(E)-N′-(4-Nitrobenzylidene)-4-(8-quinolyloxy)butanohydrazide

In the title compound, C20H18N4O4, conformation along the bond sequence linking the benzene and quinoline rings, which have a mean interplanar dihedral angle of 2.7 (5)°, is trans–(+)gauche–trans–trans–(−)gauche–trans–trans. In the crystal structure, a pair of intermolecular N—H⋯O hydrogen bonds links the molecules into centrosymmetric cyclic R 2 2(8) dimers, which are aggregated via π–π interactions into parallel sheets [quinoline–benzene ring centroid separation = 3.6173 (16)–3.6511 (16) Å]. The sheets are further connected through weak C—H⋯O interactions, giving a supramolecular two-dimensional network.


Comment
Schiff bases are one of the most prevalent mixed-donor ligands in the field of coordination chemistry, playing an important role in the development of the chemistry related to catalysis and enzymatic reactions, magnetism, and supramolecular architectures (Calligaris & Randaccio, 1987). Structures of Schiff bases derived from substituted 4-(quinolin-8yloxy)butanehydrazide and closely related to the title compound have been reported earlier (Zheng, Li et al., 2008;Zheng, 2006;, 2007Xie et al., 2008;Chen & Li, 2009;Zhang et al., 2009).
In this contribution, we present the synthesis and crystal structure of a new ligand C 20 H 18 N 4 O 4 (I), which contains oxygen and nitrogen donors and a flexible aliphatic spacer.  (Allen et al., 1987) and are comparable to those in the related compounds Zheng, 2006;, 2007Xie et al., 2008;Chen et al., 2009;Zhang, XiaHou et al., 2009). The C14-N3 and C13-O2 bond lengths [1.269 (3) and 1.235 (2) Å, respectively] indicate the presence of a typical C═N and C═O. The C═N-N angle of 115.79 (18)° is significantly smaller than the ideal value of 120° expected for sp 2 -hybridized N atoms, probably due to repulsion between the nitrogen lone pairs and the adjacent N atom (Zheng, Qiu et al., 2006). The benzene and quinoline ring systems are close to coplanar [dihedral angle, 2.7 (5)°]. In the crystal structure, intramolecular C-H···N and C-H···O interactions (Table 1, Fig. 1) produce two edge-sharing S(5) ring motifs (Bernstein et al., 1995) and a pair of intermolecular N-H···O hydrogen bonds link the molecules into centrosymmetric cyclic R 2 2 (8) dimers ( Fig. 2), which are aggregated via π-π interactions into parallel sheets [quinoline-benzene ring centroid separation: 3.6173 (16)-3.6511 (16) Å], which are further connected through weak C-H···O interactions, giving a supramolecular two-dimensional network (Fig. 3).

Experimental
Reagents and solvents used were of commercially available quality. The title compound (I) was synthesized according to the method of Zheng, Li et al., 2008. 4-(Quinolin-8-yloxy)butanehydrazide (0.01 mol), p-formylnitrobenzene (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 temperature, the solid product was separated by filtration. Yellow single crystals of (I) suitable for the X-ray diffraction study were obtained by slow evaporation of a tetrahydrofuran solution over a period of four days.
supplementary materials sup-2 Refinement All H atoms were placed in idealized positions (C-H = 0.93-0.97 Å, N-H = 0.86 Å) and refined as riding atoms with U iso (H) = 1.2U eq (C or N). Fig. 1. The molecular structure of (I), with displacement ellipsoids at the 30% probability level. Intramolecular C-H···N and C-H···O interactions are shown as dashed lines.

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 > σ(F 2 ) is used only for calculating Rfactors(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.