1-Phenyl-5-[4-(trifluoromethyl)phenyl]pyrazolidin-3-one monohydrate

In the molecule of the title compound, C16H13F3N2O·H2O, the two benzene rings are oriented at a dihedral angle of 82.55 (3)° and the pyrazole ring adopts an envelope conformation. In the crystal structure, intermolecular C—H⋯F hydrogen bonds link the molecules into chains.

In the molecule of the title compound ( Fig. 1), the bond lengths (Allen et al., 1987) and angles are within normal ranges.
In the crystal structure, intermolecular C-H···F hydrogen bonds (Table 1) link the molecules into chains (Fig. 2), in which they may be effective in the stabilization of the structure.

Experimental
The title compound was prepared by the literature method (Jia et al., 2008). For the preparation of the title compound, n-butanol (40 ml) and ethanolamine (4 ml) were added to a solution of sodium (40 mmol) in anhydrous methanol (9 ml).
Then, methanol was removed by distillation and methyl 3-(4-(trifluoromethyl)phenyl)acrylate (30 mmol) was added. The mixture was refluxed for 1.5 h at 385 K, after which phenylhydrazine (4 ml) was added. The mixture was refluxed for another 10 h, and then left to cool to room temperature. It was then acidified with acetic acid (50%), allowed to stand and filtered. The filter cake was chromatographed over silica gel (500 g) eluting with a mixture of ethyl acetate and petroleum ether to give the title compound (m.p. 413-415 K). Crystals suitable for x-ray analysis were obtained by dissolving the title compound (1.5 g) in ethyl acetate (25 ml) and evaporating the solvent slowly at room temperature for about 10 d.

Refinement
The water molecule was disordered. During the refinement process the disordered O and H atoms were refined with occu-    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.