The structure of 3,5-bis(trifluoromethyl)pyrazole in the gas phase and in the solid state

The X-ray molecular structure of the important molecule 3,5-bis(trifluorome thyl)pyrazole has been determined at 120 K and gave crystals belonging to t he triclinic PI space group. The compound forms tetramers through N-H ... N hydrogen bonds and some proton disorder is necessary to explain the geomet ric features of the monomers. The IR spectra have been recorded in the gas phase (monomers) and in the solid state (tetramers) and analyzed by compari son with the calculated normal frequencies. The use of solid-state NMR spec troscopy combined with ab initio CIAO calculations suggests that a certain amount (about 40 +/- 10%) of dynamic disorder involving intramolecular prot on transfers could be present in the crystal.