Molecular motion, phase transitions, and disorder in the pyridinium halides

Abstract

JOHN A. RIPMEESTER. Can. J. Cnem. 54, 3453 (1976). The solid pyridinium chloride, bromide, and iodide salts were studied using 1H nuclear magnetic resonance and differential scanning calorimetry. Phase transitions were observed at 345 K for the chloride, 269 K for the bromide, and 247 K for the iodide. Well below each transition, the pyridinium ions are held rigidly in the crystal lattice, whereas above each transition the ions reorientate rapidly about an axis at right angles to the ring planes. From the temperature dependence of the spin-lattice relaxation times the high temperature phase reorientational activation energies were determined to be 1.55, 2.30, and 4.20 kcal/mol for the chloride, bromide, and iodide, respcctively. [Traduit par le journal]

Dielectric nonlinear properties of pyridinium tetrafluoroborate single crystal near the ferroelectric phase transition

“…Pyridinium salts form an interesting family of crystals exhibiting structural phase transition [1][2][3][4][5]. Pyridinium tetrafluoroborate C 6 H 6 N·BF 4 (PyBF 4 ) and pyridinium perchlorate (PyClO 4 ) are particularly interesting as they exhibit successive structural phase transitions at 248 K and 232 K for PyClO 4 [6]; at 238 K and 205 K for PyBF 4 [7].…”

Domain Structure and Birefringence in Pyridinium Perchlorate and Pyridinium Fluoroborate Single Crystal

“…Chemical substances containing pyridinium cations are an interesting family exhibiting structural phase transition [1][2][3][4][5]. Pyridinium perchlorate (PClO) and pyridinium fluoroborate (PFB) are particularly interesting as they exhibit successive structural phase transitions.…”

Radicals as Probes of Ferroelectric Phase Transitions in EPR Investigations of Pyridinium Tetrafluoroborate

“…The pyridinium cation, held rigidly in the crystal lattice in temperatures well below the phase transition, shows orientational disorder at room temperature (3)(4)(5)(6)(7)(8)(9)(10). The pyridinium cation itself deserves particular attention because of its unique features: symmetry, planarity, and aromatic character.…”