PHASE-TRANSITIONS IN TRIS(3,5-DIMETHYLPYRAZOL-1-YL)METHANE - THE STRUCTURE OF THE HIGH-TEMPERATURE PHASE FROM X-RAY-POWDER DIFFRACTION

The crystal structure of the sublimated form (m.p. = 424 K) of tris(3, 5-dimethylpyrazol-1-yl)methane has been solved by Patterson search met hod from laboratory X-ray powder diffraction data. Crystal data: trigo nal symmetry with the unit-cell parameters a = 16.152 (1) and c = 5.35 3 (1) Angstrom, space group P3, C16H22N6, Z = 3, 293 K. After indexing the powder pattern by two methods, the unit-cell parameters found wer e refined by a least-squares technique. A whole pattern-fitting progra m was used to extract the integrated intensities. The structure was so lved taking a related compound as a search model and the final Rietvel d refinement converged to R-wp = 0.077 and R-p = 0.059. This study is one of the first examples of Patterson search structure determination from an hemihedral space group using powder data. The complexity of th e structural determination is increased by the presence of three molec ules in the asymmetric unit.