Phase transition and crystal dynamics of 4-bromobenzyl alcohol

For the title compound a phase transition from Phase II to Phase I (low and room temperature phases, respectively) was found at ca. 217 K. The temperature dependence of the Br-81 NQR frequency and that of the dielectric constant showed anomalies at ca. 195 K that were tentatively attributed to a higher order phase transition. A similar anomaly was found at ca. 218 K for 4-chlorobenzyl alcohol which showed a II-I transition at 236 K. The dielectric dispersion observed for both compounds at low temperatures indicates an excitation of a molecular motion with the dielectric relaxation rate of ca. 1 kHz. The temperature dependence of the Br-81 NQR frequencies of 2- and 3-bromobenzyl alcohol, measured at T > 77 K, gave no evidence of phase transition in their crystals.