The dashed lines indicate N -H···O hydrogen bond.

1-[(E)-2-(2-Hydroxy-5-methylphenyl)diazen-2-ium-1-yl]naphthalen-2-olate
Crystal data  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.44 e Å −3 Δρ min = −0.40 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0045 (9) 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.