4,5-Dichloro-2-methylpyridazin-3(2H)-one

The asymmetric unit of the title compound, C5H4Cl2N2O, contains one half-molecule: all the non-H atoms lie on a crystallographic mirror plane. In the crystal structure, molecules are linked into chains along the c axis by weak intermolecular C—H⋯O hydrogen bonds.


D-HÁ
Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009   Pyridazin-3(2H)-one derivatives represent one of the most active class of compounds possessing a wide spectrum of biological activities such as cardiovascular properties, anti-inflammatory, anti-diabetic, analgesic, anti-AIDS, anti-cancer, antimicrobial and anti-convulsant activities (Banerjee et al., 2009;Siddiqui & Wani, 2004). Effects of substituted pyridazinones on photosynthetic electron transport have been studied by various workers and are known to inhibit photosystem II (PS II) electron transport (Samuel & Bose, 1987). Herein we report the crystal structure of the title compound.
The asymmetric unit of the title compound contains one half-molecule and all atoms, with the exception of one methyl hydrogen atom [symmetry related H atom generated by 1-x, y, z], lie on a crystallographic mirror plane (Fig. 1). The bond lengths (Allen et al., 1987) and angles are within normal ranges. In the crystal structure (Fig. 2), neighbouring molecules are linked into one-dimensional chains along the c axis by intermolecular C4-H4A···O1 i hydrogen bonds (Table 1).
Experimental 4,5-dichloropyridazin-3(2H)-one (0.01 mol) and methanol (9.7 ml) was placed into a R.B. flask. The contents were stirred for 15 minutes. Sodium hydroxide (0.5 g) in de-mineralized water (10.0 ml) was added with constant stirring. As a clear solution is observed, the R.B. flask was cooled to 278 K. When the temperature fell below 278 K, dimethyl sulphate (0.01 mol) was added dropwise. Stirring was continued, maintaining the temperature between 288-293 K over 1 h. Excess methanol was distilled off under reduced pressure. The solid obtained was collected by filtration, washed with water and dried. The crude product obtained was purified by recrystallization from ethanol. Single crystals suitable for X-ray analysis were obtained recrystallization from a 1:2 mixture of DMF and ethanol by slow evaporation.

Refinement
The hydrogen atom H4A was located from difference Fourier map and allowed to refine freely. The hydrogen atoms bound to atom C5 were located geometrically and refined using a riding model with C-H = 0.96 Å and U iso (H) = 1.5 U eq (C). Fig. 1. The molecular structure of the title compound, showing 50% probability displacement ellipsoids for non-H atoms and the atom-numbering scheme [symmetry code: 1-x, y, z for one methyl hydrogen atom not lying on the mirror plane].

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cyrosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1)K.
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 > 2sigma(F 2 ) is used only for calculating R-factors(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.