Crystal structures of (E)-N′-(2-hydroxy-5-methylbenzylidene)isonicotinohydrazide and (E)-N′-(5-fluoro-2-hydroxybenzylidene)isonicotinohydrazide

The title isonicotinohydrazides adopt an E conformation about the C=N bonds and in each molecule there is an intramolecular O—H⋯N hydrogen bond, forming an S(6) ring motif. In the crystals of both compounds, zigzag chains are formed via N—H⋯N hydrogen bonds, in the [10] the first compound and [010] for the other.


Chemical context
Hydrazone-based chelators for metal ions have received a significant amount of attention (Bendova et al., 2010;Hrušková et al., 2016). Compounds from this class, such as salicyl aldehyde isonicotinoyl hydrazide (SIH), have been studied as potential metal chelators in biological systems (Hrušková et al., 2011). These compounds have also been shown to be effective in protecting against metal-based oxidative stress (Jansová et al., 2014). In our research we are interested in developing probes for metal ions (Carter et al., 2014). We have therefore synthesized the title compounds, which are derivatives of the chelator SIH containing a signalling unit.

Structural commentary
The molecular structures of the title compounds, (I) and (II), are illustrated in Figs. 1 and 2, respectively. They consist of an The molecular structure of compound (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 40% probability level. The intramolecular O-HÁ Á ÁN hydrogen bond is shown as a dashed line (see Table 1).

Figure 2
The molecular structure of compound (II), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 40% probability level. The intramolecular O-HÁ Á ÁN hydrogen bond is shown as a dashed line (see Table 2). Table 1 Hydrogen-bond geometry (Å , ) for (I).

Figure 3
Partial view along the a axis of the crystal packing of compound (I), showing the hydrogen-bonded (dashed lines; see Table 1) zigzag chains parallel to [101].

Database survey
A search of the Cambridge Structural Database (Version 5.37, last update November 2015; Groom et al., 2016) indicated the presence of 40 structures containing the (E)-N-(2-hydroxybezylydene)isonicotinohydrazide substructure. They include the isotypic crystal structures with chloride (UCAREV, Chumakov et al., 2001;UCAREV01, Yang, 2006a), bromide (XENDOK, Yang, 2006b;XENDOK01, Sedaghat et al., 2014) and methoxy (VACHAK, Kargar et al., 2010) groups substituted at the 5-position of the phenyl ring. In the crystals of all three compounds, the N-HÁ Á ÁN hydrogen bond involving the hydrazone hydrogen and the pyridine nitrogen atoms organize the molecules into a herringbone motif, while in the crystal of the methoxy compound there are also weak N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds present forming R 2 1 (6) ring motifs.

Synthesis and crystallization
A solution of isonicotinic acid hydrazide (0.184 g, 1.34 mmol) and the appropriately substituted salicyl aldehyde (1.47 mmol) in a mixture of ethanol (3 ml) and water (1 ml) containing a catalytic amount of acetic acid was heated to reflux for 5 h. The reaction mixture was allowed to cool to room temperature, resulting in the formation of a white precipitate. The reaction mixture was filtered and the isolated solid was washed with diethyl ether and dried in vacuo.   (Farrugia, 2012), DIAMOND (Brandenburg, 2006), publCIF (Westrip, 2010) and enCIFer (Allen et al., 2004).

Figure 4
Partial view along the a axis of the crystal packing of compound (II), showing the N-HÁ Á ÁN and C-HÁ Á ÁO hydrogen-bonded (dashed lines; see Table 2) sheet propagating in the bc plane.
the methyl (I) and fluoro (II) derivatives, respectively. Single crystals suitable for X-ray diffraction were grown by slow evaporation of methanolic solutions of the title compounds. Spectroscopic data for (

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3 Windows (Farrugia, 2012) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010) and enCIFer (Allen et al., 2004). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.20 e Å −3 Δρ min = −0.22 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.

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.  (9) 0.0022 (6) 0.0060 (7) 0.0051 (7)