5-Bromophthalazine hemihydrate

The title compound, C8H5BrN2·0.5H2O, is a phthalazine derivative synthesized from 3-bromobenzene-1,2-dicarbaldehyde and hydrazine. The molecule is essentially planar, the deviation from the mean plane of the phthalazine ring being 0.015 (3) Å. The O atom of the solvent water molecule is situated on a twofold rotation axis. In the crystal, O—H⋯N hydrogen bonds and short N⋯Br [2.980 (3) Å] contacts lead to the formation of a two-dimensional network parallel to (101).

The title compound, C 8 H 5 BrN 2 Á0.5H 2 O, is a phthalazine derivative synthesized from 3-bromobenzene-1,2-dicarbaldehyde and hydrazine. The molecule is essentially planar, the deviation from the mean plane of the phthalazine ring being 0.015 (3) Å . The O atom of the solvent water molecule is situated on a twofold rotation axis. In the crystal, O-HÁ Á ÁN hydrogen bonds and short NÁ Á ÁBr [2.980 (3) Å ] contacts lead to the formation of a two-dimensional network parallel to (101).

Mingjian Cai Comment
Phthalazine derivatives have played an important role in the development of corrosion science as they can inhibit the corrosion of mild steel (Musa et al., 2012). Moreover, they are of particular interest owing to their biological activity and optical properties (Caira, et al., 2011).
In this paper, the title new phthalazine derivative derived from the condensation of 3-bromo-benzene-1,2dicarboxaldehyde with hydrazine is reported. The molecular structure of the title compound ( Fig.1) is essentially planar with a deviation from the mean plane of the phthalazine ring of 0.0115 (3) Å. All bond lengths have normal values.The oxygen atom of the solvent water molecule is situated on a twofold rotation axis. In the crystal, O-H···N hydrogen bonds and short N···Br contacts lead to the formation of a two dimensional network structure (Fig.2).

Experimental
A solution of 0.1 mol of 3-bromo-benzene-1,2-dicarboxaldehyde is dissolved in 100 ml of ethanol and added dropwise with constant stirring, under a blanket of nitrogen, to an ice-cooled solution of 0.3 mol of hydrazine hydrate in 100 ml of ethanol. The light yellowish reaction mixture is kept with constant stirring for an additional three hours. Ethanol and excess hydrazine are removed under reduced pressure. The remaining yellowish solid may be purified by recrystallization from diethyl ether to yield the yellowish title compound (yield 48%). Finally, the title compound was dissolved in a small amount of methanol and the solution was kept for 10 days at ambient temperature to give rise to white flake crystals due to slow evaporation of the solvent.

Refinement
The H atom of the solvent water was located in a difference fourier map and refined as a riding atom with U iso (H) = 1.2U eq (O). Remaining H atoms were positioned geometrically with C-H = 0.93-0.98 Å and constrained to ride on their parent atoms with U iso (H) = 1.2U eq (C).

Computing details
Data collection: CrystalClear (Rigaku/MSC, 2002); cell refinement: CrystalClear (Rigaku/MSC, 2002); data reduction: CrystalClear (Rigaku/MSC, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Crystal Impact, 2009); software used to prepare material for publication: CrystalStructure (Rigaku/MSC, 2006   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