Deuterium Solid-State NMR Study of the Dynamic Behavior of Deuterons and Water Molecules in Solid D3PW12O40
The Journal of Physical Chemistry B
, E-ISSN: 1520-5207
Stepanov Alexander G.
Shegai Timur O.
Luzgin Mikhail V.
Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences, Prospekt Akademika LavrentieVa 5, Novosibirsk 630090, Russia
Department of Natural Sciences, Novosibirsk State University, Pirogova Street 2, Novosibirsk 630090, Russia
Institut de Recherches sur la Catalyse, CNRS, 2 av. Albert Einstein, 69626 Villeurbanne, France
The mobility of water molecules and deuterons of the deuterated analogue of solid 12-tungstophosphoric acid, H3PW12O40·nH2O (HPA) (n = 5.5 and 0.1), has been characterized by deuterium solid-state NMR. Analysis of the 2H NMR line shape and spin−lattice relaxation times allowed us to characterize the deuteron and water dynamics in HPA, at different water contents, in the temperature range 103−383 K. At 163−193 K and for n = 5.5, an intramolecular motion corresponding to reorientations by 180° flips around the C2 axis of water in the [D5O2]+ ion has been detected, the deuteron being probably immobile. At temperatures above 313 K, both water and deuteron become involved in fast rotation around the C3 axis of the formed [D3O]+ ion. The rotation is performed on a time scale of 30−50 ns with an activation energy Ea of 8.5 kJ/mol. For n = 0.1, three dynamically different species can be distinguished: mobile deuterons, mobile [D3O]+ ions, and immobile deuterons. Mobile deuterons are weakly bonded to polyanions and move fast with a characteristic time of a few picoseconds and Ea = 8.6 kJ/mol. [D3O]+ ions move more slowly than deuterons, but still fast, with a time scale of a few nanoseconds, and Ea = 17.6 kJ/mol. The characteristic time for immobile deuterons is much greater than a few microseconds.