The crystal structure of 4-methyl pyridine at 4.5 K

The crystal and molecular structure of deuterated 4-methyl pyridine C6D7N has been determined at 4.5 K using pulsed neutron powder diffraction. It crystallises in the space group I41/a with a = 7.5338(1) Å, c = 18.4960(1) Å and Z= 8. The structure is the same as that determined by Ohms et al. [J. Chem. Phys. 83 (1985) 273–279] for the hydrogenous material at 120 K, and there appears to be no phase transition down to 4.5 K. Our results contradict the conclusions of Biswas [Indian J. Physics 35 (1961) 261–268], who assumed a monoclinic space group P21/c in interpreting X-ray powder diffraction data at 93 K.