Crystal structures of salen-type ligands 2-[(1E)-({1-(3-chlorophenyl)-2-[(E)-(2-hydroxybenzylidene)amino]propyl}imino)methyl]phenol and 2-[(1E)-({1-(4-chlorophenyl)-2-[(E)-(2-hydroxybenzylidene)amino]propyl}imino)methyl]phenol

The title compounds are differing only by the position of the chlorine atom in the benzene ring. The molecular structures are very similar, except for the relative position of the hydroxyphenyl rings.


Chemical context
Salen-type Schiff bases possessing an unsymmetrical vicinal diamine backbone are promising candidates in synthetic and material science research. Salen ligands and their complexes are widely studied for their extensive applications in various fields, for their luminescent property (Chakraborty et al., 2015;Chen et al., 2013), photophysical properties (Cheng et al., 2013), NLO activity (Nayar & Ravikumar, 2014;Zeyrek, 2013) etc. Recent reports on a single-crystal study (Habibi et al., 2007), spectroscopic and DFT calculations (de Toledo et al., 2015) and the utility in asymmetric syntheses (Yang et al., 2011) of this type of ligand address the novelty of these compounds and speak of the impact of their efficacy. In view of the importance of the title compounds, we have undertaken a single-crystal X-ray diffraction study and the results are presented here. ISSN 2056-9890

Structural commentary
The molecular structure of the title compounds, (I) and (II), are illustrated in Figs. 1 and 2, respectively. Fig. 3 shows a superposition of the two compounds except for Cl1 using Qmol (Gans & Shalloway, 2001); the r.m.s. deviation is 2.3 Å . Compound (I) has two chiral centers with the absolute configuration determined as C8(S), C15(S). The chlorophenyl group is almost planar with atom Cl1 deviating by 0.013 (1) Å from the ring in (I) whereas in (II) the chlorine atom deviates by 0.079 (1) Å . In (I), hydroxy atoms O1 and O2 deviate by 0.051 (3) and 0.012 (3) Å , respectively, from the phenyl ring to which they are attached. In (II), hydroxy atoms O1 and O2 deviate by 0.006 (2) and 0.002 (2) Å , respectively, from the ring. The dihedral angle between these two rings is 9.2 (2) in (I) and 48.5 (1) in (II).

Figure 1
A view of the molecular structure of compound (I), showing the atom labelling. Displacement ellipsoids are drawn at the 30% probability level. Dashed lines represent intramolecular O-HÁ Á ÁN hydrogen bonds (Table 1).

Refinement
Crystal data, data collection and structure refinement details are summarized in The crystal packing of the title compound (I) viewed along the a axis. The C-HÁ Á ÁO hydrogen bonds are shown as dashed lines (see Table 1). For clarity, H atoms not involved in these interactions have been omitted.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq