On structural phase transitions in 4-aminopyridinium fluoroborate, [4-NH2C5H5N][BF4]: differential scanning calorimetry, dielectric and infrared studies

Crystal structure of the 4-aminopyridinium tetrafluoroborate, [4-NH2C5H5N][BF4], has been determined at 293 K by means of X-ray diffraction as monoclinic space group, C2. The crystal shows a reach sequence of phase transition, four solid-solid transitions: at 250, 281, 388 and 485 K on heating. Most of the phase transitions, except that at 388 K, are clearly of first order and classified as an ‘order-disorder’ type. The rotational disorder both of cations and anions was studied by differential scanning calorimetry, dielectric and infrared spectroscopy. The low temperature phase transitions are associated with plastic crystal behavior. q 2004 Elsevier B.V. All rights reserved