Received 6 April 2005
The structure of the title compound, C7H11N3O3, consists of molecules that pack in a linear hydrogen-bonded ribbon motif. This hydrogen-bonding arrangement is constructed through two dimer formations, one that is atypical of pyrazoles (N-HN) and the other via an interaction from the hydroxy OH group to one of the nitro O atoms.
Pyrazoles and related compounds are common molecules used in coordination or organometallic chemistry as bridging ligands, utilizing the ring positions of the two N atoms. There are 1388 structures in the Cambridge Structural Database (CSD; Version 5.26, November 2004; Allen, 2002) that contain a pyrazole ring with the extra search constraints `no extra cyclic routes' and `require 3D coordinates'. This number reduces to 23 for 4-nitropyrazoles, 80 for 5-tert-butylpyrazoles, and 15 for 3-hydroxypyrazoles. Interestingly, there is only one structure (CSD refcode: WILBAU), that of 3,5-di-tert-butyl-4-nitropyrazole (Llamas-Saiz et al., 1994), which contains two of the three mentioned substituents.
In a series of studies on the preparation and hydrogen-bonding properties of 3,4,5-trisubstituted pyrazoles, we now report 5-tert-butyl-4-nitro-1H-pyrazol-3-ol, (I). The structure of (I) (Fig. 1) consists of molecules that pack to form a linear hydrogen-bonded ribbon motif (Fig. 2). The hydrogen-bonding arrangement can be described by two centrosymmetric dimer formations (Table 1). The first of these dimer formations is atypical of pyrazoles and involves an N1-HN2 interaction, centred at (,0,0) described by an R22(6) graph set (Etter, 1990), while the second dimer formation, centred at (0,1,0), involves one intramolecular hydrogen-bonding association from O3-H to O42, forming an S(6) graph-set motif, and an R22(4) graph-set motif arising from the three-centre association involving H3 and two O42 atoms. The other O atom (O41) of the nitro group is not involved in the hydrogen-bond network. The ribbon motifs are stacked in the a-axis direction, the perpendicular distances between ribbon planes being 3.263 (2) and 3.195 (2) Å (calculated with PLATON; Spek, 2003).
| || Figure 1 |
The molecular configuration and atom-numbering scheme for (I). Displacement ellipsoids are drawn at the 50% probability level. H atoms are drawn as spheres of arbitrary radius.
| || Figure 2 |
A partial packing diagram for (I), showing the hydrogen-bonded (dashed lines) ribbon motif. For clarity, H atoms not involved in the hydrogen-bonding interactions have been omitted. [Symmetry codes: (i) -x + 1, -y, -z and (ii) -x, -y + 2, -z.]
Synthetically, (I) originated from 3,5-di-tert-butylpyrazole, being produced by gently warming this compound in concentrated nitric acid. In this reaction, 3,5-di-tert-butylpyrazole is attacked by nitric acid to form the onium species, which then displaces one tert-butyl group. The subsequent vacant position is then filled by an OH group that does not tautomerize to form the pyrazolone. The title compound was obtained from Key Organics Ltd and crystals were grown from ethanol solution.
All tert-butyl H atoms were included in the refinement at calculated positions, in the riding-model approximation, with C-H distances of 0.98 Å. All H atoms involved in the hydrogen-bonding associations were located in Fourier syntheses and positional parameters were refined. The isotropic displacement parameters for all H atoms were set equal to 1.25Ueq of the carrier atom.
Data collection: COLLECT (Hooft, 1998); cell refinement: DENZO (Otwinowski & Minor, 1997) and COLLECT; data reduction: DENZO and COLLECT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2003); software used to prepare material for publication: SHELXL97.
Allen, F. H. (2002). Acta Cryst. B58, 380-388.
Etter, M. C. (1990). Acc. Chem. Res. 23, 120-126.
Fletcher, D. A., McMeeking, R. F. & Parkin, D. J. (1996). J. Chem. Inf. Comput. Sci. 36, 746-749.
Hooft, R. W. W. (1998). COLLECT. Nonius BV, Delft, The Netherlands.
Llamas-Saiz, A. L., Foces-Foces, C., Cano, F. H., Jimenez, P., Laynez, J., Meutermans, W., Elguero, J., Limbach, H.-H. & Aquilar-Parrilla, F. (1994). Acta Cryst. B50, 746-762.
Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology. Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307-326. New York: Academic Press.
Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of Göttingen, Germany.
Sheldrick, G. M. (2003). SADABS. Version 2.10. Bruker AXS Inc., Madison, Wisconsin, USA.
Spek, A. L. (2003). J. Appl. Cryst. 36, 7-13.