tert-Butyl 4-{[5-(4-chlorophenyl)-1-(4-fluorophenyl)-1H-pyrazol-3-yl]carbonyl}piperazine-1-carboxylate

In the title pyrazole derivative, C25H26ClFN4O3, both benzene rings are twisted out of the plane through the pyrazole ring, with dihedral angles of 67.62 (10) and 27.63 (10)° for the fluoro- and chloro-substituted rings, respectively. The dihedral angle between the two benzene rings is 64.54 (9)°. The piperazine ring (with a chair conformation) is linked to the pyrazole ring via a carbonyl spacer and is orientated to lie to one side of the pyrazole plane. In addition to an intramolecular C—H⋯N contact, there are intermolecular C—H⋯O interactions, which generate a supramolecular chain with an undulating topology along the c axis that is sustained by alternating centrosymmetric ten-membered {⋯HCNCO}2 and {⋯HC3O}2 synthons.

In the title pyrazole derivative, C 25 H 26 ClFN 4 O 3 , both benzene rings are twisted out of the plane through the pyrazole ring, with dihedral angles of 67.62 (10) and 27.63 (10) for the fluoro-and chloro-substituted rings, respectively. The dihedral angle between the two benzene rings is 64.54 (9) . The piperazine ring (with a chair conformation) is linked to the pyrazole ring via a carbonyl spacer and is orientated to lie to one side of the pyrazole plane. In addition to an intramolecular C-HÁ Á ÁN contact, there are intermolecular C-HÁ Á ÁO interactions, which generate a supramolecular chain with an undulating topology along the c axis that is sustained by alternating centrosymmetric ten-membered {Á Á ÁHCNCO} 2 and {Á Á ÁHC3O} 2 synthons.   Table 1 Hydrogen-bond geometry (Å , ). VV is grateful to the DST, India, for funding through the Young Scientist Scheme (Fast Track Proposal). The authors are also grateful to the University of Malaya for support of the crystallographic facility.

Experimental
cytotoxic, and anti-viral activities. Since the high electronegativity of halogens (particularly chlorine and fluorine) in aromatic rings of drug molecules plays an important role in enhancing biological activity, we are interested to have 4-fluoro or 4-chloro substitution in the aryl rings of 1,5-diaryl pyrazoles. As part of our on-going research aimed at the synthesis of new anti-microbial compounds based on pyrazole (Ragavan et al., 2009(Ragavan et al., , 2010 and reflecting our interest in pyrazole structures (Samshuddin et al., 2010), herein we report the crystallographic characterization of a novel pyrazole derivative, (I).
In addition to an intramolecular C-H···N bond, there are two significant intermolecular C-H···O contacts of note,

Experimental
The compound was synthesized by the literature method (Ragavan et al., 2010). Colourless blocks of (I) were obtained by recrystallization from absolute ethanol; m.pt. 356.1-357.2 K.

Refinement
Carbon-bound H-atoms were placed in calculated positions (C-H 0.95 to 0.99 Å) and were included in the refinement in the riding model approximation, with U iso (H) set to 1.2 to 1.5U equiv (C). In the final refinement two low angle reflections evidently effected by the beam stop were omitted, i.e. (010) Fig. 1. The molecular structure of (I) showing displacement ellipsoids at the 50% probability level.  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 > 2σ(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.