(E)-1-(4-Chlorophenyl)ethanone semicarbazone

In the title compound, C9H10ClN3O, the semicarbazone group is approximately planar, with an r.m.s. deviation from the mean plane of 0.054 (1) Å. The dihedral angle between the least-squares planes through the semicarbazone group and the benzene ring is 30.46 (5)°. In the solid state, molecules are linked via intermolecular N—H⋯O and N—H⋯N hydrogen bonds, generating R 2 2(9) ring motifs which, together with R 2 2(8) ring motifs formed by pairs of intermolecular N—H⋯O hydrogen bonds, lead to the formation of a seldom-observed molecular trimer. Furthermore, N—H⋯O hydrogen bonds form R 2 1(7) ring motifs with C—H⋯O hydrogen bonds, further consolidating the crystal structure. Molecules are linked by these intermolecular interactions, forming two-dimensional networks parallel to (100).

In the title compound, C 9 H 10 ClN 3 O, the semicarbazone group is approximately planar, with an r.m.s. deviation from the mean plane of 0.054 (1) Å . The dihedral angle between the least-squares planes through the semicarbazone group and the benzene ring is 30.46 (5) . In the solid state, molecules are linked via intermolecular N-HÁ Á ÁO and N-HÁ Á ÁN hydrogen bonds, generating R 2 2 (9) ring motifs which, together with R 2 2 (8) ring motifs formed by pairs of intermolecular N-HÁ Á ÁO hydrogen bonds, lead to the formation of a seldom-observed molecular trimer. Furthermore, N-HÁ Á ÁO hydrogen bonds form R 2 1 (7) ring motifs with C-HÁ Á ÁO hydrogen bonds, further consolidating the crystal structure. Molecules are linked by these intermolecular interactions, forming twodimensional networks parallel to (100).

Comment
In organic chemistry, a semicarbazone is a derivative of an aldehyde or ketone formed by a condensation between a ketone or aldehyde and semicarbazide. Semicarbazones find numerous applications in the field of synthetic chemistry, such as medicinal chemistry (Warren et al., 1977), organometalics (Chandra & Gupta, 2005), polymers (Jain et al., 2002) and herbicides (Pilgram, 1978). 4-Sulphamoylphenyl semicarbazones were synthesized and were found to possess anticonvulsant activity (Yogeeswari et al., 2004). Herein we report the crystal structure of the title semicarbazone which may have commercial and synthetic importance.
The bond lengths (Allen et al., 1987) and angles in the molecule ( Fig. 1) are within normal ranges, and are comparable to those observed in a closely related structure (Fun et al., 2009). The semicarbazone group (C9/C6/C7/N1/N2/C8/O1/N3) is approximately planar, with an r.m.s. deviation of 0.054 (1) Å for atom N2 while the dihedral angle between the least-squares planes through the semicarbazone group and the benzene ring is 30.46 (5)°.
The molecules are linked by these intermolecular interactions to form two-dimensional networks parallel to the (1 0 0) plane.
Experimental 0.780 g (7.0 mmol) of semicarbazide hydrochloride and 0.698 g (8.5 mmol) of crystallized sodium acetate was dissolved in 10 ml of water (Furniss et al., 1978). The reaction mixture was stirred at room temperature for 10 minutes. To this (1 g, 6.5 mmol) of 4-choloacetophenone was added and shaken well. A little alcohol was added to dissolve the turbidity. It was shaken for 10 more minutes and allowed to stand. The semicarbazone crystallizes on standing for 6 h. The separated crystals were filtered, washed with cold water and recrystallized from alcohol. Yield was found to be 1.1 g, 80.35%. M.p. 478-479 K.

Refinement
All hydrogen atoms were located from the difference Fourier map and refined freely.
supplementary materials sup-2 Figures   Fig. 1. The molecular structure of the title compound, showing 50% probability displacement ellipsoids and the atom-numbering scheme. Fig. 2. Part of the crystal packing of the title compound, viewed along the a axis, showing the formation of a molecular trimer. Atom-numbering is shown for those non-H atoms involved in hydrogen bonds and intermolecular interactions are shown as dashed lines. Molecule A is is related to molecules B and C via symmetry codes of -x + 1/2, -y + 1/2, -z and -x + 1/2, y + 1/2, -z + 1/2, respectively.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cyrosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K. 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.

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