3-Methyl-1,2,4-triazolo[3,4-a]phthalazine monohydrate

In the crystal structure of the title compound, C10H8N4·H2O, the organic molecules are approximately planar [maximum deviation from the least-squares plane = 0.041 (2) Å]. Two molecules are connected by two water molecules via O—H⋯N hydrogen bonding into dimers, which are located around centres of inversion. In the crystal, molecules are stacked in the a-axis direction, with mean distances between the π systems of 3.43 (1) and 3.46 (1) Å [centroid–centroid distances are 3.604 (2) and 3.591 (2) Å].

CSC thanks the University of Mysore for research facilities.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: NC2160).

Comment
The practical interest upon phthalazine derivatives is based on their widespread applications (Coates, 1999). They are commonly used as ligands in transition metal catalysis (e.g., Yatani et al., 2001), as chemiluminescent materials (Shubin et al., 2004) and for optical applications (Cheng et al., 1999). The chemistry of phthalazine derivatives has been of increasing interest since many of these compounds have found chemotherapeutic applications, especially as antihypertensive agents (De Stevens, 1981). 3-substituted 1,2,4-triazolo[3,4-a]phthalazines have been described as high affinity ligands for benzodiazepine receptor site (e.g., Tarzia et al., 1989).
The molecules are almost planar with maximum deviation from the least-squares plane through all 13 ring atoms of 0.041 (2) Å ( Fig. 1). The dihedral angle between the planes of the phenyl and the 1,2,4-triazole rings amount to 2.84 (7)°.
In the crystal the principal motif is built of two molecules of 3-methyl[1,2,4]triazolo[3,4-a]phthalazine and two water molecules, which are connected by means of O-H···N hydrogen bonds into centrosymmetric dimers which can be described according to the graph set notation as R 4 4 (10), cf. (Fig. 2). The planar molecules are stacked in a head-to-tail manner in the direction of the crystallographic a-axis with distances between the subsequent mean planes of 3.43 (1)Å and 3.46 (1)Å.
Experimental 1-Hydrazinophthalazine (2 g, 12.5 mmol) in 10 ml acetic acid was refluxed for 4 h. The reaction mixture was quenched to ice cold water and the solid separated was collected by filteration. The solid obtained was crystallized from methanol.
Crystals for x-ray measurements were grown by a slow evaporation of ethyl acetate solution (m.p.: 421-423 K).

Refinement
Hydrogen atoms from the methyl group were placed in idealized positions and were refined as riding model with U iso values set at 1.5 times U eq of their carrier carbon atom. All other hydrogen atoms, including those from water molecule, were freely refined.
supplementary materials sup-2 Figures   Fig. 1. View of the dimers in the crystal structure of the title compound with labelling and displacement ellipsoids drawn at 50% probability level. Hydrogen atoms are depicted as spheres with arbitrary radii and hydrogen bonding is shown as dashed lines. Symmetry code: (i) -x,1y,-z.  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 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.