Received 21 April 2005
The structure of the title compound, C7H11BrN2O·H2O, exhibits an elaborate hydrogen-bonding network involving pyrazole N-HO dimers and two other hydrogen-bonding motifs, both including water molecules. One motif is a distorted hexagonal R35(11) graph set, while the other is a distorted octagonal boat conformation R64(14) graph set.
In a series of studies on the preparation and hydrogen-bonding properties of 3,4,5-tri-substituted pyrazoles, we recently characterized the structure of 5-tert-butyl-4-nitro-1H-pyrazol-3-ol (Lynch & McClenaghan, 2005). We report here the structure of the title compound, (I). Similar to 5-tert-butyl-4-nitro-1H-pyrazol-3-ol, compound (I) originated from 3,5-di-tert-butylpyrazole. Compound (I) was prepared by reacting 3,5-di-tert-butylpyrazole with bromine in chloroform solution at room temperature. In these reactions, 3,5-di-t-butylpyrazole is attacked by either nitric acid (as in the case of 5-tert-butyl-4-nitro-1H-pyrazol-3-ol) or bromine to form the onium species, which then displaces one tert-butyl group. The subsequent vacant position is then filled by an OH group that, in the case of (I), tautomerizes to form the pyrazolone.
In the structure of (I) (Fig. 1), all strong hydrogen-bonding components are involved in the hydrogen-bonding network. The hydrogen-bonding geometry for this structure is listed in Table 1. The fourfold symmetry in (I) arises because of the unique hydrogen-bonded motif that is formed via contributions from eight pyrazole molecules and four water molecules. Each pyrazole molecule forms a centrosymmetric R22(8) graph set (Etter, 1990) dimer via N1-HO5 interactions, at (x, y, z) and (-x + , -y + , -z + ), centred at (, , ). The N2/H group associates with O1W, at (x, y, z) and (y + , -x + , z + ). O1W, at (x, y, z), associates with two O5 atoms, one at (x, y, z) and the other at (-y + , x - , -z + ). Thus, each O5 atom is involved in a four-centre hydrogen-bonding association. For O5, at (x, y, z), the three non-H-atom contacts are O1W at (x, y, z), O1I at (y + , -x + , -z + ) and N1 at (-x + , -y + , -z + ) (Fig. 2). Three pyrazole molecules, at (x, y, z), (-x + , -y + , -z + ) and (-y + , x - , -z + ), and two water molecules, at (x, y, z) and (-y + , x - , -z + ), form a distorted hexagonal hydrogen-bonding motif [graph set R35(11)], adjoining the N1-HO5 dimer, fused via the same interaction (Fig. 3). The hexagonal motifs are also fused with each other via the O1W-HO5 interaction at (x, y, z). The resulting arrangement also creates a distorted octagonal boat conformation hydrogen-bonding motif [graph set R64(14)] involving four pyrazole groups, at (x, y, z), (-x + , -y + , -z + ), (x - , y, -z + ) and (1 - x, -y + , z), and two water molecules, at (y + , -x + , z + ) and (-y + , x - , z + ) (Fig. 4). A stereoview of the unit cell contents of (I) is shown in Fig. 5. The Br atom does not contribute to the hydrogen-bonding network; atom Br4 is 3.469 (3) Å from O1W, and 3.412 (3) Å from N2(-y + , x - , z - ).
| || Figure 1 |
Molecular configuration and atom-numbering scheme for (I). Displacement ellipsoids are drawn at the 50% probability level and H atoms are drawn as spheres of arbitrary radii.
| || Figure 2 |
Hydrogen-bonding environment for (I), at (x, y, z), showing the centrosymmetric R22(8) N1-HO5 dimer, the two hydrogen-bonding associations from O1W, and the four-centre hydrogen-bonding association involving O5. For clarity, H atoms not involved in the hydrogen-bonding interactions have been omitted. Hydrogen bonds are shown as dashed lines. [Symmetry codes: (i) -x + , -y + , -z + ; (ii) y + , -x + , z + ; (iii) -y + , x - , -z + ; (iv) y + , -x + , -z + .]
| || Figure 3 |
Part of the structure of (I), at (x, y, z), showing the distorted R35(11) hexagonal motif, and its position with respect to the N1-HO5 dimer. For clarity, H atoms not involved in the hydrogen-bonding interactions have been omitted. Hydrogen bonds are shown as dashed lines. [Symmetry codes: (i) -x + , -y + , -z + ; (ii) -y + , x - , z - .]
| || Figure 4 |
Part of the structure of (I), at (x, y, z), showing the distorted R64(14) octagonal boat motif and its position with respect to the N1-HO5 dimer. For clarity, H atoms not involved in the hydrogen-bonding interactions have been omitted. Hydrogen bonds are shown as dashed lines. [Symmetry codes: (i) -x + , -y + , -z + ; (ii) -y + , x - , z + ; (iii) 1 - x, -y + , z; (iv) x - , y, -z + ; (v) y + , -x + , z + .]
| || Figure 5 |
Stereoview of the unit cell contents of (I).
The title compound was obtained from Key Organics Ltd, and crystals were grown from an 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 NH H atoms involved in the hydrogen-bonding associations (Table 1) were located in Fourier syntheses and positional parameters were refined. The water H atoms were located and were refined with O-H distance restraints of 0.83 (2) Å and HH restraints of 1.40 (2) Å. 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: PLATON97 (Spek, 1997); software used to prepare material for publication: SHELXL97.
The authors thank the EPSRC National Crystallography Service (Southampton, England).
Etter, M. C. (1990). Acc. Chem. Res. 23, 120-126.
Hooft, R. W. W. (1998). COLLECT. Nonius BV, Delft, The Netherlands.
Lynch, D. E. & McClenaghan, I. (2005). Acta Cryst. E61, o2347-o2348.
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. (1997). PLATON9. University of Utrecht, The Netherlands.