3-Ethyl-4-methyl-1H-pyrazol-2-ium-5-olate

The title compound, C6H10N2O, is a zwitterionic pyrazole derivative. The crystal packing is predominantly governed by a three-center iminium–amine N+—H⋯O−⋯H—N interaction, leading to an undulating sheet-like structure lying parallel to (100).


Related literature
For related structures and the preparation of similar compounds, see: Ragavan et al. (2009Ragavan et al. ( , 2010 and references therein. For related salt-bridge-mediated sheet structures, see: Shylaja et al. (2008).
The molecular structure of the title molecule is shown in Fig 1. The methyl atom (C3B) of the 3-ethyl substituent lies out of the mean plane of the pyrazole moiety (N1,N2,C3-C5) by 1.366 (4) Å.
The crystal packing is a fine balance of strong N-H···O hydrogen bonds (Table 1) and salt bridges, which normally tend to promote the formation of a planar structure and compact packing (Shylaja et al., 2008). In the title compound all the hydrogen bonding donors, iminium N + H (N1) and amine NH (N2), and the O -(O1) acceptor, are in the plane of the pyrazole moiety, which would normally yield a planar hydrogen-bonded structure. However, in order to accommodate the out-of-plane methyl group, (C3B), an undulating hydrogen bonded sheet-like structure, lieing paralallel to (100), is formed ( Fig. 2).

Refinement
The NH atoms were located in a difference Fourier map and were freely refined: N2-H2 = 0.92 (2) Å and N1 + -H1 = 0.95 (3) Å. The methylene and methyl hydrogen atoms were placed in calculated positions and refined as riding atoms: C-H = 0.97 and 0.96 Å, for CH and CH 3 H-atoms, respectively, with U iso (H) = k × U eq (C,) where k = 1.5 for CH 3 H-atoms and 1.2 for the CH H-atoms. Fig. 1. A view of the molecular structure of the title molecule, with labelling scheme and displacement ellipsoids drawn at the 30% probability level.
3-Ethyl-4-methyl-1H-pyrazol-2-ium-5-olate 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.