Deuterium Solid-State NMR Study of the Dynamic Behavior of Deuterons and Water Molecules in Solid D₃PW₁₂O₄₀

Abstract

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 C 2 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 C 3 axis of the formed [D3O]+ ion. The rotation is performed on a time scale of 30−50 ns with an activation energy E a 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 E a = 8.6 kJ/mol. [D3O]+ ions move more slowly than deuterons, but still fast, with a time scale of a few nanoseconds, and E a = 17.6 kJ/mol. The characteristic time for immobile deuterons is much greater than a few microseconds.

Dynamic studies of Ormosil membranes

“…Their respective area is proportional to the amount of both kinds of water inside the sample, while their linewidth is associated with the mobility of the considered water as it could be observed in hydrates [26], gels and superabsorbants [27]. Similar behavior was also already reported in pure hydrated and deuterated POM [28], and associated to the presence of mobile deuterons (mobile water), mobile [D 3 O] + and immobile deuterons (water molecules without mobility). The ratio of these different species is related to the hydration ratio of the POM [29,30].…”

“…They should correspond to the presence of two kinds of water molecules with different motions, or also some charged deuterons clusters (D 3 O + , D 2 O þ 5 ) as it was also observed by deuterium NMR of pure POM [28][29][30]. At 245 K, half of the remaining signal disappears, and a much broader signal appears.…”

Characterization and Dynamics of the Different Protonic Species in Hydrated 12-Tungstophosphoric Acid Studied by2H NMR

“…The triangular pattern evolves to a narrowed axially symmetric pattern (Figure ) that originates from uniaxial rotation with the geometry of the [H 3 O] + ion (see also Figure in ref ). Upon further heating the isotropic line evolves, associated with fast proton migration . All said this brings us to the understanding that the migration of deuterons over TPA could be related with [D 3 O] + ion motion, while the formation of [D 5 O 2 ] + hinders the process of deuteron migration.…”

“…Another attempt to measure the molecular mobility at lower hydration level with a technique somewhat more robust and adapted for longer time scales was made by Stepanov et al 18 That work provided some mechanistic insight into the mobility and geometry of motion of active species (particularly the [H 3 O] + ion) formed on the Keggin anion surface upon hydration. However, some questions still remain unresolved.…”

Molecular Mobility of Tert‐butyl Alcohol Confined in a Breathing MIL‐53 (Al) Metal‐Organic Framework

“…This value is similar to E a associated with breaking of a single hydrogen bond in hydrates with hydrogen bonds of moderate strength. [30,31] We can therefore assume that this type of TBA motional mode reflects the diffusion of TBA along the MIL-53 channel by the jump exchange between the neighboring adsorption sites (Figure 2c). Taking the jump length as the distance between the neighboring OH groups, l � 7 Å, and correlation time for this diffusional motion, derived from the line shape analysis to be τ D = (2π k flip ) À 1 = 7.2 × 10 À 10 s (300 K), we estimated the coefficient D for TBA self-diffusion within the MIL-53 channel based on Einstein equation for 1D case:…”