Crystal structure of 2-{5-[2-(2-hydroxyphenyl)diazen-1-yl]-1-methylpyrrol-2-yl}phenol methanol monosolvate

The azo N=N bond adopts a trans conformation and the pyrrole N and azo group are in an anti orientation. The dihedral angles between the pyrrole ring and the two phenyl rings are 6.7 (3) and 54.7 (3)°. In the crystal, a supramolecular ring structure is formed between two azopyrrole and two methanol solvent molecules through four O—H⋯O hydrogen bonds.

In the title azopyrrole compound, C 17 H 15 N 3 O 2 ÁCH 3 OH, the azo N N bond adopts a trans configuration and the pyrrole N and azo group are in an anti orientation. The dihedral angles between the pyrrole ring and the two phenyl rings are 6.7 (3) and 54.7 (3) . In the crystal, a supramolecular ring structure is formed between two azopyrrole and two methanol solvent molecules through four O-HÁ Á ÁO hydrogen bonds.

Chemical context
Recently, azopyrrole dyes have received much attention for their promising use in the design of advanced materials and devices. For example, some thienylpyrrole azo dyes bearing heterocyclic groups have good non-linear optical properties (Raposo et al., 2011). Mikroyannidis and coworkers found that many azopyrrole dyes are efficient bulk heterojunction solar cell materials (Sharma et al., 2012). In a previous work, we reported the crystal engineering of some 5,5 0 -bis(phenyldiazo)dipyrromethane compounds and demonstrated their interlocked type self-assemblies in the solid state via quadruple N-HÁ Á ÁN hydrogen bonds (Yin et al., 2008(Yin et al., , 2009. In a continuation of this research, we report herein the crystal structure of 2-{5-[2-(2-hydroxyphenyl)diazen-1-yl]-1-methylpyrrol-2-yl}phenol methanol monosolvate.

Structural commentary
The structure of the title compound is shown in Fig. 1. The asymmetric unit contains one azopyrrole molecule and one methanol solvent molecule. The azoylazopyrrole group is almost planar, reflected by the dihedral angle between the pyrrole ring (N3/C7-C10) and the benzene ring (C1-C6) of only 6.7 (3) , which may be due to the existence of the intra-ISSN 2056-9890 molecular O1-H1Á Á ÁN2 hydrogen bond (Table 1) between the hydroxy group and the azo N atom. The dihedral angle between pyrrole ring and the other benzene ring (C12-C17) is 54.7 (3) , which may be caused by the steric repulsion between hydroxy group and methyl group. The azo N N bond adopts a trans configuration and its length is 1.286 (2) Å , which is shorter than that in the crystal of 2,5-bis(2-hydroxyphenylazo)-1H-pyrrole (1.293 Å ; Li et al. 2009). It is worth mentioning that the N1 atom of the azo group and the N3 atom of the pyrrole ring are arranged on opposite sides with respect to the C7-N2 bond, which is the same as in the crystal of 2-phenylazo-1-vinyl pyrrole (Trofimov et al., 2006) but different to many other observations (Li et al., 2009;Yin et al., 2008). The bond lengths in the pyrrole ring are more equal compared to those normally observed.

Supramolecular features
In the crystal, two azopyrrole molecules are bridged by two methanol solvent molecules through four O-HÁ Á ÁO hydrogen bonds forming a large supramolecular ring structure, in which the methanol acts as both a hydrogen-bond acceptor and a donor (Fig. 2, Table 1). This type of coordination environment is most populated (occupying 70%) for methanol molecules as revealed by a search of the Cambridge Structural Database (CSD) (Brychczynska et al. 2008). The methyl groups point to the inside of the ring. The rings are further held together through C-HÁ Á Á contacts involving the benzene rings (Table 1). There are nointeractions between the aromatic rings. The packing is shown in Fig. 3.

Figure 3
A view of the crystal packing along the b axis.

Figure 1
ORTEP diagram for the title compound, with displacement ellipsoids drawn at the 30% probability level. The methanol solvent molecule was omitted for clarity.

Synthesis and crystallization
A 273 K solution of 2-aminophenol 0.272 g (2.5 mmol) and aqueous HCl (2 mL) in water (2 mL) was treated with another 273 K solution of NaNO 2 (0.18 g, 2.5 mmol) in 3 mL water, and the mixture was stirred at 273 K for 30 min. The diazonium salt solution was added dropwise to a solution of Nmethylpyrrole (81 mg, 1 mmol) in acetonitrile (25 mL) and three drops of acetic acid. The combined solution was maintained at 273 K for 2 h with stirring. After that, EtOAc (25 mL) and water (25 mL) were added. The organic layer was separated and washed with water (20 mL) and dried with anhydrous MgSO 4 . The solution was evaporated and the residue was purified by column chromatography on silica (ethyl acetate/petroleum ether = 1:2), which gave the title compound as an orange powder (200 mg, 68%, m.p. 404 K).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. O-H atoms were located in a difference-Fourier map and refined freely. Other H atoms were positioned geometrically (C-H = 0.95 or 0.98 Å ) and included in the final cycles of refinement using a riding model, with U iso (H) = 1.2U eq (C) or 1.5U eq (Cmethyl).

Funding information
Funding for this research was provided by: National Natural Science Foundation of China (award No. 21172174). Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.21 e Å −3 Δρ min = −0.23 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 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 > 2sigma(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.