Crystal structure of tris(3-methyl-1H-pyrazol-1-yl)methane

The title molecule, C13H16N6, crystallizes from hexane as a molecular crystal with no strong intermolecular interactions (the shortest C—H⋯N contact is longer than 3.38 Å). A relatively short intramolecular contact (3.09 Å) has a C—H⋯N angle of 118° which is quite small to be still considered a hydrogen bond. The three pyrazole rings form a propeller-like motif, with one methylpyrazole unit almost perpendicular to the mean plane of the three rings [82.20 (6)°]. The other two methylpyrazole units, with nitrogen donor atoms oriented in opposite directions, are oriented at 67.26 (6) and 72.53 (6)° to the mean plane.


S1. Chemical context
This report is part of our continious effort to study substituted trispyrazolylmethanes and their complexes with various metal ions. Because all synthetic procedures yield a complex mixture of isomers, positive identification of the ligand molecule by X-ray diffractometry is essential for future research.

S2. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1.
All hydrogen atoms were located in electron difference density Fourier maps and were refined in an isotropic approximation. One methyl group (C5) was treated as disordered (SHELXL instruction AFIX 124). Isotropic parameters of atoms H1 and of disordered methyl group hydrogen atoms were constrained as U H = 1.2 U C .
Reflections 1 0 0 and 1 1 0 were too close to the beamstop to be measured reliably and were excluded from refinement.

S3. Synthesis and crystallization
Following the general method of Reger et al. (2000), 3-methylpyrazole (6.0 mL, 75.0 mmol), tetrabutylammonium bromide (1.21 g, 3.75 mmol), and sodium carbonate (47.0 g, 0.45 mol) were heated together in a biphasic mixture of deionized water (75 mL) and chloroform (40 mL). The reaction mixture was allowed to gently reflux for approximately 72 hours under argon. After cooling and filtering, the organic layer was separated from the aqueous layer. The aqueous layer was extracted three times with diethyl ether (100 mL), and the combined organic portions were washed twice with 100 mL portions of H 2 O. The organic mixture was dried (Na 2 SO 4 ) and the solvents were removed under vacuum to give a dark, brown oil. 1 H NMR analysis showed this to be mainly a mixture of all four regioisomers of the tris-(pyrazolyl)methanes derived from 3-methylpyrazole.
The crude mixture of tris(pyrazolyl)methane regioisomers was first isomerized according to the method of Jameson & Castellano (1998). The crude brown oil (1.0 g) was combined with a catalytic amount of p-toluenesulfonic acid (0.060 g) and a small amount (50 µL) of 3-methylpyrazole and heated at reflux in dry toluene (15 mL) for 24 hours under argon.
After cooling, the mixture was washed twice with 100 mL portions of saturated NaHCO 3 (aq). The aqueous extracts were then extracted once with CH 2 Cl 2 (100 mL). The organic layers were combined, dried with Na 2 SO 4 , and evaporated under reduced pressure to give a dark yellow oil. NMR analysis of this oil showed that it contained a 2:1 mixture of the desired tris(pyrazolyl)methane and another regioisomer.
For purification, the material was dissolved in a minimum amount of hot hexane and allowed to crystallize at room temperature for 24 hours. The resulting yellow/brown crystals were separated under a microscope. The larger, clear, and darker-colored lozenges were separated from the smaller, opaque, and lighter plates. These smaller crystals tend to form least 85% of target compound. This material was then carefully crystallized from hot hexanes after decolorization with carbon in the same solvent.
A suitable crystal was carefully cut from a larger block. A bigger crystal demonstrated the same structure in a preliminary X-ray experiment.