Investigation of Bistetramethylammonium Hydrogencyclotriphosphate—A Molecular Rotor?

Abstract

The crystalline phase β-[N(CH ) ] HP O undergoes a reversible phase transition to γ-[N(CH ) ] HP O , which was studied by dynamic scanning calorimetry and X-ray diffraction. The rotational dynamics of the anion [P O ] were evident from variable temperature P magic angle spinning (MAS) NMR spectroscopy. The rotational dynamics could be simulated with a 3-site jump model, which yields spectra in good agreement with experiment. An activation energy of 0.6 eV could be estimated from line shape analysis. Impedance spectra reflect a bulk proton conductivity of γ-[N(CH ) ] HP O of 6.9×10 S cm at 240 °C and an activation energy of approximately 1.0 eV. Thus this salt features bulk protonic motion, while local rotational anionic motion happens with activation energies of the same order, as suggested by the paddle-wheel mechanism.

Synthesis and characterization of methylammonium phosphates as crystalline approximants for anhydrous, low melting phosphate glasses

“…The rst had been synthesized via the Boullé process 22 which requires silver salts as starting material. A larger version of the ammonium ion is the tetrasubstituted tetramethylammonium ion [N(CH 3 ) 4 ] + , for which several phosphate phases [23][24][25] and phase transitions 26,27 between them have been observed. Methylammonium hydrogenphosphate (254.2 C) and methylammonium formate (162.1 C) have low decomposition temperatures.…”