6-Oxo-1,6-dihydropyridazine-3-carbaldehyde monohydrate

In the title hydrate, C5H4N2O2·H2O, the pyridazine ring is essentially planar, with an r.m.s. deviation of 0.0025 Å. In the crystal, O—H⋯O and N—H⋯O hydrogen bonds link the molecules into a one-dimensional chain.

In the title hydrate, C 5 H 4 N 2 O 2 ÁH 2 O, the pyridazine ring is essentially planar, with an r.m.s. deviation of 0.0025 Å . In the crystal, O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds link the molecules into a one-dimensional chain.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: JJ2141).  (Sarkhel & Desiraju, 2004). In the crystal, O-H···O and N-H···O hydrogen bonds (Table 1) link the molecules into a one-dimensional chain (Fig. 2).

Experimental
To a solid of 3-Chloro-6-methylpyridazine (5 mmol) in dry dioxane was added SeO 2 (1.5 g). The mixture was stirred for 6 h at the reflux temperature of dioxane. After evaporation of the solvent, the residue was purified by column chromatography on silica gel (ethyl acetate) to afford the title compound as a light yellow solid (497 mg, yield 70%). The title compound was recrystallized from methanol at room temperature to give the desired crystals suitable for singlecrystal X-ray diffraction.

Refinement
H1W and H2W were located by a difference map and refined isotropically. All of the remaining H atoms were positioned geometrically and treated as riding, with C-H bonding lengths constrained to 0.93 Å (aromatic CH) or 0.97 Å (methylene CH 2 ), and with U iso (H) = 1.2Ueq(C) or 1.5Ueq(methylene C).

Figure 2
The molecular packing for (I) viewed along the a axis. O-H···O and N-H···O hydrogen bonds are shown by dashed lines linking the molecules into a one-dimensional chain. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.30 e Å −3 Δρ min = −0.21 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.009 (5) Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'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 > σ(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq N1 0.2572 (2