Phase transition in the compound [C6H5CH2NH2CH3]2TlCl5

N-Benzylmethylammonium pentachlorothallate (III) exhibits one phase transition at (T = 353 ± 2 K): phase (I) – 353 K → phase (II). This transition has been characterized by differential scanning calorimetry, electric measurements, and Raman scattering on polycrystalline samples. The room-temperature phase is monoclinic P21/c and the environment of the Tl atom is a deformed trigonal bipyramid. Spectral evolution analysis and analogy with a thallium homologous compound suggest a trigonal bipyramid → square pyramid transitory conformation. Transport properties in this material appear to be due to the reorientational motion of ions.