(E)-N′-(5-Chloro-2-hydroxybenzylidene)-4-(8-quinolyloxy)butanohydrazide monohydrate

The crystal of the title Schiff base compound, C20H18ClN3O3·H2O, was twinned by a twofold rotation about (100). The asymmetric unit contains two crystallographically independent molecules with similar conformations, and two water molecules. The C=N—N angles of 115.7 (6) and 116.2 (6)° are significantly smaller than the ideal value of 120° expected for sp 2-hybridized N atoms and the dihedral angles between the benzene ring and quinoline ring system in the two molecules are 52.5 (7) and 53.9 (7)°. The molecules aggregate via C—Cl⋯π and π–π interactions [centroid–centroid distances = 3.696 (5)–3.892 (5) Å] and weak C—H⋯O interactions as parallel sheets, which are further linked by water molecules through N—H⋯O and O—H⋯O hydrogen bonds into a supramolecular two-dimensional network.


Comment
The rational construction of new matallosupramolecular architectures using logical combinations of rigid linear and angular components, has been the subject of much study during the last decade (Muraoka et al.,1998;Cai et al., 2003;Pallavicini et al., 2007). Most commonly, nitrogen heterocycles have been used to provide donors for coordination to metals within these assemblies, with pyridine rings being by far the most frequently used. More recently, flexible ligands have been employed to obtain access to topologies that are not available using more rigid ligands. Such flexibility can be introduced by means of combinations of methylene, ether, or thioether spacer groups between the donor sites, which permit the ligand to exist in various combinations as a result of rotations about single bonds. 8-Hydroxyquinoline and its derivatives are among the most extensively investigated ligands in this area (Xu et al., 2002;Cai et al., 2003;Chen et al., 2005;Park et al., 2006;Karmakar et al., 2007;Zhang et al., 2005;Wen et al., 2005, Wei et al., 2004Zheng, Li et al., 2008). In this contribution, we present the synthesis and crystal structure of a new ligand, which contains oxygen and nitrogen donors and flexible aliphatic spacers.
The bond lengths and angles are in good agreement with expected values (Allen et al., 1987) and are comparable to those in the related compounds (Zheng, Wu, Lu et al., 2006;Zheng, 2006;Zheng, Wu, Li et al., 2007;Xie et al., 2008;Chen & Li, 2009). X-ray crystallography reveals that the title compound was twinned by a 2fold rotation about (100). The crystals contain two crystallographically independent molecules with similar conformations, and two water molecules. The conformation along the C1-O1-C10-C11-C12-C13-N2-N3-C14-C15 and C21-O4-C30-C31-C32-C33-N5-N6-C34-C35 bond sequence are all trans (Fig.1). The C14-N3 and C34-N6 bond lengths of 1.290 (9) and 1.283 (9) Å respectively, indicate the presence of a typical C=N. The CN-N angle of 115.7 (6) and 116.2 (6)° are significantly smaller than the ideal value of 120° expected for sp 2 -hybridized N atoms and the dihedral angles between the benzene ring and quinoline ring system in the two molecules are 52.5 (7) and 53.9 (7)°. This is probably a consequence of repulsion between the nitrogen lone pairs and the adjacent N atom (Zheng, Qiu et al., 2006). All torsion angles involving non-H atoms are close to 180°, which indicates that the molecules are essentially planar with the C=N bond adjacent to the benzene ring and quinoline group adopting a trans configuration with respect to its substitution. In the crystal packing, intramolecular O-H···N hydrogen bonds produce S(6) ring motifs (Bernstein et al.,1995) and there are also significant π-stacking interactions between the planar sections associated with the benzene ring and quinoline group.
The organic molecules aggregate via intermolecular weak C-Cl···π and π-π interactions between the benzene ring and quinoline rings [centroid-centroid distances in the range of 3.696 (5)-3.892 (5) Å] and weak C-H···O contacts into an array of parallel sheets, and these layers are further linked by water molecules via N-H···O and O-H···O hydrogen bonds into a supramolecular two dimensional network ( Fig. 2 and Table 1).

Experimental
Reagents and solvents were of commercially available quality. The title complex was synthesized according to the method of Zheng, Li et al. 2008. 2-(quinolin-8-yloxy)butanehydrazide (0.01 mol), 5-chloro-2-hydroxybenzaldehyde (0.01 mol), ethanol (40 ml) and some drops of acetic acid were added to a 100 ml flask and refluxed for 6 h. After cooling to room supplementary materials sup-2 temperature, the solid product was separated by filtration. Yellow single crystals suitable for X-ray diffraction were obtained by slow evaporation of a tetrahydrofuran solution over a period of 2 d.
Figures Fig. 1. The molecular structure, with displacement ellipsoids at the 30% probability level.