Crystal structure of 3-[(E)-(2-hydroxy-3-methoxybenzylidene)amino]-1-methyl-1-phenylthiourea

The asymmetric unit comprises two independent molecules. In the crystal, the two independent molecules are linked by bifurcated N—H⋯O hydrogen bonds, forming a supramolecular chain with a (14)[(5)] motif.


Chemical context
Thiosemicarbazones have emerged as an important class of Sand N-containing ligands due to their propensity to react with a wide range of metals (Casas et al., 2000) and their broad spectrum of chemotherapeutic properties (Quiroga et al., 1998). Their structural diversity is due to their variable coordinative abilities (Sreekanth et al., 2004), arising from thioamido-thioiminol tautomerism. Thiosemicarbazones usually act as chelating ligands for metal ions through sulfur ( S) and azomethane ( N-) groups, though in some cases they behave as monodentate ligands through the sulfur ( S) only. They are also important intermediates for obtaining heterocylic rings such as thiazolidones, oxadiazoles, pyrazolidones and thiadiazoles (Greenbaum et al., 2004;Kü çü kgü zel et al., 2006). As a result of their long chain structure, they are very flexible and form linkages with a variety of metal ions. They have also been used for the analysis of metals and in device applications related to telecommunications, optical computing and optical information processing (Tian et al., 1997).

Structural commentary
The asymmetric unit of the compound comprises two independent molecules (A and B) with almost identical confor- ISSN 2056-9890 mations. The hydrazine carbothioamide backbone is nearly planar with a maximum deviation of 0.023 (2) Å at atom N2 for molecule A and of 0.054 (2) Å at atom N2 0 for B. The closeness of the C S bond lengths [C9-S1 = 1.666 (2) Å and C9 0 -S1 0 = 1.657 (2) Å ] to the expected distance (1.60 Å ; Allen et al., 1987;Seena et al., 2008) indicates that the compound exists in the thione form. This is further confirmed by the N-N and N-C bond lengths (Gangadharan et al., 2015). The bond lengths in the N-C( S)-N fragments indicate delocalization due to the fact that the C-N and C-S bonds are shorter than typical single bonds (ca 1.47 and 1.73 Å , respectively) and longer than corresponding double bonds (ca 1.29 and 1.55 Å , respectively; Casas et al., 2000;Tenó rio et al. 2005). The terminal phenyl and benzene rings are almost orthogonal to each other, with a dihedral angle of 87.47 (13) for A and 89.86 (17) for B. In each molecule (A and B), an intramolecular O-HÁ Á ÁN interaction (Table 1) with an S(6) ring motif stabilizes the molecular structure ( Fig. 1).

Figure 1
The two independent molecules (A and B) of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 30% probability level. Dashed lines indicate the intramolecular O-HÁ Á ÁN interactions.

Database survey
A search of Cambridge Structural Database (Version 5.36; last updated Nov. 2014; Groom & Allen, 2014) showed three closely related structures with pyridine-2-carbaldehyde thiosemicarbazones, differing from the title compound only in the presence of one or more pyridyl groups instead of the substituted phenyl group. Two of these, namely, (E)-4-methyl-4-phenyl-1-(2-pyridylmethylene)-3-thiosemicarbazide (Rapheal et al., 2007) and di-2-pyridyl ketone 4-methyl-4phenylthosemicarbazone (Philip et al., 2004) crystallize in the same P1 space group of the title compound. The third compound, 2-benzoyl pyridine-N-methyl-N-phenylthiosemicarbazone, crystallizes in P2 1 /n. The similarity in bond lengths along the hydrazine carbothioamide moieties and shortening of the C-N single bonds from the normal value (ca 1.48 Å ) indicate some degree of delocalization in the compounds. The C S bond lengths in all compared compounds lie in the range 1.66-1.67 Å , intermediate between S-Csp 2 and S Csp 2 bond lengths (ca 1.75 and 1.59 Å , respectively), showing a partial double-bond character. Similar bond lengths for the C S bond have also been observed in hydrazine carbothioamide derivatives (Gangadharan et al., 2014(Gangadharan et al., , 2015Vimala et al., 2014). The partial double-bond nature of the C S bond is a feature in the compared hydrazine carbothioamide derivatives, irrespective of the substituents.

Synthesis and crystallization
1.81 g (0.01 mol) of N-methyl-N-phenylhydrazine carbothioamide was dissolved in 20 ml of hot methanol and to this was added 1.52 g (0.01 mol) of 2-hydroxy-3-methoxybenzaldehyde in 10 ml of ethanol over a period of 10 min with continuous stirring. The reaction mixture was refluxed for 2 h and allowed to cool whereby a shining yellow compound began to separate. This was filtered and washed thoroughly with ethanol and then dried in vacuum. The compound was recrystallized from a hot ethanol solution, giving colourless block-like crystals (yield 91%). Single crystals suitable for X-ray diffraction were prepared by slow evaporation of an ethanol solution at room temperature.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms were localized in a difference-Fourier map. H atoms bound to O and N atoms were refined freely; refined distances O-H = 0.79 (3) and 0.87 (3) Å , and N-H = 0.80 (2) and 0.83 (2) Å . C-bound H atoms were treated as riding, with C-H = 0.93 or 0.96 Å , and with U iso (H) = 1.2U eq (C) for aromatic and 1.5U eq (C) for methyl groups. The rotation angles for methyl groups were optimized.
Acta Cryst. (2016). E72, 608-611 research communications  Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009). 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.  0.0459 (9) 0.0640 (12)