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Mangstl, Martin; Weber, Johannes; Jardon-Alvarez, Daniel; Burghaus, Olaf; Roling, Bernhard; Schmedt auf der Günne, Jörn (2018): Investigation of Bistetramethylammonium Hydrogencyclotriphosphate-A Molecular Rotor? In: Chemistry-A European Journal, Vol. 24, No. 35: pp. 8756-8759
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The crystalline phase beta-[N(CH3)(4)](2)HP3O9 undergoes a reversible phase transition to gamma-[N(CH3)(4)](2)HP3O9f which was studied by dynamic scanning calorimetry and X-ray diffraction. The rotational dynamics of the anion [P3O9](3-) were evident from variable temperature P-31 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 gamma-[N(CH3)(4)](2)HP3O9 of 6.9x10(-5) S cm(-1) at 240 degrees 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.