1-{3-[1-(Hydroxyimino)ethyl]-4-methyl-1H-pyrazol-5-yl}ethanone

In the title compound, C8H11N3O2, the oxime and the acetyl groups adopt a transoid conformation, while the pyrazole H atom is localized in the proximity of the acetyl group and is cis with respect to the acetyl O atom. In the crystal, dimers are formed as the result of hydrogen-bonding interactions involving the pyrazole NH group of one molecule and the carbonyl O atom of another. The dimers are associated into sheets via O—H⋯N hydrogen bonds involving the oxime hydroxyl and the unprotonated pyrazole N atom, generating a macrocyclic motif with six molecules.

In the title compound, C 8 H 11 N 3 O 2 , the oxime and the acetyl groups adopt a transoid conformation, while the pyrazole H atom is localized in the proximity of the acetyl group and is cis with respect to the acetyl O atom. In the crystal, dimers are formed as the result of hydrogen-bonding interactions involving the pyrazole NH group of one molecule and the carbonyl O atom of another. The dimers are associated into sheets via O-HÁ Á ÁN hydrogen bonds involving the oxime hydroxyl and the unprotonated pyrazole N atom, generating a macrocyclic motif with six molecules.
Data collection: COLLECT (Nonius, 1998); cell refinement: DENZO/SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO/SCALEPACK; program(s) used to solve structure: SIR2004 (Burla et al., 2005); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXL97. particular, azomethine-functionalized pyrazoles have been used extensively as ligands in the field of coordination chemistry and catalysis (De Geest et al., 2007;Roy et al., 2008). Furthermore, introduction of the potentially bridging oxime group into the ligands already having bridging moieties (such as pyrazoles) may result in significant increase of coordination versatility of such ligands and afford the formation of metal complexes of high nuclearity and coordination polymers (Kanderal et al., 2005;Moroz et al., 2010). The title compound, having different substituents in the 3-and 5-positions of the pyrazole ring (the oxime and the acetyl groups) was synthesized as a part of our study of the abovementioned ligands and we report herein its crystal structure.
In the title compound ( Fig. 1), the oxime and acetyl groups are in the transoid conformation in reference to one another, while the pyrazole proton is localized in the proximity of the acetyl group and is cis with respect to the acetyl O atom.
The molecule is virtually planar, with the maximal deviation from the mean plane defined by the non-hydrogen atoms not exceeding 0.047 (5) Å for the methyl C5. The C-C, C-N and N-N bond lengths in the pyrazole ring are normal for the 3,5-disubstituted pyrazoles (Petrusenko et al., 1997, Wörl et al., 2005a. The bond lengths and angles within the acetyl and oxime groups are normal and comparable to those in the related structures (Fritsky et al., 1998;Mokhir et al., 2002;Świątek-Kozłowska et al., 2000). The C, N, O atoms of the oxime group exist in the nitroso-form (Mokhir et al., 2002;Sliva et al., 1997).
The crystal of the title compound has a layer structure formed entirely by hydrogen bonds between the molecules. The approximately planar dimers form as the result of hydrogen-bonding interactions (Table 1) involving the pyrazole NH group of one molecule and the carbonyl O atom of another. The dimers are associated into planar sheets via O-H···N hydrogen bonds involving the unprotonated pyrazole N atom and the oxime hydroxyl, generating a macrocyclic motif with six molecules (Fig. 2).

Refinement
The crystal structure was refined with two twin components (twin matrices: 1 0 0.537 0 -1 0 0 0 -1 and 1.008 0 0.502 0 -1 0 -0.033 0 -1.008). BASF values were refined to 0.241 and 0.069, respectively. H atoms bonded to N and O atoms were located from a difference Fourier map but constrained to ride on their parent atoms, with U iso (H) = 1.2U eq (N) and 1.5U eq (O). H atoms of the methyl groups were positioned geometrically and refined as riding atoms, with C-H = 0.98 Å and with U iso (H) = 1.5U eq (C). Fig. 1. The molecular structure of the title compound, with displacement ellipsoids drawn at the 40% probability level.   (2) Geometric parameters (Å, °)