1-Ethyl-N′-[(E)-4-hydroxybenzylidene]-7-methyl-4-oxo-1,4-dihydro-1,8-naphthyridine-3-carbohydrazide

In the crystal structure of the title compound, C19H18N4O3, the fused-ring system is essentially planar [maximum deviation is 0.031 (2) Å] while the dihedral angle between the ring system and the benzene ring is 12.64 (6)°.The carbohydrazide H atom is involved in an intramolecular N—H⋯O hydrogen bond, forming a six-membered hydrogen-bonded ring. The molecules arrange themselves into centrosymmetric dimers by means of intermolecular O—H⋯O hydrogen bonds.

In the crystal structure of the title compound, C 19 H 18 N 4 O 3 , the fused-ring system is essentially planar [maximum deviation is 0.031 (2) Å ] while the dihedral angle between the ring system and the benzene ring is 12.64 (6) .The carbohydrazide H atom is involved in an intramolecular N-HÁ Á ÁO hydrogen bond, forming a six-membered hydrogen-bonded ring. The molecules arrange themselves into centrosymmetric dimers by means of intermolecular O-HÁ Á ÁO hydrogen bonds.
In continuation of our work on the synthesis, biological activity and crystal structures of various heterocyclic compounds (Zia-ur-Rehman et al., 2006;Zia-ur-Rehman et al., 2009), we herein report the synthesis and crystal structure of the title compound (I) (Scheme and figure 1). The structure of the basic naphthyridine ring consisting of two adjoined pyridine rings is planar while carbonyl oxygen O1 on C11 is involved in intramolecular hydrogen bonding giving rise to a six-membered hydrogen bond ring (Table 1). All bond distances are essentially identical to those found in the literature (Catalano et al., 2000).The molecules form centrosymmetric dimers through intermolecular O-H···O hydrogen bonds.

Refinement
H atoms were placed in geometrically idealized positions (C-H = 0.93-0.98 Å, O-H=0.82 Å) and treated as riding, with U iso (H)=1.2U eq (C) (for methine and methylene) or 1.5U eq (methyl and hydroxyl). The N3 and C13 H atoms were located in a difference Fourier map sup-2 Figures Fig. 1. An ORTEP-3 (Farrugia, 1997) drawing of the title molecule with the atom-numbering scheme. The displacement ellipsoids are drawn at the 50% probability level.

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s 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 > 2σ(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.