Crystal and mol-ecular structure of 4-fluoro-1 H -pyrazole at 150 K.

Only two 4-halo-1 H -pyrazole crystal structures are known to date (chloro and bromo, the structure of 4-iodo-1 H -pyrazole has not been reported yet). The triclinic structure of 4-fluoro-1 H -pyrazole, C 3 H 3 FN 2 ( P ), reported here is not isomorphous with those of the chloro and bromo analogues (which are isomorphous, ortho-rhom-bic Pnma ). To avoid sublimation during the measurement, diffraction data were collected at 150 K. Two crystallographically unique 4-fluoro-1 H -pyrazole moieties linked by an N-H⋯N hydrogen bond are found in the asymmetric unit. Unlike the trimeric supra-molecular motifs found in the structures of the chloro and bromo analogues, 4-fluoro-1 H -pyrazole forms one-dimensional chains by inter-molecular hydrogen bonding in the crystal.