Crystal structure of 3-methoxy-4-[2-(thiazol-2-yl)diazen-1-yl]aniline monohydrate

In the title hydrated azo dye, the benzene and thiazole make a dihedral angle of 4.69 (17)°. In the crystal, hydrogen bonds, C—H⋯π and π–π interactions resulting in the formation of a three-dimensional framework.


Structural commentary
The molecular structure of (I) is shown in Fig. 1. The thiazole and benzene rings are arranged trans to the azo bridge (-N2 N3-). The methoxy and amino groups on the benzene ring are co-planar with the ring with atoms O1 and N4 deviating by À0.010 (2) and À0.019 (4) Å , respectively. The

Figure 1
The molecular structure of compound (I) with the atom labelling and 50% probability displacement ellipsoids contacts [C-HÁ Á ÁN(azo) and C-HÁ Á ÁO(OCH 3 )]. On the shape index surface (Fig. 3b), convex blue regions represent hydrogen-donor groups and concave red regions represent hydrogen-acceptor groups. In addition, concave red regions represent C-HÁ Á Á and offsetinteractions. The amino group behaves as both a donor and an acceptor. The methyl part of the methoxy group acts as a donor while the oxygen atom is an acceptor. The two-dimensional fingerprint plots ( Fig. 4) quantify the contributions of each type of intermolecular interaction to the Hirshfeld surface (McKinnon et al., 2007). The largest contribution with 30.0% of the surface is from HÁ Á ÁH contacts, which represent van der Waals interactions, followed by CÁ Á ÁH contacts involved in C-HÁ Á Á interactions (20.0%). In the NÁ Á ÁH plot (18.8% contribution), the two sharp peaks correspond to strong hydrogen bonds. Finally, the OÁ Á ÁH (9.3%), SÁ Á ÁH (11.1%) and CÁ Á ÁC (3.3%) contacts correspond to hydrogen bonds and offsetinteractions, respectively.

Database survey
Related compounds to (I) are substituted thiazolylazo derivatives, for example 4-(2-thiazolylazo) resorcinol (TAR), 1-(2thiazolylazo)-2-naphthol (TAN) and 2-(2-thiazolylazo)-4methylphenol (TAC) (Jensen, 1960). These thiazolylazo derivatives are used as chelating agents with metal ions (Farias et al., 1992). In the crystal structure of 1-(2-thiazolylazo)-2naphthol (TAN; Kurahashi, 1976), the azo group adopts a trans configuration and the phenolic oxygen atom is linked to an azo nitrogen atom by intramolecular hydrogen bonding. The crystal structure features only van der Waals interactions. To form complexes with metal ions, both thiazole and naphthol rings are rotated by 180 to coordinate to the metal through the phenolic oxygen atom, the azo nitrogen atom adjacent to the naphthol ring and the thiazole nitrogen atom, resulting the formation of five-membered chelate rings. Complexes of TAR and TAC are formed in a similar way due to the presence of a hydroxyl group in the structure (Karipcin et al., 2010). 3-[2-(1,3-Thiazol-2-yl)diazen-1-yl]pyridine-2,6diamine monohydrate (Chotima et al., 2018) has been used as a chelating ligand to form a complex with Au III ion (Piyasaengthong et al., 2015). The crystal structure is stabilized by hydrogen bonding between the amine group, water and the thiazole nitrogen atom along withinteractions between pairs of pyridine rings and pairs of thiazole rings, resulting in the formation of a layered structure. In addition, weak C-HÁ Á ÁS hydrogen bonds between adjacent thiazole rings further contribute to the crystal packing, generating a three-dimensional network.

Synthesis and crystallization
2-Aminothiazole (9.986 mmol) was dissolved in 6 M HCl (16 ml), and 8.236 mmol of sodium nitrate solution was added slowly under stirring at low temperature 268-273 K until the diazonium salt was obtained. m-Anisidine (1.12 ml in 40 ml of 4 M HCl) was slowly dropped into the mixture and stirred at a temperature between 268 and 273 K for 1 h. After the reaction was complete, conc. NH 3 was dropped into the mixture (pH 6) until the red-orange crude produce appeared. The products were filtered, washed with cold water, purified by column chromatography and recrystallized from an acetonitrile-water (1:1) mixture by vapour diffusion.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Water and amino H atoms were refined freely while those of aromatic and methyl groups were placed in calculated positions (C-H = 0.93 and 0.96 Å , respectively) and included in the cycles of refinement using a riding model with U iso = 1.2 U eq (C-aromatic) and 1.5U eq (Cmethyl). Data collection: APEX3 (Bruker, 2016); cell refinement: SAINT (Bruker, 2016); data reduction: SAINT (Bruker, 2016); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2016 (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009). Extinction correction: SHELXL2016 (Sheldrick, 2015b), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.009 (2) 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.