Crystal structure of 4-(4-chlorophenyl)-6-(morpholin-4-yl)pyridazin-3(2H)-one

In the crystal, pairs of centrosymmetrically related molecules are linked into dimers via N—H⋯O hydrogen bonds, forming (8) ring motifs. The dimers are connected via C—H⋯O and C—H⋯Cl hydrogen bonds, forming a three-dimensional network·Semi-empirical molecular orbital calculations were carried out using the AM1 method.

In the title compound, C 14 H 14 ClN 3 O 2 , the morpholine ring adopts a chair conformation, with the exocyclic N-C bond in an equatorial orientation. The 1,6-dihydropyridazine ring is essentially planar, with a maximum deviation of 0.014 (1) Å , and forms a dihedral angle of 40.16 (7) with the plane of the benzene ring. In the crystal, pairs of centrosymmetrically related molecules are linked into dimers via N-HÁ Á ÁO hydrogen bonds, forming R 2 2 (8) ring motifs. The dimers are connected via C-HÁ Á ÁO and C-HÁ Á ÁCl hydrogen bonds, forming a three-dimensional network. Aromaticstacking interactions [centroid-centroid distance = 3.6665 (9) Å ] are also observed. Semi-empirical molecular orbital calculations were carried out using the AM1 method. The calculated dihedral angles between the pyridizine and benzene rings and between the pyridizine and morpholine (all atoms) rings are 34.49 and 76.96 , respectivelyÁThe corresponding values obtained from the X-ray structure determination are 40.16 (7) and 12.97 (9) , respectively. The morpholine ring of the title compound in the calculated gas-phase seems to have a quite different orientation compared to that indicated by the X-ray structure determination.

Chemical context
The title compound was first synthesized by Ş ü kü rog lu et al. (2006). The pharmacological properties of the compound have been investigated and it was found it possesses an analgesic effect close to that of aspirin. In recent years, the 3(2H)pyridazinone system has aroused a great deal of attention due to its structural relationship to pyrazolone derivatives such as aminopyrine and dipyrone in view of the ring enlargement of pyrazolone to pyridazinone. These drugs possess analgesic and anti-inflammatory activities although they have limitations for their clinical use due to serious side effects such as blood dyscrasias (Ş ü kü rog lu et al., 2006;Brogden, 1986).

Figure 2
View of a dimer, with R 2 2 (8) ring motif, formed by N-HÁ Á ÁO hydrogen bonds (dashed lines) between two centrosymmetrically related molecules. the title compound in the calculated gas phase seems to have a quite different orientation compared to that indicated by the X-ray structure determination. The calculated dipole moment is 2.13 Debye. The HOMO and LUMO energy levels are À9.05 and À1.01 eV, respectively.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses 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 observed criterion of F 2 > σ(F 2 ) is used only for calculating -R-factor-obs 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.